Tracking the hydrologic response of agricultural tile outlet terraces to storm events

Abstract

Agricultural practices in intensively managed landscapes are thought to be shifting hydro-bio-geochemical behavior from transformation to transport dominated systems. Here we explore the impacts of a best management practice known as tile-outlet-terraces (TOT). Tiles at this site are a set of perforated vertical pipes that can receive direct surface water, soil water and groundwater inputs that are connected to horizontal pipes that transport water to a receiving pond. Terraces are constructed, horizontal areas created to divide sloping terrains to reduce slope steepness and erosion, and in so doing they redirect surface water toward standpipes and promote soil and groundwater discharge as a result bisecting local flowpaths. While the impact of tiles on hydrologic behavior has been well studied, the combined impact of TOTs has not been well quantified. To address this knowledge gap, we focus on the response of TOT discharge and biogeochemical behavior across three adjacent agroecosystems in Kansas over three growing seasons (2016–2018). TOT discharge was measured every minute at each location and discharge during storm events was collected and analyzed for dissolved and total nutrients as well as major anion and cation chemistry. Additionally, suction cup lysimeters were installed at the ridges and depression of the terraces to capture soil water solute chemistry prior to storm events. Recession curve analysis revealed that tile inlet density was not directly related to the proportion of quickflow, mixing models showed that antecedent conditions played a critical role in the degree of connectivity of event water to the tiles, and concentration discharge behavior showed the dominant behavior for all constituents was chemostatic across all tile densities. Interestingly, these findings suggest that while TOTs shift the hydrology of agroecosystems away from natural conditions, the storm event size and antecedent conditions can still dominate the hydrologic and biogeochemical response to storm events.