Impacts of domestic grazing animals on the water quality of Lake Hume: a desktop analysis

"May 2006".

Project Number: A study of the effects of grazing on water quality in Lake Hume - M/BUS/103.

MDFRC item.

The purpose of this study was to undertake a desktop assessment of the risks to water quality both within and downstream of Lake Hume of continuing grazing on the bed of the lake, around the immediate foreshore of the lake and in the lake’s catchment. Risks were assessed using data from studies on Lake Hume where it was available. In the absence of local studies, potential impacts were estimated using the international literature. Potential risks of grazing that were identified include increased concentrations of endocrine disrupting chemicals, pathogens, sediments loads and nutrients entering into the lake and changes to soil health and vegetation in the surrounding catchment. - Accurate number of stock using the lake bed and foreshore need to be determined. - Endocrine disrupting chemicals from livestock pose little risk to water quality in Lake Hume because of their rapid rates of degradation. - Although faecal contamination in the lake (determined from measured faecal coliform levels) is often low, there is the potential for pathogen contamination from livestock grazing on the lake, its foreshore and catchment. We strongly recommended that a detailed study be undertaken in Lake Hume to determine the source, fate and virulence of pathogens (particularly Cryptosporidium oocysts) derived from livestock faecal matter. A conceptualized framework for risk assessment and pathogen monitoring framework in reservoirs has been discussed in Brookes et al. (2004). - Soil acidification in the upper catchment may pose a long-term risk to water quality in Lake Hume. We suggest that Goulburn-Murray Water consider partnering with other natural resource management agencies to examine the link between soil health and water quality and explore possible strategies for improving soil condition. - Grazing of the lake bed and foreshore probably contributes only a small fraction of the sediment and nutrient loads to the lake – the majority come from the larger catchment. - Grazing has the potential to be an effective method for weed control on the lake bed and surrounding foreshore.