氮同位素示踪季节性过水湖泊水位变化对水体氮循环的影响- - 以鄱阳湖为例

The drastic change of water level of lake with the characteristic of water carrying can cause the variation of nitrogen biogeochemical cycles in the internal lake, and then influence the eutrophication of the lake. Now, the research in this field has not been conducted in China. This research proposal chooses Poyang Lake, a typical lake with the characteristic of water carrying in the Middle and Lower Reaches of the Yangtze River, as the research object. Samples were collected seasonally from Poyang Lake and the main rivers which drain in the lake. The contents of different form of nitrogen and nitrogen isotopic composition of Poyang Lake and the main rivers which drain in the lake will be analyzed. Based on the analytical results，the variation of contents of different form of nitrogen and nitrogen isotopic composition of Poyang Lake and the main rivers which drain in the lake in different water levels will be discussed. How the change of physicochemical parameters of the waters of Poyang Lake and the main rivers which drain in the lake influence the contents of different form of nitrogen and nitrogen isotopic composition will also be discussed. The main sources of N in Poyang Lake and the contribution factors will be determined, and then the biogeochemical processes which play a decisive role in controlling the contents of different form of nitrogen and nitrogen isotopic composition in different water level will also be discussed. By using the nitrogen isotopic techniques and other methods, some scientific foundation about the prevention and treatment of lake eutrophication will be obtained．

季节性过水湖泊水位剧烈变化可能引起湖泊内部氮的生物地球化学循环的改变，从而对湖泊富营养化产生影响。目前国内外这方面的研究工作还不是很深入。本基金拟以长江中下游典型的季节性过水湖泊- - 江西鄱阳湖为例，以氮稳定同位素为研究手段，通过对不同水位条件（丰水期、平水期、枯水期）湖水、各主要入湖河流及湖口不同形态氮含量及氮同位素组成的对比研究，探讨不同水位条件下不同形态氮含量及其氮同位素组成的变化规律及由水位条件变化引起的水体物化参数改变对不同形态氮含量及其氮同位素组成的影响，判定鄱阳湖水体氮的主要来源及贡献大小，确定不同水位条件下对水体各形态氮起决定性作用的生物地球化学作用，揭示不同水位条件下湖泊内部生物地球化学过程（硝化作用、反硝化作用）对湖水各种形态氮的迁移、转化、贮存、输送的影响，为湖泊富营养化的防治和治理提供科学依据。

蚌湖是鄱阳湖边缘的一个自然小湖泊，蚌湖紧邻赣江、修河和鄱阳湖西北部水域，枯水期水位低落蚌湖因天然堤坝与它们隔离成为独立封闭湖泊；丰水期赣江、修河、鄱阳湖水位上涨，水体逐渐越过堤坝进入蚌湖并逐渐连成一片水域。本研究以蚌湖为主线，通过阴阳离子浓度、无机氮稳定同位素分析蚌湖与赣江、修河水体交换情况；探讨水位变化对蚌湖水体理化参数的影响，并利用碳氮稳定同位素技术判断无机氮和颗粒有机质的来源以及对水位变化产生的响应；揭示蚌湖在不同水位条件下污染物扩散残留机制。. 蚌湖、赣江、修河无机氮稳定同位素的分析也可以反映蚌湖与两条河流水体交换情况。枯水期蚌湖无机氮稳定同位素均为负值，而赣江修河无机氮稳定同位素均为正值，表明枯水期蚌湖与赣江、修河没有水体交换。平水期（水位上涨阶段）蚌湖无机氮稳定同位素与两条河流无机氮稳定同位素相近，同为正值，表明蚌湖水与两河流水体有交换。丰水期蚌湖、赣江、修河的氨氮稳定同位素都较负，主要来源于流域较多的雨水氨氮源，硝氮主要来源于雨水径流带入的农业氮源。平水期（水位退落阶段）蚌湖硝氮稳定同位素为负值与两河流相反，表明蚌湖水体是丰水期的滞留水体，两河流水可能没有进入蚌湖交换，而且蚌湖的硝化作用较强。. 蚌湖水样δ15N-NH4+、δ15N-NO3-在不同月份不同水位变化较大，不同水位条件下蚌湖无机氮稳定同位素都存在显著性差异，反映不同水位水体来源不同，丰水期和平水期（水位上涨）的水源是河流水和雨水，平水期（水位退落）和枯水期是丰水期的滞留水，同时湖泊内部的氨化硝化作用也很强。