西太湖水生植物时空变化

Temporal and spatial variation of aquatic macrophytes in West Taihu Lake

水生植物在浅水湖泊生态系统中具有十分重要的作用。根据中国科学院太湖湖泊生态系统研究站1989年以来的常规监测资料，将西太湖（除东太湖以外的湖区）划分为9个区，采用点截法（point intercept method），于2002～2005年对各区水生植物的种类、生物量和空间分布情况进行了6次调查。结果表明：西太湖现有水生植物16种，分属于11科12属；水生植物总面积约10220hm^2，其中沉水植物分布面积约占64．58％；挺水植物约占0．29％；漂浮植物约占38．16％。各个种之间生物量差异显著，马来眼子菜、荇菜、芦苇的生物量在所有水生植物中居前3位。多样性分析表明，水生植物种类4a来未发生明显变化，但种类和生物量季节性差异较大。水生植物呈环状分布在距湖岸5km以内的水域和部分岛屿周围，东岸和南岸为水生植物的主要集中分布区域，分布区连续性好，且水草种类齐全。挺水植物种类单一，仅有芦苇（Phragmites communis）一种，分布区域多限于水深小于1．6m的湖岸；沉水植物共有8种，为水生植物的主要组成部分，马来眼子菜（Potamogeton malaianus）的分布频度最高，在西山岛周围水域逐年扩张，成为该区域的先锋种；漂浮植物3种，主要以荇菜（Nymphoides peltata）为主，在七都水域有逐渐扩张的趋势。马来眼子菜、芦苇、荇菜表现出对水环境较强的适应能力，目前为西太湖的3个优势种。20世纪50年代以来，西太湖水生植物种类减少了50种，其中水质下降是导致水生植物种类不断减少甚至消失的一个重要原因。围网养殖和不合理的捕捞方式也对局部水域的植物造成极大的破坏。水生植物生存环境日益严峻，种群单一化趋势日益明显。

The abundance and composition of aquatic macrophytes community has a great effect on a shallow lake ecosystem. Shallow lakes that support abundant aquatic macrophytes when the water is clear may be degraded by excessive nutrient inputs. Such degraded lakes are often turbid and devoid of aquatic vegetation. Taihu Lake is among the five fresh water lakes in China. Its ecosystem has deteriorated due to the increasing amount of pollutants discharged into the water body since the 1980s. Some aquatic macrophyte species decreased gradually and some even disappeared entirely in Taihu Lake. Many researchers focus attention on the aquatic macrophytes in East Taihu Lake while a few have focused on West Taihu lake specifically in recent years. In order to have a better understanding of the temporal and spatial aquatic macrophytes, we divided West Taihu Lake into nine zones according to the data of routine aquatic variation of macrophytes investigations since 1989 by Taihu Laboratory for Lake Ecosystem Research （TLLER）, Nanjing Institute of Geogrphy ＆ limnology, CAS. From 2002 to 2005, six comprehensive investigations on the macrophyte species, biomass and distribution in the nine zones had been performed with the point-intercept method in the entire area of West Taihu Lake. The results show that there are 16 aquatic macrophyte species in 11 families, 12 genera. The total distribution area of aquatic macrophytes is about 10220hm^2, among which 64.58% is for submerged macrophytes, 0.29% for emergent vegetation and 38.16% for floating vegetation. The biomass differs greatly among the species; Potamogeton malaianus, peltata , Phragmites communis top all the species in biomass. Biodiversity suggests that no obvious changes occurred to the species over the past four years, but there exists a great seasonal difference in the species and biomass. The macrophytes distribute circularly within 5km water body from the shore and around some islands. The east and south shore are the main areas for aquatic macrophyte distribution with a fine continuity and full range of species. The only species of emergent macrophytes is Phragmites communis, mainly distributing above - 1.6m water depth. There are 8 species of submerged macrophytes, making up the majority of aquatic vegetation, The distribution frequency of Potamogeton malaianus ranks first and it among peltata Taihu. is becoming the pioneer species with its constant spreading around Xishan island. Nymphoides peltata takes the lead the three floating macrophytes and tends to increase gradually in Qidu area. P. malaianus, P. communis and N. can strongly adapt to the changing environment, and they have become the dominant species in the West Lake Taihu. The degradation of water quality is among the main causes to the continuous decrease of The difference of sediments leads to a activities also cause tremendous threat distinc to the t regularity in the macrophyte distribution. Pen aquatic macmphytes in some areas. The aquatic aquatic macmphyte species. fishing and improper fishing macmphyte species in West Taihu Lake have continuously suffered decreases and some have become extinct since the 1950s, but they have remained relatively stable during the past four years. The aquatic macmphytes community shows a simple developing tendency and the living conditions for the macmphytes are now becoming more and more severe.