Water chemistry and nutrient release during the resuspension of FeS-rich sediments in a eutrophic estuarine system

The objective of this study was to investigate the impact of resuspending FeS-rich benthic sediment on estuarine water chemistry. To address this objective, we conducted (1) a series of laboratory-based sediment resuspension experiments and (2) also monitored changes in surface water composition during field-based sediment resuspension events that were caused by dredging activities in the Peel-Harvey Estuary, Western Australia. Our laboratory resuspension experiments showed that the resuspension of FeS-rich sediments rapidly deoxygenated estuarine water. In contrast, dredging activities in the field did not noticeably lower O-2 concentrations in adjacent surface water. Additionally, while FeS oxidation in the laboratory resuspensions caused measurable decreases in pH, the field pH was unaffected by the dredging event and dissolved trace metal concentrations remained very low throughout the monitoring period. Dissolved ammonium (NH4+) and inorganic phosphorus (PO4-P) were released into the water column during the resuspension of sediments in both the field and laboratory. Following its initial release, PO4-P was rapidly removed from solution in the laboratory-based (<1 h) and field-based (<100 m from sediment disposal point) investigations. In comparison to PO4-P, NH4+ release was observed to be more prolonged over the 2-week period of the laboratory resuspension experiments. However, our field-based observations revealed that elevated NH4+ concentrations were localised to <100 m from the sediment disposal point. This study demonstrates that alongside the emphasis on acidification, deoxygenation and metal release during FeS resuspension, it is important to consider the possibility of nutrient release from disturbed sediments in eutrophic estuaries. (C) 2012 Elsevier B.V. All rights reserved.