New insights into particle transport in karst conduits using comparative tracer tests with natural sediments and solutes during low‐flow and high‐flow conditions

Colloidal particles are an important vector for the transport of contaminants in karst aquifers, characterized by a high degree hydrologic variability. Understanding this heterogeneity and hydrogeological functioning is particular importance water management strategies. Until now, parameters were mostly determined injection solutes or surrogates natural sediments. But suspended easier to analyse, less expensive better represent conditions. Therefore, tracer tests with sediments conservative solute dye conducted simultaneously active partly accessible cave system Vietnam during constant high-flow low-flow Breakthrough curves (BTCs) 10 different particle sizes classes ranging from 1 15 μm recorded situ at two main resurgences stream temporal resolution. This study gives new insights into processes highly dynamic exchange between mobile immobile regions. Major findings include: (1) conditions, inflow surrounding aquifer matrix velocity distribution inside conduits themselves lead hydrodynamic focusing, mainly affecting particles; (2) advective, preferential centre results narrow BTC. The more dispersive longer tailing; (3) conditions homogeneous indicates reversal conduit-matrix interaction; (4) comparing hydraulic activation additional flow paths increasing discharge could be identified. also presents first test field resulting pronounced double peaks particulate but only single, right-skewed BTC injected solute, including conceptual model transport.