Agricultural Water Management 103 (2012) 162–166 Contents lists available at SciVerse ScienceDirect Agricultural Water Management jo u rn al hom epag e: www.elsevier.com/locate/agwat Decreasing nitrate-N loads to coastal ecosystems with innovative drainage management strategies in agricultural landscapes: An experimental approach R. Kröger a,∗ , S.C. Pierce a , K.A. Littlejohn a , M.T. Moore b , J.L. Farris c a Department of Wildlife, Fisheries and Aquaculture, Mississippi State University, Box 9690, MS 39762, United States b USDA-Agricultural Research Service, National Sedimentation Laboratory, Water Quality and Ecology Research Unit, PO Box 1157, Oxford, MS 38655 USA c Arkansas Biosciences Institute, Arkansas State University, PO Box 639, State University Jonesboro, AR 72467, United States a r t i c l e i n f o Article history: Received 14 July 2011 Accepted 19 November 2011 Available online 12 December 2011 Keywords: Drainage ditch Nutrients Nitrate Reduction Low-grade weirs a b s t r a c t Innovative controlled drainage strategies in agricultural ditches such as spatially orientated low-grade weirs show promise to significantly improve nutrient (e.g., nitrate, NO 3 - -N) reductions by expanding the area available for biogeochemical transformations, as well as providing multiple sites for runoff reten- tion. The overall objective of this study was to identify the contributions made by low-grade weirs to source NO 3 - -N concentrations and loads to downstream coastal ecosystems. This objective was achieved by assessing, from an experimental standpoint, the effectiveness of weirs in reducing NO 3 - -N concen- trations and loads in replicated ditch systems in Jonesboro AR. Overall NO 3 - -N load reduction rates were approximately 2250 ± 718 and 1935 ± 452 mg/h for ditches with and without weirs, respectively, resulting in mean percent NO 3 - -N load reductions of 79 ± 7.5 and 73 ± 9% for ditches with and with- out weirs, respectively. Although NO 3 - -N concentration reductions were substantial in both systems, overall, for the duration of the experiment no significant treatment effect was detected. A stepwise lin- ear regression and repeated measures ANOVA analyzed the relationship of time × treatment on nitrate concentration and load in ditch effluents. The regression model explained 31.1% of the variance in NO 3 - - N concentration, which indicated a highly significant relationship between NO 3 - -N concentration and time × treatment (F = 31.9, p < 0.001). NO 3 - -N reductions were significantly higher in weir treatments based on time (t = 120 min; F = 3.25; p = 0.042) as compared to systems without weirs. Low-grade weirs show promise in improving nutrient reductions in agricultural drainage ditches, by increasing residence time and reducing on a time step basis, outflow concentrations and loads to downstream systems. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Global population growth will necessitate agricultural expan- sion within the next 50 years, so much so that food and fiber demands will play a significant role in global environmental change (Tilman et al., 2002). Agricultural production is ubiquitous in its use of inorganic fertilizers to increase yields, which results often in high loads of nutrients delivered from agricultural soils to adjacent receiving waters (Donner, 2003). Environmental issues surround- ing nutrient contamination, specifically nitrate-N (NO 3 - -N) are primarily linked to its impact on surface water eutrophication. However, causes of coastal ecosystem degradation and eutrophi- cation are rooted in nutrient loads derived from non-point sources (e.g., agricultural) high in the associated catchments and water- sheds. The relevance of this issue is no more prevalent than in coastal areas of Mississippi and Alabama in the Gulf of Mexico. ∗ Corresponding author. Tel.: +1 66 2 325 4731; fax: +1 66 2 325 8976. E-mail address: rkroger@cfr.msstate.edu (R. Kröger). Nitrogen is probably the most complex element to character- ize in aquatic biogeochemical processes (Keeney, 1973). Nitrogen as a non-point source pollutant from crop fields, typically applied as urea, occurs predominantly in the inorganic form (NH 4 + ). The dominant aqueous N species of NH 4 + , NO 3 - -N, nitrite (NO 2 •- ), and dissolved organic N, undergo simultaneous complex inter- actions and transformations of mineralization, immobilization, nitrification, denitrification, and assimilation at variable spatial and temporal scales (Braskerud, 2002; Klopatek, 1978; Ryden et al., 1984). Net N concentrations in aquatic systems are a combination of these processes as well as the rate of decomposition and the rate of sedimentation (Keeney, 1973). Biogeochemical properties of N can be manipulated through management. By managing primary aquatic systems associated with agricultural N sources, scientists and managers can greatly increase reduction effectiveness. Studies have shown managed drainage ditch systems in agricultural landscapes will result in decreased loads of nitrogen (Cooper et al., 2002, 2004; Kröger et al., 2007) entering adjacent aquatic systems. Agricultural drainage ditches are integral components and ubiquitous features of the agricultural landscape and act as major conduits of surface and 0378-3774/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2011.11.009