The Lower Mississippi River Basin (LMRB) is an internationally‐important region of intensive agricultural crop production that relies heavily on the underlying Mississippi River Valley Alluvial Aquifer (MRVAA) for irrigation. Extensive irrigation coupled with the region’s geology have led to significant aquifer decline. The response to the decline has been multi‐faceted. Research related to three responses are highlighted: innovation in rice irrigation, on‐farm reservoirs, and managed aquifer recharge. Irrigated rice grown in Arkansas, which is nearly 50% of annual U.S. rice production, accounts for a significant portion of aquifer withdrawal. As a result, strategies for using less water while maintaining rice yields are being developed. The Rice Stewardship Partnership (RSP) began in 2015 and aims to improve irrigation management in rice lands of the LMRB. Early results from the RSP are presented. Secondly, on‐farm reservoir‐tailwater recovery systems (R‐TWRS) are increasingly used to store abundant surface water in the LMRB. Over 700 R‐TWRS are currently used in rice producing areas of Arkansas. The confining clay layer that overlies the MRVAA in many locations limits rates of aquifer recharge. Locations where the confining layer is thin or non‐existent may provide opportunities for artificial (i.e., managed) recharge. A 10‐m deep excavation pit from a highway project provided an opportunity to measure infiltration rates of the uppermost section of the alluvial aquifer. Findings from this and other studies are used to demonstrate how conservation, off‐season rainfall capture and storage, and managed recharge are being investigated as means to reduce the on‐going decline of the alluvial aquifer that is both economically and ecologically important to the LMRB.
Cloud condensation and ice nuclei in the troposphere are required precursors to cloud and precipitation formation, both of which influence the radiative balance of Earth. The initial stage of hailstone formation (i.e., the embryo) and the subsequent layered growth allow hail to be used as a model for the study of nucleation processes in precipitation. By virtue of the preserved particle and isotopic record captured by hailstones, they represent a unique form of precipitation that allows direct characterization of the particles present during atmospheric ice nucleation. Despite the ecological and economic consequences of hail storms, the dynamics of hailstone nucleation, and thus their formation, are not well understood. Our experiments show that hailstone embryos from three Rocky Mountain storms contained biological ice nuclei capable of freezing water at warm, subzero (°C) temperatures, indicating that biological particles can act as nucleation sites for hailstone formation. These results are corroborated by analysis of δD and δ 18 O from melted hailstone embryos, which show that the hailstones formed at similarly warm temperatures in situ. Low densities of ice nucleation active abiotic particles were also present in hailstone embryos, but their low concentration indicates they were not likely to have catalyzed ice formation at the warm temperatures determined from water stable isotope analysis. Our study provides new data on ice nucleation occurring at the bottom of clouds, an atmospheric region whose processes are critical to global climate models but which has challenged instrument-based measurements.
Surface water is the greatest contributor to many water supplies in urbanized areas. Understanding local water sources and seasonality is important in evaluating water resource management, which is essential to ensure the sustainability of water supplies to provide potable water. Here we describe the municipal water cycle of Columbus, Ohio, USA, using δ 18 O, δD, and d-excess, and follow water from precipitation through surface reservoirs to a residential tap between May 2010 and November 2011. We show that trends in water isotopic composition of Ohio precipitation have a seasonal character with more negative values during the winter months and more positive values during the summer months. The year of 2011 was the wettest year on record in Central Ohio, with many months having high d-excess values (>+15‰), suggestive of increased moisture recycling, and possibly moisture introduced from more local sources. Tap waters experienced little lag time in the managed system, having a residence time of ~2 months in the reservoirs. Tap waters and reservoir waters preserved the isotopic signal of the precipitation, but the reservoir morphology also influenced the water residence time, and hence, the isotopic relationship to the precipitation. The reservoirs supplied by the Scioto River function like a river system with a fast throughput of water. The other reservoirs display more constant solute concentrations, longer flow-through times, and more lacustrine qualities. This work provides a basic understanding of a regional water supply system in Central Ohio and helps characterize the water flow in the system. These data will provide useful baseline information for the future as urban populations grow and the climate and hydrologic cycle changes.
On-farm water storage-tailwater recovery systems reduce groundwater usage and intercept agrochemical loads, but pesticide residue dynamics in these systems are not well understood. This study monitored concentrations of seven herbicides in seven northeast Arkansas tailwater recovery systems (April 2017-March 2018). Clomazone, glyphosate, metolachlor, and quinclorac were frequently detected, with minimal detections of 2,4-D, dicamba, and propanil. Concentrations peaked during the growing season (1 Apr.-15 Sept.), reflecting an interaction of application and precipitation. Clomazone, glyphosate, and quinclorac concentrations were greater in ditches (<0.80-67, <0.50-6.2, and <0.40-62 μg L −1 , respectively) than in the associated reservoir (<0.80-6.0, <0.50-4.1, and <0.40-6.0 μg L −1 , respectively), but metolachlor concentrations were not different between structure types (maximum 22-32 μg L −1 ). Off-season concentrations were mostly below detection, except for quinclorac. Cycling recovered tailwater through the system and irrigating from reservoirs may minimize risk of cross-crop contaminations with residual herbicides. Managed groundwater recharge should use reservoir water during winter to protect groundwater quality.Abbreviations: BMP, best management practice; MAR, managed aquifer recharge; OFWS-TWR, on-farm water storage-tailwater recovery; SPE, solid phase extraction.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
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