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Radio frequency identification (RFID) technologies, which allow wireless detection of individual buried or immersed tracers, represent a step forward in sediment tracking, especially passive integrated transponders (PIT tags) that have been widely used. Despite their widespread adoption in the scientific community, they typically have low efficiency when deployed in river systems with active bedload transport or deep wet channels, attributed to their technical specifications. A recent evaluation of active ultra‐high frequency transponders (a‐UHF tags) assessed their larger detection range and provided a methodology for their geopositioning. In this study, we test five different survey methods (one including an unmanned aerial vehicle [UAV]) in a sediment tracking study, and compare them in terms of recovery rate, field effort, geopositioning error, and efficiency. We then tested the method on a larger reach following a Q5 flood and performed cross‐comparisons between active and passive RFIDs. The results confirmed that the a‐UHF RFID technology allowed rapid (1.5 h ha−1) survey of a large area (<34 ha) of emerged bars and shallow water channels with recovery of a high percentage of tracers (72%) that had travelled large distances (mean ≈ 1000 m; max ≈ 3400 m). Moreover, the tracers were identified with low geopositioning error (mean ≈ 7.1 m, ≤1% of their travel distance). We also showed that a UAV‐based survey was fast (0.38 h ha−1), efficient (recovery rate = 84%), and low error (mean ≈ 4.2 m). Thus, a‐UHF RFID technology permits the development of a variety of survey methods, depending on the study objectives and the human and financial resources available. This allows field efforts to be optimized by determining an appropriate balance between the high equipment cost of a‐UHF tracers and the resulting reduced survey costs. © 2019 John Wiley & Sons, Ltd.

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Faecal indicator bacteria (FIB) and bacterial pathogens from combined sewer overflow (CSO) in peri-urban streams represent a major public health concern worldwide. In this study, the relationships between the hydrological regime and the loads and persistence of CSO-borne bacterial contaminants among benthic sediments of a small peri-urban stream were explored. Combined sewer overflow events and their impact on benthic sediment layers at a short distance from a CSO were monitored. Concentrations of Escherichia coli (EC) and intestinal enterococci (IE) and of two bacterial pathogens, Pseudomonas aeruginosa (PA) and Aeromonas caviae (AC), were assessed.Relations with hydraulic, hydromorphic and physicochemical factors were analysed.PA cells in benthic sediments increased exponentially with time (0.15 log PA per day), as long as the river discharge remained below the sediment transport. Cycles of erosive floods and low-flow periods were found to play a critical role in PA settling and growth among benthic riverbed sediments. These hydrological and hydraulic shear forces did not correlate with changing IE, EC, and AC concentrations in the benthic sediments. Their dynamics were rather related to changing physicochemical conditions (total N, phosphate, and organic carbon). AC population size decreases most rapidly with a mean rate of 0.04 log per day according to the duration of the low-flow period, indicating a poor tropism of AC for river systems. River sediments were found significant biotopes for PA outdoor development. These analyses demonstrate the significance of PA and AC as long-and short-term indicators, respectively, of a river microbiological quality. K E Y W O R D SAeromonas caviae, bacterial pathogen, faecal indicator bacteria, Pseudomonas aeruginosa, sediment transport

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