| After the point source pollution is gradually brought under control, the non-point source pollution has become a major source of pollution damage to the water environment. Agricultural nonpoint source pollution from agricultural production, especially nitrogen and phosphorus loss has brought great pressure on Three Gorges Reservoir environment. This dispersive, secluded, random, latent, cumulate and blurry nitrogen and phosphorus loss was hard to measure and quantization, thus it was difficult to research and control. Currently, there was a lack of effective response to is such pollution Agricultural production in the TGP reservoir area. Although the constructed wetlands can effectively remove nitrogen, phosphorus and other nutrients from sewage, river water, irrigation and drainage, it has high costs and no food productivity. Irrigated paddy field is a unique biological diversity of wetland system. This system can not only absorb nitrogen, phosphorus and other nutrients from rain water, irrigation water or sewage, but also has the ecological function of settling suspended solids in the water and digesting other toxic substances. Therefore, this paper attempts to use paddy field which widely distributed in the Three Gorges reservoir area to consume nitrogen, phosphorus and other non-point source pollutants from agriculture, study the effect of this unique wetland system in consuming nitrogen and phosphorus, and reduce the nitrogen and phosphorus load to the TGR caused by agricultural point source pollution.1) Through a simulation test, the nitrogen sequestration of the rice field ecosystem under ridge tillage, conventional tillage and different levels of fertilizer (complete and reduction) was studied. It was found that 3 days after the sewage (the total nitrogen concentration is 15 mg L-1, ammonium is 13.5 mg L-1, nitrate is 1.5 mg L-1, the total dissolved phosphorus concentration is 2.0 mg L-1) was added, the ammonium in surface water reduced 93%, and there was no significant difference between ridge and conventional tillage. The nitrate had a rapid rise after the sewage was added,3 days later it reached the peak (9.1 mg L-1); 7 days later the nitrate concentration under ridge tillage decreased to 6.8 mg L-1. but it decreased to 3.5 mg L-1 under conventional tillage; 14 days later the nitrate decreased to 1.4 mg L-1, and there was no significant difference between ridge and conventional tillage. The organic nitrogen in surface water reached the peak 1 day after the sewage was added, and the organic nitrogen under the full fertilizer management(11.6 mg L-1) was significantly higher than under the reduction fertilizer management (4.3 mg L-1). illustrated that the nitrogen in surface water was mainly from fertilizer. The nitrogen in surface water under complete fertilizer was higher than the reduction in the early after flooding. However. there was no significant difference between different levels two weeks later. It was found that 1 day after the sewage was added, the DRP (dissolved reactive phosphorus) and TDP (total dissolved phosphorus) in surface water were reduced 22%～36% and 6%～27% respectively; and 3 days later, the DRP and TDP were reduced 73%～89% and 53%～66% respectively. The DOP (dissolved organic phosphorus) had a rapid rise after the sewage was added,3 days later, they all reached the peak values (0.21～0.30 mg L-1); but 7 days later, the mean of DOP was reduced to 0.11 mg L-1. At the early stage of rice growth, the main characteristics of phosphorus forms in surface water was DRP, and DRP percentage was basically similar as DOP at medium-term of rice growth, but the DRP percentage rised at he late stage of rice growth. Research showed that rice-based ecosystems could effectively control the inorganic nitrogen and phosphorus in sewage within just 1 week.2) The adding of the sewage has also effected the dynamics of nitrogen and phosphorus in soils. Three days after the rural sewage was added, it was found that, in soils, the concentrations of NH4--N (29.4～46.5 mg kg-1), NO3--N(12.3～21.4 mg kg-1), and the pH (7.9～9.1) all reached the peak values. The concentations of NH4+-N, NO3--N. and the pH in soils under full fertilizer management were significantly higher than soils under reduction fertilizer management, but there was no significant difference between ridge and conventional tillage. Seven days latter, the concentrations of NH4--N, NO3--N, and the pH reduced significantly, and there was no significant difference among managements.3 days after the rural sewage was added, the amout of NH4+-N in soils increased 5.76～9.70 g m-2, but the amout of NH4+-N in surface waters just decreased 1.15～1.34 g m-2,shows that the decrease of NH4+-N in surface waters may have contribution to the increase of NH4+-N in soils, but the increase in the amout of NH4+-N in soils was not all from surface water. The amout of NO3--N in soils and surface waters increased 0.64～0.91 g m-2 and 2.02～4.12 g m-2,respectively, suggests that the increase in the amout of in surface water may come from soils.1 day after the sewage was added, the concentations of Alkali-hydrolyzable N and Olson-P in soils reached the peak values, and its in soils under full fertilizer management were significantly higher than soils under reduction fertilizer management, but there was no significant difference between ridge and conventional tillage. During the experiment, there was a decreasing trend in total N and total P, but it had no significant different between begenning and the end. Under the same Fertilization conditions, the ridge cound get higher biomass yield than conventional tillage, means that it can take away more of nitrogen and phosphorus.3) Purple soil is the predominant soil type of slopeland in TGR area. Its texture is soft and easy to weathering, and corrosion resistance is poor. Combined with high mountains and steep slope, focused and intensive rainfall, it is easy to form soil erosion, which provide an effective carrier for the point source pollutants migration and transformation. The excessive fertilizer using in agricultural production, resulted in substantial nitrogen and phosphorus runoff into water easily which can cause adversely affect to the TGR water environment.In this paper, the slopeland nitrogen and phosphorus lossing charactors in 6 rainfull from May 1 to July 10,2010 were analysed though sloping runoff field experiment. The results showed that:heavy rain produced 2.34 and 7.59 times runoff than moderate and light rain, while TN, TP concentations in heavy rain runoff were higher than in light rain and moderate rain runoff, causing heavy rain had a higher nitrogen and phosphorus loss than moderate and light rain. Cumulative sediment in runoff caused by heavy rain is 8.34 and 111.38 times than that caused by moderate and light rain.Runoff in the Slope Land in TN, TP is particulate nitrogen and phosphorus. Greater rainfall, particulate nitrogen and phosphorus percentage higher. Particulate nitrogen accounts for 74.9%-75.9% TN in the moderate runoff, while particulate nitrogen had a higher proportion of total TN in heavy rain, reaching 85.0% to 92.6%. Particulate phosphorus is the main form of phosphorus in runoff, heavy rain, moderate rain, light rain runoff generated particulate phosphorus accounted for the proportion of TP were 96.6%-97.7%,93.9%-96.2%,90.5%-94.4%, respectively. Sediment is the main carrier in slopeland nitrogen and phosphorus loss, Control of slopeland N and P loss should consider the control of nitrogen and phosphorus loss generated by large rainfall.4) Nitrogen and phosphorus sequestration effect of the rice field ecosystem was determined by field tests.24h after the runoff was poured into the 200 m2 paddy field, TN and particulate nitrogen concentration decreased by 60.1%-88.0% and 91.2%-98.7%, respectively, and of no significant difference between treatments. TN concentration was higher in runoff produced by heavy rain than that generated by moderate and light rain, so TN concentration of surface water was higher when the heavy rain runoff was poured into, however this difference only reflects in the first 3 h. After the runoff was just poured into the rice field, particulate nitrogen had a high proportion of total nitrogen, which accounted for 43.5%-87.7% TN in surface water. Over time, the proportion of particulate nitrogen decreased gradually, while other forms of nitrogen gradual increased.24 h after runoff was added, the proportion of particulate nitrogen decreased to 10.2%-22.7%, soluble inorganic nitrogen and organic nitrogen became the main component of TN. Paddy field ecosystem also showed a higher efficiency in phosphorus sequestration.24h after the runoff was poured into the 200 paddy field, TP and particulate phosphorus concentration decreased by 60.6%-86.0% and 82.9%-93.0%, respectively, and of no significant difference between treatments. After the runoff was just poured into the rice field, particulate phosphorus had a high proportion of total phosphorus, which accounted for 89.7%-97.7% TP in surface water. Over time, the proportion of particulate phosphorus decreased gradually, while other forms of phosphorus gradual increased.24 h after runoff was added, the proportion of particulate phosphorus decreased to 37.4%-45.7%. Paddy field ecosystem was efficient in sequestrating nitrogen and phosphorus in runoff, mainly due to its ability to quickly dissolved particulate nitrogen and phosphorus.5) Quantity-intensity (Q/I) relationships of NH4- in purple soils and purple paddy soils different in land use (paddy field, dry land, woodland and vegetable plot) were studied. It was found that in both 0-20 cm and 20～40 cm layers of the two soils the curve of NH4+ Q/I relationships were observed only when NH4- activity ratios in the soils were low, suggesting release of nonexchangeable (or specifically adsorbed) NH4- in the soils NH4+ in the two soils ranged from 71.47 to 203.7 cmol kg-1 (mol L-1)-1/2 in potential buffering capacity (PBC)., from 0.029 5 to 0.089 7 cmolc kg-1 in labile NH4 (-ΔNH40). from 0.187×10-3 to 1.255×10-3 (mol L-1)1/2 in equilibrium activity ratio (AR0NH4) and from 0.010 6-0.118 5 cmol kg-1 in specific adsorption sites (NH4-sas). Correlation analysis and path analysis indicate that the content of clay (＜0.002 mm) is in extremely significant positive relationship with both PBC and NH4.sas (p<0.01). The effect of clay (<0.002 mm) is mainly indirect on PBC (indirect path coefficient,0.585). but strong and direct on NH4-sas.. Positive linear relationships were observed of organic C with-ΔNH40 and AR0NH4 in all soil samples. The effect of organic C is high and direct on-ΔNH40 (direct path coefficient.0.966). but indirect on-ΔNH40. The concentration of exchangeable NH4+ is positively related to-ΔNH40 (r=0.876 4, n=8, p＜0.01) and they are approximate in value. Moreover, exchangeable NH4+ is also positively related to AR0NH4 (r=0.983 7,n=8,p<0.01). This study clearly demonstrates that differences between the soils in clay and organic C are the main reason for the differences in exchangeable NH4+ and Q/I parameters between purple soils different in land use. The use of exchangeable NH4+ as indicator of NH4+ availability has a similar effect as the use of Q/I relationships.
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