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Nantucket_Tech_Memo_Sesachacha WQ 2012_2014_FINAL (2)_2015051407193573641 Technical Memorandum Final Water Quality Monitoring and Assessment of Infaunal Health in Sesachacha Pond for Estuarine Resource Management and TMDL Compliance Town of Nantucket To: Jeff Carlson - Natural Resources Coordinator Kaitlyn Shaw, Water Resource Specialist Town of Nantucket - Natural Resources Department and Rosemary Blaquier Woodard and Curran, Engineers to the Town of Nantucket From: Brian Howes, Ph.D., David Schlezinger, Ph.D., Roland Samimy, Ph.D., Sara Sampieri, M.S., Michael Bartlett, B.S. Coastal Systems Program School of Marine Science and Technology (SMAST) University of Massachusetts-Dartmouth 706 South Rodney French Blvd. New Bedford, MA 02744 April 28, 2015 Background: 2 Coastal salt ponds and estuaries are among the most productive components of the coastal ocean. These circulation-restricted embayments support extensive and diverse plant and animal communities providing the foundation for many important commercial and recreational fisheries. The aesthetic value of these systems, as well as the freshwater ponds of a town, are important resources to both residents and the tourist industry alike. Maintaining high levels of water quality and ecological health in these aquatic systems (fresh and marine) is fundamental to the enjoyment and utilization of these valuable resources for all coastal communities. Nutrient over-enrichment is the major ecological threat to water quality in the salt ponds and estuaries within the Town of Nantucket, primarily via ecological degradation resulting from watershed nutrient loading exceeding the assimilative capacity (also called critical nutrient threshold) of the marine system. Of the various forms of pollution that threaten coastal waters (nutrients, pathogens and toxics), nutrient inputs are the most ubiquitous, insidious and difficult to control. This is especially true for nutrients originating from non-point sources, such as nitrogen and phosphorous transported in the groundwater from on-site septic treatment systems. On-site septic treatment systems are the primary mechanism for waste disposal within most of the coastal watersheds of the Town of Nantucket with the exception of the Nantucket Harbor watershed where the high density areas are primarily on sewers with disposal of treated effluent outside of the watershed. As a result of nutrient loading to Nantucket's coastal watersheds, a portion of the 5 estuaries within the Town presently show signs of nutrient impaired water quality and resource loss. In response to the observed degradation of the estuarine resources of Nantucket, the Town of Nantucket participated in the Massachusetts Estuaries Project for the assessment of all the estuaries of the Town and development of estuarine specific nitrogen thresholds to guide management and restoration of these critical habitats. Through the coupling of monitoring data, the Massachusetts Estuaries Project (MEP) nutrient threshold analysis was conducted in collaboration with the Coastal Systems Program (CSP). Restoration will start with the most cost-effective management strategies tailored for each specific estuary/salt pond within the Town of Nantucket. Moreover, as nutrient load reduction strategies become implemented across the Island and in specific estuarine watersheds, maintaining the regular monitoring of nutrient related water quality in the estuaries is critical for answering questions related to whether or not a particular implementation approach is having the ecological effect predicted and if additional implementation is needed, as is the case specifically for the Sesachacha Pond embayment system. Water quality monitoring in Sesachacha Pond was continued and now allows determination of the level of improvement in the Pond associated with the periodic breaching and if the improvement has reached the level that the Pond can be removed from the Massachusetts list of impaired waters, e.g. has met its Total Maximum Daily Load (TMDL) requirement. Compliance Monitoring for Sesachacha Pond: 3 The water quality monitoring project undertaken in the summers of 2012, 2013 and 2014 complements data collected in 2010 and extends a water quality baseline data set that spans 1992-2005 and which was used by the MEP to establish the embayment specific nitrogen threshold. The monitoring program allows tracking restoration progress and management "success" in Sesachacha Pond relative to the established MassDEP/USEPA TMDL1 in place for that estuarine system. However, to determine TMDL compliance additional data collection beyond water column nutrient chemistry is needed (e.g. oxygen level, benthic animal assessment). The main objective of the monitoring effort was to track long-term changes resulting from the implementation of management alternatives to restore this nitrogen impaired system as they are put in place. For Sesachacha Pond, the primary restoration strategy put forth through the MEP analysis was to increase flushing of the Pond by adding an additional breach into the annual breach schedule, thereby further reducing overall nitrogen concentration in the pond. The present monitoring program built upon the more intensive efforts conducted previously in advance of the Massachusetts Estuaries Project and is consistent with the baseline water quality data that was used in the development of the MEP nitrogen threshold for Sesachacha Pond. In addition to traditional water column sampling, this compliance monitoring effort included high frequency data collection on dissolved oxygen and chlorophyll undertaken via the deployment of a mooring in order to clearly document improvements in oxygen conditions. This was complemented by a survey of benthic infauna communities to properly assess present habitat conditions in Sesachacha Pond as a result of a modified schedule of pond openings as recommended in the Massachusetts Estuaries Project analysis of Sesachacha Pond.2 Water Column Nutrient Sampling: Consistent with water quality monitoring activities undertaken by the Town of Nantucket in the years preceding the Massachusetts Estuaries Project analysis of Sesachacha Pond, the Coastal Systems Analytical Facility analyzed estuarine water quality samples from four previously established water quality monitoring stations in the Pond (S1, S2, S3, S4) as depicted in Figure 1. These stations were to be sampled six (6) times during the critical summer months with samples collected from multiple depths (surface, mid, bottom). In order to document a trend of increasing/decreasing water quality resulting from the modified schedule of pond openings, water quality in the pond was tracked during the 2012 field season as well as in the summers of 2013 and 2014. Ultimately, six events were completed in 2012 (June 20, July 19, August 23, September 25, October 23 and November 6), five events were completed in 2013 (May 22, June 5, July 9, August 21 and September 19) and 5 events in 2014 (May 20, June 12, July 30, 1 TMDL or Total Maximum Daily Load is the regulatory requirement for restoration of an aquatic system under the Clean Water Act as proscribed by MassDEP and USEPA. 2 This compliance assessment was completed by scientists in Coastal Systems Program (Dr.’s Howes, Schlezinger and Samimy and Sara Sampieri, Coastal Systems Analytical Facility Manager. SMAST Staff worked directly with the Nantucket Natural Resources Department to organize and conduct the water quality monitoring. 4 August 19 and September 4). It should be noted that for the analysis of 2012 summer conditions in Sesachacha Pond, data from only 4 of the six events was utilized as those events were during typical summer time conditions. Samples were collected at each of the four stations (Figure 1). As a point of comparison and separate from the 2012, 2013 and 2014 sampling effort summarized in this memo, in the summer of 2010, five sampling events were completed (May 26, June 24, July 26, August 26 and September 23). Figure 1. Town of Nantucket Water Quality Monitoring Program sampling stations (1992-2005) for Sesachacha Pond as provided by the Town of Nantucket Marine Department. Average Sesachacha Pond Total Nitrogen values in 2014 were 0.923 mg N/L and 2013 (0.669 mg N/L), 2012 (0.639 mg N/L) and 2010 (0.704 mg N/L). Average TN levels in Sesachacha Pond are significantly higher than average values in the “offshore” stations NAN 4 and MH4 which average >0.344 [0.302] and 0.297 [0.285] mg/L, respectively, but significantly lower than the long-term average observed in the MEP (1.197 mg N/L). Results from all years of sampling indicate that in Sesachacha Pond, there is no noticeable nutrient or chlorophyll gradient among the 4 Stations (Figure 2, Table 1a,b,c,d). 5 In reviewing the 2010, 2012, 2013 and 2014 dissolved oxygen data individually, it does not appear that there is sufficient temporal sampling in any one year to capture the critical minimum oxygen levels. Therefore, a multi-year composite analysis was performed based on the four years of data in addition to a high frequency assessment of dissolved oxygen and chlorophyll-a conditions in Sesachacha Pond in the summer of 2012. This was completed via a long term (2 months) deployment of a DO/CHLA mooring near water quality station 1. The 2012 mooring deployment was undertaken using the same methodology as the 2002 mooring deployment completed for the MEP threshold analysis. 6 Figure 2. Comparison of nitrogen species in the Nantucket estuaries (Summer 2010,2012,2013,2014 sampling season) 7 Table 1a. Summary of Water Quality Parameters, 2014 Sesachacha Pond Sampling Program. Values are Station Averages of all sampling events, May-September. Table 1b. Summary of Water Quality Parameters, 2013 Sesachacha Pond Sampling Program. Values are Station Averages of all sampling events, May-September. Table 1c. Summary of Water Quality Parameters, 2012 Sesachacha Pond Sampling Program. Values are Station Averages of all sampling events, May-September. 8 Table 1d. Summary of Water Quality Parameters, 2010 Sesachacha Pond Sampling Program. Values are Station Averages of all sampling events, May-September. 9 Comparison of the 2012-2014 and 2010 data with historical (1992-2005) data used in MEP: At all sites in Sesachacha Pond, historical TN levels from previous years (1992- 2005) of sampling were compared to 2014-2012 and 2010 TN concentrations. Historical data presented here are from the Massachusetts Estuaries Project (MEP) report for Sesachacha Pond. All sites (Stations 1-4) were sampled in 2014, 2013, 2012 and 2010, however, historically (1992-2005) TN levels were available for only 1 station (Figure 3). In Sesachacha Pond, historic data from Station SES-1 collected between 1992 and 2005 was compared to Station 1 water quality data collected in 2014, 2013, 2012 and 2010. The historical mean for TN was 1.197 + 0.078 mg/L while 2014, 2013, 2012 and 2010 TN levels were similar to each other but significantly lower than historically at 0.919, 0.714, 0.678 and 0.684 mg/L respectively (Table 2). The lower TN levels in Sesachacha Pond versus historic levels is a critical finding, as it clearly indicates improvement of pond resources and the positive effects of the modified breach schedule as recommended by the MEP analysis. While it takes multiple years to document "restoration" the consistency of results in 2010, 2012 and 2013 ranging from 0.678-0.714 mg/L supports the contention that nitrogen enrichment within the pond had been reduced. The fact that only small differences exist between Station 1 and the average of all 4 stations each year provides further support. However, the rise in TN in the 2014 sampling suggests that a poor inlet opening may have occurred in spring 2014 and inlet opening efficacy has a significant effect on pond water quality. Since there has been no major shift in nitrogen loading within the Sesachacha Pond watershed, it is almost certain that the amount of tidal flushing during the artificial breaching is creating the variability in the observed summer TN level. Anecdotal reports on breaches to Sesachacha Pond and recent data from Hummock Pond support this contention. If 2010, 2012 and 2013 represent the typical condition and 2014 conditions can be corrected by management actions in 2015, it appears that Sesachacha Pond, based on water quality data alone, may be very near its nitrogen threshold level and compliance with the TMDL. This contention is supported in all 4 years by the dramatic reduction in total chlorophyll a pigments, <8 ug/L compared to >20 ug/L with blooms to ~100 ug/L historically (Figure 6). Since there is no evidence of eelgrass habitat in this system, an assessment of bottom water D.O. and benthic animal habitat were conducted relative to TMDL goals and water quality standards. 10 Figure 3. 2005 aerial photo showing monitoring station location in Sesachacha Pond that was used in the MEP water quality analysis (1992-2005). Sampling Station Location Historical MEP Mean TN (mg/L) s.d. 2010 Mean TN (mg/L) 2012 Mean TN (mg/L) 2013 Mean TN (mg/L) 2014 Mean TN (mg/L) Sesachacha Pond 1.197 0.078 0.684 [0.704] 0.678 [0.639] 0.714 [0.669] 0.919 [0.922] Table 2. Comparison of MEP mean values of TN with Town TN data (all values are mg/L) from Sesachacha Pond. MEP data were collected in the summers of 1992 through 2005. Town data were collected in the summer of 2010, 2012 and 2013 by the Town of Nantucket Marine and Coastal Resources Department. Values in 2010, 2012 and 2013 represent the average at Station 1, with the average of stations 1-4 depicted in Figure 1 presented in [ ]. 11 Analysis of Dissolved Oxygen Conditions in Sesachacha Pond: Dissolved oxygen levels near atmospheric equilibration are important for maintaining healthy animal and plant communities. Short-duration oxygen depletions can significantly affect communities even if they are relatively rare on an annual basis. Dissolved oxygen depletion is frequently the proximate cause of habitat quality decline in coastal embayments (the ultimate cause being nitrogen loading). However, oxygen conditions can change rapidly and frequently show strong tidal and diurnal patterns. Even severe levels of oxygen depletion may occur only infrequently, yet have important effects on system health. The largest levels of oxygen depletion (departure from atmospheric equilibrium) and lowest absolute levels (mg L-1) are found during the summer in southeastern Massachusetts salt ponds when water column and sediment respiration rates are greatest. Since oxygen levels can change rapidly, several mg L-1 in a few hours, traditional grab sampling programs typically underestimate the frequency and duration of low oxygen conditions within shallow embayments (Taylor and Howes, 1994). To more accurately capture the degree of bottom water dissolved oxygen depletion during the critical summer period, an autonomously recording oxygen sensor was moored 30 cm above the embayment bottom within the central region of the Sesachacha Pond System in 2002 and again in 2012 (Figure 4). In order to compare 2002 DO conditions with observations made in 2012, the CSP Technical Team deployed a dissolved oxygen sensor within Sesachacha Pond in the same location as the DO mooring deployed under the Massachusetts Estuaries Project in 2002. Similar to 2002, the 2012 mooring deployment was conducted to record the frequency and duration of low oxygen conditions during the critical summer period and also to collect supporting information on phytoplankton biomass measured as chlorophyll-a. Consistent with MEP protocols for DO/CHLA mooring deployments, the sensors (YSI 6600) were first calibrated in the laboratory and then checked with standard oxygen mixtures at the time of initial instrument mooring deployment. In addition, periodic calibration samples in both 2002 and 2012 were collected during deployment at the sensor depth and assayed by Winkler titration (potentiometric analysis, Radiometer).. The instrument mooring was serviced and calibration samples collected at least biweekly and sometimes weekly during the 67 day (2002) deployment as well as during the 57 day (2012) deployment which focused on the same summer period, the critical August through October interval. Summary of 2012 and MEP 2002 DO/CHLA Mooring Deployments: Similar to many other embayments in southeastern Massachusetts, Sesachacha Pond showed high frequency variation in dissolved oxygen levels in both 2002 and 2012, apparently related to diurnal patterns of photosynthesis and respiration. The degree of the diurnal variation and observed hypoxia in summer 2002 are consistent with a nitrogen enriched, eutrophic, salt pond and is consistent with the parallel measurements of chlorophyll-a (Figures 5 and 6). Nitrogen enrichment of embayment waters generally manifests itself in the dissolved oxygen record, both through oxygen depletion and through the magnitude of the daily excursion. The temporal record of dissolved oxygen also captured a very low oxygen event, where levels declined to below 4 mg L-1 for 12 extended periods and below 2 mg L-1 on multiple dates. During this low oxygen period in late August-early September, there was an interval of extremely large diurnal variations (~6 mg L-1) that coincided with a very large phytoplankton bloom. Chlorophyll levels at the height of the bloom were in the hyper-eutrophic range, exceeding 100 ug L- 1 (Figure 6). The observed high degree of temporal variation in bottom water dissolved oxygen and chlorophyll concentration underscores the need for continuous monitoring within these types of systems. These patterns observed in the 2002 record were not observed in 2012. In 2012 the daily oxygen excursions existed but were much smaller, generally only 2 mg/L compared to 6 mg/L in 2002 (Figure 7). Most important is the finding of generally high oxygen levels (>6 mg/L) in bottom waters throughout the entire record with only periodic depletion to between 5-6 mg/L (7% of record). These are high D.O. levels for a coastal salt pond, especially a deep pond like Sesachacha Pond. The low oxygen levels in 2002 and high oxygen levels in 2012 mirror the parallel measurements of phytoplankton biomass (as chlorophyll a, Figure 8). It appears that the lower TN levels since 2010 support less phytoplankton, hence organic matter, and higher oxygen levels and that the D.O. levels are consistent with a significantly improved water quality in this system. Specifically in 2002 and 2012, dissolved oxygen and chlorophyll a records were examined both for temporal trends and to determine the percent of the 67 day deployment period that these parameters were below/above various benchmark concentrations (Tables 3 and 5). These data indicate both the temporal pattern of minimum or maximum levels of these critical nutrient related constituents, as well as the intensity of the oxygen depletion events and phytoplankton blooms. However, it should be noted that the frequency of oxygen depletion needs to be integrated with the actual temporal pattern of oxygen levels, specifically as it relates to daily oxygen excursions. The dissolved oxygen records indicate that the Sesachacha Pond system in 2002 showed seasonal oxygen stress, consistent with nitrogen enrichment (Table 3). That the cause was eutrophication is supported by the high levels of chlorophyll a, >25 µg/L 55% of the time (Table 4). Oxygen conditions and chlorophyll a levels improved in the system with the onset of autumn, although the system showed oxygen depletions below 5 mg L-1 (21% of the deployment record) and <3 mg L-1 (5% of the deployment record of 67 days). The level of oxygen depletion and the magnitude of daily oxygen excursion and chlorophyll a levels indicated highly nutrient enriched waters and significantly impaired habitat quality within the pond in 2002. In contrast, in 2012 D.O. levels remained above 6 mg/L 93% of the record and never declined to even 5 mg/L, while chlorophyll a was <15 ug/L 82% of the record (Tables 5 and 6). In both 2002 and 2012, the oxygen data was consistent with organic matter loads from phytoplankton production, as indicated by the observed chlorophyll a levels (high in 2002, low in 2012). Both the oxygen and chlorophyll records in 2002 indicated a highly nitrogen enriched system, significantly over its nitrogen threshold, the upper limit which supports healthy habitat quality, with relatively good water quality in 2012 (certainly in the range stipulated by water quality standards). 13 Sesachacha Pond DOSesachachaPond DO Figure 4. Aerial Photograph of the Sesachacha Pond system in Nantucket showing locations of Dissolved Oxygen mooring deployments conducted in the summers of 2002 and 2012. Sesachacha Pond 0 2 4 6 8 10 12 14 16 8/7 8/17 8/27 9/6 9/16 9/26 10/6 10/16 TimeDissolved Oxygen (mg/L) Figure 5 Bottom water record of dissolved oxygen at the Sesachacha Pond station, summer 2002. Calibration samples represented as red dots. 14 Sesachacha Pond 0 20 40 60 80 100 120 140 160 180 8/7 8/17 8/27 9/6 9/16 9/26 10/6 10/16 TimeTotal Chlorophyll Pigment (ug/L) Figure 6. Bottom water record of chlorophyll-a at the Sesachacha Pond station, summer 2002. Calibration samples represented as red dots. 15 Table 3. Percent of time during deployment of in situ sensors that bottom water oxygen levels were below various benchmark oxygen levels. Massachusetts Estuaries Project Town of Nantucket: 2002 Dissolved Oxygen: Continuous Record, Summer 2002 Deployment Days < 6 mg/L (% of days) < 5 mg/L (% of days) < 4 mg/L (% of days) < 3 mg/L (% of days) Sesachacha Pond 67.1 33% 21% 10% 5% Table 4. Duration (% of deployment time) that chlorophyll a levels exceed various benchmark levels within the embayment system. “Mean” represents the average duration of each event over the benchmark level and “S.D.” its standard deviation. Data collected by the Coastal Systems Program, SMAST. Embayment System Start Date End Date Total Deployment (Days) > 5 ug/L Duration (Days) > 10 ug/L Duration (Days) > 15 ug/L Duration (Days) > 20 ug/L Duration (Days) > 25 ug/L Duration (Days) Sesachacha Pond 8/9/2002 10/15/2002 67.1 96% 90% 86% 71% 55% Mean 4.62 2.87 2.30 1.44 1.12 S.D. 10.72 7.53 5.89 3.24 2.59 16 Figure 7 Bottom water record of dissolved oxygen at the Sesachacha Pond station, summer 2012 (August 27, 2012 to October 23, 2014). Dissolved oxygen in mg/L (thick blue line) and as % of atmospheric equilibrium (thin red line). Calibration samples represented as red dots. 17 Figure 8. Bottom water record of chlorophyll-a at the Sesachacha Pond station, summer 2012 (August 27, 2012 to October 23, 2014). Calibration samples represented as red dots. Total <6 mg/L <5 mg/L <4 mg/L <3 mg/L Embayment Start Date End Date Deployment Duration Duration Duration Duration (Days)(Days)(Days)(Days)(Days) Sesachacha Pond 2012 8/27/2012 10/23/2012 57.1 7%0%0%0% Mean 0.45 NA NA NA Min 0.04 0.00 0.00 0.00 Max 0.78 0.00 0.00 0.00 S.D.0.23 NA NA NA Table 5. Percent of time during deployment of in situ sensors that bottom water oxygen levels were below various benchmark oxygen levels. 18 Total >5 ug/L >10 ug/L >15 ug/L >20 ug/L >25 ug/L Embayment Start Date End Date Deployment Duration Duration Duration Duration Duration (Days)(Days)(Days)(Days)(Days)(Days) Sesachacha Pond 2012 8/27/2012 10/23/2012 57.10 65%38%18%6%1% Mean 1.38 0.90 0.36 0.23 0.33 Min 0.04 0.04 0.04 0.04 0.33 Max 12.17 6.50 1.25 0.88 0.33 S.D.2.73 1.53 0.30 0.24 NA Table 6. Duration (% of deployment time) that chlorophyll-a levels exceed various benchmark levels within the embayment system. “Mean” represents the average duration of each event over the benchmark level and “S.D.” its standard deviation. Data collected by the Coastal Systems Program, SMAST. Assessment of Existing Benthic Infaunal Community: In areas that do not support eelgrass beds, benthic animal indicators are used to assess the level of habitat health from “healthy” (low organic matter loading, high D.O.) to “highly stressed” (high organic matter loading-low D.O.). The basic concept is that certain species or species assemblages reflect the quality of their habitat. Benthic animal species from sediment samples collected in 2013 were identified and the environments ranked based upon community metrics of diversity (H’), evenness (E) and the community size (number of individuals and species) as well as the fraction of healthy, transitional, and stressed indicator species. The analysis is based upon life- history information on the species and a wide variety of field studies within southeastern Massachusetts waters, including the Wild Harbor oil spill, benthic population studies in Buzzards Bay (Woods Hole Oceanographic Institution) and New Bedford (SMAST), and the Woods Hole Oceanographic Institution Nantucket Harbor Study (Howes et al. 1997). To mirror benthic infaunal survey work completed by the MEP in 2002, quantitative sediment sampling was conducted in 2013 at the same 15 locations as in the 2002 survey throughout the Sesachacha Pond System and using the same methodology (Figure 9). Benthic animal species from sediment samples were identified and ranked as to their association with nutrient related stresses, such as organic matter loading, anoxia, and dissolved sulfide. Species assemblages were classified as representative of healthy conditions, transitional, or stressed conditions. Summary of MEP 2012 and 2002 Benthic Infaunal Community Characterization: As part of the 2012 and 2002 MEP analysis of Sesachacha Pond, quantitative sediment sampling was conducted at 15 locations throughout the Sesachacha Pond System (Figure 9). In some cases multiple assays were conducted. In all estuarine basins and particularly those that do not support eelgrass beds (such as Sesachacha Pond), benthic animal indicators can be used to assess the level of habitat health. The basic concept is that certain species or species assemblages reflect the quality of the habitat in which they live. Benthic animal species from sediment samples are identified and ranked as to their association with nutrient related stresses, such as organic matter loading, hypoxia/anoxia, and dissolved sulfide. The analysis is based upon life-history information and animal-sediment relationships (Rhoads and Germano 1986). Assemblages are classified as representative of healthy conditions, transitional, or 19 stressed conditions. Both the distribution of species and the overall population density are taken into account, as well as the general diversity and evenness of the community. It should be noted that, given the lack of eelgrass beds, high chlorophyll levels and low dissolved oxygen concentrations, the Sesachacha Pond System was clearly impaired in 2002 by nutrient enrichment, primarily from the lack of circulation and tidal exchange. However, to the extent that it can still support healthy infaunal communities, the benthic infauna analysis is important for determining the level of impairment (moderately impairedsignificantly impairedseverely degraded). This assessment is also important for the establishment of site-specific nitrogen thresholds (presented in MEP Threshold Report for Sesachacha Pond, Section VIII). Analysis of the evenness and diversity of the benthic animal communities was also used to support the density data and the natural history information. The evenness statistic can range from 0-1 (one being most even), while the diversity index does not have a theoretical upper limit. The highest quality habitat areas, as shown by the oxygen and chlorophyll records and eelgrass coverage (when present), have the highest diversity (generally >3) and evenness (~0.7). The converse is also true, with poorest habitat quality found where diversity is <1 and evenness is <0.5. The 2002 infauna study indicated that Sesachacha Pond was supporting significantly to severely degraded benthic infauna habitat quality (Table 7). In virtually all samples a single species indicative of organic matter enriched conditions, Streblospio benedicti, was dominant, typically accounting for more than two thirds of the individuals present. In addition, at about half the stations stress indicator species represented between 10% and 65% of the community (tubificids). While most stations along the eastern (A) and western (C) transects had moderate numbers of individuals, the number of species was low (<5), for each of the transects and species diversity (0.39-1.32) indicative of poor habitat quality. The middle transect (B) showed an impoverished community with total individuals averaging only 45 per sample. The 2002 MEP infauna survey results clearly indicated that Sesachacha Pond was supporting significantly impaired to severely degraded benthic infaunal habitat and the communities present were consistent with organic matter enrichment associated with nitrogen enrichment of pond waters. However, it appeared that the system should be capable of supporting healthy infaunal communities should the organic matter loadings be reduced. In contrast, the 2013 survey indicated recovering benthic animal habitat over the 2002 system. In the 2013 survey a major shift was seen in that the stress indicators were nearly absent (<8% of total individuals) for each transect. Significant improvements were seen in the other metrics where diversity (H’) was 1.44 – 1.76 compared to 0.39- 1.32; Evenness (E) improved overall but especially on Transect A increasing to 0.77 indicating a relatively uniform distribution of species from 0.15 in 2002, typical of domination by a single species. The number of species and individual also generally increased in 2013 over 2002. 20 Transect A-1 through 5 Transect C-1 through 5 Transect B-1 through 5 Transect A-1 through 5 Transect C-1 through 5 Transect B-1 through 5 Figure 9. Aerial photograph of the Sesachacha Pond system showing location of benthic infaunal sampling stations (red symbol) in both 2002 and 2012. Station 1 in each of the transects is at the southern end of the pond (bottom). Table 7. Benthic infaunal community data (2002 and 2012) for the Sesachacha Pond embayment system. Estimates of the number of species adjusted to the number of individuals and diversity (H’) and Evenness (E) of the community allow comparison between locations. Samples represent surface area of 0.018 m2, N/A indicates that numbers of individuals prevent calculation of species numbers @ 75 individuals. Species Weiner Location Total Actual Total Actual Calculated Diversity Evenness Stations a Species Individuals @75 Indiv.(H')(E)I.D. Sesachacha Pond 2002 East Transect [A]5.0 420 3.1 0.39 0.15 A-1 thru A-5 West Outer [B]3.0 45 NA 1.32 0.90 B-1 thru B-5 West Nearshore [C]3.8 210 3.6 1.27 0.65 C-1 thru C-5 Sesachacha Pond 2012 East Transect [A]5.4 88 NA 1.76 0.77 A-1 thru A-5 West Outer [B]4.6 155 NA 1.44 0.83 B-1 thru B-5 West Nearshore [C]6.0 342 6.5 1.48 0.54 C-1 thru C-5 a - stations refer to 2002 and 2012 location maps below. 21 Current Status of Sesachacha Pond: Sesachacha Pond, as a closed coastal salt pond, has its water quality managed primarily by periodic breaching of the barrier beach to open the basin to tidal exchange with the adjacent low nutrient 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 as part of the pond management strategy to enhance flushing of the pond and improve water quality to reach the threshold. The nitrogen threshold analysis from the MEP Technical Report for Sesachacha Pond states, “Sesachacha Pond currently has a low watershed nitrogen load, with external loading dominated by direct atmospheric input, and moderate summer input from its sediments and only periodic tidal exchange. The result is nitrogen levels reaching 1.5 mg TN L-1 and average TN levels of ~ 1 mg TN L-1. Therefore it is not clear if average summer TN levels can be reduced to <0.5 mg L-1 or if this level has been achieved at any time in past centuries. The Pond was always cited to be used for shellfish transplanting and therefore likely has been somewhat nitrogen enriched, supporting moderate phytoplankton levels. Therefore, the MEP Technical Team determined that a higher TN level <0.6 mg TN L-1 would likely support a moderately impaired infaunal community, yet conditions that should also support shellfish… reflective of the natural condition of this system in its present configuration.” The water quality monitoring program in 2010, 2012, 2013 and 2014 is showing that the pond nitrogen levels are converging on the 0.60 mg/L total nitrogen threshold established by the MEP, with 2014 showing slightly higher levels possibly due to the somewhat ineffective spring 2014 breaching. Generally, total nitrogen (TN) levels have dropped significantly from 1.20 mg/L to ~0.68 mg/L, with associated improvements in the levels of water clarity and chlorophyll-a. The monitoring data suggest that the pond has not yet been fully restored, based upon the 2013 observed moderate impairment to the benthic animal community. However, the benthic community is likely continuing to improve as the stresses from organic matter loading and periodic low D.O. appear to be diminishing and there can be a lag between habitat improvements and their reflection in the community metrics. It appears that the present average TN levels, ~0.7 mg TN/L slightly above 0.6 mg TN/L, is consistent with the improved but still moderately impaired benthic animal habitat. The benthic animal habitat is consistent with the water quality improvements, where hypoxia common in 2002 was not seen in 2012 and chlorophyll a levels have declined to those found in moderate to high quality waters. It is recommended that monitoring of this system is extended and continued care is taken in the conduct of the opening, with appropriate documentation (duration open to tides as well as wind and wave conditions). Overall, if the periodic openings can be managed at the level of the 22 2012 and 2013 openings, it is likely that Sesachacha Pond will continue to improve and meet its designated TMDL.