|ELLIOTT, HERSCHEL - Pennsylvania State University|
Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/10/2015
Publication Date: 4/10/2015
Citation: Williams, M.R., Buda, A.R., Elliott, H.A., Collick, A.S., Dell, C.J., Kleinman, P.J. 2015. Linking nitrogen management, seep chemistry, and stream water quality in two agricultural headwater watersheds. Journal of Environmental Quality. 44(3):910-920.
Interpretive Summary: Identifying factors that affect nitrogen losses from groundwater seeps to streams is vital to developing sound management strategies for water quality protection. We studied two small agricultural watersheds in central Pennsylvania to determine the effects of land-applied nitrogen sources and in-seep nitrogen cycling on nitrate concentrations in seeps and streams. While seeps had some capacity to retain or remove nitrate, applied nitrogen sources exerted the greatest control on nitrate concentrations that were delivered from seeps to streams. Findings from this study highlight the need for land management practices that reduce nitrate leaching losses to shallow groundwater systems that feed riparian seeps.
Technical Abstract: Riparian seepage zones in headwater agricultural watersheds represent important sources of nitrate-nitrogen (NO3-N) to surface waters, often connecting N-rich groundwater systems to streams. In this study, we examined how NO3-N concentrations in seep and stream water were affected by NO3-N processing along seep surface flow paths, as well as by upslope applications of N from fertilizers and manures. The research was conducted in two headwater agricultural watersheds, FD36 (40 ha) and RS (45 ha), which are fed, in part, by a shallow fractured aquifer system possessing high (3 to 11 mg L**1) NO3-N concentrations. Data from in-seep monitoring showed that NO3-N concentrations generally decreased downseep (top to bottom), indicating that most seeps retained or removed a fraction of delivered NO3-N (16% in FD36 and 1% in RS). Despite this finding, N applications in upslope fields (as determined by annual farmer survey data) were highly correlated with NO3-N concentrations in seeps in both watersheds (slope = 0.06; R2 = 0.79; p<0.001). Strong positive relationships also existed between seep and stream NO3-N concentrations in FD36 (slope = 1.01; R2 = 0.79; p<0.001) and in RS (slope = 0.64; R2 = 0.80; p<0.001), further indicating that N applications control NO3-N concentrations at the watershed scale. Findings clearly point to NO3-N leaching from upslope agricultural fields as the primary driver of NO3-N losses from seeps to streams in these watersheds, and therefore suggest that appropriate management strategies (cover crops, limiting fall/winter nutrient applications, decision support tools) be targeted in these zones.