Submitted to: American Water Resources Association Summer Specialty Conference
Publication Type: Abstract Only
Publication Acceptance Date: 4/15/2008
Publication Date: 6/10/2008
Citation: McCarty, G.W., Angier, J., Rice, C., Bialek, K. 2008. Impact of temporal and spatial variations in agrochemical fluxes within the Riparian Buffer on exports from a first order watershed [abstract]. American Water Resources Association Summer Specialty Conference. 2008 CDROM.
Technical Abstract: Both agricultural nitrogen and metolachlor ethane sulfonic acid (MESA), a prevalent metabolite of metolachlor, are primarily delivered to streams via groundwater flows. The ability of riparian ecosystems to remove agrochemicals from exfiltrating groundwater is a potentially important control on their export from first order catchments. Most riparian zone hydrologic models assume uniform groundwater flow through organic-rich soil under reducing conditions, leading to effective removal of groundwater nitrate prior to discharge into a stream. In the case of MESA, however, little is known about the ability of wetland processes to mitigate fluxes. We found that in the small first-order stream under study, baseflow generation was highly variable both spatially and temporally. This study reviews 5 years of data for agrochemical fluxes from the catchment. Average baseflow nitrate and MESA loads were greater in winter than summer, and higher during wet years versus dry years. Specific sections of the stream consistently received greater amounts of high nitrate and MESA containing groundwater than others. Areas within the riparian zone responsible for most of the agrochemicals exported from the watershed are termed “critical areas.” For example, over the study period most of the nitrogen exported during baseflow originated from a critical area comprising less than 10% of the total riparian zone land area. Although substantial amounts of nitrate were exported from the watershed, we found that wetland processes significantly reduced fluxes. In contrast, we found little evidence for corresponding flux reductions for MESA. This study supports the concept that targeted use of resources to address and improve mitigation function in critical areas within riparian buffers can permit cost effective improvement of ecosystem function for removal of nitrate but that mitigation of an organic pollutant like MESA may be more difficult.