HomeMy WebLinkAboutIsland-wide Quality Report (PDF) 1
Technical Memorandum
FINAL
Water Quality Monitoring and Assessment of the
Nantucket Island-Wide Estuaries and Salt Ponds
Update 2019
To:
Town of Nantucket
Marine and Natural Resources Department
2 Bathing Beach Road
Nantucket, MA 02554
From:
Brian Howes Ph.D. and Roland Samimy Ph.D.
Coastal Systems Program
School of Marine Science and Technology (SMAST)
University of Massachusetts-Dartmouth
706 South Rodney French Blvd.
New Bedford, MA 02744
July 2020
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Executive Summary
Water Quality Monitoring and Assessment of the
Nantucket Island-Wide Estuaries and Salt Ponds
Update 2019
As in previous years, this annual Technical Memorandum summarizes the water quality
monitoring results of the estuarine sampling undertaken through the ongoing Nantucket Island-
wide Water Quality Monitoring Program. The program is a multi-year collaboration between the
Town of Nantucket Natural Resources Department and the Coastal Systems Program within the
University of Massachusetts-Dartmouth, School for Marine Science and Technology. Water
sample collection and analysis has been undertaken according to specific protocols developed at
the outset of the monitoring first started in 2010 such that year to year results would be cross
comparable from one Nantucket estuary to another but also, so that Nantucket results would
also be cross comparable to water quality data collected from other programs managed by the
Coastal Systems Program (e.g. Cape Cod monitoring programs as well as Martha's Vineyard
Island-wide monitoring program). The 2019 summary memo is focused specifically on the
following: 1) Water Quality Results for Nantucket Harbor, Madaket Harbor, Long Pond,
Hummock Pond, Miacomet Pond, Sesachacha Pond, Polpis Harbor Streams and Oyster
Aquaculture Potential Sites and 2) Trophic State - Water Quality/Eutrophication Status and
trends.
The goals of the monitoring program remain unchanged from previous years, primarily to:
1. determine the present (2019) ecological health of each of the main salt ponds and
estuaries within the Town of Nantucket,
2. gauge (as historical data allows, 2010-2019) the decline or recovery of various salt ponds
and embayments over the long-term (also part of TMDL compliance), and
3. provide the foundation (and context) for development of potential alternatives for nutrient
and resource management and quantitative measures of success.
Point (3) is critical for restoration planning should a system be found to be impaired or
trending toward impairment, which requires targeted management actions for restoration
or a system is improving due to Town actions which then should be improved/enhanced.
As was the case in 2010, 2012 - 2018 sampling efforts, the 2019 sampling program focused on
the summer/early fall months (June - September) as this time frame is typically representative of
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worst case water quality conditions and the basis for habitat management decisions. Samples
collected in 2019 were obtained from the same sampling station locations and the same depths
as in previous years to maximize cross comparability and to gauge temporal changes. It should
be noted that the Town of Nantucket did undertake water quality monitoring in 2011, however,
those samples were analyzed by a lab other than the Coastal Systems Analytical Facility at the
UMASS School for Marine Science and Technology and data was presented in the report on the
2012 monitoring effort.
The Town of Nantucket has been working for decades to protect and more recently restore its
estuaries and their aquatic resources. At present and based on the 2010 - 2019 water quality
database developed under the Island-wide unified water quality monitoring program, activities to
lower nitrogen enrichment and its negative impacts to water and habitat quality have been
planned and implementation is ongoing in 4 estuarine systems: Nantucket Harbor (jetties and
sewers), Madaket/Long Pond (landfill and possible dredging), Sesachacha Pond (openings),
Hummock Pond (refined opening protocol). In addition, all of the Town’s estuaries should benefit
from the recent fertilizer application by-law. As a result, it is anticipated that the efficacy of these
management activities should be seen in the on-going monitoring results.
Summer 2019 appears to have sustained high water quality for the Nantucket Harbor and
Madaket Harbor systems. In contrast, Hummock Pond water quality appears to have continued
the decline started in 2016 which showed a decrease in overall water quality compared to
system reset for the 2015 summer season. The reset was accomplished through a highly
successful opening, which has not been repeated at that level since 2016, hence the recent
decline. The variations in TN levels results primarily from opening success. For instance, in
spring 2017 the opening was only 1.5 days with high precipitation, although the spring opening in
2016 was comparable to the duration of the opening in 2015 (18 days and 15 days respectively).
In contrast, Long Pond has continued to show declines in TN concentrations over historic levels
with parallel improvements in water and habitat quality, although the inter-annual reductions
appear to be stabilizing.
Miacomet Pond, which is now functionally a eutrophic freshwater pond, saw a slight
improvement in 2017 as seen in lower TN concentrations and lower total pigments (CHLA +
Pheophytin) but worsened again in 2018 and remains a nutrient degraded system in 2019.
Miacomet Pond in 2017 and 2018 as in 2016-2014 appears to have had phytoplankton
production (e.g. chlorophyll-a) stimulated by both N and P inputs as pond salinities declined to
present freshwater levels, although in 2019 it appears that nitrogen was most important.
Miacomet Pond exceeds by several fold both known N and P levels needed to maintain a high
quality aquatic system.
Water Quality in Sesachacha Pond appears to be directly related to the efficacy of its seasonal
openings. Water quality in 2010, 2012, 2013 was significantly improved over the levels observed
previously in the MEP analysis (November 2006). The lower TN levels in Sesachacha Pond
(2010-2013) versus historic levels documented by the MEP indicated significant improvement of
pond resources. Since there was no major shift in nitrogen loading within the Sesachacha Pond
watershed during that period of improvement, it is almost certain that the amount of tidal flushing
during a given artificial breaching is driving the variability in the observed summer TN level. The
rise in TN observed during the 2014 sampling suggests that a poor inlet opening may have
occurred in spring 2014, as watershed loading was unchanged. Short openings in subsequent
years (2015 {5 days}, 2016 {3 days}, 2017 {7 days}) suggests that inlet opening efficacy has a
significant effect on pond water quality as TN concentrations from 2014 to 2017 have steadily
increased to nearly the same level as when the MEP analysis was completed. Since a focused
opening management plan has evolved over the past decade, TN levels have recently generally
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declined and averaged 0.784 mg TN/L over 2018 and 2019 field seasons (Table 4). Although
Sesachacha Pond is still above its threshold the increased attention to pond opening have
lowered TN from historic levels (1.2 mg N/L). This underscores that even at present levels of
success openings play a critical role in lowering eutrophication in this estuary.
Trophic State of Nantucket Estuaries: The Trophic State of an estuary is a quantitative
indicator of its nutrient related ecological health and is based on key ecological metrics:
concentrations of inorganic and organic Nitrogen, water clarity (Secchi Depth), lowest measured
concentrations of Dissolved Oxygen (average of lowest 20% of summer measurements), and
Chlorophyll-a pigments (surrogate for phytoplankton biomass/blooms). Nutrient related trophic
health scales generally range from Oligotrophic (healthy-low nutrient) to Mesotrophic (showing
some signs of deterioration of health due to nutrient enrichment) to Eutrophic (habitats
significantly impaired and degraded, high levels of nutrients and organic matter and community
shifts).
Nantucket Harbor (with Madaket Harbor) is presently supporting the highest water
quality of Nantucket's estuaries. In 2019 and 2018, all of the Nantucket and Polpis
Harbor monitoring stations were showing high water quality, slightly better than in 2017.
Over the past 5 years, the main basin of Nantucket Harbor has supported high quality
waters, with only a periodic small level of decline in the uppermost basin, Wauwinet
basin. Summer 2017 saw a slightly lower TN level at station NAN-2A (MEP sentinel
station) and 2018 lower still. Summers 2016-2018 generally showed similar water quality
in this basin as 2014 which also showed improved chlorophyll-a and TN levels versus
prior years. Nutrient management activities associated with the Harbor (additional sewer
hookups, jetty improvement and oyster aquaculture) should result in even lower TN and
chlorophyll levels and reduce the likelihood of large phytoplankton blooms in the future.
Polpis Harbor basins which after showing moderate impairment in 2010 and 2012 have been
showing only low to no impairment in recent years, suggesting some improvement over historic
conditions. Polpis Harbor showed 2018 & 2017 TN levels similar to 2010, 2012 and 2015,
slightly higher than 2013 and 2014. This variation makes continued monitoring essential to
clarify any trends in water quality and linkages to stream nitrogen discharges. While the overall
Nantucket Harbor System is generally supporting high quality waters, the variability in the index
in Wauwinet and Polpis basins should be monitored to ascertain their long-term health and to
determine the effectiveness of restoration effort by the Town as it continues to move forward to
meet the MassDEP TMDL for this system. Overall, Nantucket Harbor appears to be relatively
stable from year to year with a continuing improvement into 2019 with high index scores and
higher level metrics that support the contention that it is approaching its TMDL threshold, as is
also the case for Polpis Harbor. Planned sewering within the Nantucket watershed should
complete the restoration on nitrogen mitigated impairment within this estuarine system
Madaket Harbor main basin in 2019 continued to support a high level of nutrient related water
quality. It has been the more enclosed basins of Hither Creek and Long Pond with their reduced
tidal flushing that have had nitrogen impairment problems. Over the 9 years of monitoring,
Hither Creek (Station 1), which receives discharge from Long Pond via Madaket Ditch, has
consistently supported the poorest “health” status within the Madaket Estuary. Hither Creek is
clearly nitrogen enriched and showing continuing impairment based on a variety of parameters,
but has clearly improved since 2010. Over the past 9 years the Trophic Index indicates that this
basin has improved slightly each year, going from fair-poor water quality and improving in a step-
wise manner to moderate water quality since 2014 with the exception of 2017 where TN levels
rose, but stayed within the range that has developed over the past 4-5 years. The main basin of
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Madaket Harbor is showing relatively high water quality in each year but also shows a possible
improvement from 2010 to 2012 and has been generally stable at high water quality in more
recent samplings to 2019.
Long Pond is a large tributary basin to Madaket Harbor, which receives tidal flow
through the artificial connection of Madaket Ditch. Given the structure of the basin and its
watershed, Long Pond operates semi-independently from Madaket Harbor. Long Pond’s
Trophic Index scores for both monitoring stations (5 & 6) in the 9 years of monitoring
(2010, 2012-2019) clearly indicate poor nutrient related water quality. However, based
upon the 2019 results and the 9 year time-series, it appears that the Town’s management
of the landfill, has reduced the nitrogen load from this source with the associated
observed lowering of TN levels. While the water quality Index for Long Pond is starting to
improve in response to the lower TN levels, the basin remains moderately impaired.
While continued monitoring will determine the final level of improvement, it does appear
that the reduction in N loading is occurring with beneficial effects. It should be noted that
the lack of major change in the Health Index for Long Pond results in part from the
relative coarseness of the Index, where sometimes large index score changes are
required to change the Index value. The analysis of key metrics (Chlorophyll-a, water
clarity-Secchi and total nitrogen) individually do show improving water quality at stations
5 and 6 in 2012-2019 compared to 2010, which is particularly striking in the declining TN
levels. A recent Town supported benthic animal analysis parallels and underscores the
water quality improvements.
Sesachacha Pond is a closed coastal salt pond that has its water quality managed by
periodically breaching the barrier beach to open the basin to tidal exchange with the
adjacent Atlantic Ocean waters. Sesachacha Pond was evaluated under the
Massachusetts Estuaries Project (MEP) which recommended an additional mid-
summertime opening (if logistically possible) as part of the pond management strategy to
enhance flushing of the pond and improve water quality to reach the threshold without
any need for infrastructure. The water quality monitoring program in 2010, 2012 and
2013 showed that the pond nitrogen levels were converging on the MEP Threshold (0.60
mg/L total nitrogen). Improved openings resulted in total nitrogen (TN) levels dropping
significantly from historical levels in 2010 and 2012 with associated improvements in the
levels of water clarity and chlorophyll-a. However, with limited openings in 2014-2017,
TN has risen and has returned to near historic levels (~0.9 mg/L), with an improvement in
2018 (0.752 mg N/L), and with continuing impaired conditions in 2019. It appears that
these changes relate to the quality of the pre-summer opening. Given the 2010-2013
period when robust openings occurred, it appears that a solid opening program has the
capability to improve the water quality metrics pond-wide to levels near the TMDL
nitrogen threshold.
Based upon the Index alone, changes in water quality in Sesachacha Pond over the 2010-2013
period were stabilized at moderate impairment of this estuary, with more recent monitoring 2015-
2017 seeing a trend toward poor water quality conditions with a slight rebound in 2018 as TN
levels rose (2015-2017) then declined (2018). It appears that like other periodically opened
ponds, the quality of the opening (amount of water exchanged) controls the level of water quality
in the following months. A closer examination of the opening protocol and the linkage to
resultant water quality is needed for management of this system.
Hummock Pond is a closed coastal salt pond that is only periodically opened to the
ocean to flush out nutrients and organic matter on the ebb tide and receive low nutrient
saline waters on the flood tide. Creating sustained openings that are sufficient to allow
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exchange of tidal waters for more than 4-5 days has been difficult for this system due to
its location on the coast and the large amount of sand migration in the coastal zone which
can rapidly reseal the inlet.
The present non-tidal state and level of watershed nutrient inputs have resulted in
moderate to poor nutrient related water quality throughout the pond, with poor water
quality conditions the present norm (2005-2007, 2010, 2012, 2013, 2014, 2015).
Unfortunately, in 2016 the pond appears to have had lower water quality in its upper and
mid reaches than in previous years, although the lower basin did not show this inter-
annual variation. Similarly, in 2017 and 2018 water quality declined even further
throughout most of the estuary, including the lower basin. This resulted from the poor
spring 2017 and 2018 openings. There is generally a small gradient in water quality with
moderate to poor conditions near the ocean and poor conditions in the uppermost basins,
but this collapsed to generally poor water quality throughout the system in 2017, 2018
and 2019. All of the metrics are consistent with a nutrient impaired basin in all years.
Based upon the monitoring results it is clear that the nutrient related health of Hummock
Pond is significantly related to the success of its periodic openings and that the pond is
presently significantly impaired by nitrogen enrichment.
Miacomet Pond is a closed coastal salt/fresh pond that is rarely (over a decade ago) opened to
the ocean to flush out nutrients and organic matter on the ebb tide and receive low nutrient
saline waters on the flood tide. As a result of the lack of tidal flow and continuous groundwater
inputs, the pond is presently freshwater, with salinity levels in each of the past 7 years of
monitoring of <0.5 ppt, reaching a low of 0.1 ppt, 2015-2017. The present non-tidal state and
extent of watershed nutrient inputs has resulted in a decline in nutrient related water quality
throughout the pond for both nitrogen and phosphorus, with poor water quality and habitat
impairment the present norm and observed in 2019. All of the metrics for Miacomet Pond are
consistent with a highly nutrient impaired basin. However, as the freshening of this basin has
become complete and sustained, it likely will have to be managed as a transitional freshwater
system and will need to be reassessed as such. Since Miacomet Pond may have storm over-
wash in the future due to climate change related storm intensification and sea level rise, it may
be necessary for management to create both a nitrogen and a phosphorus budget for this
system and to conduct short-term incubations to determine which nutrient is controlling pond
health under present and varying salinity conditions. It is likely that regions of the pond may be
sensitive to both nitrogen and phosphorus, such that overall both nutrients need to be monitored
and considered for management of Miacomet Pond, although phosphorus management is
clearly needed at this time.
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Table ES-1. Summary of present status and trends of water/habitat quality of estuaries of
Nantucket based on present (2019) water quality monitoring data reconciled against historic data
collected from 2010-2018 and MEP nutrient threshold analyses undertaken for each system
except Miacomet Pond.
Monitoring and Specific Results: The Technical Memorandum on the 2019 Nantucket Water
Quality Monitoring Program is organized consistent with previous SMAST water quality
monitoring summaries (2010 and 2012 - 2018) but is now focused more on temporal trends while
still allowing comparisons to data from the previous years of monitoring. However, the bulk of
the prior data tables that were summarized in the report on the 2018 field season are not
repeated again here. Similarly, as in prior annual reports, the 2019 summary does not include
an overview of the program or the summary of the sampling approach as these have not
changed from previous years, instead they are included by reference. This tech memo does
include the 2019 summary tables and synthesis of results in tabular and graphical form which
includes all data collected under this program from its inception (2010 and 2012 - 2019). The
2019 summary is focused specifically on the following:
1. Results of Sampling: Summary of Water Quality Results
Nantucket Harbor
Madaket Harbor
Long Pond
Hummock Pond
Miacomet Pond
Sesachacha Pond
Polpis Harbor Streams
Oyster Aquaculture Potential Sites
2. Trophic State: Water Quality/Eutrophication Status
3. Recommendations for Future Monitoring
Estuary Type TMDL Status Trend Remedial Actions
Madaket Harbor Marine In Place Approaching N Target Improving Landfill Remediation
Long Pond Brackish In Place Approaching N Target Improving Landfill Remediation
Nantucket Harbor -
Polpis Harbor Marine In Place Approaching N Target Improving New Jetties, Planned
Sewers
Sesachacha Pond Brackish In Place Moderate Improvement Variable Targeted opening
Hummock Pond Brackish/Fresh In Place??Significantly Impaired Variable Targeted opening
Miacomet Pond Fresh None Significantly Impaired Unchanged Unknown
Summary of Present Status and Trend of Water Quality in Nantucket's Estuaries
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As in previous years, the 2019 water quality monitoring of Nantucket's fresh and saltwater
systems was focused on summer-time conditions, as the warmer months typically have the
lowest water quality conditions, hence are the critical period for resource management. As in
previous years (2010, 2012-2018), the 2019 approach utilized the same sample collection and
analysis approach for assessing the water quality of each of the estuaries of Nantucket. This
consistency is intended to maximize the value of the results by making the data perfectly cross-
comparable to water quality monitoring data collected across the Island of Nantucket from
previous years and to previous Massachusetts Estuaries Project results for Nantucket estuaries
as well as more broadly to estuaries throughout the region (Cape Cod, Martha's Vineyard). In
this manner, inter-ecosystem comparisons can be made to better assess system
health/impairment and function and to formulate appropriate nutrient management strategies.
This allows individual towns such as Nantucket to directly benefit from lessons learned
throughout the wider region. It should be noted that in 2019 (as was the case in 2018),
compliance monitoring samples were collected from sentinel locations in Nantucket Harbor,
Sesachacha Pond and Madaket Harbor as established under the Massachusetts Estuaries
Project. Those samples are required of the Town by MassDEP and are denoted by a (C) in the
sample ID.
As in past years, UMD-SMAST Coastal Systems Program (CSP) scientists focused primarily on
the analysis of samples collected from the field effort (led by Thais Fournier, Nantucket NRD),
the associated data analysis, and overall program coordination. The Nantucket Natural
Resources Department staff primarily focused on coordination of field efforts, field sampling and
data collection on physical parameters and water quality improvement efforts.
The goals of the monitoring program remain unchanged from previous years, primarily to:
1. determine the present (2019) ecological health of each of the main salt ponds and
estuaries within the Town of Nantucket,
2. gauge (as historical data allows) the decline or recovery of various salt ponds and
embayments over the long-term (also part of TMDL compliance), and
3. provide the foundation (and context) for development of potential alternatives for nutrient
and resource management and quantitative measures of success.
This latter point (3) is critical for restoration planning should a system be found to be impaired or
trending toward impairment, which requires targeted management actions for restoration.
As was the case in 2010, 2012 - 2018 sampling efforts, the 2019 sampling program focused on
the summer/early fall months (June - September). Additional monitoring of the openings of
Sesachacha Pond and Hummock Pond were NOT continued in 2019. However, a detailed plan
for refining pond openings was developed for future implementation.
Water samples were collected from each of Nantucket’s 6 estuarine systems (Figures 1-6) on
multiple dates (“events”) in 2019 following the schedule presented in Table 1. Samples were
obtained from the same sampling station locations and the same depths as in previous years to
maximize cross comparability and to gauge temporal changes. It should be noted that the Town
of Nantucket did undertake water quality monitoring in 2011, however, those samples were
analyzed by a lab other than the Coastal Systems Analytical Facility at the UMASS School for
Marine Science and Technology. The 2011 water quality data were presented in tabular form in
Appendix A in Annual Technical Memoranda of 2012 and 2013 and are not being reproduced
again herein.
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As in all previous years, the physical/environmental parameters measured in the estuaries during
the 2019 sampling season included: total depth, Secchi depth (light penetration), temperature,
conductivity/salinity (YSI meter), general weather (rain, cloudiness, etc.), wind force and
direction, dissolved oxygen levels and observations of moorings, birds, shell fishing and unusual
events (fish kills, algal blooms, etc.). Laboratory analyses of estuarine waters included: salinity,
nitrate + nitrite, ammonium, dissolved organic nitrogen, particulate organic carbon and nitrogen,
chlorophyll-a and pheophytin-a and orthophosphate. As initiated in the summer of 2015, the
estuarine water quality monitoring undertaken in 2016-2019 included an additional 3 stream
locations. During the summer 2016 season, stream station STA-3 was dropped due to no flow
and a station STA-4a was added to clarify water quality conditions in the stream outflow
associated with cranberry bogs up-gradient of STA-4. In 2017-2018 a fourth stream station was
added (WPH outlet) to directly measure flow and nutrient load into Western basin of Polpis
Harbor. In 2019 stream sampling took place at 3 stations: STA-4, STA-6B and WPH outlet.
In 2019, 25 field duplicates (11% of the total number of samples collected {n=232}) were taken
as part of the field sampling protocol for QA analysis. Data were compiled and reviewed by the
laboratory for accuracy and evaluated to discern any possible artifacts caused by improper
sampling technique, physical disturbance, etc. In addition, some samples were rerun to confirm
initial results.
The Town of Nantucket has been working for decades to protect and more recently restore its
estuaries and their aquatic resources. At present, activities to lower nitrogen enrichment and its
negative impacts to water and habitat quality are ongoing in 4 estuarine systems: Nantucket
Harbor (jetties and sewers), Madaket/Long Pond (landfill and possible dredging), Sesachacha
Pond (openings), Hummock Pond (refined opening protocol). In addition, all of the Town’s
estuaries should benefit from the recent fertilizer application by-law. As a result, it is anticipated
that the efficacy of these management activities should be seen in the on-going monitoring
results.
Summer 2019 appears to have sustained high water quality for the Nantucket Harbor system
(2019 embayment wide TN average of 0.34 mg/L, 2018 = 0.31 mg/L, 2017 = 0.35 mg/L, 2016 =
0.35 mg/L, 2015 = 0.37 mg/L). In contrast, Hummock Pond water quality appears to remain poor
in years 2014-2016 and 2017-2019 after an initial improvement after 2010-2013. Overall water
quality was highest in 2015 (TN = 0.58 mg/L) but became poor again and has remained poor
(2019, 2018, 2017 and 2016 embayment wide average TN levels remain high at 0.88, 0.83, 1.01
and 0.80 mg/L, respectively). The variations in TN levels result primarily from opening success,
for instance in spring 2017 the opening was only 1.5 days with high precipitation, although the
spring opening in 2016 was comparable to the duration of the opening in 2015 (18 days and 15
days respectively). Long Pond estuary wide TN concentrations have improved over historic
levels although the reduction appears to be stabilizing (0.630 mg/L and 0.587 mg/L in 2019 and
2018, respectively). Miacomet Pond, which is now functionally a eutrophic freshwater pond, is
eutrophic with 2019 chlorophyll pigment levels averaging 23.9 ug/L, TN = 0.935 mg/L and TP =
127 ug/L1 (TP many fold higher than in high quality freshwater systems). Water Quality in
Sesachacha Pond appears to be directly related to the efficacy of its seasonal openings. Water
quality in 2010, 2012, 2013 (mean TN = 0.671 mg/L, Chla = 5.5 ug/L) was significantly improved
over the levels observed previously in the MEP analysis. The lower TN levels in Sesachacha
Pond (2010-2013) versus historic levels documented by the MEP indicated improvement of pond
resources most likely due to modified breaching of the pond as recommended by the MEP
1 Total Phosphorus levels in freshwater ponds/lakes on Cape Cod with high water and habitat quality general have
TP <20 ug/L)
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analysis. Since there was no major shift in nitrogen loading within the Sesachacha Pond
watershed during that period of improvement, it is almost certain that the amount of tidal flushing
during a given artificial breaching drives the variability in the observed summer TN level. The
rise in TN observed during the 2014 sampling suggests that a poor inlet opening may have
occurred in spring 2014, as it is unlikely a significant change in the watershed load occurred to
drive the increase in TN from one summer to the next. Short openings in subsequent years
(2015 {5 days}, 2016 {3 days}, 2017 {7 days}) suggests that inlet opening efficacy has a
significant effect on pond water quality as TN concentrations from 2014 to 2017 have steadily
increased to nearly the same level as when the MEP analysis was completed. In 2014-2017
water quality has declined (mean TN = 0.933 mg/L, Chla = 8.4 ug/L) and is again approaching
MEP levels of enrichment. The amount of flushing with the openings is reflected in the
significantly higher salinities in 2010-2013 versus 2014-2017, 17.9 PSU and 11.6 PSU,
respectively. Higher salinities reflect more flushing which is correlated with lower TN and total
chlorophyll a levels. The 2018 and 2019 water quality analysis confirmed that the pond remains
impaired but did show a mild improvement (TN = 0.752 and 0.840 mg/L and Chla = 13.9 and 8.9
ug/L, respectively) likely due to improved openings. The important role of the pond openings is
further supported by the fact that average TN concentration in Sesachacha Pond was higher
(1.00 mg/L TN) in 2016 which received a 3-day opening compared to average TN concentrations
observed in 2017 (0.88 mg/L TN) given a 7-day opening. These results indicate that the level of
water quality observed in Sesachacha Pond since 2014 does respond positively if sufficient
flushing can be maintained. The effect of improved pond flushing is discussed in detail in the
MEP Sesachacha Pond Nutrient Threshold Report submitted to the Town of Nantucket in 2006.
Table 1. Sampling Schedule for 2019 Nantucket Water Quality Monitoring Program
Oyster
Sites
Jan
Feb
Mar
April
May
June 7-Jun 4-Jun 5-Jun 12-Jun 12-Jun 5-Jun 14-Jun 7-Jun
July 22-Jul 9-Jul 8-Jul 10-Jul 10-Jul 8-Jul 2-Jul 22-Jul
August 5-Aug 7-Aug 6-Aug 15-Aug 15-Aug 13-Aug 12-Aug 5-Aug
September Sept. 17 Sept. 3 Sept. 4 Sept. 10 Sept. 10 Sept. 4 Sept. 11 Sept.17
October
November
December
Total Events 4 4 4 4 4 4 4 4
Hummock
Pond
Polpis
Streams
Month Nantucket
Harbor
Madaket
Harbor
Long Pond Sesachacha
Pond
Miacomet
Pond
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12
Figure 1. Madaket Harbor and Long Pond sampling stations 2010, 2012, 2013, 2014, 2015,
2016, 2017, 2018 and 2019.
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Figure 2. Nantucket Harbor sampling stations 2019. Station NAN-8 (the cut) was only sampled in 2010 and location changed in 2011 -
2019. Nantucket Harbor and Polpis Harbor each have nitrogen thresholds in the MassDEP/USEPA TMDL for this system.
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Figure 2a. Sampling locations associated with potential oyster aquaculture deployments in Nantucket Harbor (ORS-2,3,4,5,6) sampled in
2015. ORS-2,4,6 sampled in 2016, 2017, 2018 and 2019. Sites are associated with possible oyster aquaculture areas (yellow pins).
ORS4 was the selected reef location and reef construction began in June 2017. Spat on shell was deployed in the Fall 2017.
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Figure 3. Sesachacha Pond sampling stations 2010, 2012, 2013, 2014, 2015, 2016, 2017, 2018 and 2019. This system has a nitrogen
threshold set in its site-specific MassDEP/USEPA TMDL.
16
Figure 4. Hummock Pond sampling stations 2010, 2012, 2013, 2014, 2015, 2016, 2017, 2018 and 2019. Station 7 is in Head of
Hummock, a kettle pond connected by an artificial channel to the estuary with limited exchange from Station 7 to Station 8.
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Figure 5. Miacomet Pond sampling stations 2010, 2012, 2013, 2014, 2015, 2016, 2017, 2018
and 2019. Miacomet Pond is currently functioning as a fresh pond.
Station 3
Station 1
Station 2
Station 3
Station 1
Station 2
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Figure 6. Polpis Harbor Stream Sampling locations shown in yellow pins (ST-4, 4A, 6B)
sampled in 2016, 2017 and 2019. WPH-outlet stream site sampled only in 2017, 2018 and
2019. Water samples from mid depth in water exiting culverts.
Figure 6a. Polpis Harbor Stream Sampling locations (ST-4, 4A, 6B and WPH-outlet) relative to
estimated direction of flow as determined by the Town of Nantucket.
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Table 2. Summary of Water Quality Parameters, 2019 Nantucket Sampling Program. Values are Station Averages of all sampling
events, June-September for sampling sites. Station NAN-2A represent an MEP sentinel location for monitoring in Nantucket Harbor.
NAN-2A is a new station that was first sampled in 2016 and is in a different location than NAN-2. It should be noted that in 2019 and
2018, TP was only evaluated at sites dominated by freshwater: Sesachacha Pond, Hummock Pond, Long Pond, Miacomet Pond and
stream because of the low salinity values in those closed ponds and the possibility that the Miacomet system maybe phosphorous
limited rather than nitrogen limited. Further study should investigate the possibility of P-limitation and TP paired with salinity should
continue to be monitored during the summer 2020 field season.
20% Low 20% Low
2019 Secchi Secchi Field Field Avg.Avg.Avg.Avg.Avg.Avg.Avg.Avg.Avg.Avg.Avg.Avg.Avg.Chla/T-Pig Avg.
average Depth DO DO Salinity PO4 TP NH4 Nox DIN DON TDN POC PON TON TN Chla Phaeo Ratio Total Pig
Sample ID (meters)% of WC Sat Sat (ppt)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(ug/L)(ug/L)(ug/L)
(mg/L)(% sat)
HUM7 1.37 44%1.36 14%2.79 0.139 0.306 0.148 0.007 0.155 0.371 0.526 3.899 0.393 0.764 0.919 14.12 8.52 0.72 22.64
HUM8 0.86 45%4.68 47%2.83 0.024 0.181 0.048 0.015 0.063 0.563 0.626 9.331 0.538 1.101 1.164 24.31 26.06 0.69 50.37
HUM5 0.91 42%6.77 73%3.50 0.020 0.162 0.010 0.010 0.020 0.400 0.420 5.351 0.304 0.704 0.724 16.46 6.80 0.74 23.26
HUM3 1.06 45%7.34 78%4.48 0.020 0.085 0.021 0.006 0.027 0.467 0.494 6.737 0.281 0.747 0.774 6.05 6.52 0.50 12.56
HUM1 1.20 38%5.96 63%4.75 0.016 0.091 0.014 0.006 0.020 0.443 0.463 5.091 0.394 0.837 0.857 6.97 4.31 0.65 11.28
LONG6 0.91 72%4.59 55%17.52 0.031 0.150 0.008 0.006 0.014 0.352 0.366 2.142 0.270 0.622 0.636 7.78 2.43 0.78 10.20
LONG5 0.75 57%2.03 25%15.06 0.071 0.227 0.008 0.004 0.013 0.360 0.372 1.628 0.253 0.613 0.626 11.01 1.83 0.83 12.84
HC1 1.43 63%ND ND 29.10 0.007 0.028 0.008 0.002 0.010 0.193 0.203 1.087 0.154 0.347 0.358 3.53 1.60 0.67 5.12
HC2 0.98 67%ND ND 25.30 0.020 0.045 0.039 0.008 0.047 0.305 0.352 1.244 0.218 0.523 0.570 4.77 3.94 0.55 8.71
HC3 ND ND ND ND 22.00 0.018 0.040 0.052 0.012 0.064 0.325 0.389 0.493 0.051 0.376 0.440 0.57 2.45 0.19 3.02
MH1 1.24 76%5.30 66%27.46 0.019 ND 0.013 0.005 0.018 0.297 0.316 1.060 0.184 0.482 0.500 6.52 2.50 0.70 9.02
MH2 1.71 100%6.18 77%30.38 0.011 ND 0.011 0.004 0.015 0.195 0.210 0.652 0.108 0.304 0.318 2.85 1.20 0.67 4.05
MH3 2.31 100%6.83 80%30.77 0.012 ND 0.008 0.005 0.013 0.176 0.188 0.682 0.102 0.278 0.291 2.34 0.71 0.70 3.05
MH4 2.87 73%6.56 83%30.89 0.017 ND 0.006 0.002 0.009 0.164 0.173 0.378 0.058 0.222 0.231 1.44 0.79 0.68 2.23
MP3 0.85 53%5.32 52%0.10 0.039 0.197 0.042 0.023 0.065 0.413 0.478 6.274 0.430 0.843 0.908 16.57 12.50 0.53 29.08
MP1 1.38 73%6.17 63%0.15 0.005 0.111 0.018 0.005 0.023 0.512 0.535 6.530 0.380 0.892 0.915 11.04 9.50 0.53 20.54
MP2 1.45 49%7.75 81%0.15 0.004 0.074 0.010 0.004 0.014 0.546 0.560 4.237 0.423 0.969 0.983 14.84 7.28 0.68 22.12
NAN1 3.63 71%6.02 72%30.93 0.017 ND 0.014 0.005 0.020 0.169 0.189 0.500 0.073 0.242 0.262 1.59 0.90 0.67 2.48
NAN2 2.46 44%5.93 76%30.75 0.018 ND 0.014 0.003 0.016 0.202 0.219 0.456 0.073 0.275 0.292 1.80 1.94 0.44 3.74
NAN2A 2.17 30%5.27 69%30.68 0.021 ND 0.022 0.003 0.025 0.248 0.273 1.343 0.119 0.367 0.392 2.05 3.55 0.43 5.60
NAN3 2.13 34%5.65 74%26.84 0.021 ND 0.022 0.004 0.026 0.220 0.246 0.655 0.113 0.310 0.336 2.20 1.96 0.50 4.16
NAN4 3.37 66%6.43 81%30.94 0.016 ND 0.012 0.003 0.016 0.191 0.206 0.703 0.101 0.292 0.307 1.58 0.85 0.60 2.42
NAN5 1.46 57%4.58 60%28.78 0.020 ND 0.009 0.003 0.012 0.255 0.267 0.914 0.149 0.404 0.416 2.90 1.66 0.61 4.56
NAN6 1.91 83%5.34 70%30.26 0.017 ND 0.012 0.004 0.015 0.255 0.271 0.638 0.107 0.363 0.378 1.39 2.00 0.47 3.39
NAN7 1.85 81%6.13 78%30.81 0.017 ND 0.018 0.002 0.020 0.164 0.184 2.252 0.090 0.253 0.274 4.10 1.62 0.70 5.72
NAN8N 1.38 100%5.78 73%30.52 0.016 ND 0.009 0.005 0.014 0.197 0.211 0.491 0.077 0.277 0.291 1.09 1.03 0.50 2.12
ST4 0.52 83%0.62 6%0.03 0.212 0.315 0.030 0.013 0.043 1.188 1.230 25.913 0.036 1.281 1.327 ND ND ND ND
ST6B 0.80 100%6.32 59%0.00 0.061 0.130 0.019 0.012 0.031 0.672 0.703 9.381 0.470 1.176 1.209 ND ND ND ND
WPH OUTLET 0.54 100%6.58 63%0.43 0.063 0.110 0.027 0.017 0.045 0.963 1.008 1.361 0.081 1.046 1.094 ND ND ND ND
SESA3 1.06 30%7.80 84%8.80 0.235 0.315 0.002 0.004 0.007 0.461 0.468 2.756 0.378 0.840 0.846 4.05 0.83 0.75 4.87
SESA2 1.01 20%5.72 60%8.84 0.238 0.338 0.012 0.006 0.018 0.446 0.464 9.020 0.461 0.907 0.925 6.66 5.91 0.67 12.58
SESA4 1.04 24%7.77 84%8.84 0.228 0.320 0.006 0.005 0.010 0.425 0.435 5.061 0.340 0.765 0.776 4.39 0.79 0.73 5.18
SESA1 1.06 20%4.65 51%8.87 0.265 0.338 0.026 0.007 0.033 0.411 0.445 2.760 0.388 0.799 0.833 6.45 6.54 0.70 12.98
ORS2 1.33 100%6.29 81%30.73 0.016 ND 0.010 0.005 0.015 0.190 0.205 0.528 0.079 0.269 0.284 1.62 1.11 0.64 2.73
ORS4 1.49 100%3.64 46%29.90 0.019 ND 0.020 0.011 0.030 0.253 0.283 0.916 0.135 0.388 0.419 2.32 3.37 0.53 5.70
ORS6 1.03 88%4.19 55%29.70 0.024 ND 0.011 0.003 0.015 0.282 0.297 0.720 0.118 0.400 0.415 3.13 1.76 0.74 4.89
20
Table 3. Summary of Stream Water Quality Parameters (ST4, ST6, WPH OUTLET, Stream 1,2,3 {into Sesachacha Pond})
and stations associated with potential oyster aquaculture locations (ORS,2,4,6), 2019 Nantucket Sampling Program. STA4A
was added in 2016 to further interpret flow and load results from STA4, however, in 2017 there were dates when there was
no flow at STA4A and in 2018 and 2019 samples were not collected from STA4A.
Lab Avg.Avg.Avg.Avg.Avg.Avg.Avg.Avg.Avg.Avg.Avg.Avg.Avg.Avg.
DATE Salinity PO4 TP NH4 Nox DIN DON TDN POC PON TON TN Chla Phaeo Total Pig
(2019)Embayment Sample ID ppt (mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(ug/L)(ug/L)(ug/L)
6/14/2019 NANTUCKET STREAM ST4 0.00 0.0503 0.0740 0.0132 0.0067 0.0199 0.8235 0.8434 0.5079 0.0285 0.8520 0.8719 ND ND ND
7/2/2019 NANTUCKET STREAM ST4 0.00 0.1090 0.1371 0.0233 0.0190 0.0423 1.2559 1.2982 0.7057 0.0428 1.2987 1.3410 ND ND ND
8/12/2019 ND ST4 0.10 0.6468 0.9416 0.0675 0.0087 0.0762 1.6571 1.7333 0.6068 0.0357 0.7842 2.3650 ND ND ND
9/11/2019 ND ST4 0.00 0.0409 0.1065 0.0141 0.0186 0.0327 1.0139 1.0466 ND ND ND ND ND ND ND
6/14/2019 NANTUCKET STREAM ST6B 0.00 0.0645 0.1075 0.0185 0.0146 0.0331 0.9071 0.9402 2.5308 0.1251 1.0323 1.0654 ND ND ND
7/2/2019 NANTUCKET STREAM ST6B 0.00 0.1132 0.1351 0.0222 0.0071 0.0293 0.8723 0.9016 8.0355 0.3278 1.2001 1.2294 ND ND ND
8/12/2019 ND ST6B 0.00 0.0357 0.1667 0.0275 0.0119 0.0394 0.3375 0.3769 17.5777 0.9566 1.2942 1.3336 ND ND ND
9/11/2019 ND ST6B 0.00 0.0303 0.1097 0.0076 0.0144 0.0220 0.5725 0.5945 ND ND ND ND ND ND ND
6/14/2019 NANTUCKET STREAM WPH OUTLET 0.10 0.0486 0.0659 0.0120 0.0077 0.0197 0.8413 0.8610 0.5341 0.0262 0.8675 0.8873 ND ND ND
7/2/2019 NANTUCKET STREAM WPH OUTLET 0.30 0.0884 0.1449 0.0261 0.0230 0.0491 1.1724 1.2215 0.9122 0.0486 1.2210 1.2701 ND ND ND
8/12/2019 ND WPH OUTLET 1.10 0.0764 0.1420 0.0577 0.0172 0.0749 0.8821 0.9570 2.6375 0.1677 1.0499 1.1248 ND ND ND
9/11/2019 ND WPH OUTLET 0.20 0.0392 0.0860 0.0141 0.0215 0.0356 0.9556 0.9911 ND ND ND ND ND ND ND
2/5/2019 SESACHACHA POND STREAM 1 0.10 0.0651 ND 0.0724 0.0129 0.0852 0.2195 0.3047 1.6804 0.1556 0.3751 0.4604 3.52 1.04 4.56
2/5/2019 SESACHACHA POND STREAM 2 3.00 0.0634 ND 0.0707 0.0129 0.0836 0.2105 0.2942 2.1037 0.4034 0.6139 0.6975 4.41 0.83 5.24
5/28/2019 SESACHACHA POND STREAM 2 3.80 0.0837 0.0879 0.0152 0.0032 0.0183 0.3321 0.3505 1.8542 0.2060 0.5381 0.5564 4.36 3.47 7.83
Lab Avg.Avg.Avg.Avg.Avg.Avg.Avg.Avg.Avg.Avg.Avg.Avg.Avg.Avg.
DATE EMBAYMENT SAMPLE ID Salinity PO4 TP NH4 Nox DIN DON TDN POC PON TON TN Chla Phaeo Total Pig
(2019)ppt (mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(ug/L)(ug/L)(ug/L)
6/7/2019 Old North Wharf - Oyster ORS2 30.9 0.003 NS 0.005 0.003 0.008 0.211 0.219 0.358 0.062 0.272 0.280 3.183 0.638 3.822
7/22/2019 Old North Wharf - Oyster ORS2 31.2 0.018 NS 0.008 0.005 0.012 0.204 0.217 0.741 0.106 0.311 0.323 0.563 1.513 2.075
8/5/2019 Old North Wharf - Oyster ORS2 30.0 0.021 NS 0.011 0.004 0.015 0.170 0.185 0.561 0.086 0.256 0.271 1.973 2.278 4.250
9/17/2019 Old North Wharf - Oyster ORS2 30.8 0.023 NS 0.018 0.008 0.025 0.176 0.201 0.452 0.062 0.238 0.263 0.750 0.025 0.775
6/7/2019 Shimmo - Oyster ORS4 29.9 0.008 NS 0.013 0.003 0.015 0.235 0.250 0.295 0.050 0.284 0.300 1.745 0.761 2.506
7/22/2019 Shimmo - Oyster ORS4 30.4 0.018 NS 0.021 0.008 0.029 0.247 0.276 1.148 0.184 0.431 0.460 0.360 7.637 7.997
8/5/2019 Shimmo - Oyster ORS4 29.6 0.023 NS 0.020 0.012 0.031 0.237 0.268 1.605 0.223 0.460 0.492 6.375 4.933 11.308
9/17/2019 Shimmo - Oyster ORS4 29.7 0.026 NS 0.026 0.019 0.045 0.293 0.338 0.614 0.085 0.377 0.423 0.810 0.167 0.977
6/7/2019 Polpis - Oyster ORS6 29.6 0.011 NS 0.014 0.000 0.014 0.226 0.240 0.324 0.051 0.277 0.292 2.719 0.655 3.374
7/22/2019 Polpis - Oyster ORS6 29.9 0.025 NS 0.006 0.003 0.009 0.337 0.346 1.105 0.188 0.524 0.533 4.515 3.144 7.659
8/5/2019 Polpis - Oyster ORS6 29.6 0.026 NS 0.004 0.003 0.007 0.278 0.286 0.967 0.168 0.446 0.453 4.403 3.200 7.603
9/17/2019 Polpis - Oyster ORS6 29.7 0.035 NS 0.021 0.008 0.029 0.289 0.318 0.484 0.064 0.352 0.382 0.885 0.025 0.910
21
Status and Trends in Water Quality of Nantucket’s Estuaries: Based on the water quality
data collected by the Nantucket Island-wide Monitoring program since 2010, it is now possible
to conduct an initial trend analysis. While trends have been noted in previous reports, due to
the now available 9 years of data, trends are becoming clearer and coming through the noise of
interannual natural variations. For this analysis temporal trends are assessed in each of the 6
estuaries by combining data from 2010, 2012 and 2013; 2014, 2015 and 2016; 2017, 2018 and
2019. Key water quality parameters were examined to determine if changes in estuarine health
have occurred over the past decade.
Nantucket Harbor has had a number of nitrogen mitigations: a) raising the jetties, b) new
sewering, c) fertilizer by-law. From the time course of Total Nitrogen (TN) it is clear that the
most recent 3 years of monitoring at each harbor station show lower TN levels than in the prior
2 three year groupings going back to 2010 with the 2014-2016 grouping showing intermediate
levels. This indicates a lowering of TN harbor-wide over the past decade (Figure 7). Similarly
when examined by basin, again there is a consistent decline in TN and the rate of decline is
consistent among the basins (Figure 8). This pattern is consistent with the Town’s mitigation
efforts, which may not have fully impinged upon Nantucket Harbor at this time.
Phytoplankton biomass as total chlorophyll a pigments, shows a more variable pattern as the
levels are controlled by a variety of factors in addition to nitrogen levels. Overall, chlorophyll
levels within the main basin of Nantucket Harbor have been indicative of a modest level of
impairment (averaging <10 ug/L), with slightly higher levels in Polpis Harbor. However, it is
clear that chlorophyll a has also declined from the early period (2010,2012,2013) to recent
sampling, with 2019, 2017, 2016 and 2014 being relatively low and indicating high water quality
(Figure 9). Both chlorophyll a and TN are consistent with improving estuarine conditions. TN
levels throughout the Harbor are approaching the TMDL targets for this system.
Figure 7. Temporal trends in Nantucket Total Nitrogen levels at all stations. Note that in all
cases the 2017-2019 levels are lower than the earliest grouping with 2014-2016 being in the
middle. Clearly TN levels have declined harbor-wide over the past 10 years due to nitrogen
mitigation strategies implemented by the Town.
22
Figure 8. Temporal trends in Nantucket Total Nitrogen levels within the key basins. Years were
combined as 2010, 2012 and 2013; 2014, 2015 and 2016; 2017, 2018 and 2019.
Figure 9. Average Chlorophyll-a concentrations by station in the well flushed Nantucket Harbor
system. Stations Nan-5 and 6 are in Polpis Harbor the rest relate to the main basin. Note that
2019 levels were slightly lower in the upper basins (Nan-5 slightly lower in 2019 vs. 2018 and
2017, Nan-6 slightly lower in 2019 vs. 2018 and 2017) and low and relatively constant
throughout the Harbor. The large blooms of 2012 and 2010 have not reoccurred in recent years.
23
Figure 10. Components of Total Nitrogen pool in Nantucket Harbor waters by station (2019). At
all stations TN is almost entirely in organic forms due to phytoplankton uptake of inorganic
nitrogen entering from the watershed and recycled from the sediments and conversion to
organic forms. Note that the TN levels are approaching the MEP TN Threshold level codified in
the present TMDL.
Table 3. TN levels by station and year in Nantucket Harbor for comparison to TMDL targets of
0.35 mg/L in Wauwinet (Stations 3 and 2A) and 0.355 mg/L in Polpis Harbor (Station 6)
[1] It is almost certain that this does not represent the TN level in the inflow to Nantucket Harbor
on the flood tide, but rather the 2012 data is influenced by mixing with TN enriched out-flowing
waters. An attempt to control for this issue was implemented in the 2013 monitoring program. It
should be noted that the 2019 concentration may also be high due to influence from out-flowing
waters. Concentration at station 4 is very sensitive to timing of sampling.
Historical 2010 2010 2012 2013 2014 2015 2016 2017 2018 2019
MEP Town Mean TN Mean TN Mean TN Mean TN Mean TN Mean TN Mean TN Mean TN Mean TN
Mean TN ID
(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)
Head of the Harbor - Upper 2 0.408 0.188 NA NS NS NS NS NS NS NS NS NS
Head of the Harbor - Mid Town 3 0.401 0.115 3 0.392 0.411 0.415 0.345 0.436 0.355 0.366 0.325 0.336
Head of the Harbor - Lwr 2A 0.339 0.07 2A NS NS NS NS NS 0.415 0.377 0.337 0.392
Pocomo Head 3 0.335 0.081 NA NS NS NS NS NS NS NS NS NS
Quaise Basin 3A+Town 2 0.336 0.112 2 0.297 0.364 0.345 0.314 0.374 0.314 0.302 0.256 0.292
East Polpis Harbor 4+Town 6 0.362 0.105 6 0.438 0.484 0.401 0.378 0.404 0.371 0.405 0.327 0.378
West Polpis Harbor 4A+Town 5 0.388 0.119 5 0.431 0.419 0.385 0.389 0.422 0.42 0.429 0.341 0.416
Abrams Point 5 0.335 0.06 NA NS NS NS NS NS NS NS NS NS
Monomoy 6 0.297 0.086 NA NS NS NS NS NS NS NS NS NS
Mooring Area 7+Town 1, 1A 0.326 0.106 1, 7 0.332,
0.377
0.335,
0.379
0.323,
0.323
0.294,
0.284
0.390,
0.330
0.304,
0.319
0.317,
0.333
0.212,
0.253
0.262,
0.274
Nantucket Sound OS+Town 4 0.239 0.041 4 0.283 0.344[1]0.3171 0.277 0.297 0.283 0.288 0.192 0.307
Sub-Embayment Monitoring
Station s.d.
MEP TN
Threshold
NAN3 = 0.350 mg/l
NAN6 = 0.355 mg/l
24
Madaket Harbor is similar to Nantucket Harbor in that it generally supports high water quality
and is flushed with high quality low nitrogen offshore waters. There is typically a gradual
nitrogen gradient from Hither Creek (MH-1) into the main basin (MH-2 and MH-3) with lowest
levels near the offshore boundary (MH-4). Only the levels in Hither Creek exceed the TMDL
target level (0.45 mg TN/L), which was also the case in 2019 (Figure 11). Similar to Nantucket
Harbor, inorganic nitrogen levels are very low and represent only a minor fraction of the total N
pool. This is due to the rapid uptake of this plant available form of nitrogen by phytoplankton
and supports the contention that nitrogen is the key nutrient for managing phytoplankton blooms
and maintaining clear waters. After uptake by phytoplankton the inorganic forms are converted
to phytoplankton biomass, seen as PON, and can be released upon phytoplankton death and
decay as DON.
There appears to be a trend towards lower TN levels at the Hither Creek Stations in recent
years compared to 2010-2014 which may be related to changes in Long Pond (Figure 12 and
see below). Phytoplankton biomass (as total chlorophyll a) follows the TN gradient from inshore
to offshore quite well in each year (Figure 13). This is due to the mixing of higher nitrogen
higher chlorophyll a waters discharging from Hither Creek with the lower nitrogen lower
chlorophyll a waters of Madaket Harbor. The variable temporal decline in TN in recent years,
therefore, may be resulting from lower TN discharges from Hither Creek which is significantly
fed from outflowing waters from Long Pond and direct watershed inputs to Hither Creek itself.
Examining Hither Creek in combination with Long Pond suggest that there may have been a
slight decline in TN levels over the past decade, although the trend is not statistically significant.
However, the large continuing decline in TN levels in Long Pond is significant (Figures 14 and
15) and is likely due at least in part to modifications of the Town Landfill resulting in a lessening
of nitrogen emanating from this source. At present the TN level in Long Pond is approaching
the target in the TMDL for this basin.
The effects of this lower TN can be seen in the generally lower chlorophyll a levels at station 6
in Long Pond adjacent the Landfill. Although variable, the values tend to be lower in recent
years and significantly lower than in 2003 when the Massachusetts Estuaries Project (MEP)
found average summer chlorophyll a levels of >40 ug/L compared to >15 ug/L in summer 2019.
Overall, the Nantucket Monitoring Program will continue to closely track improvements in Long
Pond relative to its regulatory TMDL, but it seems at present that this estuarine basin has
improved since the MEP and during the past decade of consistent monitoring.
25
Figure 11. TN, dissolved inorganic nitrogen (DIN), dissolved organic nitrogen (DON) and
particulate organic nitrogen at stations within Madaket Harbor 2019.
Figure 12. Total nitrogen levels by station over time in Madaket Harbor, horizontal line it TMDL
TN level.
26
Figure 13. Average Total Chlorophyll-a concentrations by station in the well flushed Madaket
Harbor system during the 2010-2019 summer sampling seasons. Stations MH-2,3,4 are in the
main open basin and consistently show moderate to low chlorophyll a pigments, MH-1 is the
MEP sentinel station in Hither Creek and recorded the highest levels to date. The 2010 blooms
had not been as prevalent in follow-on years and 2019 total pigment levels appear lower at all
stations compared to 2018 levels.
Figure 14. TN levels in Madaket Harbor main basin (MH-2,3-4), Hither Creek (MH-1) and Long
Pond (stations Long 5 & 6) over the past decade. Note that in all cases the 2017-2019 levels
are similar to (but slightly lower than) the earlier grouping in Hither Creek and Madaket Harbor.
In contrast Long Pond shows significant reductions in TN from 2010,2012, 2013 to 2014-2016 to
2017 to 2019. Clearly TN levels have declined in Long Pond and possibly Hither Creek over the
past 10 years.
0.000
0.200
0.400
0.600
0.800
1.000
1.200
1.400
Madaket Harbor / Long Pond
TN concentration (mg/L)
TN (avg. 2010,12,13)TN (avg. 2014,15,16)TN (avg. 2017,18,19)
27
Figure 15. Change in TN level in Madaket Harbor main basin (MH-2,3-4), Hither Creek (MH-1)
and Long Pond (stations Long 5 & 6) over the past decade. Note the significant decline in TN in
Long Pond such that 2017-2019 levels are approaching the TN level target in the TMDL for this
estuary, likely linked to Town efforts to remediate the Town Landfill in the watershed to the
upper basin.
Figure 16. Average Total Pigment (Chlorophyll-a +Pheophytin) concentrations by station in the
Long Pond portion of the Madaket Harbor system during the summer 2019 sampling season
compared to 2010, 2012, 2013, 2014, 2015, 2016, 2017 and 2018. T-pigment levels slightly
higher in 2019 compared to summer 2018.
y = -0.0615x + 0.65
R² = 0.5916
y = -0.0275x + 0.3693
R² = 0.9868
y = -0.2405x + 1.3597
R² = 0.953
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
Madaket Harbor / Long Pond
TN concentration (mg/L)
TN (MH1)TN (avg. MH2,3,4)TN (avg. LONG5,6)
Linear (TN (MH1))Linear (TN (avg. MH2,3,4))Linear (TN (avg. LONG5,6))
0
5
10
15
20
25
30
2010 2012 2013 2014 2015 2016 2017 2018 2019
Long Pond Total Chlorophyll a (ug/L)
Long-6 Long-5
28
Sesachacha Pond is a periodically opened salt water kettle pond that is managed by the
Nantucket Natural Resources Department. Due to coastal processes it is not possible to
maintain an open tidal inlet to this system or the other major coastal pond of Hummock Pond
(brackish) and Miacomet Pond (once brackish now freshwater). Given the general lack of
flushing of these ponds makes them particularly sensitive to nutrient inputs and the negative
effects of eutrophication.
Sesachacha Pond has only a moderate level of watershed nitrogen inputs, but they have a
magnified effect as the system only periodically receives tidal flushing (1-2 times/yr). Prior
monitoring results have determined that successful openings (those of >5 days) have a positive
effect on water and habitat quality. In fact, it appears that Sesachacha Pond can nearly achieve
or even achieve its regulatory TMDL level for TN if openings can be prolonged. At present,
Sesachacha Pond’s total nitrogen levels are above its TMDL target level at all stations (Figure
17). Although Sesachacha Pond remains above its TMDL target of 0.60 mg/L, the summer
average TN levels have changed. While the openings 2010-2019 have not achieved the TMDL
TN level, this salt pond has generally had higher water quality than historically (MEP). The
baseline TN level for this pond found by the MEP was 1.197 mg TN/L, which supported
degraded water quality and periodic chlorophyll a blooms of 100 ug/L. Since a focused opening
management plan has evolved over the past decade, TN levels have generally declined and
averaged 0.784 mg TN/L over 2018 and 2019 field seasons (Table 4). This underscores that
even at present levels of success openings play a critical role in lowering eutrophication in this
estuary.
Although the system is brackish due to its reduced salt water input, its nitrogen components are
similar to the tidally flushed estuaries in that, entering dissolved inorganic N (DIN) is rapidly
taken up by phytoplankton and converted to organic forms. The result is that almost all water
column nitrogen can be found in growing or senescent phytoplankton (PON) or as dissolved
organic nitrogen after release from senescent or decaying phytoplankton in the water column or
after being deposited to the sediments (Figure 17). Sesachacha Pond waters do contrast with
Nantucket and Madaket Harbor waters in the fraction of particulate organic nitrogen (PON) held
in suspended phytoplankton, consistent with the elevated phytoplankton biomass indicated by
the elevated total chlorophyll a levels in 2019 (see below).
The variation in pond openings can be seen in the variation in summer TN levels between years
(Figure 18). The variation in TN causes large interannual variations in total chlorophyll a, but
the elevated TN supports periodic blooms supporting the contention that the system is still
eutrophic (Figure 19). Chlorophyll a levels >10ug/L typically indicate eutrophic conditions
resulting from elevated nitrogen (which is also observed, Figure 17). However, as a variety of
factors modify phytoplankton levels established by nitrogen inputs, the variation in
phytoplankton levels show more variation than the TN levels from year to year. However, the
general pattern of openings to TN levels to overall water quality is clear.
29
Figure 17. TN, dissolved inorganic nitrogen (DIN), dissolved organic nitrogen (DON) and
particulate organic nitrogen at stations throughout Sesachacha Pond 2019. Note that at all
stations the TN level exceeds the regulatory TMDL, indicating that this system remain nitrogen
impaired.
Table 4. Summer average TN levels for Sesachacha Pond for comparison to its TMDL target of
0.60 mg/L. Note that while the openings 2010-2019 have not achieved the TMDL TN level, The
salt pond has generally had higher water quality than historically (MEP).
Historical 2010 2012 2013 2014 2015 2016 2017 2018 2019
MEP Mean TN Mean TN Mean TN Mean TN Mean TN Mean TN Mean TN Mean TN Mean TN
Mean TN (mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)(mg/L)
Sesachacha Pond 1.197 0.078 0.684
(0.704)
0.678
(0.639)
0.714
(0.669)
0.919
(0.922)
0.918
(0.904)
1.01
(1.003)
0.960
(0.884)
0.734
(0.752)
0.833
(0.845)
Sampling Station Location s.d.
30
Figure 18. Total nitrogen levels by station over time in Sesachacha Pond, horizontal line it
TMDL TN level. Longer openings in 2010-2014 resulted in lower TN levels (<0.75 mg/L), recent
opening attempts are again being more successful (2018), but TN levels remain above the
target level.
Figure 19. Average Total Pigment (Chlorophyll-a +Pheophytin) concentrations by station in the
seasonally opened Sesachacha Pond system during the summer 2019 sampling season
compared to 2010, 2012, 2013, 2014, 2015, 2016, 2017 and 2018. T-pigment levels appeared
variable across the stations (2 stations high close to 2018 levels and 2 stations low).
31
Hummock Pond is a periodically opened river valley pond that is managed by the Nantucket
Natural Resources Department. Due to coastal processes it is not possible to maintain an open
tidal inlet to this system or the other major coastal pond of Sesachacha Pond (brackish) and
Miacomet Pond (once brackish now freshwater). Given the general lack of flushing of these
pond makes them particularly sensitive to nutrient inputs and the negative effects of
eutrophication. Managing openings of Hummock Pond has been particularly difficult due to
longshore transport and the location of the opened inlet relative to dominant wind direction and
storm flows. For this pond to be effectively opened analysis of weather and wave/wind direction
needs to be monitored. The Town NRD and SMAST have developed a plan to establish this
system for the periodically opened pond of Nantucket and are working jointly with the Martha’s
Vineyard Commission (who has the same problems) towards implementation. At present, we
have variable openings that generally do not sufficiently lower pond TN levels before the inlet
closes with resulting eutrophic conditions.
Hummock Pond has only a moderate level of watershed nitrogen inputs, but they have a
magnified effect, as the system only periodically receives limited tidal flushing (at most 2
times/yr). At present, Hummock Pond’s total nitrogen levels are well above its TMDL target
level at all stations (Figure 20). This is true for the main drown river valley basin and its tributary
salt pond (Head of Hummock).
Although Hummock Pond remains above its TMDL target of 0.50 mg/L, the summer average TN
levels have varied over time. While the openings 2010-2019 have not achieved the TMDL TN
level, this salt pond has shown a range of water quality associated with the success of its tidal
openings and sometime storm overwash. Overall the pond has an increasing level of TN
moving from near the barrier beach toward its headwaters (Figure 20). Head of Hummock does
not have good exchange with the main basin and sometimes functions as a separate eutrophic
basin.
Although the system is brackish due to its reduced salt water input, its nitrogen components are
similar to the tidally flushed estuaries in that, entering dissolved inorganic N (DIN) is rapidly
taken up by phytoplankton and converted to organic forms. The result is that almost all water
column nitrogen can be found in growing or senescent phytoplankton (PON) or as dissolved
organic nitrogen after release from senescent or decaying phytoplankton in the water column or
after being deposited to the sediments (Figure 20). Hummock Pond waters are similar to
Sesachacha Pond and contrast with Nantucket and Madaket Harbor waters in the large fraction
of particulate organic nitrogen (PON) held in suspended phytoplankton. This is consistent with
the elevated phytoplankton biomass indicated by the elevated total chlorophyll a levels in 2019
(see below).
The baseline TN level for this pond, (2010-2014 monitoring) was generally lower than over the
past 3-4 years, except for HUM-7 which have exceedingly levels in the baseline period (Figure
21). It appears that this recent period TN levels have been higher at most stations (HUM-1,3,8)
and at some stations (HUM-7) have been rising consistently from year to year from 2015 to
2019. It appears that after the successful opening prior to the 2015 field season, the tidal
flushing significantly lowered TN throughout Hummock Pond and reset the system to new lower
32
TN levels. However, following years were not as successful and the TN levels rose over time to
their new much higher (than 2015) levels. Apparently, (a) even a single very successful
opening can have a multiyear positive impact on Hummock Pond water quality and (b) it takes
multiple years after a solid opening for the system to be reset to higher TN levels. This
underscores that even a modest improvement in openings of Hummock Pond can play a critical
role in lowering eutrophication in this estuary.
The variation in pond openings can be seen in the variation in summer TN levels between years
(Figure 21). The variation in TN causes large interannual variations in total chlorophyll a, but
the elevated TN supports periodic blooms supporting the contention that the system is still
eutrophic (Figure 20). Chlorophyll a levels >10ug/L typically indicate eutrophic conditions
resulting from elevated nitrogen (which is also observed, Figure 22). Chlorophyll a levels in
Hummock Pond are generally well above 10 ug/L exceeding 30 ug/L over some summers
(2010, 2017-2019), matching the level of nitrogen enrichment throughout this estuary.
However, as a variety of factors modify phytoplankton levels established by nitrogen inputs, the
variation in phytoplankton levels show more variation than the TN levels from year to year. The
general pattern of openings to TN levels to overall water quality is clear with the high TN levels
in 2017-2019 (Figure 23) and highest chlorophyll a levels (Figure 22) and conversely the lowest
TN levels in 2014-2016 and more moderate chlorophyll a levels.
Overall, Hummock Pond remains eutrophic and is currently declining further. Unless nitrogen
mitigations become possible, it appears that improvement to flushing are the primary
mechanism to improving this ponds water quality and meeting its regulatory nitrogen TMDL.
The positive news is that new approaches are being developed and the Nantucket Monitoring
Program working with Nantucket NRD has demonstrated that periodic flush can make major
improvement to the health of this estuarine system.
33
Figure 20. TN, dissolved inorganic nitrogen (DIN), dissolved organic nitrogen (DON) and
particulate organic nitrogen at stations along the main axis of Hummock Pond, with HUM-7
being the tributary deeper basin at the head of the estuary. Note that at all stations the TN level
greatly exceeds the regulatory TMDL (0.50 mg TN/L), indicating that this system remain
nitrogen impaired.
Figure 21. Summer average total nitrogen levels by station over time in Hummock Pond,
horizontal line is the TMDL TN level (0.50 mg TN/L). The long opening in 2015 lowered TN
levels (<0.65 mg/L), but recent opening attempts have been difficult and TN levels have risen
>0.75 mg/L well above the target level for high water quality.
34
Figure 22. Average Total Pigment (Chlorophyll-a +Pheophytin) concentrations by station in the
seasonally opened Hummock Pond system, during the summer 2019 sampling season
compared to 2010, 2012, 2013, 2014, 2015, 2016, 2017 and 2018. T-pigment levels in 2019
equally high as in 2018 for the upper to middle portions of the system and slightly lower at
stations Hum-3 and Hum-5 closer to the periodic opening.
Figure 23. Change in TN level in Hummock Pond main basin (HUM-1,3,5,7) and the Head of
Hummock basin (HUM-7) over the past decade grouped to reduce the variation to see if any
trends existed. Note that the 2014-2016 (best openings) showed the highest water quality
(lowest TN levels) throughout the pond, while the previous period and recent period had higher
TN levels.
35
Miacomet Pond was a periodically opened salt water pond managed by the Nantucket Natural
Resources Department. However, due to coastal processes it is not possible to maintain an
open tidal inlet to this system or the other major coastal pond of Sesachacha Pond (Brackish)
and Hummock Pond (brackish). Due to its not being opened for over a decade, Miacomet Pond
is now functioning as a freshwater pond with freshwater salinities throughout. As a fresh pond,
Miacomet is highly eutrophic with periodic needs for nitrogen and phosphorus management,
with nitrogen being the primary nutrient for management in 2019 (Table 5).
Nitrogen levels in Miacomet Pond in 2019 were exceedingly elevated, >0.8 mg N/L, indicative of
a highly eutrophic pond (Figure 24). Target thresholds for estuaries to maintain a high water
and habitat quality are generally in the range of 0.35 – 0.50 mg N/L, less than half of Miacomet
Pond (Figure 24). Although this pond is not opened by the Town, this salt pond has shown a
range of TN levels from year to year the cause of which is being investigated. Overall the pond
has an increasing level of TN moving from near the barrier beach toward its headwaters (Figure
24), a common patter if nutrient enter more into the headwaters than from the margins.
Although the system is fresh due to its lack of salt water input, its nitrogen components are
similar to the brackish water estuaries in that, entering dissolved inorganic N (DIN) is rapidly
taken up by phytoplankton and converted to organic forms. The result is that almost all
watercolumn nitrogen can be found in growing or senescent phytoplankton (PON) or as
dissolved organic nitrogen after release from senescent or decaying phytoplankton in the
watercolumn or after being deposited to the sediments (Figure 24). Miacomet Pond waters are
similar to Hummock and Sesachacha Pond in the large fraction of particulate organic nitrogen
(PON) held in suspended phytoplankton. This is consistent with the elevated phytoplankton
biomass indicated by the elevated total chlorophyll a levels in 2019 (see below).
Since Miacomet Pond is not opened to tidal flushing the large variations that take place from
year to year are a bit unclear (Figure 25). One explanation being investigated is associated with
rainfall and groundwater recharge. In periods of high rainfall, groundwater levels increase and
watershed discharge (carrying nitrogen as nitrate) increases, which would increase nitrogen
levels in Miacomet Pond. The region has had variable recharge over the past decade with wet
and drought periods.
As part of the monitoring effort, total phosphorus is measured as in some years phosphorus is
also a nutrient of concern. In 2019 total phosphorus levels were: at MP-3 in the innermost
basin, 120 ug P/L (s.d.=82 ugP/L). aat MP-2 in the mid basin, 69 ug P/L (s.d. = 30) and in the
basin nearest the barrier beach, 60 ug P/L (s.d.=27 ug/L). For Cape Cod ponds the target for a
high quality pond is a total phosphorus level of <20 ug/L, based upon either TN or TP levels,
Miacomet Pond is highly eutrophic.
Phytoplankton biomass, as total chlorophyll a also varies widely from year to year and generally
exceeds the 10 ug/L level indicative of a nutrient enrich water body (Figure 26). Given the high
nitrogen and phosphorus levels throughout Miacomet Pond and prior indications that both
nutrient may periodically cause phytoplankton or algae blooms, at present management actions
should focus on both nutrients. However, is phosphorus control is implemented, it is likely that
the blooms would decline, since most freshwater systems have an overabundance of nitrogen
36
(like Miacomet) but very low phosphorus levels. This approach requires some simple feasibility
study but may indicate a way forward for this eutrophic pond. Over the past decade Miacomet
Pond has supported degraded water quality and poor habitat health, it’s condition, though
variable is not improving measurably.
Table 5 - Nitrogen to phosphorous ratios from Miacomet Pond during the summer 2019
sampling season indicating that in 2019 the nutrient for managing eutrophication was
primarily phosphorus as DIN/DIP and TN/TP ratios at all stations were <16, the Redfield
ratio.
Figure 24. TN, dissolved inorganic nitrogen (DIN), dissolved organic nitrogen (DON) and
particulate organic nitrogen at stations along the main axis of Miacomet Pond, with MP2 in the
basin nearest the barrier beach. Note that at all stations the TN level greatly exceeds the
threshold for brackish and estuarine systems.
Station Id.N/P PC/PN DIN/DIP TN/TP
(2019)organic particulate inorganic total
MP-3 16.2 9.9 3.7 2.6
MP-1 26.0 10.2 8.7 3.1
MP-2 35.3 9.2 9.4 6.8
37
Figure 25. Summer average total nitrogen levels by station over time in freshwater Miacomet
Pond. As a freshwater pond a regulatory TMDL target for nitrogen or phosphorus has yet to be
established.
Figure 26. Average Total Pigment (Chlorophyll-a +Pheophytin) concentrations by station in the
Miacomet Pond system during the summer 2019 sampling season compared to 2010, 2012,
2013, 2014, 2015, 2016. 2017 and 2018. Miacomet Pond is not opened to the Atlantic Ocean
and now contains freshwater (<0.2 PSU). Total chlorophyll a pigment levels remain elevated in
2019 compared to past years.
38
Trophic State of the Estuaries of Nantucket Island
The Trophic State of an estuary is a quantitative indicator of its nutrient related
ecological health and is based on key ecological metrics: concentrations of inorganic
and organic Nitrogen, water clarity (Secchi Depth), lowest measured concentrations of
Dissolved Oxygen (average of lowest 20% of measurements), and Chlorophyll-a
pigments (surrogate for phytoplankton biomass/blooms). Nutrient related trophic health
scales generally range from Oligotrophic (healthy-low nutrient) to Mesotrophic (showing
some signs of deterioration of health due to nutrient enrichment) to Eutrophic (habitats
significantly impaired and degraded, high levels of nutrients and organic matter and
community shifts). The Trophic Health Index Score used here is a standard numerical
scale based on criteria for open water embayments and uses the above mentioned
measured parameters to create a habitat quality scale (Howes et al. 1999,
http://www.savebuzzardsbay.org). For the estuaries within the Town of Nantucket, a
trophic index score was calculated for each sampling location for each year (2010 and
2012- 2019) using the summer monitoring results. The Index scores were calculated in
2 ways, one which included the low dissolved oxygen for each year in the index ("with
DO", Table 6a) and one which excluded the oxygen metric ("without DO", Table 6b).
The reason for this dual approach is that in some estuaries, such as those on Nantucket,
there are only periodic depletions in bottom water dissolved oxygen, generally related to
meteorological events acting on nutrient enriched basins. While these short-term
depletions have important ecological consequences, they are difficult to capture in
programs that sample 4 or 5 dates per summer. In these cases, inclusion of the oxygen
can bias the Index upwards (i.e. higher quality) because of the greater probability of
capturing high versus low oxygen events (i.e. missing periodic low oxygen events). This
bias was found in the previous analysis of the 2010 dataset, as well as for other
estuaries insoutheastern Massachusetts. However, this is not always the case and
there was no substantive “biasing high” between the "with DO" and "without DO" Index
scores based on the 2013 and 2014 data and again in 2016 and 2017 none-the-less, the
index analysis by both methods is presented for informational purposes herein (Tables
6a,6b). It should be noted that to the extent the bias does exist in a given year, it relates
only to the oxygen data, the other water quality parameters do not change as rapidly as
dissolved oxygen and therefore the sampling program adequately captures accurate
concentrations of nutrient related metrics (DO changes by the hour). Further analysis of
the with DO and without DO index values for all stations and monitoring years indicates
that there is very little difference in the determined index value between the methods
(RPD <10%; generally <5%). The exception was in Miacomet Pond and Head of
Hummock Pond which have significant DO depletions in some years and therefore
higher variability between the methods (RDP up to 20%). Given that inclusion of oxygen
data did not generally change the bay health rank, the index calculated by including DO
appears to be most appropriate based upon 9 years of data, but both approaches are
developed each year and presented herein.
For the present analysis the standard Index (with DO) was used for assessment and the
Health Status was determined for each site based on the data collected during the
39
sampling events. The ranges of Index scores that fall within a particular Health Status
determination are given below with the Index values and description for each monitoring
station. Figures 27-31 show the distribution of Health Status throughout each estuary
based on each of the 8 years of monitoring (2010, 2012-2019). For the location maps,
only the “with DO” index is shown as in 4 of the past 5 years the inclusion of DO made
no substantive difference in the index value and in 2015 the difference was minor.
Therefore, the Index maps shown for the “with DO” index are comparable to other
estuaries in the region for assessing Trophic Status. Numerical results in the tables are
color coded in the figures for ease of interpretation. The colors of each triangle
represent the Bay Health Index status of each site and follow the designation scheme
below:
Color Health Status
Blue High Quality
Blue/Yellow High-Moderate
Yellow Moderate
Yellow/Red Moderate/Fair
Red Fair/Poor
The integrated water quality scores, as represented by the Index were generally
consistent among all 9 years of monitoring. Although change at some sites was
observed, change was gradual and large inter-annual changes were typically related to
major management actions. This relative stability is typical as nutrient related health
does not generally change rapidly unless a significant alteration has occurred to the
watershed nitrogen loading or to tidal flushing of a basin (e.g. Hummock Pond, Long
Pond). However, 4 systems do appear to show a potential shift in nitrogen related
health over the past 9 years, Hither Creek, lower Hummock Pond and Long Pond and
after 9 years, slight improvements in Nantucket Harbor seem to be emerging (see
below). Based upon the results it is possible to assess the nutrient related health of the
basins within each of the 5 estuarine systems within the Nantucket Water Quality
Monitoring Program. The following assessments rely mainly on the Index "with DO"
scores as it appears to accurately represent current conditions:
High >69 Blue
High-Moderate 61-69 Blue-Yellow
Moderate 39-61 Yellow
Moderate-Fair 31-39 Yellow-Red
Fair-Poor <31 Red
40
Madaket Harbor
Madaket Harbor main basin in 2019 continued to support a high level of nutrient related water
quality as was observed in 2018. It has been the more enclosed basins of Hither Creek and
Long Pond with their reduced tidal flushing that have had nitrogen impairment problems. Water
quality generally changes gradually, unless there has been a major change in loading or
flushing. Within the Madaket Harbor/Long Pond watershed there has been a significant change
in the nitrogen sourced at the Town Landfill. The Landfill has recently been undergoing
management actions that reduce nitrogen loading to the groundwater, hence to upper Long
Pond. It appears that the long-term gradual reduction in TN levels within the upper portions of
this complex estuary is consistent with a lowering of watershed nitrogen loading. Over the 9
years of monitoring, Hither Creek (Station 1), which receives discharge from Long Pond via
Madaket Ditch, has consistently supported the poorest “health” status within the Madaket
Estuary (Table 6a,b, Figure 29). Hither Creek is clearly nitrogen enriched and showing
continuing impairment based on a variety of parameters but has clearly improved since 2010.
Over the past 9 years the Index indicates that this basin has improved slightly each year, going
from fair-poor water quality and improving in a step-wise manner to moderate water quality
since 2014. The exception was 2017 where TN levels increased stayed within the range that
has developed over the past 4-5 years, TN level declined to pre-2017 levels in 2018 (0.41 mg/L)
but went up slightly in 2019 (0.50 mg/L). It is expected that this variability will be reduced in
coming years as the system reaches a new equilibrium with the new lower landfill TN loading
rate. The main basin of Madaket Harbor is showing relatively high water quality in each year
but also shows a possible improvement from 2010 to 2012 and has been generally stable at
high water quality in more recent samplings to 2019. It appears that Station 2, near the outlet to
Hither Creek can receive low quality waters on the ebb tide from Hither Creek and that can
modify water quality at this nearshore location (e.g. 2010). But with improvements in the water
quality in Hither Creek, its effect on water quality at Station 2 in nearshore Madaket Harbor has
been insufficient to affect the Harbor waters, which have maintained high quality status since
2012. The offshore sites (3 & 4) support high quality waters resulting from low nitrogen inputs
and very high rates of water exchange. The 9 year positive trend in health index is at least
partially the result of the reduced loading from the landfill to upper Long Pond and an
improvement in the ebbing waters through Madaket Ditch. This trend is consistent with the
upper basin feeding Madaket Ditch. In 2014-2018 the previously observed gradient in water
quality metrics between the 2 Long Pond stations is only periodically detectable, lessening
concern over a potential tidal restriction, however, slightly higher TN and chla. levels observed
in 2019 in Long Pond indicate that the system does exhibit variability and careful management
is still required. While a further analysis of the mechanism underlying this periodic gradient
would be useful, it is not needed at this time, tracking the phenomenon through the on-going
monitoring program should be sufficient. If the improvement in Hither Creek becomes stabilized
at the lower end of its range (0.8 – 0.6 mg/L) and 2018 was 0.59 mg N/L (2019 TN 0.50 mg/L at
station MH1), it is possible that the TMDL for Madaket Harbor may require somewhat less
nitrogen load reduction, making the success of other nitrogen management actions (other than
associated with the landfill and any needed septic system work in Madaket) more certain.
However, at this point it is likely that additional nitrogen management will be required to meet
41
the TMDL in Hither Creek as it remains of moderate quality, although it appears the reduced
load discharging from Madaket Ditch has resulted in somewhat lower TN levels already. It
should be noted that the “fair/poor" quality water designation in Long Pond relates primarily to
Long Pond being not supportive of eelgrass. But the MEP and TMDL for Long Pond is based
on infaunal animals living in the bottom sediments (i.e. not eelgrass) so the water quality index
should not cause concern. However, additional analysis is required to determine if landfill
activities will be sufficient to meet the TMDL for Long Pond (see below). Additional study to
clarify the drivers of the improvement (controllable such as the landfill improvements or fertilizer
management) will further assist in determining the magnitude of septic system management as
posited through the MEP analysis. This further analytical effort is in progress in parallel with the
Town’s actual and potential management actions.
Long Pond
Long Pond is a large tributary basin to Madaket Harbor, which receives tidal flow through
the artificial connection of Madaket Ditch. Given the structure of the basin and its
watershed, Long Pond operates semi-independently from Madaket Harbor (Figure 29).
Unlike Madaket Harbor which is marine, Long Pond is a brackish water system resulting
from mixing of groundwater inflows and salt water entering through its restricted tidal
channel (2018 and 2019 salinity = 16 PSU). Long Pond’s Bay Health scores for both
stations (5 & 6) in the 8 years of monitoring (2010, 2012-2018) clearly indicate poor
nutrient related water quality and this continues to be the case in 2019. It is nearly
certain that the water quality of Hither Creek is partially dependent on the nitrogen load
from Long Pond via Madaket Ditch during the ebb tide. However, it should be noted that
the TMDL targets restoration of sediment animal communities (infauna) which do not
require the same high water quality as eelgrass.
Based upon the 2019 results and the 9 year time-series, it appears that the Town’s
management of the landfill, has reduced the nitrogen load from this source with the
associated observed lowering of TN levels. The connection is strengthened by the
parallel timing of the landfill work and the lowering of TN in the adjacent waters, which
are only a short travel time from the landfill. While still small, the water quality Index for
Long Pond is starting to improve in response to the lower TN levels although the basin
remains impaired. TN levels in 2015-2017 and 2018-2019 were almost half that of
historical and 2010 measurements although they still show inter-annual variations as
2019 TN values were slightly higher (0.63 mg/L TN) compared to 2018 (0.59 mg/L TN).
While continued monitoring will determine the final level of improvement, it does appear
that the reduction in N loading is occurring with beneficial effects. If TN levels stabilize
at 2018-2019 levels, the TN target in the TMDL will be achieved and in summer 2021 a
habitat and DO survey should be conducted to remove Long Pond from the MassDEP
list of impaired waters, assuming summer 2020 levels are in line with 2018-2019 levels.
It should be noted that the lack of major change in the Health Index for Long Pond
results in part from the relative coarseness of the Index, where sometimes large index
score changes are required to change the Index value. The analysis of key metrics
(Chlorophyll-a, water clarity-Secchi and total nitrogen) individually do show improving
42
water quality at stations 5 and 6 in 2012-2018 compared to 2010 and in the MEP
threshold analysis (see analysis and figures above), however there was a slight decline
at station 5 (fair-poor). This may just be attributable to inter-annual variability and careful
monitoring should continue.
Nantucket Harbor
Nantucket Harbor with Madaket Harbor are presently supporting the highest water
quality of Nantucket's estuaries. In 2019, all of the Nantucket and Polpis Harbor stations
were showing high water quality, slightly better than in 2017. Over the past 6 years, the
main basin of Nantucket Harbor has supported high quality waters, with only a periodic
small level of decline in the uppermost basin, Wauwinet basin (Figure 27). Wauwinet
basin (station 3) had the highest average total nitrogen values for the Harbor System in
2013 (0.415 mg/L) and 2015 (0.436 mg/L) consistent with its designation as the
surrogate for the sentinel station for the main basin and its documented past eelgrass
loss. It should be noted that in summer 2016, SMAST added station 2A and established
it as the official MEP sentinel station for which the nitrogen threshold was established
(refer to Figure 2, TN 0.399 mg/L), along with station 3 in order to meet TMDL
compliance monitoring criteria. Summer 2017 saw a slightly lower TN level at station
NAN-2A (0.368 mg/L) and 2018 lower still (0.337 mg/L) but a slight increase in 2019
(0.392 mg/L). Summers 2016-2019 generally showed similar water quality in this basin
as 2014 which showed improved chlorophyll-a and TN levels versus prior years. The
main driver of the poorer 2015 water quality was a phytoplankton bloom in the upper
Harbor, which was relatively large for Nantucket Harbor but only moderate for more
enriched estuaries in the region. While it is unclear if blooms will become more
commonplace in the future, the levels in 2016 reflected more historic conditions and
2017/2018 again higher levels but lower in 2019, clearly these blooms need to be
tracked. However, other activities associated with the Harbor (additional sewer
hookups, jetty improvement and oyster aquaculture) should result in even lower TN and
chlorophyll levels and reduce the likelihood of large phytoplankton blooms in the future.
A similar pattern was seen in the enclosed sub-basins of Polpis Harbor (East and West)
as in the main basins of Nantucket Harbor. Polpis Harbor basins which after showing
moderate impairment in 2010 and 2012 have been showing only low to no impairment in
recent years, suggesting some improvement over historic conditions. As in Wauwinet,
Polpis Harbor showed 2018 & 2017 TN levels similar to 2010, 2012 and 2015, slightly
higher than 2013 and 2014. In 2019 TN levels were slightly higher than 2018. This
variation makes continued monitoring essential to clarify any trends in water quality and
linkages to stream nitrogen discharges. Polpis Harbor did not show a phytoplankton
bloom in 2015 and supported only moderate-low phytoplankton biomass in 2015-2017,
2018 and 2019 (average <6 ug/L) and appears to have attained generally high water
quality status from moderate status in 2010 and 2012. While the overall Nantucket
Harbor System is generally supporting high quality waters, the variability in the index in
Wauwinet and Polpis basins should be monitored to ascertain their long-term health and
to determine the effectiveness of restoration effort by the Town as it continues to move
43
forward to meet the MassDEP TMDL for this system. Overall, Nantucket Harbor
appears to be relatively stable from year to year with a gradual slight improvement with
high index scores and higher level metrics that support the contention that it is
approaching its TMDL threshold, as is also the case for Polpis Harbor. Equally
important, although variable, it appears that slight positive changes have been occurring
in recent years.
Sesachacha Pond
Sesachacha Pond is a closed coastal salt pond that has its water quality managed by
periodically breaching the barrier beach to open the basin to tidal exchange with the
adjacent Atlantic Ocean waters. This management action serves to flush out nutrients
and organic matter on the ebb tides and receive saline waters on the flood tides.
Sesachacha Pond was evaluated under the Massachusetts Estuaries Project and a
nitrogen threshold (0.60 mg/L) was established for restoration of this system.
Additionally, the MEP analysis recommended an additional mid-summertime opening (if
logistically possible) as part of the pond management strategy to enhance flushing of the
pond and improve water quality to reach the threshold without any need for
infrastructure. The water quality monitoring program in 2010, 2012 and 2013 showed
that the pond nitrogen levels were converging on the 0.60 mg/L total nitrogen threshold
established by the MEP. Total nitrogen (TN) levels dropped significantly from historical
levels of 1.20 mg/L to ~0.68 mg/L in 2010 and 2012 and 0.67 mg/L in 2013, with
associated improvements in the levels of water clarity and chlorophyll-a. However, with
limited openings in 2014-2017, TN has risen and has returned to near historic levels,
~0.9 mg/L but with an improvement in 2018 (0.752 mg N/L) but a more elevated level in
2019 (0.84 mg/L), associated with continuing impaired conditions. It appears that these
changes relate to the quality of the pre-summer opening. Given the 2010-2013 period
when robust openings occurred, it appears that a solid opening program continues to
have the capability to improve the water quality metrics pond-wide to levels near the
TMDL nitrogen threshold.
Based upon the Index alone, changes in water quality in Sesachacha Pond over the
2010-2013 period were stabilized at moderate impairment of this estuary, with more
recent monitoring 2015-2017 seeing a trend toward poor water quality conditions with a
rebound in 2018 (Figure 28) as TN levels rose (2015-2017) then declined (2018). In
2019, conditions appear to have worsened slightly compared to 2018 which is consistent
with higher TN levels in 2019. Additional higher level assessment of Sesachacha Pond
initiated based on the 2010 monitoring results was conducted and confirmed that the
pond was improving by 2013, but was impaired in 2014 consistent with the monitoring
results. The 2015-2019 data underscores the reversal of improvement with
phytoplankton biomass (as chlorophyll) averaging >10 ug/L at all stations over the
summer of 2018, 2017 and 2015 and 6-10 ug/L in 2016, consistent with nitrogen
enrichment. The high chlorophyll values are consistent with the elevated TN values in
2014-2019. It appears that like other periodically opened ponds, the quality of the
opening (amount of water exchanged) controls the level of water quality in the following
44
months. Fortunately, the data indicate that attaining pond openings of the quality of
2012 and 2013 (done under Town supervision) in the future may be sufficient to attain
the TMDL for this system. In addition, the impaired but improved conditions in 2018,
while high in TN, did not show bottom water D.O. depletion, but with high chlorophyll-a,
consistent with the MEP threshold target of 0.60 mg N/L. Similarly, while TN was higher
in 2019 than 2018, DO depletions were not apparent (4.7 to 7.8 mg/L, 20% low DO
values). A closer examination of the opening protocol and the linkage to resultant water
quality is needed for management of this system.
Hummock Pond
Hummock Pond is a closed coastal salt pond that is only periodically opened to the
ocean to flush out nutrients and organic matter on the ebb tide and receive low nutrient
saline waters on the flood tide. Creating sustained openings that are sufficient to allow
exchange of tidal waters for more than 4-5 days has been difficult for this system due to
its location on the coast and the large amount of sand migration in the coastal zone
which can rapidly reseal the inlet.
Hummock Pond is opened at a sufficient frequency to sustain salinity levels in the 4-8
ppt range, with only small inter-annual differences (2012 slightly higher than 2010). The
pond continues to support a small but clear salinity gradient from Station 1 nearest the
ocean to Station 7 in the uppermost basin (Head of Hummock). The present non-tidal
state and watershed nutrient inputs have resulted in moderate to poor nutrient related
water quality throughout the pond, with poor water quality conditions the present norm
(2005-2007, 2010, 2012, 2013, 2014, 2015). Unfortunately, in 2016 the pond appears to
have had lower water quality in its upper and mid reaches than in previous years,
although the lower basin did not show this inter-annual variation. Similarly, in 2017 and
2018 water quality declined further throughout most of the estuary, including the lower
basin. This resulted from the poor spring 2017 and 2018 opening which is reflected in
the very low salinities throughout summer 2017 (3.5 PSU), 2018 (4.8 PSU) and even
more so in 2019 (2.8-4.8 PSU). There is generally a small gradient in water quality with
moderate to poor conditions near the ocean and poor conditions in the uppermost
basins, but this collapsed to generally poor water quality throughout the system in 2017
and 2018 (Figure 31). These poor conditions remain unchanged in 2019. The
uppermost basin, Station 7, is approaching fresh/brackish conditions (4 ppt and 3.7 in
2018) and is currently supporting mainly freshwater plant and animal habitats (2.8 ppt in
2019). This basin is particularly eutrophic with phytoplankton blooms periodically
exceeding 70 ug/L (offshore waters are ~2 ug/L), although 2017 & 2016 showed levels
~15 ug/L and 21 ug/L in 2018 (consistent with is decline in salinity). In 2019 station 7
showed 14 ug/L chla. and station 8 showed 24 ug/L, consistent with the poor levels
observed in 2018. This basin appears to have been artificially connected to the adjacent
estuary and is the recipient of much of the freshwater inflow. It continues to be one of
the most highly eutrophic basins within the Town of Nantucket with oxygen depletions to
3 mg/L (1.36 mg/L DO in 2019). All of the metrics are consistent with a nutrient impaired
basin in all years. It should be noted that the lower third of the Hummock Pond Estuary
45
is currently supporting impaired benthic animal habitat even though conditions are the
"best" in the overall impaired system.
Based upon the monitoring results it is clear that the nutrient related health of Hummock
Pond is significantly related to the success of its periodic openings. The individual
metrics and the Health Index for summer 2014 and 2015 appear to support that tidal
flushing was improved as nutrient related health was highest in 2014 and 2015 of the
years monitored. It also appears that the continued successful inlet openings from April
2014 into 2015 have resulted in additional improvements in water quality from 2014 to
2015, with 2015 showing the lowest TN levels in records back to 2005, although it is still
above its threshold value to support high quality habitat. Unfortunately, this pattern was
not seen in the 2016-2019 water quality data, which showed further decline in the upper
and mid reaches, and even the lower basin. This opening program and associated
monitoring around the openings and in the summer will need to be used to set metrics
for a “successful” opening, to produce a simplified assessment protocol for opening
success and to document and further refine the opening protocol for the Town’s on-
going program. To date this joint effort has shown the potential for significant benefits to
Hummock Pond water quality and associated natural resources at low cost to the Town,
but successful openings appear to vary from year-to-year.
Miacomet Pond
Miacomet Pond is a closed coastal salt pond that is rarely (over a decade ago) opened
to the ocean to flush out nutrients and organic matter on the ebb tide and receive low
nutrient saline waters on the flood tide. As a result of the lack of tidal flow and
continuous groundwater inputs, the pond is presently freshwater, with salinity levels in
each of the past 8 years of monitoring of <0.5 ppt, reaching a low of 0.1 ppt, 2015-2017.
In summer 2018 salinity ranged from 0.1 to 0.55 pp whereas in summer 2019 it ranged
from 0.1 to 0.15 ppt. Clearly, Miacomet remains a very fresh water dominated system.
The present non-tidal state and extent of watershed nutrient inputs has resulted in a
decline in nutrient related water quality throughout the pond for both nitrogen and
phosphorus, with poor water quality and habitat impairment the present norm (Figure 30)
and it remained that way in the summer of 2019. This can be seen, for example, in the
high chlorophyll levels (2010: 12-50 ug/L); 2012: 10-20 ug/L; 2013: 20-26 ug/L; 2014:
23-70 ug/L; 2015: 38-53 ug/L) several times greater than the levels found in the high
quality basins of Nantucket and Madaket Harbors with a maximum in 2018 (25 ug/L)
following highs in 2017 and 2016 (mean = ~14 ug/L). Summer 2019 chlorophyll levels
ranged between 11-16 ug/L. All of the metrics for Miacomet Pond are consistent with a
highly nutrient impaired basin. As previously discussed in previous years, as the
freshening of this basin has become complete and sustained, it likely will have to be
managed as a transitional freshwater system and will need to be reassessed as such.
As salt ponds freshen and become fresh ponds the nutrient causing eutrophication can
shift to phosphorus from nitrogen or become both nitrogen and phosphorus (seasonally
varying nutrient limitation). Since Miacomet Pond may have storm over-wash in the
future due to climate change related storm intensification and sea level rise, it may be
46
necessary for management to create both a nitrogen and a phosphorus budget for this
system and to conduct short-term incubations to determine which nutrient is controlling
pond health under present and varying salinity conditions. None-the-less, phosphorus
should be a part of pond management, with phosphorus limitation to phytoplankton
growth throughout Miacomet Pond in 2019, 2018 and 2016/2017, although only for the
middle and lower pond in 2015.
Another challenge in managing Miacomet Pond is that it will be difficult for the Pond to
maintain itself as a purely freshwater system as storm over-wash and rising sea level (as
well as increasing storm intensity and frequency related to climate change) will tend to
periodically cause seawater intrusion into its lower basin. An analysis of future
conditions for Miacomet Pond as sea level rises may be in order in the near future, as
remediation is considered. But at present the system is a highly nutrient impaired aquatic
system with poor water quality. It would be prudent for the Town to continue the
development of a management plan that takes into account not only the nutrient related
impairment of Miacomet Pond, but also accommodates the likely shifting between fresh
and salt water over the long term.
47
Table 6a. 2019 Trophic Health Index Scores and status for water quality monitoring stations in
Nantucket estuaries based upon open water embayment (not salt marsh) habitat quality scales.
Index calculated with Dissolved Oxygen data (described in Howes et. al., 1999 at
www.savebuzzardsbay.org)
With DO
2019 Low20%2019
Secchi Oxsat DIN TON T-Pig EUTRO Health Status
EMBAYMENT SCORE SCORE SCORE SCORE SCORE Index
HUM7 51.45 0.00 0.00 0.00 0.00 10.29 Fair-Poor
HUM8 22.68 20.60 34.93 0.00 0.00 15.64 Fair-Poor
HUM5 25.93 74.26 83.94 0.00 0.00 36.83 Moderate-Fair
HUM3 35.40 82.31 71.41 0.00 0.00 37.82 Moderate-Fair
HUM1 43.07 56.24 84.60 0.00 0.00 36.78 Moderate-Fair
LONG6 25.88 40.17 100.00 0.00 0.00 33.21 Moderate-Fair
LONG5 13.86 0.00 100.00 0.00 0.00 22.77 Fair-Poor
HC1 53.75 100.00 100.00 71.67 55.56 76.20 High
HC2 30.17 100.00 47.11 18.05 11.48 41.36 Moderate
HC3 100.00 100.00 33.83 61.49 99.39 78.94 High
MH1 45.19 62.09 88.01 28.85 8.58 46.54 Moderate
MH2 64.97 80.89 97.78 89.39 75.13 81.63 High
MH3 83.68 86.05 100.00 100.00 98.62 93.67 High
MH4 97.25 89.34 100.00 100.00 100.00 97.32 High
MP3 21.64 32.87 33.07 0.00 0.00 17.52 Fair-Poor
MP1 51.75 55.66 78.75 0.00 0.00 37.23 Moderate-Fair
MP2 54.68 86.34 99.52 0.00 0.00 48.11 Moderate
NAN1 100.00 73.31 85.55 100.00 100.00 91.77 High
NAN2 87.75 79.70 93.32 100.00 81.62 88.48 High
NAN2A 79.88 67.03 75.29 64.48 48.19 66.98 High-Moderate
NAN3 78.57 75.78 73.35 86.76 72.89 77.47 High
NAN4 100.00 87.67 95.20 94.72 100.00 95.52 High
NAN5 55.11 49.64 100.00 51.98 65.23 64.39 High-Moderate
NAN6 71.84 68.35 95.66 66.11 89.81 78.35 High
NAN7 69.85 82.57 84.32 100.00 46.45 76.64 High
NAN8N 51.65 74.86 100.00 100.00 100.00 85.30 High
ST4 0.00 0.00 51.48 0.00 0.00 10.30 Fair-Poor
ST6B 17.87 47.52 65.56 0.00 0.00 26.19 Fair-Poor
WPH OUTLET 0.00 56.01 49.48 0.00 0.00 21.10 Fair-Poor
SESA3 35.61 91.19 100.00 0.00 59.70 57.30 Moderate
SESA2 32.62 49.95 88.75 0.00 0.00 34.26 Moderate-Fair
SESA4 33.92 91.54 100.00 0.00 54.58 56.01 Moderate
SESA1 35.19 29.35 62.11 0.00 0.00 25.33 Fair-Poor
ORS2 49.22 86.26 96.78 100.00 100.00 86.45 High
ORS4 56.59 16.87 66.39 57.14 46.73 48.74 Moderate
ORS6 33.53 38.59 97.22 53.20 59.48 56.40 Moderate
Station Average 2019 (with DO)
48
Table 6b. 2019 Trophic Health Index Scores and status for water quality monitoring stations in Nantucket estuaries based upon open
water embayment (not salt marsh) habitat quality scales. Index calculated with and without Dissolved Oxygen data
Station Average 2019 (with DO)Station Average 2019 (with DO)Station Average 2019 (with DO)With DO No DO With DO No DO
2019 %Sat 2019 Low20%2019 2019 2019 2019
Salinity Secchi m DO DIN TON T-Pig Secchi Oxsat DIN TON T-Pig EUTRO Health Status EUTRO Health Status EUTRO EUTRO
ppt EMBAYMENT YR All 20%ppm ppm ug/L SCORE SCORE SCORE SCORE SCORE Index Index Colors Colors
2.79 HUM7 2019 1.37 14%0.155 0.764 22.64 51.4 0.0 0.0 0.0 0.0 10.3 Fair-Poor 12.9 Fair-Poor Red Red
2.83 HUM8 2019 0.86 47%0.063 1.101 50.37 22.7 20.6 34.9 0.0 0.0 15.6 Fair-Poor 14.4 Fair-Poor Red Red
3.50 HUM5 2019 0.91 73%0.020 0.704 23.26 25.9 74.3 83.9 0.0 0.0 36.8 Moderate-Fair 27.5 Fair-Poor Yellow-Red Red
4.48 HUM3 2019 1.06 78%0.027 0.747 12.56 35.4 82.3 71.4 0.0 0.0 37.8 Moderate-Fair 26.7 Fair-Poor Yellow-Red Red
4.75 HUM1 2019 1.20 63%0.020 0.837 11.28 43.1 56.2 84.6 0.0 0.0 36.8 Moderate-Fair 31.9 Moderate-Fair Yellow-Red Yellow-Red
17.52 LONG6 2019 0.91 55%0.014 0.622 10.20 25.9 40.2 100.0 0.0 0.0 33.2 Moderate-Fair 31.5 Moderate-Fair Yellow-Red Yellow-Red
15.06 LONG5 2019 0.75 25%0.013 0.613 12.84 13.9 0.0 100.0 0.0 0.0 22.8 Fair-Poor 28.5 Fair-Poor Red Red
29.10 HC1 2019 1.43 ND 0.010 0.347 5.12 53.7 100.0 100.0 71.7 55.6 76.2 High 70.2 High Blue Blue
25.30 HC2 2019 0.98 ND 0.047 0.523 8.71 30.2 100.0 47.1 18.0 11.5 41.4 Moderate 26.7 Fair-Poor Yellow Red
22.00 HC3 2019 ND ND 0.064 0.376 3.02 100.0 100.0 33.8 61.5 99.4 78.9 High 73.7 High Blue Blue
27.46 MH1 2019 1.24 66%0.018 0.482 9.02 45.2 62.1 88.0 28.9 8.6 46.5 Moderate 42.7 Moderate Yellow Yellow
30.38 MH2 2019 1.71 77%0.015 0.304 4.05 65.0 80.9 97.8 89.4 75.1 81.6 High 81.8 High Blue Blue
30.77 MH3 2019 2.31 80%0.013 0.278 3.05 83.7 86.0 100.0 100.0 98.6 93.7 High 95.6 High Blue Blue
30.89 MH4 2019 2.87 83%0.009 0.222 2.23 97.2 89.3 100.0 100.0 100.0 97.3 High 99.3 High Blue Blue
0.10 MP3 2019 0.85 52%0.065 0.843 29.08 21.6 32.9 33.1 0.0 0.0 17.5 Fair-Poor 13.7 Fair-Poor Red Red
0.15 MP1 2019 1.38 63%0.023 0.892 20.54 51.8 55.7 78.8 0.0 0.0 37.2 Moderate-Fair 32.6 Moderate-Fair Yellow-Red Yellow-Red
0.15 MP2 2019 1.45 81%0.014 0.969 22.12 54.7 86.3 99.5 0.0 0.0 48.1 Moderate 38.6 Moderate-Fair Yellow Yellow-Red
30.93 NAN1 2019 3.63 72%0.020 0.242 2.48 100.0 73.3 85.6 100.0 100.0 91.8 High 96.4 High Blue Blue
30.75 NAN2 2019 2.46 76%0.016 0.275 3.74 87.8 79.7 93.3 100.0 81.6 88.5 High 90.7 High Blue Blue
30.68 NAN2A 2019 2.17 69%0.025 0.367 5.60 79.9 67.0 75.3 64.5 48.2 67.0 High-Moderate 67.0 High-Moderate Blue-Yellow Blue-Yellow
26.84 NAN3 2019 2.13 74%0.026 0.310 4.16 78.6 75.8 73.3 86.8 72.9 77.5 High 77.9 High Blue Blue
30.94 NAN4 2019 3.37 81%0.016 0.292 2.42 100.0 87.7 95.2 94.7 100.0 95.5 High 97.5 High Blue Blue
28.78 NAN5 2019 1.46 60%0.012 0.404 4.56 55.1 49.6 100.0 52.0 65.2 64.4 High-Moderate 68.1 High-Moderate Blue-Yellow Blue-Yellow
30.26 NAN6 2019 1.91 70%0.015 0.363 3.39 71.8 68.3 95.7 66.1 89.8 78.4 High 80.9 High Blue Blue
30.81 NAN7 2019 1.85 78%0.020 0.253 5.72 69.9 82.6 84.3 100.0 46.4 76.6 High 75.2 High Blue Blue
30.52 NAN8N 2019 1.38 73%0.014 0.277 2.12 51.7 74.9 100.0 100.0 100.0 85.3 High 87.9 High Blue Blue
0.03 ST4 2019 0.52 6%0.043 1.281 ND 0.0 0.0 51.5 0.0 0.0 10.3 Fair-Poor 12.9 Fair-Poor Red Red
0.00 ST6B 2019 0.80 59%0.031 1.176 ND 17.9 47.5 65.6 0.0 0.0 26.2 Fair-Poor 20.9 Fair-Poor Red Red
0.43 WPH OUTLET 2019 0.54 63%0.045 1.046 ND 0.0 56.0 49.5 0.0 0.0 21.1 Fair-Poor 12.4 Fair-Poor Red Red
8.80 SESA3 2019 1.06 84%0.007 0.840 4.87 35.6 91.2 100.0 0.0 59.7 57.3 Moderate 48.8 Moderate Yellow Yellow
8.84 SESA2 2019 1.01 60%0.018 0.907 12.58 32.6 49.9 88.8 0.0 0.0 34.3 Moderate-Fair 30.3 Fair-Poor Yellow-Red Red
8.84 SESA4 2019 1.04 84%0.010 0.765 5.18 33.9 91.5 100.0 0.0 54.6 56.0 Moderate 47.1 Moderate Yellow Yellow
8.87 SESA1 2019 1.06 51%0.033 0.799 12.98 35.2 29.4 62.1 0.0 0.0 25.3 Fair-Poor 24.3 Fair-Poor Red Red
30.73 ORS2 2019 1.33 81%0.015 0.269 2.73 49.2 86.3 96.8 100.0 100.0 86.5 High 86.5 High Blue Blue
29.90 ORS4 2019 1.49 46%0.030 0.388 5.70 56.6 16.9 66.4 57.1 46.7 48.7 Moderate 56.7 Moderate Yellow Yellow
29.70 ORS6 2019 1.03 55%0.015 0.400 4.89 33.5 38.6 97.2 53.2 59.5 56.4 Moderate 60.9 Moderate Yellow Yellow
49
Figure 27. Nantucket Harbor Eutrophication Index 2010 (top triangle) and 2019 (bottom triangle). Index was calculated with
dissolved oxygen. Colors indicate High (Blue), Moderate (Yellow), Fair/Poor (Red) nutrient related water quality. Station Nan-2A MEP
Sentinel Station.
50
Figure 28. Sesachacha Pond Eutrophication Index 2010 (top triangle) and 2019 (bottom
triangle). Index was calculated with dissolved oxygen. Colors indicate High (Blue), Moderate
(Yellow), Fair/Poor (Red) nutrient related water quality.
51
Figure 29. Madaket Harbor Eutrophication Index 2010 (top triangle) and 2019 (bottom triangle). Index was calculated with dissolved
oxygen. Colors indicate High (Blue), Moderate (Yellow), Fair/Poor (Red) nutrient related water quality.
52
Figure 30. Miacomet Pond Eutrophication Index 2010 (top triangle) and 2019 (bottom triangle). Index was calculated with dissolved
oxygen. Colors indicate High (Blue), Moderate (Yellow), Fair/Poor (Red) nutrient related water quality.
53
Figure 31. Hummock Pond Eutrophication Index 2010 (top triangle) and 2019 (bottom triangle).
Index was calculated with dissolved oxygen. Colors indicate High (Blue), Moderate (Yellow),
Fair/Poor (Red) nutrient related water quality.