洪湖水体藻类藻相特征及其对生境的响应

藻类是水生态系统的重要成分,它的群落结构、细胞密度变化与水环境相适应,随水环境的变化而改变,因此藻相变化是评价水体质量的一项重要指标。2009—2010年在洪湖水面不同方位布点采样,对水体的浮游藻类藻相(群落结构、密度)和水质状况(水位(water level,H)、水温(water temperature,tw)、透明度(transparency,SD)、总氮(total nitrogen,TN)、总磷(totalphosphorus,TP)、高锰酸盐指数(permanganate index,CODMn)和叶绿素含量(chlorophyll a,Chl-a)等)进行了逐月的调查、监测,采用湖库营养状态指数法对湖泊富营养化评价,并运用多元逐步回归方法建立水体藻类与生境因子的回归方程。结果表明:洪湖水体总体上已达到轻度富营养化状态;藻类以蓝藻门、硅藻门和绿藻门为主,共鉴定出7门65属,藻细胞密度为1.14×106—3.24×107个/L,藻相季节变化特征明显。藻类组成以蓝藻门密度最高(52.93%),硅藻门(25.96%)和绿藻门(16.83%)次之,隐藻门(1.98%)、金藻门(1.64%)、裸藻门(0.42%)和甲藻门(0.25%)相对较低。藻类藻相及优势种在不同季节有所差异,冬春季节(12—5月)以硅藻门的直链藻、小环藻和针杆藻为优势种,夏秋季节(7—11月)以蓝藻门的鱼腥藻和微囊藻为优势种;湖泊藻类细胞密度与tw、CODMn呈正显著相关关系,与H、TN、TP、SD相关关系不显著;藻细胞生长逐步回归方程为y=3.7815+0.0794tw+0.5670CODMn-1.3467SD,藻细胞生长主要受水温和有机污染物等的影响,氮磷不是藻类生长的控制因子;在湖泊不同区域,环境条件存在差异,导致藻类生长过程中起主导作用的环境因子存在一定的差异,蓝藻生长主要受tw、CODMn和SD控制,绿藻生长主要受H、tw和CODMn影响,而硅藻生长决定于水体CODMn。

Characteristics of algous facies of planktonic algae in lake honghu and its response to habitat

Lake Honghu, crossing over Honghu county and Jianli county in Hubei Province, China, is situated in the north of the middle reaches of Yangtze River. Because of unreasonable exploitation of wetland resources and discharge of pollutants,it confronted with series problems such as decrease of the lake area and wetland biodiversity, sharp reduction of rare species and its eutrophication of water body. Study for planktonic algae reflecting water ecological environment change will provide a scientific basis for protection of Lake Honghu. Algae are important composition of aquatic ecosystem; their community structure and function are adaptable to water environment, and vary with changing water environment. The characteristics of community structure can be used as an important index in the assessment of water quality. In order to understand the change of water environment in Lake Honghu, Hubei, China, we measured a set of variables related to water quality, including structure and density of algous community, water level(H),water temperature (t_w), transparency(SD), permanganate index (COD_Mn), total nitrogen (TN), total phosphorus (TP) and chlorophyll a content(Chl-a). The above experiments were conducted monthly between 2009 and 2010 at the five sections in Lake Honghu. The nutrition state was evaluated with eutrophication index for Lake and Reservoir; the influence of some environmental factors on algous cell density was analyzed by correlation analysis and stepwise multiple regression; and some stepwise multiple regression equations were established. Analytical results showed that the water was in light eutrophication in Lake Honghu. Totally, 7 phylum and 65 genera of planktonic algae were identified in the lake. The algous cell density ranged from 1.14 million cells per litre water to 32.4 million per litre water. Bacillariophyta was the most abundant phylum of planktonic algae, the following were Chlorophyta and Cyanophyta, in view of algous population distribution. Its algous community are 52.93% for Cyanophyta, 25.96% for Bacillariophyta, 16.83% for Cyanobacteria, 1.98% for Cryptophyta, 1.64% for Chrysophyta, 0.42% for Euglenophyta, and 0.25% for Pyrrophyta. In light of structure and density of algous community change seasonally, the dominant species are Melosira and Cyclotena within Bacillariophyta in winter and spring, Anabaena of Chlorophyta in summer and autumn. There is a statistically significant positive relationship between algous cell density, water temperature and permanganate index, whereas there is no obvious relationship between algous cell density, water level, total phosphorus, total nitrogen and transparency. The Stepwise regression equation of growth for planktonic algae was that: y=3.7815+0.0794t_w+0.5670COD_Mn-1.3467SD (R²=0.618, F=8.087, P<0.02). This indicates that algous cell density could be used to reflect the pollution level caused by water temperature and organic pollutants, and the controlling of nitrogen and phosphorus has not been tone of the key factors. The characteristics of algous cell density are controlled by the different environmental conditions at the five sections, such as Bacillariophyta controlled by water temperature, permanganate index and transparency, Chlorophyta controlled by water level (H), water temperature and permanganate index, and Cyanophyta controlled by permanganate index. Based on the results, there are great significance for the effective measures on slowdown of water eutrophication and inhibit of the algous growth process in Lake Honghu, by controlling nitrogen, phosphorus and organic pollutants inputs of Sihu Main Cannal, reducing cages culture area, and restoring water connectivity of Yangtze River and Lake Honghu.