Influence of Temperature and Vegetation on Selenium Removal in Constructed Wetland Microcosms

Intense precipitation events over coal fly ash sediments produce large runoff volumes that can accumulate and transport selenium (Se) into surrounding watersheds and degrade the quality of aquatic ecosystems. Constructed wetland (CW) phytoremediation is a cost-effective, ecological water treatment alternative that relies on plant metabolic processes to improve the quality of Se-impacted runoff. This research was conducted to evaluate the seasonal influence on Se removal in simulated CWs planted with either cattail (CAT; Typha angustifolia L.) or duckweed (DWD; Lemna minor L.) compared to an unplanted (UNP) control over four consecutive, week-long flood events. CWs were simulated in 110 L microcosms containing 25 kg of Catalpa silty clay loam. Microcosms were acclimated for 14 d before the first flood event, when each received 30 L of simulated selenate-impacted runoff. Runoff treatments included 0, 1x or 2x Se rates. Water, plant, and soil samples were collected at application and six d after treatment application. Total Se concentration [Se] was determined with inductively coupled plasma mass spectrometry (ICP-MS). Data were analyzed with PROC MIXED (=0.05). Overall, CAT and DWD significantly decreased aqueous [Se] by 47% compared to 36% for UNP (P<0.0001). Results indicate the greatest aqueous Se removal was observed in the summer (73%) followed by the fall (42%) and spring (41%). Temperature was strongly correlated with Se removal (0.65, P<0.0001). At temperatures between 15 and 20C, CAT and DWD are suitable aquatic species for phytoremediation of selenate-impacted waters in CWs.