Biofouling, metal sorption and aggregation are related to sinking of microplastics in a stratified reservoir

Authors

Rico Leiser, Gi-Mick Wu, Thomas R. Neu, Katrin Wendt-Potthoff

Microplastic particles entering aquatic systems are rapidly colonized by microbial biofilms. The presence of microbial biomass may cause sinking of particles and as a consequence prevent their transport to the oceans. We studied microbial colonization of different polymer particles exposed in the epi-, meta- and hypolimnion of a freshwater reservoir during late summer for 47 days. Parameters measured included biofilm formation, metal sorption and sinking velocities. Microbial biofilms contained bacteria, cyanobacteria and algae as well as inorganic particles such as iron oxides. Regardless of biofilm thickness and biovolumes of different biofilm constituents, single polyethylene (PE) particles stayed buoyant, whereas the sinking velocity of single polystyrene (PS) and polyethylene terephthalate (PET) particles did not change significantly compared to initial values. During exposition, a mixing event occurred, by which anoxic, iron-rich water from the hypolimnion was mixed with water from upper layers. This induced aggregation and sinking of hypolimnetic PE particles together with organic matter, cyanobacteria colonies and iron minerals.

Diurnal variations in sulfur transformations at the chemocline of a stratified freshwater lake

Authors

Khoren Avetisyan,Werner Eckert, Alyssa J. Findlay, Alexey Kamyshny Jr.

In order to characterize biogeochemical sulfur cycling in the metalimnion of a thermally stratified freshwater lake, we followed changes in the concentrations and isotopic composition of sulfur species during a 24-h period, during which the chemocline oscillated at an amplitude of 5.3 m due to internal wave activity. Hourly sampling at a fixed depth (17.1 m) enabled study of redox changes during the transition from oxic to sulfidic conditions and vice versa. The oxidation–reduction potential, pH, conductivity and turbidity correlated linearly with the water temperature (a proxy for depth relative to the chemocline). The highest concentrations of thiosulfate and sulfite were detected approximately 2.5 m below the chemocline. Concentrations of zero-valent sulfur increased ~ 10 fold when the chemocline rose into the photic zone due to phototrophic sulfide oxidation. Triple isotopic composition of sulfur species indicates a shift with depth from values typical for sulfate reduction right below the chemocline to values which may be explained by either sulfate reduction alone or by a combination of microbial sulfate reduction and microbial sulfate disproportionation. We conclude that consumption of hydrogen sulfide at the chemocline of Lake Kinneret is controlled by the combination of its chemical and/or chemotrophic oxidation to sulfur oxoanions and predominantly phototrophic oxidation to zero-valent sulfur.

Variation in phytoplankton pigment composition in relation to mixing conditions in temperate South-Central Chilean lake

Authors

Evelien Van de Vyver, Jeroen Van Wichelen, Pieter Vanormelingen, Wim Vannieuwenhuyze, Ilse Daveloose, Rixtde Jong, Reinhoudde Blok, Roberto Urrutia, Bjorn Tytgat, Elie Verleyen, Wim Vyverman

Thermal lake properties are sensitive to changes in windiness and precipitation, and affect the physical and chemical properties of the water column, which in turn control phytoplankton dynamics and primary production. We assessed the use of phytoplankton pigment profiling as a potential indicator of stratification conditions in temperate lakes in South-Central Chile. Spring and early summer phytoplankton pigment profiles and the physical and chemical limnology were analyzed in 43 lakes ranging in size, depth, altitude and catchment characteristics. Eleven lakes were sampled during both seasons. Variation in pigment composition between lakes was primarily related to stratification conditions and mixed layer light availability at the time of sampling. The dinoflagellate marker pigment peridinin was more abundant in more deeply mixed lakes with a lower mean irradiance, while chlorophyte pigments (chlorophyll b, lutein) tended to be higher in shallow (high-light) epilimnia. Diatom and chrysophyte pigments (fucoxanthin) dominated under less thermally stable and more variable light conditions. Cyanobacteria pigments (zeaxanthin), probably derived from picocyanobacteria, were relatively more abundant in very transparent, low productive lakes. Lakes in close vicinity of active volcanoes were enriched in silica and PO₄-P concentrations and characterised by elevated chlorophyte marker pigments. Within strongly stratified lakes, in which the euphotic zone extended in the hypolimnion, cryptophyte pigments (alloxanthin) characterized the deep chlorophyll maxima while the epilimnion was consistently enriched with the photoprotective xanthophyll-cycle pigment violaxanthin. We conclude that major algal groups, represented by pigment biomarkers, are largely driven by changes in lake water column stratification and related mixed layer light availability as well as nutrient concentrations in temperate Chilean freshwater lakes.

Impact of enhanced summer temperatures on the distribution and structure of zooplankton communities in the heated stratified lakes: implications for climate change

Authors

Vladimir I. Razlutskij, Irina Yu. Feniova, Jolanta Ejsmont-Karabin, Anna L. Palash, Jacek Tunowski, Elena Sysova, Natalia S. Zilitinkevich

Long-term studies demonstrated that temperature increases of 3-6 °C above natural levels caused reduction in zooplankton biomass. We hypothesized that large-bodied species would respond more strongly to temperature increases than small-bodied species because they are less adapted to high temperatures. Studies were conducted in three similar stratified meso-eutrophic lakes with different thermal regimes. Enhanced temperature, migrations, food abundance and dissolved oxygen concentrations were analyzed as potential factors that could affect zooplankton biomass. The warmest lake differed from the other lakes by lower total biomass of zooplankton less abundance of large-bodied zooplankton species, smaller population body sizes of abundant cladoceran species and higher food concentrations. Day and night abundances of zooplankton did not differ between the vertical strata and between the pelagic and littoral zones in the three study lakes suggesting that zooplankton did not vertical or horizontal migrations. We suggest that decreases of dissolved oxygen below the epilimnion prevented zooplankton from vertically migrating. As a result, zooplankton accumulated in the epilimnion where temperatures were higher than in the lower strata. Regression analysis showed that temperature had a significant negative impact on the total biomass of zooplankton in the epilimnion of the warmest study lake. Therefore, our results are in accordance with the ecological Bergmann’s and James’ rules dealing with the temperature-size relationships.

Seasonal Dynamics of Glyphosate and AMPA in Lake Greifensee: Rapid Microbial Degradation in the Epilimnion During Summer

Authors

Sebastian Huntscha, Michael A. Stravs, Andreas Bühlmann, Christian H. Ahrens, Jürg E. Frey, Francesco Pomati, Juliane Hollender, Ignaz J. Buerge, Marianne E. Balmer, and Thomas Poiger

Occurrence and fate of glyphosate, a widely used herbicide, and its main metabolite AMPA was investigated in Lake Greifensee, Switzerland. Monthly vertical concentration profiles in the lake showed an increase of glyphosate concentrations in the epilimnion from 15 ng/L in March to 145 ng/L in July, followed by a sharp decline to <5 ng/L in August. A similar pattern was observed for AMPA. Concentrations of glyphosate and AMPA in the two main tributaries generally were much higher than in the lake. Simulations using a numerical lake model indicated that a substantial amount of glyphosate and AMPA dissipated in the epilimnion, mainly in July and August, with half-lives of only ≈2–4 days which is ≫100 times faster than in the preceding months. Fast dissipation coincided with high water temperatures and phytoplankton densities, and low phosphate concentrations. This indicates that glyphosate might have been used as an alternative phosphorus source by bacterio- and phytoplankton. Metagenomic analysis of lake water revealed the presence of organisms known to be capable of degrading glyphosate and AMPA.

Spatio-temporal dynamics of sulfur bacteria during oxic–anoxic regime shifts in a seasonally stratified lake

Authors

Muhe Diao, Jef Huisman, Gerard Muyzer

Sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria drive major transformations in the sulfur cycle, and play vital roles in oxic–anoxic transitions in lakes and coastal waters. However, information on the succession of these sulfur bacteria in seasonally stratified lakes using molecular biological techniques is scarce. Here, we used 16S rRNA gene amplicon sequencing to study the spatio-temporal dynamics of sulfur bacteria during oxic–anoxic regime shifts in Lake Vechten. Oxygen and sulfate were mixed throughout the water column in winter and early spring. Meanwhile, SRB, green sulfur bacteria (GSB), purple sulfur bacteria (PSB), and colorless sulfur bacteria (CSB) exclusively inhabited the sediment. After the water column stratified, oxygen and nitrate concentrations decreased in the hypolimnion and various SRB species expanded into the anoxic hypolimnion. Consequently, sulfate was reduced to sulfide, stimulating the growth of PSB and GSB in the metalimnion and hypolimnion during summer stratification. When hypoxia spread throughout the water column during fall turnover, SRB and GSB vanished from the water column, whereas CSB (mainly Arcobacter) and PSB (Lamprocystis) became dominant and oxidized the accumulated sulfide under micro-aerobic conditions. Our results support the view that, once ecosystems have become anoxic and sulfidic, a large oxygen influx is needed to overcome the anaerobic sulfur cycle and bring the ecosystems back into their oxic state.