Baltimore Ecosystem Study Institute of Ecosystem Studies

2010 BES Annual Meeting Presentation and Poster Abstracts

Tracking nonpoint nitrogen pollution from human-dominated watersheds
Kaushal, Sujay
Co-Authors: Sujay S. Kaushal, Peter M. Groffman, Lawrence E. Band, Emily M. Elliott, Catherine A. Shields, and Carol Kendall

Abstract: Nonpoint source nitrogen (N) pollution is a leading contributor of water quality impairments including coastal eutrophication and hypoxia in the U.S. Improved identification of nonpoint N sources will be critical in prioritizing strategies for watershed N reductions. We combined long-term monitoring, watershed mass balances, and stable isotope source methods to investigate effects of land use and climate variability on transport/transformation of nonpoint source N in forest, agricultural, and urbanized watersheds at the Baltimore Long-term Ecological Research site in the Chesapeake Bay region. Mass balances from 1999-2005 suggested that (35-99%) of nonpoint N entering watersheds was retained, and watershed N retention showed a significant inverse relationship with annual runoff. Nonpoint sources showed differential susceptibility to climate variability with an agricultural watershed showing significantly higher N export per unit runoff than urban and forest watersheds. Isotope data indicated denitrification in watersheds was removing septic system and agriculturally-derived N, but N from leaking sewers was less susceptible to denitrification. Nitrate in urbanized watersheds was a mixture of sewage and atmospheric sources that varied across storm runoff and streamflow, and denitrification in an agricultural watershed showed a significant decrease with runoff. Our results suggest that efforts to reduce nonpoint N sources should enhance watershed denitrification sinks across climate variability, and repair of aging urban infrastructure and leaking sewer lines should be a priority. Targeting nonpoint N sources based on proximity and hydrologic flowpaths to streams and groundwater may play a disproportionately large role in regulating N exports in human-dominated watersheds.