| dc.description.abstract | Title outlet terrace (TOT) systems have been employed for the last century as a best management practice (BMP) to control surface runoff and associated erosion in agricultural fields. By altering the topography (artificial subsurface drainage and terraces), the hydrology of the landscape is also altered which affects the transformation, transport, and fate of applied fertilizer (nitrogen and phosphorus compounds) and their effect on other solute behavior. The study of storm events in agricultural fields is useful in identifying mechanisms of nutrient transport and transformation during runoff events under varying antecedent soil moisture conditions (pre-event) and varying growing conditions. Here we aim to track the hydrologic response of agroecosystems to storm events in TOTs to elucidate the relationship between hydrology and fertilizer use on chemical weathering fluxes by: 1) separating runoff into matrix, intermediate, and conduit flow using karst hydrology analytical methods; and, 2) pairing these results with measurements of water chemistry to identify mechanisms of nutrient transport and transformation. We focus on TOT’s with constructed wetlands in the Upper Wakarusa watershed to characterize the water flux of storm events in agricultural fields. Stormwater samples were collected directly from tiles coming off three of these TOT agricultural fields and the receiving wetlands constructed to reduce nutrient runoff. Soil water samples were also collected from nested suction-cup lysimeters that are installed at 30, 60, and 90 cm at the ridge top and depression couplet of one terrace at each field site to quantify spatial variability in nutrient concentrations. All water samples were analyzed for total and dissolved nitrogen and phosphorus, total suspended solids, alkalinity, anions and cations. Storm resolved samples (every 30 mins during flow events) from tile outlets (influent storm water) and wetland outlets (effluent wetland water) were collected using automated water samplers. The digital recursive filter approach was used to separate quickflow and baseflow, as exponential fitting and master recession curves approaches failed to partition hydrographs into their components as the discharge did not behave linearly in log-space. Here the proportion of baseflow increased with the amount of incoming precipitation the week prior to the event. Mixing models derived from measured solutes show that Harvest Hills Middle (HHM, the smallest site) was closest to the atmospheric signature while Cain and Harvest Hills North (HHN) had signatures closer to nested lysimeters. This study suggests that higher tile densities led to lower hydrologic flashiness but greater chemodyanmic behavior, specifically addition behavior, and greater weathering fluxes. This was a surprising result as more chemostatic behavior (i.e., invariant solute concentrations with large variations in discharge) was expected. These results demonstrate that there is likely an interactive effect between tile densities and terraces that may lead to non-linear behavior in solute generation and transport compared to just the effect of tiling alone. | |
