Uncertainties of Atrazine Leaching and Accumulation in the Vadose Zone under Future Climate Ensembles

Abstract:

Atrazine, a prevalent herbicide to prevent weeds on croplands, is widely detected in groundwater and surface water, and threatens public health as a potent endocrine disrupter. To balance the tradeoff between sustainable water resources and increasing food demand, it is essential to evaluate the impact of uncertainty on predicting the leaching and accumulation of atrazine in the vadose zone beneath agricultural production areas. In this research, the study area is a center pivot-irrigated cornfield in Nebraska and related uncertainty includes climate variability, atrazine fate, and transport processes. To evaluate the climate variability, thirty-two Localized Constructed Analogs downscaled climate projections under an ensemble of Earth System Models were selected for each of the two RCP scenarios (RCP 4.5, RCP 8.5). Additionally, uncertainties in fate and transport processes were evaluated by estimated probability functions of atrazine application rates, initial atrazine concentration in groundwater, sorption, and biodegradation coefficients, based on extensive literature review. To reduce the computation cost and to produce 100 combinations of parameters for three-dimensional atrazine fate and transport models under each climate scenario (years 2057 to 2060), Latin hypercube sampling was utilized with five stratified levels. Future groundwater recharge and elevation at the field site were estimated using an inverse modeling method and a calibrated groundwater model. Preliminary findings indicate the mean predicted groundwater elevation from 32 climate scenarios under RCP 8.5 will gradually decrease 6.5 ft from years 2057 to 2060. In the same period, uncertainties of atrazine accumulation are directly related to the atrazine application rate and irrigation management strategies.