Water quality of gully drainage from texture-contrast soils in the Adelaide Hills in low rainfall years

Abstract

The volume and quality of drainage water in a gully cutting through a series of waterlogged, saline, sodic, and sulfidic Xeralfs in the Adelaide Hills, South Australia, was studied over 3 years. This was done to gain a better perspective of the relative quantities of contaminants being exported from agricultural catchments in low rainfall agricultural environments. It was found that in low rainfall years, when little overland flow occurs and gully flow is predominantly groundwater discharge and throughflow, loads in the drainage gully were up to 41 kg/ha.year of sodium and 2 kg/ha.year of sulfur. Losses of sulfur, magnesium, and calcium followed a similar trend to sodium losses and could be predicted with significant accuracy. The losses of phosphorus (5–7 g/ha.year) and nitrate (<2 g/ha.year) were less predictable. Phosphorus concentrations were of environmental concern each year whereas nitrate concentrations were only above environmental guidelines in the driest year. All phosphorus in the gully drainage was transported in the dissolved form. Dissolved organic carbon concentrations were usually >26 mg/L and will be costly to treat if used for public water supply.