| With the development of economy and the increment of urban population,more and more municipal solid waste has been generated.The enhancement of land price and the difficulty in site selection lead to inefficient waste management.The mineralized municipal solid waste went through long period of microbial digestion in the landfill and can be sieved and separated.This soil-like material,which is termed landfill stabilized waste(LSW)hereafter,contains high value of organic matter and nutrients,and thus is a potential topsoil substitute for plants growth during reclamation in abandoned mines and quarries.In this research,firstly the physical and chemical properties of LSW were studied;the effects of LSW on seed germination and seedling growth were tested.Secondly,LSW was mixed with quarries(2-3 cm in size,representing the rock fragments which are produced during the quarrying process and left in the abandoned quarries)in different percentages to form artificial soil.The physical and engineering properties of artificial soil were studied.Runoff plots were set;the dynamics of volumetric water content,evapotranspiration,and runoff under natural precipitation or artificial storms were monitored;the suitability for plant growth was analyzed.When the proportion of LSW was too low,the artificial soil had low water holding capacity and poor water condition.To deal with this problem,artificial soil with a low proportion of LSW(20%by mass)was mechanically compacted to different degrees,and the soil water dynamics and plant growth were monitored,which was the third part of this research.The results showed that:(1)LSW was a soil-like material with high porosity,water holding capacity and infiltration rate,which also had low bulk density and shear strength.The contents of available K,available N,available P,and organic matter of LSW were 5.0?21.6 times higher than the values of surrounding farm soil.The waste samples from 3/5 landfills were suitable for cultivation based on their heavy metal contents,but two samples contained over-limit Hg and/or Zn.Among the 153 tested SVOCs,2 phenols,9 PAHs,2 PAEs and 1 OCP were determined,but the concentrations were lower than Standard of Soil Quality Assessment of Exhibition Sites or similar to the values of urban and/or farm soil.The MPN of coliforms was similar to the value of short-term compost.The amount of total dissolved salts was similar to lightly-to-heavily salinized soil.The cation exchange capacity was lower than planting soil for greening.The water extract of LSW had no significant effect on seed germination,and the effect of LSW on seedling growth depended on plant species.(2)Compared to LSW,artificial soil had a significantly higher bulk density and shear strength,but a significantly lower porosity and field capacity.Under natural precipitation,as the fraction of LSW decreased,the average water content of the artificial soil decreased,the effects of precipitation and the antecedent soil moisture content on water content decreased,diurnal variation of water content decreased,the amounts of underground runoff and total runoff increased,the effect of precipitation on runoff increased and the daily evapotranpiration decreased.Daily evaportranpiration of a certain soil layer and relative daily evapotranspiration(which was the proportion it accounted for the total amount of evaportranpiration along the soil profile)were positively correlated to the water content of the same soil layer,and these relationships weakened with an increment of soil depth.Soil water contents at 10 cm and 20 cm depths were negatively correlated to relative daily evapotranspiration at 40 cm and 50 cm depths,and water contents at 40 cm and 50 cm depths were negatively correlated to relative daily evapotranspiration at 10 cm depth.Vegetation coverage varied significantly among different artificial soil plots,and when the volume fraction of LSW was 1/9,the vegetation coverage and the growth of the target species were very low during the growing season.(3)Compaction significantly enhanced the water content and the water holding capacity of artificial soil(the LSW:gravel ratio was 8:2).During the rainy season,the water content of artificial soil depended on the precipitation and the antecedent soil moisture content,and their effects increased with an increment of compaction degree.The daily evapotranspiration of artificial soil was affected by compaction degree,soil depth and soil water content.As the compaction degree increased,the leaf water contents of Robinia pseudoacacia and Medicago sativa decreased,the survival rate and growth of R.pseudoacacia decreased,the survival rate and growth of Platycladus orientalis increased,and the biomass of M.sativa increased.The survival rate of R pseudoacacia living in the margin of the compacted area was 19%?63%higher than the plants living in the interior of the compacted area,and when the porosity was lower than 21.1%,almost all individuals lived in the margin.The growths of marginal and interior R.pseudoacacia were not significantly different.The survival rate,height and ground diameter of P.orientalis living in the margin were 11%?25%,0%?34.8%,19.7%?39.9%higher than those living in the interior,respectively.Summarily,the results indicate that LSW can be utilized as topsoil substitute during restoration in abandoned quarries.The artificial soil made up of LSW and gravels can support plant growth,improve site conditions and accelerate revegetation.Artificial soil with a LSW:gravel ratio of 7:3?5:5 is recommend because of the good nutrient level,water condition and aeration.When LSW:gravel ratio is lower than 3:7,compaction can be used to improve its physical quality and facilitate plant growth.A mild compaction(with total porosity of 22.1%?26.8%)is recommended for plants which are not well adapted to compacted soils such as R.pseudoacacia and a heavy compaction(with total porosity of 13.3%)can be used for plants which are well adapted to compacted soils such as P.orientalis and M.sativa. |
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