How Toxicants Influence Organic Matter Decomposition in Streams

The ecosystem process of organic matter decomposition (OMD) in fresh waters is realised by a complex interaction among different groups of microorganisms (including bacteria and fungi) and detritivorous animals. As a consequence of this multi-level interaction, biotic (e.g., competition, predation) and abiotic (e.g., flow, temperature, toxicants) factors may influence the performance of either (micro)organism group with potential feedback to detritivores, and in turn OMD. In this chapter, we discuss how the abiotic factor toxicants affects OMD. We organised the chapter along a conceptual model that pinpoints groups of organisms and their interactions, which are critical for OMD. We focus on four toxicant classes (i.e., fungicides, antibiotics, insecticides and metals) that specifically affect fungi, bacteria or detritivorous invertebrates or have a broad activity spectrum. We summarize the effects caused by these toxicant classes on relevant groups of organisms, which are often determined by the toxicant mode of action. On this basis, we develop effect pathways leading to alterations in OMD dynamics. Finally, we discuss whether and how these effect pathways may support the interpretation of effect patterns observed under (semi-)field conditions and highlight research gaps we suggest addressing in order to improve understanding and prediction power.