Formation of macroscopic organic aggregates (lake snow) in a large lake: The significance of transparent exopolymer particles, plankton, and zooplankton

Abstract

Macroscopic organic aggregates (lake snow) were collected and their abundance quantified by scuba divers at a distinct pelagic site in Lake Constance (Germany) at least twice a week throughout the growing season in 1993. Furthermore, concentrations of transparent exopolymer particles (TEP), chlorophyll, particulate organic carbon (POC), and the species composition of phytoplankton and zooplankton in the ambient water were determined. In addition, the formation of aggregates was studied in laboratory experiments by incubating water samples in rolling tanks. The abundance and composition of aggregates showed a pronounced seasonal and vertical pattern in close relation to phytoplankton and zooplankton dynamics and wind conditions. Numbers of aggregates ranged between <l and 50 liter-', with maximum concentrations at 6 m depth in summer and fall. In spring, the peak of TEP concentration occurred simultaneously with that of lake snow, whereas the peaks in summer and fall followed those of aggregate abundance. More detailed analyses indicated that the role of TEP in aggregate formation varies throughout the season. The laboratory experiments revealed an inverse correlation between time of aggregate formation and the concentration of POC. Two different correlations, one for the spring bloom and one for the rest of the year, were established. The results show that multiple mechanisms of aggregate formation occurred throughout the seasons due to variations in source particles and physical conditions.

The utiquity and many roles of exopolymers (EPS) in aquatic systems

“…As would be expected, these flocs are also found in lakes and rivers and are referred to as "lake snow" and "river snow" respectively (Grossart et al, 1997;Neu, 2000). Flocs are moved by currents and thus collect other materials and organisms by impaction.…”

Changes in abundance and community structure of bacteria associated with buoyantMicrocystiscolonies during the decline of cyanobacterial bloom (autumn–winter transition)

“…A possible explanation for the appearance of these distinct bacteria is the release of different extracellular compounds from the phytoplankton cell during the period of the bloom decline. For example, transparent exopolymer particles (TEP), composed of extracellular polysaccharide, dead algal cells and so on, are frequently formed during the decline of diatom and cyanobacterial bloom (Schuster and Herndl, 1995;Grossart and Simon, 1997), and many TEP are considered as excellent substrates for bacteria (Berman and VinerMozzini, 2001). However, the extracellular compounds from buoyant Microcystis cells during the bloom decline period are not very clear and need to be studied in the future.…”

Abundance and size distribution of transparent exopolymer particles (TEP) in a coccolithophorid bloom in the northern Bay of Biscay

“…Transparent exopolymer particles (TEP) merge the two properties of (1) being retained onto 0.4 mm membrane filters and (2) being stainable by Alcian Blue, a specific dye for acidic (-COO À ) or sulphated (-O-SO 3 À ) reactive groups of carbohydrates (Alldredge et al, 1993). Several studies indicate that TEP are natural constituents of the bulk particulate matter in marine (Passow and Alldredge, 1995b;Mari and Kiorboe, 1996;Krembs and Engel, 2001;Garcia et al, 2002;Engel, 2004;Brussaard et al, 2005;Radic et al, 2005;Shackelford and Cowen, 2006;Prieto et al, 2006;Sugimoto et al, 2007) (Logan et al, 1995;Grossart et al, 1997;Berman and Viner-Mozzini, 2001;Arruda-Fatibello et al, 2004) ecosystems. Most of the field sites where TEP have been described so far were dominated by diatoms, dinoflagellates or cyanobacteria.…”