Seasonal Impact on Selenium Removal Efficiency in Simulated Constructed Wetland Microcosms.

Constructed wetlands (CWs) are a popular passive treatment option for improving the water quality of runoff impacted by a broad range of elements, including selenium (Se). However, the efficiency of these plant-based systems is dependent on environmental conditions. This research is being conducted to evaluate the seasonal impact on Se removal in cattail (Typha angustifolia L.) or duckweed (Lemna minor L.) planted CWs receiving selenate-impacted runoff over four weekly flood events. During the spring, summer, and fall of 2018, simulated CW microcosms planted to either cattail, duckweed, or unplanted (control) were flooded with 30 L of fresh runoff water at zero, 1x, or 2x Se concentrations. After six days, microcosms were discharged for 24 hours, completing one flood event. This was repeated three times within each season. During each flood event, aqueous, plant, and soil samples were collected and analyzed for total Se concentration. Significant main and interaction effects were determined at α=0.05 with PROC GLM (SAS v.9.4). Selenium removal efficiency was greater in the summer (73%) corresponding to increased mean temperature; compared to the spring (41%, 20°C) and fall (42%, 16°C). Results indicate a significant correlation (0.67) between Se removal efficiency and seasonal mean temperature. Overall, planted microcosms removed 55% of the applied Se compared to 46% in unplanted controls (p<0.0001). This study demonstrates the potential for cattail and duckweed to improve the water quality of selenate-impacted runoff over four weekly flood events, but Se removal efficiency does vary with season.