关键词: 冗余分析(RDA), 沉积指标, 硅藻, 富营养化, 太白湖

Abstract: Taibai Lake, a shallow lake with a surface area of 26.1 km², is a presently algae-dominant lake and experiences obvious eutrophication. A multi-proxy analysis including diatoms, pollen, grain size, magnetic susceptibility and selected elements were applied to a 50 cm long sediment core extracted from Taibai Lake. Series of multivariables analysis such as canonical correspondence analysis (CCA), redundancy analysis (RDA) based on those proxies revealed that the minimum variables combination including Pinus percentage, sediment phosphorus, frequency-dependent susceptibility and total organic carbon percentage could explain significantly most of the variation of diatom community, which could reflect the changes of lake's nutrient status. The four proxies explained 51.5% of the diatom variance, only 6.4% less than those explained by all the sedimentary proxies, which is 57.9%. Based on the four indices mentioned above and the reconstructed historical total phosphorus concentration, four developmental phases were distinguished as follows. (1) 1800-1863AD: the earlier deforestation led to much intensive erosion, which resulted in much nutrient input. While the lake kept lower nutrient status as nutrient concentration was diluted by the sufficient precipitation. (2) 1863-1924AD: the lake was still in a mesotrophic status for the weakened human impacts. (3) 1924-1970AD: human activities became stronger and nutrient input increased. However with the flourish of aquatic plant, parts of nutrient were absorbed and consequently the nutrient concentration increased slowly. (4) Since 1970 the lake has gradually become much obvious eutrophic with the development of much stronger human activities including reclamation, fish-stocking and modern agriculture, as well as the discharge of waste water from local factories and dwellers. The four phases were also illustrated clearly by the RDA bi-axis plot, which indicated different driving mechanism for lake environmental change in different periods. The sediment records in Taibai Lake showed that human activities played an important role in the recent eutrophication process. It also concluded that lakes with higher nutrient background is much apt to become eutrophicated enforced by human activities, consequently rational management or exploitation will be necessary to protect Taibai Lake from further water quality deterioration.

Key words: redundancy analysis (RDA), sedimentary proxy, diatom, eutrophication, Taibai Lake