Considerations for assessments of wadable drainage systems in the agriculturally dominated deltas of Arkansas and Mississippi.

The watershed approach, currently used to assess regional streams in the United States, emphasizes least-disturbed reference conditions. Consideration of extensive wadable drainage systems found in Arkansas and Mississippi deltas challenges concepts of disturbance within a landscape of historic agricultural land use. Seventeen wadable drainage ditch sites in Arkansas and Mississippi deltas were characterized using water quality parameters and rapid bioassessment protocols. In all, 19 fish and 105 macroinvertebrate taxa were identified. Macroinvertebrate assemblages were dominated by coleopteran, dipteran, and hemipteran taxa at most drainage sites. Predominance of mobile, early colonists in ditches limits applicability of some metrics for assessment of stream integrity beyond prevalent conditions of ephemeral water quantity and habitat maintenance. This study provides evidence of considerable variability of physical characteristics, water quality, and fish and invertebrate metrics in wadable drainage systems. It indicates a disparity in usefulness of the watershed approach, emphasizing least-disturbed reference conditions, in assessing ecological integrity for a region with ditches as dominant landscape features.

Evaluated fate and effects of atrazine and lambda-cyhalothrin in vegetated and unvegetated microcosms.

Contaminants such as nutrients, metals, and pesticides can interact with constructed wetlands and existing drainage ditches used as agricultural best-management practices. Our research has shown that the presence of macrophytes and a hydrologic regime aid in the transfer and transformation of pesticides associated with agricultural runoff. This study consisted of application of both atrazine (triazine herbicide) and lambda-cyhalothrin (pyrethroid insecticide) to vegetated and unvegetated microcosms in order to measure the fate and effects of pesticides applied at suggested field application rates. Exposures focused on monocultures of Ludwigia peploides (water primrose) and Juncus effusus (soft rush). Pesticide sorption was evident through concentrations of atrazine and lambda-cyhalothrin in plant tissue as high as 2461.4 and 86.50 microg/kg, respectively. Toxicity was measured in water from unvegetated microcosms for 28 days and in Chironomus tentans (midge larvae) exposed to sediment collected from 3 h to 56 days in microcosms receiving the pesticide combination. The comparative survival of test organisms in this study suggests that effective mitigation of pesticides from runoff can depend on the macrophyte contact and vegetative attributes associated with ditches.