. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. ECOLOGY: BIOGEOCHEMISTRY AND NUTRIENT CYCLING 255 GPP and chlorophyll a. Because tidal ranges reach, at most, m in Waquoit Bay. and coverage of vegetation occurs only during a few days of spring tides each month, this mechanism does not seem convincing. More likely, denitritication and storage of wa- tershed-derived nitrogen in salt marshes could he responsible for a sufficient reduction of nitrogen supplies to lower phyto- plunkton production. Similar results were obtained when we compared GPP or chlorophyll a in relati
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. ECOLOGY: BIOGEOCHEMISTRY AND NUTRIENT CYCLING 255 GPP and chlorophyll a. Because tidal ranges reach, at most, m in Waquoit Bay. and coverage of vegetation occurs only during a few days of spring tides each month, this mechanism does not seem convincing. More likely, denitritication and storage of wa- tershed-derived nitrogen in salt marshes could he responsible for a sufficient reduction of nitrogen supplies to lower phyto- plunkton production. Similar results were obtained when we compared GPP or chlorophyll a in relation to the percent of the periphery of each estuary that is composed of salt marsh fringes (Fig. 1. bottom panels). We therefore conclude that the increase in producer activity due to nitrogen loading from watersheds may be mediated by the extent of salt marsh interposed between land and estuary. Further, salt marshes can decrease the nutrient supply to the estuaries and limit phytoplankton production and chlorophyll a levels. This work was supported by the WBMLER Research Expe- rience for LIndergraduates Grant and by a grant from NOAA Coastal Ocean Studies Program. Literature Cited 1. Nixon, S. 1988. Oceunot;. 33: 1005-1025. 2. Howarth, R. VV. 1992. .-Inn Rev Ecol 19: 89-110. 3. Valiela, I., et al. 1992. E\tmiries 15: 443-457. 4. Lorenzen, C. J. 1979. Oceanog. 24: 1117-1120. Reference: Bio/. Bull 189: 255-256. (October/November, 1995) Macrophyte Abundances in Waquoit Bay Estuaries Subject to Different Nutrient Loads and the Potential Role of Fringing Salt Marsh in Groundwater Nitrogen Interception Julie Lyons. Jenny Ahern, James McClelland, and Ivan ralie/a (Boston University Marine Program, Marine Biological Laboratory) Increased nutrient loading has shifted seagrass-dominated habitats to macroalgae-dominated habitats in many coastal re- gions (1). In Waquoit Bay, Massachusetts, eelgrass (/.usicni ma- rina) has diminished markedly in abundance over th
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