Identification of a minimal adequate model to describe the biomass dynamics of river epilithon

Abstract

The present study sought to identify a minimal adequate model to describe the biomass dynamics of river epilithon, a functional indicator of river health. Identification of minimal adequate models is particularly necessary in river management, given the reduced number of variables authorities are willing to measure routinely. A model previously developed for epilithon dynamics in a pre-alpine river was applied to epilithon biomasses recorded in contrasting hydrological, trophic and light conditions at various sites in the Agüera stream (Spain) over 3 years (11 case studies). A model selection tool, the Akaike Information Criterion (AIC), was used to determine the optimal combination of parameters. In nine of 11 case studies, the best model described epilithon biomass dynamics as the equilibrium between phototrophic growth and discharge-dependent loss and ignored light, temperature and nutrient influences. The best adequate minimal model i.e. the model that is the best trade-off between goodness-of-fit and model simplicity performed best, in years in which clearly contrasting short low and high water periods occurred. During years with less marked hydrodynamics, many other abiotic or biotic processes influenced epilithon biomass dynamics. In these cases, weaker goodness-of-fit had to be accepted to avoid excessively increasing model complexity. RESULTSResults of AIC statistics for each sub-model at every study site are listed in Table III. The set of candidate sub-models (R) varied between years: in 2001 R was 7; in 1990 R was 6 because discharge was always lower than critical and subsequently k cat was never activated; and in 1992 R was 5, as phosphate and temperature data were not available and thus k P and b were not activated. One single sub-model was clearly the best of all: in 7 of 11 study 46 S. BOULÊ TREAU ET AL. i < 2 and to an evidence ratio < 2.7 are in bold. The selected 'best' sub-model is italicized.

Viability of differentiated epilithic bacterial communities in the River Garonne (SW France)

“…The highest viable fractions (62.4%) were associated with intermediate discharges values between 48 and 80 m 3 s -1 , whereas for established low flow periods (DMF below 48 m 3 s -1 ) viable fractions were the lowest (41.9%), and for high flow periods (DMF above 80 m 3 s -1 ) viable fractions were intermediary (50.0%). A modelling approach demonstrated that hydrodynamics played a substantial role in biofilm biomass loss through a discharge-dependent detachment (Boulêtreau et al, 2008). This would indicate that following a disturbance and a biomass loss, biofilm bacterial communities tend to exhibit more important proportions of viable cells, likely active and growing (Werner et al, 2004), and involved in colonization processes.…”

Modeling the effect of tides and waves on benthic biofilms

“…Here we apply a model that was initially proposed for riverine peryphyton [ Uehlinger et al , 1996], and recently modified and tested in the field and in laboratory experiments, using different types of sediment substrate [ Labiod et al , 2007; Boulêtreau et al , 2006, 2008, 2010]. The model describes the evolution of the biofilm biomass X , measured as mg Chl‐a/m 2 : Term 1a is the biofilm growth according to a logistic law, where μ max is the maximum growth rate, and K s is the half‐saturation constant.…”

Temporal Dynamics of River Biofilm in Constant Flows: A Case Study in a Riverside Laboratory Flume

“…Models applied to long time-series suggested that, in natural conditions, epilithic biomass dynamics can roughly be considered as the result of equilibrium between phototrophic growth and discharge-dependant loss (UEHLINGER et al, 1996;BOULÊTREAU et al, 2006;BOULÊTREAU et al, 2008). Models that account for epilithic detachment only considered the effect of fluid forces, using current velocity or discharge as variables (HORNER et al, 1983;MOMO, 1995;UEHLINGER et al, 1996;SARAVIA et al, 1998).…”