Submitted to: Archives of Environmental Contamination and Toxicology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/21/2008
Publication Date: 9/18/2008
Citation: Stephens, W.W., Moore, M.T., Farris, J.L., Bouldin, J.L., Cooper, C.M. 2008. Considerations for assessments of wadeable drainage systems in the agriculturally dominated deltas of arkansas and mississippi. Archives of Environmental Contamination and Toxicology. 55:432-441. Interpretive Summary: Drainage ditches are a significant component of the production agriculture landscape, carrying runoff water directly into rivers, streams, and lakes. Little research has examined the ecological aspects of these systems in regard to water quality and diversity of organisms present. The current study examined and compared drainage ditches of similar size in northeast Arkansas, southeast Arkansas, and west central Mississippi for water quality and organism diversity. Results indicated more potential toxic conditions in southeast Arkansas sites compared to other sites. Additionally, currently used approaches for determining the ecological health of rivers, streams, and lakes do not represent the unique ecosystems of drainage ditches. This study provides baseline data for structure and function of the water quality and ecological diversity found in drainage ditches in both the Arkansas and Mississippi deltas.
Technical Abstract: The watershed approach, currently used to assess regional streams, emphasizes least-disturbed reference conditions. Consideration of the extensive drainage systems found in the deltas of Arkansas and Mississippi at times challenges such concepts of disturbance among a landscape of historic agricultural land-use. During the summer of 2001, 17 drainage ditch sites in Arkansas and Mississippi deltas were characterized using a suite of 14 water quality parameters and Rapid Bioassessment Protocols (RBPs). Additional biological impairment testing was conducted on aqueous samples to further characterize ambient water resources. Significant toxicity was measured at three Arkansas and one Mississippi drainage sites compared to controls. Within the 17 ditch sites sampled, 19 fish and 105 macroinvertebrate taxa were identified. Macroinvertebrate taxa richness was reduced in sites from southeast Arkansas compared to northeast Arkansas. While a metric for Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa could be used to indicate relative condition of these systems, macroinvertebrate assemblages were still dominated by Coleopteran, Dipteran, and Hemipteran taxa at most drainage sites. The dominance of such mobile, early colonists in ditches limits applicability of some metrics for assessment of stream integrity beyond the prevalent conditions of ephemeral water quantity and habitat maintenance related to drainage use. This study of delta ditch conditions provides evidence of considerable variability of physical characteristics, water quality, and fish and invertebrate metrics. Furthermore, it indicates a disparity in the usefulness of the current watershed approach in assessing the ecological integrity for a region with ditches as a dominant landscape feature.