FLUXES OF MAJOR IONS AND AGRICULTURAL CHEMICALS FROM INFILTRATION TO RECHARGE

Providing water in the right amounts and in the right places is an essential goal for a healthy society and ecosystem. Attaining that goal is often elusive for want of more accurate predictions of weather, climate, and a better understanding of the complex interactions of energy and moisture at the interfaces of atmosphere, land, and surface waters. High-resolution regional general circulation models can now reliably predict the time and amount of precipitation expected to fall onto each four-kilometer parcel across the United States. Predicting the time and amount of water flowing into the streams draining those parcels, however, is much less certain, primarily because of poorly understood fluxes into and out of the unsaturated zone. Rick Healy developed field methods, along with conceptual and numerical models to reduce this uncertainty.

My research over the last twenty years benefitted greatly from the tutelage of Rick Healy, Ed Weeks, Don Rosenberry, Brent Troutman, Dave Stannard, Dean Anderson and other emeriti of the Central Region National Research Program in Lakewood. This presentation will highlight results from two programs I contributed to where unsaturated zone processes were a major focus: (1) The National Water Quality Assessment’s Agricultural Chemical Transport project. Results included a regression model converting LEACHM simulations to predictions of pesticide leaching potential as a function of organic carbon normalized sorption coefficient, depth, and degradation rate; and documentation of chloride and pesticides transported by diffuse and focused recharge beneath agricultural fields; and (2) The Water, Energy, and Biogeochemical Budget program where I developed a model driven by weather, precipitation chemistry, and soil properties to determine daily variations in overland flow, interflow, and baseflow contributions to headwater streams.