The combined effects of water level reduction and an increase in ammonia concentration on organic matter processing by key freshwater shredders in alluvial wetlands
Résumé
In a global change context, the intensity and the frequency of drastic low flow periods or drought events will most likely increase to a substantial extent over the coming decades, leading to a modification in the abiotic characteristics of wetlands. This change in environmental parameters may induce severe shifts in plant and animal communities and the functioning of ecosystems. In this study, we experimentally estimated the effect of drought and the accumu- lation of ammonia (NH3) on the feeding activities of three generalist macroinvertebrates (i.e. Gammarus pulex, Gamma- rus roeselii and Asellus aquaticus) on three types of organic matter: leaves of Berula erecta growing in submerged conditions, leaves of the same species growing in emerged conditions and dead leaves of Alnus glutinosa. We observed a modification in the biomechanical and stoichiometric characteristics of the plants as a result of the emer- sion of the aquatic plants. This shift produced a substantial decrease in organic matter recycling by invertebrates and in their associated physiological ability (i.e. the energy stores of the animals) to face conditions associated with envi- ronmental change. Moreover, the accumulation of NH3 amplified the negative effect of emersion. This snowball effect on invertebrates may profoundly modify the functioning of ecosystems, particularly in terms of organic matter pro- duction/degradation and carbon mineralization.