基于土壤水分变化的砷与土壤碱性磷酸酶活性关系探讨

砷作为土壤主要污染元素之一,其毒性受到存在形态等的影响.土壤酶是土壤重要组成部分,但水分对二者关系的影响鲜见报道.本文采用室内模拟方法,在35%、65%和110%最大饱和持水量(WHC)条件下,较为系统地分析了不同水分下土壤有效砷及土壤碱性磷酸酶活性的变化规律.结果表明:外源砷浓度、老化时间是影响土壤有效砷含量的主要因素,且有效砷浓度随老化时间延长降幅减缓,Elovich方程较好表征了二者关系,揭示出水分对土壤有效砷向其他形态转变速率影响的大小顺序为:110%WHC65%WHC35%WHC;干燥(35%WHC)和淹水(110%WHC)导致土壤碱性磷酸酶活性减小;砷抑制土壤碱性磷酸酶活性,模型U=A/(1+B×C)可较好表征砷浓度(C)与土壤酶活性(U)的关系,揭示出土壤碱性磷酸酶活性在一定程度上可表征土壤砷污染程度,并反映出其机理为完全抑制作用;计算得到了土壤砷轻度污染的临界浓度Ecological dose 10%(ED10)总砷99 mg·kg-1和有效砷39 mg·kg-1,从侧面表明土壤碱性磷酸酶在土壤砷浓度达到国家土壤质量标准中的二级标准前不会对土壤酶产生严重毒害;水分由于对砷的存在状态等的作用,从而对土壤碱性磷酸酶活性产生重要影响.

Relationship between arsenic and soil alkaline phosphatase activity based on changes of soil moisture

Arsenic (As) is one of the major heavy metals in soil and its toxicity is affected by speciation. Soil enzyme is also a key composition in soil, but few studies had been focused on the relationship between arsenic and soil enzymes affected by soil moisture conditions. In this study, we investigated the correlation between available arsenic and soil alkaline phosphatase activity at three soil moistures 35%, 65% and 110% maximum water holding capacity (WHC). The results showed that total arsenic concentration in soil and the period of aging were major factors to impact available arsenic in soil. Available arsenic content was declined with aging which can be described using Elovich equation. Available arsenic was converted into other forms rapidly with increasing soil moisture content. Soil alkaline phosphatase activity was reduced in both drought and flooding. Arsenic in soil significantly inhibited soil alkaline phosphatase activity. The model U=A/(1+B×C) is fitted well in the relationship between soil enzymatic activities (U) and arsenic concentration (C). Soil alkaline phosphatase activity is a good bioindicator for the extent of soil arsenic pollution. Ecological dose 10% (ED₁₀) of total concentration and available arsenic were 99 mg·kg^-1 and 39 mg·kg^-1, respectively. No significant toxic impact from Arsenic on soil enzyme was observed when As concentration meets the national guideline. Soil moisture can impact the soil alkaline phosphatase activity because soil moisture affects the form of arsenic in soil.