Nutrient and gilvin levels in waters of coastal-plain wetlands in an agricultural area of Western Australia

Abstract

The Peel-Harvey catchment lies on a sandy coastal plain, largely cleared for agriculture, and drains into a eutrophic estuarine system. Sixty-eight wetlands in the catchment had total phosphorus concentrations of 0.4-7.8 mg I^-1, the high values being atrributed to agricultural activity. Conductivity was 150-8770 µS cm^-1, pH 4.1-9.3. Waters contained high concentrations of gilvin, up to 262 g440 m^-1 with a mean ratio of 6.2. Particulate material contributed little to light absorption at lower wavelengths (400-450 nm) but governed absorbance at 600-700 nm. Wetlands with the largest concen- trations of gilvin were located in the grey Bassendean sands, leachates from which had gilvin levels up to 748 g440 m^-1. NO phytoplankton blooms were observed, and it is suggested that high gilvin levels and the consequent reduction in light penetration are important in maintaining low phytoplankton biomass in these lakes.