Department of Physical Geography, Stockholm University, 10691 Stockholm, Sweden.
Bolin Centre for Climate Research, Stockholm University, 10691 Stockholm, Sweden.
Environ Sci Technol. 2022 Oct 18;56(20):14427-14438. doi: 10.1021/acs.est.2c03397. Epub 2022 Sep 27.
Microbial pesticide degraders are heterogeneously distributed in soil. Their spatial aggregation at the millimeter scale reduces the frequency of degrader-pesticide encounter and can introduce transport limitations to pesticide degradation. We simulated reactive pesticide transport in soil to investigate the fate of the widely used herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA) in response to differently aggregated distributions of degrading microbes. Four scenarios were defined covering millimeter scale heterogeneity from homogeneous (pseudo-1D) to extremely heterogeneous degrader distributions and two precipitation scenarios with either continuous light rain or heavy rain events. Leaching from subsoils did not occur in any scenario. Within the topsoil, increasing spatial heterogeneity of microbial degraders reduced macroscopic degradation rates, increased MCPA leaching, and prolonged the persistence of residual MCPA. In heterogeneous scenarios, pesticide degradation was limited by the spatial separation of degrader and pesticide, which was quantified by the spatial covariance between MCPA and degraders. Heavy rain events temporarily lifted these transport constraints in heterogeneous scenarios and increased degradation rates. Our results indicate that the mild millimeter scale spatial heterogeneity of degraders typical for arable topsoil will have negligible consequences for the fate of MCPA, but strong clustering of degraders can delay pesticide degradation.
微生物农药降解剂在土壤中呈异质分布。它们在毫米尺度上的空间聚集降低了降解剂与农药相遇的频率，并可能给农药降解带来传输限制。我们模拟了土壤中反应性农药的传输，以研究广泛使用的除草剂 4-氯-2-甲基苯氧乙酸（MCPA）在应对降解微生物不同聚集分布时的命运。定义了四个情景，涵盖了从均匀（伪 1D）到降解剂极度异质分布的毫米尺度异质性，以及连续小雨或大雨事件的两种降水情景。任何情景都没有底土的淋溶。在表土中，微生物降解剂空间异质性的增加降低了宏观降解速率，增加了 MCPA 的淋溶，并延长了残留 MCPA 的持久性。在异质情景中，农药降解受到降解剂和农药空间分离的限制，这可以通过 MCPA 和降解剂之间的空间协方差来量化。大雨事件暂时缓解了异质情景中的这些传输限制，并提高了降解速率。我们的结果表明，耕地表土中典型的轻度毫米尺度空间异质性对 MCPA 的命运几乎没有影响，但降解剂的强烈聚集会延迟农药的降解。
