Publikationsdatum:
2013-06-12
Beschreibung:
Coastal wetlands have the capacity to retain and denitrify large quantities of reactive nitrogen (N), making them important in attenuating increased anthropogenic N flux to coastal ecosystems. The ability of coastal wetlands to retain and transform N is being reduced by wetland losses resulting from land development. Nitrogen retention in coastal wetlands is further threatened by the increasing frequency and spatial extent of saltwater-inundation in historically freshwater ecosystems, due to the combined effects of dredging, declining river discharge to coastal areas due to human water use, increased drought frequency, and accelerating sea-level rise. Because saltwater incursion may affect N cycling through multiple mechanisms, the impacts of salinization on coastal freshwater wetland N retention and transformation are not well understood. Here, we show that repeated annual saltwater incursion during late summer droughts in the coastal plain of North Carolina changed N export from organic to inorganic forms and led to a doubling of annual NH 4 + export from a 440 hectare former agricultural field undergoing wetland restoration. Soil solution NH 4 + concentrations in two mature wetlands also increased with salinization, but the magnitude of increase was smaller than in the former agricultural field. Long-term saltwater exposure experiments with intact soil columns demonstrated that much of the increase in reactive N released could be explained by exchange of salt cations with sediment NH 4 + . Using these findings together with the predicted flooding of 1661 km 2 of wetlands along the NC coast by 2100, we estimate that saltwater incursion into these coastal areas could release up to 18,077 Mg N, or approximately half the annual NH 4 + flux of the Mississippi River. Our results suggest that that saltwater incursion into coastal freshwater wetlands globally could lead to increased N loading to sensitive coastal waters. This article is protected by copyright. All rights reserved.
Print ISSN:
1354-1013
Digitale ISSN:
1365-2486
Thema:
Biologie
,
Energietechnik
,
Geographie
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