Response Of The Organic Geochemical Records Of Sediments From Liangzi Lake To Environmental Change

Liangzi Lake is located in the southeastern part of Hubei Province, within the subtropicalclimate area. It has received least contaminants and been protected best among the large numbersof lakes in Hubei Province, and its adjacency to the Tonglushan ancient cupper site makes it apossible witness to the environmental change and the anthropogenic activities around the lake ina long historic period. The presented thesis provides an initiative systematic research of organicgeochemical sediment records of Liangzi Lake, aiming to reconstruct the history ofenvironmental change and identify the impact of anthropogenic activities on the sediment recordof Liangzi Lake, and has redressed the deficiency of organic sediment research in the LiangziLake area. The sediment core, 345cm long, was collected in 2002, sliced into 1cm sections andanalyzed using GC for aliphatic compounds (n-alkanes, n-alkanols, n-alkanoic acids), by GC-MSfor PAHs (polycyclic aromatic hydrocarbons) in the State Key Laboratory of OrganicGeochemistry, Guangzhou Institute of Geochemistry, CAS. The four kinds of biomarkers wereapplied in this research to obtain detailed histories of the local paleoenvironment and regionalpaleoclimate. For each biomarker, multi parameters were used and linked together to infer thereliable information including the contamination trend, source of organic matter, and sedimentaryenvironment in Liangzi Lake. The data reveal that sedimentation in Liangzi Lake has changed through time. An abruptincrease of the concentrations of aliphatic compounds and PAHs from depth 181-194cm is foundin the sediment core, indicating a sudden enhancement of organic inputs to Liangzi Lake. Thediagnostic ratios of aliphatic compounds show that the proportion of long-chained compoundshas increased dramatically from depth 181cm in core, and its change pattern is highly consistentwith that of the total concentrations of organic matter throughout the sediment core, implying thatthe increase in the content of organic matter in sediments is mainly a7ttributed to the increasinginputs of land-derived organic matter from the transition point, which corresponded to theSpring & Autumn Period and Warring States Period in China's history based on C dating. When 14compared with historical materials, the recorded increase of land-derived organic matter toLiangzi Lake is found to be coincidence to the exploitation of Tonglushan ancient copper ore andthe environmental change in Liangzi Lake area. It's suggested the variations along the core aremost probably related to the climatic evolution of this area, and the consequent anthropogenicinfluences on the organic matter inputs to this lake. It's also found that PAHs not only serve as agood index environmental contamination, but also work well to track the historical record ofnaturally and anthropogenically derived matter inputs to sediments in a long historic period.