title: Use of continuous monitoring to assess stream nitrate flux and transformation patterns.
abstract: Delivery of nitrogen from farmed fields to the stream network is an ongoing water quality issue in central North America and other parts of the world. Although fertilization and other farming practices have been refined to produce environmental improvements, stemming loss of nitrogen, especially in the soluble nitrate form, is a problem that has seemingly defied solution. The Iowa Nutrient Reduction Strategy is a policy initiative designed to implement conservation and other farm management practices to produce reductions in nitrate loading. The strategy does not focus on how the streams themselves may or may not be processing nitrogen and reducing downstream loading. We used continuous high-frequency nitrate and discharge monitoring over 3 years at two sites separated by 18 km in a low-order, agricultural stream in eastern Iowa to estimate how nitrogen is processed, and whether or not these processes are reducing downstream loading. We conclude that the upstream to downstream nitrate concentration decline between the two sites was not driven by denitrification. These data also show that nitrate concentrations are closely coupled to discharge during periods of adequate moisture, but decoupling of concentration from discharge occurs during dry periods. This decoupling is a possible indicator of in-stream nitrate processing. Finally, nitrate concentrations are likely diluted by water sourced from non-row crop land covers in the lower reaches of the watershed.
authors.affiliation: University of Iowa, Iowa City, IA, USA. christopher-s-jones@uiowa.edu.
authors.forename: Christopher
authors.initials: C
authors.lastname: Jones
authors.affiliation: University of Iowa, Iowa City, IA, USA.
authors.forename: Sea-Won
authors.initials: SW
authors.lastname: Kim
authors.affiliation: Iowa Geological Survey, Iowa City, IA, USA.
authors.forename: Keith
authors.initials: K
authors.lastname: Schilling
mesh_terms: D000383:Agriculture; D003247:Conservation of Natural Resources / Q000379:methods; D058440:Denitrification; D004784:Environmental Monitoring / Q000379:methods*; D007484:Iowa; D009566:Nitrates / Q000032:analysis* / Q000737:chemistry; D009584:Nitrogen / Q000032:analysis; D009589:Nitrogen Oxides; D045483:Rivers; D014867:Water; D014872:Water Movements; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000737:chemistry; D060753:Water Quality
chemical_list: D009566:Nitrates; D009589:Nitrogen Oxides; D014874:Water Pollutants, Chemical; D014867:Water; D009584:Nitrogen
keywords: Assimilation; Denitrification; Nitrate nitrogen