HR: 17:00h
AN: H44B-06    [Abstracts]
TI: Hydrogeologic and Geochemical Controls on The Transport and Fate of Agricultural Chemicals in Ground Water Beneath Riparian Zones
AU: * Puckett, L J
EM: lpuckett@usgs.gov
AF: U.S. Geological Survey, 12201 Sunrise Valley Drvie, Reston, VA 20192 United States
AB: Numerous studies have documented the potential water-quality benefits provided by riparian buffer zones. However, many of the hydrogeologic and geochemical processes controlling the transport and fate of solutes in riparian zones are poorly documented. Over the past decade, the National Water-Quality Assessment (NAWQA) Program has investigated the transport and fate of agricultural chemicals along ground-water flow paths in study areas across the United States. In these studies, riparian zone efficiency in removing nitrate from ground water flowing from uplands to streams, varied from negligible to 100 percent as a result of variations in hydrogeologic and geochemical factors. These factors include (1) total denitrification in the upgradient aquifer; (2) long residence times (>50 years) along ground-water flow paths allowing even slow reactions to completely remove nitrate; (3) dilution of nitrate-enriched waters with older ground water containing low concentrations of nitrate; (4) bypassing of riparian zones due to extensive use of drains and ditches; (5) movement of ground water along deep flow paths below shallower, organic-rich reducing zones; and (6) movement of ground water through riparian-zone sediments along preferential flow paths. An important outcome of these studies has been an increased understanding of the effect of long residence times of ground water along flow paths on the transport and fate of nitrate, with some exceeding 50 years in shallow aquifers less than 20 m thick. Such long residence times have important implications for nutrient management programs since it may take several decades before the full benefits of reduced inputs are realized in receiving surface waters. Another important finding is the impact of widespread use of drains and ditches as a management tool for lowering seasonally high water tables. Such artificial drainage circumvents natural hydrologic flow paths, and routes shallow ground water directly to surface waters, bypassing riparian buffer zones in the process. Increased understanding of the hydrogeologic settings in which riparian buffer zones are likely to be inefficient at nitrate removal can aid managers in developing improved nutrient management plans.
DE: 1800 HYDROLOGY
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting