Invertebrate grazers affect metal/metalloid fixation during litter decomposition Jörg Schaller ⇑ , Carsten Brackhage Institute of General Ecology and Environmental Protection, Technische Universität Dresden, D-01062 Dresden, Germany highlights  Invertebrate grazer enhance the fixation of most elements into organic sediments.  Invertebrate grazers enhance the mobilization of DOC and nitrogen.  Higher trophic level control elemental fixation/remobilization. article info Article history: Received 23 October 2013 Received in revised form 2 July 2014 Accepted 3 July 2014 Handling Editor: J. de Boer Keywords: Arsenic Carbon turnover Higher trophic levels Organic sediments Pollution Sorption abstract Plant litter and organic sediments are main sinks for metals and metalloids in aquatic ecosystems. The effect of invertebrates as key species in aquatic litter decomposition on metal/metalloid fixation by organic matter is described only for shredders, but for grazers as another important animal group less is known. Consequently, a laboratory batch experiment was conducted to examine the effect of inverte- brate grazers (Lymnaea stagnalis L.) on metal/metalloid fixation/remobilization during aquatic litter decomposition. It could be shown that invertebrate grazers facilitate significantly the formation of smal- ler sizes of particulate organic matter (POM), as shown previously for invertebrate shredders. The metal/ metalloid binding capacity of these smaller particles of POM is higher compared to leaf litter residuals. But element enrichment is not as high as shown previously for the effect by invertebrate shredders. Invertebrate grazers enhance also the mobilization of selected elements to the water, in the range also proven for invertebrate shredders but different for the different elements. Nonetheless invertebrate graz- ers activity during aquatic litter decomposition leads to a metal/metalloid fixation into leaf litter as part of sediment organic matter. Hence, the effect of invertebrate grazers on metal/metalloid fixation/remo- bilization contrasts partly with former assessments revealing the possibility of an enhanced metal/ metalloid fixation. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Enhanced concentrations of metals/metalloids in freshwater and aquatic sediments are a global problem for several types of freshwater ecosystems (Kouba et al., 2010; Schaller et al., 2013). This results in an enhanced environmental risk for associated eco- systems and organisms especially with concentrations of metals/ metalloids becoming toxic to many species and thereby affecting many processes within these ecosystems (Nriagu and Pacyna, 1988). The metals/metalloids are transported by running water as cations, inorganic complexes and/or organic complexes of humic/fulvic acids as part of dissolved organic carbon (DOC) (Christensen et al., 1999; Alberic et al., 2000). Some part of metals is also transported in association with suspended particles. Ele- ment complexes may themselves adsorb on organic and inorganic particles, leading to a deposit in sediments (Sridhar et al., 2008), particularly in slowly flowing or standing water, like wetlands, pools in streams and lakes. Leaf litter but also other plant litter is the most important energy source in e.g. littoral zones, wetlands or the krenal (spring region) and rhitral (stream) region of running water ecosystems being allochthonous systems. Leaf litter, settled on the bottom of the water body, will eventually be decomposed. Leaf litter decom- position proceeds in three distinct temporal stages of leaching, conditioning and fragmentation (Gessner et al., 1999). During pri- mary decomposition by microorganisms, DOC emerges from the litter and microorganisms and their exudates form a heterotrophic http://dx.doi.org/10.1016/j.chemosphere.2014.07.002 0045-6535/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +49 351 463 31375; fax: +49 351 463 31399. E-mail address: schaller@forst.tu-dresden.de (J. Schaller). Chemosphere 119 (2015) 394–399 Contents lists available at ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere