The Stability Mechanism Of Remediating Gully With Filling Stalks And Its Environmental Effect

Straw filling reclamation technology is mainly used to repair the erosion gully in cultivated land in Northeast China.The drainage capacity,decomposition rate of straw,environmental effect and reclamation effect of the original gully after reclamation were studied to provide scientific basis for the restoration of gully-damaged cultivated land.In this study,a reclaimed gully was selected as the experimental area in Guangrong Village,Hailun City,Heilongjiang Province,and the capacities of the soil and seepage pit infiltration,water holding of straw layer and soil drainage were systematically measured and analyzed to evaluate the drainage capacity after reclamation.The reclaimed gullies after 3,7,13 and 20 years with straw filling were selected in Yinlonghe state farm of Wudalianchi City,Heilongjiang Province,and the straw was sampled and analyzed to evaluate the decomposition rate.The water quality of subsurface pipe drainage was sampled and analyzed in the straw-filled reclamation area of Hailun Soil and Water Conservation Monitoring and Research Station of Chinese Academy of Sciences to evaluate the water environment quality.The topsoil of reclamation site and cultivated land were sampled and analyzed in the reclamation test area of Guangrong Village,Hailun City,Heilongjiang Province.The physical and chemical properties were compared to evaluate the soil environmental quality after reclamation.The water and soil environmental quality were evaluated respectively,and the environmental effect was comprehensively evaluated.The soil moisture and nutrient characteristics during the whole growth period were systematically observed in the reclamation experimental area of Guangrong Village,Hailun City,Heilongjiang Province,and the crop grain yields were measured in the autumn.The spatial heterogeneity and correlation of soil moisture,nutrient and yield were analyzed,and the influence of gully slope erosion on soil quality and crop productivity was clarified.The drainage capacity of erosion gully after reclamation.After reclamation,the water storage in the straw filling layer was 463 kg/m~3.The total surface runoff could be completely stored by straw layer during rain season.The cultivated land could withstand the uniform rainfall of 44-80 mm/h after reclamation,and 95%of the surface runoff went into underground drainage system,with greatly reducing the risk of the surface runoff.Duo to the change of surface runoff into underground drainage,no secondary erosion gully would be formed after the reclamation.The decomposition rate of straw.After 20 years of the gully reclamation,the decomposition rates of different components of straw were different.Among them,hemicellulose and cellulose decomposed fastly,and lignin almost would not be decomposed.The lignin proportion increased from 26.8%to 38.8%.The filled straw was in an anaerobic environment,saturated in water,and frozen alomost half year,these insuced its decomposition was slow.The thickness of straw bale decreased by an average of 1.4 cm per year,and the decline part of straw layer could be filled by ploughing and sediment deposition.After reclamation,the original gully area did not collapse.The environmental effects.Single factor pollution index evaluation results showed the five days biochemical oxygen demand exceeded 1.8 times,chemical oxygen demand exceeded 3.9 times than their permission values;The Nemerow evaluation results showed that the wastewater discharged by the underground pipe exceeded the standard,which would cause certain polution to the environment.Firstly,the sewage discharged by the underground pipe was diluted continuously through the river.At the exit small watershed,all indicators in the water body have reached the standard.Secondly,the decomposition rate of straw was getting slower and slower,the pollutants generated by decomposition were decreasing.The pollution caused by discharge into the water body would continue to decrease.Therefore,the pollution to the river water environment was limited.The contents of soil organic matter,total nitrogen,total phosphorus,alkali-hydrolyzable nitrogen,available phosphorus and available potassium in the plough layer of reclaimed area were lower 30%than those in farmland.Overall,the waste water discharged from the pipe would cause a certain degree of pollution to the drainage outlet environment,but the river water does not cause pollution;The soil environment of reclaimed arable layer is different from that of arable layer,but there is little difference.The reclamation effect.(1)Both of the gully and slope erosion had a significant impact on soil properties of slope farmland in black soil area.The coefficient of variation of soil water content in the depth of 0-20 cm of ridge in the small watershed during the whole growth period was 12.2%-17.4%,which was medium variation;The nugget/sill<0.2 in spring indicated a strong spatial correlation,and it was close to 0 in the rain season indicating that the soil water content in gully catchment was completely affected by the runoff migration caused by structural factors such as topography.The spatial effective correlation distance was the smallest,only 55.2 m in the rain season.(2)The content changes of soil organic matter,total nitrogen,total phosphorus,alkali-hydrolyzable nitrogen,available phosphorus and available potassium in gully slope catchment area were 23.9-49.7 g/kg,0.8-1.7 g/kg,0.3-0.6 g/kg,70.3-183.8 mg/kg,27.8-78.9 mg/kg and 71.2-202.1 mg/kg,respectively,which were mainly affected by structural factors.The effective spatial correlation distance of soil organic matter content was less than 100 m,and the effective spatial correlation distance of total phosphorus content was the largest,closed to 500 m.(3)Soybean yield in catchment area varied from 1669 kg/hm~2to 3223 kg/hm~2,and maize yield varied from 8177kg/hm~2 to 10871 kg/hm~2.The average yield of soybean and maize in the reclaimed area were 84.1%and 86.6%of cultivated land,respectively.The lowest yield of soybean and maize appeared at the downstream reclamation site,and the effect of gully erosion on soybean yield was greater than that of maize.The gully erosion aggravated the spatial heterogeneity of soil moisture and nutrients in catchment area,and reduced the productivity of cultivated land.