Water quality and the effects of different pastoral animals

Water quality in agricultural catchments tends to be worse than in forested (native or exotic) catchments. Reduced water quality tends to have significant effects on the ecosystem of streams, including increased nuisance algal and plant growth (eutrophication) associated with nutrient input, toxicity to aquatic life due to ammonia, faecal contamination, and loss of habitat or spawning areas due to sedimentation. An analysis of catchment contaminant loads from 38 studies conducted since 1975 was carried out to determine if there were differences in loads between land uses under different livestock (dairy, sheep, sheep-and-beef (mixed), deer) and non-agricultural. Significantly more N was lost from dairy catchments than catchments with other land uses, and more sediment lost from deer catchments than other catchments. Median loads of N were greatest from dairy > deer = mixed > sheep > non-agricultural; while loads of P were greatest for deer = mixed > dairy > sheep > non-agricultural; and for sediment, deer > sheep > mixed > dairy > non-agricultural. This information should be considered in catchments of mixed stock types to target the most pertinent mitigation practice for improving water quality. For example, if a stream in a catchment with deer and sheep present is choked with algae and limited by inputs of P, mitigation should focus on deer rather than sheep.