| As a rapid economic growth city located in the estuary and coastal area, Shang-hai is listed as water shortage city. Is imminently how to command and master the river water resources, and use reasonable. So Qingcaosha Reservoir’s (located in changjiang estuary) construction and operation are given highly valued. As primary producers in aquatic ecosystems of river reservoir, Phytoplankton plays an important role in ecosystem succession, and water quality variation. During the10months of2012(except February and March), we monitored11points of Qingcaosha (totally19samples)13times. To evaluate the water quality of Qingcaosha reservoir, analyze community structure, density variation, dominant species distribution, diversity index and Chlorophyll a concentration, and explore the correlations between those indicators of phytoplankton standing stock and environmental factors, methods of comprehensive nutrition state index, community structure characteristics index, canonical correspondence analysis, principal component analysis and Monte Carlo permutation test and national standard of surface water were used. Constructing eutrophication management system, and providing reference for Dongfengxisha Reservoir. The main results as follows:1) Phytoplankton species, density and dominant speciesDuring the investigation, a total of8phylum,96genera,253species of phytoplankton were identified(with mutant and genera). Includes Chloroyta(47genera126species), Bacillarioyta(29genera83species), Euglenoyta(5genera20species), Cyanoyta(7genera13species), Cryptoyta(2genera7species), Chrysoyta(1specie), Pyrroyta(2genera2species), Xanthoyta(1specie). There are63～166phytoplankton species in reservoir every month, from May to October the number of species are more than100. Finding125～170species in monitoring points over the year.The phytoplankton density is about2.05×106～2.95×108cells/L in a single monitoring, average3.87×107cells/L, reach to the eutrophication level, especially in late summer and early autumn multi-point phytoplankton density over108cells/L. Months phytoplankton density is between7.15×106cells/Land1.04×108cells/L, and2.63×107～6.12×107cells/L in points, reached the early warning line of rich nutrition. The seasonal phytoplankton density from low to high is winter, spring, autumn, summer. The phytoplankton showes highly significant difference, so divides the reservior into three regions (head, middle and tail), the regional phytoplankton density exist significant difference. In each region: different of phytoplankton diversity in tail is minimal, in head is maximum. The composition of phytoplankton quite difference in various regions, middle and tail mainly in Chlorophyta and Cyanophyta, head is dominated by Bacillariophyta.High phytoplankton dominant species, Microcystis aeruginosa, Oscillatoria, Cryptomonas erosa, Melosira granulata, closterium kuetzingii, Cyclotella become dominant species for times, and occupied absolute superiority. As algal bloom phytoplankton, Anabaena became dominant in several sample, dominance of Microcystis aeruginosa was high in the whole year. Seasonal variation characteristics of dominant species showed as follows:sumrner>autumn=spring> winter.2) phytoplankton diversityMonth average of Shannon-Wiener index(H’) is about2.62～4.00, Evenness index(J) range0.50～0.89, Margalef diversity index(D) range2.73～4.62. Distribution of diversity index from low to high show as: head, middle, tail. Indicates the water is no or slight pollution.3) Chlorophyll a and water qualityThe annual mean of Chlorophyll a of Qingcaosha is about2.73mg/L, monthly variation range is0.04～13.19mg/L, seasonal variation of chlorophyll a is the same as phytoplankton density. Chlorophyll a in interlayers is differences. Influenced in Changjiang River, the nitrogen in Qingcaosha far exceed quota. Reservoir operation make flow speed slow, is good for suspended particles for sedimentating, great capacity, larger wind speed and maximum water depth exceeds10m, finally, make the water basically achieve II quality standard requirements,except TP and TN.Comprehensive nutrition state index value is between12.11and37.80, mainly for the poor nutrient level, several point in nutrition level. Seasonal variation of comprehensive nutrition state index like:spring (27.30)<winter (27.34)<autumn (28.04)<summer (28.46), the index shows that the Qingcaosha water quality is relatively good in spring, is relatively poor in summer.4) Correlation among algal density, chlorophyll a and environmental factorsEffects of environmental factors on phytoplankton are not identical, factors of transparency, total organic carbon, potassium permanganate index, total phosphorus, particulate matter, turbidity, chlorophyll a and phytoplankton density are significant correlation. Effects of environmental factors on chlorophyll a is different, chlorophyll a has significant negative correlation with dissolved oxygen (DO), total nitrogen (TN), suspended solids (SS), turbidity, total phosphorus (TP), and significant positive correlation to water temperature (T), transparency (SD). Although there are only2monitoring points of11, linear correlation between chlorophyll a and algae density is obviously, correlation between the month averages is significant positive.5) Correlation between diversity, dominant species and environmental factorsInfluence (Interpretation) of environmental factors on diversity index is different. By comparison, transparency main effects of Margalef index D (furthermore, D increasing when CODMN, T, chlorophyll a, pH, etc. increasing), ammonia nitrogen mainly affects the Shannon-Wiener index H’, and the dissolved oxygen is more likely to affect the pielou, other environmental factors make a different contribution to the diversity. The same environmental factors paly a different role on diversity index in different areas of the same season, or the same area in different seasons. Effect of different environmental factors on diversity in the same region of the same season is not the same. Results show that the turbidity, temperature and total nitrogen are the most important influence factors for dominant species (31species including varieties and Genus). Effect of environment factors on dominance species is different, the contributing of dominant species to environmental factors have overlap part. Some dominant species are great contribution to many kinds of environmental factors. Among, Cyanophyta such as Microcystis cyanobacteria, Anabaena, Chroococcus etc. on a larger contribution to chlorophyll a (result in chlorophyll a increased in summer). Coscinodiscus lacustris, oscillatoria, Selenastrum capricornutum etc. are more sensitive to temperature. Scenedesmus quadricanda, Anabeana etc. susceptible to permanganate index. Dominant species on a larger contribution to total nitrogen and total phosphorus is in the most.6) Environmental management system constructionFor nutrient concentrations exceed in upper reaches of Changjiang River, with slow water flow, transparency increasing leading to soluble nutrient concentrations in reservoir rise, Qingcaosha with the sign of seasonal and local Cyanophyta outbreak. Management control of Qingcaosha should take prevention and control measures in the Cyanophyta outbreak season and local region first, reduce nutrient inputing with macro-control, and establish emergency response system. Implement the management pattern combined early warning monitoring and eutrophication prevention together. |
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