Response of aquatic invertebrates to vegetation management and agriculture

Abstract

Wetland managers rely on a variety of vegetation management techniques to set back plant succession, enhance seed production, create hemi-marsh conditions, and reduce the coverage of invasive plants in wetlands. We evaluated the effects of vegetation management techniques (prescribed burning, cattle grazing, mowing, and disking) on aquatic invertebrate communities in seasonal wetlands in the Rainwater Basin Region of Nebraska, USA. Because many of these wetlands are embedded in an agricultural landscape, we also evaluated the effects of agriculture on aquatic invertebrates. We conducted the study in 24 wetlands during spring 2004 and 2005. In general, aquatic invertebrate richness and diversity were similar among wetlands subjected to different management regimes. However, richness and diversity were highest in grazed wetlands and lowest in disked wetlands. Regardless of the management regime, total benthic and nektonic invertebrate biomasses were higher in managed wetlands than unmanaged wetlands. In 2004, naidid oligochaete biomass was highest in farmed wetlands. Cattle grazing, mowing, and prescribed burning seemed to have the greatest influence on individual taxa; 12, eight, and seven of the taxa (out of 32) had higher biomasses in grazed, mowed, and burned wetlands, respectively. Within mowed wetlands, the biomasses of some taxa (Gyraulus, Lymnaea, and Physa) were lower in managed areas than unmanaged areas, emphasizing the need to leave some areas unmanipulated to provide cover. Because of high spatial and temporal variability in wetlands and aquatic invertebrate communities, the response of aquatic invertebrates to vegetation management techniques was not consistent and no management regime offered a particular advantage in enhancing aquatic invertebrate communities. However, managers should be aware that some type of physical manipulation of aquatic vegetation in wetlands is still warranted on a regular basis to reduce nuisance vegetation, enhance seed production, and create optimal habitat conditions for migratory waterfowl and other wetland-dependent birds.