Organic matter in lake sediments contains information that can be used to reconstruct lake environmental histories over decades or centuries. In this study, we used organic geochemical proxies (i.e., total organic carbon [TOC], TOC/total nitrogen [TN] atomic ratios [C/N], stable carbon isotope ratios of TOC [δ13CTOC] and palmitic acid [δ13CC16:0], and nitrogen isotope ratios of bulk sediment [δ15Nbulk]) in sediments from Lake Kawaguchi, Japan, to reconstruct detailed histories of the organic matter accumulation and lake productivity over the past 130 years. Vertical profiles of the mass accumulation rate (MAR) of TOC in the eastern lake basin (core KAW14-7A) showed parallel increases with the C/N ratio from the 1960s to the 1980s, indicating an accelerated delivery of terrestrial organic matter via anthropogenic land-use change. In contrast, the C/N ratios in the western and central basins (cores KAW14-1A and KAW14-4B, respectively) were almost constant prior to the 1980s, suggesting that the increasing trends in the TOC MAR values in these cores are most likely attributable to the onset of eutrophication associated with rapid economic growth after the mid-1950s. On the other hand, the δ15Nbulk showed a gradual increase from the late 1870s, providing evidence for anthropogenic nitrogen input to the lake prior to the apparent eutrophication. After the 1960s–1970s, the δ15Nbulk values rapidly increased, demonstrating water deterioration associated with the direct nutrient discharge into the lake from domestic wastewater. The δ13CC16:0 profiles displayed similar increasing trends to δ15Nbulk from the mid-1960s, demonstrating a close relationship between lake productivity and anthropogenic nitrogen input in Lake Kawaguchi. Our geochemical records as a whole clearly show high algal productivity and enhanced deposition of organic matter in recent decades, suggesting that the amelioration of the lake water is a likely consequence of the transfer of nutrients to the sediment by enhanced productivity, rather than a decrease in the amount of nutrient inflow into the lake.

中文翻译：

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使用有机地球化学代理重建的河口湖（日本中部）过去 130 年的有机碳积累和生产力

湖泊沉积物中的有机物质包含可用于重建数十年或数百年的湖泊环境历史的信息。在本研究中，我们使用了有机地球化学指标（即总有机碳 [TOC]、TOC/总氮 [TN] 原子比 [C/N]、TOC [δ13CTOC] 和棕榈酸 [δ13CC16:0] 的稳定碳同位素比]，以及日本河口湖沉积物中大量沉积物的氮同位素比率 [δ15Nbulk])，以重建过去 130 年来有机物积累和湖泊生产力的详细历史。从 1960 年代到 1980 年代，东部湖盆（核心 KAW14-7A）TOC 质量积累率 (MAR) 的垂直剖面显示与 C/N 比平行增加，表明通过人为土地加速输送陆地有机质-使用变化。相比之下，西部和中部盆地（分别为 KAW14-1A 和 KAW14-4B 核心）的 C/N 比在 1980 年代之前几乎保持不变，这表明这些核心中 TOC MAR 值的增加趋势很可能归因于1950 年代中期后与经济快速增长相关的富营养化的开始。另一方面，δ15Nbulk 从 1870 年代后期开始逐渐增加，为在明显富营养化之前人为输入湖泊提供了证据。1960 年代至 1970 年代之后，δ15Nbulk 值迅速增加，表明与生活污水直接向湖中排放养分有关的水质恶化。从 1960 年代中期开始，δ13CC16:0 剖面显示出与 δ15Nbulk 相似的增长趋势，证明了河口湖湖泊生产力与人为氮输入之间的密切关系。我们的地球化学记录总体上清楚地表明近几十年来藻类生产力高，有机物质沉积增加，这表明湖水的改善可能是由于生产力提高而将营养物质转移到沉积物的结果，而不是减少流入湖泊的养分量。