Effect Of Freeze-thaw On Soil Erosion And Release Of Colloid Heavy Metal In Alpine Mining Area

Xinjiang is an essential origin of mineral resources in our country,especially rich in mineral resources along the Tianshan areas,continuously motivating the development of economy in Xinjiang.However,in recent years,exploitation of mineral resources has been destroying local environment in varied degrees.With the increasingly serious phenomena of water and soil loss as well as heavy metal contamination,environmental problems have been exposed.As a result,in this research,mining soil in Tianshan,Xinjiang was studied.By utilizing methods such as indoor freezing and thawing cycle simulation and artificial precipitation,etc.,the effect of freezing and thawing under different situations on slope soil and nutrient loss was studied and analyzed,with the different situations referring to freezing-thawing and no freezing-thawing,frequency of freezing and thawing cycle and different soil moisture contents;furthermore,the inhibitor effect of different additive amount of biochar on soil and nutrient loss was studied under the action of freezing and thawing,discussing repair mechanisms of biochar towards soil in alpine mining lots;finally,indoor freezing and thawing cycle simulation was conducted towards colloidial heavy metals and nutrients in soil,and the releasing rule of colloidial heavy metals in soil was discovered under the action of freezing and thawing.Main conclusions were as follow:(1)Both of the action of freezing and thawing and preliminary soil moisture content in the early stage posed significant effect on sediment and runoff as well as nutrient loss of soil.Within the frequency of freezing and thawing ranging from 0 to 5 times,the total amount of both sediment and runoff and nutrient loss reached the highest with the increasing frequency of freezing and thawing cycle and preliminary soil moisture content,compared to the group with no freezing and thawing.Under the preliminary soil moisture content of 20%and the frequency of freezing and thawing of 5,total amount of both sediment and runoff and nutrient loss reached the highest,compared to the group under the preliminary soil moisture content of 10%and the frequency of freezing and thawing of 0,with an increased total amount of sediment and runoff being 38.9%and 63.6%separately,total loss of ammonium nitrogen and nitrate nitrogen being 41.5%and 133.1%separately and total loss of total phosphorus and dissolved total phosphorus being 308.8%and 199.9%respectively.(2)The addition of biochar could effectively inhibit soil and nutrient loss,reducing initial loss concentration,thereby reducing cumulative total loss.With the increase of the biochar additive amount,cumulative total loss also dropped.When the additive amounnt of bichar reached 1000kg/hm2,total amount of slope sediment and runoff was reduced by 11.2%and 14.3%respectively,total loss of ammonium nitrogen and nitrate n itrogen by 63.5%and 37.1%separately and total loss of total phosphorus and dissolved total phosphorus by 40.9%and 109.1%respectively when the frequency of freezing and thawing was 3,compared to the group with no freezing and thawing.(3)The action of freezing and thawing posed different effects on the amount of.soil colloidial heavy metal release.With the elevated frequency of freezing and thawing cycle,the releease amount of Cu dropped,while the action of freezing and thawing had no significant effect on the release of colloidial Ni and Cd.Before the addition of biochar,there was no correlation between total nitrogen,total carbon,Ni,Cu and Cd.When biochar was added,Cd and Ni presented significant positive correlation,while TN and TC showed extremely significant positive correlation.