Assessing effects of confined animal production systems on water quality, ecological integrity, and macroinvertebrates at small piedmont streams (Patagonia, Argentina)

Abstract

Breeding of livestock in confined areas has recently become an alternative of production for farmers in Northwest Patagonia. Strong concern about how these practices can alter health and integrity of streams exists and mitigation measures from livestock impact have been recently incorporated to the legislation. We examined changes in water quality, riparian integrity, habitat conditions, and macroinvertebrates community at three low order streams having different modalities of animal production management. The general design included visits at 11 sites (comprising references sites) in a bimonthly scheme. We assessed hydrological and physicochemical features including oxygen, conductivity, nutrients and total suspended solids. Epilithic chlorophyll and bacteria (total coliforms and E. coli) were also measured. Integrity of each site was assessed by two adapted indexes for Patagonian streams: riparian ecosystem quality (QBRp) and habitat condition (HA). A suite of 12 qualitative bioindicator measures based on aquatic macroinvertebrates were utilized at two flow contrasting periods. Compared to reference sites, intensive and semi-intensive practices produced low to moderate impact regarding to oxygen saturation, conductivity and nutrient levels, but strong alteration of the riparian ecosystem and of the in-stream habitat condition were detected. E. coli counting resulted in declining of water quality at both intensive and semi-intensive management, and exceeded the recommended critical value for recreational purposes. Plecoptera and Trichoptera richness significantly diminished at most impacted sites during low water period. In addition, several macroinvertebrate metrics displayed negative and significant responses to ammonia level increases, evidencing a possible toxicity effect. Our findings suggest that these emergent practices, which are rapidly expanding in a relatively undeveloped area, might have negative impacts. Mitigation measures for stream protection should be recommended to landowners through conservation programs.