Study On The Losses Of Nitrogen And Phosphorus On Coal Mining Subsidence Land

Aimed at addressing the spatio-temporal distribution of nitrogen and phosphorus in topsoil and water of Paibei coal mining subsidence land in Huainan, time-lapse monitoring was taken in this study. Moreover, simulation experiments were implemented to test the release mechanism and adsorption characteristics of nitrogen and phosphorus after soil submerge in this area. Based on the ArcInfo technique amount changes of soil erosion and losses of nitrogen and phosphorus in soil pre and post the formed of coal mining subsidence land were evaluated. The results are as follows:1) The content of nitrogen decreases significantly from the edge of subsidence basin to catchments. Phosphorus decreases slightly compared to nitrogen. Vertical distribution of nitrogen presents a consistent trend, which indicates that the contents of nitrogen gradually decrease with the depth. The contents decreases larger in wet season than in dry season2) Nitrogen and phosphorus have obvious seasonal variation in water body of Panbei coal mining subsidence wetlands. The high contents of Nitrogen and phosphorus arised the risk of water eutrophication in both April and December.The concentration of different species of nitrogen and phosphorus in July is low due to plentiful of precipitation in this season.3) Results of release experiment indicate that the pH of overlying water is the key factor controlling release of nitrogen and phosphorus from soil. The intensity of phosphorus release from soil is the highest when pH of the overlying water equals to 10, higher when pH equals to 4 and the lowest when pH equals to 7 separately. Nitrogen and phosphorus releases more in anaerobic condition than in aerobic condition. The effect of illumination on phosphorus release from soil is not obvious.4) Adsorption experiment of nitrogen and phosphorus on soil presents that when concentration of nitrogen and phosphorus is more than 0.5mg/L for phosphorus and 5.0mg/L for nitrogen, the adsorption isotherm of phosphorus fits Langmuir model with the maximum adsorption Qm of 0.28mg/g. And the adsorption isotherm of nitrogen fits Henry adsorption model. According to adsorption-desorption equilibrium of nitrogen and phosphorus in the submerge soil of Panbei coal mining subsidence land, nitrogen and phosphorus are still releasing from the submerge soil.5) According to the interpretation of remote sensing image, the catchments area of coal mining subsidence land in the east part of Panbei coal mine are respectively 0.29km2, 0.53km2 and 0.51km2 in April, July and December, 2009. Therefore, up to 2015, the maximum subsidence depth is 4 meter and subsidence area is about 7.25km2 of which including catchments of 1.8km2; and the amount of soil erosion around catchments within the scope of subsidence land will be 800.93t/a. Soil erosion modulus increases by 58% after subsidence compared to those before the subsidence. The losses of total nitrogen and phosphorus are 251.87 kg/km2 and 67.38 kg/km2 respectively.