Land use controls on the delivery, processing, and removal of nitrogen from small watersheds: Insights from the dual isotopic composition of stream nitrate

Urban Farm DB summary

This study examined nitrate export from small, closely spaced headwater watersheds in the United States representing urban, agricultural, and forested land uses, using the dual isotopic composition of stream nitrate (δ15N-NO3− and δ18O-NO3−) together with a numerical model to control for variation in geology, surficial materials, and climate. The isotopic values varied significantly among the three land-use types, with δ15N-NO3− reflecting nitrogen source and δ18O-NO3− reflecting biogeochemical processing; the highest nitrate concentrations coincided with the highest stream δ15N-NO3− values because of enriched anthropogenic sources — septic systems in urban watersheds and manure in agricultural watersheds — and average net removal of the available nitrate pool across urban and agricultural catchments was estimated at 45%, with the degree of removal varying by drainage area and organic carbon availability.