Potential Denitrification and Possible Environmental Drivers in Floodplains in the Wabash River Basin

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<p>This project aimed to identify environmental drivers of denitrification capacity that can be leveraged through strategic design and management of floodplain restorations to maximize water quality outcomes. </p>

<p>Denitrifying enzyme activity and potential environmental drivers of denitrification capacity were evaluated seasonally in four floodplains, which represented different approaches to floodplain restoration, along the Wabash and Tippecanoe Rivers from Summer 2018 to Spring 2020. Soil samples were collected from a depth of 0 to 10 centimeters at nine locations along three transects within each floodplain, which spanned various hydrologic, geomorphic, soil, and vegetation conditions. The denitrification enzyme activity of these soils was measured in redox-optimized slurries with river water from adjacent channels and water amended with glucose and nitrate using the acetylene block method. </p>

<p>Potential environmental drivers of denitrification were concurrently characterized at each location and sampling date. Soil properties included gravimetric soil moisture content, soil organic matter content, calcium carbonate content, total soil carbon content, total soil nitrogen content, bulk density, and particle size as characterized by the distribution of nominal particle diameter and proportions of sand, silt, and clay. Hydrogeomorphic variables included height above the nearest drainage area (HAND), horizontal distance to the nearest drainage (HDND), slope to the nearest drainage area, cumulative days flooded, distribution of flood velocity, inter-arrival period of inundation, and geomorphic feature type. The dominant plant species at each location was also considered as a potential driver of denitrification capacity. Weather properties included mean of minimum, maximum, and mean daily air and soil temperatures; standard deviation of these daily temperature metrics; and cumulative snowfall and total precipitation in the previous one week, one month, three months, and six months prior to each sampling date.</p>

<p>Denitrification rates were highest in the floodplain restored as a wetland. Higher denitrification rates were also associated with soils characterized by elevated organic matter and moisture, and these soil conditions covaried with vegetation community and hydrogeomorphic characteristics. </p>
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