PARENT SESSION
Oral Session #68: Nutrient Cycling. Presiding: D. Johnson.
Thursday, August 9, 2001. 1:00 PM to 5:00 PM. Hall of Ideas G.
Nutrient dynamics in two tidal freshwater marshes in Virginia.
Morse, Jennifer1, Megonigal, J.1,2, Walbridge, Mark1, 1 2
ABSTRACT- The Mattaponi River in Virginia is one of the most pristine tributaries of the Chesapeake Bay, providing habitat for rare plants, bald eagles, and migratory birds. The river is under consideration for a hydrologic withdrawal project to create a reservoir for the city of Newport News. Alteration of the river's hydrological regime could affect adjacent tidal freshwater marshes (TFM) by changing rates of sediment and nutrient deposition. Because land-use changes in the watershed might further alter the river by increasing nutrient inputs, understanding ecosystem nutrient limitation would assist in predicting the effects of nutrient enrichment. We examined nitrogen (N) and phosphorus (P) in surface sediments, soils, and vegetation in two TFM on the Mattaponi River, to quantify nutrient inputs associated with sediment deposition. We also compared N:P ratios in sediments, soils, and vegetation, and examined plant response to N and P additions through an in situ fertilization experiment, to determine whether N or P limits production. Sedimentation was higher (410.2 ± 62.7 g/m2/month versus 108.5 ± 11.9 g/m2/month) and N:P ratios were lower in sediments (9.9 versus 14.5) and soils (11.0 versus 22.8) at Gleason Marsh, the downstream site. Vegetation N:P ratios were similar, with 7.8 at Gleason and 8.6 at Walkerton. Our results are relevant to management decisions for the Chesapeake Bay watershed and provide a baseline of ecological data for assessing the impacts of development in the watershed.
KEY WORDS: nitrogen, phosphorus, sediment, wetland