鄱阳湖典型湿地沉积物粒度分布及其动力解释

GRANULOMETRIC CHARACTERISTICS AND THEIR DYNAMIC INTERPRETATION ON PRESENT DEPOSITS OF TYPICAL WETLAND IN POYANG LAKE

通过对沉积物粒度分析,揭示出鄱阳湖典型湿地现代沉积物主要由含泥细粉砂至泥质极细粉砂组成,反映出三角洲前缘低能沉积环境。控制湿地粒度分布的动力,主要为重力型湖流,但波浪和风的作用也参与了沉积物的搬运与沉积。汛期,重力型湖流不仅控制了粒度分布的区域特征,而且决定了由草滩顶部-草滩下部-过渡带-泥滩沉积断面上粒度特征递变规律;枯水期,波浪作用的改造,使得沉积断面上的过渡带沉积物粗化,并使各粒度参数相应变化,特别是面积较大洼地的迎风岸,在过渡带地面坡度转折处,出现了粒度突变或跃变;风蚀“沙山”物质的搬运,使得“沙山”附近的湿地含砂量猛增,粒径变粗。这些动力作用,还控制着湿地的演化,即湿地范围增大,草滩扩张,过渡带以及泥滩下移,枯水期洼地水面缩小且趋于消亡,严重影响湿地的生态环境,但可通过建造人工闸坝加以控制。

Based on granulometric analysis on the present deposits of the typical wetland in Poyang Lake, the components of these present deposits are exposed to range mainly from fine silt with mud to very fine muddy silt, showing low-energy depositional environment of the delta front. The grain-size distributions are mainly controlled by the gravitative lake current and partly reworked by wind wave actions. During flood periods, the lake gravitative current is dominative since it controls not only grain-size regional distributions, but also the rule which granulometric characteristics gradually change from the top of meadow bottomlands to muddy bottomlands. During low water periods, the wave and wind actions are active. In transitional bottomland at the wind-faced bank at the sedimentary section profile, the wave action reworks sediments much coarser, and results in granulometric features accordant change and, especially, abrupt change at the topographic gradient break of larger depression. The wind erodes 'Sand Hill' and moves eroded materials to the wetland nearby, which makes sediment coarser and richer in sand in part of the wetland. These dynamic actions also control the wetland evolution and result in the following eco-environment aggravation, i.e. , the wetland, the meadow bottomland, the transitional bottomland and the muddy bottomland expansed, and water area gradually replaced by the meadow bottomland during low water periods. However, the above-mentioned problem can be solved by building sluice-dams.