RESEARCH ARTICLE Invertebrates control metal/metalloid sequestration and the quality of DOC/DON released during litter decay in slightly acidic environments Jörg Schaller & Susanne Machill Received: 5 December 2011 / Accepted: 8 May 2012 / Published online: 29 May 2012 # Springer-Verlag 2012 Abstract Plant litter and organic sediments are a main sink for metals and metalloids in aquatic ecosystems. The effect of invertebrate shredder (a key species in litter decay) on metal/metalloid fixation by organic matter is described only under alkaline water conditions whereas for slightly acidic waters nothing can be found. Furthermore, less is known about the effect of invertebrate shredders on the quality of dissolved organic carbon (DOC) and nitrogen (DON) re- leased during litter decay. We conducted an experiment to investigate the impact of invertebrate shredder (Gammarus pulex) on metal/metalloid fixation/remobilization and on the quality of DOC/DON released under slightly acidic water conditions. During decomposition of leaf litter, invertebrate shredder facilitated significantly the emergence of smaller particle sizes of organic matter. The capacity of metal fixa- tion was significantly higher in smaller particles (POM 2,000–63 μm) compared to original leaf litter and litter residues. Thus, G. pulex enhanced metal fixation by organic partition of sediments by increasing the amount of smaller particle of organic matter in aquatic ecosystems. In contrast, the capacity of metal/metalloid fixation in the smallest frac- tion of POM (<63 μm) was lower compared with leaf residues in treatment without invertebrates. Remobilization of metals and metalloids was very low for all measured elements. A significant effect of invertebrates on quantita- tive formation of DOC/DON was confirmed. The quality of released DOC/DON, which may affect metal/metalloid re- mobilization, was also significantly affected by invertebrate shredders (e.g., more carboxylates). Hence, invertebrate shredder enhanced significantly the fixation of metals/met- alloids into POM in slightly acidic environments. Keywords Adsorption . Carbon quality . Ecosystem processes . FT-IR . Metalloids Introduction High concentrations of metals, metalloids and radionuclides are of global concern in freshwater ecosystems and environ- mental health where concentration levels are mainly affected by element release from ores and contaminated soils (Baborowski and Bozau 2006; Dinelli et al. 2001). Metals and metalloids dissolve at low pH (predominantly as cati- ons), low Eh and within a neutral to alkaline aerobic milieu (e.g., as carbonate complexes) (Burton et al. 2008). They readily form organic complexes with humic and fulvic acids as part of dissolved organic carbon (DOC) (Zhao et al. 2009), are fixed to colloids, and consequently remain mo- bile. The dissolved elements may also adsorb on organic and inorganic compounds in the water body, for instance, inor- ganic particles and leaf litter, which settle forming water sediment (Dienemann et al. 2006; Karbassi et al. 2008). Small streams as allochthonous ecosystems depend on ex- ternal input of energy by organic matter entry including leaf litter. During the first step of litter decomposition (e.g., in small streams), DOC emerges (Wallace et al. 2008) with microorganisms (e.g., hyphomycetes and bacteria) being the Responsible editor: Elena Maestri J. Schaller (*) Institute of General Ecology and Environmental Protection, Technische Universität Dresden, PF 1117, 01737 Tharandt, Germany e-mail: Schaller@forst.tu-dresden.de S. Machill Bioanalytical Chemistry, Technische Universität Dresden, Bergstrasse 66, 01069 Dresden, Germany Environ Sci Pollut Res (2012) 19:3942–3949 DOI 10.1007/s11356-012-0975-0