Remediation of water quality and macroinvertebrate communities in an urban artificial lake affected by acid sulphate soils

Worldwide human-induced acidification and the commonly associated metal-metalloid toxicity is one of the top issues affecting inland waterbodies (e. g., DENT & PoNs 1995). Ihree key processes are responsible for the acidification: acid rain, acid mine drainage (AMD), and exposure of acid sulphate soils. Reduced forms of sulphate are oxidised to produce sulphuric acid in all processes, and the resulting low pH mobilises metals and metalloids. Ihe extent and significance of acid sulphate soils are only now starting to be recognised in Australia (SAMMUT & LINES-KELLY 2000, RusSELL & HELMKE 2002), and particularly in Westem Australia (WA; SOMMER & HORWITZ 2001, APPLEYARD et al. 2004, 2006). In Perth (state capital of WA), the appearance of a number of localised acid sulphate soil issues in the City of Stirling, around canal developments along the Peel Harvey estuary and in Lake Jandabup have largely caught govemment agencies by surprise. Although acid sulphate soil issues associated with developments around estuaries are relatively common in Australia (SAMMUT et al. 1995, 1996), the acidification o f a large conservation status lake north of Perth following a drying event highlighted risks associated with drought-induced acidification in the State. Perth has experienced a trend of declining rainfall since the 1970s, coupled with increasing demand for scheme water that cannot be met through dams, and has seen substantive use of groundwater resources ( domestically for watering gardens, drinking via scheme water, and agriculture ). Declining groundwater tables expose potential acid sulphate soils to oxidation, a problem compounded by urban development, which is also dewatering areas and excavating potential acid sulphate soils in areas where oxidation can occur. Ihese acid sulphate soil issues have been initially presented as largely contamination of groundwater, which is then expressed in groundwaterdependant wetlands, in drains, or in groundwater wells used to water gardens. Ihis latter use is of particular concem because in many areas the acidity is generated from arsenopyrites, exposing residents to arsenic through consumption of home-grown food crops (HINWOOD et al. 2006). A number oftechniques have been deve1oped to remediate anthropogenic acidification, AMD in particular (see McCULLOUGH 2007). Many AMD treatment technologies are now starting to be transferred to acid sulphate soil issues, including water management approaches to prevent further oxidation, neutralising technologies (typically requiring active management), and "passive remediation" technologies that require limited maintenance. Nevertheless, the nature of these technologies has generally seen them applied in agricultural rather than urban settings. Perth is situated on the Swan Coastal Plain (SCP), which consists o f a series of sand dune systems o f varying ages running parallel to the coastline. Ihis situation poses some unusual problems for acidification problems because frequently groundwater rather than surface water is contaminated, and groundwater is not suited to most of the standard acid sulphate soil remediation techniques. W e reported the impact of discharges from a low-cost pilot treatment system for treating acid sulphate soil caused acidification in an urban area, using a range o f technologies commonly used to treat AMD. Ihe impact of treated waters on water quality and macroinvertebrate communities were used to assess the success o f the system.