You are here:
TOWARDS DEVELOPING INDICATORS OF SALT MARSH CONDITION
Citation:
Wigand, C, R A. McKinney, AND M Charpentier. TOWARDS DEVELOPING INDICATORS OF SALT MARSH CONDITION. Presented at New England Estuarine Research Society, Block Island, RI, November 2, 2000.
Description:
Five ecosystem services: water quality maintenance, erosion and flood control, recreation and cultural use, wildlife habitat, and food production were identified from the literature as key services to characterize salt marshes of high integrity. We describe a systems approach to link metrics of structure and function with indicators of these services. For example, plant zonation is linked to erosion control and wildlife habitat. Ten salt marshes in Narragansett Bay, RI, with similar geological bedrock and sea exchange, were identified to examine plant zonation. Sub-watersheds adjacent to the salt marshes were characterized by land use practices and stream nutrient concentrations. We use a space-for-time approach: gradients of low to high % residential land use and low to high nitrate concentrations in the headwater streams were measured for the salt marshes. In the Fall, there was a significant correlation (p < 0.05; r = +0.84) between total dissolved nitrogen and % residential land use among the ten sites. The stable nitrogen isotopic signatures of ribbed mussel Geukensia demissa and smooth cordgrass Spartina alterniflora reflected the nitrogen sources from the adjacent watersheds and were significantly correlated with % residential land use. Because human wastewater is known to enrich stable nitrogen isotope ratios in organisms, our results suggest that with increasing residential development, the salt marshes are receiving increasing nitrogen loads associated with human activities. Results from plant zonation transects in the salt marshes showed a significant correlation between the extent of salt meadow hay Spartina patens and the total number of plant zones (p < 0.05; r = +0.69). Furthermore, the transects revealed an inverse relationship between the extent of S. patens and % residential (p < 0.05; r = -0.66). Since the root structure of S. patens is known to promote peat accumulation, we propose that salt marshes are more susceptible to erosional processes when enriched with nitrogen. Finally, we describe how the number of plant zones and areal extent ofS. patens may be good indicators of some salt marsh services. However, additional metrics of structure and function are needed to make a strong link with salt marsh condition.