Evaluating Wetland Enhancement: Impacts on Groundwater and Surface-Water.

Levees built for alluvial floodplain systems deprive frequent flooding to wetland plant species. Big Oak Tree State Park, once part of a remnant of cypress swamps stretching over 800,000 ha of Missouri, has supplemented its water supply with agriculture water runoff for decades. Understanding the domain of this wetland system is essential in determining the local water budget for this distinct forested area next to the Mississippi River. The goal of this study is to understand water levels entering and exiting the park, seasonal variability in water table behavior, water quality, and explore the effects of management scenarios on the underlying aquifer during a dry month (June). In this paper, we examine the impacts of surface water (SW) diversion and groundwater (GW) pumping on channel flow, GW recharge, and SW-GW interactions using locally scaled remote sensing data and 3D models.

A hydrologic model was structured for an 18.5 km² grid, centering cells around irrigation wells. The subsurface layers defining the aquifer depth in the shallow 10.0 m and lower 27.7m were subject to the hydraulic conductivity of the dominant matrix material. The model then compares the transport of nitrates, flow, recharge, river conductivity, and evapotranspiration (ET) in the watershed under current and future layouts of control structures. Using six Landsat images from the study site, we validate our results based on a series of NDVI calculations from June 1995 - 2018 considering the hydrologic responses such as climate, topography, land cover, soil properties, irrigation pumping, drainage structures, and flooding. Our results suggest: (1) from spring to summer, the mean Mississippi River surface and groundwater levels decline -3.0 m and -0.6 m, respectively; (2) seasonal flooding occurs regularly in the crop field northwest of the park; (3)water commonly pools above lowland hydric soils (Sharkey silt clay). From our model predictions, the pumping activities at the irrigation well creates a cone of depression that has the largest impact on local groundwater behavior. This was noted to decreases the available GW ET in the low-lying field and wetlands. The height of the water table also increases in close proximity to the Mississippi River. This point suggests that the regional water table dynamics influence local groundwater behavior.