Restored oxbow wetlands within an agricultural landscape: using physical and biological characteristics to evaluate impacts of tile drainage input

Abstract

Abstract Oxbow wetlands have been restored in the Midwestern United States to sequester sediment and nutrients originating from agricultural activities and to provide habitat for wetland-dependent species. Intensive agriculture may have adverse impacts on oxbow functions, especially if wetlands receive water inputs from subsurface drainage systems (e.g., tile drainage). To explore the influence of tile drainage on oxbow wetland ecology, we quantified relationships between physical and biotic variables in 12 Iowa, USA oxbows over a two-year period. Six oxbows received direct water inputs from tile drainage (multipurpose oxbows), whereas remaining sites did not (non-tiled oxbows). In each oxbow, we measured physical variables and documented taxonomic composition, diversity, and abundance of macrophytes, macroinvertebrates, and fishes. Although water temperature was lower in multipurpose oxbows, values for remaining physical variables were similar across sites. No significant difference was detected for any biotic variable across oxbow type. Across field seasons, 44 invertebrate taxa were observed in both oxbow types with an average richness of 18.6 in non-tiled oxbows and 17.5 in tile-fed oxbows. We sampled 35 fish species, with an average richness of 8.2 in non-tiled oxbows and 11.4 in multipurpose oxbows. A total of 2682 Topeka shiner were found in both non-tiled and multipurpose oxbows. Non-metric multidimensional scaling revealed that potential physical determinants of macrophyte, invertebrate, and fish abundance were unrelated to tile drainage. Our results suggest that tile drainage has negligible ecological impact on multipurpose oxbows in agricultural landscapes and does not cause physical or biological characteristics to differ significantly between oxbow types.