EXECUTIVE SUMMARY

Background: One of the most significant long-term threats to coastal ecological health, both locally and globally, is the over-fertilization or eutrophication of our near shore coastal salt ponds and embayments. Functioning as the "sentinels of the coast", these circulation restricted embayments are among the most productive of our coastal waters. Healthy systems support extensive and diverse plant and animal communities and have important aesthetic, commercial and recreational value. At the same time, however, these systems are also the first to be impacted by human activities within their watersheds. The steady and progressive increase in nutrient inputs to these fragile environments, resulting primarily from on-site septic systems, fertilizers and runoff associated with increased coastal development, can have long ranging impacts on both ecosystem health and the economic health of coastal communities which depend on the commercial, recreational and aesthetic resources provided by these systems. As the problem of nutrient overload to coastal water bodies has only been seriously recognized in recent decades. Our limited understanding of the long-term impacts of chronic nutrient loading, the natural processes controlling nutrient cycling and the ability of these systems to assimilate additional nutrients frequently hinders the development of management strategies. In addition, as new approaches for restoring embayments are implemented evaluation of "success" is needed, but requires long-term water quality data.

The potential detrimental impacts of chronic nutrient overloading to coastal systems are clear, with the primary source of this loading being associated with the steady and progressive increase in development along our coastlines. Degradation of coastal waters and development are tied together through inputs of pollutants in runoff and groundwater flows, and to some extent through direct disturbance, i.e. boating, oil and chemical spills, and direct discharges from land and boats. Excess nutrients, especially nitrogen, promote phytoplankton blooms and the growth of epiphytes on eelgrass and attached algae, often with adverse consequences. Where waters are made turbid by excessive plankton blooms, light penetration to benthic plants (like eelgrass) is reduced, thereby reducing their rate of photosynthesis and growth. Algal slime and other epiphytic growth on these plants may shade them further, so that they sicken or die. Decaying phytoplankton and macro-organic matter build up on the bottom, increasing the oxygen demand upon bottom waters. At excessive levels of nitrogen inputs, bacterial decay processes combine with animal respiration and night-time plant respiration to draw down the dissolved oxygen supply, especially in the hot, still weather typical of July and August. Fish and shellfish kills and changes in overall benthic animal communities are a common result. This process of increasing nutrient inputs resulting in algal blooms, low oxygen and stressed animal communities is called eutrophication and if the increased nutrient loads result from human activities, cultural eutrophication.

Three Bays Nutrient Related Health: Overall the Three Bays Estuary is showing relatively good nutrient related health compared to most of the embayments on the south shore of Cape Cod. However, there are some areas within the Estuary which are presently showing nutrient related water quality declines and there is a wide variation in habitat quality within the Three Bays System. In general the quality of habitat in Three Bays shifts from high quality near the inlets to Nantucket Sound to poor quality (eutrophic) in the inland reaches. At present, Prince Cove, and the region of the mouth of the Marstons Mill River through the narrows to North Bay are showing poor nutrient related environmental health. However, the loss of eel grass beds from most of the Three Bays proper indicates that the system has undergone nutrient loading related shifts. As there is only a single field season of monitoring data, refinement of the precise health of the various sub-systems awaits additional data collection. However, the effects of watershed nutrient inputs can be seen in diminished water transparency, increased chlorophyll and nitrogen levels in the upper system and North Bay. Sampling of benthic animals and high frequency sampling of chlorophyll and oxygen levels will help to better define the level of habitat health in these component systems. Specific findings and recommendations for the data collection in the coming field season are given below. It should be noted that the monitoring program and all proposed additional data collection are specifically to support the linked watershed-embayment quantitative assessment the direct target of which is the restoration and protection of the health of the Three Bays Estuary.

(1) The Three Bays Estuary appears to be nitrogen limited, i.e. additions of nitrogen will increase algal production. Therefore, managing the nutrient related health of these marine waters requires management of nitrogen inputs from the watershed and removal by tidal exchanges to adjacent Nantucket Sound.

(2) The upper estuary from the mouth of the Marstons Mills River through the channel to North Bay and Prince Cove is currently showing poor nutrient related health. Additional high frequency sampling performed by CMAST during summer 2000 clearly supports that Prince Cove is currently being over-fertilized (i.e. it is eutrophic).

(3) The Marstons Mills River appears to be a major "point source" of nitrogen loading to the Estuary. The River carries nitrogen gathered through surface and groundwater inflows to the Bay.

(4) The organic matter within the Three Bays Estuary appears to be produced by phytoplankton supported by inputs of watershed nitrogen and recycled nitrogen within the Bays, as opposed to entering the system in surface water flows.

(5) Fecal coliform levels are generally low within the lower estuary , but high (relative to shellfish harvest limits and safe swimming levels) within the upper estuary. However, examination of the long-term record of fecal coliform levels collected by DMF (1985-1998) indicates that levels over the shellfish limit occasionally occur in the near shore regions throughout most of the Three Bays System.

(6) Elevated fecal coliform levels are not always associated with rain events, suggesting potential direct discharges to the upper system from waterfowl, boats, direct wastewater discharges (in violation of health code). Additional sampling by Three Bays Preservation during the summer of 2000 is aimed at further elucidating the fecal coliform sources.

(7) Water quality monitoring should support water quality modeling of the effect of a new tidal flow between Grand and Little Islands. This effort would be part of the quantitative water quality study, but would rely (in part) on the monitoring data.

(8) Shellfish upwellers to take advantage of high phytoplankton biomass, but avoid the periodic low bottom water dissolved oxygen. Upwellers should include measurements of nitrogen removals by shellfish.

(9) Deployment of moored instruments (like in Prince Cove in 2000) in embayment areas of special concern to better elucidate the frequency and duration of low oxygen conditions and phytoplankton blooms.

(10) Establishment of a freshwater inflow and nutrient load gauging station on the Marstons Mills River and possibly the Little River. The data provide essential data input to the linked watershed-embayment water quality models and are central to validating the freshwater balance of the system. A flow station was established during the summer 2000 as part of the Water Quality Monitoring Program, using a grant from the Cape Cod Commission for hardware.

(11) Nutrient related environmental stress is clearly evident within the upper portions of the Three Bays System and other areas have undergone declines from historic levels. Nitrogen loading to the Three Bays System is still continuing both through increasing watershed loading and the time lag between the initiation of a new nitrogen source and the arrival of the associated nitrogen in the Bay. In addition, bacterial contamination within the upper estuary is occurring. While it is clear that additional water quality monitoring is needed, the implementation of the state-of-the-art linked watershed-embayment management study is warranted. This quantitative assessment and modeling of the Three Bays System is needed to develop realistic and efficient watershed management options focused on improving habitat quality. This estuarine restoration and management effort requires a solid foundation of nutrient-related water quality monitoring information (multi-year) from which to base the higher level modeling and management effort. However, some aspects of estuarine restoration and management planning have already begun, based upon the initial monitoring results (i.e. the implementation has started and should continue to be fostered).

(12) Water quality monitoring is a long-term commitment required for proper management of coastal embayments. The data is initially used to guide higher level studies for restoration or protection efforts. Over time monitoring is used to gauge the effectiveness of implemented management practices and to support adaptive management of these systems.