Using sedimentary diatoms to identify reference conditions and historical variability in shallow lake ecosystems in the Yangtze floodplain

Abstract

The reference condition and historical variability of aquatic ecosystems are key ecological characters for understanding the dynamic and ecological assessment of wetland systems. Based on high-resolution chronological sequences of diatom records from 10 lakes in the Yangtze floodplain, this study aims to determine their ecological and chemical reference conditions, the historical variability and its controlling factors. Mesotrophic species Aulacoseria granulata, along with non-planktonic species Fragilaria spp., Navicula spp., Cocconeis placentula, Achnanthidium minutissimum, Cymbella spp. etc, were most abundant in the reference samples (1800–50). Accordingly, a relatively high chemical reference (50 µg L–1 in diatom-inferred total phosphorus concentration) was defined. The degree of floristic change comparing present with reference samples reveals that six of the 10 lakes have undergone significant ecological changes. The historical variability in those lakes was found to be regulated by the distance from the Yangtze River (negatively) and the lake catchment area (positively). This reflects the mechanism driving ecological change in floodplain lakes: the ecological conditions were sensitive to the nutrient input from the catchment and disturbance by the Yangtze River. This study demonstrates the robustness of palaeolimnological techniques in reconstructing the historical ecological characters of lake ecosystems, which may provide essential information for the management of wider types of wetland.