A century of change in sediment accumulation and trophic status in Lake Fuxian, a deep plateau lake of Southwestern China

Abstract

Lake sediments are often regarded as archives enabling the reconstruction of environmental change. However, little is known about the modern sedimentary environmental change in lakes in vulnerable elevated plateau regions. This study was conducted to investigate a century change of sediment accumulation and trophic status in Lake Fuxian, a deep plateau lake of Southwestern China. Seven sediment cores were collected during an axial transect of Lake Fuxian. The sediment cores were sectioned, oven-dried, ground, and weighed. Sediment ages and sediment accumulation rates (SARs) were determined from the activity of radionuclides (210Pb, 214Pb, and 137Cs). Grain sizes in the cores were determined using an automated laser optical particle-size analyzer. The particulate concentrations of total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) were determined using the concentrated sulfuric acid-potassium dichromate digestion method followed by quantification with a UV-3600 spectrophotometer. SARs were similar over ~ 100 years, with an average of 0.096 g cm−2 a−1 (1.6 mm a−1), which is lower than that of other shallow lakes in the plateau area. Prior to the 1910s, SARs were relatively constant, suggesting little human influence, whereas post-1910s, significant fluctuations occurred coincident with an increase in human activities. Since the 1980s, the SARs recovered due to improvements in land management and strategies for reducing soil loss from the catchment area. The grain size indicated that the hydrodynamic process near the outlet of the lake was higher than that in other regions. The temporal distributions of sedimentary nutrients and C/N ratios in the lake indicated that the onset of nutrient enrichment in different parts of the Lake Fuxian was not synchronous. The maximum values of nutrient and C/N ratios were focused on the central-northern and southern part of the lake. Changes in human activities are important drivers influencing environmental impacts on Fuxian Lake over the past century. More attention should be paid to the control of nutrient inputs from sub-catchments to minimize further environmental pollution of this plateau lake. The results are of significance to the management of plateau lakes elsewhere, such as those in Tibet.