| Pesticides and fertilizers are used heavily in the process of vegetable and flower cultivations in Dianchi Lake basin. They increase the risk of nitrogen and phosphorus erosion and create heavy agricultural non-point pollution which has been an important source of nitrogen and phosphorus to water of Dianchi. Simultaneously, mass of pesticides and fertilizers residue may reduce the self-purification capacity of agricultural ecosystems. To reveal the serious phenomenon, systematic investigates and researched are needed.We chosed four typical farmlands in Shangsuan Village from Chai river sub-basin, Dianchi Lake basin. Those are a new rose greenhouse, an old greenhouse, a lettuce greenhouse and a corn field. We investigated the pesticides application and rainfalls. And the interflows of these farmlands were collected and tested, the self-purification capacity of the interflow was analyzed by the change of main pollutants. Also, we designed indoor simulated experiments to find out how pesticides and fertilizers influence the self-purification capacity of agricultural interflow. Main results are showed as follws:(1) There was the information of fertilizers and pesticides application in these filed. The average of nitrogen fertilizers usage was 90.14 Kg/Mu (1Mu= 0.0667 hectare). Vegetable greenhouse used the most nitrogen fertilizers, which was 195.10 Kg/Mu. The average of phosphate (P2O5) fertilizers usage was 50.64 Kg/Mu. Vegetable greenhouse used the most phosphate (P2O5) fertilizers, which was 80.40 Kg/Mu. The average of farmyard manure usage was 352.50 Kg/Mu. Rose greenhouse used the most farmyard manure, which was 500 Kg/Mu. The rose greenhouse used the most pesticides, it used pesticides 21 kinds, these pesticides were used one time pers 4-5 days, at total of 53 times.(2) N element changing in farmland interflows showed that TN content was decreased with increasing depth, the removal rates of TN in addition to the open farmland substantially showed increasing with depth increasing. Vegetable greenhouse had the most TN content in the 20 cm soil, which was 49.57-114.63 mg/L; the open farmland had the biggest removal rates of TN in the 40cm soil, which was 27.28%. NO3--N was the mainly form of losing soil nitrogen; it took the proportion of 70%-90%. In the study areas, NO3--N content, NHU+-N content and TN content showed the similar trends.(3) P element changing in farmland interflow showed that in all levels, TP content presented 20 cm> 40 cm> 60 cm> 80 cm, but in a separate soil depth, the TP content did not show significant difference in those filed. New Rose greenhouses interflow TP removal rate was highest in the 60 cm soil depth, which was 49.61%. The highest removal rate of TP in the old rose greenhouses was 40.26%, in the 80cm soil depth. The highest removal rate of TP appeared in the 80 cm soil depth, which was 29.16%, and there was little difference between the different depths.(4) COD Changing in farmland interflow showed that COD content increased with depth decreasing, the removal rate of COD showed no law. The highest COD content of New Rose greenhouses was 441.48 mg/L in 20cm soil depth, the highest removal rate of COD appeared 40.91% in 40cm. The highest COD content of Old Rose greenhouses was 269.92 mg/L in 20cm soil depth, the highest removal rate of COD appeared 47.39% in 60cm. The highest COD content of Vegetable greenhouse was in 20cm soil depth, which was 269.44mg/L, the highest removal rate of COD appeared in 80cm, which was 14.44%. The highest COD content of open farmland was 127.80mg/L in 20cm soil depth, the highest removal rate of COD appeared 29.78% in 40cm.(5) The simulation results showed that COD removal rate was significantly related to hydraulic retention time (HRT), and the correlation with amount of pesticides and fertilizer was not significant. To the removal of the TN, the amount of fertilizer, the amount of pesticides and hydraulic retention time (HRT) were very significant positive correlated. To the removal rate of TP, the amount of pesticides and hydraulic retention time (HRT) were significant positive correlated, and fertilizers correlation was not significant. The removal rate of ammonia nitrogen, the amount of pesticides, the amount of fertilizers and hydraulic retention time (HRT) were very significant positive correlation. In the simulation of subsurface flow nutrient concentration, horizontal hydraulic retention time (HRT) and pesticides dosages discovered that COD removal rate was-10%, TN removal rate was 11%, TP removal rate of 2.5%, ammonia nitrogen removal rate was 10%. Suggested that in field conditions, there could be a lot of nitrogen and phosphorus left in the subsurface flow, and it could occur nutrient enrichment and leaching.Above all, the experimental results shows that a large number of pesticides and fertilizers use significantly affect the water quality characteristics of farmland soil interflow, also showed a significant impact on the self-purification capacity of the soil system. The impact of this effect in the facility farmland was greater than that in the open fields, the impact of this effect in the top soil was greater than in lower influences. Reduce the use of pesticides and fertilizers, reduced the inhibition to the self-purification capacity of the soil, which was an important way to solve the agricultural non-point source pollution. |
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