Impact of agroecosystems on groundwater resources in the Central High Plains, USA

Agroecosystems impact water resources by consuming most fresh water through irrigation and by changing water partitioning at the land surface. The study assesses impacts of agroecosystems on groundwater resources in the Texas Central High Plains (37,000 km(2) area) by evaluating temporal variations in groundwater storage and quality. Percolation/recharge rates were estimated using groundwater Cl data and using unsaturated zone matric potential and water-extractable chloride and nitrate from 33 boreholes beneath different agroecosystems. Total groundwater storage decreased by 57 km(3) since the 1950s when irrigation began and individual well hydrographs had declines <= 1.3 m/yr. The renewable portion of groundwater is controlled by percolation/recharge, which is related to soil texture and land use. In fine-medium (f-m) grained soils, there is no recharge beneath natural ecosystems or rain-fed agroecosystems; however, recharge is focused beneath playas and drainages. In medium-coarse (m-c) grained soils, percolation/recharge is low (median 4.8 mm/yr) beneath natural ecosystems and is moderate (median 27 mm/yr) beneath rain-fed agroecosystems. Although irrigation increased percolation under all soil types (median 37 mm/yr), irrigation return flow has not recharged the aquifer in most areas because of deep water tables. Groundwater depletion (21 km(3) over 52 yr) is 10 times greater than recharge (11 mm/yr; 2.1 km(3)) where water table declines are greatest (>= 30 m). Therefore, current irrigation practices are not sustainable and constitute mining of the aquifer, which is being managed as a nonrenewable resource. (C) 2010 Elsevier B.V. All rights reserved.