Benthic biofilm controls on fine particle dynamics in streams

Abstract

Benthic (streambed) biofilms metabolize a substantial fraction of particulate organic matter and nutrient inputs to streams. These microbial communities comprise a significant proportion of overall biomass in headwater streams, and they present a primary control on the transformation and export of labile organic carbon. Biofilm growth has been linked to enhanced fine particle deposition and retention, a feedback that confers a distinct advantage for the acquisition and utilization of energy sources. We quantified the influence of biofilm structure on fine particle deposition and resuspension in experimental stream mesocosms. Biofilms were grown in identical 3 m recirculating flumes over periods of 18–47 days to obtain a range of biofilm characteristics. Fluorescent, 8 µm particles were introduced to each flume, and their concentrations in the water column were monitored over a 30 min period. We measured particle concentrations using a flow cytometer and mesoscale (10 µm to 1 cm) biofilm structure using optical coherence tomography. Particle deposition‐resuspension dynamics were determined by fitting results to a stochastic mobile‐immobile model, which showed that retention timescales for particles within the biofilm‐covered streambeds followed a power‐law residence time distribution. Particle retention times increased with biofilm areal coverage, biofilm roughness, and mean biofilm height. Our findings suggest that biofilm structural parameters are key predictors of particle retention in streams and rivers.

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

“…Biofilms grow throughout the stream, including within hyporheic sediments, and have been shown to biostabilize sediments and inhibit remobilization during high flows [ Vignaga et al ., ]. Biofilms at the sediment‐water interface may reduce the hydraulic conductivity [ Battin et al ., , 2016; Roche et al ., ], but our results demonstrate that they also capture fine particles that would otherwise deposit within hyporheic sediment and contribute to clogging.…”

Fine particle transport dynamics in response to wood additions in a small agricultural stream

“…Specifically, it is unknown if the balance between fine particle immobilization and remobilization processes will lead to an overall increase in retention, or less retention due to the possibility of a higher likelihood of remobilization. The altered hydrological processes in streams with added wood may also enhance the deposition of fine particles into sediments and onto biofilms on cobbles, previously shown to be important transient storage areas for fine particles that extend particle residence times for months to years, altering the exchange of oxygen, carbon, and nutrients into the sediments (Drummond et al, 2015;Drummond, Larsen, González-Pinzón, Packman, & Harvey, 2017;Roche et al, 2017). Fine particle immobilization is expected to increase in streams with added wood and differ based on orientation of the wood in the stream.…”

Deposition of Suspended Clay to Open and Sand‐Filled Framework Gravel Beds in a Laboratory Flume

“…While a standard method to account for the loss of suspended clay to natural river beds farther up in the fluvial system does not exist, there have been studies conducted in both the laboratory and field that have shown that very fine organic and inorganic sediment, and even bacteria, can be detained within the bed under certain conditions. One mechanism for the delivery and retention of fine particulates within sand‐bed rivers is that of hyporheic exchange setup by the presence of bed forms (Drummond et al, ; Newbold et al, ; Packman & Brooks, ; Packman et al, ; Rehg et al, ; Roche et al, ) and the straining or filtering of the particulates within the bed (Fries & Taghon, ; Packman et al, ; Royal et al, ). More recently, studies have also shown that fine sediment can be captured within biofilms that coat the bed surface (Drummond et al, ; Roche et al, ).…”

“…One mechanism for the delivery and retention of fine particulates within sand‐bed rivers is that of hyporheic exchange setup by the presence of bed forms (Drummond et al, ; Newbold et al, ; Packman & Brooks, ; Packman et al, ; Rehg et al, ; Roche et al, ) and the straining or filtering of the particulates within the bed (Fries & Taghon, ; Packman et al, ; Royal et al, ). More recently, studies have also shown that fine sediment can be captured within biofilms that coat the bed surface (Drummond et al, ; Roche et al, ). One interesting observation that has come from studies of deposition of fine sediment to sand beds is that the effective flux of suspended sediment to the bed can be enhanced over that predicted by the product of the still‐water settling velocity and local concentration due to sediment being filtered in the bed (Fries & Taghon, ; Fries & Trowbridge, ; Royal et al, ).…”