鄱阳湖水体垂向分层状况调查研究

湖泊水体混合或分层对环境和生态具有显著指示意义,能够提高对未来湖泊水环境状况的评价与管理。针对洪泛鄱阳湖水位季节性变化显著等特点,基于剖面温度和稳定氢氧同位素的调查分析来探明多因素影响下鄱阳湖水体垂向分层或混合状况。结果发现:鄱阳湖枯水期和洪水期水体垂向温差大多处于0~1.0℃,大部分水域温差小于0.5℃,但偶见洪水期部分水域会达到1.5℃的较大温差。总体表明,在季节变化尺度上,鄱阳湖具有较为稳定的等温层,没有明显温度分层特征。同位素分析结果得出,枯水期和洪水期的氢氧稳定同位素值在深度剖面上呈均一分布,表明鄱阳湖水体混合状况较好或完全混合。虽然湖区气象条件和水文条件均是影响鄱阳湖水体分层或混合的重要因素,但鄱阳湖入流和出流等水文条件是影响鄱阳湖水体垂向混合的主要因素。鄱阳湖水体混合同时对湖泊水环境因子的垂向分布特征可能产生重要的影响或控制作用。首次基于大量野外监测有针对性地开展鄱阳湖水体分层研究,结果有助于对湖泊水流结构的深入认识,可为湖区水体污染物的输移模拟与作用机制阐释等方面提供科学参考。

STUDY ON THE VERTICAL STRATIFICATION IN POYANG LAKE

Although mixing in lakes has significant environmental and ecological implications,knowledge of mixing dynamics for shallow floodplain lakes has received little attention.In this study we used a combination of hydrological and thermal investigations to provide evidence for the mixing in a large,shallow floodplain of Poyang Lake (China).Depth profiles of water temperature and stable hydrogen and oxygen isotope compositions were measured throughout the lake.Results showed that although the water temperature differences of up to 1.5 ℃ were observed occasionally during the high lake water level period,Poyang Lake appeared to have isothermal mixed-layers from the upper epilimnion to the bottom hypolimnion attributed to the presence of mostly small temperature differences (0.5-1 ℃).The stable isotope composition revealed that the water columns of the lake were almost homogeneous during low and high lake water level periods.Poyang Lake appears to be well mixed or full mixing on a seasonal basis,depending on hydrological forcing within the lake,rather than meteorological conditions.Additionally,the vertical mixing of Poyang Lake appeared to have a close relationship with the aquatic environment due to mostly small differences in the vertical distributions of suspended sediments,TN and TP.The current study is the first to explore the stratification of Poyang Lake,which will help to improve our knowledge of water flow patterns and pollutant transport within the lake.