Nitrogen Loading in the Neuse River Basin, North Carolina: The Rivernet Monitoring Program

Abstract

Coastal eutrophication is a major concern in many estuarine systems around the world. Nitrogen has been demonstrated to be the limiting nutrient in many coastal systems. In recent years, the Neuse River Basin in North Carolina has experienced large fish kills, which has heightened the need for better monitoring of riverine nitrogen loading. The RiverNet Monitoring Program was initiated to provide high-resolution (hourly) measurement of nitrate (NO3-) using in-stream nutrient analyzers. Three sites on the Neuse River mainstem and two on Contentnea Creek were monitored continuously from January 2001 through December 2002. Bear Creek, an agricultural watershed, was continuously monitored from May 2002 to May 2003. Water samples were taken for analysis of nitrogen speciation: dissolved inorganic nitrogen (DIN), dissolved organic nitrogen (DON)) and total dissolved nitrogen (TDN). Large NO3- variability was discovered at sites downstream of wastewater input and urban runoff, while the variability diminished farther downstream. The NO3- load in the Neuse River mainstem at Fort Barnwell was 11 + 1.0 x 105 kg N yr-1, with 26% (2.9 + 0.5 x 105 kg N yr-1) of that total coming from Contentnea Creek during the 2001-02 study period.

Nitrate yields in the Neuse River mainstem and Contentnea Creek Basin varied from 99 to 130 kg N km-2, while Bear Creek exceeded 810 kg N km-2. δ15N and δ 18O isotopes of NO3- provide a way to characterize monitoring sites as urban, agricultural, or mixed source N-dominated.