Effect Of Deicing Salts On The Content Of Water-soluble Salt Ions And Nitrogen Transformation In Highway Roadside Soil

Deicing salts have been widely used for winter maintenance in northeast China.Its harm to the environment, especially to the soil environment, is of primaryconcern. In this study, two possible pathways of deicing salt to enter in to roadsidesoil （the drainage-impacted soil and the spray and splash-impacted soil） and two landuse patterns of the roadside soil （farmland and pine forests） were investigated. Theconcentrations of water soluble ions, the microbial activity and nitrogen levels in theroadside soil and the nitrogen transformation, microbial activity and urease activityunder simulated conditions of deicing salts were studied to clarify the effect ofdeicing salts on the soil microbial activity, nitrogen transformation process and theirinteraction relationships.The study of salinity, conductivity, the concentrations of water-soluble salt ionsin the highway roadside soils at different distances from the road showed that:（1）salinity and conductivity in the roadside soil increased with the use of deicing salt.The greatest harm to the roadside soil was found in the drainage-impacted soil. At2m and4m from the road, the soil was moderate salinization, and at6m and8mfrom the road, the soil was mild salinization in the drainage-impacted soil. Thedistance impacted by deicing salt was8m. At2m from the road, the soil was mildsalinization and the distance impacted by deicing salt was2m in the spray andsplash-impacted soil.（2） The significantly negative correlations between pH valueand conductivity, the concentrations of Na⁺, Cl^-and HCO₃^-showed that the pH valuein the roadside soil increased with the use of deicing salts. There was a significantincreasement in the concentrations of water-soluble salt ions with the use of deicingsalts in the roadside soil, such as Cl^-, HCO₃^-, Na⁺, Ca²⁺, K⁺and Mg²⁺, especially Cl^-and Na⁺. The most Cl^-and Na⁺were found in the drainage-impacted soil and theimpacted distance was8m. In the drainage-impacted soil, the impacted distance ofCl^-was6m in the farmland soil and4m in pine forest soil, and the impacteddistance of Na⁺were2m in both the farmland soil and the pine forest soil. More Cl^- and Na⁺were found in the farmland soil than in the pine forest soil. The content ofSO₄^2-in roadside soil had nothing to do with the use of deicing salts.The study of microbial activity and nitrogen morphological characteristics inthe highway roadside soil showed that:（1） The decrease of microbial biomasscarbon and microbial biomass nitrogen with the use of deicing salts showed thatdeicing salts inhibited the growth of microorganisms in the soil. Microbial biomasscarbon/organic matter was negatively correlated with the concent of deicing salts.Significantly negative logarthmic correlations were found between microbialbiomass carbon/organic matter and Na⁺, K⁺, Ca²⁺, respectively. Significant negativelogarthmic correlations were found between microbial biomass carbon/organicmatter and Cl^-. There was a highly significant linear correlation between microbialbiomass carbon/organic matter and pH value, HCO₃^-, respectively. It showedthat the toxic effects of deicing salt ions, especially Cl^-, and the increase of pHvalue led to a decrease of microbial communities.（2） Microbial biomass C/Ndecreased the inceasing content of deicing salts. The toxic effects of Cl^-and theincrease of pH value in the soils polluted by deicing salts inhibited the growth offungi community, resulting in bacterial communities dominated. The increase of themicrobial metabolic quotient roadside soil showed the stress of decing salts onmicrobial community.（3） Deicing salts had no significant impact on total nitrogenin the roadside soils. Ammonium and nitrate were not sensitive to deicing salt inroadside soil.The simulated experiment of the effect deicing salts on the on soil nitrogentransformation process under different deicing salts concentration treatment (0g·kg^-1,1g·kg^-1,3g·kg^-1,5g·kg^-1,8g·kg^-1) showed that:（1） The soil mineralizationdecreased with the increasing concentration of deicing salts, but no significantdifferences were found between different deicing salts treatments （p>0.05）. The soilnitrification decreased with the increasing concentration of deicing salts, significantdifferences were found at the5g·kg^-1（p<0.05）.（2） The dynamical characteristics ofmineralization fitted the first-order kinetic model of mineralization. The dynamicalcharacteristics of nitrification fitted well the linear equation and the logistic equation.（3） The microbial biomass C decreased with the increasing content of deicing salt, and significant differences were found at the5g·kg^-1. The microbial biomass Ndecreased with the increasing content of deicing salt, and significant differenceswere found at the5g·kg^-1. The decrease of microbial biomass C/N with theinceasing content of deicing salts showed that the use of deicing salts inhibited thegrowth of fungi community, resulting in bacterial communities dominated. Positivelinear correlation between the microbial metabolic quotient and the concentration ofdeicing salts showed stress effect on soil microorganism. When the concentration ofdeicing salts was more than5g·kg^-1, soil urease was signifacantly lower thancontrol.