Study On The Correlation Between Phytoplankton And Environmental Factors In Dianshanhu

Dianshanhu as the only natural freshwater lake in Shanghai, is an important partof the upper reaches of the Huangpu River water source protection areas. In recentyears, growing Dianshanhu eutrophication, especially outbreaks of algal blooms insummer, play a serious impact on the health of ecosystems and ecological functions. Itis also a serious threat to water environment security. From August2012to December2013, we had taken phytoplankton sampling survey in the whole lake. Dianshanhuwater area were setted12sampling sites, sampling once a month, the massive growthof phytoplankton in summer sampling twice a month in July and August, a total of19samples. Not only phytoplankton species composition, quantity changes, the dominantspecies were studied, but also measured physical and chemical indicators of water,combined with phytoplankton community structure correlation analysis to identify theimpact of the distribution of the key environmental factor. Combined with thephytoplankton functions group theory, characteristics and seasonal changes in theconsolidated summary Dianshanhu algae habitat, ecological function to matchseasonal succession of phytoplankton group relationship with algae habitat changes,and explore how Dianshanhu algae habitat change affects the growth of algae and thecommunity succession. Outbreaks of blue-green algae in summer, we detect MC-LRin the water, provide basic data for Dianshanhu eutrophication and algal blooms forecast management. The main results are as follows:1、 From August2012and December2013, were identified Dianshanhuphytoplankton142taxa, belonging to7phylum56genera. Chlorophyta were foundamong28genera60species, accounting for43%of the total; Diatoms were found14genera32species accounted for20%of the total; Cyanophyta were found6generaand22species, accounting for13%of the total; Euglenophyta were found3genera14species, accounting for8%of the total; rest of the identified species include:Chrysophyta were found4genera5species, Dinophyta were found2genera and4species, Cryptophyta were found2genera5species.2、The average number of phytoplankton in the range between180-2435tenthousand/L, it was rather changeable. The maximum Phytoplankton amount was inAugust2013in the5th sample sites, reaching33,681,500/L, the minimum was inFebruary2013in the4th sample sites about337,500/L; The maximum biomass wasin August2013in the7th sample sites, reaching16.61mg/L, the lowest was inJanuary2013in the4th sample sites, only about0.13mg/L. Phytoplankton amountfrom August2012to February2013, showing a downward trend month by month;from February2013to August2013, demonstrates a gradually rising trend. Thehorizontal distribution of phytoplankton has a certain trend that it is decrease fromnorthwest to the southeast.3、Dianshanhu phytoplankton dominant species change over time, the successionhas obvious characteristics. The dominant species throughout the year areChroomonas acuta, Cyclotella sp., Merismopedia minima, Anabaena sp. Each seasonappears different species, there is a significant phenomenon that the dominant specieshave seasonal.4、We observed21phytoplankton functional groups in Dianshanhu, statisticalfrequency of various phytoplankton functional groups appeared in Dianshanhu, foundthat B, P, D, X1, X2, J, L0, MP have higher frequency, and occupy a higherabundance ratio. The group E, XPH, N group appeared only in a particular season.With seasonal variations caused by changes in Dianshanhu environmental conditions,there is a significant succession rule among phytoplankton functional groups. In spring, phytoplankton functional groups are C, P, B, L0, in summer, phytoplanktonfunctional groups are LM, P, G, J, L0, in autumn, it changes to W2, Y, MP, X1, theultimate succession of winter is E, Y, B.5、In The algae outbreak period，we detect water content of MC-LR. The resultsshow that in some sample sites in August, which the strip is visible on the surface ofthe water, detecting the presence of a small amount of toxin, the mean content ofMC-LR is about0.34ug/L, most of the remaining water area is not detected. Thisresult may be related to pollution control and algae control in recent years inDianshanhu.6、Use of canonical correspondence analysis showed that the water temperature,transparency, dissolved oxygen, total nitrogen, total suspended solids are the mainfactors affecting the distribution of phytoplankton, while pH, total phosphorus,salinity play little impact on phytoplankton.