Characteristics and significance of liquid effluent from woodchip corrals in Scotland

Woodchip corrals are increasingly used as cost effective means of over-wintering livestock in temperate regions but there is little information on their potential environmental impact. Four woodchip corrals of varying characteristics were instrumented to capture and quantify the flows reaching the base, where pollutant fluxes may move either vertically to groundwater, or laterally to a water course. Samples for chemical analysis were collected daily by auto-sampler. Samples for bacterial analysis were aseptically hand-sampled. Sampling frequency was increased during high flow events and sampling was conducted over a 12-month period. Microbiological samples were analysed for total coliform (TC), presumptive Escherichia coli (EC) and intestinal enterococci (IE). Leachate was also analysed for total phosphorus, phosphate, total nitrogen, ammonium, total oxidised nitrogen, nitrite and nitrate. Each corral had a recording rain gauge sited within 10 m of the corral surface. Mean total nitrogen concentration in leachate was 339.5 mg l(-1), of which ammoniacal-N comprised approximately 57%. Mean total phosphorus concentration was 94.7 mg l(-1). Geometric mean concentrations of TC, EC and IE were 95,461, 94,983 and 55,552 cfu100 ml(-1), respectively. Significant flows of leachate occurred at the base of the corrals on most days during the 1-year sampling period and flow rate increased with stocking density. Strong positive linear relationships were found between the concentrations of the nutrient parameters and discharge. Strong positive curvilinear relations were found between faecal indicator concentrations and discharge. Different relationships were observed in the stocked and unstocked corrals. The resulting fluxes are sufficient to give concern and to indicate that corral development is worthy of regulatory attention.