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 t ank system, was studied in an area adjacent to a stream on the Darling Plateau in the Shire of Mundaring near Perth in Western Australia. Lo sses of nitrogen in soil were determined by adding bromide to the sept ic tank and monitoring the decrease in the ratio of nitrogen to bromid e in groundwater, downgradient of the leach drain of the septic tank. At least 80% of inorganic nitrogen leaching into the soil appears to b e 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, a ffected by domestic septic tank systems, seems to indicate that losses of nitrogen are less at higher latitudes.