Inundation and nutrient assessment of farmed prairie potholes during a cropping season with high precipitation

Abstract

Abstract Enclosed topographical depressions that retain water intermittently are abundant across the prairie pothole region of the United States. These depressional wetlands (potholes) are located at local minimum elevations with small contributing micro‐watersheds. These features are often located in areas where the primary land use is row crop agriculture; thus subsurface tile drainage has been implemented to improve crop production and field accessibility. However, even with drainage improvements, farmed potholes still tend to retain water during high precipitation periods. This study monitored 10 farmed potholes in 2018, a year with 32% more precipitation than the 30‐year average. Potholes were inundated between 12% and 81% of the monitored growing season; the highest inundation percentage occurred in a pothole without surface intakes. Nutrient concentrations in 2018 were lower on average than previously reported for the same potholes, possibly due to higher precipitation and less fertilizer applied because most of the potholes were in soybeans rather than corn. Total nitrogen and nitrate‐N median concentrations were 16.71 and 14.82 mg N L−1 lower (p‐value < 0.0001) during the early season (May 15–July 7) than concentrations in 2016–2017. Total phosphorus and dissolved reactive P median concentrations, conversely, were slightly but significantly lower during the late season (July 8–November 1) with 0.15 and 0.13 mg P L−1 difference (p‐value < 0.01), respectively. Observed DRP concentrations increased by 63% during multiday inundation periods. Our monitoring results suggest during seasons of heavy precipitation, farmed potholes might act as hotspots, contributing elevated levels of P to downstream waters.