Employing Constructed Wetlands to Sustainably Manage Nutrient-Bearing Water: A Review with an Emphasis on Soil Behavior and Effluent Nutrient Reduction

Constructed wetlands are engineered structures designed to simulate processes of natural wetlands to mitigate anthropogenic organic and inorganic materials to shelter soil and water resources. This review focuses on the global interest in constructed wetland application to sustain soil health and water quality and water abundance. Engineering criterion remains a function of nutrient chemistry and load with suitability factors including the local soil and hydrogeology constraints, climate, vegetation selection, the degree of required influent improvement, and reactor types and sizes. Future research needs to focus on: 1) reactor designs criteria, 2) the biology of the microbial community, 3) selection criteria for native vegetation, and 4) criteria to reapply treated water to foster land productivity, especially for region’s experiencing water deficiencies.

Tile-Drain and Denitrification Bioreactor Water Chemistry for a Soybean (<i>Glycine max</i>(L.) Merr.)-Corn (<i>Zea mays</i>L.) Rotation in East-Central Missouri (USA)

Nitrogen transport from agriculture production fields raises the specter of environmental degradation of freshwater resources. Our objectives were to document and evaluate nitrate-N, ammonium-N, phosphorus and other nutrients emanating from a 40-ha controlled subsurface irrigation drainage technology coupled in series with a denitrification bioreactor. The intent of the denitrification bioreactor is to create an environment for anoxic microbial populations to support denitrification. We monitored the tile-drainage effluent and denitrification bioreactor water chemistry under a corn-soybean rotation to estimate the nutrient concentrations and the competence of the denitrification bioreactor to foster denitrification. Nitrate-N bearing tile drainage effluents ranged from less than 1.5 to 109 mg NO3- -N/L, with the nitrate concentration differences attributed primarily to the: 1) timing of nitrogen fertilization for corn, 2) soil mineralization and residue decomposition, and 3) intense rainfall events. The denitrification bioreactor was highly effective in reducing drainage water nitrate-N concentrations providing the rate of water flow through the denitrification bioreactor permitted sufficient time for equilibrium to be attained for the nitrate reduction reactions. The nitrate-N concentrations entering the denitrification bioreactor ranged from 0.4 to 103 mg NO3-?-N/L in 2018, whereas the outlet nitrate concentrations typically ranged from 0.3 to 5.2 mg NO3- -N/L in 2018. Nitrate tile-drainage effluent concentrations in 2019 were marginal, given soybeans obtain nitrogen from biological nitrogen fixation. Nutrient uptake by corn reduced the soil nitrate leaching pool and created nitrogen-bearing biomass, features important for formulating best management practices.

Improving Forest Soil Health and Ecosystem Services to Minimize the Impact of Climate Change

The presence of increasing quantities of greenhouse gases is fostering climate change. This review chronicles the emerging research addressing the role of soil to sequester carbon across biomes, understand the soil mechanisms responsible for soil carbon preservation and indicate the need to estimate the intensity for site-specific carbon sequestration. To negate the continuing increase of atmospheric greenhouse gases requires using well-documented soil pathways to sequester carbon. For deciduous forests, emerging concepts center around two approaches: 1) increasing the ecosystem’s net primary productivity coupled with increasing the carbon supply into soil using appropriate land management practices, and 2) supporting soil processes that increase soil carbon retention. New perspectives suggest that soil carbon may be preferentially preserved because organic materials are adsorbed onto phyllosilicates and oxyhydroxides and subsequently protected from microbial degradation because of soil structure improvement. Thus, augmenting soil structure may promote soil organic matter persistence. Each soil has a soil carbon carrying capacity;however, soil survey databases infer that soil organic matter concentrations have a significant variance at the soil series level. The need exists for more precise estimates of the soil’s carbon carrying capacity at the pedon level to support land management practices that encourage land management options designed to preserve soil carbon. However, the complexity of the soil system may limit its usefulness for routine soil management decisions. Our modern understanding of soil carbon preservation processes and emerging soil carbon saturation deficit concepts may potentially improve decision support tools for managing soils for carbon sequestration.

Soil Water Infrastructure to Eliminate Off-Site Nutrient Migration and Support Farm Profitability

Nutrient migration from agricultural land to freshwater resources is a fundamental global concern. The Department of Agriculture at Southeast Missouri State University has installed technology to research aspects of nutrient migration and propose mitigation strategies. The installed technologies include: 1) controlled subsurface drainage and irrigation technology, 2) a denitrification bioreactor to reduce nitrate concentrations in tile-drainage effluent, 3) an off-season water storage reservoir to capture and retain nitrate-bearing tile-drain effluent which will be applied as in-season liquid fertilizer, 4) riparian buffers, and 5) cover crops. For our beef livestock operation, we are installing a constructed wetland to capture nutrient-laden runoff from manure amended pastures associated with a confined feeding facility. Modern pasture management and row-crop nitrogen research augment the environmental stewardship potential of these infrastructures, while preserving farm profitability. The goal is to demonstrate that environmental stewardship, agriculture production and farm profitability are synergistic and may be explicitly demonstrated to the agriculture community.