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Estimation of nitrogen inputs to catchments: comparison of methods and consequences for riverine export prediction

“…In addition to the NANI approach at the catchment scale, some N mass balance estimates have restricted the system boundary to the soils compartment (Burkart and James 1999). Most such studies find a high correlation between net N inputs to catchments and riverine N exports across a wide range of spatial settings, and a substantial excess of anthropogenic N inputs relative to riverine export (Van Breemen et al 2002). However, such studies also agree that estimates of net N input terms contain considerable uncertainty and potential bias, because estimates of N sources, losses, and the net N input balance can vary widely depending on the definition of the system boundary, the assumptions and approximations used to estimate N flows, and on the quantity and quality of available data over space and time David and Gentry 2000;Howarth et al 1996;Meisinger and Randall 1991).…”

Dual isotope analyses indicate efficient processing of atmospheric nitrate by forested watersheds in the northeastern U.S.

“…Aber et al 1998), increased nitrate (NO 3 -) export (Stoddard 1994), and the degradation of coastal waters (NRC 2000). These problems occur despite the suggestion that the vast majority of nitrogen added to our landscape is not exported to the coastal ocean Schaefer and Alber 2007;Van Breemen et al 2002). Atmospheric N deposition is one source of anthropogenic nitrogen loading affecting the northeastern U.S., with nitrate (NO 3 -) comprising the majority of inorganic nitrogen (66%) delivered via precipitation in Connecticut (Luo et al 2003).…”

Application of watershed deposition tool to estimate from CMAQ simulations the atmospheric deposition of nitrogen to Tampa Bay and its watershed

“…Calculation of indirect N loading is challenging, and several approaches for determining N export from watersheds have been used, including (1) a watershed-level mass balance (Castro et al, 2004;Groffman et al, 2004;Van Breemen et al, 2002), (2) land use-specific N export modeling (Poe et al, 2005;Whitall et al, 2003), (3) process-based modeling (Pan et al, 2004), and (4) a conserved tracer study (Pollman and Poor, 2003). For this analysis, we used the export coefficient of 18% determined by Pollman and Poor (2003).…”

“…For 2002-2006, Poe et al (2005 and JEI (2008) estimated total N loading to Tampa Bay from direct atmospheric deposition, nonpoint sources, domestic and industrial point sources, springs, groundwater, and material losses. They calculated direct atmospheric deposition from monthly bay segment-specific rainfall rates, rainfall N concentrations, and seasonal dry:wet deposition ratios.…”