| Lake that collects various materials, including organic matters, pollutants and nutrients is an important basin gathering catchment water, and thus it is abundant in biological and physico-chemical information. Based on these proxy indexes from the score profile, we will be able to know the hydrology features, ecological environment,and pollution status for lake and its catchment, which is important to know the lake environment evolution history and forecast future environment changes. In the recent decades, with the regional climate change and growing human activities on the environment, many lakes faced many problems, including the degradation of ecosystem, eutrophication of lakes, these of which have passive influence on the eco-economic sustainable development of the catchment.Yilong Lake is a shallow lake located in Yunnan-guizhou plateau, and it is facing many problems, such as water pollution, eutrophication of lake, the degradation of ecosystem, and the decline of biodiversity and so on together with the economic development and unreasonable human activities. As a consequence, it is necessary to know the history of the lake evolution, and to offer a proof that improves the environment and alleviate the worsening trend.In this paper, based on columnar sediments form Yilong Lake, we tested the particles, organic matter, and their stable isotopes, used the unit component models,combined with 210 Pb and 137 Cs, and analyzed the origin of organic matters and the lake ecosystem changes over the past century. We have got the following conclusions:(1) The results show that: the ratio of carbon and nitrogen isotopic were-25.89‰~-22.47‰ and 0.54‰~4.74‰, and their average values is-25.03‰ and2.49‰, respectively. It was found that C/N value range is wide between 16.43~16.43,with a mean of 18.08 and the maximum amplitude of 4.01. Additionally, TOC changes range is 8.46~21.87%, and the fluctuation is not big, with the average of13.23%. It was also found that TN content is low with the range between 1.17% ~3.10%, and the average is 1.89%.(2) Based on the qualitative and quantitative analysis, we found that the lake organic matters mainly come from lake, and the large aquatic plant is a significant contributor to the sediment YLH-1. And algae significantly increased, while exogenous contribution is relatively small. Combined with comprehensive comparison between water quality parameters and proxies, we found that the carbon isotope can reflect the process of lake eutrophication, which is related with the absorption of dioxide carbon dissolved in water algae and organic matter degradation of dioxide carbon, while nitrogen isotope reveals the history nitrate pollution, which is influenced by industrial pollutants and agricultural fertilizers.(3) Based on the various indexes trend, combined with the history of human activities within a basin, the evolution process in Yilong Lake is divided into three states: between the 1880 s and the early 1970 s, primary productivity level is low, the lake aquatic ecological environment is good, and the aquatic ecological environment is good and the human activity level is weak. Form 1970 s to the 1990 s, with the strengthening of human activity, a large amount of nutrient matters were input into lake, the water eutrophication levels rise, and the algae blooms. Submerged plants fade, and lake primary productivity grows vastly. After the 1990 s, with the continued development of industry and agriculture, the water is at a high level of productivity,the lake is serious eutrophication, and frequent outbreak of algal blooms. |
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