三江平原中东部沼泽湿地形成及其演化趋势的探讨

三江平原中东部是沼泽湿地集中连片分布地区。研究区有阶地沼泽和河漫滩沼泽两大类型沼泽分布，进一步可划分为4个沼泽体，即小叶章（Calamagrostis angustifolia）—毛苔草（Carex lasiocarpa）沼泽；毛苔草沼泽；睡菜（Menyanthes trifoliata）—水木贼（Equisetum limosum）沼泽；漂筏苔草（Carex pseudocuraica）—毛苔草沼泽。研究区沼泽湿地形成的主要自然因素为：①新构造运动的大面积沉降；②地势低平，坡降平缓、河道变迁，复杂的微地貌，易于积水，促使沼泽湿地的大面积形成；③厚3～17m的第四纪粘土层沉积地表，使地表渗透性差；④气候因素，研究区处于温带大陆性湿润季风气候区，雨量集中于夏季，且多秋雨，冬季积雪深度大，封冻期长，季节性冻土层厚；⑤水文因素，河流比降小，糙率大，流速缓，多为沼泽性河流，春汛与夏汛之间只出现平水不出现枯水，洪水期间，洼地和河流受松花江、黑龙江等大河、大江的洪水顶托，研究区的承泄条件差，内水不能外排，长期积蓄地表。目前研究区沼泽有变干的趋向。

Formation and Evolvement of Marshes in the Middle-east of the Sanjiang Plain

The marshes mainly lie in the middle-east part in the Sanjiang Plain.Marshes can be divided into terrace marsh and flood land.According to marsh wetland vegetation,marshes can be divided further into 4 bodies,Deyeuxia angustifolia-Carex lasiocarpa marsh,Carex lasiocarpa marsh,Menyanthes trifoliate-Equisetum limosum marsh and Carex pseudocuraic-Carex lasiocarpa marsh.Five factors contribute to the formation of the marshes in study region.They are the large area subsidence during Cenozoic Tectonic Movement period;the low altitude,large smooth relief,gentle slope grading together with the variance of river-way and complex micro-relief which benefit for the water-lagging and formation the marshal wetland in large area;the neozoic clay layer with depth of 3-17 m distributed in surface of this region,which results in weak soil infiltration,become another important factor of the formation of marshal wetland;the climate feature,the region has temperate continental humid monsoon climate with short and hot summer,the precipitation mainly occurs in summer and occasionally in fall as well,winter is long and cold featured with heavy snow and long soil frozen;hydrological feature,the river in this region belongs to typical marshal river with small river slope ratio,large coarse rate and slow velocity of flow,it only presented normal water in volume between 2 floods,never dry however,influenced by flood water of Songhua River and Heilong River,the water in water-lagging area and river in this area can not be drained out off this area during flooding period,causing the formation of marshal wetland.The marshes have drying trend in the present.