| Biochar is a solid substance produced by biomass combustion under anoxic conditions.Because of its large specific surface area and strong cation exchange capacity,it is considered that it can increase the content of organic carbon in soil and maintain soil fertility.In addition,biochar contains a large number of quinone and aromatic ring structures,which can act as an electron donor for microbial anaerobic respiration or as an electron shuttle between microorganisms and heavy metals,participate in the oxidation-reduction of iron in nature,and then drive the biogeochemical cycle of arsenic.The toxicity and bioavailability of arsenic are closely related to its occurrence form.It is very important to study the effect of biochar on arsenic and arsenic form transformation.Based on the study of the effect of biochar on the migration and transformation of arsenic in high arsenic soil,this paper constructs a variety of anaerobic microcosm systems dominated by sterilized soil biochar Lake Oneida shiwarella（MR-1）,and studies the differential mechanism of biochar mediated arsenic migration and transformation in soils with different arsenic concentrations under the induction of MR-1,so as to provide a scientific basis for enriching the biogeochemical cycle of arsenic in soils with high geological background.The main conclusions are as follows:1.The experimental results show that the concentration and electron yield of as（Ⅴ）/Fe（Ⅲ）in the group with biochar are higher than those in the group without biochar,indicating that biochar can significantly promote the reduction and release of as（Ⅴ）/Fe（Ⅲ）.During the reduction of as（Ⅴ）/Fe（Ⅲ）by biochar coupled MR-1,the effect of biochar as electron shuttle on the reduction and release of as（Ⅴ）/Fe（Ⅲ）is more significant than that as electron donor.The results of three-dimensional fluorescence measurement and parallel factor results show that the continuous change of fluorescence intensity of aromatic proteins（C1）and humic acids（C3 and C4）shows that biochar can promote the metabolic activities of microorganisms and act as an electronic mediator to promote the reduction and release of as（Ⅴ）and Fe（Ⅲ）.2.The results of arsenic form proportion show that F6 is an important state in soils with different concentrations.Driven by microorganisms,biochar significantly promotes its migration and transformation to available arsenic,and the proportion of Available Arsenic increases with the increase of soil arsenic concentration,which intensifies the potential harm to the surrounding environment.3.The results of potential path analysis show that in low concentration soil,F3 significantly affects the content of as（Ⅲ）in overlying water.With the participation of microorganisms,biochar significantly promotes the mutual transformation between F6 and F1,and then affects the content of as（Ⅴ）and as（Ⅲ）in overlying water.In medium and high concentrations of soil,biochar significantly promoted the mutual migration between iron bearing states（F3,F4,F5）and overlying water,making the relationship between various forms more closely connected.4.The results show that biochar can significantly promote the redox reaction in the system and accelerate the reduction rate of Fe（Ⅱ）to as（Ⅴ）under the action of microorganisms.In addition,because the surface potential of biochar is negatively charged and can effectively absorb positively charged Fe（Ⅱ）,the Fe（Ⅱ）concentration of biochar added group in overlying water is lower than that of biochar not added group. |
