Distribution Characteristic Analysis And Control Strategy Of Non-point Source Polution In Ashi River Basin

The experience of developed countries has shown that, the water quality can not be solved absolutely only by controlling point source(PS) pollution, and people are getting more concerned about non-point source(NPS) pollution gradually. Ashi River Basin is one of the major grain producing areas of China. High-intensity agricultural production mode makes the fertilizer application grow day by day, while its usage factor turns down, so that the stream-flow and base-flow are contaminated the by residual fertilizer. Related research results show that, Ashi River, for now, is becoming one of the most contaminated branch of Songhua River, and the load of NPS pollution is more than PS pollution. Intense human activities have been changing land-use type, landscape patten and water yielding and runoff routing, so that the water quality is impacted. Therefore, discussing the relationship between land-use and NPS pollution is meaningful for the acknowledgement of contaminated process and management of Ashi River Basin.The study area of this research is Ashi River Basin. SWAT(Soil and Water Assessment Tool) model was established based on the localizable non-point source pollution database. The calibration and validation results showed that SWAT model was capable of simulating the runoff, total nitrogen(TN), and total phosphorus(TP) in Ashi River Basin.The temporal and spatial process was analyzed based on SWAT model. The analyzing results indicated that: in interannual timescale, non-point source TN(NPS-TN) and non-point source TP(NPS-TP) were influenced by stream-runoff and fertilizer both, but stream-runoff is more directly than stream-runoff; in annual timescale, NPS-TN and NPS-TP mainly occurred in flood season(from May to September); NPS-TN which occurred in flood season accounted for 72.47%, 59.86% and 53.92% respectively in wet year, normal year and dry year; NPS-TP which occurred in flood season accounted for 87.25%, 87.02% and 87.30% respectively in wet year, normal year and dry year; in spatial, spatial difference of NPS-TN and NPS-TP were significant; The left bank of downstream was the most polluted region, the middle-stream took second place, and the rest of region polluted less.Arc GIS and Fragstat were used to analyze land-use type and landscape pattern change, and the relationship between NPS-TN, NPS-TP and land-use was discussed. The results prove that: agricultural land and forestland were the major land-use type of Ashi River Basin, and total sum of them accounted for over 92% of the area; the NPS pollution had close relation with land-use type and landscape pattern, and the export risk of NPS-TN and NPS-TP was agricultural land > urban land > grassland > forestland; the more imbalance and unevenness the landscape pattern distributed, the more serious the NPS pollution was; the more fragmentized and connected the landscape pattern distributed, the less serious the NPS pollution was.Returning farmland to forest mode, terracing mode, fertilizer reducing mode, filter strips mode and their syntaxic mode were simulated through scenario simulation technology. Results showed that: returning farmland to forest mode could reduce 1.03-5.35% of NPS-TN load and 0.94-8.09% of NPS-TP load; terracing mode could reduce 0.51-2.77% of NPS-TN load and 0.49-4.54% of NPS-TP load; fertilizer reducing mode could reduce 0.65-6.52% of NPS-TN load and 0.01-2.95% of NPS-TP load; filter strips mode could reduce 42.62-69.51% of NPS-TN load and 80.09-86.27% of NPS-TP load; syntaxic mode could reduce 34.90-54.36% of TN load and 35.32-60.89% of TP load; for reaching the water quality goal of <Environmental quality standards for surface water>(GB3838-2002), 45.87-82.53% of PS-TN load and 35.58-66.85% PS-TP load should be reduced yet.At last, take geographical position, land-use, slope, dry and wet condition and NPS pollution load into consideration, pollution control zones were divided in Ashi River Basin. Relevant management advices of non-point source pollution were given for watershed management and planning.Above all, theory and method of numerical modelling, geographical informatics, geography of landscape and ecology were integrated applicated in this study. The load of NPS-TN and NPS-TP was quantitative calculated. The relationship between NPS-TN, NPS-TP and land-use was analyzed. Reducing methods and effectiveness of NPS pollution were quantitative measured. Based on all these above, pollution control zones were divided and relevant management advices were given. This study not only has significant scientific meaning for fully understanding the water pollution causes of Ashi River Basin, but also has concernful realistic meaning for the water conservation and comprehensive management of the whole Ashi River Basin. At the same time, it could help on integrated basin management and scientific decision with the river which has similar natural conditions.