PARENT SESSION
Oral Session #88: Wetland Ecology.
Presiding: K. Ewel
Thursday, August 8. 1:00 PM to 3:45 PM. Gila Meeting Room, TCC.
Spatial scale in agricultural wetlands: effects of land and pesticide use on multiple biological parameters.
Threlkeld, Stephen*,1, Britson, Carol1, Robinson, Hal2, Easson, Greg2, 1 Department of Biology, University, MS2 Department of Geology and Geological Engineering, University, MS
ABSTRACT- Our research group has been examining the effects of spatial scale on biological responses to natural and anthropogenic stressors through a field sampling program conducted at randomly selected sites in the Little Tallahatchie River Basin in northern Mississippi. We developed a Geographic Information Systems (GIS) database for the basin that incorporated physical features, land use practices, and potential pesticide loads for approximately 8700 wetlands. Land use practices were characterized from crop data (in acres) obtained through county Farm Services Agency (FSA) offices for all crops planted in 1998 and 1999. Potential load for four pesticides (chlorpyrifos, atrazine, methyl parathion, and MSMA) was estimated by calculating percent of maximum use in the basin for each pesticide. These steps allowed us to objectively identify areas where multiple pesticides were used, and expression of biological effects to multiple, interacting stressors was possible. Landowners of 103 agricultural (pesticide-impacted) and 408 non-agricultural ponds (distributed across seven major geologic units in the study basin) that met selection criteria were contacted requesting access for sampling. Of the ponds for which access was granted, 41 agricultural ponds and 103 non-agricultural ponds were determined to be suitable for sampling, which took place from March to August 2001. Across the study basin, endpoints (from multiple levels of biological organization) measured from agricultural site samples exhibited extremes, largely unanticipated, in basic water quality parameters, physiological measures such as genetic stress in fish, and community structure in vertebrates and invertebrates. On the local scale (i.e., pond to pond), these extremes were not consistently associated with the use of a single pesticide or specific mixture. These results indicate that when measuring a biological response to single or multiple stressors across several spatial scales, the conclusions must be referenced to the entire suite of stressors present across all scales examined.
KEY WORDS: agrichemical, multiple stressors