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Mosley L.M.,Water Quality Science
Earth-Science Reviews | Year: 2015

Droughts are increasing in frequency and severity in many regions of the world due to climate change. The meteorological drivers of drought often cause subsequent hydrological effects such as reduced catchment runoff, river flows and lake levels. Hydrological droughts may also result in significant changes in water quality. This review provides a synthesis of past observational research on the effects of drought on the water quality of freshwater systems (rivers, streams, lakes, reservoirs). Over the last 10-20. years there has been an increasing amount of studies on the water quality effects of drought, mostly in North America, Europe, and Australia. In general droughts, and the immediate recovery period, were found to have profound water quality effects. These effects were varied, depending on the characteristics of the water body and its catchment. Key drivers of water quality change were identified and integrated across different systems using quantitative analysis where possible. Water flow and volume decreases during drought typically led to increased salinity due to reduced dilution and concentration of mass. Temperature increases and enhanced stratification occurred during drought in some systems due to air temperature increases and longer hydraulic residence times. This also enhanced algal production, promoted toxic cyanobacterial blooms, and lowered dissolved oxygen concentrations. Nutrient, turbidity and algal levels also often increased in lake systems due to reduced flushing and enhanced productivity, and resuspension in some shallow lakes. In contrast, nutrients and turbidity often decreased during droughts in rivers and streams with no significant loading from point and agricultural non-point sources. This was due to disruption of catchment inputs and increased influence of internal processes (e.g. biological uptake of nutrients, denitrification, settling). Where point sources of pollution were present, water quality generally showed deterioration due to less dilution, particularly for nutrients. Storage and buildup of material and changed geochemistry (e.g. sulfide oxidation) in catchments during drought resulted in mobilisation of large post-drought flood loadings of constituents such as major ions, nutrients and carbon. In some cases this caused severe downstream water quality effects such as deoxygenation. Key areas for further research are process-level understanding of the key drivers of water quality change in catchments and receiving water bodies during drought, development of predictive models, and studying the resilience of systems to the predicted increase in frequency of drought and floods. The maintenance of long term water quality monitoring programmes is also critical. © 2013 Elsevier B.V.

Mosley L.M.,Water Quality Science | Mosley L.M.,University of Adelaide | Willson P.,Khan Research Laboratories | Hamilton B.,Khan Research Laboratories | And 2 more authors.
Environmental Science and Pollution Research | Year: 2015

We tested the capacity of biochar (made at 450 °C from a common reed species) to neutralise pH and remove metals in two acid drainage waters (pH 2.6 and 4.6) using column leaching and batch mixing experiments. In the column experiments, the acid drainage water was neutralised upon passage through the biochar with substantial increases (4–5 pH units) in the leachate pH. In the batch experiments, the leachate pH remained above 6.5 when the drainage:biochar ratio was less than approximately 700:1 (L acid drainage:kg biochar) and 20:1 for the pH 4.6 and pH 2.6 drainage waters, respectively. Dissolved metal concentrations were reduced by 89–98 % (Fe ≈ Al > Ni ≈ Zn > Mn) in the leachate from the biochar. A key mechanism of pH neutralisation appears to be solid carbonate dissolution as calcite (CaCO3) was identified (via X-ray diffraction) in the biochar prior to contact with acid drainage, and dissolved alkalinity and Ca was observed in the leachate. Proton and metal removal by cation exchange, direct binding to oxygen-containing functional groups, and metal oxide precipitation also appears important. Further evaluation of the treatment capacity of other biochars and field trials are warranted. © 2015, Springer-Verlag Berlin Heidelberg.

Yuan C.,University of Adelaide | Mosley L.M.,Water Quality Science | Mosley L.M.,University of Adelaide | Fitzpatrick R.,University of Adelaide | Marschner P.,University of Adelaide
Journal of Environmental Management | Year: 2015

Acid sulfate soils (ASS) with sulfuric material can be remediated through microbial sulfate reduction stimulated by adding organic matter (OM) and increasing the soil pH to >4.5, but the effectiveness of this treatment is influenced by soil properties. Two experiments were conducted using ASS with sulfuric material. In the first experiment with four ASS, OM (finely ground mature wheat straw) was added at 2-6% (w/w) and the pH adjusted to 5.5. After 36 weeks under flooded conditions, the concentration of reduced inorganic sulfur (RIS) and pore water pH were greater in all treatments with added OM than in the control without OM addition. The RIS concentration increased with OM addition rate. The increase in RIS concentration between 4% and 6% OM was significant but smaller than that between 2% and 4%, suggesting other factors limited sulfate reduction. In the second experiment, the effect of nitrate addition on sulfate reduction at different OM addition rates was investigated in one ASS. Organic matter was added at 2 and 4% and nitrate at 0, 100, and 200mg nitrate-N kg-1. After 2 weeks under flooded conditions, soil pH and the concentration of FeS measured as acid volatile sulfur (AVS) were lower with nitrate added at both OM addition rates. At a given nitrate addition rate, pH and AVS concentration were higher at 4% OM than at 2%. It can be concluded that sulfate reduction in ASS at pH 5.5 can be limited by low OM availability and high nitrate concentrations. Further, the inhibitory effect of nitrate can be overcome by high OM addition rates. © 2015 Elsevier Ltd.

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