Abstract: Samples of surface soils near the outlets of farmer household septic tanks and samples of the effluents from the tanks were collected in a plain river network region typical of the Taihu Lake Basin for use in an in-laboratory experiment with simulated rainfall (for summer, 30 mm per event and for winter 5 mm per event, typical of the region) controlled temperature (27℃ for summer and 5℃ for winter,typical of the region) and simulated pollutant load [TN: (2.35±0.06) g·m^-2·d^-1, NH₄⁺-N: (2.08±0.04) g·m^-2·d^-1, TP: (0.21±0.01)  g·m^-2·d^-1, COD: (11.14±0.59)  g·m^-2·d^-1] to estimate pollutants abatement rate in the polluted surface soils and to explore rules of the abatement as affected by seasons (summer and winter) and synoptic process (before the rain, during the rain, after the rain). Results show that TN abatement rates, no matter whether before the rain, in the rain, or after the rain, all showed a tendency of summer < winter (P<0.01), and on the contrary, NH₄⁺-N abatement rates all showed a reverse trend of summer > winter (P<0.01). TP abatement rates showed a tendency of summer > winter (P<0.001) before the rain and after the rain, but COD abatement rates did not differ much between summer and winter. TP and COD abatement rates in the rain both showed a tendency of summer < winter (P<0.01 or P<0.001). As to difference between weather processes, TN abatement rates in summer showed a tendency of after the rain > before the rain> in the rainy days (P<0.01), TP and COD abatement rates in summer showed a tendency of after the rain≈after the rain> in the rainy days (P>0.05, P<0.01), whereas, NH₄⁺-N abatement rates in summer did not differ much between  synoptic processes and TN, NH₄⁺-N, TP and COD abatement rates in winter did not either (P>0.05). So, the TN abatement rate before the rain, in the rainy days, after the rain in summer and in winter was 38.5%, -25.0%, 46.0% and 50.4%, respectively. The NH₄⁺-N abatement rate in summer and in winter averaged 91.5% and 85.5%, respectively. The TP abatement rate in the rainy days in summer, in the rest of summer and in winter averaged 63.3%, 93.1% and 82.7%, respectively. The COD abatement rate in the rainy days in summer and in the rest of the year was 8.2% and 66.2%, respectively, on average.

Key words: Taihu Lake basin, surface soil, rural sewage, abatement rate, estimation