Distribution, Migration And Control Of Nutrient In Lanlingxi Watershed, Three Gorges Reservoir Area

Analyzing consecutive processes and mechanisms of non-point source was helpful to study the forming cause of the eutrophication, and provided the basis for controlling measure in Three Gorges Reservoir Area. Experiments were conducted in a conversion of cropland to forest watershed—Lanlingxi watershed in Three Gorges Reservoir Area. Historical data collection, watershed investigation, rainfall-runoff events monitoring and sampling activities were carried out all along. Temporal and spatial distribution of soil nutrient was analyzed, comparative researches on nutrient transfer via surface runoff at plot-scale, slope-scale and catchment-scale were also discussed. Finally, the controlling suggestions for agricultural non-point source pollution in Three Gorges Reservoir Area were given. The main results were showed as following:1. Infiltration was impacted by terrain factor greatly. The soil water infiltration rates showed a single-hump curve with slope gradient, the tip appeared in 20-25°, the peak in layer 0-5 cm and 5-10 cm were 10.78 and 6.07 mm/min, respectively. Initial and stable water infiltration rate both slowed down with decreasing altitude. The correlation between the soil water infiltration rates and non-capillary porosity was very significant positive, the correlation between the soil water infiltration rates and capillary porosity was significant positive, and the total porosity was the same.2. Spatial heterogeneity and spatial dependence were apparent in SWC,pH,AP,TP,NH4+-N,NO3--N and TN, the ratio of random variance(nugget) to total variance (sill) were 6-50 %,50 %,7-50 %,30-50 %,100 %,40-100 % and 63-100 % for them in different seasons, respectively. SWC and AP less involved by human activity, NH4+-N,NO3--N and TN more involved human activity, spatial variability of pH and TP were mainly affected by a co-working of the structural factors with random factors. pH, AP and TP of soil decreased sharply as SWC increased, while NH4+-N,NO3--N and TN of soil increased slowly as SWC increased. pH, AP and TP of soil increased sharply as soil SPC increased, while NH4+-N,NO3--N and TN of soil decreased slowly as SPC increased. 3. Phosphorus loss decreased after conversion of cropland to forest because of the silt loss considerably reduced as well. Nitrogen loss was the chief form of agricultural non-point pollution in Heigou watershed and nitrate nitrogen accounted for 40-60% of total nitrogen. The order of total phosphorus loss loading of different land use was that: farmland(521.55 g/hm2)>citrus park(80.66 g/hm2)>tea garden (67.30 g/hm2)>bamboo forest(63.58 g/hm2) > chestnut forest(47.16 g/hm2) > woodland (43.78 g/hm2), The order of total nitrogen loss loading of different land use was that: tea garden(2598.99 g/hm2)>farmland(2267.03 g/hm2)> citrus park(1679.7 g/hm2)> bamboo forest(1151.66 g/hm2)>chestnut forest(550.47 g/hm2)> woodland(426.10 g/hm2). Orthophosphate and total phosphorus loss loading were effect by shrub -herbous layer and total coverage. The higher of soil ammonium nitrogen the ammonium nitrogen loss loading was more. Total nitrogen and nitrate nitrogen loss loading decreased with the tree layer coverage increased, slightly related with soil properties.4. The soil pH was correlated positively with soil depth. Ammonium nitrogen, nitrate nitrogen and total nitrogen of soil decreased as soil depth increased, exceeding fertilizer application leaded to leaching phenomenon of nitrogen in soil. Distribution characteristics of phosphorus in soil profiles under different land use closely related with slope position. Along the soil depth, available phosphorus and total phosphorus of soil increased at upper slope, increased at beginning and then decreased at middle slope, decreased at lower slope. Terrain factors (slope and slope length), land use type and distribution had important effect on the transfer ability of soil nutrient in slope scale. At single-land-use slope, the higher of slope position the soil PH, available phosphorus and total phosphorus were less, and the soil ammonium nitrogen, nitrate nitrogen and total nitrogen were more. At different-land-use slope, because of residential was the important"sink"landscape and the phosphorus adsorption capacity of woodland was great, soil PH, available phosphorus and total phosphorus decreased at beginning, increased at middle slope, and then decreased again as slope position deceased. Migration and leaching leaded to the accumulation of nitrogen in soil at lower slope.5. The higher of the antecedent moisture contents of the soil the peak of surface runoff appeared earlier. Phosphorus loss occurred mainly during strong rainfall processe, the particle phosphorus was the dominant form. Nitrogen loss by groundwater occurred more easily than phosphorus loss. There was a good linearity relationship between runoff volume and loss load of orthophosphate, total phosphorus, ammonium-N, nitrate-N, nitrite-N and total nitrogen. The annual total nitrogen and phosphorus exported from Heigou watershed were 1498.19 kg/a and 41.67 kg/a, respectively.6. Based on the mechanisms of non-point source in Three Gorges Reservoir Area, the control pattern of source area of controlling key source-reducing surface runoff-intercepting nutrient was presented firstly.