HomeMy WebLinkAboutHarbor Watershed Map_201401290850460863
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Report
of the
Nantucket Harbor Watershed
Work Group
Endorsed by the Nantucket Harbor Watershed Work Group
on
January 22, 2003
Final Version – June 1, 2003
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Preface
Nantucket Harbor is a product of the last continental glacial advance that occurred more
than 10,000 years ago. Blocks of ice from the stagnating glacier created glacial kettle
holes – depressions in the unconsolidated sand that were initially freshwater lagoons, but
were later occupied by ocean water following dramatic rises in sea leveli. The barrier
beach that is now Coatue is the result of post-glacial reworking of glacial deposits by
wind and tides, creating a buffer from the rougher waters of Nantucket Sound, and of the
open Atlantic. Since the historic arrival of settlers, the entrance of the Harbor leading to
the open ocean has been manipulated to maintain its open connection to the Sound,
through the construction of the Jetties, and through periodic maintenance dredging. From
time to time, catastrophic events have created new, but always transient, connections
between the Ocean and the Harbor, such as the breach that opened at the end of the 19th
century at the Haulover. Since then, the tides and winds continue to shape and re-shape
the shoreline and ocean bottom beneath it.
The quality of the waters of Nantucket Harbor has always been important to
Nantucketers, although the reasons for valuing that quality may have changed through the
years, as well as the influences on that quality. Following the decline of whaling in the
latter half of the 19th century, fishing and shell-fishing took on greater importance to
Nantucketers who no longer had the lucrative whaling trade to support their existence,
and the quality of Nantucket’s waters spawned healthy crops through the middle of the
20th century. International exploitation of the rich fishing grounds that lie east of
Nantucket, and later, regulation, drastically reduced commercial catches, and,
consequently, Nantucket’s economic reliance on the sea. The latter half of the 20th
century brought different values. Not only was the water quality of Nantucket’s Harbor
valued for its ability to produce fish, but its recreational value and its intrinsic
environmental value are now cherished by all. And yet, ironically, in large measure it is
new growth that has spawned the current threat to Nantucket’s harbor water quality – that
threat in the form of growing numbers of boats docked, buoyed and anchored in the
Harbor, and the growing numbers of homes that have developed within the Harbor’s
watershed - the majority of them seasonal residences. These homes and the practices of
their occupants have introduced nutrients and pollutants that have had a measurable effect
on the quality of the Harbor’s waters. Higher nutrient levels, compounded by low rates of
tidal flushing, and phytoplankton bloom, have resulted in low concentrations of oxygen –
anoxia - in certain Harbor basins. It is the purpose of this report to suggest a strategy to
mitigate these impacts, and ensure the quality of Nantucket’s waters for future
generations. We wish to note, however, that the primary focus of this report is on nutrient
impacts, primarily nitrogen, and not on all pollutants.
A. History of Work Group Activities
The Nantucket Harbor Watershed Work Group (the “Work Group”) was initially formed
in 1997 by the Nantucket Planning and Economic Development Commission
(NP&EDC”) for the purpose of developing a strategy to address water quality issues in
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Nantucket Harbor. The impetus for the formation of the Work Group was the long-
awaited issuance in March of 1997 of the Nantucket Harbor Study: A Quantitative
Assessment of the Environmental Health of Nantucket Harbor for the Development of a
Nutrient Management Plan, by Woods Hole Oceanographic Institute (“Woods Hole”).
That report capped a 10-year collaborative effort between the Town of Nantucket, the
Nantucket Land Council, and Woods Hole to study the environmental health of the
Harbor, and to make general recommendations. These recommendations included:
• strategic land acquisition;
• extension of sanitary sewers in areas of the watershed with higher density and / or
poor soils, thus removing nutrients from the watershed that would otherwise be
added through septic systems;
• encouragement of denitrifying systems;
• cessation of direct storm water discharges into the Harbor;
• continuation of harbor pump-out facilities;
• enforcement of the Federal “no-discharge” zone;
• reduction of lawn fertilizer usage;
• determination of the role of eelgrass deposition on oxygen depletion;
• exploring the feasibility of alternative fishing methods to avoid the “mowing” of
eelgrass;
• considering further limitation of the commercial harvest season;
• directing runoff to vegetated surfaces, rather than through underground rapid
infiltration systems; and,
• maintenance of the Harbor circulation system.
A critique by a subcommittee of the Harbor Watershed Work Group determined that the
quantitative assessment contained in the Nantucket Harbor Study report was flawed in
the following manner:
• it failed to include atmospheric deposition sources;
• it used a disproportionately high and non-scientifically based fertilizer leaching
rate percent;
• It failed to use Nantucket-based on-site septic system and sewer information;
• It used surface water sampling data (except for Millbrook) of questionable
scientific validity; and,
• It failed to highlight the role of education / community participation in addressing
harbor needs and in promoting harbor health.
The Work Group at that time consisted of the individuals and groups listed in Exhibit
“A” – a collaboration of representatives from government, the private sector, and from
the scientific community who were dedicated to one cause – seeking a solution to the
water quality problems of the Harbor. The work of the Work Group culminated in a
report dated December 1, 1997, that recommended the following:
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• a Town Meeting appropriation to fund a Engineering, modeling, and dredging of
a channel in the Harbor to enhance circulation in the Harbor;
• an appropriation for the design of sanitary sewers for the Monomoy and Shimmo
portions of the watershed;
• an appropriation for the design, engineering, and environmental assessment of
improvements to existing storm drainage systems within the watershed;
• the formation of a Harbor Watershed district encompassing Nantucket Harbor;
• adoption of elements of an Open Space Work Group report associated with the
development of the Comprehensive Plan related to open space initiatives in the
Watershed;
• encouragement of open space acquisition preference to Nantucket Islands Land
Bank and non-profit entities; and,
• a public education component that focused on educating the public on prudent
application of fertilizers within the watershed.
Of the initiatives requiring Town Meeting action, the following actions took place:
• the appropriation of $50,000 for the study of the circulation patterns in
Nantucket Harborii;
• the appropriation of approximately $700,000 for the construction of sewers in
Monomoy, recently completediii;
• the inclusion in the Department of Public Works Enterprise fund an
appropriation to inventory drainage systems in the watershediv;
• the adoption of a Harbor Watershed District (Exhibit “B”) as a general bylaw in
1999v.
Of the initiatives not requiring Town Meeting action, the following publicly sponsored
actions were initiated:
• The design and construction of a stormwater mitigation area for a stormwater
discharge on Washington Street extension;
• the acquisition by the Town, the County, the Land Bank, and environmental
organizations of the fee interest conservation restrictions in over 60 acres of land
situated in the Harbor Watershedvi;
• The production of a poster highlighting water quality issues and best
management practices, with the funding assistance of the Massachusetts
Executive Office of Environmental Affairs.
B. Watershed Nutrient Model / Harbor Nutrient Model; Re-constitutes
Harbor Watershed Work Group
The Work Group suspended its meetings pending the completion of a Watershed Nutrient
Model and a Harbor Nutrient Model, funded by Article 28, 1998 ATM. The Marine and
Coastal Resources Department commenced these studies in late 1999, retaining Applied
Science Associates (“ASA”), who subcontracted with the Boston University Marine
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Program (“BUMP”), Applied Marine Ecology Lab, and Nucci Vine Associates as
consultants to design the models.
In May of 2000, the Watershed Model and report by BUMP were released. The report
provided the best information available concerning the contribution of nutrients by
sanitary sewers in the Watershed. However, the model did not factor in the 20 +/- year
equilibrium rate for on-going and past loading on nutrients already in transit in the
watershed system. The model underscored the importance of atmospheric contribution of
nutrients into the Harbor. Shortcomings of the model included a failure to factor in the
contribution of storm water discharges into the nitrogen load; non-septic-related nitrogen-
loading rates (atmospheric, storm water, fertilizers) were not Island-specific, or they were
based on disproportionately non-science based leaching rates; and nitrogen loading
values attributed by the study were found not to be based on scientific data, although it
was found that “hot spot” nitrogen loading areas may exist. Yet, despite some of its
drawbacks, the Work Group considers the report as the best information available on
Harbor nutrient loading. To the extent that the Nantucket Harbor Study and the BUMP
report conflict, these conflicts will be discussed in the following discussion.
The final results of the Harbor Circulation Model prepared by ASA were released in
November of 2000. The model was considered a necessary “first step” – a two-
dimensional model that demonstrated the dynamics of tidal flushing in the Harbor. The
model allows the user to apply various scenarios, or “solutions” to Harbor circulation
problems, and to measure the effectiveness of these solutions in terms of increased
circulation. Among the scenarios tested were structural solutions including various
dredging scenarios; removal of the jetties; repair of the breach in the east jetty; and the
introduction of a man-made connection between the Head of the Harbor and the Atlantic
Ocean by creating a connection through the Haulovervii. The model concluded that nearly
all actions, including dredging scenarios, had a marginal effect on circulation in the
Harbor. One solution involving dredging the shoaled areas between the basins yielded
decreased circulation. The most effective “solution” was the construction of a breach at
the Haulover, but the total effects of such a permanent breach on sediment transport and
the overall Harbor ecosystem would have to be carefully studied before it could be
considered a viable optionviii.
The Work Group was reconstituted upon the development and release of the models, and
in reaction to a citizen-sponsored Article 47 of the 2000 Annual Town Meeting
(Appendix “C”). The new Harbor Watershed Work Group consisted of the membership
listed in Appendix “D.” The Work Group began its activities in earnest in December of
2000, developing a Work Program based on the scope suggested in the Article.
In evaluating the report conclusions, the Work Group found that conclusions based on a
two-dimensional model could be considered problematic, because it was the sense of the
Work Group that the Harbor was multidimensional in function. The Work Group also
concluded that sound judgment should be exercised in the use application, and
development of conclusions and / or recommendations reached by employing the model –
changing patterns may lead to other adverse effects on the Harbor, such as eel grass
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destruction, sediment re-suspension, and effects on navigation. Reliance solely on a
water-based solution should not be taken in isolation from watershed-related impacts.
The final recommendation of the Work Group was to explore the need for a three-
dimensional model, and to implement this model if further tests of the dynamics of the
water column support the need for such an advanced model.
II. Assessment of the “State of Nutrient Loading to Nantucket Harbor”
This report attempts to summarize the most current scientific information available
concerning the nutrient inputs into Nantucket Harbor. The primary sources of information
are the Nantucket Harbor Study (the “Harbor Study”) and Land-derived nitrogen
loading to Nantucket Harbor (the “BUMP Study”). The Harbor Study concludes that
“nutrient inputs are necessary for the healthy growth of phytoplankton, macro-algae, and
eelgrass within Nantucket Harbor.”ix However, it is an over-supply of nutrients, both
naturally occurring and man-made, that exceeds the assimilative capacity of the harbor
system, leading to death of phytoplankton and eelgrass, and the resulting anoxia,
particularly at the Head of the Harbor, Quaise, and Polpis Harbor.
The BUMP Study reaches similar conclusions concerning the overall nutrient budget for
the Harbor, but the two reports differ in the relative contribution of nutrients from
different sources.
In order to manage nutrient inputs, it is also necessary to understand nutrient
contributions and loading rates from a number of sources, together with circulation and
transport patterns in the Harbor.
A. Sources of Nutrient Loading in Nantucket Harbor
Sources of nutrient inputs that are addressed in this report must include land-based
contributions from the Nantucket Harbor Watershed (Exhibit “E”); water-based sources;
and atmospheric sources; all of which are addressed in the Harbor Studyx and the BUMP
Study.
1. Land-based Sources:
Because of the predominantly sandy character of the soils within the Harbor watershed,
and the relatively high infiltration capacity of these soils, the ground water is the most
significant conduit for the transport of nutrients from throughout the watershed. But
because the Harbor consists of a series of basins which have differing nutrient levels, the
Harbor Study and the BUMP Study divide the overall harbor watershed into sub-
watersheds for the purpose of both evaluating and managing nutrient loading. The Harbor
Study and the BUMP Study both identify atmospheric sources, stream flow, and
groundwater as land-based conduits for nutrient transport, although the BUMP study’s
estimates of atmospheric contributions to nutrient loads in the watershed is more
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comprehensive than the Harbor Study. Although atmospheric sources include wetfall and
dryfall sources that add nutrients to the watershed, that discussion is deferred to a section
that follows below.
Stream flow from the ten (10) small streams identified in the harbor watershed
contributes only an estimated 36 kg of Nitrogen per year, compared to the estimated
atmospheric contribution of more than 10,000 kg per yearxi.
Groundwater, by far, contributes the most Nitrogen to the waters of the Harbor. The
groundwater nutrient loading model developed specifically for Nantucket Harbor
estimates the contributions of nutrients, and Nitrogen in particular, that are transported
through groundwater to the Harbor. The following sections of this report examine the
relative contributions of a variety of land uses, sources, and other contributors to nutrient
loading in the Harbor.
Sewage / Septic System Discharges
Aside from direct atmospheric contributions, septic systems cause one of the greatest
contribution of Nitrogen (“N”) (over 3,000 KG per yearxiiper the Harbor Study, but only
1201 KG per the BUMP Studyxiii) loading to groundwater of any other source within the
harbor watershed. This discrepancy between the reports may be due to significant
differences in the numbers of assumed septic systems actually located within the
watershed. The estimate in the Harbor Study is based on the numbers of year-round and
seasonal residences in the watershed at the time of the study, adjusted for projected
occupancy rates.
Additional development has taken place in the five (5) years since the issuance of the
Harbor Study. Based on our review of the building permit records of the Town of
Nantucket Building Department, we estimate that of the approximately 160 new dwelling
units that have been constructed in the Harbor watershed since 1997, 75 were constructed
within the unsewered area, representing a 7.8 % increase in the number of dwelling units
on septic systems over the number of dwelling units estimated in that report. Using the
same assumptions of the Harbor Study, we estimate that the Nitrogen loading has now
increased to approximately 3,300 KG per year. Using the same assumptions under the
BUMP study, we conclude that the addition of 75 new septic systems is a nearly 13%
increase in the number of septic systems in the watershed, bringing the N load to
approximately 1356 KG of N. However, based on the same variables and assumptions,
the recent construction of sanitary sewers in Monomoy can result in the reduction of
Nitrogen loading by approximately 145 KG (54 KG, under the BUMP Study
assumptions) when all the homes served by the sewer abandon their septic systems. The
extent of properties serviced by septic systems within the Harbor watershed versus the
extent of lots served by sanitary sewer is illustrated in Exhibit “F” (a Geographic
Information Systems map of the watershed).
The Comprehensive Wastewater Management Plan (“CWMP”), still in the process of
development by Earth Tech under contract with the Town of Nantucket, has identified ten
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(10) areas of wastewater need Island-wide, i.e., areas where conventional Title V septic
systems would not be effective in disposing of wastewater. The rating criteria established
for the purpose of defining need were based on the numbers of actual septic system
failures; the numbers of imminent septic system failures; the numbers of septic systems
with a high likelihood of failure; and the number of systems that have health or water
quality issuesxiv. This last criterium includes consideration for location of septic systems
within the Nantucket Harbor Watershedxv. A second stage analytical analysis also
identified septic system age, lot size, and severe soils and groundwater as added factors in
determining need. Of the ten needs areas identified, five are located within the Nantucket
Harbor Watershed (see Exhibit “G”). Three of the areas are based largely on location
within the watershed (Monomoy, Shimmo, and Pocomo), while the final two (Polpis and
Wauwinet) are based on a series of criteria the importance of which supersedes the
watershed inclusion criteria. In terms of need, Wauwinet ranked first, Polpis third,
Monomoy seventh, and Pocomo ninth.
The next step in the CWMP planning process is the evaluation of a variety of wastewater
solutions to address each area.
b. Storm water runoff / sedimentation
Stormwater runoff from impervious (impermeable) surfaces, according to the Harbor
Study, accounts for an estimated N load of 1465 KG per yearxvi, or 19% of all non-
atmospheric sources, while the BUMP Study estimates an N load of 583 KG. This
amount, according to the Harbor Study, represents the third highest contribution,
following septic systems and fertilizers as a principal non-atmospheric contributor of N to
the watershed.
Impermeable surfaces take the form of paved roads, driveways, and roofs within the
watershed. These surfaces become traps for atmospheric N, as well as pollutants
generated by automobiles and animal waste. How these N sources are directed into the
ground and eventually to the Harbor determines how much total N is not attenuated, and
therefore is contributed to Harbor waters. The following section divides these
contributors into point and non-point sources.
i. Point Sources
Point sources may constitute the biggest stormwater runoff threat because nutrients,
including N, are discharged directly into the Harbor, or into the underlying soils, usually
with little or no attenuationxvii. Within the Harbor watershed, the area west of the Creeks
and the Rotary consists almost exclusively of a paved road network with a developed
storm drainage system, nearly all of which discharges directly into the Harbor, or directly
into the ground through leaching catch basinsxviii. Stormwater discharges from that
portion of the historic Nantucket Town often include road and roof runoff combined.
These discharges are usually in the form of stormwater outlet pipes that discharge
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directly into the Harbor, or in the form of direct discharge to leaching basins from roofs
and roads. Because some discharges are often directly through harbor bulkheads, open air
or vegetative retrofit is often difficult or impossible. In this dense network of roads, only
3.2 miles of road are unpavedxix. This area drains to the extreme west end of the Harbor,
which has the greatest degree of tidal flushing. East of the Creeks and the Rotary, it is
estimated that there are approximately 36 miles of roads, paved and unpaved, public and
private. This number includes approximately 15 miles of unpaved “roads” located within
preserved land south of Polpis Road, controlled predominantly by the Nantucket
Conservation Foundation. The remaining 21 miles of roads in this part of the watershed
serves developed areas, and consists of 11.1 miles of paved roads, and 10 miles of
unpaved roads. Of the 11.1 miles of paved roads, approximately 5 ¼ miles, or 47%, have
leaching catch basins, and therefore constitute point discharges. An example is all of the
paved portion of Pocomo Road. Point discharges often include sediment generated from
winter road applications, or from natural erosion, and often contain concentrations of
nutrientsxx.
Some point discharges, however, are via specially designed stormwater systems that are
designed to filter runoff through vegetated surfaces, or through underground systems that
provide some capture and treatment of nutrients.
ii. Non-point Sources (including development
activities; agricultural and landscaping
practices)
Non-point sources generate nutrients to a lesser extent than point sources, because they
are often filtered by vegetation, which has significant attenuation potential. These non-
point sources include runoff from roads without storm drainage systems consisting of
pipes and catch basins. East of the Creeks and the Rotary, these include the 15 miles of
unpaved roads in protected land, 10 miles of unpaved roads in developed areas, and 5.85
miles of paved roads without storm drainage systems. Most of the driveways serving
homes in this area of the watershed are unpaved, and therefore non-point sources. West
of the Creeks and the Rotary, only 3.2 miles of unpaved roads constitute non-point
sources.
Development activities have the potential to contribute sediment to Harbor waters, and
associated nutrients borne by sediment, although the general porosity of the soils reduces
the risk to a considerable extent. The Conservation Commission, in its capacity as
wetlands agency, routinely requires erosion and sedimentation measures to protect
adjacent wetlands. The Planning Board and the Zoning Board, through the Site Plan
Review process, has the discretion to require similar measures in connection with
commercial permits, and the Planning Board can require such measures for Definitive
Subdivision Plans. However, lots of record, and lots created by ANR are not subject to
erosion control requirements, unless they are otherwise under the jurisdiction of the
Conservation Commission. The storm drainage system within the streets of Nantucket
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Town can act as a conduit for sediment generated by infill development, transporting it
directly to the Harbor.
Agricultural activities are quite limited within the watershed, with the 15 +/- acres of
Moors End Farm being the greatest contributor, and Windswept cranberry bog, which has
been inactive for several years. Again, the agricultural erosion potential of Moors End is
limited, due to the porosity of the soils. Only 1% of the estimated Nitrogen is generated
by farming within the watershed, according to the Harbor Studyxxi.
Landscaping practices can contribute nutrients generated by runoff within the watershed
by clearing large areas of natural vegetation. Nutrients are generated both during
construction, but also as a consequent of increases rates of runoff due to the loss of
vegetation that is more efficient at attenuating runoff and nutrients.
c. Landscaping and Agricultural Practices
The most common way that landscaping and agricultural practices contribute nutrients
within the Harbor Watershed is through the addition of organic and chemical fertilizers.
i. Agricultural practices
The contribution of fertilizers due to agricultural practices of the two farms (Moors End
and Windswept Bog) is estimated by the Harbor Study as contributing only 63 KG of N,
or approximately 0.8% of the total N generated in the watershed from non-atmospheric
sourcesxxii. With the closure of Windswept bog to active agricultural production since the
time of the Harbor Study, it is anticipated that the nutrient generation is at the present
time is less than that cited in the Harbor Study.
ii. Landscaping practices
The Harbor Study and the BUMP Study both cite fertilizer as a major non-atmospheric
source of N in the watershed.
The 1997 WHOI Harbor Study model included an estimate of 2898 Kg N from lawn
fertilizers. The WHOI model assumed that 100% of lawn areas within the watershed are
fertilized each year, at a rate of 3 lbs N/ 1,000 sq. ft., and estimated that 20% of the
applied nitrogen leached to the groundwater as nitratexxiii.
After requesting documentation from WHOI in support of their assumptionsxxiv, the Work
Group formed a subcommittee (November, 1997) to review all available scientific
literature. The subcommittee was able to identify four factors that most significantly
influence the degree of leaching: 1) amount of fertilizer applied, 2) type of fertilizer
applied, 3) stage of growth at time of application, and 4) amount of irrigationxxv.
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The August 2000 BUMP Study estimated 1322 Kg Nxxvi, assuming that 61% of applied
material leached to the groundwaterxxvii.
In November, 2000, the Massachusetts Executive Office of Environmental Affairs,
Watershed Initiative Team, sponsored a forum on Nantucket to bring some clarity to the
question of fertilizer leaching, and introduced experts in turf science. Presentations by the
speakers documented differences between actual ground testing / monitoring derived data
and statistical data compilation modeling approach for evaluation of leaching impacts by:
1. Providing scientific field study data showing actual nitrogen
leaching rates.
a. In glacial outwash soils ranging between 0-6%, and
b. In glacial and/or lab created soils ranging between 0-12%
2. Providing model-based compiled and/or statistically derived
nitrogen leaching rates ranging between 15-20%xxviiixxix
The Harbor Watershed Work Group recognizes the need for further science-based
research and education, and recommends some specific practices that are scientifically
known to reduce the potential for nitrogen loading from lawn fertilizer.
d. Natural Contributions
Natural contributions of N are generated both from portions of developed lots that are
naturally vegetated and undeveloped privately owned land, as well as the significant
acreage of land preserved. by various public entities, and private environmental
organizations. This total contribution is estimated at the time of the Harbor Study at 358
KG of N, or 4.5 % of the non-atmospheric N contribution in the watershed. The BUMP
Study disputes this amount, stating that the Harbor Study understates the atmospheric
contribution within the watershed. The BUMP Study estimates that between wetlands,
freshwater ponds, and natural vegetation, 3,978 KG of non-attenuated N enter the Harbor,
their ultimate source being atmospheric depositionxxxiii. With the development of 160 new
homes in the watershed, the amount of natural N has been modified by N generated by
impervious surfaces and septic systems. But converting undeveloped land to open space
does not affect the N contribution to the watershed or the Harbor because they were
assigned the same rate of contribution on N.
2. Water-based Sources
Water-based sources are not addressed or quantified in the Harbor Study, although there
is an acknowledgment that dumping of septage from boats is a factor in determining
nutrient loading.
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a. Commercial and recreational activities
Commercial activities that are water-based are generally limited to commercial fishing
and recreational fishing and scalloping pursuits. The commercial fishing activities
contribute little to the contribution of N to the Harbor, since most of these activities are
carried on outside of the Harbor, generally. The act of commercial might generate
organic material that decays and is arguably a contributor of N to the Harbor waters. The
precise effects of scalloping harvest practices are unknown, and require further study.
Despite the designation of the Harbor as a federal “No Discharge” zone, it is
acknowledged that some clandestine dumping occurs. The practice of boat washing
contributes phosphates, but is also a contributor of N to Harbor waters. Although
biodegradable washing products are prescribed, the increasing volume of boats moored,
docked, and at anchor make enforcement difficult. An aggressive pump-out program by
the Marine Department yields increasing volumes of sewage annually.
b. Natural Contributions
As stated earlier in this report, N generated from streamflow is in the order of 36 KG
annually. But if continued development occurs within the watershed, it is anticipated that
this contribution will increase.
Atmospheric contributions of N on the water surface of the Harbor is a major contributor
of N, as discussed in more detail below.
3. Atmospheric Sources
Deposition of N on the surface waters of the Harbor is estimated in the Harbor Study as
over 10,000 KG per year, and is therefore the greatest contributor of N to the Harbor of
any sourcexxxv. Because the BUMP Study is a watershed model, and deals only with
applications of N from land within the watershed, atmospheric contributions in that report
are strictly limited to those contributions on land. If we assume the atmospheric
contributions to Harbor waters of over 10,000 KG in the Harbor Study in combination
with the BUMP Studies estimates of atmospheric contributions within the watershed,
then we might conclude that 83% is ultimately attributable to atmospheric deposition.
Only 5 % of that amount is attributable to activities under our control, i.e., deposition on
turf, bogs, agricultural areas, roofs, and impervious surfaces.
N deposited on land from atmospheric sources is largely attenuated by the renovation
potential of natural vegetation. But the N that falls upon impervious surfaces adds to the
regimen of N that is potentially discharged directly to the Harbor or underlying
groundwater as a point sourcexxxvi.
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C. Results - Watershed Nutrient Model / Harbor Nutrient Model
The ASA Harbor Nutrient Model was useful in providing positive flushing rate data
affecting the Harbor. The analyses of various structural solutions led the Work Group to
conclude that such solutions may not provide the water benefits that it had hoped for. The
“solution” of developing a permanent breach in the barrier beach at the Head of the
Harbor raises more questions than it answers at the present time, and requires further
study if it is to be seriously considered.
The watershed analysis (BUMP Study), although conflicting in some respects with the
details of the Harbor Study, still corroborates many of the conclusions of the latter study.
The BUMP Study emphasizes the vast contributions of atmospheric N to the problems of
the Harbor, and points to fertilizers, septic systems, and roads and other impervious
surfaces as the principal non-atmospheric contributors. Based on a presentation by
BUMP to the Work Group, the Work Group concludes that, given the large atmospheric
contribution that, for the most part, cannot be mitigated, and given the fact that N loading
of the Harbor is at a critical juncture, it is logical to conclude that we must manage the
sources that we have control over, namely, sources of N from septic systems, fertilizers,
storm outfalls, roads, and other impervious surfaces.
D. Physical Characteristics / Limitations of the Harbor
Remediating the concentrations of N in the Harbor is a complex undertaking. Circulation
in the Harbor, as attested by the ASA Study, cannot be easily changed, except by radical
actions (i.e., breach at the Head of the Harbor) that may have negative effects on the
overall environmental health of the Harbor. Some subwatersheds are more critical than
others, and because of their unique characteristics, may deserve different solutions. Even
if an aggressive watershed management program is implemented, benefits may not seem
obvious for decades, because of the lag time in the travel of N through the soils and
groundwater within the watershed. These are not reasons not to proceed. The purpose of
the recommendations that follow are to ensure the quality of the waters of the Harbor for
future generations; we must therefore have a long view. We must also continue to study
those issues for which we do not have an adequate understanding, and expand our
monitoring and observation of variables that affect Nantucket Harbor water quality so
that we can rely in the future on information specific to out own Harbor and watershed,
and not on data derived from other sources and extrapolated to fit Nantucket’s
circumstances.
III. Recommended Strategies and Actions to Limit / Control / Regulate Nutrient
Loading of Nantucket Harbor
As stated previously, the Harbor Study and the BUMP Study produced overall results that
were roughly consistent in their estimation of total N loads for Nantucket Harbor.
However, they differ greatly in the breakdown of the various contributors. Rather than
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get hung up on the numbers, the Work Group has looked at the bottom line conclusions
of each, which lead to these recommended solutions:
A. Educate the Public on Nutrient Influences on the Harbor, and on
Practices to Mitigate those Influences.
The Work Group voted to place this first in order of importance, because it feels strongly
that getting stakeholders to understand the problem, and understand that they all must be
a part of the solution, is a critical step. Although regulation is an essential part of this
overall strategy, not everything can be regulated or practically enforced. Seeking
voluntary compliance is therefore an important part of this strategy.
1. Continue a public education campaign to educate both year-
round and seasonal residents concerning responsible nutrient
management practices in the Harbor Watershed.
a. Support development and distribution of educational
pamphlets concerning Harbor water quality issues, and
responsible management actions that homeowners need
to engage in.
b. Support development of an “information resource
center” on Harbor watershed issues at the library or at
select Town Offices.
c. Conduct educational forums on Harbor Watershed
issues pertaining to nutrient loading.
d. Provide speakers for civic meetings on Harbor
Watershed issues, particularly before Neighborhood
Associations whose geographic boundaries fall within
the Harbor Watershed.
B. Public and Private Infrastructure Policy and Improvements
A public-private partnership is required for this program to be successful, because the
area of the watershed serviced by the public infrastructure (public roads, sanitary sewers,
and storm drainage systems) covers a relatively small part of the watershed. Private roads
and their drainage systems fall under the jurisdiction of the Town only insofar as they are
subject to jurisdiction of the Planning or the Zoning Board, and, even then, only for new
or modified development plans. Septic systems and sanitary sewer extensions, in contrast,
fall under the development and regulatory authority of the Town.
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1. Septic Systems / Sanitary Sewers
a. Support and implement a comprehensive survey and
program of inspections of failed or failing septic
systems, and enforcement actions.
b. Develop septic system standards for new and
replacement septic systems in the Nantucket Harbor
Watershed; draft and implement Nantucket Health
Code Regulation changes tailored to Nantucket Harbor.
c. Recommend sanitary sewer extensions within the
Harbor Watershed in keeping with the
recommendations of the CWMP, and provide for
funding of these extensions through bonding, loans, and
the Town’s capital program and enterprise fund
accounts.
d. Implement solutions tailored to circumstances of each
Priority Area identified in the Town’s CWMP.
e. Adhere to the Sanitary Sewer Policy of the Nantucket
Board of Public Works, adopted on January 6, 1999
and revised on June 26, 2002.
2. Storm Drainage Systems
a. Conduct a Comprehensive Inventory of Storm Drainage
System and Point Source Discharge Points.
b. Mitigate point source discharges (Harbor outfalls and
leaching catch basins) on public storm drainage systems
by establishing a long-range capital program.
Mitigation may include retrofit of storm water
discharges which issue directly into the Harbor, or the
creation of roadside ditches in lieu of leaching catch
basins (i.e., Pocomo Road).
c. Develop a plan to retrofit the storm drainage system
throughout the Harbor Watershed, including private
systems, such as Quaise Pasture, North Pasture, and
Moors End Road. Prioritize improvements through a
long-range capital program, and work with
Neighborhood and Homeowners Associations to retrofit
systems.
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d. Draft and adopt a Zoning Bylaw amendment and
amendments to the Rules and Regulations Governing
the Subdivision of Land to implement storm drainage
standards consistent with the goal of reducing and
attenuating nitrogen within the Harbor Watershed.
e. Develop standards for storm drainage systems and
improvements to be employed by the Town of
Nantucket, Department of Public Works in the
construction, maintenance, and retrofit of storm
drainage systems.
f. Mount a public relations campaign to encourage
retrofit of roof drain systems and private storm systems
on individual lots to eliminate leaching basins in lieu of
discharge onto vegetated areas.
C. Development Practices
The following measures are meant to close the gap in requirements for erosion and
sedimentation measures in the Harbor Watershed:
1. Amend the Zoning Bylaw, the Rules and Regulations
Governing the Subdivision of Land, and the Wetlands
Regulations to require more stringent erosion and
sedimentation controls within the Nantucket Harbor
Watershed.
2. Amend the Wetland Regulations to specifically require the
reservation of vegetation / vegetated buffers within the Harbor
Watershed.
3. Amend the Town Code to require Erosion and Sedimentation
measures in connection with any Building Permit located in the
Harbor Watershed that is not regulated by the Planning
Board, Zoning Board, or the Conservation Commission.
4. Storm water management (see above).
E. Agricultural Practices
Although agriculture is a relatively small contributor of nitrogen within the watershed,
the following measures can provide incremental benefits to the watershed:
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1. Encourage agricultural businesses within the Harbor
Watershed to employ winter cover crops, which attenuate
leaching on nitrogen during winter months.
2. Encourage agricultural businesses within the Harbor
Watershed to use slow-release fertilizers.
3. Encourage agricultural businesses within the Harbor
Watershed to establish and maintain buffers from the Harbor
or its bordering wetlands and streams.
F. Landscaping Practices
Since nitrogen levels play a key role in the ecological health of all bodies of water, in
particular our Harbor on Nantucket (because of its physical shape and geological history
which have resulted in less than optimum circulation and flushing patterns), homeowners
and lawn care professionals should be encouraged to adopt the following measures to
ensure that lawn fertilization practices here, particularly in the Harbor watershed area, are
based on the most current accepted practices scientifically known to reduce the potential
for nitrogen loading as regards lawn fertilizer:
1. Educate the landscaping professional and the consumer about
best management practices to control and limit nutrients.
2. Identify, and encourage use of, slow-release fertilizers by
consumers and landscaping professionals. The following
measures are based on scientific evidence:
a. A maximum application rate of 3 lbs. Nitrogen per
1,000 sq. ft. per year.
b. The use of lawn fertilizers that contain a high ratio
of slow release forms of nitrogen to water soluble
forms of nitrogen, which are less likely to leach to
ground water.
c. Lawn fertilization only during the active growing
season, usually starting in May. Discourage fall
applications after growth has slowed. Several lighter
applications versus one large dose are preferable.
3. Support scientific research to collect and analyze data
regarding nitrogen leaching associated with lawns here on
Nantucket.
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4. Educate the landscaping professional and the consumer
concerning the value of preserving existing vegetation; the use
of indigenous vegetation; the value of buffers; and the use of
plant species that are drought-tolerant, and which require little
fertilization.
5. Educate the landscaping professional, irrigation installers, and
the consumer about controlled irrigation and the inclusion of
rain gauges on irrigation systems. Careful monitoring and
control of irrigation on lawns, as excess irrigation, particularly
over sandy soils, contributes to higher losses of nitrogen to
leaching before turf grasses can take it up; one inch of water a
week should suffice, and lighter watering more frequently to
reach the one inch amount is preferable to one heavier dose of
water.
6. Educate developers, builders, and prospective and existing
homeowners concerning best management practices in
activities that disturb the soil and remove indigenous
vegetation.
F. Land and Conservation Restriction Acquisition; Deed Restrictions;
Tax Incentives
Acquisition of land and easements will have the effect of decreasing future
contributions of nitrogen to the Harbor by removing the development potential of
land, and therefore the nitrogen associated with septic systems, landscaping
practices (application of fertilizers, removal of natural vegetation), and new
impervious surfaces (roofs and roads / driveways:
1. Encourage the Town, the County, the Land Bank, and
environmental organizations to acquire land, conservation,
and deed restrictions within the Harbor Watershed to control
and limit development in the watershed, and manage further
nutrient releases into the Harbor. Support tax incentives as an
inducement to implementing these mechanisms.
G. Management of Use of Harbor Waters
The Marine Department has a monumental task during the peak season in
regulating and enforcing “no discharge” zone requirements:
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1. Support Marine Department management of Harbor use
(boating, dredging), etc. to limit nutrient contributions into the
Harbor; support an increase in funding to accomplish these
activities, if necessary.
H. Regulatory Policies and Practices
In addition to the specific recommendations for increased regulatory oversight,
implement the following:
1. Support local regulatory agency implementation of existing
regulations and policies that are consistent with best
management practices. Assist these agencies with revisions /
upgrades of existing regulations and policies affecting the
Nantucket Harbor Watershed and Nantucket Harbor
including, as appropriate, “basic arguments / support data.”
I. Phase II of Harbor Circulation Model
The ASA Study raised the question of the adequacy of a 2-dimensional model to replicate
the dynamics of the Harbor. The following second stage is recommended:
1. Support preparation of a 3-dimensional model of Harbor
circulation only if testing of Harbor circulation warrants
further analysis.
J. Conclusion
These recommendations of the Harbor Watershed Work Group come at a time of
increasing evidence of degradation of water quality in Nantucket Harbor. Recent closings
of shellfish beds and decreasing yields of scallops are clear signs of this trend. These are
not recommendations that should be taken lightly - water quality is important to the well-
being of our environment, but is also important to our economic well-being.
K. Bibliography
1. Nantucket Harbor Water Quality Survey: Water Quality Survey Data: Summary
of Significant Findings. Prepared by Christine Duerring, Environmental Analyst
and Catherine O’Riordan, Environmental Engineer (Massachusetts Department of
Environmental Protection - February, 1990).
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2. Nantucket and Madaket Harbors Action Plan, Prepared by the Nantucket Harbor
Planning Advisory Committee and the University of Rhode Island Coastal
Resources Center for the Town of Nantucket, Massachusetts (May, 1993).
3. Nantucket Harbor Study: A Quantitative Assessment of the Environmental Health
of Nantucket Harbor for the Development of a Nutrient Management Plan, by
Woods Hole Oceanographic Institute (March, 1997).
4. Report of Nantucket Harbor Watershed Work Group (December 1, 1997).
5. Proposed Recommendations to the Nantucket Harbor Watershed Work Group,
concerning fertilizer management, dated November 19, 1997, and adopted on
March 19, 1998 by the Harbor Watershed Work Group.
6. Land-derived nitrogen loading to Nantucket Harbor, by Ivan Valiela, Marci L.
Cole, and Joanna K. York, Boston University Marine program, Marine Biological
Laboratory, Woods Hole, MA, Draft Final Report, May, 2000.
7. Computer Modeling of Nantucket Harbor: Project Summary, by Craig Swanson
and Matthew Ward, Applied Science Associates, Inc., Narragansett, RI,
November 10, 2000.
8. Landscaping Workshop, October, 2000, co-sponsored by the Nantucket
Conservation Commission, the NP&EDC, Mass. DEP, and the Nantucket
Landscapers Association.
9. Brochure entitled: “Landscaping Practices That Make a Difference,” Nantucket
Landscape Association, in cooperation with NP&EDC, Harbor Watershed Work
Group, the Nantucket Landscape Association, the Nantucket Conservation
Commission, and the Nantucket Land Council.
10. Poster entitled: “Nantucket Harbor Watershed: Ours to Enjoy and Protect,” 2000,
created by Harbor Watershed Work Group, and funded by EOEA.
i Nantucket Harbor Study, pp. 10 and 11 ii Article 28, 1998 ATM. iii Article 12, 1999 ATM iv Article 10, 1999 ATM v Article 70, 1999 ATM vi Communications with Jim Lentowski, Executive Director, Nantucket Conservation Foundation, and Eric
Savetsky, Executive Director, Nantucket Land Bank vii Project Summary: Computer Modeling of Nantucket Harbor, Applied Science Associates, November
10, 2000, pp. 10 and 11 viii Idem. ix Nantucket Harbor Study p. 20 x Ibid., pp. 20 through 36 xi Ibid., pp. 25 through 27 xii Ibid., p. 29 xiii Land Derived Nitrogen, pp. 14 through 16 xiv Comprehensive Wastewater Management Plan and Environmental Impact Report, Phase I, Needs
Analysis and Screening of Alternatives, Nantucket, MA, Earth Tech, Inc., August, 2002; pp. 3-23
through 3-33 xv Ibid, p.3-24 xvi Nantucket Harbor Study, pp. 32 and 33 xvii Ibid., p. 33 xviii Field and GIS Analysis by NP&EDC staff, December, 2002 xix Idem. xx Idem. xxi Nantucket Harbor Study, p. 31
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xxii Ibid., p. 30 xxiii Ibid., p. 32 xxiv Minutes, Harbor Watershed Work Group, October 22, 1997, pp. 1, 7 xxv Report and Recommendations of Harbor Watershed Work Group, December 1, 1997 xxvi Land Derived Nitrogen, p. 14 xxvii Valiela, I., et al, Nitrogen loading from watersheds to estuaries: Biogeochemistry 49: 277-293 xxviii EOEA Landscape Workshop: Branham, Cohen, Nelson, Talbot xxix Collier, Cormac; Fantozzi, Peggy: Report Summaries: 4/4/2001 Prepared for Nantucket Harbor
Watershed Work Group xxxiii Land Derived Nitrogen…, p. 14 xxxv Nantucket Harbor Study, pp. 24 and 25 xxxvi Land Derived Nitrogen…, p. 14