Microbial Transport, Retention, and Inactivation in Streams: A Combined Experimental and Stochastic Modeling Approach

Abstract

Long-term survival of pathogenic microorganisms in streams enables long-distance disease transmission. In order to manage water-borne diseases more effectively we need to better predict how microbes behave in freshwater systems, particularly how they are transported downstream in rivers. Microbes continuously immobilize and resuspend during downstream transport owing to a variety of processes including gravitational settling, attachment to in-stream structures such as submerged macrophytes, and hyporheic exchange and filtration within underlying sediments. We developed a stochastic model to describe these microbial transport and retention processes in rivers that also accounts for microbial inactivation. We used the model to assess the transport, retention, and inactivation of Escherichia coli in a small stream and the underlying streambed sediments as measured from multitracer injection experiments. The results demonstrate that the combination of laboratory experiments on sediment cores, stream reach-scale tracer experiments, and multiscale stochastic modeling improves assessment of microbial transport in streams. This study (1) demonstrates new observations of microbial dynamics in streams with improved data quality than prior studies, (2) advances a stochastic modeling framework to include microbial inactivation processes that we observed to be important in these streams, and (3) synthesizes new and existing data to evaluate seasonal dynamics.

Modelling the transport of environmental DNA through a porous substrate using continuous flow-through column experiments

“…Additionally, other size fractions, likely larger particles, appear to get caught in the porous medium or on biofilm, either permanently or at least over the timescales of our current experiments with less mass breaking through the system than being injected into it, although the fraction of mass retained varied significantly from experiment to experiment with no clear and identifiable control on what drove this behaviour. Similar results have been shown in sand-packed columns for monodisperse particles such as Cryptosporidium oocysts [48] and for E. coli [49]; however, eDNA that is shed from macroorganisms is a particle with a wider range of sizes and sources than noted in the microbial transport literature [29,30]. In another context, organic particles have been shown to slowly release after initial deposition [49,50]; for the case of NOM, which is also polysdisperse, but more homogeneous than eDNA, different size fractions are adsorbed and released at different rates [45] leading to a broad distribution of travel times and models that reflect these broad distributions appear capable of describing their anomalous behaviour [46,47].…”

Less Fine Particle Retention in a Restored Versus Unrestored Urban Stream: Balance Between Hyporheic Exchange, Resuspension, and Immobilization

“…However, the low particle retention rates within the restored stream indicate low potential for clogging of interstitial pores. These results support previous observations showing that processes such as filtration initially immobilize particles within the streambed, but other processes such as scour and fill resuspend accumulated fine particle deposits and drive particle deposition deeper in the bed (Drummond et al, ; Gartner et al, ; Rehg et al, ). Thus, the long‐term maximum depth of fine particle infiltration is ultimately limited by a combination of particle infiltration in the bed, deposition within the bed, and the depth to which scour remobilizes sediment and restores the permeability and porosity of the bed.…”

“…For the same reason, we assume that delivery of fine particles to transient storage areas is controlled purely by advective exchange and that gravitational settling is negligible. In this case, hyporheic exchange of solute and fine particles is also similar, and Λ S ≈ Λ P. Based on prior investigations of solute and fine particle dynamics in rivers (Boano et al, ; Drummond, Davies‐Colley, et al, ; Drummond et al, ; Haggerty et al, ; Stonedahl et al, ), we assume a power law residence time distribution within the immobile region, φ S ( t ) ~ for 0 < β S < 1.…”

Fine particle retention within stream storage areas at base flow and in response to a storm event

“…A more detailed description of the model, previously applied to solute and fine particle transport in rivers in Drummond et al . [; ] without any modifications, is included in the supporting information [ Cortis and Berkowitz , ; Boano et al ., ]. Here we provide a brief review of the key equation and parameters.…”