入湖河流的河口区域是地表径流与湖泊的交汇处，它是陆源污染物迁移进入湖泊的主要途径，也是污染物进行沉积的主要区域。分析入湖河口的沉积物中重金属的分布情况，有助于全面认识湖泊沉积物重金属污染情况，帮助全面了解全流域沉积物重金属污染的分布、来源、风险。洞庭湖作为我国最大淡水湖之一，汇聚湘江、资江、沅江、澧水“四水”和长江荆江段三口来水来沙，在城陵矶注入长江。随着河湖关系演变，洞庭湖来水量来沙量发生显著变化，流域内污染突出的典型重金属的沉积过程和湖区重金属的输入输出情况也在不断演变之中。

本研究以洞庭湖流域为研究区，重点关注各个入湖和出湖河口区域，首先分析了流域自然条件的年际变化趋势，其次实地采集各河口沉积柱芯并进行实验分析，系统探究了洞庭湖各个出湖河口沉积物中砷、铬、镉、铜、铅、锑等典型重金属的垂向分布及赋存形态，分析影响重金属迁移、沉积的环境影响因素。利用铅铯同位素定年技术，确定沉积物柱芯的沉积年代，并估算各个河口重金属的沉积通量、输入输出量，明晰几十年来不同河口对湖区重金属贡献的差异；分析了洞庭湖四水流域重金属沉积对自然条件变化的响应情况；对各出入湖河口沉积物重金属进行来源解析和环境风险分析。本研究得到的主要结果和结论如下：

（1）洞庭湖流域自然条件在近十年发生显著变化，受其影响重金属污染情况也明显变化，呈现先增加后减少的趋势。洞庭湖流域平均气温为16.50 ℃，呈现缓慢上升趋势；流域年平均降水量为1381.53 mm，历年来保持相对稳定，仅有澧水流域轻微下降；洞庭湖流域平均归一化植被指数（NDVI）指数为0.76，植被覆盖度大小和植被覆盖的增加速度排序均为沅江流域＞澧水流域＞资江流域＞湘江流域。

（2）洞庭湖各河口沉积物重金属在垂向上均呈现先增加后减少的趋势，Cr、Sb等重金属污染严重，四水河口污染显著严重于长江三口和城陵矶。Cr是洞庭湖四水河口污染最突出的重金属，资江口（ZJK）是四水中重金属污染最严重的河口，资江污染最突出的重金属是Cd和Sb；湘江次之，污染突出的重金属是Cr和Pb。长江三口和城陵矶出水口污染最严重重金属是Cr和Pb。垂向分布上，四水河口沉积物重金属从深到浅呈现先增加后减少的趋势，长江三口呈现持续增加趋势。

（3）四水河口重金属沉积通量显著高于其他河口，且近年来成为湖区重金属的主要来源。资江口、太平口、城陵矶出水口三个河口沉积柱芯的平均沉积速率分别为1.27 cm/yr、0.95 cm/yr、1.05 cm/yr；1980年以来，四水对洞庭湖湖区的重金属输入量从多到少排序为：湘江（XJK）＞沅江（YJK）＞澧水（LSK）＞资江（ZJK），长江三口中：松滋口（SZK）＞太平口（TPK）＞藕池口（OCK）；各河口除资江口外，重金属年度输入输出量均呈现下降趋势，累计输入输出量持续增加，但增速不断放缓；长江三口累计重金属输入量高，但四水河口目前是湖区重金属的主要来源，其中湘江占比最高。

（4）洞庭湖各河口沉积物重金属对植被覆盖、径流量等自然条件响应明显，主要来源为自然来源，整体环境污染风险中等。植被覆盖、径流量与重金属沉积通量相关性显著；在沅江、澧水等植被覆盖更高的流域，重金属迁移、沉积对自然条件变化的响应更为明显。富集系数法和APCS-MLR模型法计算得到的流域重金属平均人为来源比例分别为32.81 %和21.79 %，自然源是流域重金属的最主要来源，Sb是受人为活动影响最大的重金属，各河口中湘江口重金属人为来源占比最高。Cd和Sb是洞庭湖流域环境风险最突出的重金属，资江口是环境风险最高的河口，流域整体为中等环境污染风险。

基于上述结论，Cr是洞庭湖全流域污染最突出、环境风险最高的重金属，各河口中资江河口污染程度最严重；洞庭湖四水河口目前是湖区重金属污染的主要来源，其中湘江贡献占比最高，近年来洞庭湖污染呈现改善趋势。本研究丰富了对洞庭湖全流域重金属污染历史和现状的认识，可为长江中游重金属污染治理和生态环境保护提供支持。

The estuarine area where inflowing rivers meet the lake surface is the primary conduit for terrestrial pollutants to migrate into the lake and the main region for pollutant deposition. Analyzing the distribution of heavy metals in sediment at river estuaries into the lake assists in comprehensively understanding the heavy metal pollution in lake sediments, aiding in a thorough understanding of the distribution, extent, sources, and risks of heavy metal pollution in the entire watershed. Dongting Lake, one of China's largest freshwater lakes, receives inflows of water and sediment from the Xiangjiang, Zijiang, Yuanjiang, and Lishui Rivers, as well as the Yangtze River's Jingjiang section, which merges at Chenglingji and flows into the Yangtze River. With changes in the relationship between rivers and lakes, significant variations have occurred in the water and sediment inputs to Dongting Lake, leading to evolving processes of sedimentation of typical heavy metals with prominent pollution in the basin and the input-output status of heavy metals in the lake area.

This study focused on the Dongting Lake basin, with a particular emphasis on various inflow and outflow river estuarine areas. Firstly, the annual trends in natural conditions in the basin and the heavy metal pollution in Dongting Lake reflected in previous studies were analyzed. Secondly, sediment cores were collected from various river estuaries for experimental analysis to systematically explore the vertical distribution and speciation of typical heavy metals such as arsenic, chromium, cadmium, copper, lead, and antimony in sediment at various outflow river estuaries of Dongting Lake, and to analyze the environmental factors influencing heavy metal migration and deposition. Lead-cesium isotope dating techniques were used to determine the sediment ages of sediment cores and to estimate the sediment fluxes, input-output volumes of heavy metals at various river estuaries, clarifying the differences in contributions of different river estuaries to heavy metals in the lake area over the past several decades. The response of heavy metal sedimentation in the Dongting Lake basin to natural conditions was analyzed, and the Source analysis and ecological risk analysis of sediment heavy metals at various river estuaries were analyzed. The principal findings and conclusions of this study are as follows:

(1) The natural conditions of the Dongting Lake basin have undergone significant changes in the past decade, and heavy metal pollution has also changed significantly due to these changes, showing a trend of first increasing and then decreasing. The average temperature of the Dongting Lake basin is 16.50°C; the annual average precipitation in the basin is 1381.53 mm, with a slight decrease only in the Lishui River basin; the average normalized difference vegetation index(NDVI) of the Dongting Lake basin is 0.76, with vegetation coverage and the rate of increase in vegetation coverage ranking as follows: Yuanjiang River basin > Lishui River basin > Zijiang River basin > Xiangjiang River basin.

(2) Heavy metals in sediment at various river estuaries of Dongting Lake exhibited a trend of first increasing and then decreasing vertically, Chromium and antimony pollution is serious, and pollution at the Four river estuaries was significantly more serious than at the three outlets of the Yangtze River and Chenglingji. Chromium is the most prominent heavy metal pollutant at the four rivers estuary of Dongting Lake, and the most severe heavy metal pollutants at the four rivers estuary are cadmium and antimony; Xiangjiang River is next, with prominent pollutants being chromium and lead. The outlets of the Yangtze River and Chenglingji have the most serious pollution of chromium and lead. Vertically, heavy metals in sediment at the four rivers estuary exhibited an increasing and then decreasing trend from deep to shallow, while the outlets of the Yangtze River showed a continuous increasing trend.

(3) The sediment flux of heavy metals at the four rivers estuary was significantly higher than at other river estuaries and has become the main source of heavy metals in the lake area in recent years. The average sedimentation rates of sediment cores at the Yuanjiang River estuary, Taiping estuary, and Chenglingji outlets were 1.27 cm/yr, 0.95 cm/yr, and 1.05 cm/yr, respectively; since 1980, the order of heavy metal input from the four rivers to the Dongting Lake basin has been Xiangjiang > Yuanjiang > Lishui > Zijiang, and the order at the three outlets of the Yangtze River has been Songzi > Taiping > Ouchi; except for the Yuanjiang River estuary, the annual input-output volumes of heavy metals have shown a decreasing trend, while the cumulative input-output volumes have continued to increase, albeit at a slower rate; the cumulative heavy metal input volume at the three outlets of the Yangtze River is high, but the four rivers estuary is currently the main source of heavy metals in the lake area, with the Xiangjiang River contributing the highest proportion.

(4) The response of heavy metals in sediment at various river estuaries of Dongting Lake to natural conditions, such as vegetation coverage and runoff, was significant, mainly from natural sources, with an overall moderate environmental pollution risk. There was a significant correlation between vegetation coverage, runoff, and heavy metal sediment flux; in watersheds with higher vegetation coverage such as the Yuanjiang and Lishui, the response of heavy metal migration and sedimentation to natural condition changes was more pronounced. The average anthropogenic source proportions of heavy metals in the watershed calculated by the enrichment coefficient method and the APCS-MLR model were 32.81% and 21.79%, respectively, with natural sources being the main source of heavy metals in the watershed, and antimony being the heavy metal most influenced by human activities, with the highest proportion of anthropogenic sources at the Xiangjiang River estuary. Cadmium and antimony were the most prominent heavy metals in environmental risk in the Dongting Lake basin, with the highest environmental risk at the four rivers estuary, and the overall environmental pollution risk in the watershed was moderate.

Based on the above conclusions, chromium is the most prominent pollutant and has the highest environmental risk in the entire Dongting Lake basin, with the most severe pollution in the Si river region among various river estuaries; the Four rivers estuary of Dongting Lake is currently  main source of heavy metal pollution in the lake area, with the highest contribution from the Xiangjiang River, and Dongting Lake pollution has shown an improving trend in recent years. This study enriches the understanding of the past and current status of heavy metal pollution in the entire Dongting Lake basin, providing support for controlling heavy metal pollution and ecological environment protection in the middle reaches of the Yangtze River.