Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/27/2018
Publication Date: 3/6/2018
Citation: Williams, M.R., Livingston, S.J., Penn, C.J., Smith, D.R., King, K.W., Huang, C. 2018. Controls of event-based nutrient transport within nested headwater agricultural watersheds of the western Lake Erie basin. Journal of Hydrology. 559:749-761.
Interpretive Summary: Harmful algal blooms in Lake Erie have been linked with increasing inputs of soluble nutrients from agricultural non-point sources. Understanding how storm events influence the transport of nutrients is critical for targeting conservation practices in tile-drained watersheds. In this study, we explored the relationship between watershed discharge and nutrient concentrations during 47 storm events to determine which factors (e.g., storm magnitude, temperature, antecedent moisture, and baseflow) influenced nutrient delivery from agricultural fields to the stream channel. Study results indicated that the sources and flow pathways for nutrient delivery varied among water quality parameters (i.e., nitrogen vs. phosphorus). Complex nutrient transport pathways observed in this study highlight the challenge of managing nutrients in tile-drained watersheds. For example, conservation practices that address one nutrient or flow pathway may unintentionally increase the loss of other nutrients or in other flow pathways. In tile-drained watersheds, a combination of both nutrient management practices (e.g., 4R practices [right rate, right source, right place, right time for nutrient application]) and practices that decrease hydrologic connectivity (e.g., drainage water management, blind inlets) will be needed to decrease nutrient loads and improve water quality in Lake Erie.
Technical Abstract: Understanding the processes controlling nutrient delivery in headwater agricultural watersheds is essential for predicting and mitigating eutrophication and harmful algal blooms in receiving surface waters. The objective of this study was to elucidate nutrient transport pathways and examine key components driving nutrient delivery processes during storm events in four nested agricultural watersheds (298 to 19,341 ha) in the western Lake Erie basin with poorly drained soils and an extensive artificial drainage network typical of the Midwestern U.S. Concentration-discharge hysteresis patterns of nitrate-nitrogen (NO3-N), dissolved reactive phosphorus (DRP), and particulate phosphorus (PP) occurring during 47 storm events over a 6 year period were evaluated. An assessment of the factors producing nutrient hysteresis was completed following a factor analysis on a suite of measured environmental variables representing the fluvial and wider watershed conditions prior to, and during the monitored storm events. Results showed the artificial drainage network (i.e., surface tile inlets and subsurface tile drains) in these watersheds was the primary flow pathway for nutrient delivery to streams, but nutrient behavior and export during storm events was regulated by the flow paths to and the intensity of the drainage network, the availability of nutrients, and the relative contributions of upland and in-stream nutrient sources. Potential sources and flow pathways for transport varied among NO3-N, PP, and DRP with results underscoring the challenge of mitigating nutrient loss in these watersheds. Conservation practices addressing both nutrient management and hydrologic connectivity will likely be required to decrease nutrient loss in artificially drained landscapes.