Nitrogen pollution is emerging as a major threat to coastal watersheds, estuaries and embayments, and the communities within their watersheds. Excess N in aquatic systems can contaminate potable drinking water supplies. Nitrogen loading from watersheds can spur harmful algal blooms, hypoxia, decline of eelgrass, and destruction of critical spawning habitats in coastal waters. Coastal communities in New England and along the entire East Coast of the Atlantic [e.g., Long Island Sound, CT; Cape Cod, AM; Pawcatuck River, RI; Christina Reservoir, ME; Neuse River estuary, NC] have been forced to address N pollution as a result of state and federal water quality programs such as TMDLs (Total Maximum Daily Loads) that can mandate community investments in N controls.
The sources, sinks, and conveyance of N are highly landscape and hydrology dependent. N export from urban and suburban watersheds is much higher than from forested watersheds, although lower than from agricultural watersheds. High concentrations of nitrate in shallow groundwater and streams are correlated with agricultural land use and unsewered residential developments. Sink areas include wetlands, hydric soils, reservoirs, small-order streams and impoundments. In particular, riparian wetlands can be a significant sink for N due to the combination of surface filtering of sediments, plant and microbial uptake, and subsurface denitrification. Studies in both urbanizing and agricultural watersheds have demonstrated that riparian restoration can reduce the delivery of nitrogen to streams
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