Clinton Mccullough

Vulnerability of organic acid tolerant wetland biota to the effects of inorganic acidification.

Inland waterbodies are often naturally acidic but are these ecosystems pre-adapted to inorganic acidification e.g., by acid sulfate soils (ASS)? We conducted a controlled mesocosm experiment with inorganically acidified wetland water and wetland sediment replicates to pH 3 from a naturally acidic (pH 3.9, conductivity=74microScm(-1)) wetland in south-western Australia. Following acidification, dissolved organic carbon and nitrogen declined, and chlorophyll a dropped to zero. Inorganic acidification mobilised metals from sediment sods with increased water concentrations of Cu, Fe, Mn, Ca, Mg and Al. Acidification showed no significant effect on diatom assemblage. Nonetheless, greatly reduced abundance and diversity of grazing zooplankton was observed. Macroinvertebrates generally showed abundance decreases, although filterer-collector taxa increased. Decreased primary production reduced functional diversity and consumer biomasses. These results suggest likely impact to ecosystem functioning of low pH, weakly-buffered and stained wetlands if exposed to inorganic acidification.

Upper and lower concentration thresholds for bioremediation of acid mine drainage using bulk organic substrates

Acidic pit lakes may form in open cut mine voids that extend below the groundwater table and fill from surface and groundwater in-flows at the cessation of mining. Pit lake water quality may often be affected by acid mine drainage (AMD). Among the many remediation technologies available, sulphate reducing bacteria (SRB) based bioremediation using organic wastes appears to have significant potential towards ameliorating AMD effects of elevated acidity, metal and sulphate concentrations. A microcosm experiment was carried out under controlled conditions to assess the effect of different substrate concentrations of sewage sludge on AMD bioremediation efficiency. Experimental microcosms were made of 300 mm long and 100 mm wide acrylic cores, with a total volume of 1.8 L. Four different concentrations of sewage sludge (ranging 30–120 g/L) were tested. As the sewage sludge concentration increased the bioremediation efficiency also increased reflecting the higher organic carbon concentrations. Sewage sludge contributed alkaline materials that directly neutralised the AMD in proportion to the quantity added and therefore plays a primary role in stimulating SRB bioremediation. The lowest concentration of sewage sludge (30 g/L) tested proved to be inadequate for effective SRB bioremediation. However, there were no measurable beneficial effects on SRB bioremediation efficiency when sewage sludge was added at concentration >60 g/L.

Importance of topography and topsoil selection and storage in successfully rehabilitating post-closure sand mines featuring pit lakes

Abstract Rehabilitation at a silica sand mine on the Swan Coastal Plain of Western Australia, where the post-mine landscape consists of small pit lakes (dredge ponds) with surrounding battered slopes, and where a range of ecological restoration techniques have been applied, was monitored for several years to gauge success or otherwise of these techniques. Results clearly showed the benefits of using fresh topsoil for restoration over topsoil that has been stockpiled for several years. Most topsoil used in restoration was from seasonal wetlands and consequently restoration was most successful in the riparian zone from the edge of pit lakes to ∼2 m vertically above the water table. Rehabilitated areas above this level remained poor in plant species and cover with remedial actions largely unsuccessful. We believe that matching topsoil to site and development of topographic profiles similar to natural wetlands of the region are the keys to optimising rehabilitation success around pit lakes formed by sand mining in areas with shallow groundwater.

Setting goals and choosing appropriate reference sites for restoring mine pit lakes as aquatic ecosystems: case study from south west Australia

Abstract Pit lakes may form when open cut mining leaves a pit void behind that fills with ground and surface water. Often replacing terrestrial ecosystems that existed prior to mining, the pit lake may offer an alternative ecosystem with aquatic biodiversity values that can be realised through planned restoration. Restoration theory and mine closure regulatory requirements guides us toward restoring disturbed systems towards landscapes that are of regional value and relevance. However, how do we identify a restoration target for a novel aquatic habitat that did not exist prior to the new post-mining landscape? This paper presents a process of first identifying and then surveying local analogue aquatic systems to provide a direction for pit lake restoration efforts and achievement criteria for pit lake relinquishment. We illustrate this process using a case study from a sand mining operation located 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 water table by dredging. Assessment of wetland and riparian vegetation in the surrounding area was completed through the establishment and measurement of temporary monitoring transects across five natural wetlands in the Kemerton area with several more visited and observations made. Distinct zonation of vegetation 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 Melaleuca rhaphiophylla and 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 areas more likely to experience regular flooding and accumulate organic matter and nutrients. We consider that, with good planning, rehabilitation, monitoring and management interventions to achieve a restoration trajectory, these new mining pit lakes can positively contribute to regional ecological values.