Study On Water Quality Characteristics Of Forest Ecosystem In Chaocha River Basin Of Daxinganling,inner Mongolia

Larix gmelinii ecosystem is a typical bright forest ecosystem in Daxinganling area,which plays an important role in water conservation and water purification.By measuring the atmospheric precipitation of Xing’an Larch ecosystem and the water quality indexes of different hydrological regulation layers and sections in Chaocha River Basin,this experiment provides a scientific basis for the scientific evaluation of the environmental benefits of Xing’an Larch ecosystem,such as water purification and water conservation.The results show that:（1）During the observation period,the total rainfall of Larix gmelinii forest in Xing’an was 397.7mm,and all selected indicators were detected except fecal coliform;The rain outside the forest is weakly alkaline,the average turbidity is only 1.790 NTU,and the total ion concentration is low;Metal elements Fe,Cu,Zn,Mn,Pb,Cr⁶⁺and non-metallic elements PO₄^3-,NH₄⁺-N and NO₃^--N were detected,but their input was low;The measured values of COD,DO and BOD₅are small,and the overall water quality is relatively clean.（2）The whole Larix gmelinii forest can only purify Mn and NH₄⁺-N,and the purification rates are 78.04%and 12.01%respectively;The soil layer is the main purification layer,but it does not have the ability to purify Zn,Pb and Cr₆⁺;The canopy and trunk of Larix gmelinii forest will cause obvious acidification to precipitation;Canopy layer,litter layer and soil layer have strong turbidity effect;The leaching amount of total ions in each regulation layer is greater than the absorption amount;The four biochemical indexes of COD,DO,BOD₅and fecal coliform group deteriorate step by step after passing through the layer above the surface,and only the soil layer shows purification;Stem flow determines the input of various elements in Larix gmelinii forest in Daxing’an Mountains,followed by litter infiltration water.（3）Under the influence of Larix gmelinii forest the p H value and conductivity of different sections in Chaocha River show an increasing trend along the river direction;Cu,Zn,Mn and NO₃^--N are internal storage migration relative to atmospheric precipitation,while Fe,PO₄^3-,NH₄⁺-N,COD,BOD₅and fecal coliform are leaching migration;Do,Pb and Cr₆⁺are not affected by forests;The main sources of Pb and Cr₆⁺in each section are atmospheric precipitation,and the main sources of Fe are Stem flow and litter infiltration water;The main organic pollutants in each section are non degradable organic pollutants,and the purification rate of degradable organic pollutants in the whole Larix gmelinii forest has reached more than 85%;4,5 and 6 Sections are artificially polluted,and the contents of NH₄⁺-N and PO₄^3-are higher than those of the upstream section.（4）The evaluation results of comprehensive index evaluation method are as follows:except that the water quality of litter infiltration water is class II,other water samples are class I water quality.Although the chemical composition and concentration of atmospheric precipitation flowing through Larix gmelinii forest change significantly,it does not affect the overall water quality.