水位变化对湖泊沉积物营养释放的影响

水位波动可有效调节湖泊生态系统的结构与功能,干湿交替过程引起的沉积物生物地球化学循环途径的改变是其重要机制之一。大量研究结果表明,干湿交替将加速沉积物有机碳的分解,强化沉积物硝化与硝化作用的偶联,促进沉积物磷的酶促水解和厌氧解离,从而增加再度淹没之后水中溶解有机碳和生物可利用性磷的浓度,并减少溶解无机态氮的浓度。有机质的分解是上述过程的关键步骤。因此,必须系统描述湖泊水陆界面土壤和沉积物基本理化性状与水生生物特征,分析干旱过程中沉积物生物地球化学循环途径的变化,了解淹没过程中水柱营养状态与浮游生物群落对沉积物营养释放的响应,从而揭示水位波动调控富营养化过程的机制,即诱发营养脉冲或维系其持续补给,改变营养阈值,进而导致稳态转换。

Effects of Fluctuation of Water Level on Sediment Nutrient Releases in Lakes

Fluctuation of water level effectively regulates structure and function of lake ecosystems,behind which changes in biogeochemical pathways of sediments caused by drying and rewetting cycles served as one of the most important mechanisms.As shown by quite a few studies,the drying and rewetting enhanced decomposition of organic carbon,strengthened the coupling of nitrifying and denitrifying processes and accelerated enzymatic hydrolysis and anaerobic desorption of phosphorus in sediments,which gave rise to concentrations of dissolved organic carbon and bioavailable phosphorus and simultaneously decreased that of inorganic nitrogen in water column.Decomposition of organic matter is the key step driving this process.Therefore,it is necessary to fully describe basic,physical and chemical properties of soils and sediments along lake shoreline,and characterize aquatic organisms.As a result,the changes in sediment biogeochemical pathways in drying can be analyzed,and trophic status and biological responses to it in rewetting process can be understood further.Accordingly,mechanisms underlying eutrophication related to fluctuations of water level can be revealed.In details,the drying and rewetting facilitates the shoreline sediments to give nutrient pulse or release persistently,thereby altering the nutrient threshold and leading to the shift of alternative stable state in lakes.