Quantitative Evaluation And Engineering Optimization Of Reclamation Practices In Coastal Saline Soil

Coastal saline soil area accounted for 27.45% of total coastal soil in China. In eastern coastal regions like Tianjin, the Yellow River Delta and Eastern Jiangsu, the area of saline soil is even equal to that of arable land. For example, a new resource of coastal saline is being deposited every year in the Yellow River Estuary. Characterized by low nutrient, shallow depth of groundwater, high salinity and clayed texture, the coastal saline soil is the major research focus of this dissertation.1. COMSOL-1D was used to simulate the classic Warrick field test and the "one-clay-layer-sandwiched-by-two-silt-loam" soil column test. Water and salt transport process of the two tests was simulated under one-dimensional (1-D) condition. The comparison of simulated and observed values revealed that the simulated values fit the observed values with very small error deviations, showing that COMSOL-1D is applicable to simulate the soil water and solute transport.2. The applicability of COMSOL-2D software to simulate the two-dimensional salt transport in coastal sandy soil under water saturation condition was testified. The lab-installed experimental apparatus was set up to quantitatively observe the two-dimensional transport process of salt (KC1) in saturated sandy soil, with a rectangular transparent organic glass tank selected as the soil tank. Eight representative points were selected to measure the electrical conductivity—transient salt concentration, using Rex DDS-11 platinum black conductance electrodes. The salinity readings were manually recorded for every 5 minutes and backup per minute with data logger. Fluid Flow Module and solute transport Modules available in COMSOL (3.4) were used to simulate the two-dimensional (2-D) water and salt transport in rectangular-shape soil pedon. the simulated results showed that:the determination coefficient (R2) between simulated and observed values at points 3#, 4#, 5#, 7#, 8# all reached 0.9, with only the exception of a bit lower R2(0.8863) at the points close to the surface. Hence, COMSOL-2D is applicable to simulate the two-dimensional water and salt transport in soil.3. Field observations was carried out at Coastal Saline Soil Experimental Station of Qingdao Agricultural University at Tingluo Town, Lijin County, Dongying City, Shandong Province. The reclamation practices of coastal saline land was surveyed, including raised cotton field and strip transformation at MaoTuo Village of Tingluo Town in Lijin, and tile drainage technology at Xinhu town of Hekou District. The above field observation data was analyzed in the dissertation, which is helpful to improve the utilization technology of the coastal saline soil and provides reference for the improvement and utilization of coastal saline soils.4. A COMSOL-2D model was setup base on the actual scale of 7# raised cotton field in Dongying, the soil physical parameters of each soil layer was predicted out by Rosstta software, the upper boundary values were calculated from the meteorological conditions, S—water absorption of cotton root- was calculated by empirical formula, the influence of groundwater level was also considered. Comparison and error analysis are made between simulated and measured values, which showed that the simulated trend of water and salt dynamics fit fairly well with the real situations, COMSOL-2D is applicable to simulate the two-dimensional water and salt transport in field scale soil.5. According to the poor permeability of clayed coastal saline soil, the field-constructed sand-column (FCSC) technology was an effective measure to accelerate desalination of coastal saline soil. In this study, based on COMSOL (3.4), two-dimensional transient cross-sectional models were used to investigate water and salt transport in FCSC coupled with variable sand column forms, with a denoting no sand column, b one vertical middle sand column, c one long slanged sand column, d two long slanged X-shaped sand columns. The results showed that FCSC substantially increased the transport efficiency of water and salt, which may be attributable to the higher hydraulic conductivity and higher diffusion coefficients in FCSC than clay-loam coastal saline soils. The efficiency of FCSC depends on its position and angle of installment accordingly. The slanted columns were overall superior to the vertical ones in transport efficiency. Overall, d is the best type, c is the second best and b is the third, in terms of the efficiency of salt leaching and the efficiency of the utilization of water resources.