Analysis On Main Phosphorus Sources Of Water Body And Their Driving Factors In Hulunbeier Steppe Wetland,Inner Mongolia

The wetland located in Hulun Buir grassland(hereinafter referred to as Hulun Buir Steppe Wetland)is an important part of the Daurian Steppe Wetlands.Daurian steppe area is situated in China,Mongolia and Russian,the area possesses a very high level of biodiversity and its very important for the protection of the world's remaining natural structures and endangered species of plants and animals,especially the world's most important rare birds and large number of migratory waterfowl.In recent years,the arid climate,the few precipitation and the overgrazing in the grassland surrounding the wetland resulted in the reduction of wetland area and the trend of eutrophication in the wetland water body.These reasons lead the ecological function of the wetland can't be used normally,and the ability to resist natural disasters is reduced.Nevertheless,Phosphorus(P)in wetland water body is one of the most important factors of eutrophication.In view of the deterioration of water quality in Steppe Wetland,through field sampling and laboratory simulation experiments,this paper reveals the phosphorus source of rainfall runoff,snowmelt runoff and phosphorus release from the sediment of water body and its main influencing factors.By using a self-made simulated rainfall device,the phosphorus transport of rainfall surface runoff of 6 different types of grassland soil was analyzed and combined with the ultrasonic snow thickness measurement device and snowmelt simulation device,the phosphorus transport of snowmelt surface runoff of 6 different types of grassland soil was studied.At the same time,the influence of the release of the sediment on the phosphorus content of the water body was discussed under the simulated temperature warming system of the self-made wetland habitat device.The main conclusions were as follows:(1)Different types of soil under different slope,the total phosphorus content in runoff showed a different trend.When the slope was 0 degrees,total phosphorus loss with rainfall surface runoff was ranged from 0.01 to 0.16 mg·L-1,the range was 0.01 to 0.15 mg·L-1 in the slope of 5 degrees and the range was 0.01 to 0.38 mg·L-1 in the slope of 15 degrees.(2)Soil hardness,soil water content(SW),soil conductivity,soil pH(pH),soil Olsen-P(SO)and total nitrogen content of soil(SN)were important factors affecting total phosphorus loss with rainfall surface runoff.The multiple regression equation of total phosphorus loss with rainfall surface runoff was Y=7.429-0.439 SN-6.834 pH+1.721 SO+0.183 SW(r=0.487,P<0.01).(3)The change trend of total phosphorus loss with snowmelt surface runoff under different slopes was as follows:when the slope was 0 degrees,the change range of total phosphorus content was 0.04 to 0.20 mg.L-1,and when the slope was 5 degrees,the change range of total phosphorus content was 0.03 to 0.12 mg L-1.Furthermore,when the slope was 0 degrees,the order of total phosphorus loss with snowmelt surface runoff was Alkaline saline soil(S5)>Chernozem soil(S6)>Aeolian sandy soil(S1)>Meadow soil(S3)>Bog soil(S4)>Chestnut soil(S2),and when the slope was 5 degrees,the order was S5>S4>S3>S6>S2>S2.(4)The content of total phosphorus in soil(TP),the content of Aluminum phosphate(Al-P)and the content of Ferric phosphate in soil(Fe-P)were important factors affecting the total phosphorus loss with snowmelt runoff.The multiple regression equation of total phosphorus loss with snowmelt runoff was Y=0.971+0.031 TP+0.056 Al-P-0.023 Fe-P(r=0.928,P=0.046).(5)Under the ambient temperature incubation,the variation of total phosphorus(TP)release rates ranged from 0.01 to 0.13 mg·m-2·d-1,and the range of change was 0.07 to 0.16 mg·m-2·d-1 after cultivated at temperature raise at 2.5 degree(hereinafter referred to as warming).The total phosphorus release rates in four types of wetlands were increased after two months of warming cultivated.Under ambient temperature,the change of dissolved reactive phosphorus(DRP)ranged from 0.00 to 0.07 mg·m-2·d-1,and the range of change were-0.03 to 0.03 mg·m-2·d-1 after warming.(6)Olsen-P content in soil(Olsen-P),organic matter content in sediment(SOM),labile organic carbon(LOC),medium labile organic carbon(MLOC),high labile organic carbon(HLOC),SO42-content in sediment(S-SO42-),microbial biomass nitrogen(MBP),inorganophosphate degradation bacterium(IODB),ratio of organic carbon and total phosphorus(SOC:TP),ratio of microbial biomass carbon and phosphorus(MBC:MBP)and clay content can directly and indirectly affect the phosphorus release rates,the content of LOC,Olsen-P and SOC:TP in wetland sediments and the interaction of them were the main driving factors for TP release from sediment.(7)Under the ambient temperature incubation,the TP release potential were ranged from-0.42 to 0.73 mg·m-2·d-1.After warming,the change ranged from-0.26 to 0.68 mg·m-2·d-1.The DRP release potential of four types of wetlands were varied from-0.38 to 0.70 mg·m-2·d-1 under ambient temperature,and the range were-0.36 to 0.48 mg·m-2·d-1 after warming.(8)Total phosphorus content in overlaying water(W-TP),dissolved reactive phosphorus content in overlaying water(W-DRP),silt percentage,sand percentage,microbial biomass carbon(MBC),pH,SO42-content in overlying(W-SO42-)and alkaline phosphatase activity(APA)can directly and indirectly influence the release potential of dissolved reactive phosphorus(Fp-DRP).The silt content,sand content,APA and the interactions between them,were the main driving factors of Fp-DRP.