Water quality characteristics of tailwater recovery systems associated with agriculture production in the mid-southern US

In the Lower Mississippi River Basin, tailwater recovery (TWR) systems are water conservation practices implemented to mitigate downstream nutrient losses and alleviate groundwater depletion as supplemental irrigation sources. This study was conducted to characterize water quality within TWR systems and assess the influence of precipitation and fertilizer application events, as well as reservoir levee protection, on water quality. Three TWR systems were selected, and water samples were collected during the growing seasons of 2014-2016. Nitrate (NO3) and dissolved inorganic orthophosphate (DIP) were observed to be significantly lower (p < 0.001) in reservoirs when compared with TWR influent and effluent; hence, reservoirs demonstrate a vital role in reducing downstream nutrient contribution. Mean NO3 in the reservoirs, TWR influent, and TWR effluent was 0.05 +/- 0.01 mg L-1, 0.10 +/- 0.01 mg L-1, and 0.14 +/- 0.02 mg L-1, respectively. Mean DIP concentrations in the reservoirs, TWR influent, and TWR effluent was 0.39 +/- 0.03 mg L-1, 0.96 +/- 0.04 mg L-1, and 1.03 +/- 0.08 mg L-1, respectively. Mean NO3 concentration was also significantly lower (p = 0.001) in the reservoir with levees protected with vegetation (0.02 +/- 0.01 mg L-1) compared to (0.06 +/- 0.01 mg L-1) reservoirs with levees protected with concrete rubble. Total suspended solids (TSS) of the influent and reservoir were significantly different, with the reservoir TSS reduced on average by 43% compared to the influent. Water quality was influenced by reservoir levee protection materials, especially NO3 and dissolved oxygen concentrations which were lower with vegetated protection.