Tracking the effect of pollution deposition from coal fired power stations over the past 200 years on southern African lakes, using diatoms as a proxy.

Abstract

Coal-fired power stations are sources of potentially harmful atmospheric emissions and deposition within both local and distal environments, on land and water surfaces. Sediment cores were obtained from Lake Chrissie in the Mpumalanga Province in relative proximity to these pollution sources and from Letšeng-la Letsie, a remote mountain lake in Lesotho, where deposited pollutants are solely atmospherically derived. This study is uses diatoms as they display sensitivities to pollutant loads and can provide the baseline information necessary to determine both the nature and extent of pollutant loading over time. This study investigated evidence for a diatom-based response, comparing findings for the sites. Both lake systems were characterised as nutrient enriched for ~80-years between the ~1930-2010s, with a more enriched environment and polluted conditionsindicative from ~1960-1980s and within the ~2010s. Fragilaria famelica which signifies nutrient enrichment was found abundant in both lake systems. Lake Chrissie is described with increased levels of industrial pollution for ~60-years, during the ~1950s and between the ~1970-2010s. Letšeng-la Letsie is described as industrially polluted for ~50-years between the ~1940-1950s, ~1970-1980s and during the ~2010s. This is consistent with previous studies exploring pollution from coal-fired power stations on Letšeng-la Letsie, but these pollutant trends were found inconsistent with emissions over the same periods that increased continuously until the last ~20-years. Results show that diatom responses to increasing deposition do not follow the same unidirectional trend but are rather impacted by climatic variations which may have greater impact on diatom assemblages than the pollution load. The implication of this study highlights the importance of southern African aquatic systems, the effects pollution has on human health and potential mitigation action.