James W. Cox

Sorption of dissolved organic matter in salt-affected soils: effect of salinity, sodicity and texture.

Loss of dissolved organic matter (DOM) from soils can have negative effects on soil fertility and water quality. It is known that sodicity increases DOM solubility, but the interactive effect of sodicity and salinity on DOM sorption and how this is affected by soil texture is not clear. We investigated the effect of salinity and sodicity on DOM sorption in soils with different clay contents. Four salt solutions with different EC and SAR were prepared using combinations of 1M NaCl and 1M CaCl(2) stock solutions. The soils differing in texture (4, 13, 24 and 40% clay, termed S-4, S-13, S-24 and S-40) were repeatedly leached with these solutions until the desired combination of EC and SAR (EC(1:5) 1 and 5dSm(-1) in combination with SAR <3 or >20) was reached. The sorption of DOC (derived from mature wheat straw) was more strongly affected by SAR than by EC. High SAR (>20) at EC1 significantly decreased sorption in all soils. However, at EC5, high SAR did not significantly reduce DOC sorption most likely because of the high electrolyte concentration of the soil solution. DOC sorption was greatest in S-24 (which had the highest CEC) at all concentrations of DOC added whereas DOC sorption did not differ greatly between S-40 and S-4 or S-13 (which had higher concentrations of Fe/Al than S-40). DOC sorption in salt-affected soil is more strongly controlled by CEC and Fe/Al concentration than by clay concentration per se except in sodic soils where DOC sorption is low due to the high sodium saturation of the exchange complex.

Off-site Transport of Pesticides in Mt. Lofty Ranges, South Australia, Australia: The Importance of Partitioning Processes

Local runoff from the catchments in the Mount Lofty Ranges watershed provides a major source (up to 60%) of drinking water for the city of Adelaide, South Australia, Australia. In this study two major land uses (apples and cherries) in the Mount Lofty Ranges were monitored for off-site transport of pesticides over approximately 30 months. The pathways of off-site transport (soluble or colloidal) of pesticides were also monitored. There were several pesticides detected in surface drainage water from the apples site but two pesticides (chlorpyrifos and fenarimol) were of particular concern. The average chlorpyrifos concentrations were 0.12 and 0.15 µg/L in 2007 and 2009, respectively, which are more than ten times the Australian environmental guideline value, suggesting potential deleterious effects on aquatic organisms downstream of the apple site. The form in which chlorpyrifos was transported off-site varied throughout the season but over time a greater proportion moved in the soluble (<1.2 µm) phase.

Characterization of the transport of sediment and nutrients in the Mt Lofty Ranges watershed, South Australia

Local runoff from the catchments in the Mount Lofty Ranges watershed provides a major source (up to 60%) of drinking water for Adelaide, South Australia. In this study major land uses in the Mount Lofty Ranges were monitored for off-site transport of sediment and nutrients over approximately 40 months. Runoff from three case-study sites (apple, cherry and grape cultivation) was monitored using automatic samplers for collection of water samples on a flow-weighted basis. Selected nutrients and the total suspended sediment (TSS) were measured in unfiltered and filtered water samples to provide information about pollutant characterization and the mode of off-site transport. Flow meters were installed at each site to measure runoff and enabled concentration loads to be calculated.