Research On The Impact Mechanism Of Human Activities On The Ecological Environment Of The Small Watershed Of Dianchi Lake

The sustainable development of population,resources,environment and economy has become the focus of governments of all countries.In the lake basin,population expansion and economic development destroy ecological environment.Human activities have become the main driving force of the ecological environmental degradation.Resources shortage and ecological environment deterioration have seriously hindered the sustainable development of regional economy.Dianchi basin has an important status in Yunnan Province.As a plateau lake under the special geographical environment,the river basin faces significant environment degradation,such as shortage of water resources,lake eutrophication,soil erosion,soil pollution and so on.These threaten people's health and daily life.Taking Xibaisha catchment as the study area,temporal and spatial distribution of surface soil and sediment biogenic elements,heavy metal pollutants were analyzed.The ecological and environmental deterioration history was traced.Also the ecological environment damage driving force was compared.Population expansion,industrial and agricultural economic development and human activities were investigated to give scientific evaluation for watershed ecology,provide theoretical support for the reconstruction of basin environment and to maintain regional sustainable development.(1)The physical and chemical properties and texture of soil in Xibaisha catchment were related to land use types.Cultivated land,grassland and woodland were fine texture that they had higher clay and silt particle contents.Unplanted land's texture was reduced for the lower clay and silt particle contents.TOC,TN and TP contents were mainly found in the soil surface layers.The distribution of TOC and TN in different land use types were as follows,respectively:grassland>woodland>cultivated land>unplanted land;woodland>grassland>cultivated land>unplanted land.Except the cultivated land was in high content of TP,grassland,woodland and unplanted land had some difference.The C/N,C/P and N/P values showed that the soil was fertile and the nutrients in the basin were high in availability.However,the risk of eutrophication was higher correspondingly.The average contents of heavy metals including Cu,Zn,Pb,Cd and Cr in soil samples were 43.58,136.38,98.05,2.44 and 74.99 mg/kg,respectively.In addition to Cu,the other four elements were contaminated.Using Nemero pollution index to judge the heavy metals pollution,the pollution level was:unplanted land>grassland>cultivated land>woodland.(2)The accumulation rate of the catchment decreased with the increase of burial depth.The deposition of 0?31cm column dated the year from 1881 to 2011.The contents of TOC,TN and TP in the sedimentary column decreased with the increase of burial depth,and the ?13C value changed with the time to the negative direction.The fluctuation of organic matter revealed the change of sedimentary environment in the basin.The overall change trends of TOC,TN and TP deposition fluxed increased exponentially.The estimated value of TOC,TN and TP deposited in 2010 were 85.20,9.52,and 4.24t,respectively.The average values of C/N,C/P and N/P in sedimentary column were 16.99,19.98 and 2.32.Nitrogen was main control factor affecting the water environment in the catchment.Organic index showed that the organic pollution degree of the basin sediment had increased with time,resulting in the risk of environmental pollution.The heavy metal elements including Pb,Cu,Zn,Cd and Cr in the sediment column were under the enrichment state.Estimating the total depositions of Pb,Cu,Zn,Cd and Cr in 2010,which were:0.55,1.70,0.55,37.57 and 5.56t.The accumulation index of heavy metals in sedimentary column revealed the extent of pollution:Cd>Zn>Cr>Cu>Pb.The evaluation of potential ecological risk indexes of E ri for Cu,Zn,Pb,Cd and Cr were 79.78,49.89,20.86,2024.00 and 20.08,corresponding to the degrees of harm:moderate harm,moderate harm,slight harm,strong harm and slight harm.The ecological risk of heavy metals pollution in sediment mainly came from Cd.Four kinds of heavy metal speciation distributions:acid extractable,reducible,oxidizable and residual fractions showed that four kinds of heavy metals in the different stages of the environmental risked differences.The risk of the order was:Cd>Zn>Cu>Cr>Pb.(3)Results of radioisotope tracers showed that soil erosion status of the catchment belonged to micro-moderate erosion.In the soil profile,TN,TP,TOC,Cu,Zn,Pb,Cd and Cr average annual erosion loss estimates were 35.84,6.18,2.02,0.13,0.42,0.30,0.01 and 0.23t/a,accounting for the total deposition ratioes of 42.06%,64.91%,47.64%,7.65%,1.12%,54.55%,1.45%and 4.14%.A small amount of storage erosion produced,contrarily the heavy metal pollutants in the sediments mainly came from the industrial and agricultural activities.Using the environmental indication information of C/N and?13C values,it can be concluded that the organic matter of sediment was affected by both internal and terrestrial sources.The proportion of terrigenous organic matter increased with time.Correlation analysis showed that Pb and Cu,Zn and Cr reached at the 0.05 level were significantly correlated.The correlation coefficients were 0.46 and 0.38.The principal component analysis extracted three principal components and the main sources and the contribution rates were:steel chemical wastewater emissions,accounting for 27.06%;mining processing and transportation of dust accounting for 25.03%;mining processing wastewater discharge accounting for 21.94%.Three main sources cumulative contribution rated 74.03%of the total pollution source.A comprehensive study of different pollutants sources of damage to the ecological contribution by principal component analysis extracted three main factors:industrial production wastewater was the main factor of ecological destruction,the total contribution rate was 49.41%;followed by soil erosion,accounting for 27.74%;and the waste gas and dust pollution in industrial production and the proportion of 10.19%.(4)Population growth,social economic development and environmental management had a good coupling with the change of ecological environment in Xibaisha catchment.Population growth,economic and social development were the main factors causing pollutants increasing and destructing the ecological environment of small watershed.Management polices of gain mode protected environment,and polices of impairment mode had damaging effect on the environment.Applicating the ecological environment quality index method,the ecological quality of the catchment evaluation score of 42.75 was got,which belonged to the "general" level.That meaned the general level of biodiversity,vegetation coverage,more suitable for lives.But factors which were not suitable for human life exist.The main factor restricting the catchment was pollution load.The result of evaluation indicated that the main environmental problem in Xibaisha catchment was caused by human activities of the industrial pollution.Four suggestions were put forward for environmental restoration and protection:improving environmental conditions,improving the regional industrial structure,the scientific management of cultivated land and protection of forest resources.