Geomorphology, soils and landuse in the Swan Coastal Plain in relation to contaminant leaching

摘要

A detailed study of the soils of the southern part of Gnangara Mound in the Swan Coastal Plain was carried out to determine their soil-water characteristics and their leaching capacity to nutrient and pesticides. Physical. chemical and hydraulic characteristics of the topsoil (0-15 cm) and the subsoil (40-50 cm) were measured at 21 sites representing the major soils under the different landuses in the area. The results show that Bassendean Sands have higher coarse sand particles and consequently, higher hydraulic conductivity than Spearwood Sands. The Bassendean Dunes generally have low relief: minor variations in topography translate into variable depths to watertable, which are the basis for division into soil mapping units. For example the Gavin soil has higher organic carbon content than all other soils sampled. The Spearwood Dunes are divided mainly on the depth of soil over the limestone substrate and the incidence of karst features. The Spearwood and Jandakot soils have lower coarse sand and lower carbon content, while the Karrakatta soils have the least amount of organic carbon. Detailed soil maps were compared with GIS-produced hydrogeomorphic maps. The results show that the distribution of HGUs in the catchment is controlled by the geological formations on which they were developed. The results also show that the hydrogeomorphic maps can be used in the absence of detailed soil maps to classify the catchment into areas that have similar soil characteristics. Filtering capacity of the soils is dependant on organic material, clays and other minerals. Based on these criteria, Spearwood Sands have the highest filtering capacity, followed by Bassendean and Quindalup.