NITROGEN LOSSES FROM A DOMESTIC SEPTIC-TANK SYSTEM ON THE DARLING PLATEAU IN WESTERN-AUSTRALIA

Movement in groundwater of nitrogen, leaching from a domestic septic tank system, was studied in an area adjacent to a stream on the Darling Plateau in the Shire of Mundaring near Perth in Western Australia. Losses of nitrogen in soil were determined by adding bromide to the septic tank and monitoring the decrease in the ratio of nitrogen to bromide in groundwater, downgradient of the leach drain of the septic tank. At least 80% of inorganic nitrogen leaching into the soil appears to be lost within a distance of 10 m from the leach drain. Published work on changes in N-15/N-14 isotope ratios of nitrate in sandy aquifers, affected by domestic septic tank systems, seems to indicate that losses of nitrogen are less at higher latitudes.