Using a mathematical model to simulate the influence of tubificid worms (Oligochaeta) on oxygen concentrations in hyporheic sediments

Abstract

The aim of the study was to present a model to simulate the infl uence of tubifi cid worms (Limnodrilus sp. and Tubifex sp.) on O2 concentrations in hyporheic sediments. A mathematical model was developed to reproduce vertical distribution of O2 in experimental columns of sediments. Vertical columns were simulated as grids with cells of 1-cm depth each. The model took into account the hydrodynamic properties, the microbial respiration and distribution, the stimulation effect of tubifi cids on microbial activity, and the vertical distribution of worms in the system. Parameters of the mathematical model were determined to fit experimental oxygen concentrations obtained during two experiments: one experiment testing the infl uence of 100 Tubifex sp. (mainly Tubifex tubifex) and one experiment testing the effect of 100 Limnodrilus sp. (80 % Limnodrilus hoffmeisteri). The spatial model gave an adequate assessment of the vertical profi les of O2 concentrations in columns with and without tubifi cid worms. The parameters used to fi t simulations with experimental data supposed that Limnodrilus burrowed deeper and produced a higher stimulation of microbial respiration than Tubifex in our experimental system. Such results are in accordance with literature data and clearly suggest that this spatial model could be easily used to characterize the effects of animals (modifi cation rate of the microbial respirations by animals and location of the animal effect) on biogeochemical processes in hyporheic sediments