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首页> 外文期刊>Journal of Paleolimnology >Environmental variability in Lake Naivasha, Kenya, over the last two centuries
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Environmental variability in Lake Naivasha, Kenya, over the last two centuries

机译：过去两个世纪以来肯尼亚奈瓦沙湖的环境变化

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Lake Naivasha, Kenya, is one of a number of freshwater lakes in the East African Rift System. Since the beginning of the twentieth century, it has experienced greater anthropogenic influence as a result of increasingly intensive farming of coffee, tea, flowers, and other horticultural crops within its catchment. The water-level history of Lake Naivasha over the past 200 years was derived from a combination of instrumental records and sediment data. In this study, we analysed diatoms in a lake sediment core to infer past lacustrine conductivity and total phosphorus concentrations. We also measured total nitrogen and carbon concentrations in the sediments. Core chronology was established by 210Pb dating and covered a ~186-year history of natural (climatic) and human-induced environmental changes. Three stratigraphic zones in the core were identified using diatom assemblages. There was a change from littoral/epiphytic diatoms such as Gomphonema gracile and Cymbella muelleri, which occurred during a prolonged dry period from ca. 1820 to 1896 AD, through a transition period, to the present planktonic Aulacoseira sp. that favors nutrient-rich waters. This marked change in the diatom assemblage was caused by climate change, and later a strong anthropogenic overprint on the lake system. Increases in sediment accumulation rates since 1928, from 0.01 to 0.08 g cm−2 year−1 correlate with an increase in diatom-inferred total phosphorus concentrations since the beginning of the twentieth century. The increase in phosphorus accumulation suggests increasing eutrophication of freshwater Lake Naivasha. This study identified two major periods in the lake’s history: (1) the period from 1820 to 1950 AD, during which the lake was affected mainly by natural climate variations, and (2) the period since 1950, during which the effects of anthropogenic activity overprinted those of natural climate variation.
机译：肯尼亚的奈瓦沙湖是东非裂谷系统中许多淡水湖之一。自20世纪初以来，由于流域内咖啡，茶，花卉和其他园艺作物的集约化耕种，它受到了更大的人为影响。过去200年中奈瓦沙湖的水位历史是结合仪器记录和沉积物数据得出的。在这项研究中，我们分析了湖泊沉积物核心中的硅藻，以推断过去的湖相电导率和总磷浓度。我们还测量了沉积物中的总氮和碳浓度。核心年代学是通过 210 Pb测年建立的，涵盖了约186年的自然（气候）和人为环境变化历史。使用硅藻组合物确定了岩心中的三个地层区域。沿岸/附生硅藻（如Gomphonema gracile和Cymbella muelleri）发生了变化，这种变化发生在大约从2000年开始的干旱时期。在一个过渡时期，从1820年到1896年，到现在的浮游Aulacoseira sp。有利于营养丰富的水域。硅藻集合体的显着变化是由于气候变化引起的，后来又在湖泊系统上形成了强烈的人为叠印。自1928年以来的沉积物累积速率从0.01增至0.08 g cm −2 year −1 与20世纪初以来硅藻推断的总磷浓度的增加有关世纪。磷积累的增加表明淡水奈瓦沙湖的富营养化增加。这项研究确定了该湖历史上的两个主要时期：（1）公元1820年至1950年这一时期，该湖主要受到自然气候变化的影响；（2）自1950年以来的这一时期，其中人为活动的影响覆盖了自然气候变化的那些。

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