Due to high spatiotemporal variability of aquatic systems, relationships between microplastic sources and sinks are highly complex and transportation pathways yet to be understood. Field data acquisitions are a necessary component for monitoring of microplastic contamination but alone cannot capture such complex relationships. Remote sensing is a key technology for environmental monitoring through which extrapolation of spatially limited field data to larger areas can be obtained. In this field study we tested whether microplastic distribution follows the same transport pattern as water constituents depictable from satellite images, namely chlorophyll-a, suspended particulate matter, and colored dissolved organic matter, and discuss their applicability as proxies. As rivers are a major source for marine microplastic contamination, we sampled three example river systems: the lower courses and river mouths of the Trave and Elbe estuary in Germany and the Po delta in Italy. For a full quantitative analysis of microplastics (>300 μm), ATR- and FPA-based μFT-IR spectroscopy and NIR imaging spectroscopy were utilized. Comparing water constituents with in-situ data using regression analysis, neither a relationship for the Elbe estuary nor for the Po delta was found. Only for the Trave river, a positive relationship between microplastics and water constituents was present. Differences in hydrodynamic conditions and spatiotemporal dynamics of water constituents and microplastic emissions among the river systems are possible explanations for the contrary results. Based on our results no conclusions on other river systems and likewise different seasons can be drawn. For remote sensing algorithms of water constituents to be used as microplastic proxy an adaption for each system as well as for different seasons would thus be necessary. The lower detection limit of 300 μm for microplastics could also have influenced relationships as microplastic abundance exponentially increases with decreasing size class. Further studies with improved sampling methods are necessary to assess our proposed method.

中文翻译：

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能否将水成分用作绘制过渡水域和沿海水域内微塑料扩散情况的代理？

由于水生系统的高时空变异性，微塑料源和汇之间的关系非常复杂，运输途径尚待了解。现场数据采集是监测微塑料污染的必要组成部分，但仅靠采集无法捕捉到如此复杂的关系。遥感是环境监测的一项关键技术，通过它可以将空间有限的现场数据外推到更大的区域。在这项实地研究中，我们测试了微塑料的分布是否遵循与卫星图像中可描述的水成分（即叶绿素 a、悬浮颗粒物和有色溶解有机物）相同的传输模式，并讨论它们作为替代物的适用性。由于河流是海洋微塑料污染的主要来源，我们采样了三个示例河流系统：德国特拉韦河和易北河河口以及意大利波河三角洲的下游和河口。为了对微塑料 (>300 μm) 进行全面定量分析，使用了基于 ATR 和 FPA 的 μFT-IR 光谱和 NIR 成像光谱。使用回归分析将水成分与原位数据进行比较，未发现易北河河口和波三角洲的关系。仅对于 Trave 河，微塑料和水成分之间存在正相关关系。河流系统之间水动力条件和水成分和微塑料排放的时空动态的差异是相反结果的可能解释。根据我们的结果，无法得出关于其他河流系统的结论，同样也无法得出不同的季节。对于用作微塑料代理的水成分遥感算法，因此需要针对每个系统以及不同季节进行调整。微塑料 300 μm 的检测下限也可能影响关系，因为微塑料丰度随着尺寸等级的降低呈指数增加。需要进一步研究改进的采样方法来评估我们提出的方法。