Study On The Characteristics Of Water Quality Parameters And Stable Isotopes In Lake Qilu

Lakes play an important role in regional climate regulation and regional social and economic development.As the “mother lake” of Tonghai County,Lake Qilu has faced many threats to the ecological environment in recent years under the dual influence of nature and human activities.Based on this situation,in this article,we first used the water quality parameters including water temperature(Temp),dissolved oxygen(DO),chlorophyll-a(Chl-a),total phosphorus(TP)and total nitrogen(TN)of lake Qilu from November 2016 to October 2017 monitored monthly,further discussing the ecological environment and the monthly variation of water quality in Lake Qilu.At the same time,combined with the available meteorological data and used the composition characteristics of stable hydrogen and oxygen isotopes of various water in Lake Qilu drainage area to study hydrodynamics,water vapor sources and seasonal changes of Qilu lake,and discussed the effects of water quality parameters on lake water isotopes.By analyzing the composition and seasonal variation characteristics of hydrogen and oxygen isotopes in various water bodies,deeply discussed the water cycle process of the basin,and analyzed the water replacement process and cycle of Lake Qilu.The main conclusions of this article are as follows:(1)Lake Qilu plays a significant role in regulating the climate and environment of the basin,maintaining relatively stable temperature and reducing the impact of extreme weather on the regional climate.The heat distribution of lake water is more balanced at different depths.Water temperature is greatly affected by wind force and lake dynamics.At the same time,temperature is a controlling factor that affects the water cycle of the lake and the intensity of aquatic organisms.(2)Lake Qilu was strongly influenced by human activities in the basin,and the influence of exogenous input was the main factor that caused the physicochemical properties(dissolved oxygen ? chlorophyll-a ? p H)of lake water.The increase of algae activity caused by the input of nutrients and the discharge and decomposition in p H and alkalinity in different regions of Lake Qilu.The decomposition of organic pollutants simultaneously consumed the dissolved oxygen in the water body,thus,the lower dissolved oxygen concentration and p H value were found in the lakeside and southwest of Lake Qilu where inflowing rivers concentrated.The differences of nutrients in different lake area caused different spatial distribution of algae.in the eastern and southwestern regions of Lake Qilu where industrial and agricultural emissions are concentrated,the concentration of chlorophyll a in the water is much higher than in other lake regions.It also causes many environmental problems,such as the increase of lake sediment release,the simplificaton of aquatic species structure,the decline of water body self-purification ability and so on.(3)The degree of eutrophication in Lake Qilu is relatively high.During the monitoring period,the lake is in a medium-heavy eutrophication state,the concentration of nitrogen and phosphorus in water was at a high level throughout the year.Phosphorus is the limiting factor of algae growth and reproduction in Lake Qilu.The total phosphorus concentration in Lake Qilu fluctuates seasonally.It increased by nearly 40% in summer compared with the winter,the seasonal variation of total nitrogen was relatively small,and it is higher in summer than in winter.The discharge of chemical industry in the lakeside area increases the content of nitrogen and phosphorus(especially total phosphorus)in Lake Qilu.Agricultural discharge has a greater impact on total nitrogen in water bodies,and has a smaller impact on total phosphorus.The concentration of nutrients in rivers and groundwater of drainage area of Lake Qilu is also high,and the problems of local water resources and water safety are prominent.(4)The isotopic composition of the lake water does not change significantly with depth,and the role of evaporation and river water recharge determines the special distribution characteristics of lake water isotopes.The water temperature has a certain influence on the isotopic fractionation of the surface lake water,and the effect on its spatial distribution also exists,but the overall effect is not significant.There is no necessary relationship between other water quality parameters and isotope composition of lake water,and there is no obvious rule of spatial distribution change.(5)The slopes and intercepts of lake water evaporation equations in Lake Qilu have significant deviations from the global atmospheric waterline in the whole year and in all seasons.The lake water was affected by the long-term evaporative fractionation.The isotope composition of river water and groundwater in Lake Qilu Basin is negative with respect to the lake water,and the deviation of evaporation line is also smaller than lake water.The non-equilibrium fractionation of groundwater is weaker.Marine water vapor is the main source of local precipitation,and river replenishment into lakes is the main supply method for lake water.(6)According to the difference of the isotopic composition of the lake water before and after the rainy season,we can draw a conclusion that the water exchange cycle of the lake water is short,only 1.32 years.The rapid renewal of water can help to purify lake waterthrough other water importing to Lake Qilu,and improve the water quality of the lake.however,the eutrophication status is more severe due to the water pollution of other water bodies in the basin,and the renewal of lake water does not play a role in purifying water quality.Therefore,adjusting industrial structure and advocating green economy are of great significance in improving lake water quality and promoting economic and environmental friendly development.Therefore,adjusting industrial structure and advocating green economy are of great significance in improving lake water quality and promoting economic and environmental friendly development.