Setting Restoration Goals for Restoring Pit Lakes as Aquatic Ecosystems – A Case Study from Southwest Australia

摘要

Pit lakes may form when open cut mining leaves a pit void that then fi lls with ground and surfacernwaters. This often replaces terrestrial ecosystems that existed prior to mining with an aquaticrnecosystem, affording an opportunity to improve regional aquatic biodiversity values through targetedrnaquatic restoration (McCullough and van Etten, 2011). Restoration theory provides guidance whenrnrestoring disturbed systems towards landscapes that are of regional value and relevance. But how dornwe identify a restoration target for a novel aquatic habitat that only exists in the new post-miningrnlandscape? This paper presents a process of fi rst identifying and then surveying local representativernaquatic systems, to provide a direction for pit lake restoration efforts and achievement criteria for pitrnlake relinquishment, using a case study from a sand mining operation amongst wetlands in southwesternrnAustralia.rnThe company mines silica sands following mechanical removal of topsoil and then extraction ofrnthe ore from below the watertable by dredging. Assessment of wetland and riparian vegetation wasrnachieved through the establishment and measurement of temporary monitoring transects acrossrnfi ve natural wetlands in the Kemerton area. Several more regional wetlands were also visited andrnobservations made to supplement and validate these data.rnDistinct vegetation zonation was found across each wetland, although typically wetland basinsrnwere unvegetated or fi lled with younger woody plants with patchy distributions. Fringing riparianrnvegetation consisted of few species (commonly the paperbark Melaleuca rhaphiophylla and the sedgernLepidosperma longitudinale), but community composition and structure were variable betweenrnwetlands. The pattern of vegetation seen across natural wetlands was best explained by topographyrnand soil chemistry, with low lying wetland areas more likely to experience regular fl ooding andrnaccumulate organic matter and nutrients.rnIn conclusion, where they are available, regional natural waterbodies may constitute the best validrnrestoration goal. Nevertheless, the goal may need to consist of a range of closure design opportunities,rnrather than a single target.