Octanol partition coefficients for wetland humus

Many of the wetlands on the Swan Coastal Plain, Western Australia are nutrient-rich and subject to blooms of blue-green algae. Some of these wetlands, however, are dystrophic and are less likely to experience algal blooms possibly because of high gilvin levels. Gilvin (yellow colour determined by absorbance at 440 nm) levels and the octanol/water partition coefficient (Khow) for humic stained waters from eleven wetlands and the leachate from the leaves of two Eucalyptus tree species and Bassendean soil, all major components of the Swan Coastal Plain, Western Australia were determined. Gilvin levels in the wetlands were high (20–58 m−1) while gilvin in leachate from Eucalyptus marginata leaves soaked for 30 days was 349 m−1 and gilvin in Bassendean soil leachate was 610 m−1. Gilvin from E. calophylla leaves soaked for 30 days was markedly less (67 m−1). Three samples, the leachate from the leaves of E. calophylla, the leachate from the top 50 cm of Bassendean soil and water from one wetland (Gingin) showed ecologically significant Khow values ranging from 1.68 to 3.59 at pH 4. These Khowʹs derived are similar to many organic chemicals in use today including algicides and herbicides. It is suggested that inhibition of algal growth and production will occur in the humic stained waters of Gingin wetland. A probable source of this humus rich material is decomposing Eucalyptus leaves and other material in the upper horizon of Bassendean soils of the wetland catchment.