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Interaction between land use and climate variability amplifies stream nitrate export
Citation:
Kaushal, S., P. M. Groffman, L. E. Band, C. A. Shields, R. P. Morgan, K. T. Belt, AND P. M. MAYER. Interaction between land use and climate variability amplifies stream nitrate export. Presented at The North American Benthological Society, Salt Lake City, UT, May 25 - 30, 2008.
Impact/Purpose:
To present information at the North American Benthological Society
Description:
We investigated regional effects of urban land use change on nitrate concentrations in approximately 1,000 small streams in Maryland, U.S.A. during record drought and wet years in 2001-2003. We also investigated changes in nitrate-N export during the same time period in 8 intensively monitored streams across an urbanization gradient in Baltimore, Maryland. During the period of record drought and wet years, nitrate-N exports in Baltimore varied by up to an order of magnitude in 6 suburban/urban streams, 1 agricultural stream, and 1 forest stream. Variability in nitrate-N loads was similar for small Baltimore streams and nearby larger rivers and coincided with record hypoxia in Chesapeake Bay. Nitrate-N retention during the 2002 drought was 85%, 99%, and 94% for suburban, forest, and agricultural watersheds respectively and declined to 23%, 76%, and 43% during wet years. There was a hysteresis in discharge-weighted mean annual nitrate-N concentrations potentially due to “drying and re-wetting” of streams, contributing to unexpected peaks in nitrate-N export following peak runoff. Our results suggest that urban land use change increases the vulnerability of ecosystem nitrogen retention functions to climatic variability. We discuss strategies for restoring river network structure to improve ecosystem N-retention function under a varying climate.