Integration of Hydrogeology and Soil Science for Sustainable Water Resources—Focus on Water Quality

Salinization and failures to manage soil, carbon, and nutrients have plagued human societies since ancient times. The sustainability of water resources depends on water-quality determining unsaturated-zone fluxes and processes; i.e., on atmospheric and anthropogenic influxes and effluxes of water, solutes, carbon, and energy across the land surface; on biologically mediated processes within the root zone that control and modify these fluxes—especially of nutrients; on chemical processes beneath the root zone that selectively release elements from the solid phase and remove others from solution; and on hydraulic fluxes of advected solutes to the saturated zone. Transported soil can have substantial water-quality impacts when material eroded from the unsaturated zone moves into surface-water bodies. A scarcity of data limits our understanding of unsaturated-zone effects on water quality, which cannot easily be measured from space. Nevertheless, substantial advances in understanding are emerging from ground-based monitoring networks and multi-disciplinary studies. For example, understanding salinization due to land-use change is greatly benefitting from recent findings about natural salinity cycles. Isotopic systems offer a wealth of information about processes, to cite another example. Isotopic discrimination by microbial processes (strongly fractionating), phase changes (moderately fractionating), and atmospheric-generation processes (weakly fractionating) help identify the movement of water and sources of oxyanion salts. Evolving analytical and modeling techniques will continue to spur development of improved process-based knowledge that is essential for addressing agricultural and other land-use pressures on water quality—pressures that can only be expected to intensify in the face of continued population and economic growth.