| The Taihu Lake Basin has been affected by long-term acid deposition,causing a large amount of calcium and magnesium to be lost into the Taihu Lake,and resulting in an increase in the calcium and magnesium concentration in the water body and changes in the distribution in different media.The loss of large amounts of calcium and magnesium from the catchment not only causes the hardness of the water body to increase,but also has a significant impact on the land and water environment and the water ecosystem.In order to reveal the impact of acidification in the Taihu Lake Basin on the changes of the morphology and proportion of calcium and magnesium in the process of geochemical migration,this study systematically collected and analyzed samples of different media in the Taihu Lake Basin and Taihu Lake and collected and analyzed relevant historical data Including:field sampling of wetland soil in Yili water system,wetland soil and farmland soil samples near Dapu town in the lower reaches of Yili water system to compare the effect of watershed acidification on the proportion of calcium and magnesium in different land types,collected the hydrochemical data of Taihu Lake in the past 60 years,and 2017—2019,the Taihu Lake water,algae,sediments and benthic animals were sampled and tested many times.The analysis results show that:(1)The total Ca/Mg of the surface wetland soil in the Yili water system is significantly higher than that in the deep layer(p<0.05).Further analysis of different forms of Ca and Mg found that there is no significant difference in the distribution characteristics of exchangeable Ca/Mg in the upper,middle and lower reaches of the Yili water system.The exchangeable Ca/Mg of the soil is basically maintained at 4;as the soil pH decreases,the surface acid-extracted Mg is faster than that of acid-extracted Ca(r=-0.43,p<0.01).The acid-extracted Ca/Mg of the soil surface is significantly higher than that of the deep layer(p<0.05);In addition,the acid-extracted Ca/Mg of the soil(6.34±5.21)significantly greater than the exchanged Ca/Mg(4.06±1.20)(p<0.01),the change of Ca/Mg in the top soil is mainly driven by environmental acidification.(2)The pH of the farmland soil is reduced by acid deposition and nitrogen fertilizer superposition and acidification.The acid-extracted Mg loses more than the wetland soil(r=-0.37,p<0.01),so the farmland soil acid-extracted Ca/Mg is significantly higher in wetland soil(p<0.01)There is no significant difference in the profile of total Ca/Mg in the farmland soil,which may be due to the absorption and utilization of Ca by crops,so that the Ca content in the surface layer is significantly lower than that in the deep layer(p<0.05).The acid-extracted Ca/Mg of farmland soil was significantly positively correlated with organic matter(r=0.54,p<0.01).(3)Although Ca2+ and Mg2+ in Taihu Lake have shown a significant upward trend in the past 60 years(p<0.01),there is no significant change in Ca2+/Mg2+ in the lake water.The pH of Taihu Lake water was significantly negatively correlated with Ca2+/Mg2+ in the lake water(r=-0.46,p<0.05),indicating that algae increased the pH of the water through photosynthesis to promote the formation of carbonate precipitation of Ca2+ in the lake water.In addition,the acid-extracted Ca/Mg in the sediments of Taihu Lake was 3.85±3.70.The acid-extracted Ca/Mg in the northwest algal lake area was significantly lower than that in the southeast grass-type lake area.The outbreak of algal blooms in the northwest lake area was frequent,indicating that the algae may reduce the absorption and utilization of Ca.The content of CaCO3 in the sediment.The algae Ca/Mg(2.76±0.09)in the northwestern lake area was significantly higher than that in the southeast lake area(2.00±0.30)(p<0.01).The absorption and utilization of Ca2+ by the algae in the lake water may be much greater than Mg2+,resulting in the Ca2+/Mg2+ in the lake water.The algal blooms fell during the outbreak.(4)The value of Ca2+/Mg2+ in pore water of Taihu Lake sediments is 2.53±0.75,which is slightly higher than that of overlying water.The exchangeable Ca/Mg of sediments in Taihu Lake was 4.02±1.03 and there was no significant difference between the soil exchangeable Ca/Mg of the watershed.The total Ca/Mg of Taihu sediments is 0.82±0.35.which is slightly lower than the total Ca/Mg of soils in the Yili water system of the Taihu Lake Basin.Because the Ca/Mg of benthic benthic organisms in the Taihu sediments is 1462.52±468.08,it is speculated that it may be due to benthic the absorption and utilization of Ca in sediments during the formation of animal bioshells is much greater than that of Mg,which reduces the total Ca/Mg of sediments.Basin acidification and algae and other biological effects have important effects on the distribution characteristics of calcium and magnesium in different media in the Taihu Lake Basin.At present,Ca2+ and Mg2+ in Taihu Lake still have an upward trend,and Ca2+/Mg2+may also change due to strong human interference and will further affect the aquatic environment of Taihu Basin.In the study of the water environment of Taihu Lake,the changes in water chemistry and aquatic ecology caused by anthropogenic acidification in the Taihu Lake Basin need to be strengthened. |
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