太湖梅梁湾水动力及相关过程的研究

Studies on the Hydrodynamic Processes and Related Factors in Meiliang Bay, Northern Taihu Lake, China

太湖是位于长江下游的一个大型浅水湖泊 .水动力过程和要素对浅水湖泊的环境演化有着复杂和深远的影响 .本文基于 1998年开展的有关太湖梅梁湾的水动力过程的野外调查结果 ,总结了梅梁湾在夏季盛行风向条件下的湖流特征 .发现了梅梁湾在夏季偏南风条件下 ,表层湖流以顺时针环流为主要特征 .但在湾内靠近梁溪河口地区 ,流场受地形影响而有所不同 .反映在叶绿素浓度和总磷、总氮浓度分布上 ,因受湖流影响较大而富集在梁溪河口周围 ,即偏于梅梁湾的东部 .较少受湖流影响的总溶解磷和总溶解氮则仍以西部的闾江口为浓度最高地区 .利用 1998年夏季湖流调查结果 ,计算发现梅梁湾与太湖的水量交换以梅梁湾流入太湖为主要特征 ,交换量为2 80m3·s- 1.受动力作用影响较大的悬浮物浓度 ,在冬季偏北风作用下 ,湾口的浓度远高于湾内 .当风速达 5m·s- 1以上时 ,悬浮物浓度将显著增加 ,特别是底部泥沙悬浮增加 ,但在小风速条件下 ,悬浮物浓度的垂直变化不显著 .指示着有机物颗粒在水表层悬浮物中占相当大的比重 .上述这些结论对梅梁湾水源地的保护 ,对进一步认识水动力作用与悬浮物浓度分布 ,进而影响透明度和初级生产力 ,影响底泥内源污染释放 ,并在此基础上建立太湖生态环境管理模型非常重要 .

Taihu Lake is a large shallow lake, located in the Delta of the Yangtze River. The hydrodynamic processes exert a profound influence on the lake environmental evolution. Based on the field investigation in Meiliang Bay, Taihu, in the summer of 1998, this paper attempts to summarize the water current pattern during the summer prevailing wind forcing. With the prevailing of southeast wind, the water current shows a clockwise circle, i.e. the water flows northward in the western coast and southward along the eastern coast. But in the northeast, close to the mouth of Liangxi River, a small inconsistent water current pattern is presented. In the presence of above water current pattern, the distribution of Chl a concentration, as well as the total nitrogen (TN) and total phosphorus (TP), shows a pattern associated with directions of water flow in the Meiliang Bay, i.e. Chl a, TN and TP mostly concentrated in the northeast of Meiliang Bay. But the total dissolved nitrogen (TDN) and total dissolved phosphorus (TDP) concentrated in the northwest of bay because these components are less affected by the transportation of water flow. The solid suspension (SS) concentration changed with the intensity of wind forcing and with water depth. The investigation found that the concentration of SS at the mouth of bay is greater than that in the bay. Moreover, SS increased dramatically when the wind speed greater than 5m·s -1 , but slight difference with the water depth if wind speed less than 4-5m·s -1 , which indicated a high concentration of organic matter in the upper layer of water. These findings will be very helpful for the protection of drinking water source, and understanding the relation between hydrodynamic processes and water transparency, primary productionn, etc. It is also of importance for the construction of Taihu Lake environmental management model.