DISTRIBUTION CHARACTERISTICS AND EVALUATION OF SOIL SOM, TN, TP IN THE WATER-LEVEL-FLUCTUATING ZONE OF THREE GORGES RESERVOIR

Distribution characteristics and evaluation of soil organic matter (SOM), total nitrogen (TN), and total phosphorus (TP) in the surface soil of water-level-fluctuating zone (WLFZ) of Three Gorges Reservoir were investigated by soil sampling and data analysis. Concentrations of SOM, TN and TP in soil samples were measured. The results showed that average value of SOM in study area was 10.42 mg/g ranging between 3.47-12.72 mg/g, TN was 1.23 mg/g (0.91-1.69 mg/g), and TP was 0.62 mg/g (0.32-0.85 mg/g). It was found that patterns of spatial distribution of SOM and TN were rather similar and showed large spatial variation. The spatial distribution pattern of TP in the study area was quite different from that of SOM and TN, and showed small spatial variation. Results of C/N analysis showed that SOM in surface soils derived mainly from sedimentation of biomass. The SOM and TN values were significantly and positively correlated, which indicates that they are probably derived from the same source. Nitrogen and phosphorus in soils of WLFZ could become potential pollution sources. Therefore, more attention should be paid to the potential impact of N and P in soils of WLFZ on reservoir eutrophication. Data analysis showed that single standard indexes of TN ranged from 1.66 to 3.07, and were generally above 1, indicating that N pollution is relatively serious. However, TP was relatively low, with standard indexes ranging from 0.53 to 1.42, indicating that P pollution is not very serious.