Climate Variation Overwhelms Efforts to Reduce Nitrogen Delivery to Coastal Waters

We calculated watershed nitrogen (N) retention (inputs–outputs)/inputs) each year from 1999–2013 for nine sub-watersheds along an urban–rural gradient near Baltimore MD to determine how land use and climate influence watershed N flux. Retention is critical to efforts to control coastal eutrophicatio...

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Bibliographic Details
Published in:Ecosystems (New York) 2015-12, Vol.18 (8), p.1319-1331
Main Authors: Bettez, Neil D, Duncan, Jonathan M, Groffman, Peter M, Band, Lawrence E, O’Neil-Dunne, Jarlath, Kaushal, Sujay S, Belt, Kenneth T, Law, Neely
Format: Article
Language:English
Subjects:
Biomedical and Life Sciences
Climate
Climate change
Climate variability
coastal water
Coastal waters
Coastal zone
Ecology
Environmental Management
Eutrophication
Geoecology/Natural Processes
Growing season
Harbors
Hydrology/Water Resources
Land use
Life Sciences
Nitrogen
nitrogen content
Plant Sciences
Receiving waters
Retention
subwatersheds
surface water
Total maximum daily load
Urban areas
Urbanization
Water quality
Watersheds
winter
Zoology
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Summary:We calculated watershed nitrogen (N) retention (inputs–outputs)/inputs) each year from 1999–2013 for nine sub-watersheds along an urban–rural gradient near Baltimore MD to determine how land use and climate influence watershed N flux. Retention is critical to efforts to control coastal eutrophication through regulatory efforts that mandate reductions in the total maximum daily load (TMDL) of N that specific water bodies can receive. Retention decreased with urbanization as well as with increases in precipitation with retention decreasing from an average of 91% in the forested sub-watershed to 16% in the most urban sub-watershed. Export was 23% higher, and retention was 7% lower in winter (November–April) than during the growing season. Total N delivery to Baltimore Harbor varied almost threefold between wet and dry years, which is significant relative to the total annual export allowed for all non-point sources to the harbor under the TMDL. These results suggest that expectations for TMDLs should consider watershed land use and climate variability, and their potential for change if they are to result in improvements in receiving water quality.
ISSN:1432-9840
1435-0629
DOI:10.1007/s10021-015-9902-9