Supplemental Data Files for "Benthic Biofilm Controls on Fine Particle Dynamics in Streams". Water Resources Research

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-mm particles were introduced to each flume, and their concentrations in
the water column were monitored over a 30-minute 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 retention timescales for particles within the
biofilm-covered streambeds followed a power-law residence time distribution. Particle
retention timescales 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.