| The Qinghai-Tibet Plateau agroecosystem is unique and fragile,and its arable soil quality not only directly restricts food security and sustainable agricultural development in the region,but also affects ecosystem stability and is closely related to the ecological environmental protection and regulation role of the Qinghai-Tibet Plateau.There are two core components of cultivated soil quality: cultivated land strength and cultivated land environmental quality.The core element of cultivated land strength is soil nutrients,while the main factor affecting the quality of cultivated land environment is soil heavy metal pollution.Therefore,the study of the characteristics and linkage between soil nutrients and heavy metal pollution in arable land on the Qinghai-Tibet Plateau is of great significance for the high-quality development of agriculture and ecological environmental protection on the Qinghai-Tibet Plateau.In this study,120 soil samples were collected from representative and typical croplands in Huzhu County,a typical agricultural county in the Hehuang Valley of the Qinghai-Tibet Plateau,and the content characteristics and spatial distribution patterns of soil nutrients(organic matter(OM),total nitrogen(TN),available phosphorus(AP),available potassium(AK))and heavy metals(chromium(Cr),cadmium(Cd),plumbum(Pb),arsenic(As),hydrargyrum(Hg))were analyzed using mathematical and geostatistical methods;the risk index was used to study the pollution of heavy metals The risk level was studied;the influence factors of heavy metal sources and spatial heterogeneity were studied by combining spatial analysis,multivariate statistical analysis and geographic detector model.The main research results are as follows.(1)The characteristics and spatial distribution patterns of soil nutrient contents were revealed.The average contents of OM,TN,AP and AK in cultivated soils of Huzhu County were 23.41 g/kg,1.52 g/kg,33.50 mg/kg and 164.26 mg/kg,respectively,and the average content of organic matter was at level 3 and the other three at level 2according to the nutrient content grading standard of The Second National Soil Census,rich in soil nutrients.The spatial variability of OM and TN is small and has a similar spatial variability trend,with the content gradually increasing from southwest to northeast;the spatial distribution of AP is blocky and regionalized;the content of AK is high in the cultivated land in the River valley and low in the cultivated land at higher altitudes.(2)The characteristics and spatial distribution patterns of soil heavy metal contents were revealed.The average contents of Cr,Cd,Pb,Hg and As in cultivated soils in Huchu County were 70.80 mg/kg,0.24 mg/kg,23.70 mg/kg,0.08 mg/kg and 12.20mg/kg,respectively,and the first four exceeded 1.01,1.71,1.14 and 4.00 times of the average background value of soils in Qinghai Province,but As did not exceed the average background value,and none of them exceeded the soil quality standard for agricultural land in China.The spatial distribution of Cr,Pb and As had some similarity,with high value areas in Nanmenxia Township and Linchuan Township in the north,and As in Danma Township;the spatial distribution pattern of Cd was complex,with high value areas scattered in various townships in Huzhu County;Hg had high value areas in the junction of Tangchuan Township and Xishan Township and in Wufeng Township.(3)The contamination risk of heavy metals was clarified.According to the contamination assessment of the ground accumulation index at the sampling site level,Cr,As and Pb showed no contamination,Cd showed slight contamination in 76% of the sample sites,Hg showed light contamination in 43% of the sample sites,and 49.5% of the sample sites showed general contamination or more serious contamination.The comprehensive contamination assessment of heavy metals based on the potential ecological risk index showed that the vast majority of arable land was at low and medium ecological risk,the arable land with high ecological risk is mainly located near the towns where the population is concentrated.(4)The main sources of heavy metals and the influencing factors of spatial heterogeneity were clarified.Cr,Pb and As mainly originated from natural soil formation processes;Cd mainly originated from agricultural activities;Hg mainly originated from coal combustion and industrial activities.Geo Detector analysis showed that the spatial distribution of soil p H,OM,TN and Cr,Pb and As were similar,all mainly influenced by natural factors;the spatial distribution of SAP and mercury had some similarity;the spatial distribution of SAK and five heavy metals had little similarity.The population density of townships was the strongest factor influencing the spatial heterogeneity of Hg;soil subtype and elevation had great explanatory power on the spatial heterogeneity of Cr,Pb and As.The results of the Geo Detector analysis validate the source analysis results and quantify the influence of environmental factors. |
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