题目 Title

Modeling microplastic transport in open channel flows and ingestion dynamics by benthos

期刊 Journal

Water Research (IF=12.9)

作者 Author

Mingming Jiao, Kai Wang, Chenwei Zhao, Yan Liu, Hongwei Fang

摘要 Abstract

Understanding the dynamics of unintentional microplastic (MP) ingestion by benthos in aquatic environments is crucial for assessing the ecological impacts of MPs. Yet, this process remains poorly understood. To address this, we developed a high-fidelity, two-way coupled numerical model that integrates large-eddy simulation and Lagrangian point-particle tracking techniques. Three key parameters are examined: benthos predation types (filter-feeders, grazers, and burrowers), MP density, and benthos density, with benthos density emerging as the dominant factor. Specifically, an eightfold increase in benthos density results in a 5- to 22-fold rise in ingested MPs. Benthos types influence the final ingestion proportion (defined as the ratio of ingested to released MPs), with grazers showing the highest ingestion efficiency, followed closely by filter feeders—both approximately doubling the ingestion rate observed in burrowers at equivalent benthos density. MP density has minimal influence on ingestion across all benthic groups and densities, except under high-density filter-feeder conditions. Two distinct MP transport models during ingestion are identified: (i) a suspension mode observed in filter-feeders and (ii) a sliding mode prevalent in grazers and burrowers. The Rouse number (P) effectively differentiates these models, with the suspension mode dominating when P < 2.5 and the sliding mode dominating when P > 2.5. The Rouse number and spanwise turbulence intensity govern the number of MPs ingested by each benthic individual, while the cumulative predation width of all benthos accounts for the impact of benthos density and types. Consequently, the product of these two parameters serves as a robust predictor for the final MP ingestion proportion, where a strong linear relationship is observed across all simulations.

简介 Brief introduction

了解水生环境中底栖生物意外摄入微塑料（MP）的动态行为，对于评估微塑料的生态影响至关重要。然而，这一过程仍知之甚少。为此，我们开发了一种高精度的双向耦合数值模型，该模型整合了大涡模拟和拉格朗日点粒子追踪技术。研究考察了三个关键参数：底栖生物摄食类型（滤食性、食草性、穴居性）、微塑料密度和底栖生物密度，其中底栖生物密度是主导因素。具体而言，底栖生物密度增加8倍，会导致摄入的微塑料增加5至22倍。
底栖生物类型会影响最终的摄入比例（定义为摄入微塑料与释放微塑料的比值）：食草性生物的摄入效率最高，滤食性生物紧随其后—在相同底栖生物密度下，二者的摄入率均约为穴居性生物的两倍。微塑料密度对所有底栖生物类群及不同密度下的摄入过程影响极小，但高密度滤食性生物条件除外。研究发现了摄入过程中两种不同的微塑料传输模式：（1）滤食性生物中观察到的悬浮模式；（2）食草性和穴居性生物中普遍存在的滑动模式。劳斯数（P）可有效区分这两种模式：当 P <2.5 时，悬浮模式占主导；当 P> 2.5 时，滑动模式占主导。
劳斯数和展向湍流强度控制着每个底栖生物个体摄入的微塑料数量，而所有底栖生物的累积摄食宽度则解释了底栖生物密度和类型的影响。因此，这两个参数的乘积可作为最终微塑料摄入比例的可靠预测因子，所有模拟中均观察到二者存在强烈的线性关系。

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