Assessing the transport and reactive processes of contaminants in freshwater streams is crucial in managing water resources sustainably. Particularly the hyporheic zone, the sediment-water interface where surface water and groundwater mix, may possess significant contaminant removal capacities due to its myriad physical, chemical, and microbiological processes. However, modelling approaches aiming at assessing the hyporheic zone’s reactivity are either based on simple assumptions, such as, predefining the shape of the residence times distribution (RTD) function, or are computationally not feasible due to a too detailed system characterisation. In addition, parent-daughter reactions of contaminants are barely investigated. The present study introduces a numerical modelling framework for assessing hyporheic reactions of contaminant transformation reactions based on a non-parametric residence time approach combined with multiple sorption models and first-order removal reactions. The proposed framework uses natural electrical conductivity fluctuations to determine conservative transport properties and is demonstrated by interpreting time series of hyporheic point measurements of trace organic compounds, such as pharmaceuticals, and their transformation products using two commonly-used sorption models, namely the simple retardation and the first-order kinetic sorption model. The developed approach gives similar reaction rate coefficient estimates for all contaminants considered for both sorption models tested. The findings highlight that (i) the accurate shape of the RTD is most certainly important for reactive parameter determination and (ii) the daughter reaction rate coefficient may be underestimated if its parent transformation is ignored. The model provides reactive parameter estimates of contaminant transformation reactions with high parameter identifiability and informs which specific parent-daughter-pathway has occurred.

评估淡水流中污染物的迁移和反应过程对于可持续管理水资源至关重要。特别是潜流带，即地表水和地下水混合的沉积物-水界面，由于其无数的物理、化学和微生物过程，可能具有显着的污染物去除能力。然而，旨在评估低流带反应性的建模方法要么基于简单的假设，例如预定义停留时间分布 (RTD) 函数的形状，要么由于过于详细的系统特征而在计算上不可行。此外，几乎没有研究污染物的母子反应。本研究介绍了一种数值建模框架，用于评估基于非参数停留时间方法结合多个吸附模型和一级去除反应的污染物转化反应的下流反应。所提出的框架使用自然电导率波动来确定保守的传输特性，并通过使用两种常用的吸附模型（即简单延迟和一级动力学吸附模型。开发的方法为测试的两种吸附模型中考虑的所有污染物提供了类似的反应速率系数估计值。研究结果强调 (i) RTD 的准确形状对于反应参数确定最重要，并且 (ii) 如果忽略其母体转换，则子反应速率系数可能会被低估。该模型提供了具有高参数可识别性的污染物转化反应的反应参数估计，并告知发生了哪些特定的亲子途径。