Effectiveness of Different Kinds of Irrigation and Drainage Projects on Reducing Pollutants from Agricultural Drainage

Four different kinds of irrigation and drainage projects - the concrete ditch, brick ditch, soil ditch and pond were constructed to study the removal capacity of nutrients from agricultural drainage. Experimental results showed that the highest pollutants concentrations in ditches and pond occurred in July and November, associated with fertilizer application, wheat or rice straw returning, rainfall and cropland drainage. The most seriously polluted water occurred in concrete ditch, with the highest concentrations of total nitrogen (TN), total phosphorus (TP), chemical oxygen demand (COD_Mn) and ammonia nitrogen (NH₃-N). The secondly polluted water was in the pond grown over with weeds. Water in soil and brick ditches was lower polluted. The soil and brick ditches had high ability to absorb and purify non-point source pollutants. But compared with the brick ditch, the overgrowing weeds in soil ditch were difficult to be harvested and could spread the seeds to paddy field. Therefore, the brick ditch is recommended to be built and applied widely in irrigation and drainage area in order to reduce water pollutants in catchments, to control weed infestation, and to prevent the secondary pollution of aquatic plants after death in autumn and winter.