EIGHTH INTERNATIONAL HEAVY MINERALS CONFERENCE / PERTH, WA, 5 - 6 OCTOBER 2011 339 INTRODUCTION Open-cut/cast mining has left a legacy of many thousands of mining pit voids worldwide (Castendyk and Eary, 2009) and across Australia (Kumar, McCullough and Lund, 2009). Restoration of mining landform terrestrial habitats has now become a well-researched practice that borrows from the disciplines of ecology and engineering to rehabilitate landscapes left completely altered, often scaling across entire bioregions. However, mining restoration typically ceases at the edge of these pit voids (McCullough et al, 2009; van Etten, 2011). Where backfill of pits is not an economic or feasible option and the pit extends into the watertable, then pit lakes with aquatic ecosystems may be desirable beneficial end uses (McCullough and Lund, 2006). Planning for such end uses is best made early in the life-of-mine to maximise opportunities and to minimise restoration costs (McCullough, 2011). 1. Senior Lecturer, Terrestrial Ecology Research Group, 270 Joondalup Drive, Perth WA 6027. Email: e.van_etten@ecu.edu.au 2. MAusIMM, Principal Environmental Scientist, Golder Associates, West Perth WA 6005. Email: cmccullough@golder.com.au 3. Senior Research Fellow, Mine Water and Environment Research Centre (MiWER), 270 Joondalup Drive, Perth WA 6027. Email: c.mccullough@ecu.edu.au 4. Associate Professor, Mine Water and Environment Research Centre (MiWER), 270 Joondalup Drive, Perth WA 6027. Email: m.lund@ecu.edu.au Setting Restoration Goals for Restoring Pit Lakes as Aquatic Ecosystems – A Case Study from Southwest Australia E J B van Etten 1 , C D McCullough 2,3 and M A Lund 4 ABSTRACT Pit lakes may form when open cut mining leaves a pit void that then fills with ground and surface waters. This often replaces terrestrial ecosystems that existed prior to mining with an aquatic ecosystem, affording an opportunity to improve regional aquatic biodiversity values through targeted aquatic restoration (McCullough and van Etten, 2011). Restoration theory provides guidance when restoring disturbed systems towards landscapes that are of regional value and relevance. But how do we identify a restoration target for a novel aquatic habitat that only exists in the new post-mining landscape? This paper presents a process of first identifying and then surveying local representative aquatic systems, to provide a direction for pit lake restoration efforts and achievement criteria for pit lake relinquishment, using a case study from a sand mining operation amongst wetlands in south- western Australia. The company mines silica sands following mechanical removal of topsoil and then extraction of the ore from below the watertable by dredging. Assessment of wetland and riparian vegetation was achieved through the establishment and measurement of temporary monitoring transects across five natural wetlands in the Kemerton area. Several more regional wetlands were also visited and observations made to supplement and validate these data. Distinct vegetation zonation was found across each wetland, although typically wetland basins were unvegetated or filled with younger woody plants with patchy distributions. Fringing riparian vegetation consisted of few species (commonly the paperbark Melaleuca rhaphiophylla and the sedge Lepidosperma longitudinale), but community composition and structure were variable between wetlands. The pattern of vegetation seen across natural wetlands was best explained by topography and soil chemistry, with low lying wetland areas more likely to experience regular flooding and accumulate organic matter and nutrients. In conclusion, where they are available, regional natural waterbodies may constitute the best valid restoration goal. Nevertheless, the goal may need to consist of a range of closure design opportunities, rather than a single target.