RESPONSES OF FORESTED WETLAND VEGETATION TO PERTURBATIONS OF WATER CHEMISTRY AND HYDROLOGY

Nineteen mature Atlantic white-cedar swamps, located in four categorie s of undeveloped and suburban watersheds of the New Jersey Pinelands, were studied to determine the relationship between perturbations of wa ter quality and hydrology and changes in species composition and commu nity structure. Rank-orders of the 19 sites were compared for key vari ables (ground-water and surface-water NH4 and PO4, mean water-table le vel and water-table range). Rank orders for the sites were different f or the various parameters, suggesting little congruence among water qu ality and hydrologic changes at wetlands within urban basins. Changes in species composition, measured as the number of invading species, we re correlated with the number of perturbed chemical and hydrologic par ameters and were not related to the absolute magnitude of any one para meter. Sites in developed watersheds supported a larger fraction of fa cultative upland and upland species than did sites in undisturbed wate rsheds: this change could affect wetland delineation of urban wetlands . Urbanization thus increases variability in environmental quality amo ng sites of a given type of wetland and fosters an increase in proport ion of non-hydrophytic vegetation within such wetlands.