Invertebrate shredder as a factor controlling the fixation potential for metals/metalloids in organic matter during decay

Wetlands are well known for water treatment and as a sink for elements (e.g. metals/metalloids). The elements are mainly fixed by sediments, microbial biofilms and plants, whereas the organic part of the sediment has a potential important role. These organic sediments underlie the process of organic matter decomposition, which proceeds in the three distinct steps of leaching, microbial conditioning and fragmentation by aquatic fauna. The effect of organic matter fragmentation on elemental fixation was shown previously only under neutral pH conditions. Hence, a batch experiment was conducted to assess the effect of invertebrate shredder on elemental accumulation during litter decay under low acidic conditions. Here it is shown that this fragmentation of the organic material by aquatic fauna enhances the elemental fixation potential of the organic sediments significantly, also under low acidic conditions. During the process of fragmentation the surface area of the organic matter increases by increasing amount of smaller particles. This in turn results in higher adsorption capacity of a larger amount of growing biofilm enhancing the surface even more (heterotrophic microorganisms). The growing biofilm (periphyton) with its larger surface area and hence more functional groups result in higher elemental fixation. Therefore, invertebrate shredders as ecosystem engineers enhance the capability for elemental fixation by fragmentation of organic matter, which is an important process in wetlands ecosystems usable in a broad pH range.

► Aquatic fauna controls the fixation potential for elements in organic sediments.
► The aquatic fauna increases the formation of smaller particles of organic matter.
► The activity of aquatic fauna has only low effects on elemental mobilization.