Effects of livestock grazing on aquatic macroinvertebrates in southern interior wetlands of British Columbia, Canada

Grasslands in the southern interior of British Columbia are extensively grazed by free ranging livestock. Water sources are limited in these grassland landscapes and wetlands are commonly used by livestock for drinking water and forage. My study examined the impacts of livestock disturbance on the abundance, biomass and community composition of aquatic macroinvertebrates residing in these wetlands. Aquatic macroinvertebrates were collected in the spring and summer of 2008 from 17 wetlands with a range of grazing disturbance. Three sweep and core samples were collected from each wetland and grazing intensity was determined by the amount of bare ground at each site. Spring sweep total abundance (r2=0.464, p=0.003) and biomass (r2=0.728, p<0.001) were negatively correlated with livestock disturbance as were spring abundance and biomass of zygopterans (r2=0.593, p<0.001; adj. r2=0.513, p=0.001). Spring sweep family richness (r2=0.462, p=0.003), Shannon’s family diversity (r2=0.569, p<0.001) and Simpson’s family diversity (r2=0.385, p=0.008) also decreased as livestock disturbance increased. Resource managers should consider Zygoptera (damselflies) as a potential indicator of wetland water quality and livestock impact. Range plans should adopt only light grazing in wetland areas and limit livestock access to sustain the biodiversity and productivity of these valuable aquatic ecosystems.