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Contrasting Nitrogen Fate in Watersheds Using Agricultural and Water Quality Information
Author(s) -
Essaid Hedeff I.,
Baker Nancy T.,
McCarthy Kathleen A.
Publication year - 2016
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2016.02.0071
Subject(s) - tile drainage , environmental science , surface runoff , hydrology (agriculture) , water quality , watershed , soil water , drainage , streamflow , benthic zone , infiltration (hvac) , denitrification , surface water , ditch , drainage basin , nitrogen , environmental engineering , ecology , soil science , geology , geography , physics , geotechnical engineering , cartography , quantum mechanics , machine learning , computer science , meteorology , biology
Surplus nitrogen (N) estimates, principal component analysis (PCA), and end‐member mixing analysis (EMMA) were used in a multisite comparison contrasting the fate of N in diverse agricultural watersheds. We applied PCA‐EMMA in 10 watersheds located in Indiana, Iowa, Maryland, Nebraska, Mississippi, and Washington ranging in size from 5 to 1254 km 2 with four nested watersheds. Watershed Surplus N was determined by subtracting estimates of crop uptake and volatilization from estimates of N input from atmospheric deposition, plant fixation, fertilizer, and manure for the period from 1987 to 2004. Watershed average Surplus N ranged from 11 to 52 kg N ha −1 and from 9 to 32% of N input. Solute concentrations in streams, overland runoff, tile drainage, groundwater (GW), streambeds, and the unsaturated zone were used in the PCA‐EMMA procedure to identify independent components contributing to observed stream concentration variability and the end‐members contributing to streamflow and NO 3 load. End‐members included dilute runoff, agricultural runoff, benthic‐processing, tile drainage, and oxic and anoxic GW. Surplus N was larger in watersheds with more permeable soils (Washington, Nebraska, and Maryland) that allowed greater infiltration, and oxic GW was the primary source of NO 3 load. Subsurface transport of NO 3 in these watersheds resulted in some removal of Surplus N by denitrification. In less permeable watersheds (Iowa, Indiana, and Mississippi), NO 3 was rapidly transported to the stream by tile drainage and runoff with little removal. Evidence of streambed removal of NO 3 by benthic diatoms was observed in the larger watersheds. Core Ideas Stream NO 3 discharge trends reflect contributions from different NO 3 sources. Watersheds with more permeable soils had greater Surplus N. More permeable watersheds experienced greater N removal by denitrification. Less permeable watersheds transported surplus N directly to the stream. N removal by benthic processing was discerned in larger watersheds.