| Temperature is the basic condition of various physical,chemical and biological reaction processes in ecosystems.It plays an important role in eutrophication of lakes and algae growth.The temperature coefficients of various reaction processes are different.With the change of temperature,the relative variation and change trend of each reaction rate in the ecosystem are different,which can change the relative equilibrium state of the system and affect the growth of phytoplankton.This paper is mainly based on the large-scale shallow eutrophic lake-Taihu Lake.Through the long-term field observations of different points in different areas of Taihu Lake,the effects of temperature on main water quality indicators such as nutrients and chlorophyll-a(Chl-a)in the lake are systematically studied to understand the temperature effects in the lake.The relative contribution of temperature and water condition to the concentration of Chl-a in the water body under different temperature conditions and correlation between main water quality indicators and Chl-a are highly concerned.The results showed that:(1)There were spatial differences in the main factors affecting water quality in three lake areas(Meiliang Bay,Central Area and Estuary Area)of Taihu Lake.Among them,Meiliang Bay and Central Area had certain similarities,and the most important factors affecting water quality were related to phosphorus,Chl-a and CODmn.However,at the same time,nitrogen in Meiliang Bay also had important influence,while in the lake center,suspended solids had an important influence.The Estuary Area was quite different from Meiliang Bay and Central Area.The most important factors affecting water quality were related to TN,NH4+-N and water temperature.(2)Water temperature had an important impact on lake eutrophication,but there were differences in the impact on different areas.With the increase of water temperature,the overall eutrophication of Meiliang Bay and Estuary Area increased,mainly due to the increase of Chl-a and the increase of permanganate index.The eutrophication in the Estuary Area was the most serious,and it was always moderately eutrophic with the change of water temperature;Meiliang Bay was mildly eutrophic at lower temperature and would rise to moderate eutrophication with the increase of water temperature.The eutrophication degree in the Central Area decreased with the increase of water temperature.The eutrophication in the Central Area was milder than that in the other two areas,but it was also in a state of mild eutrophication.(3)In Meiliang Bay,when the water temperature was lower than 18 ?(low temperature interval),the concentration of Chl-a was low and the amplitude was small,and the water temperature was significantly correlated with Chl-a when the water temperature was greater than 18?(high temperature interval),Chl-a concentration was high and prone to extremely high values,but the correlation between water temperature and Chl-a was not significant,temperature had an interval effect on Chl-a,and high temperature was the basic condition for abnormally high values of Chl-a.The lake Central Area was similar to Meiliang Bay,but the interval effect of temperature effect was weak.(4)Water temperature fluctuation was an important factor affecting Chl-a in the high temperature interval.In the cooling month of high temperature interval,the abnormal high value of Chl-a was prone to occur;in the high temperature interval of the Cnetral Area,the water temperature change was significantly negatively correlated with Chl-a.(5)The variance decomposition results showed that for the variance contribution rate of Chl-a,the temperature factor of the low temperature section of Meiliang Bay was higher than the high temperature interval,and the contribution rate of the water quality factor in the low temperature interval was extremely small,but the high temperature interval was extremely high;The water quality factor and temperature factor were higher than the low temperature interval in the high temperature interval,but the relative contribution rate of the temperature factor was higher in the low temperature interval.In general,the ecological effect of temperature factor on Chl-a was prominent in the low temperature interval,while the high temperature interval Chl-a was mainly affected by water quality factors.The common interpretation rate of temperature factor and water quality factor in Meiliang Bay was higher,while the correlation between the two types of factors in Central Area was weak. |
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