Project Overview

INTRODUCTION

Coastal embayments are enclosed areas of the coastline where the fresh water from groundwater and streams is mixed with salt water from the surrounding oceans. This ever-changing environment creates an ecological niche that is important for seagrasses, scallops, soft shelled clams, and as a breeding ground for commercially important offshore fish. These areas are also the primary recreational areas of Cape Cod.

The attractiveness of these areas has helped to spur large population increases on Cape Cod over the past decades; between 1970 and 1980 the population increased 53% and then increased by 26% between 1980 and 1990 (CCC, 1996a). These increasing populations have spurred a dramatic increase in land development; 35,246 new housing units were build between 1980 and 1990.

These population increases have created coastal water quality impacts. Shellfish bed closures in Cape Cod embayments increased from 712 acres in 1980 to 7,235 acres in 1992 (DMF files). Eelgrass has nearly disappeared from certain embayments within the past decade (Costa, 1988; Costello and Stone, 1994). In Waquoit Bay, one of the most impacted and best studied embayments, scallop harvests have decreased from thousands of bushels to just tens of bushels (Valiela, et al., 1992).

The key contaminant causing the degradation of the water quality within Cape Cod's coastal embayments is nitrogen. Nitrogen is introduced into Cape Cod's coastal waters from atmospheric deposition and from groundwater or streams flowing from their watersheds. The nitrogen that gets into the groundwater comes from wastewater via septic systems and treatment plants, stormwater runoff, and fertilizers. The plants (algae and submerged) that form the base of embayment ecosystems can be "fertilized" by the addition of nitrogen (Ryther and Dunstan, 1971; Taylor, et al., 1995a) (Figure 1).

Too much nitrogen in an embayment system increases the growth of these plants, which leads to diminished water clarity, losses of shellfish habitat, depressed dissolved oxygen levels, build-up of bottom sediments, and in extreme cases, fish kills (NRC, 1993; Valiela, et al., 1992; Rosenburg, 1985; Taylor, et al., 1995b; Howes and Goehringer, 1995). Long term exposure of shallow coastal waters to excessive nitrogen gradually alters their ecosystems, causing scallop and eelgrass populations to be replaced by dense algae or macroalgae, such as sea lettuce (Valiela, et al., 1992; Costa, et al., 1992; Nixon, et al., 1986). This process is also known as eutrophication.

Because of the significant links between Cape Cod's economy and its coastal environment, the Cape Cod Commission initiated the Coastal Embayment Project. This project, which began in 1993, was undertaken to begin the process of determining the nitrogen loading capacity (i.e., the ability of an embayment to assimilate nitrogen without becoming eutrophied) of a select number of embayments: Round Cove, Allens, Saquatucket and Wychmere Harbors in Harwich, Popponesset Bay in Barnstable and Mashpee, the Three Bay System in Barnstable, West Falmouth Harbor, the Upper Bass River System in Yarmouth, Dennis, and Brewster, and the Nauset Marsh Estuary System in Orleans and Eastham (Figure 2). Additional embayments where work has been undertaken by the Commission include: the Centerville River/Scudder Bay system and Pleasant Bay (CCC, 1998).

This report describes and evaluates the nitrogen loading assessments, critical load determination methods, and the application of these methods to the project embayments, including potential nitrogen management options. This report also details recommendations for the Executive Office of Environmental Affairs (EOEA), the Department of Environmental Protection (DEP) and the towns of Cape Cod that can assist in the protection of water quality in coastal embayments.

PROJECT EMBAYMENT ASSESSMENTS

The Commission utilized a four step process to assess the potential impacts of existing and future land uses on the water quality and ecosystem function of an embayment. These steps include: 1) delineating the watershed to the embayment; 2) conducting a flushing study to determine how long it takes for the water volume within the embayment to be exchanged and the amount of nitrogen that the embayment ecosystem can assimilate (usually referred to as a "critical load"); 3) evaluating the steady-state nitrogen load coming from existing development within the watershed and the potential future load based on the development of undeveloped land under existing zoning; and 4) comparing the nitrogen loads from existing and future development in the watershed to the critical load from the flushing study and developing nitrogen management strategies based on this comparison (Figure 3).

An accurate and regionally consistent groundwater map was developed to delineate the watersheds to the major coastal embayments around Cape Cod and the project embayments. Tidal flushing studies were conducted for all project embayments, usually including the collection of system bathymetry and 30 days of tidal data and the development of a tidal model. The tidal models were used to determine local and system residence times (Figure 4).

While the regional 5 ppm nitrogen concentration is protective of drinking water, coastal embayments are much more sensitive to nitrogen. Background total nitrogen concentrations in coastal waters are generally between 0.1 and 0.3 ppm and additions of between 0.05 and 0.1 ppm can have significant impacts how a coastal ecosystem functions. The Commonwealth of Massachusetts does not currently have nitrogen standards for coastal waters, but does have a surface water classification system. Under this system, coastal waters are assumed to be classified as SA, unless greater degradation is allowed (SB classification) or no degradation is allowed (ORW (Outstanding Resource Waters) classification). Project staff reviewed a number of coastal nitrogen limits, including those previously developed by the Buzzards Bay Project (BBP), and used the state classifications as guidance in evaluating these standards. The standards reviewed represent 0.05 ppm (ORW-N), 0.1 ppm (BBP ORW), 0.15 ppm (SA-N), and 0.2 ppm (BBP SA) nitrogen additions. These standards used the local residence times to determine nitrogen limits, which are presented as the amount of nitrogen per area of each of the project watersheds in Table 1. Additional effort is necessary to refine which of these available limits are the most appropriate for the development of nitrogen management strategies.

Within each of the project watersheds, existing land use was evaluated and nitrogen loads were determined using a modified version of the Commission's Technical Bulletin on Nitrogen Loading (TB91-001) (Eichner and Cambareri, 1992). The basic input values from TB91-001 were used, but calculations were modified to account for seasonal occupancy within each of the towns, water use from commercial establishments, landfill and wastewater treatment plant monitoring data, and other pertinent information. Following the review of existing land use, projected nitrogen loads following the development of all available land within each of the watersheds (i.e., buildout) was determined. These nitrogen loads were also compared to the available nitrogen limits.

Following the determination of the existing and buildout nitrogen loads, project staff developed potential management options to attain the various nitrogen limits. Project staff have considered management strategies that have included reductions in nitrogen loads from wastewater and lawn fertilizers, dredging of embayment systems to increase flushing and increase critical loads, and purchase and preservation of developable land as open space. Listed below are the results from each of the project embayments, which are also presented in Table 1.

HARWICH EMBAYMENTS

Watersheds to all four of the Harwich project embayments are located wholly within the Town of Harwich (see Figure 2) and are classified by the Commonwealth of Massachusetts as SA waters. Round Cove also has the designation of ORW because of its location within the Pleasant Bay Area of Critical Environmental Concern (ACEC). Current and buildout nitrogen loadings within the Saquatucket Harbor watershed exceed only the ORW-N limit (see Table 1). Existing and buildout nitrogen loadings to Allens Harbor (arm) exceed all the limits examined. Existing nitrogen loads to Round Cove exceed the ORW-N limit and buildout nitrogen loads exceed both ORW limits. The existing and buildout nitrogen loads to Wychmere Harbor exceed the ORW limits and SA-N limit, but are less than the BBP SA limit. The existing nitrogen loading to Allens Harbor (Main) exceeds the ORW limits, but is less than the SA limits. Buildout within the Allens Harbor (Main) watershed causes the nitrogen load to exceed the SA-N limit, but not the BBP SA limit. Project staff reviewed potential management strategies to reduce nitrogen loads within each of the watersheds to meet the limits examined.

POPPONESSET BAY

The watershed to Popponesset Bay is located mostly in the towns of Barnstable and Mashpee with a smaller portion within Sandwich (see Figure 2). The waters of Popponesset Bay, including the Mashpee River and Shoestring Bay, are classified as SA waters by the Commonwealth of Massachusetts. Existing and buildout nitrogen loading within the subwatershed to the Mashpee River exceeds all the nitrogen limits examined (see Table 1). Existing nitrogen loading within the watersheds to Shoestring Bay and the whole Popponesset Bay system exceed only their respective ORW-N limits and buildout causes both respective ORW limits to be exceeded. Project staff reviewed potential management strategies to reduce nitrogen loads within each of the watersheds to meet the limits examined.

WEST FALMOUTH HARBOR

West Falmouth Harbor is located on the Buzzards Bay side of Falmouth (see Figure 2). The waters of West Falmouth Harbor, including Snug Harbor, South Cove, Harbor Head, and Oyster Pond, are classified as SA waters by the Commonwealth of Massachusetts. Existing nitrogen loads in all subembayments exceed both ORW limits, while existing conditions also exceed both SA limits for Oyster Pond and the SA-N limit for Snug Harbor (see Table 1). Buildout nitrogen loading, including full capacity at the town wastewater treatment facility (WWTF), causes the ORW-N limit for the whole system to be exceeded, as well as all limits for Snug Harbor and the SA-N limit for the combined watersheds of Oyster Pond/Harbor Head. Management options to meet the various limits are presented and the spreadsheets developed to analyze the nitrogen loads can be used to evaluate additional options.

Quantifying the impact of the WWTF is a key to developing appropriate management options for Snug Harbor and the whole West Falmouth Harbor system. The current system-wide water quality monitoring effort underway by the town Pond Watchers and the current University of Massachusetts-Dartmouth/ Center for Marine Science and Technology (UMASS/CMST) study of Snug Harbor should help to provide additional insights into the selection of appropriate nitrogen management activities. All of this work, including the nitrogen loading analysis completed in this report and the previously completed hydrodynamic model, should be used as tools under a process to select appropriate activities to protect and improve water quality in the West Falmouth Harbor system.

UPPER BASS RIVER

The Upper Bass River system is located between the Sagamore and Monomoy groundwater lenses and the watershed contains portions of Dennis, Yarmouth, and Brewster (see Figure 2). The waters of Upper Bass River, including Mill Pond, Follins Pond, and Dinahs Pond, are classified as SA waters by the Commonwealth of Massachusetts. Existing nitrogen loading within the subwatersheds to Mill Pond and Dinahs Pond exceed all nitrogen limits examined, while existing loading to Follins Pond exceeds only the ORW-N limit and existing loading to the whole system exceeds both ORW limits (see Table 2). Buildout within the watersheds maintains these relationships to the limits examined. Management options to meet the various limits are presented and the spreadsheets developed to analyze the nitrogen loads can be used to evaluate additional options.

Water quality monitoring data is required to resolve the nitrogen sensitivity of Mill Pond and help to better calibrate the above analyses for the rest of the system. Most of the Upper Bass River system is near buildout conditions, except for the watershed to Follins Pond. Since nitrogen loads in these other areas are expected to increase between 13 and 22%, the nitrogen concentrations measured in this system should be close to steady-state conditions.

The potential additional nitrogen load from the reuse of the Town of Yarmouth landfill site is an immediate concern for the water quality in Mill Pond and the Upper Bass River system. Additional nitrogen loads from this site either comparable to or greater than existing loads from the landfill will create the need for comparable reductions in nitrogen loads from residential development within the watershed.

WELLFLEET HARBOR

Wellfleet Harbor is located in the Town of Wellfleet, Massachusetts (see Figure 2). Most of Wellfleet Harbor is classified as SA waters by the Commonwealth of Massachusetts. Portions of the Harbor system adjacent to or within the Cape Cod National Seashore are also considered ORWs under these regulations. Since most areas designated as ACECs are considered ORWs under these regulations, the ACEC designation of Wellfleet Harbor in 1989 may officially add the ORW designation to the entire HarborŐs official classification once the surface water classification regulations are updated.

While the watershed delineation and nitrogen loading assessments have been completed for Wellfleet Harbor, local residence times have not been developed for the Harbor. However, Wellfleet Harbor is one of the few Cape Cod embayments where water quality information has been collected. UMASS/CMST has overseen the collection using funding from the Wellfleet Harbor Project. The water quality information collected to this point does not indicate degraded water quality in any portion of the Harbor, except Duck Creek. The comparison of the nitrogen loads to critical loads based on the available conservative system residence times indicate that ORW-level water quality exists in Harbor, except for Duck Creek, Drummer Cove, and upper portions of Hatches Harbor and Blackfish Creek (see Table 1). Additional water quality and tidal flushing data should be collected and reviewed before formulating management recommendations for existing development within the Drummer Cove, Upper Blackfish Creek, and Upper Hatches Creek subwatersheds.

THREE BAY SYSTEM

The Three Bay (3-Bay) embayment system is located in the southwest portion of the Town of Barnstable and includes North Bay, Cotuit Bay, and West Bay (see Figure 2). The watershed to the 3-Bay system includes portions of the towns of Barnstable, Mashpee, and Sandwich. The 3-Bay system is classified as SA waters by the Commonwealth of Massachusetts. Existing and buildout nitrogen loading to Prince Cove Proper and Prince Cove Arm exceed all nitrogen limits examined (see Table 1). Existing nitrogen loading to North Bay exceeds its ORW-N limit, while buildout causes both ORW limits to be exceeded. Existing and buildout in all other subwatersheds are below all of their respective nitrogen limits. However, the excess nitrogen loading in the upper portion of the 3-Bay system has the potential to impact water quality throughout the system. When the system is considered as a whole, without subwatersheds, all nitrogen limits are exceeded under buildout conditions.

NAUSET MARSH/TOWN COVE

The Nauset Marsh System is located between the Towns of Eastham and Orleans and includes Town Cove (see Figure 2). In June 1994, the CCC awarded the Town of Orleans $20,000 to conduct a flushing study of Town Cove. In October 1994, CCC and town staff learned that the National Biological Survey (NBS) was also planning to complete a tidal flushing study of the Nauset Marsh system. Town, county, and federal staff agreed to conduct a jointly funded flushing study. Unfortunately, resolving details within contracts between the NBS and the CCC and two shutdowns of the federal government delayed the completion of the flushing study (Aubrey, et al., 1997) too long for the completion of the nitrogen loading assessments under this project. Watershed and subwatershed delineations have been completed.

CONCLUSIONS

The nitrogen loading analyses completed for this project found that existing nitrogen loading exceeded at least one of the nitrogen loading limits for all 9 of the project embayments. If subembayments are considered, 23 of 37 coastal waters have existing nitrogen loads exceeding at least one nitrogen loading limit. Buildout within subwatersheds increases this ratio to 24 of 37.

Project findings found that determining nitrogen loading within a coastal watershed can be as complex or as simple as desired. On-going discussions among Commission and numerous scientists, including two large meetings hosted by the Commission in January 1995 and February 1998, have identified the differences between data gathering and modeling approaches, as well as areas for further investigation. Attendees at these meetings included representatives from DEP, BBP, UMASS/CMST, Woods Hole Oceanographic Institute (WHOI), US Geological Survey, Waquoit Bay National Estuarine Research Reserve (WBNERR), Boston University Marine Program/Marine Biological Laboratory (BUMP/MBL), Barnstable County Department of Health and the Environment, University of Connecticut, and University of Rhode Island. Preliminary analyses and discussion at these meetings suggest that loading approximations using various methods, including criteria from DEP, CCC, and BBP models, result in acceptable ranges, but recent research claims of extensive denitrification in the Cape Cod aquifer require further assessment.

Project staff suggest that the use of the modified TB91-001 method obtains the necessary information for development water quality models, examination of wastewater treatment options, and requires relatively little data input, especially with the use of existing Geographic Information System (GIS) coverages. Development of GIS parcel coverage information is necessary for subsequent wastewater facilities planning assessments for areas that are identified as having excessive nitrogen loads.

Flushing studies of coastal embayments are also a key for developing water quality protection options. Comparing nitrogen loads to local residence time calculations can produce estimates of average expected nitrogen concentrations and reasonable assessment of general ecosystem conditions. Water quality data can later be incorporated into appropriate flushing study models to accurately predict nitrogen concentrations throughout a coastal embayment and refine the assessment of ecosystem conditions and potential management options. Flushing studies should be conducted by qualified coastal scientists. Both system and local residence times should be determined.

Critical attention needs to be focussed on the development of appropriate nitrogen loading limits. The assessment of nitrogen loads to and water movements within an embayment are adequate at this point for regulatory and planning decisions, but definition of the appropriate nitrogen limit requires additional attention. Through the work of the BBP, UMASS-D/CMST, WHOI, BUMP/MBL, the Coalition for Buzzards Bay, WBNERR, and numerous citizen groups, additional water quality information has been developed for a number of Cape Cod embayments. The Commission suggests that this data should be reviewed, and considered with the available nitrogen loading information, to provide more refined nitrogen loading standards for coastal embayments. Additional review of this data also should be able to help refine the predictive ability of nitrogen loading and coastal flushing models. In parallel, the state should similarly look to develop eutrophication standards for coastal waters with an eye towards to inclusion of this information in the Massachusetts 305(b) reports that are submitted to EPA.

Even given some of the uncertainty surrounding the recommended nitrogen limits, discussions and analysis of nitrogen loading management options should be initiated and/or continued in watersheds to embayments where limits are exceeded. In the subembayments where existing loading exceeds even the highest loading standard considered (i.e., the BBP SA standard), the process of evaluating options should be accelerated, including: 1) identifying areas of high density development for potential sewering, 2) identifying potential parcels for neighborhood or larger wastewater treatment facilities, and 3) clarification of potential costs and institutional arrangements for septic system management and/or sewer districts. In addition, discussions should also focus on ways to limit impacts from future development within these watersheds, since additional development will further stress these ecosystems. Subwatersheds to the following embayments are in this category: Mashpee River in Popponesset Bay, Prince Cove Proper and Prince Cove Arm in the Three Bay System, Oyster Pond in West Falmouth Harbor, Dinahs Pond and Mill Pond in Upper Bass River, and Allens Harbor (arm).

Town Boards of Health currently have the authority under Title 5 to assist in the protection of coastal embayments by designating embayments as nitrogen sensitive. The materials gathered under this grant provide sufficient information for the embayments of concern to be designated as nitrogen sensitive embayments. Communities should recognize that a Title 5 nitrogen sensitive designation will require all septic systems within the respective watersheds to be 440 gpd/acre or less (310 CMR 15.214). This limit will provide some level of protection, but will be insufficient for adequate protection of certain, more sensitive, embayments.

Although the Commission has the ability to assist the towns in adopting coastal water quality protection strategies through the review of Local Comprehensive Plans (LCPs), new construction within the fairly limited undeveloped areas of the Cape will occur prior to formal adoption of regulations to implement the LCPs. In addition, since many coastal systems are already overloaded by existing development within their watersheds, improved wastewater treatment will have to involve the retrofitting of existing septic systems or sewering. Since the CCC will be reviewing only a small percentage of redevelopment of parcels and hardly any single family residences upgrading septic systems, towns will have to provide the bulk of implementation of coastal water quality protection plans.

With the limitations of Title 5 to address coastal water quality and the longer time frame inherent in LCP implementation in mind, staff recommend that towns immediately begin consideration of BOH regulations requiring denitrifying septic systems for all new and replacement septic systems within the delineated watersheds, unless a flushing study and nitrogen loading assessment indicate that this is not necessary or it is anticipated that aggregated nitrogen removal treatment (large or small community sewering) can be provided within five years.

In addition, since many water quality problems are masked by the slow flow of groundwater and lack of observation until they are manifested in a significant way (e.g., a fish kill or algal bloom), project staff suggest that a coordinated citizens coastal water quality monitoring network be developed for Cape Cod. Significant efforts in Falmouth and along Buzzards Bay can be used as templates for this network and the existing expertise at the Commission, WBNERR, BBP, UMASS-Dartmouth, Cape Cod Nation Seashore, WHOI, BUMP/MBL, the Coalition for Buzzards Bay and others can be tapped to bring it to fruition. Data gathered by this network could be used to refine management strategies, help inform the public of the water quality problems, and help involve more of the public in the protection of coastal water quality.

REFERENCES

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Cape Cod Commission. 1996a. Cape Trends: Demographic and Economic Characteristics and Trends, Barnstable County - Cape Cod. 3rd Edition. Cape Cod Commission, Barnstable, MA.

Cape Cod Commission. 1998. draft Pleasant Bay Nitrogen Loading Study: Final Report. Cape Cod Commission, Barnstable, MA.

Costa, J.E. 1988. Distribution, production, and historical changes in abundance of eelgrass (Zostera marina) in southeastern Massachusetts. Ph.D. Thesis. Boston University.

Costa, J.E., B.L. Howes, A.E. Giblin, and I. Valiela. 1992. Monitoring Nitrogen and Indicators of Nitrogen Loading to Support Management Action in Buzzards Bay. in Ecological Indicators, Volume 2, Edited by D.H. MacKenzie, D.E. Hyatt, and V.J. McDonald. Elsevier Applied Science, NY.

Costello, C.T. and J.S. Stone. 1994. Southern Cape Cod Eelgrass Mapping Inventory - 1994 Report. Department of Environmental Protection, Boston, MA.

Eichner, E.M. and T.C. Cambareri. 1992. Technical Bulletin 91-001: Nitrogen Loading. Cape Cod Commission, Water Resources Office, Barnstable, MA.

Howes, B.L. and D.D. Goehringer. 1995. Falmouth Pond Watchers: Water Quality Monitoring of Falmouth's Coastal Ponds, Results form the 1994 Season. Woods Hole Oceanographic Institution, Woods Hole, MA.

National Research Council. 1993. Managing Wastewater in Coastal Urban Areas. National Academy Press, Washington, DC.

Nixon, S.W., C. Oviatt, J. Frithsen, and B. Sullivan. 1986. Nutrients and productivity of estuaries and coastal marine ecosystems. Journal of the Limnological Society of South Africa. 12: 43-71.

Rosenberg, R. 1985. Eutrophication - the Future Marine Coastal Nuisance. Marine Pollution Bulletin. 16: 227-231.

Ryther, J.H. and W.M. Dunstan. 1971. Nitrogen, Phosphorous and Eutrophication in the Coastal Marine Environment. Science. 171: 1008-1013.

Taylor, D., S. Nixon, S. Granger, and B. Buckley. 1995a. Nutrient limitation and the eutrophication of coastal lagoons. Marine Ecology Progress Series. 127: 235-244.

Taylor, D.I., S.W. Nixon, S.L. Granger, B.A. Buckley, J.P. McMahon, and H.-J. Lin. 1995b. Responses of coastal lagoon plant communities to different forms of nutrient enrichment - a mesocosm experiment. Aquatic Botany. 52: 19-34.

Valiela, I., K. Foreman, M. LaMontagne, J. Costa, P. Peckol, B. DeMeo-Anderson, C. D'Avanzo, M. Babione, C. Sham, J. Brawley, and K. Lajtha. 1992. Couplings of Watersheds and Coastal Waters: Sources and Consequences of Nutrient Enrichment in Waquoit Bay, Massachusetts. Estuaries. 15(4): 443-457.