Freshwater suspended particulate matter (SPM) plays an important role in many biogeochemical cycles and serves multiple ecosystem functions. Most SPM is present as complex floc-like aggregate structures composed of various minerals and organic matter from the molecular to the organism level. Flocs provide habitat for microbes and feed for larger organisms. They constitute microbial bioreactors, with prominent roles in carbon and inorganic nutrient cycles, and transport nutrients as well as pollutants, affecting sediments, inundation zones, and the ocean. Composition, structure, size and concentration of SPM flocs are subject to high spatiotemporal variability. Floc formation processes and compositional or morphological dynamics can be established around three crucial components: phyllosilicates, iron oxides/(oxy)hydroxides (FeOx) and microbial extracellular polymeric substances (EPS). These components and their interactions increase heterogeneity in surface properties, enhancing flocculation. Phyllosilicates exhibit intrinsic heterogeneities in surface charge and hydrophobicity. They are preferential substrates for precipitation or attachment of reactive FeOx. FeOx form patchy coatings on minerals, especially phyllosilicates, which increase surface charge heterogeneities. Both, phyllosilicates and FeOx strongly adsorb natural organic matter (NOM), preferentially certain EPS. EPS comprise various substances with heterogeneous properties that make them a sticky mixture enhancing flocculation. Microbial metabolism, and thus EPS release, is supported by the high adsorption capacity and favorable nutrient composition of phyllosilicates and FeOx supply essential Fe.
<p>Nano-scale volcanic ash particles (nanotephra) are produced during explosive volcanic eruptions. They can travel laterally above the tropopause for thousands of kilometers before returning to Earth&#8217;s surface. Within a short time, they will aggregate, settle, and end up in sedimentary sinks, such as lakes and oceans, and might be used as a tephrochronological age marker. These ultra-distal tephra deposits can be highly diluted by geogenic or biogenic background sedimentation. Consequently, the identification of nanotephra in these environmental archives poses an immense analytical challenge. A new generation of time-of-flight mass spectrometers (TOF-MS) can deliver particle specific multi-element information providing the analytical prerequisite to tease out a signal of trace amounts of nanotephra among a majority of background nanoparticles.</p><p>Here, we present the first single-particle geochemical data of Eyjafjallaj&#246;kull nanotephra, Iceland. The sub-micron particles were separated from bulk reference ash collected close to the eruption site and measured in a single-particle inductively coupled plasma TOF-MS. We tested their identification based on trace element heterogeneities in a mixture of tephra and sediment from Millst&#228;tter Lake, Austria, serving as a model archive deposition. We are developing this method to identify the source eruption of nanotephra deposited in lake sediment and thereby allow for better dating of the corresponding layer.</p>
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