Changes and influencing factors of topsoil organic carbon pool in the typical region of Haihe Plain:a case study of Jinnan District,Tianjin
The changes in topsoil organic carbon pool and its main influencing factors were investigated in the typical area of the Haihe Plain,based on soil survey data obtained in 1980 and 2016.Geostatistical methods were employed to analyze the changes in soil organic carbon density(SOCD)and soil organic carbon pool.Linear regression and random forest models were used to analyze the primary influencing factors of soil organic carbon(SOC).The results showed that the storage capacity of the topsoil organic carbon pool of 2016 in Jinnan District was 1.14×106 t,which increased by 6.61×104 t compared with that in 1980.SOCD was closely related to the soil-forming parent material,and the SOCD values were ranked as follows:alluvium>alluvial-marine deposit>lake marsh deposit in different periods.The distribution of high SOCD values in two periods was similar,mainly distributed in the northwest of Jinnan District and near Xianshuigu Town in the center of Jinnan District,and the variation of SOCD from 1980 to 2016 showed a decreasing and increasing trend in the north and south,respectively.The change in organic carbon(∆SOC)was affected by soil physicochemical properties and land use change(LUC),in which the changes in soil total nitrogen(∆TN),carbon to nitrogen ratio(C/N),and nitrogen to phosphorus ratio(N/P)were significantly positively correlated with∆SOC(P<0.01),and initial soil organic carbon(ISOC),CaO content,and change in pH(∆pH)were significantly negatively correlated with ∆SOC(P<0.05).The findings indicated that the SOC pool acts as"carbon source"when agricultural land is converted to urban land,whereas it serves as a"carbon sink"when the nature of the agricultural land remains unchanged,and the changes in∆TN,C/N,N/P,and LUC play an important role in SOC dynamic changes.
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