Sediment Based Analysis Of Long-term Change In Aquatic Environments Of Two Typical Large Reservoirs In South China

Based on paleolimnological analysis of the sediment cores from the two typical large and deep reservoirs in South China(Guangdong province), long-term changes in eutrophication and heavy metal pollution history after daming in 1950 s were explored against the existing historical data of environmental and hydrological data records. Sediment chemistry and diatom proxies for the two reservoirs were comprehensively analyzed to determine the characteristics and differences of the sediment records in this region and the application feasibility of paleolimnological methods to the water quality management of reservoirs. Well preserved and undisturbed sediment core samples were collected in the deep and pelagic zones of Liuxihe Reservoir and Xinfengjinag Reservoir in March of 2013. The contents of TN, TP, TOC, LOI, BSi, δ13C, δ15N and other chemical vairables and diatom assemblages were measured or accounted. In Xinfengjiang Reservoir, chemical proxies are able to indicate the change in the reservoir water quality and human activity. The sediment core record was divided into three consecutive zones by using a cluster analysis of chemical proxies, which were highly consistent with other historical records. In Liuxihe Reservoir, the chemical proxies and diatom assemblages consistently indicated long-term change in water quality and hydrological records, the sediment core record was divided into five consecutive zones by a cluster analysis of chemical proxies and diatom assemblages. These two group proxies all indicated eutrophication of the reservoir, although small difference existed in the historical stage division of the change. δ13C, BSi, LOI550, TN/TP, LOI950 and TOC/TN proxies dominantly explained variation of the diatom assemblages The historical record of the eutrophication and heavy metal pollution in Xinfengjang Reservoir is not consistent, but the heavy metal pollution and eutrophication intensified process is consistent in Liuxihe Reservoir where both have the same driving factor and sediment heavy metal had good response records responsed to the country economic environment background and basin environment background. This consistency strongly demonstrates that the analysis of multi-index proxies is preferred for such long term exploration. The present study also showed that paleolimnological methods have a high potential in revealing pollution history of large reservoirs in South hina. As the recording quality of sediment cores always individually changes with reservoirs and sampling locations, effectiveness of paleolimnological methods depend on the representativeness of sediment cores and diverse proxies of limnological signals.