| According to different land use and administrative divisions,162sampling pointswere arranged to collect soil samples, in the farmlands of Zhuangmu town in LakeWabuhu watershed. Based on the experimental data, we analyzed the different forms ofnitrogen and phosphorus, the spatial distribution characteristics, the bioavailability of Nand P in the soil, and P sorption characteristics by simulation. Further, the riskassessment of N and P loss was conducted by using the nitrogen and phosphorus indexmethod, and N and P loss flux of non-point sources was estimated on the basis of theoutput factor model. The main results were summed up as follows:(1) The average concentrations of TN and TP in farmlands of Zhuangmu town were1658.59mg·kg-1and716.95mg·kg-1, respectively. Soil organic matter content rangedfrom1.64%to2.45%and pH ranged from6.79to7.37in the soil of the administrativevillages. Results showed that the average contents of NH4-N，NO3-N，TN，Ex-P，Fe/Al-P and TP were highest in Houji village.(2)The spatial interpolation simulation result showed that: in the study area, TNcontent distribution in space did not have significant differences and was relativelyevenly, and the sampling situations with lower contents of TN were scattered in thevillages of Lizhuang village, Jinqiao village and Zhangwei; On the contrary, the spatialdistribution of TP had sharp distinction, decreasing gradually from the middle to theeast, and the highest was in the north of Yangwan village and the lowest was at theborder of Yangwan and Xugang village.(3) Based on the correlation analysis, various forms of N and P related significantly.Besides, TN and TP had a significant correlation. The principle component ananlysis ofN and P in the farmland soil suggested that the first were TP, Ca-P and Ex-P withcontribution rate of32.07%, and the second was NH4-N, NO3-N, TN and Fe/Al-P withcontribution rate of16.95%.(4)Bioavailable nitrogen and phosphorus accounted for14.93%and47.30%of theTN and TN, respectively. The spatial interpolation simulation results indicated that thesampling situations with higher contents of bioavailable nitrogen were scattered in thevillages of Xueqiao village, Houji village, Zhuangmu village and Xugang, and the soilcontained higher contents of bioavailable phosphorus were mainly in Houji village.(5) The experiment of P dynamic adsorption in soil showed that: the phase of fast Padsorption was in0~5min of the experiment and the slow adsorption phase was in5~10 min. The fitting results indicated that the isothermal equation of Langmuir wasappropriate to the adsorption process in this study, while the first-order kinetic modelwas not. Soil in different sampling sites had different quantities in P adsorption. Amongthem, the highest was garlic gardens soil in Yangwan village (2202.27mg·kg-1)，and thelowest was rape planting soil in Zhangwei village (91.43mg·kg-1).(6) Soil nitrogen and phosphorus indexes in Zhuangmu town were2.11and2.13,respectively. The risk of N loss was dominated by low and medium risk. The primaryrisk of P loss was low risk. Based on the export coefficient model, TN and TP losseswere680868.17kg·a-1and48027.80kg·a-1, respectively. According to the rate ofcontribution by pollution sources, the order of the sources was cultivated land>residential land> livestock> people> pig> poultry. In general, Zhuangmu town wasnot seriously polluted by N and P and the loss risks were relatively low. |
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