Using high-frequency in-situ stream nitrate concentration sensors to understand importance of extreme precipitation events in nitrogen loading

Abstract:

Nitrate loading is inherently complex, particularly under increasingly dynamic hydrology in the Midwestern Corn Belt (USA). High-resolution stream monitoring in agriculturally dominated landscapes provides near-continuous observation of real-time, in situ response of nitrate (NO₃^-) to storm events. In this study, we investigate seasonal trends in nitrate concentration (C) response for more than 500 storms across 17 sites in Iowa. Storm fluxes were characterized into two response types: “concentrating” and “diluting”. A “concentrating” pattern indicated positive storm NO₃^- flux when normalized by the pre-storm NO₃^- C, while a “diluting” pattern exhibited a normalized negative storm flux. The spatial extent and long-term high-temporal resolution of the data promoted broad scale characterization of events and allowed us to pose the questions: How does the nitrate concentration pattern in agricultural streamflow change with season and does characterization of the event-response indicate dominant hydrologic processes (i.e. transport or supply limitation)?and how does nitrate response vary with storm event intensity and antecent watershed conditions? Analysis of general event patterns revealed concentrating events occurring more often in the spring and fall, and diluting events dominating in the summer. Patterns observed under extreme precipitation events (e.g., 5% most intensive events) will be discussed.