RESUMO
The literature from a long-term fertilization experiment in the Yangtze River Economic Belt from January 1992 to May 2022 was collected, and the data of farmland soil organic carbon were extracted and integrated. Using the normalization treatment and the analysis method of relative annual variation, the overall change in soil organic carbon content in farmland in the Yangtze River Economic Belt under different long-term fertilization measures was studied, and the change differences of soil organic carbon content under three tillage modes were compared so as to judge and analyze the influence of the duration of the experiment on soil organic carbon dynamics. The results showed that under different long-term fertilization measures, the organic carbon content of farmland soil in the Yangtze River Economic Belt in China showed an overall upward trend. The NP, NPK, O, and NPKO treatments all increased the organic carbon content of agricultural soils, with that of the NPKO treatment being the largest. The sole application of inorganic nitrogen fertilizer reduced the organic carbon content of the soil. The rates of change in soil organic carbon content were 0.22 g·(kg·a)-1, 0.24 g·(kg·a)-1, and 0.16 g·(kg·a)-1for dryland, paddy, and water-dry rotation farmland, respectively. Additionally, the relatively rapid increase effect of organic carbon brought by the O and NPKO treatments could last for no more than 28 years in dryland soil but could still last for more than 28 years in paddy field and paddy-upland rotation soil. There was some variation in the rate of change of soil organic carbon content between soil types. The average rate of change of organic carbon was 0.25 g·(kg·a)-1for red soils, 0.14 g·(kg·a)-1 for brown soils, 0.19 g·(kg·a)-1 for tidal soils, and 0.15 g·(kg·a)-1 for rice soils. The trend of NPKO>O>NPK>NPK>NP>N was basically maintained for the rate of change in soil organic carbon content. The NPKO treatments were all significantly higher than the chemical fertilizer (N, NP, and NPK) treatments alone. The N treatment showed a reduction in organic carbon content in both red soil and rice soils. Considering the carbon fixation of farmland soil, the combined application of organic and inorganic fertilizers is a more suitable fertilization method in this area.
RESUMO
The concentrations of 16 organochlorine pesticides (OCPs) in 7 water samples collected from different sites of water source areas of Guangdong and Guangxi were detected by SPE-GC-MS, and then the pollution characteristics were analyzed. This study established species sensitivity distribution(SSD) curves with Burrâ ¢ distribution model. In the meantime, HC5 values were calculated by BurrliOZ software, which were used to evaluate the toxicity effects of OCPs towards aquatic organisms. Finally, margin of safety concentration values were calculated to assess the ecological risk. The results showed that the concentration of OCPs varied from 6.64 to 34.19 ng·L-1, with a mean value of 16.76 ng·L-1, while HCHs and DDTs contributed a lot. HCHs were predominately originated from lindane, which is a component in household insecticide, while DDTs were from dicofol contamination or historical residues. Vertebrates could stand severer toxicity in comparison with invertebrates. α-endosulfan showed a greater toxicity towards aquatic plants and microorganisms than others, while p, p'-DDT turned out to be the most hazardous pollutant to vertebrates and invertebrates among the 16 OCPs studied. Generally speaking, OCPs in study areas didn't show conspicuous ecological risks towards aquatic organisms, DDTs and α-endosulfan, however, are still worth paying close attention due to their high potential risks.