Mosley Luke M, Palmer David, Leyden Emily, Cook Freeman, Zammit Benjamin, Shand Paul, Baker Andrew, W Fitzpatrick Rob
Environment Protection Authority (South Australia), GPO Box 2607, Adelaide, SA 5001, Australia; CSIRO Land and Water, Private Bag No. 2, Glen Osmond, SA 5064, Australia; Acid Sulfate Soils Centre, The University of Adelaide, SA 5005, Australia.
Environment Protection Authority (South Australia), GPO Box 2607, Adelaide, SA 5001, Australia.
J Contam Hydrol. 2014 Jun;161:10-23. doi: 10.1016/j.jconhyd.2014.03.003. Epub 2014 Mar 31.
A severe drought from 2007 to 2010 resulted in the lowest river levels (1.75 m decline from average) in over 90 years of records at the end of the Murray-Darling Basin in South Australia. Due to the low river level and inability to apply irrigation, the groundwater depth on the adjacent agricultural flood plain also declined substantially (1-1.5 m) and the alluvial clay subsoils dried and cracked. Sulfidic material (pH>4, predominantly in the form of pyrite, FeS2) in these subsoils oxidised to form sulfuric material (pH<4) over an estimated 3300 ha on 13 floodplains. Much of the acidity in the deeply cracked contaminated soil layers was in available form (in pore water and on cation exchange sites), with some layers having retained acidity (iron oxyhydroxysulfate mineral jarosite). Post drought, the rapid raising of surface and ground water levels mobilised acidity in acid sulfate soil profiles to the floodplain drainage channels and this was transported back to the river via pumping. The drainage water exhibited low pH (2-5) with high soluble metal (Al, Co, Mn, Fe, Mn, Ni, and Zn) concentrations, in exceedance of guidelines for ecosystem protection. Irrigation increased the short-term transport of acidity, however loads were generally greater in the non-irrigation (winter) season when rainfall is highest (0.0026 tonnes acidity/ha/day) than in the irrigation (spring-summer) season (0.0013 tonnes acidity/ha/day). Measured reductions in groundwater acidity and increases in pH have been observed over time but severe acidification persisted in floodplain sediments and waters for over two years post-drought. Results from 2-dimensional modelling of the river-floodplain hydrological processes were consistent with field measurements during the drying phase and illustrated how the declining river levels led to floodplain acidification. A modelled management scenario demonstrated how river level stabilisation and limited irrigation could have prevented, or greatly lessened the severity of the acidification.
2007年至2010年的严重干旱导致南澳大利亚墨累-达令盆地末端90多年有记录以来的最低河流水位（比平均水平下降1.75米）。由于河流水位低且无法进行灌溉，相邻农业洪泛平原的地下水位也大幅下降（1 - 1.5米），冲积粘土层土壤干涸并出现裂缝。这些土壤中的硫化物质（pH>4，主要以黄铁矿FeS₂形式存在）在13个洪泛平原上约3300公顷的区域内氧化形成硫酸物质（pH<4）。深度开裂的受污染土壤层中的大部分酸度呈可利用形式（存在于孔隙水中和阳离子交换位点上），有些层保留了酸度（羟基硫酸铁矿物黄钾铁矾）。干旱过后，地表水和地下水位迅速上升，使酸性硫酸盐土壤剖面中的酸度进入洪泛平原排水渠道，并通过抽水被带回河流。排水水的pH值较低（2 - 5），可溶性金属（铝、钴、锰、铁、锰、镍和锌）浓度较高，超过了生态系统保护指南。灌溉增加了酸度的短期输送，然而，在降雨量最高的非灌溉（冬季）季节（0.0026吨酸度/公顷/天），负荷通常比灌溉（春夏季）季节（0.0013吨酸度/公顷/天）更大。随着时间的推移，已观察到地下水中酸度降低和pH值升高，但干旱过后两年多，洪泛平原沉积物和水体中仍持续存在严重酸化现象。河流 - 洪泛平原水文过程的二维模拟结果与干旱期的实地测量结果一致，并说明了河流水位下降如何导致洪泛平原酸化。一个模拟管理方案表明，稳定河流水位和有限灌溉如何能够预防或大大减轻酸化的严重程度。
