Study On The Hydrology And Water Quality Characteristics Of The Ditch Wetland In Salinate Fields

Agricultural non-point source pollution has become one of the most important sources of the world's water pollution. The farmland drainage of the salinate fields, which contains high concentrations of salt, is also a part of agricultural non-point source pollution. ditch wetland as a buffer between the farmland and the receptible water can play a role of removing the pollutants and purifying the drainage water. After saline-alkali soil improvement projects was completed, a lot of ditch wetland formed, and become influx tank for the drainage of saline-alkali soil. Therefore, migration, transformation, and distribution of the high-concentration salt in the ditch wetland needs to further understand.In this paper, take the ditch wetland formed from Saline-alkali soil improvement project of LuBoTan in Shaanxi Province for example, based on the field observation and the half-year measured data about water quantity and water quality of 16 monitoring points, the rainfall, water evaporation and water quantitative change in ditch wetland were calculated, and the main factors which affect the water quantity in ditch were found. Furthermore, the spatio-temporal distribution of salt was analyzed, main affecting factors are discussed, and the enrichment result of salt in ditch wetland was concluded. The main conclusions are as follows:(1) The ditch wetland in salinate fields of LoBoTan are formed from saline-alkali soil improvement project. Phragmites is the dominant species of aquatic plants in the ditch wetland, the area of saline-alkali ditch wetland of LuBoTan approximately is 22.7 ha, the controlling area of arable land is about 170 ha, and the open water area is about 13.3% of total controlling area.(2) From June to November in 2009,the rainfall recharges about 67.2mm water in ditch wetland. Surface evaporation of Wetlands is 720.3mm. The water from water withdrawal of the upper reaches of Yellow River is about 88.4mm. Upstream water withdrawal in a short time to replenish wetlands is the main factor of water changing in wetlands.(3) Monitoring results show that the conductivity and sodium adsorption ratio in the water of wetlands was negatively correlated with the water quantity. The conductivity is about 4-6ms/cm in sub-ditch and 6-8ms/cm in main ditch. From upstream to downstream, the conductivity have little change in the same ditch, this result means the salt enrichment effect is not obvious. The monitoring results of sodium adsorption ratio show that the water of the ditch wetland in the most time belongs to a very high sodium water and is not suitable for irrigation.(4) In this study, conductivity of sediments' leachates was used to reflect the salt content in the ditch wetland sediments. Monitoring results show that the salt concentration in the top layer sediments decreased with the increasing of the water quantity in wetlands, so the salt enrichment effect by the wetland sediments is not obvious. During the same period, the salt concentration in sediment layer increased with the increasing of the depth of the vertical deposition, which means that the salt input of ditch wetland in LuBoTan is in the reduction trend.