Wetlands in Coastal Settings: Water Contaminant Treatment and Restoration as a Function of Elevation and Hydroperiod

An important function of coastal wetlands is as a buffer between upland runoff and the marine environment. Coastal wetlands worldwide, such as salt marshes, are being degraded by changes in source water, tidal restrictions and human development. Long-term restoration and survivability of these wetlands will require migration of their landscape position inland with global climate change and resulting sea-level rise. Recent conservation measures for wetlands in urban areas, such as New York City, recognize the ecohydrologic role wetlands play in improving coastal water quality. Meaningful characterization of both the wetlands water quality improvement function and their projected landscape position is needed to focus restoration efforts in these environments.

Assessing the performance of flow-through treatment wetlands, long used for municipal wastewater remediation, is relatively straightforward, and widespread data exist on inflow-outflow water quality for different hydraulic loadings. However, in coastal settings, where hydraulic loading and hydroperiod depend on tidal fluctuations and reversing flow directions, such evaluation is more complex. We present a simplified wetland conceptual model and results showing that contaminants such as fecal coliforms are expected to be reduced by 27% to 94% depending on characteristic wetland hydrographs and surface elevations.

In New York City, relative sea level rise due to global climate change is exacerbated by local subsidence. Increasing inundation of low-lying areas will change the salinity conditions and habitat ranges for wetland vegetation species targeted for restoration. Such conditions can be predicted using a recently developed numerical model, SLAMM5 (Clough and Park 2007), that accounts for subsidence, IPCC projections of sea-level rise and saltwater intrusion. Preliminary modeling projections will be presented for two urbanized watersheds with existing wetlands: Flushing Meadows-Corona Park and Alley Pond Park. Scientifically-based wetlands restoration planning involving such projections represents the most promising way of ensuring the preservation of coastal wetlands ecohydrologic functions.