Prepared by the University of Connecticut and the Connecticut DEP, with the support of researchers and organizations throughout the Long Island Sound watershed.
Establishing restoration objectives for eelgrass in Long Island Sound

Mumford Cove -
Case Study

History

Eelgrass provides a nursery ground and refuge for many organisms, such as this well-hidden juvenile winter flounder (Pleuronectes americanus). (photo courtesy of P. Auster, University of Connecticut)

Increasing Nutrient Inputs

Mumford Cove provides an opportunity to examine the natural recovery of a seagrass community following the reduction of nitrogen loads to the local ecosystem. In 1945, a waste treatment facility designed to serve local Navy housing began discharging into Fort Hill Brook, which drains to Mumford Cove. By 1971, ~0.4 million gallons per day were discharged from the sewage treatment facility into Mumford Cove (Buck 1971). During the late 1960ís, the Town of Groton evaluated the growing need for increasing the available sewerage to town residents and construction of a new plant was started in 1970. By 1974, the sewage treatment plant had been expanded in size, output, and area serviced, with a temporary outflow to Mumford Cove. In 1976, the town storm drain system was expanded (Benoit 1975). These improvements resulted in a steady increase in the volume of the discharge to 3.5mgd (Curtis and Dunbar 1985) until diversion of the outflow to the Thames River in 1987.

Removing the Nutrient Point Source

As early as 1968, residents of the Mumford Cove area began working together to pressure the state and local agencies to amend the impairment of Mumford Cove created by the local discharge. The residents formed the Mumford Cove Association and brought litigation against the town of Groton in response to permit violations. The Connecticut Department of Environmental Protectionís predecessor, the Water Resources Commission, first ordered the Groton Sewer Authority to relocate the outfall to another site on November 18, 1971. The original order was modified and appealed a number of times (Curtis and Dunbar 1985; Greci and Banach 1986). The discharge into Mumford Cove was finally relocated to the Thames River in October 1987 (French et al. 1989a).

Results of the Nutrient Reduction

Higher nutrient concentrations were seen in the 1970's with a reduction in levels in the 1980's, possibly due to the extension of the storm drain system in the early 1980's (Buck & Feng 1983) or to more of the nutrients being tied up in the macroalgae biomass (Curtis & Dunbar 1985) (Fig. 1). While waste water outflow was entering Mumford Cove in 1987, water column concentrations of DIN and DIP were well over 1.4 mg/L during the summer months, with average DIN around 2.1 mg/L and average DIP of 2.6 mg/L (Buck and Feng 1983). By the summer of 1988, just a few months following the diversion of the wastewater outflow, the average water column nutrient concentrations was 0.015 mg/L DIN and 0.03 mg/L DIP (French et al. 1989).

Figure 1. Dissolved inorganic nitrogen concentration in the water column in the upper reach of Mumford Cove, where Fort Hill Brook discharges into Mumford Cove, and further from the influence of the wastewater outfall in the Middle Cove. The vertical line at October, 1987 represents the diversion of the wastewater outfall from Mumford Cove to the Thames River.

The change in nutrient load to Mumford Cove was mirrored by a change in the community of primary producers. While no data are available from Mumford Cove prior to the establishment of the waste treatment facility, Z. marina was likely present in the cove prior to 1945 and prior to the wide-scale die off in the early 1930s when eelgrass was abundant throughout Long Island Sound (Conard 1935; Rozsa 1994). By 1987, the cove contained a near monoculture of Ulva lactuca L., a green macroalgae, with no seagrass found throughout the cove (Curtis & Dunbar 1985). By 1988, less than one year after the diversion, the biomass of U. lactuca was reduced by 99% (French et al. 1989) and within ten years after diversion, Z. marina was once again the dominant primary producer in the cove.

The areal coverage of seagrass in the upper and middle coves increased from 0% in 1989 to 26% in 1999 and continued to increase to 50% areal coverage by 2002. In 1999, only 6% of the bottom area coverage was by single-species stands of Z. marina, while mixed beds of R. maritima and Z. marina and single-species stands of R. maritima occupied 7% and 13% of the bottom area respectively. By 2004, Z. marina was the dominant seagrass, with only trace amounts of R. maritima appearing in the grab surveys (Fig. 2)

Figure 2. Macrophyte biomass at the four stations established by A.S.A. in 1988 (French et al. 1989). These stations were visited by other researchers in 1992 (Short 2004), 1999, and 2002 to 2004 (Kremer et al. 2007). Station locations and legend are shown in the Zostera marina panel.

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Present Status

Data included in this analysis cover the period when R. maritima was initially present in the cove with a modest coverage of Z. marina (1999) extending through the regrowth of Z. marina (and decline of R. maritima) throughout most of the mid portion of the cove (2004). In a 2007 mid-summer visual and grab survey, Z. marina had continued to expand into previously uncolonized areas of the mid-cove but had not moved to the upper cove. Thus, the site serves as a reference for conditions suitable for eelgrass colonization and growth.

Primary Requirement - Light

The summertime average (5/15 to 9/15) light extinction coefficient hovered around the 0.7 m-1 value proposed by Yarish et al. (2006) for management criteria in LIS (figure 3). The 0.7 m-1 value predicts that eelgrass should be able to colonize deeper portions of the upper arm of Mumford Cove, up to 2.3m in depth, assuming a conservative requirement of 20% of surface irradiance by seagrass. Based on the bathymetry of Mumford Cove, only the "left fork" of the upper arm is deeper than 2.3m and thus uninhabitable by eelgrass based on the Kd.

However, it appears that the Kd in the upper arm was occasionally higher than in the lower portions of the cove, though overall it was not statistically significantly different (p-value = 0.152). These higher values may indicate that greater impairment in the upper reach was limiting the spread of eelgrass into what should theoretically be eelgrass habitat. With relatively few sampling dates during the summertime growing season, the reason behind the lack of eelgrass in the upper reach can not be substantiated.

Figure 3. Light extinction coefficient data from Mumford Cove. Data presented were from the Kremer et al. data set. The black line was the summertime average (May 15 to Sep 15). The dashed lines represent the recommended seagrass habitat requirements: 1.5 m-1 (Batiuk et al. 2000) and 0.7 m-1 (Yarish et al. 2006). Dry weight biomass of Zostera marina at three reference "eelgrass" stations (indicated by the green, red and black "X" with drop lines to the x-axis) were plotted to indicate annual success of the macrophyte for comparison to the annual variability of Kd.

Secondary Requirements - Chlorophyll, Nitrogen

The summertime chlorophyll a data hover around the 5.5 mg L-1 value proposed by Yarish et al. (2006) for management criteria in LIS, versus the Chesapeake Bay guideline of 15 mg L-1. Values from the upper arm were statistically different from the other two sections in the estuary (p-value 0.033) (see Case Study Report for figures).

The average summertime dissolved inorganic nitrogen was well below the 0.03 mg/L value recommended by Yarish et al. (2006) and the 0.15 mg/L recommended in the Chesapeake Bay guidelines (figure 4). However, some fall samples taken in 2003 did show slight elevations in DIN. Without a year round monitoring effort, annual DIN could not be estimated. The concentration of inorganic nitrogen in the water was rapidly depleted during the summertime due to uptake by the nitrogen limited primary producers. DIN in the two sections were not statistically significantly different (p-value 0.145).

Figure 4. Dissolved Inorganic Nitrogen (NH4+, NO3-, NO2-) data from Mumford Cove. DIN was determined for filtered water samples from near surface (0.25m) and near bottom (0.5m from bottom). Data presented were from the Kremer et al. data set. The black line was the summertime average (May 15 to Sep 15). The dashed lines represent the recommended seagrass habitat requirements: 0.15 mg/L (Batiuk et al. 2000) and 0.025 mg/L (Yarish et al. 2006). Dry weight biomass of Zostera marina at three reference "eelgrass" stations (indicated by the green, red and black "X" with drop lines to the x-axis) were plotted to indicate annual success of the macrophyte for comparison to the annual variability of Kd.

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Future Outlook

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Selected Web-Links and References

1989 Tidal Wetland Restoration Project

Benoit, R. J. 1975. The prospects for deterioration of water quality in Mumford Cove. Norwich, CT: EcoScience Laboratory, prepared for the Mumford Cove Association. p. 15.

Buck, J. D. 1971. Biological and chemical observations in Mumford and Palmer Coves (Groton, CONN.) September 1970 - September 1971. Noank, CT: University of Connecticut, prepared for Connecticut Department of Environmental Protection (Water Resources Commission).

Buck, J. D. & S. Y. Feng. 1983. Environmental studies: Fort Hill Brook and Mumford Cove, CT; July 1982 - July 1982. In. Noank, CT: prepared for Hayden, Harding, and Buchanan, Inc. Consulting Engineers.

Conard, H. S. 1935. The plant associations of central Long Island Sound. A study in descriptive plant sociology. American Midland Naturalist 16:433-516.

Curtis, M. D. & L. E. Dunbar. 1985. Water quality analysis of Mumford Cove final report: model development and waste load allocation. Storrs, CT: University of Connecticut, prepared for Connecticut Department of Environmental Protection, Water Compliance Unit. p. 55.

French, D., M. M. Harlin, E. Gundlach, S. Pratt, H. Rines, K. Jayko, C. Turner & S. Puckett. 1989. Mumford Cove Water Quality: 1988 Monitoring Study and Assessment of Historical Trends. Narragansett, RI: Applied Science Associates. p. 126.

Greci, D. J. & F. Banach. 1986. Groton wastewater treatment facility outfall: environmental impact evaluation. Hartford, CT: Connecticut Department of Environmental Protection, Water Compliance Unit.

Kremer, J. N., J. M. P. Vaudrey, and A. Branco. 2007. Habitat characterization of ten New England estuaries: a technical report. Groton, CT: Department of Marine Sciences, University of Connecticut. report.

Rozsa, R. 1994. Long term decline of Zostera marina in Long Island Sound and Fishers Island Sound. In: Office of Long Island Sound Programs, CT Department of Environmental Protection.

Short, F. T. 2004. personal communication.

Tiner, R., H. Bergquist, T. Halavik, and A. MacLachlan. 2003. Eelgrass survey for Eastern Long Island Sound, Connecticut and New York. U.S. Fish and Wildlife Service, National Wetlands Inventory Program, Northeast Region, Hadely MA. National Wetlands Inventory Report. report.

Tiner, R., H. Bergquist, T. Halavik, and A. MacLachlan. 2007. 2006 Eelgrass Survey for Eastern Long Island Sound, Connecticut and New York. U.S. Fish and Wildlife Service, National Wetlands Inventory Program, Northeast Region, Hadely MA. National Wetlands Inventory Report. report.

2006 maps from Tiner et al. (2007) - Lookup "Eastern Long Island Sound 2006 Inventory Maps"

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