湖泊是重要的水生生态系统，其与陆地生态系统之间有强烈的物质能量交换，湖泊碳、氮循环对于生源要素循环和湖泊生态系统有重要影响，有机碳、氮是湖泊碳的重要组成部分，其中有机碳的来源复杂，影响因素多，有内外源之分。进一步认识有机碳可为湖泊水体污染来源及碳氮的迁移转化机制提供重要科学数据。国内关于高原草型浅水湖泊的碳循环研究较少，因此深刻认识湖泊碳循环的过程可以为制定合理的富营养化防治策略提供依据。

本文选取贵州省威宁县草海自然保护区流域水体作为研究对象，分别于丰水期、平水期、枯水期对水体的颗粒有机碳（Particulate Organic Carbon，简称POC）、颗粒有机氮（Particulate Organic Nitrogen，简称PON）、溶解无机碳（Dissolved Inorganic Carbon，简称DIC）、溶解有机碳（Dissolved Organic Carbon，简称DOC）的含量及其稳定同位素的测定研究，揭示了草海水体不同形态碳的时空分布规律和控制因素。最后通过对颗粒物潜在端元值的确定，利用SIAR同位素模型对水体颗粒有机质的来源进行定量示踪，主要结论如下：

（1）草海水体的水化学指标具有明显的季节变化特点，主要受到湖泊中水生植物的光合作用强弱控制。

（2）草海水体POC含量具有明显的季节性差异，表现为丰水期＞平水期＞枯水期， 呈现出自东向西POC含量逐渐降低的趋势。POC含量分布主要受藻类生物量控制，外源输入和沉积物再悬浮也是重要来源。草海水体δ¹³C_POC值的季节差异较为明显，丰水期较枯水期偏正约2.2‰。草海水体POC主要来源自沉水植物，受到光合作用控制。δ¹³C_POC的空间分布也受到藻类分布和外源输入的影响。

（3）草海水体PON含量的季节差异不显著，其含量变化主要受人为输入和动物排泄、植物分解的影响。草海水体的δ¹⁵N值没有明显的季节性变化，三个时期的分布特征大体相同。其空间分布主要受到不同湖区污染情况以及水生植物、藻类的分布特点影响。

（4）草海水体DIC含量有较明显的季节性变化，表现为丰水期＜平水期＜枯水期。DIC含量的季节差异主要受水生植物的光合作用控制，空间变化受到水生植物分布控制。草海水体DIC的δ¹³C值有明显的季节性差异。枯水期较平水期偏正，平水期较丰水期偏正，枯水期水体δ¹³C_DIC主要受到水-气界面CO₂交换导致的δ¹³C分馏控制；丰水期和平水期的水体δ¹³C_DIC主要受陆源输入控制。

（5）草海水体DOC含量的季节变化显著，表现为丰水期＞平水期＞枯水期，其DOC含量受到水生植物活动以及外源输入的影响。三个时期草海δ¹³C_DOC值相差不大，说明不同时期草海的DOC来源接近；空间上δ¹³C_DOC主要受沉水植物光合作用控制。

（6）草海水体颗粒物丰水期主要受到沉水植物和沉积物再悬浮控制；平水期水体颗粒物主要受挺水植物和沉积物再悬浮控制；枯水期水体颗粒物主要受沉积物再悬浮控制。草海东部湖区颗粒有机质来源主要受到粪便污水、沉水植物控制；中部湖区颗粒有机质来源主要受到沉积物、沉水植物控制；西部湖区颗粒物的来源分布较为平均。

Lakes are important aquatic ecosystems, and there is a strong material energy exchange with terrestrial ecosystems. The lake carbon and nitrogen cycles have an important impact on the biogenic element cycle and lake ecosystems. Organic carbon and nitrogen are important components of lake carbon. Among them, the sources of organic carbon are complex, there are many influencing factors, there are internal and external sources. Further understanding of organic carbon can provide important scientific data for the sources of lake water pollution and the mechanism of carbon and nitrogen migration and transformation. There are few studies on the carbon cycle of plateau grass type shallow lakes in China. Therefore, a deep understanding of the process of lake carbon cycle can provide a basis for formulating reasonable eutrophication control strategies.

This study selects the Caohai Nature Reserve in Weining County, Guizhou Province as the research object. Measuring the concentrations of Particulate Organic Carbon (POC), Particulate Organic Nitrogen (PON), Dissolved Inorganic Carbon (DIC), Dissolved Organic Carbon (DOC) and their stable isotopes in the water body during the wet season, normal season and dry season. Revealing the spatial and temporal distribution of different forms of carbon in grassland and seawater Controlling factor. Finally, by determining the potential end-member values of the particulate matter, the SIAR isotope model is used to quantitatively trace the source of the water particulate organic matter. The main conclusions were as follows:

（1）The water chemistry index of Caohai Lake has obvious seasonal changes, which is mainly controlled by the photosynthesis of aquatic plants in the lake.

（2）The POC contents of Caohai has obvious seasonal difference, which is expressed in wet season>normal season>dry season, showing a trend of gradually decreasing POC contents from east to west. The distribution of POC contents is mainly controlled by algal biomass, and foreign sources and sediment resuspension are also important sources. The seasonal difference of the δ¹³C_POC values of the Caohai is obvious, and the δ¹³C_POC values of wet season is about 2.2‰ more positive to the dry season. The POC of grassland seawater mainly comes from submerged plants and is controlled by photosynthesis. The spatial distribution of δ¹³C_POC is also affected by algae distribution and external input.

（3）The seasonal difference of PON contents in Caohai is not significant, and its content change is mainly affected by human input, animal excretion and plant decomposition. There is no obvious seasonal change in the δ¹⁵N value of Caohai, and the distribution characteristics of the three periods are almost the same. Its spatial distribution is mainly affected by the pollution of different lakes and the distribution characteristics of aquatic plants and algae.

（4）The DIC contents of Caohai seawater has obvious seasonal changes, which is expressed in wet season<normal season<dry season. The seasonal difference of DIC content is mainly controlled by the photosynthesis of aquatic plants, and the spatial variation is controlled by the distribution of aquatic plants. The δ¹³C value of DIC in Caohai Sea has obvious seasonal difference. The dry season is more positive to the normal season, and the normal season is more positive to the wet season. The δ¹³C_DIC of the water body in the dry season is mainly controlled by the isotopic fractionation caused by the CO₂ exchange at the water-gas interface; The δ¹³C_DIC of the water body in the wet season and normal season is mainly controlled by the terrestrial input.

（5）The seasonal change of DOC content in Caohai water body is significant, which is expressed in wet season>normal season>dry season. Its contents is affected by aquatic plant activity and foreign input. The δ¹³C_DOC values of Caohai in the three periods are not much different, indicating that the sources of DOC in Caohai are close at different periods; δ¹³C_DOC is mainly controlled by photosynthesis of submerged plants in the space.

（6）The particulate matter of the water body of Lake Caohai is mainly controlled by the resuspension of sediments and submerged plants during the wet season; the particulate matter of the water body in the normal season is mainly controlled by the resuspension of sediments and emergent plants; The water particles in the dry season are mainly controlled by sediment resuspension. The source of particulate organic matter in the eastern lake area of Caohai is mainly controlled by fecal sewage and submerged plants; the source of particulate organic matter in the central lake area is mainly controlled by sediments and submerged plants; the source distribution of particulate matter in the western lake area is relatively even.