The URL can be used to link to this page

Home My WebLink About2021 WQ exe summary1 TOWN OF NANTUCKET NATURAL RESOURCES DEPARTMENT THAÏS M. FOURNIER, WATER RESOURCE SPECIALIST TFOURNIER@NANTUCKET-MA.GOV 131 PLEASANT ST. 508-228-7200 NANTUCKET, MA 02554 EXT 7604 2021 Executive Summary Water Quality Assessment of Nantucket’s Harbors and Great Ponds Abstract: The executive summary reviews 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 (TON) Natural Resources Department and the Coastal Systems Program within the University of Massachusetts-Dartmouth, School for Marine Science and Technology. The objectives of the monitoring program are: 1. To determine the present (2021) ecological health of each of the main salt ponds and estuaries within the Town of Nantucket, 2. To gauge (as historical data allows, 2010-2021) the decline or recovery of various salt ponds and embayments over the long-term (also part of TMDL compliance), and 3. To provide the foundation (and context) for development of potential alternatives for nutrient and resource management and quantitative measures of success. Introduction: As increasing numbers of people occupy coastal watersheds, the associated coastal waters receive increasing pollutant loads. Coastal embayments throughout the Commonwealth of Massachusetts are becoming nutrient enriched. The primary nutrient causing the increasing impairment of our coastal embayments is nitrogen, with its primary sources being wastewater disposal, and nonpoint source runoff that carries nitrogen (e.g., fertilizers) from a range of other sources. Nantucket proactively monitors the quality of its water systems to develop action plans to ensure public safety and strengthen the islands ecosystems. As in previous years, this annual Water Quality Technical Memorandum summarizes the water quality monitoring results of the estuarine sampling undertaken through the ongoing Nantucket Island-wide Water Quality Monitoring Program. Water sample collection and analysis has been performed 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. The sampling program focuses on the summer/early fall months (June - September) as this time frame is typically representative of worst case water quality conditions and the basis for habitat management decisions. The physical/environmental parameters measured in the estuaries during the 2021 sampling season included: total depth, Secchi depth (light penetration), temperature, conductivity/salinity, 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, 2 dissolved organic nitrogen, particulate organic carbon and nitrogen, chlorophyll-a and pheophytin-a and orthophosphate. 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, lowest measured concentrations of dissolved oxygen, and Chlorophyll-a pigments (proxy 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). Results: Table 1. Summary of present status and trends of water/habitat quality of estuaries of Nantucket based on the long-term water quality monitoring data reconciled against historic data and MEP nutrient threshold analyses undertaken for each system except Miacomet Pond. A TMDL for Hummock Pond has not yet been released by MassDEP. The trends in the table for Long Pond and Sesachacha Pond need to be interpreted as multi-year, since in 2021 these ponds showed a modest increase in water quality impairment. Embayment TMDL Status Trend Trophic Health Score Remedial Actions Nantucket Harbor 0.35mg/L (0.36mg/L Polpis) Approaching N target Improving High-moderate quality New jetties, Planned sewering, Fertilizer Program Madaket Harbor 0.45 mg/L Approaching N target Improving High-moderate quality Landfill remediation Hummock Pond 0.50mg/L Significantly impaired Variable Moderate-fair quality Pond openings Long Pond 0.80mg/L Approaching N target Improving Moderate quality Landfill remediation Miacomet Pond 0.60mg/L (not regulated) Significantly impaired Unchanged Fair-poor quality Potential dredging/chemical treatment of nutrient laden sediment Sesachacha Pond 0.60mg/L Moderate improvement Variable High-moderate quality Pond openings 3 Conclusion: The Town of Nantucket has been working for decades to protect and more recently restore its estuaries and their aquatic resources. Overall, the water quality trends in Nantucket’s major estuaries have been positive over the past 5-10 years. Nantucket Harbor, Long Pond and Sesachacha Pond are showing improvements and are approaching their TMDL targets to meet restoration goals. Madaket Harbor is supporting high water and habitat quality. Hummock and Miacomet Ponds are experiencing water quality and habitat health issues. At present and based on the 2010 - 2021 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 four estuarine systems: Nantucket Harbor (raised jetties and planned sewering), Madaket/Long Pond (lined landfill cells and future potential dredging), Sesachacha Pond (biannual openings), Hummock Pond (biannual openings). In addition, the TON’s fertilizer application by-law should reduce nutrient inputs into Nantucket’s embayments. As a result, it is anticipated that the efficacy of these management activities should be seen in the present and future water quality monitoring results. 4 Figure 1. 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. TN levels have declined harbor-wide over the past 10 years due to nitrogen mitigation strategies implemented by the Town. 2020 data generally confirms the trend (with exception Nan-4), lower Harbor still showing TN decline, however 2021 shows increased TN mainly in the upper basin Nan-3. Figure 2. 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. Long Pond shows reductions in TN from 2010,2012, 2013 to 2014-2016 to 2017-2020, however 2021 (0.766 mg TN/L) did show an increase from this trend. 5 Figure 3. Summer average total nitrogen levels by station over time in Hummock Pond. The long opening in 2015 lowered TN levels (0.75 mg/L) well above the target level for high water quality. Lower TN in levels in 2020 and 2021 show water quality improvement in the lower basins maybe from longer opening duration. Figure 4. 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. Miacomet Pond remains a nutrient degraded system in 2021. Note that at all stations the TN level greatly exceeds the threshold for brackish and estuarine systems. 6 Figure 5. Total nitrogen levels by station over time in Sesachacha Pond. Longer openings in 2010-2014 resulted in lower TN levels, recent opening attempts are again being more successful (2018), but TN levels remain above the target level. 2020 pond opening duration may have been longer than past years resulting in the lowest TN level on record, half of the MEP 2003 average. However, it appears lower exchange during the fall 2020 opening resulted in lower salinities and higher TN and pigments in 2021.