Dead Diatoms Research Articles

Sustainable treatment of dye wastewater by recycling microalgal and diatom biogenic materials: Biorefinery perspectives

Discharge of untreated or partially treated toxic dyes containing wastewater from textile industries into water streams is hazardous for environment. The use of heavy metal(s) rich dyes, which are chemically active in azo and sulfur content(s) has been tremendously increasing in last two decades. Conventional physical and chemical treatment processes help to eliminate the dyes from textile wastewater but generates the secondary pollutants which create an additional environmental problem. Microalgae especially the diatoms are promising candidate for dye remediation from textile wastewater. Nanoporous diatoms frustules doped with nanocomposites increase the wastewater remediation efficiency due to their adsorption properties. On the other hand, microalgae with photosynthetic microbial fuel cell have shown significant results in being efficient, cost effective and suitable for large scale phycoremediation. This integrated system has also capability to enhance lipid and carotenoids biosynthesis in microalgae while simultaneously generating the bioelectricity. The present review highlights the textile industry wastewater treatment by live and dead diatoms as well as microalgae such as Chlorella, Scenedesmus, Desmodesmus sp. etc. This review engrosses applicability of diatoms and microalgae as an alternative way of conventional dye removal techniques with techno-economic aspects.

First evaluation of the periphyton recovery after glyphosate exposure

The potential environmental risk of glyphosate has promoted the need for decontamination of glyphosate-polluted water bodies. These treatments should be accompanied by studies of the recovery potential of aquatic communities and ecosystems. We evaluated the potential of freshwater periphyton to recover from glyphosate exposure using microcosms under laboratory conditions. Periphyton developed on artificial substrates was exposed to 0.4 or 4 mg l−1 monoisopropylamine salt of glyphosate (IPA) for 7 days, followed by translocation to herbicide-free water. We sampled the community 1, 2 and 3 weeks after the transfer. Dry weight, ash-free dry weight, chlorophyll a, and periphyton abundances were analysed. The periphyton impacted with the lowest IPA concentration recovered most of the structural parameters within 7 days in clean water, but the taxonomic structure did not entirely recover towards the control structure. Periphyton exposed to 4 mg IPA l−1 could not recover during 21 days in herbicide-free water, reaching values almost four times higher in % of dead diatoms and four times lower in ash-free dry weight concerning the control at the end of the study. Results suggest a long-lasting effect of the herbicide due to the persistence within the community matrix even after translocating periphyton to decontaminated water. We conclude that the exposure concentration modulates the recovery potential of IPA-impacted periphyton. The current research is the first to study the recovery in glyphosate-free water of periphyton exposed to the most commonly used herbicide in the world. Finally, we highlight the need for more studies focused on the recovery potential of freshwater ecosystems and aquatic communities after glyphosate contamination.

Water quality and spatial and seasonal dynamics in the largest water supply reservoir in Brazil and implications for diatom assemblages

Abstract: Aim in this paper we investigated how spatial factors and seasonal dynamics influenced the diatom community in a tropical deep environment of low productivity waters in Brazil. Methods we used physical and chemical characteristics of the water and planktonic diatoms from 9 sampling stations during dry (austral winter) and wet (austral summer) seasons (N = 18) as the outline to identify water quality, spatial and seasonal patterns. To evaluate spatially and temporally integrated events from the recent past (approximately the last 5 years before sampling), and the species from diverse habitats of the system, we used diatoms from the surface sediment (top 2 cm, N = 9). Since we used the top 2 cm of surface sediment containing the dead diatoms that were deposited over recent past of the reservoir, seasonal sampling of the sediment was not needed. Results during the dry season heavily silicified long colonial planktonic diatom species associated mainly with higher mixing depth, pH, and transparency dominated the plankton, whereas in the wet season the reservoir became stratified, favoring planktonic solitary diatoms with high surface volume ratios. For the sediment, a general pattern emerged where planktonic species dominated in the deep sections of the reservoir, and the abundance of benthic species in shallow areas near the tributaries increased. Conclusions the diatom assemblages was mainly influenced by seasonal variations and mixing regime. Surface sediment samples provided longer-term information, and revealed habitat differentiation shaping diatom assemblages. Overall, the small centric planktonic Aulacoseira tenella (Nygaard) Simonsen stood out as the most abundant species in the entire reservoir in both, the plankton and the sediment, indicating that size and shape serve as adaptive strategies for buoyancy and nutrient uptake stand as a competitive advantage in deep low productivity environments.

Evaluation of three preparation methods for living diatoms at a sandy river-mouth tidal flat: conventional acid-cleaning, nuclear staining, and sieving

Three preparation methods for the identification of diatom flora at a river mouth tidal flat were evaluated in terms of species richness, diversity, and composition using a conventional acid-cleaning method, a nuclear staining method, and a newly introduced sieving method. Twenty-five diatom samples were collected from Fujimae Tidal Flat sediments, Nagoya, Japan, in July 2014. Three methods respectively showed different aspects of the diatom flora. The acid-cleaning method indicated the highest species diversity, but it extracted dead diatoms with living ones indiscriminately. In comparison with the acid-cleaning method, the staining method effectively extracted diatoms with fragile and small-sized cells. The sieving method scraped the sessile diatoms selectively and supplemented the staining method in which sessile diatoms were mostly neglected. A combination of these three methods enables to describe precise diatom flora of a tidal flat.

The effect of hydrological conditions and bioactivities on the spatial and temporal variations of streambed hydraulic characteristics at the subtropical alpine catchment

The endangered Formosan landlocked salmon that habitats only in Chichiwan Creek has been successfully rehabilitated in one of its tributaries, Yusheng Creek. However, the stream fragmentation, no surface streamflow, seriously reduced the salmon population, hampering the restoration work. The surface water-groundwater (SW-GW) interactions in a 500-m reach were examined by installing 6 monitoring wells at 3 sites to record temperatures and groundwater levels at every 15-min for two months. The automatic estimator of VFLUX and numerical model of VS2DH are used to quantify the streambed hydraulic characteristics along the reach. It is found that the entire study reach is a losing stream and the fragmented reaches have significantly higher streambed vertical hydraulic conductivity (VK) compared to the perennial one. The streambed VK at the up-stream perennial reach increased by about double after a rainfall event, probably resulting from the removal of fine grain in the streambed by the rainfall event. Although the fragmented reaches reflowed after the event, streambed VK at the mid- and down-stream fragmented reaches decreased by about 75% and 50%, respectively, compared to the pre-fragmented period. The clogging layers formed by the remains of dead diatom deposited in the streambed during the fragmented period were very likely responsible for the decreased streambed VK. The spatial and temporal variations of streambed VK influenced by hydrological conditions and even bioactivities within such a short distance reveal the complexity of SW-GW interactions. Further studies about the forming processes of clogging layer and its effect on the hydraulic characteristic should be conducted to create a more holistic and reliable picture of interaction processes.

Arctic (Svalbard islands) active and exported diatom stocks and cell health status

Abstract. Diatoms tend to dominate the Arctic spring phytoplankton bloom, a key event in the ecosystem including a rapid decline in surface-water pCO2. While a mass sedimentation event of diatoms at the bloom terminus is commonly observed, there are few reports on the status of diatoms' health during Arctic blooms and its possible role on sedimentary fluxes. Thus, we examine the idea that the major diatom-sinking event which occurs at the end of the regional bloom is driven by physiologically deteriorated cells. Here we quantify, using the Bottle-Net, Arctic diatom stocks below and above the photic zone and assess their cell health status. The communities were sampled around the Svalbard islands and encompassed pre- to post-bloom conditions. A mean of 24.2±6.7 % SE (standard error) of the total water column (max. 415 m) diatom standing stock was found below the photic zone, indicating significant diatom sedimentation. The fraction of living diatom cells in the photic zone averaged 59.4±6.3 % but showed the highest mean percentages (72.0 %) in stations supporting active blooms. In contrast, populations below the photic layer were dominated by dead cells (20.8±4.9 % living cells). The percentage of diatoms' standing stock found below the photic layer was negatively related to the percentage of living diatoms in the surface, indicating that healthy populations remained in the surface layer. Shipboard manipulation experiments demonstrated that (1) dead diatom cells sank faster than living cells, and (2) diatom cell mortality increased in darkness, showing an average half-life among diatom groups of 1.025±0.075 d. The results conform to a conceptual model where diatoms grow during the bloom until resources are depleted and supports a link between diatom cell health status (affected by multiple factors) and sedimentation fluxes in the Arctic. Healthy Arctic phytoplankton communities remained at the photic layer, whereas the physiologically compromised (e.g., dying) communities exported a large fraction of the biomass to the aphotic zone, fueling carbon sequestration to the mesopelagic and material to benthic ecosystems.

Silicic acid limitation drives bloom termination and potential carbon sequestration in an Arctic bloom

The spring diatom bloom in the Arctic Ocean accounts for significant annual primary production leading to the most rapid annual drawdown of water-column pCO2. Late-winter waters in the Atlantic Arctic & Subarctic Provinces (AASP) have lower silicic acid concentrations than nitrate, which suggests diatom blooms may deplete Si before N. Here we test a facet of the hypothesis that silicic acid limitation terminates the spring diatom bloom in the AASP and the sinking of the senescent and dead diatoms helps drive carbon sequestration. During a 6-week study, diatoms bloomed and progressively consumed silicic acid to where it limited their growth. The onset of growth limitation was concurrent with the minimum pCO2 in the surface waters and increases in both the proportion of dead diatoms and the diatom assemblage sedimentation rate. Data reanalysis within the AASP shows a highly significant and positive correlation between silicic acid and pCO2 in the surface waters, but no significant relationship with nitrate and pCO2 was observed unless data were smoothed. Therefore, understanding the future of the AASP spring diatom bloom requires models that explicitly consider changes in silicic acid supply as a driver of this process.

Mutual interaction between arsenic and biofilm in a mining impacted river

Gold mining activities in fluvial systems may cause arsenic (As) pollution, as is the case at the Anllóns River (Galicia, NW Spain), where high concentrations of arsenate (AsV) in surface sediments (up to 270 mg kg−1) were found. A 51 day-long biofilm-translocation experiment was performed in this river, moving some biofilm-colonized substrata from upstream (less As-polluted) to downstream the mine area (more As-polluted site), to explore the effect of As on benthic biofilms, as well as their role on As retention and speciation in the water-sediment interface. Eutrophic conditions (range: 0.07–0.38 mg L−1 total phosphorus, TP) were detected in water in both sites, while sediments were not considered P-polluted (below 600 mg kg−1). Dimethylarsenate (DMAV) was found intracellularly and in the river water, suggesting a detoxification process by biofilms. Since most As in sediments and water was AsV, the high amount of arsenite (AsIII) detected extracellularly may also confirm AsV reduction by biofilms. Furthermore, translocated biofilms accumulated more As and showed higher potential toxicity (higher As/P ratio). In concordance, their growth was reduced to half that observed in those non-translocated, became less nutritive (less nitrogen content), and with higher bacterial and dead diatom densities. Besides the high As exposure, other environmental conditions such as the higher riparian cover at the more As-polluted site could contribute to those effects. Our study provides new arguments to understand the contribution of microorganisms to the As biogeochemistry in freshwater environments.

Interannual and (multi-)decadal variability in the sedimentary BIT index of Lake Challa, East Africa, over the past 2200 years: assessment of the precipitation proxy

Abstract. The branched vs. isoprenoid tetraether (BIT) index is based on the relative abundance of branched tetraether lipids (brGDGTs) and the isoprenoidal GDGT crenarchaeol. In Lake Challa sediments the BIT index has been applied as a proxy for local monsoon precipitation on the assumption that the primary source of brGDGTs is soil washed in from the lake's catchment. Since then, microbial production within the water column has been identified as the primary source of brGDGTs in Lake Challa sediments, meaning that either an alternative mechanism links BIT index variation with rainfall or that the proxy's application must be reconsidered. We investigated GDGT concentrations and BIT index variation in Lake Challa sediments at a decadal resolution over the past 2200 years, in combination with GDGT time-series data from 45 monthly sediment-trap samples and a chronosequence of profundal surface sediments.Our 2200-year geochemical record reveals high-frequency variability in GDGT concentrations, and therefore in the BIT index, superimposed on distinct lower-frequency fluctuations at multi-decadal to century timescales. These changes in BIT index are correlated with changes in the concentration of crenarchaeol but not with those of the brGDGTs. A clue for understanding the indirect link between rainfall and crenarchaeol concentration (and thus thaumarchaeotal abundance) was provided by the observation that surface sediments collected in January 2010 show a distinct shift in GDGT composition relative to sediments collected in August 2007. This shift is associated with increased bulk flux of settling mineral particles with high Ti / Al ratios during March–April 2008, reflecting an event of unusually high detrital input to Lake Challa concurrent with intense precipitation at the onset of the principal rain season that year. Although brGDGT distributions in the settling material are initially unaffected, this soil-erosion event is succeeded by a massive dry-season diatom bloom in July–September 2008 and a concurrent increase in the flux of GDGT-0. Complete absence of crenarchaeol in settling particles during the austral summer following this bloom indicates that no Thaumarchaeota bloom developed at that time. We suggest that increased nutrient availability, derived from the eroded soil washed into the lake, caused the massive bloom of diatoms and that the higher concentrations of ammonium (formed from breakdown of this algal matter) resulted in a replacement of nitrifying Thaumarchaeota, which in typical years prosper during the austral summer, by nitrifying bacteria. The decomposing dead diatoms passing through the suboxic zone of the water column probably also formed a substrate for GDGT-0-producing archaea. Hence, through a cascade of events, intensive rainfall affects thaumarchaeotal abundance, resulting in high BIT index values.Decade-scale BIT index fluctuations in Lake Challa sediments exactly match the timing of three known episodes of prolonged regional drought within the past 250 years. Additionally, the principal trends of inferred rainfall variability over the past two millennia are consistent with the hydroclimatic history of equatorial East Africa, as has been documented from other (but less well dated) regional lake records. We therefore propose that variation in GDGT production originating from the episodic recurrence of strong soil-erosion events, when integrated over (multi-)decadal and longer timescales, generates a stable positive relationship between the sedimentary BIT index and monsoon rainfall at Lake Challa. Application of this paleoprecipitation proxy at other sites requires ascertaining the local processes which affect the productivity of crenarchaeol by Thaumarchaeota and brGDGTs.

Diatom-based biosynthesis of gold-silica nanocomposite and their DNA binding affinity

We report an eco-friendly method for biosynthesis of gold-silica (Au-SiO2) nanocomposite using a diatom, Amphora copulata, as reducing agent. The live cells of Amphora covered by siliceous frustules reacted with hydrogen tetra-auro chlorate (HAuCl4), and Au-SiO2 particles were synthesized after 72 h of reaction. Energy-dispersive X-ray (EDAX) analysis confirmed the presence of Au and SiO2 nanoparticles in a composite form, and their characterization was done by UV-vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), and scanning (SEM) and transmission (TEM) electron microscopy. The SEM study revealed that composite particles were deposited on the siliceous frustules of live cells, whereas in dead diatom cells, the surface remained unchanged. The TEM analysis confirmed the synthesis of triangular-, spherical-, and hexagonal-shaped Au-SiO2 particles with 5 to 45-nm size range. Biogenic Au-SiO2 nanoparticles were tested for DNA binding affinity by agarose gel electrophoresis and TEM study after 30 min of interaction with isolated DNA from the green alga, Pithophora. The synthesized nanoparticles were found to bind with DNA molecules without any surface modification. The TEM images of Au-SiO2 particles, taken after interaction with DNA, showed the arrangement of particles in specific manner which formed a “Y”-shaped, chain-like, and coiling structure, indicating that the diatom-based bio-synthesized Au-SiO2 particles were very efficient in binding with DNA which could be applied in the bio-medical field directly.

Behaviour of Different Levels and Grades of Diatomite as Silicon Source in Acidic and Alkaline Soils

Diatomite or Diatomaceous earth (DE) is a sedimentary rock that results from the deposition of Si rich unicellular life forms (diatoms) found in both salt and fresh water. The cell walls of these dead diatoms consist of amorphous silica. Amorphous silica is more easily solubilised than crystalline silica and is expected to release more PAS (Plant available silicon). Information on use of DE as the source of Si in different crops is very limited and hence there is a need to know the effect of different levels and grades of DE on availability of nutrients in acidic and alkaline soil under field capacity and submergence level. An incubation study was conducted by using acidic and alkaline soil in a plastic pot with different levels (0, 150, 300 and 600 kg ha −1) of diatomite under field capacity and submergence. In another study, five different grades of diatomite at different levels (0, 250, 500, 750, 1000 and 1500 kg ha −1) were incubated under the field capacity moisture regime alone. During the incubation studies, soil samples were periodically analyzed for pH and PAS at 7, 15, 30, 60, 90 and 120 days after incubation (DAI). Increase in pH of acidic and decrease in pH of alkaline soil was recorded irrespective of application rates of diatomite under both the moisture regimes. Increase in PAS was observed at 30 DAI in both types of soil. Among the different grades, diatomite-3 and diatomite-4 recorded significantly higher PAS in acidic soil under the field capacity moisture regime.

Impact of Drought on Diatom Communities and the Consequences for the use of Diatom Index Values in the River Maureillas (Pyrénées‐Orientales, France)

AbstractIn the context of climate change, with an increase in the incidence of seasonally dry streambeds, we examined the impact of drought, and its duration, on the structure of diatom communities and the consequences of this on diatom index values (Biological Diatom Index; Specific Polluosensitivity Index) in the Mediterranean river Maureillas. The effects of several durations of droughts or low flow events (1, 2 and 4 weeks) on diatom‐dominated biofilms were studied by removing pebbles from the river and comparing the growing communities after rewetting with those of control biofilms (pebbles left in the streambed) and with those of newly formed biofilms (cleaned‐up pebbles). Sampling was performed six times during the 28‐day rewetting phase. We determined the specific composition of diatom communities, the mortality rate after rewetting, and the Biological Diatom Index and Specific Polluosensitivity Index scores for each sample, distinguishing between potentially living diatoms (full frustules with chloroplasts) and dead diatoms (empty frustules). Our results showed a notable and durable impact of even short drought on diatom communities. The different trajectories of biofilm communities observed between the types of pebbles showed the importance of the biofilm history for the community structure. This should be taken into account to improve the sampling practices used for monitoring. We also observed a stable mortality rate whatever the drought duration was. Diatom index values were stable despite the observed impact of treatment on diatom communities. These results emphasize the reliability of the diatom index to evaluate biological quality according to European requirements. In addition, the distinction of empty and full frustules did not induce significant differences, but it may reduce biases in interpretation. Copyright © 2014 John Wiley & Sons, Ltd.

Seasonal Hypoxia of Amursky Bay in the Japan Sea: Formation and Destruction

Based on detailed hydrological and hydrochemical surveys carried out in each of the four seasons of 2008, Amursky Bay in the north west quadrant of the Japan Sea was found to experience seasonal hypoxia. The primary process of hypoxia formation is a microbiological degradation of the ”excess” amount of diatoms under rather low photosynthetic active radiation in bottom layer and weak water dynamics. The microbiological decay of dead diatoms under light deficient conditions intensively consumes dissolved oxygen and produces phosphates, ammonium, silicates, and dissolved inorganic carbon. Existence of a phytoplankton ”excess” is caused by phytoplankton bloom resulting from nutrient pulses into Amursky Bay. There are two main sources of these nutrients: the waste waters of Vladivostok city and discharge from Razdolnaya River. The river delivers more than two times the amount of nutrients than the waste waters of Vladivostok. It is suggested that the phytoplankton ”excess” might be caused by an enhanced supply of nutrients delivered into the surface layer resulting from the increased discharge of the river on a short time scale. Our data suggest that hypoxia is seasonal, with a peak at the end of summer. The upwelling of the Japan Sea water in the beginning of the fall season and its advection across the shelf is the primary process by which the hypoxia is destroyed. During the winter, strong vertical mixing due to termohaline convection makes the water column uniform and brings more oxygen into the water along with high primary production under the ice. Thus, during the winter season, the ecosystem of Amursky Bay recovers completely.

Changes in Epipelic Diatom Diversity from the Savannah River Estuary

Littoral zones can be characterized with temporal exposure of algae to diurnal desiccation at low tides. Combinations of diverse freshwater, marine, and brackish diatoms dominate exposed mud samples. With enlargement of the delta of the Savannah River, Georgia and other anthropogenic influences, changes in the rich epipelic community will not be estimated accurately without baseline data. In the current study, mud samples were taken from the Savannah River estuary along with physicochemical characteristics every two months throughout 2011. Live algal communities were assessed in every sample and live to dead diatom proportions in the communities were calculated. Cleaned diatoms were analyzed following standard protocols. Community indices were compared between sampling events and with literature reports from similar habitats in the Southeastern USA diverse diatom community of 241 species was documented and 39 of those species should be described as new to science. Decrease in species richness and diversity was due to dominance of representatives of the genera Cymatosira and Minidiscus during the summer months.

EFFECTS OF LIGHT AND SUBSTRATE ON THE BENTHIC DIATOMS IN AN OLIGOTROPHIC LAKE: A COMPARISON BETWEEN NATURAL AND ARTIFICIAL SUBSTRATES(1).

Benthic diatoms form a particularly important community in oligotrophic lakes, but factors influencing their distribution are not well known. This study reports the depth distribution of living motile and total diatoms (living plus dead diatoms) on both natural (from sand to fine organic mud) and artificial substrates in an oligotrophic lake. On artificial substrates, motile diatom densities peaked in abundance (24-30 cells · mm(-2) ) between 0.6 and 1.9 m depth; on natural sediment surfaces, motile diatoms were generally more numerous and peaked in abundance (925 cells · mm(-2) ) at 1.3 m depth. Total diatom densities on artificial substrates were highest (1260 valves · mm(-2) ) at 0.6 m depth, with very low values below 3 m depth; on natural sediment surfaces, total diatom abundances were generally much higher (21600 valves · mm(-2) ) at 3 m depth and declined gradually with depth. Significant relationships were found between light and diatom densities on the artificial substrate. Ordination analysis indicated that substrate type significantly correlated with the variation of diatom composition on artificial and natural substrates. Our results suggest that in oligotrophic lakes, light influences benthic diatom abundance, whereas substrate type has more influence on benthic diatom composition.

Size distribution of diatom frustules and sedimentary process of dead diatoms in a tidal zone

古環境復元する上で，珪藻遺骸群集の現地性・異地性を識別することは重要である．その識別のため，現世の干潟において，珪藻遺骸群集の形成過程を珪藻殻のサイズ（殻長）と底質の対応関係から明らかにした．その結果，現地性遺骸群集の個体数と分布は，底質のLOI（強熱減量）と相関が高かった．また，異地性遺骸群集の分布と個体数は，底質のシルト含有率と相関が高かった．さらに，異地性遺骸群集の主要な個体は，砂質干潟のような波浪が卓越する環境から洗い流された，シルトサイズのものだった．これらの結果は，特定のサイズの異地性珪藻が選択的に運搬され，シルト含有率が高い環境で特徴的に堆積していることを示唆している．よって粒径など堆積物の特徴を踏まえた上で，珪藻のサイズから遺骸群集の性質を捉え，現地性・異地性の識別が可能になる．以上の珪藻のタフォノミーに着目すれば，よりよい環境指標種を設定することも可能である．

Controls on the Recycling and Preservation of Biogenic Silica from Biomineralization to Burial

The recycling of biogenic silica (bSiO2) produced by diatoms is a vital process sustaining a significant fraction of primary production in the oceans. The efficiency with which bSiO2 dissolves controls the availability of nutrient silicon in the water column, and modulates the export of organic carbon to the deep sea. Environmental conditions during biomineralization (temperature, nutrient availability, light, etc.) affect the silicification and weathering resistance of diatom frustules, while ecosystem processes, including grazing and aggregation, are determining factors for the recycling of bSiO2 in the water column. Bacterial colonization of dead diatoms leads to the decomposition of the protective organic layers allowing for the dissolution of bSiO2 to begin. The dissolution rate of diatom frustules is a function of the physicochemical properties of both the silica (e.g., specific surface area, degree of hydration and condensation, impurities) and the aqueous medium (e.g., temperature, pH, pressure, electrolyte composition). In sediments, the dissolution of bSiO2 is controlled by the presence of lithogenic minerals, aging processes and the build up of dSi in the pore waters. In particular, interactions between lithogenic silicate minerals and bSiO2 may initiate rapid diagenetic alterations that favor the preservation of bSiO2.

Taxonomic characterization of the microorganisms associated with the cultivable diatom Synedra acus from Lake Baikal

Determination of the taxonomic position of microorganisms associated with diatoms was carried out using microscopic, microbiological, and phylogenetic methods. Examination of the cultures of the fresh-water diatom Synedra acus grown in Lake Baikal water by epifluorescence and electron microscopy revealed that bacterial cells colonized the mucilage surrounding the cells of living microalgae and their cell surfaces and penetrate into the frustules of dead diatoms. A total of 13 strains of heterotrophic bacteria were isolated in pure cultures and described. Based on the results of analysis of their morphological, physiological, and biochemical properties, as well as on data obtained by 16S rRNA gene analysis, the following strains were identified to the species level: Sphingomonas sp., Variovorax paradoxus, Pseudomonas fluorescens, Microbacterium trichothecenolyticum, Rhodococcus sp., Caulobacter vibrioides, and Brevundimonas vesicularis.

Should only live diatoms be used in the bioassessment of small mountain streams?

It is unclear whether differentiating live and dead diatoms would enhance the accuracy and precision of diatom-based stream bioassessment. We collected benthic diatom samples from 25 stream sites in the Northern Oregon Coast ecoregion. We counted live diatoms (cells with visible chloroplasts) and then compared the counts with those generated using the conventional method (clean counts). Non-metric multidimensional scaling (NMDS) showed that the diatom assemblages generated from the two counts were overall similar. The relationships between the two diatom assemblages (summarized as NMDS ordination axes) and the environmental variables were also similar. Both assemblages correlated well with in-stream physical habitat conditions (e.g., channel dimensions, substrate types, and canopy cover). The conventional diatom method provides taxonomic confidence while the live diatom count offers ecological reliability. Both methods can be used in bioassessment based on specific assessment objectives.

Environmental impact of the Laacher See eruption at a large distance from the volcano: Integrated palaeoecological studies from Vorpommern (NE Germany)

In order to investigate the environmental impacts of the Laacher See eruption (12,900 calendar years B.P.) and the deposition of the Laacher See tephra at a large distance from the volcano, fine-resolution micromorphological, diatomological, and palynological investigations were carried out on closely spaced areas in the Reinberg basin (Vorpommern, NE Germany). The lower part of the LST originates from atmospheric input, whereas the upper part was washed-in from the surrounding basin slopes. Diatom populations expanded as a consequence of the input of silica, while simultaneously dissolution of dead diatoms decreased. The tephra provided a favourable habitat for many epilithic and epipelic diatom taxa. The diatoms show a slight acidification and an increase in specific conductivity of the water, whereas no eutrophication is indicated. These effects disappeared after lake sediments covered the tephra. The pollen diagrams from the Reinberg basin as well as many other pollen diagrams from NE Germany indicate that the vegetation reacted to rising temperatures after the cooler Gerzensee fluctuation, to a short-lived water-level rise connected with higher precipitation after the volcanic eruption, and to minor openings in the forest vegetation due to increased fire probably connected with severe thunderstorms.