Research Project: Enhancing Long-Term Agroecosystem Sustainability of Water and Soil Resources Through Science and Technology

Location: Water Quality and Ecology Research

2023 Annual Report

Objectives
1. Assess and quantify impacts of soil and water management strategies in agroecosystems of the Lower Mississippi River Basin (LMRB). 1.A. Examine water management strategies to assess tradeoffs between groundwater sustainability benefits and ecological costs. 1.B. Quantify the influence of soil and water management strategies on water availability and quality, soil health, and wildlife habitat. 2. Evaluate and measure how management practices influence processes to improve water quality, ecosystem services, and ecological integrity. 2.A. Evaluate novel ecological indicators and stressor-response relationships to measure success of best management practices in agricultural watersheds. 2.B. Evaluate how management practices influence processes related to soil health and water quality in agricultural watersheds. 3. Analyze, synthesize, and forecast impacts of implementing conservation practices within agricultural landscapes. 3.A. Forecast and analyze impacts of climate change on the effectiveness of conservation practices. 3.B. Quantify the impacts of conservation practices on aquatic and terrestrial resources in the LMRB. 4. Enhance long-term sustainability of agroecosystems through regional and national (LTAR network) studies that quantify agronomic and environment responses to aspirational management strategies and changing climate. 4.A. Develop the LMRB LTAR site through contributions in monitoring and experimentation to meet network goals. 4.B. Establish a network of LTAR sites distributed regionally and nationally to quantify changes in soil health, water quality and aquatic ecology in LTAR watersheds.

Approach
Many experiments described in the following involve collection and analysis of water quality samples from field sites within the Lower Mississippi River Basin. Data acquisition (sample collection, preservation, handling, analysis, quality control), except where otherwise noted, follows standard procedures (APHA, 2005). Base flow samples are collected manually, while storm event or runoff samples are collected using automated pumping samplers (ISCO GLS Compact Composite Samplers) activated by acoustic Doppler water level and area velocity water flow sensors (ISCO 2100). All samples are placed on ice for transport to the laboratory for analysis and held in cold storage (4o C). Storm samples are retrieved within 24 h of collection. All water samples are analyzed for total and dissolved solids (drying at 105o C), total P and total Kjeldahl N (block digestion and flow injection analysis using a Lachat QuikChem® 8500 Series 2 Flow Injection Analysis System). Additional analyses conducted for certain experiments include hardness (EDTA titrimetric method), alkalinity (titration method), turbidity (calibrated Hach electronic turbidimeter); NH4-N, NO3-N, NO2-N, and soluble (filterable) P (all with the Lachat system), and chlorophyll a (pigment extraction with spectrophotometric determination). Pesticide analyses are conducted using solvent (hexane) and KCl extraction prior to analysis on a gas chromatograph. Soil gas flux is measured using a LiCOR 870 soil gas flux system.

Progress Report
A manuscript is in final stages of preparation to evaluate ecological needs of Mississippi lakes and how surface water contributions may reduce the need for groundwater pumping for irrigation needs in the Delta. Additionally, macroinvertebrate, migratory shorebird, soil, and water data were collected as part of a larger research project examining the possibility of using shallow flooded, post-harvest corn and soybean fields for migratory shorebird habitat. Data is being analyzed for the first manuscript from this project. Soil, water, and crop data were compiled from the 21-Gun long-term research plot to support investigation into conservation and irrigation technology management for improved soil health in cotton systems. Manuscripts were submitted and published describing microbial, algal, and macroinvertebrate responses to nutrient enrichment in the Mississippi Delta. Primary stakeholders such as the Mississippi Department of Environmental Quality have been presented with the data and manuscripts to help them make informed management decisions regarding nutrient criteria development in the Delta ecoregion of the state of Mississippi. A series of experiments in limnocorrals has also led to the publication of manuscripts describing the balance between nitrogen fixation and denitrification in regulating nitrogen availability. Small-scale experiments were conducted that examined the use of woodchip-bioreactors in filter sock material (typically used for erosion control in construction) to mitigate nitrogen and phosphorus in simulated storm runoff. Data were analyzed and a manuscript prepared that demonstrated the bioreactor’s effectiveness at mitigating nitrogen, but less so, for phosphorus. Variables examined included bioreactor orientation (parallel to flow, perpendicular to flow, or a hybrid) and saturation (wet versus dry). The constantly wet bioditch reactor mitigated more nitrate than the dry bioreactor. Laboratory bioassays were conducted to examine the effect of increased temperature on algal nutrient limitation and thresholds. With climate change, rising temperatures will also alter water quality and affect outbreaks of harmful algal blooms. Within the Conservation Effects Assessment Project (CEAP), long-term monitoring of lake water quality and ecology continued within the Beasley Lake watershed. The non-cropland areas of the watershed were highly modified by the landowners, resulting in shifting of research sites and priorities. Data continues to be centralized for multiple landscape-scale manuscripts, including those with collaborators focusing on modeling aspects. Long-Term Agroecosystem Research (LTAR) Project samples of soil, biomass, as well as eddy covariance data continued to be collected as part of the common experiment across LTAR sites. This year, two additional field sites were scouted and implemented. One is a business-as-usual (BAU) treatment to complement a current aspirational (ASP) treatment. The second is an additional BAU and ASP farm owned and operated by a minority farmer in Mound Bayou, Mississippi. Additionally, a cross-site (national) experiment with seven locations was initiated to assess phytoplankton algal nutrient limitation and thresholds in order to determine eutrophication in watersheds with different agricultural land use.

Accomplishments
1. Bacteria can help determine water quality goals. Bacterial communities in streams can potentially mitigate many ecosystem impacts, like excessive nutrient concentrations. It is critical to understand how agricultural practices affect bacterial diversity in agricultural streams to improve resource management. ARS researchers in Oxford, Mississippi, discovered bacterial diversity increases with increasing agricultural land use and is strongly impacted by increasing salinity and sediment deposition, two agricultural water quality stressors. Because of their increased diversity in agricultural watersheds, bacterial communities may be useful for establishing water quality goals and monitoring improvements from conservation practices in agroecosystems, rather than traditional expensive fish and insect community assessments.

2. Let gas guide nutrient reduction strategies. Excess nitrogen from agriculture can cause harmful algal blooms (HABs), hypoxia, and habitat degradation in aquatic ecosystems. Dissolved nitrogen gas import (nitrogen fixation) and export (denitrification) from water bodies are keys to understanding the role of nitrogen in water quality. ARS researchers in Oxford, Mississippi, quantified nitrogen fixation and denitrification rates while also measuring nitrogen gas concentrations from water samples in 12 experimental ponds dosed with different amounts of nitrogen. When systems were importing nitrogen (fixation), gas concentrations were below expected values, and when systems were exporting nitrogen (denitrification), gas concentrations were above expectations. Simply by measuring nitrogen gas concentrations, scientists can track primary processes and provide critical information to develop strategies for reducing nutrient impacts to aquatic ecosystems.

3. "Epic" Analysis detects small improvements in water quality. Determining relationships between stream fish and insect populations and water nutrient concentrations has historically measured success of conservation practices targeted to improve water quality. In the Lower Mississippi River Basin, most streams have been structurally altered and water quality is already poor. This makes it harder to see if even small improvements in water quality affect fish and insect responses. ARS researchers in Oxford, Mississippi, demonstrated changes in insect populations in streams with different levels of water quality could be detected using a specialized sensitive statistical analysis called Threshold Indicator Taxa Analysis (TITAN). These changes occurred at higher nutrient concentrations when compared to results from other areas with less agriculture. This demonstrated that current water quality goals for intensive agricultural regions should take these parameters into consideration and establish realistic goals that can be achieved.

4. Agricultural environments in the conterminous United States are well-represented by the USDA Long-Term Agroecosystem Research Network. The USDA Long-Term Agroecosystem Research (LTAR) Network coordinates agricultural research in the United States across multiple research sites. Research outcomes have the potential for very high impact, but only if the Network represents the totality of agricultural working lands in the conterminous United States. ARS researchers in Tifton, Georgia; Columbia, Missouri; and Oxford, Mississippi, in collaboration with Oak Ridge National Laboratory; the University of Arizona; and the US Forest Service, defined and mapped representativeness and constituency of the current LTAR network based on an analysis of 15 global environmental variables. Representativeness shows how well environmental conditions are represented by one of the LTAR sites, while constituency shows which LTAR site is the closest match for each location. LTAR representativeness was good across most of the country, but there were regions not as well represented. For those, targeted collaborations with existing sites from the Long-Term Ecological Research (LTER) Network and the National Ecological Observatory Network (NEON) would be beneficial. While this analysis considered environmental characteristics related to production on working lands, a similar process could be applied to variables that describe the primary agronomic systems or the socio-economic context. These are important aspects of socio-agroecosystems that, if considered in future analyses, could lead to a deeper understanding of how well the LTAR Network represents working lands of the continental USA, and help research leaders identify future sites’ locations.

Review Publications
Nelson, A.M., Moore, M.T., Witthaus, L.M. 2022. Pesticide trends in a tailwater recovery system in the Mississippi Delta. Agrosystems, Geosciences & Environment. 2(4):e20325. https://doi.org/10.1002/agg2.20325.
Nelson, A.M., Witthaus, L.M., Moore, M.T., Griffith, M.K., Locke, M.A., Taylor, J.M., Lizotte Jr, R.E. 2023. Seasonal water quality trends in a tailwater recovery system in the Mississippi Delta. Agricultural Water Management. 78(1):26-32. https://doi.org/10.2489/jswc.2023.00090.
Chatterjee, A., Taylor, J.M., Moore, M.T., Locke, M.A., Hoeksema, J.D. 2023. Shallow water habitat management influences soil CO2 efflux from agricultural fields in the Lower Mississippi River Basin (LMRB), USA. Agrosystems, Geosciences & Environment. 211–224 (2019). https://doi.org/10.1002/agg2.20365.
Chao, X., Witthaus, L.M., Bingner, R.L., Jia, Y., Locke, M.A., Lizotte Jr, R.E. 2023. An integrated watershed and water quality modeling system to study lake water quality responses to agricultural management practices. Environmental Modelling & Software. 164. https://doi.org/10.1016/j.envsoft.2023.10569.
Hoover, D.L., Abendroth, L.J., Browning, D.M., Saha, A., Snyder, K.A., Wagle, P., Witthaus, L.M., Baffaut, C., Biederman, J.A., Bosch, D.D., Bracho, R., Busch, D., Clark, P., Ellsworth, P.Z., Fay, P.A., Flerchinger, G.N., Kearney, S.P., Levers, L.R., Saliendra, N.Z., Schmer, M.R., Schomberg, H.H., Scott, R.L. 2022. Indicators of water use efficiency across diverse agroecosystems and spatiotemporal scales. Science of the Total Environment. 864. Article e160992. https://doi.org/10.1016/j.scitotenv.2022.160992.
Carpenter, B., Goodwiller, B., Wren, D.G., Taylor, J.M., Aubuchon, J., Brown, J., Posner, A. 2022. Field testing a high-frequency acoustic attenuation system for measuring fine suspended sediments and algal movements. Applied Acoustics. 198: 2022. 108980. https://doi.org/10.1016/j.apacoust.2022.108980.
Nifong, R.L., Taylor, J.M. 2021. Vegetation and residence time interact to influence metabolism and nutrient assimilation in experimental agricultural drainage systems. Water. https://doi.org/10.3390/w13101416.
Taylor, J.M., Devilbiss, S.E., Hicks, M. 2023. Macroinvertebrate assemblage responses to nutrient stressor gradients in alluvial plain streams: Using taxa-based approaches to delineate assemblage responses in modified agroecosystems. Freshwater Biology. 153. Article 110377. https://doi.org/10.1016/j.ecolind.2023.110377.
Faucheux, N.M., Miranda, L.E., Taylor, J.M., Farris, J.L. 2023. Impact of dams on stream fish diversity: a different result. Diversity. 2023,15,728. https://doi.org/10.3390/d15060728.
Firth, A.G., Brooks, J.P., Locke, M.A., Morin, D.J., Brown, A., Baker, B.H. 2022. Soil microbial community dynamics in plots managed with cover crops and no-till farming in the Lower Mississippi Alluvial Valley, USA. Journal of Applied Microbiology. 134(2); 1-13. https://doi.org/10.1093/jambio/lxac051.
Contasti, A.L., Firth, A., Baker, B.H., Brooks, J.P., Locke, M.A., Morin, D.J. 2023. Balancing trade-offs in climate smart-agriculture: will selling carbon credits offset potential losses in the net yield income of small-scale soybean (Glycine max L.) producers in the mid-southern United States?. Decision Analysis. 20(4):243-344. https://doi.org/10.1287/deca.2023.0478.
Taylor, J.M., Andersen, I.M., Hoke, A.K., Kelly, P.T., Scott, J.T. 2023. In-situ N2:Ar ratios describe the balance between nitrogen fixation and denitrification in shallow eutrophic experimental lakes. Biogeochemistry. 166:283-301. https://doi.org/10.1007/s10533-023-01063-6.
Kelly, P., Taylor, J.M., Anderson, I.M., Scott, J.T. 2021. Highest primary production achieved at high nitrogen levels despite strong stoichiometric imbalances with phosphorus in hypereutrophic experimental systems. Limnology and Oceanography Journal. Pages 4375-4390. https://doi.org/10.1002/lno.11968.