Unexpected Increases in Fecundity of Ceriodaphnia dubia Exposed to Reused Rice Irrigation Water

Steady increases in agricultural irrigation raise concerns about environmental impacts. Rice producing regions face declining irrigation groundwater and have started reusing irrigation water as a substitute. The goal of this project was to determine if reused irrigation water is potentially toxic compared to conventional well irrigation water. Reused and well water samples, collected from three Arkansas rice farms at field inlets and outlets on three dates corresponding to fertilizer/chemical applications or crop management, were used in acute 48-h (Pimephales promelas) and chronic (Ceriodaphnia dubia) toxicity evaluations. Acute toxicity tests indicated no effects on P. promelas. Fecundity of C. dubia was significantly increased in the reused water inlet and in both the reused and well water rice field outlets compared to well water inlets and laboratory reference water. This study suggests that, compared to well water, reused rice irrigation water has reduced potential for significant negative environmental impact on biota in receiving waters.