RII Track-4: Elucidating Controls of Sediment Phosphorus Delivery to Tile-Drains

Harmful Algal Blooms in midwestern waterbodies have persisted in recent years due to high rates of nutrient losses from tile-drained agroecosystems. Recently, studies have highlighted the importance of dissolved reactive phosphorus (DRP) that is regenerated from streambed sediments as a major source of watershed-scale DRP loading. Subsequently, there is now renewed interest in quantifying and managing sediment-bound particulate P (PP) delivered through tile-drains. Preliminary results by the PI’s research team suggest PP fluxes in tile drainage vary seasonally and reflect a mixture of surface and subsurface P sources. However, two major gaps in knowledge hinder our ability to manage PP delivery through tile-drains. First, mechanisms controlling sediment erosion and transport dynamics in macropores are not well understood, particularly the impact of biological crust development on macropore walls and how it influences flow pathway dynamics and sediment erodibility. Second, field-scale controls on PP delivery to tile drains have been hypothesized, but not quantified, which stems from a lack of field datasets and limited representation of subsurface PP delivery through tile drains in agricultural water management models. This EPSCoR Research Fellows program will provide an opportunity for the PI to propel research in this new field of study through collaboration with Dr. Mark Williams, and Dr. Dennis Flanagan of the USDA-ARS National Soil Erosion Research Laboratory (NSERL). Dr. Williams has established a laboratory methodology for studying preferential flow in undisturbed soil lysimeters. The PI will collaborate with Dr. Williams to study the impact of macropore biological crust development on sediment erosion and flow pathway dynamics using rainfall experiments on undisturbed soil lysimeters with a growth and control condition. We will test the hypothesis that biological crusts decrease matrix-macropore interaction and increase shear resistance of soils. Dr. Dennis Flanagan is a world-renowned expert in soil erosion modeling and has developed the Watershed Erosion Prediction Project (WEPP) model. The PI will collaborate with Dr. Flanagan to modify the WEPP model to include subsurface flow pathway and sediment P erosion and transport routines for tile drainage. The model will be evaluated at both field and watershed scales using long-term datasets managed by NSERL in order to identify the importance of subsurface erosion and flow pathway dynamics to sediment P budgets. Sustainability of the infrastructure developed in the project will be met through collaborative proposal submissions with researchers at the USDA and Purdue University, as well as an NSF CAREER award submission in July 2022. Intellectual Merit: The proposed research activities will improve mechanistic understanding of subsurface erosion processes, advance numerical modeling infrastructure at field-watershed scales for subsurface drained agroecosystems and will quantify the prominent mechanisms causing sediment P transport to tile drains. The infrastructure and research techniques built through the EPSCoR fellows program will provide transferrable technology that will enhance institutional and jurisdictional research capacities by 1) building expertise in laboratory-scale rainfall simulation on undisturbed soil lysimeters, which does not currently exist in the PI’s home institution, 2) improving infrastructure to evaluate how tile-drain intensification currently occurring across the jurisdiction will impact water quality, and 3) transferring tools to fluvial karst landscapes which comprise more than 55% of the drainage area in the state of Kentucky, and often have flow and contaminant transport dynamics that are comparable with tile-drained landscapes. Broader Impacts: The infrastructure developed in this proposal may be used to inform weighting factors and model structure for empirically based tools used by practitioners, such as P-indices. Regarding jurisdictional impacts, the PI’s home institution currently lacks curriculum for engineers working in vadose zone hydrology and contaminant transport, despite the importance of these processes in the jurisdiction. The laboratory methodology and numerical modeling are transferable to course modules of a graduate-level Vadose Zone Hydrology and Contaminant Transport class, which the PI plans to develop and include in the ‘Stream and Watershed Science’ graduate certificate that he directs at UK. Further, the PI will leverage existing programs at the University of Kentucky such as the Minorities in Agriculture, Natural Resources and Related Sciences (MANRRS) and will call upon his network of professors throughout Kentucky and West Virginia that have been developed through his NSF EPSCoR RII-2 interjurisdictional project to recruit an under-represented student in STEM for the project. The proposal closely aligns with NSF CBET’s “Environmental Engineering” and the Earth Sciences “Hydrologic Sciences” programs.