Interaction between local hydrodynamics and algal community in epilithic biofilm

Abstract

Interactions between epilithic biofilm and local hydrodynamics were investigated in an experimental flume. Epilithic biofilm from a natural river was grown over a 41-day period in three sections with different flow velocities (0.10, 0.25 and 0.40 m s(-1) noted LV, IV and HV respectively). Friction velocities u* and boundary layer parameters were inferred from PIV measurement in the three sections and related to the biofilm structure. The results show that there were no significant differences in Dry Mass and Ash-Free Dry Mass (g m(-2)) at the end of experiment, but velocity is a selective factor in algal composition and the biofilms' morphology differed according to differences in water velocity. A hierarchical agglomerative cluster analysis (Bray-Curtis distances) and an Indicator Species Analysis (IndVal) showed that the indicator taxa were Fragilaria capucina var. mesolepta in the low-velocity (u*. = 0.010-0.012 m s(-1)), Navicula atomus, Navicula capitatoradiata and Nitzschia frustulum in the intermediate-velocity (u*. = 0.023-0.030 m s(-1)) and Amphora pediculus, Cymbella proxima, Fragilaria capucina var. vaucheriae and Surirella angusta in the high-velocity (u*. = 0.033-0.050 m s(-1)) sections. A sloughing test was performed on 40-day-old biofilms in order to study the resistance of epilithic biofilms to higher hydrodynamic regimes. The results showed an inverse relationship between the proportion of detached biomass and the average value of friction velocity during growth. Therefore, water velocity during epilithic biofilm growth conditioned the structure and algal composition of biofilm, as well as its response (ability to resist) to higher shear stresses. This result should be considered in modelling epilithic biofilm dynamics in streams subject to a variable hydrodynamics regime.

Seasonal biostabilization and erosion behavior of fluvial biofilms under different hydrodynamic and light conditions

“…In laboratory studies Stoodley et al (1999) found that in laminar flow the colonization rate was higher than under turbulent conditions (and obviously higher than the detachment), resulting in an earlier development of biofilm. Similar results for a delayed colonization were obtained recently by Graba et al (2013). They reported higher detachment rates in the early stages of biofilm formation induced by higher bed shear stress during cultivation.…”

Multi-scale temporal dynamics of epilithic algal assemblages: evidence from a Chinese subtropical mountain river network

“…and environmental factors (e.g., nutrients, irradiance, hydrodynamic regimes, predatory pressures, etc.) (Rosemond et al, 2000;Soininen & Eloranta, 2004;Yang et al, 2009;Graba et al, 2013). Algal short-term dynamics usually involve two phases: the first, accrual phase, which is driven by immigration/colonization and exponential growth, and the second, loss phase, which is dominated by processes of death, emigration, sloughing, and grazing (Biggs, 1996).…”

Quantifying biostabilisation effects of biofilm-secreted and extracted extracellular polymeric substances (EPSs) on sandy substrate

“…Many studies have attempted to quantify biostabilisation in a variety of environments (Paterson, 1989;Dade et al, 1990;Amos et al, 1998;Tolhurst et al, 1999Tolhurst et al, , 2003Friend et al, 2003a;Droppo et al, 2007;Righetti and Lucarelli, 2007;Vignaga et al, 2012;Graba et al, 2013;Thom et al, 2015). These studies generally show a positive correlation between EPS content and sediment stability measured as the threshold for erosion, although variations in space and time (Friend et al, 2003b;Thom et al, 2015) and between cohesive and noncohesive sandy environments are large.…”