A review of contaminant losses to water from pastoral hill lands and mitigation options

Abstract

Pastoral hill lands deliver a range of contaminants to receiving environments that are of concern to the wider sector stakeholder community: principally sediment, phosphorus, nitrogen and faecal microorganisms. Thermal energy may also be considered a contaminant. Pastoral waterways generally have higher concentrations of suspended sediments, nutrients, faecal micro-organisms, and water temperature relative to forested waterways. These effects can be quantitatively linked to animal stocking rates and management. The large variation in the micro-climates, parent materials, soil types and vegetation resources inherent in hill country is the major driver of spatial and temporal dynamics of contaminant losses. This variation is modified by animal behaviour and physiology. Stores of contaminants in surface or sub-surface flow paths create important temporal lags resulting from land use and management change. The concept of critical source areas has become a key focus for the development of mitigation options. A wide range of biophysical options are now available, covering multiple scales and levels of cost-benefit. The use of farm planning tools is critical in balancing the implementation of mitigations with farm system objectives to improve whole-system sustainability. More research is needed on long-term impacts, given spatial and temporal variation in drivers and known spatial and temporal lag effects. There will be ongoing demand for mitigations that have been developed through co-innovation processes. Keywords: environmental mitigations, erosion, hill country, nutrient loss, pastoral, sediment export