Location: Hydrology and Remote Sensing Laboratory
Project Number: 8042-13610-030-091-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Feb 1, 2025
End Date: Aug 19, 2027
Objective:
The effectiveness of conservation practices and the ecosystem services they provide is a function of numerous environmental processes that need well understood. Nitrogen inputs from agricultural lands has proven to be one of the most difficult watershed conservation problems to address, in part because groundwater nutrient source movement is complicated by many inherent soil and water properties and processes, by weather inputs, and by agronomic practices. This agreement describes a collaboration between researchers at UMD and ARS between the Agricultural Research to increase the effectiveness of conservation practices. Legacy nutrients are defined as nitrogen or phosphorus in groundwater, soils, stream beds, stream banks, reservoirs, lakes, and/or other locations within a watershed that are emitted downstream of their original source with temporal lags. Our capability to quantify the extent of legacy nutrients contribution to current agricultural inputs is a critical obstacle to increasing the effectiveness and efficiency of conservation planning at multiple scales. This project builds on existing cooperative research with ARS researchers on the use of MESA, {2-[2-ethyl-N-(1-methoxypropan-2-yl)-6-methylanilino]-2-oxoethanesulfonic acid} a degradation product of the commonly used herbicide metolachlor, and its enantiomeric ratio change as a temporal marker. MESA and nitrate-N move through the soil and groundwater systems together, but because MESA is very stable, it can be used as a conservative tracer to assess the fate of nitrate-N concentrations in an ecosystem. Furthermore, the fraction of old MESA, which is calculated using the amounts of R-MESA relative to S-MESA, is a direct indicator of water age and can help to shed light on the dominant transport pathways, long flow paths versus short flow paths, for groundwater transport to surface stream water. The overall goal of this project is to identify sources of legacy nitrate in fields and watersheds and to assess conservation options to capture and treat these sources. This project will obtain data and process understanding that can be utilized by the SWAT+ modeling team to improve the algorithms and assumptions concerning groundwater transit times in different regions of the U.S.
Approach:
The cooperator will be involved watershed sampling, acquisition of analytical data, chain of custody and quality control, while implementing safety protocols. Additional watershed characterization data will be synthesized to examine the variance of input sources and the possible factors affecting delivery of legacy N to stream and surface waters. While nitrogen is typically delivered via groundwater, overland flow provides much of the phosphorus and sediments to surface waters. Thus, throughout the project, the team will consult regularly with the Legacy P and Legacy Sediment teams to coordinate efforts to maximize synergies, to share data streams on one platform, and to address competing processes in nutrient delivery so that we can advance a more holistic understanding and simulation of processes going forward. The cooperator will also provide GIS data and support to modeling teams as they examine approaches to modifying models to improve ground water lag time and legacy N fate. This effort will provide information to assess the effectiveness of conservation practices.