Effects Of Arsenic Contamination On Greenhouse Gas Emissions From Paddy Soils

Paddy fields have been identified as a major source of increasing atmospheric CO2,CH4 and N2O emissions.China is one of the most important rice-producing countries in the world.The rice-planting area accounts for about 20%of the world total.Therefore,the emissions of CO2,CH4 and N2O from rice paddy fields in China have gained much attention.Currently,numerous paddy fields in China have been subject to different levels of arsenic contamination,which is directly harmful to human health and associated with activities of functional microbes driving soil gas emissions,such as N2O involved nitrification and denitrification or CH4 related production or oxidation processes.The greenhouse gas emissions as affected by arsenic contamination in paddy fields have been poorly constrained.In this study,the arsenic contamination in paddy soils was simulated by adding sodium arsenite solution.We investigated the responses of three major soil gas emissons to different arsenic levels,different water conditions and also biochar amendment.The main results of this study are as follows:Under flooded conditions,paddy soils with different arsenic concentrations had little influence on the CO2 emissions,and the CO2 emissions from four treatments showed consistent decline trends.Cumulative emissions of CO2 in L treatment(Low Concentration Arsenic contamination),M treatment(Medium Concentration Arsenic contamination)and H treatment(High Concentration Arsenic contamination)were greater than CK treatment,but there was no significant difference between the four treatments.The CH4 emission rates of the four treatments gradually increased with the incubation time,and there were two emission peaks on the 11th day and 31st day.Among them,M treatment had the highest CH4 emission rate,just higher than CK treatment.The CH4 cumulative emissions of L treatment and H treatment were lowest,and the relationship between the four treatment was M>CK>L>H.The CH4 cumulative emissions of M treatment and CK treatment were significantly higher than L treatment and H treatment,but there was no significant difference between M treatment and CK treatment,as well as L treatment and H treatment.The N2O emission rates of the four treatments were highest on the 1st day,and declined rapidly.After 4 days incubation,the N2O emission rates of the four treatments were at a lower level,stabled at 0.07 ?g·kg-1·h-1.The N2O cumulative emissions of L treatment and M treatment were 0.42 mg·N·kg-1 and 0.40 mg·N·kg-1 respectively,significantly higher than that of H treatment and CK treatment.Under flooding condition and 60%WHC moisture,the CO2 emission trends of the four treatments were similar.At the first 3 days incubation,the CO2 emission peaks of four treatments appeared,and then showed fluctuated downward trends.The CO2 emission rates of flooding treatments were higher than that of 60%WHC treatments at first 9 days incubation,and the CO2 cumulative emissions of AsOF(flooding)treatments and AsF(flooding arsenic)treatments were significantly higher than that of AsOW(60%WHC)treatments and AsW(60%WHC+arsenic)treatments.The CH4 emission rates of 60%WHC moisture condition in paddy soils was very low,and fluctuated at 0 ?g·kg-1·h-1.The CH4 emission rates under flooding condition peaked at the 5th and the 10th day,but were stable at 0 ?g·kg-1·h-1 during most time.The CH4 cumulative emission of AsOF treatment was significantly higher than that of the other three treatments,and the cumulative emissions of CH4 in these three treatments was negative.The N2O emission rates of flooding treatment was higher than that of 60%WHC treatments,but the emission trends were consistent.And the N2O emission peak appeared at the initial time,among which the peak value of AsF treatment was the highest and AsOW was the lowest.From the start of the second week of incubation,the N2O emissions of four treatments were stable at lower levels until the end of incubation.The cumulative emissions of N2O from AsOF treatment and AsF treatment was significantly higher than that of AsOW treatment and AsW treatment.Among them,AsF>As0F,AsW>As0W,and four treatments had significant differences.The application of biochar and arsenic to paddy soils had few effects on the CO2 emission rates.The dynamic variation of CO2 emission rates of AsOCO treatment(without addition of biochar and arsenic),AsCO treatment(added arsenic),AsOC treatment(adding biochar)and AsC treatment(adding biochar and arsenic)showed a declining trend.Among the four treatments had little difference.The CO2 cumulative emissions of AsOC treatment and AsC treatment were significantly lower than that of AsOCO treatment and AsCO treatment,but there were no significant difference between AsOCO treatment and AsCO treatment or AsOC treatment and AsC treatment.The CH4 emission rates of AsOCO treatment,AsCO treatment,AsOC treatment and AsC treatment fluctuated at 0 ?g·kg-1·h-1,but the fluctuation of AsOC and AsC treatments were greater than AsOCO and AsCO treatments.There were significant differences in the CH4 cumulative emissions of four treatments,and the relationship between them was:AsOC>AsCO>AsOCO>AsC.Biochar addition significantly reduced soil N2O emission rates and N2O cumulative emissions.The addition of arsenic to soils stimulated N2O emissions.The N2O emission rate of AsCO treatment was higher than that of AsOCO treatment in the first week,and the cumulative emissions of N2O from AsCO treatment and AsC treatment were significantly higher than that of AsOCO treatment and AsOC treatment.