Diatom Composition Research Articles

Phytoplankton Community in The Lembeh Strait, Bitung and Wori Beach, Manado, North of Sulawesi, Indonesia

This study was conducted to understand phytoplankton community in the Lembeh Strait at Bitung and Wori Beach at Manado in October 2015. The phytoplankton samples were collected with vertical towing using Kitahara plankton net (mesh size 80 µm). Identification and enumeration were done using Sedgwick Rafter Counting Chamber (SRCC) under 100-400X magnification. Phytoplankton abundance in Wori, Manado were lower than Lembeh Strait. There were 24 genera of diatom group and nine genera of dinoflagellate group found in Wori and Lembeh Island waters. Total phytoplankton abundance in Wori ranged from 16,293.28 – 464,358.45 cells m-3 (station 6 and station 5, respectively). Whilst, In Lembeh Strait, Bitung, the highest abundance of phytoplankton was 2,300,407.33 cells m-3 and the lowest was 16,089.61 cells m-3. The composition of diatoms and dinoflagellates in Wori and Lembeh Strait was dominated by diatom which ranged from 80.70 % to 100.0%. Based on the mean contribution at each station among the two locations, there were 11 dominance genera of diatom and dinoflagellate groups which the mean contribution value above five percent. Those were including six genera of diatom group (Chaetoceros, Bacteriastrum, Nitzchia, Rhizosoleria, Thalassiothrix, and Thalassiosira) and five genera of dinoflagellate group (Ceratium, Prorocentrum, Protoperidinium, Pyrodinium, and Scriepsiella, Chaetoceros (diatom) and Protoperidinium (dinoflagellate) exhibit the highest genera representation in all diatom and dinoflagellate group among the two locations, with a 38 % and 36 % (respectively) mean contribution. Three genera which commonly known to cause harmful algal blooms (HABs) were observed in those two locations. Nitzschia from diatom group, Prorocentrum, and Pyrodinium from dinoflagellate group. Nitzschia was the most frequently found, almost recorded at all station in Wori, Manado and Lembeh strait, Bitung. The less frequent found of HABs causative organisms in those two locations was Pyrodinium.

Enhanced glacial discharge from the eastern Antarctic Peninsula since the 1700s associated with a positive Southern Annular Mode

The Antarctic Peninsula Ice Sheet is currently experiencing sustained and accelerating loss of ice. Determining when these changes were initiated and identifying the main drivers is hampered by the short instrumental record (1992 to present). Here we present a 6,250 year record of glacial discharge based on the oxygen isotope composition of diatoms (δ18Odiatom) from a marine core located at the north-eastern tip of the Antarctic Peninsula. We find that glacial discharge - sourced primarily from ice shelf and iceberg melting along the eastern Antarctic Peninsula – remained largely stable between ~6,250 to 1,620 cal. yr BP, with a slight increase in variability until ~720 cal. yr. BP. An increasing trend in glacial discharge occurs after 550 cal. yr BP (A.D. 1400), reaching levels unprecedented during the past 6,250 years after 244 cal. yr BP (A.D. 1706). A marked acceleration in the rate of glacial discharge is also observed in the early part of twentieth century (after A.D. 1912). Enhanced glacial discharge, particularly after the 1700s is linked to a positive Southern Annular Mode (SAM). We argue that a positive SAM drove stronger westerly winds, atmospheric warming and surface ablation on the eastern Antarctic Peninsula whilst simultaneously entraining more warm water into the Weddell Gyre, potentially increasing melting on the undersides of ice shelves. A possible implication of our data is that ice shelves in this region have been thinning for at least ~300 years, potentially predisposing them to collapse under intensified anthropogenic warming.

Benthic Diatom Composition of Iztuzu Coastal Lake, Dalyan (Aegean Sea, Turkey)

<div><!--block-->Coastal lakes are shallow lakes that have variable characteristics through fluctuations and marine winds. In this study, benthic diatom composition in the coastal lake of Iztuzu, Dalyan of Muğla was investigated from the material collected in 2011 and 2015. Little research has been done on coastal lakes and lagoon diatom flora in Turkey; this study contributes a total of 49 taxa identified to species level and 9 of the taxa for the first time recorded for diatom flora of Turkey. The most abundant taxa were; Cocconeis placentula Ehrenberg, Diploneis bombus (Ehrenberg) Ehrenberg, Mastogloia sp. and Chamaepinnularia alexandrowiczii Witkowski, Lange-Bertalot and Metzeltin. The results reveal a habitat-specific flora for Iztuzu Lake and give an aspect of understanding the marine-brackish distribution of diatoms in coastal lakes and lagoons. The results extend the knowledge of marine and brackish diatoms in Turkey and could provide data for similar lagoon and lakes which are under protection.</div>

Epiphytic diatom assemblages on invasive Caulerpa taxifolia and autochthonous Halimeda tuna and Padina sp. seaweeds in the Adriatic Sea – summer/autumn aspect

Abstract This study focuses on the taxonomy of epiphytic diatoms in the area of invasive macroalgae from the genus Caulerpa. Caulerpa species are characterized by the presence of secondary metabolites, such as caulerpenyne (CYN), the main function of which is a chemical defense mechanism against herbivores and epiphytes. Epiphytic diatoms were studied on fronds of Caulerpa taxifolia (“killer seaweed”) and, for comparison, on autochthonous macroalgae Padina sp. and Halimeda tuna at the eastern Adriatic Sea coast (Island of Hvar) in the summer and autumn of 2010. The qualitative analysis was performed with the use of light and scanning electron microscopy. The Shannon–Wiener Diversity Index determined for Caulerpa taxifolia showed a wide range of values (3.11–4.88), with a maximum in August and a minimum in October. While the number of taxa on Caulerpa taxifolia fronds increased from June (41) to August (88), it declined in autumn due to the high relative abundance of Cocconeis caulerpacola, which is a diatom typical for Caulerpa. On the other hand, the largest number of taxa on Padina sp. was observed in September (82). The detailed composition of epiphytic diatoms and seasonal dynamics in the area affected by the invasive macroalga Caulerpa taxifolia have been determined for the first time.

An extreme drought event homogenises the diatom composition of two shallow lakes in southwest China

In the context of global warming, extreme drought events have occurred more frequently and this is projected to continue in the future in many parts of the world. However, their ecological consequences on shallow lakes are not well studied. Here we compare the succession of diatom assemblages of two medium-sized shallow lakes in southwest China during the past ~70 years, comprising an extreme drought event between ~2009 and ~2013. The diatom community of Lake Chahei showed a clear response to eutrophication from ~1980. The pioneer species Achnanthes minutissima increased strongly with elevated sedimentary total nitrogen content and at the expense of Epithemia sorex. In contrast, the diatom community of Lake Yuxian was stable and constantly dominated by the Fragilaria construens/pinnata complex. For both lakes, the most striking change occurred with the extreme drought event when environmental conditions and diatom compositions were homogenised. With strongly shrinking lake areas, peaks in the proportion of silt were observed in the sediments, suggesting increased particle burial rates and decreased light availability. These conditions selected for motile and presumably heterotrophic species mainly of the genera Navicula and Nitzschia which exhibited abrupt increases in their relative abundances at both lakes. Meanwhile, the degree of community homogeneity (inferred by Jaccard’s similarity index) of the formerly distinct diatom assemblages increased strongly between both lakes. Hence, the extreme drought event has overridden and homogenised previous abiotic conditions and led to a decrease in beta diversity between the two study sites. Navicula and Nitzschia species may be reliable (paleo)indicators for extreme drought events in comparable shallow lake systems.

Nitrogen as the main driver of benthic diatom composition and diversity in oligotrophic coastal systems

Phytoplankton is the main indicator group for eutrophication in coastal ecosystems, however its high dispersal potential does not enable the assessment of localized effects of coastal nutrient enrichment. Benthic diatoms are sessile microalgae associated with sandy substrates and have the potential to reflect more localized pollution impacts. Although benthic diatoms are widely used bioindicators in freshwater systems, they have rarely been used for assessing the eutrophication status of oligotrophic environments such as the eastern Mediterranean Sea. In the present study, we assess the efficiency of benthic diatoms as bioindicators of nutrient enrichment in oligotrophic coastal systems, by investigating the effect of different physicochemical conditions and nutrient concentrations on the assemblage composition, diversity and individual species populations. To do this, we sampled along a eutrophication gradient formed by anthropogenic nutrient inputs from a metropolitan area. The main driver of assemblage composition, diversity and biomass of diatoms was nitrogen concentration and its temporal and spatial changes. Nitrogen loadings were positively correlated with increased biomass of Cocconeis spp. and negatively correlated with Mastogloia spp. Our findings suggest that in coastal ecosystems of oligotrophic marine ecoregions, benthic diatom assemblage structure and specific taxonomic groups can be reliable predictors of coastal eutrophication offering higher spatial resolution compared to phytoplankton.

The importance of different juvenile habitats as nursery areas for a ubiquitous estuarine-dependent marine fish species

Estuarine-dependent marine fish species rely on shallow, sheltered and food rich habitats for protection from predators, growth and ultimately recruitment to adult populations. Hence, habitats within estuaries function as critical nursery areas for a variety of fish species. Results from stomach content analysis and dietary diatom composition of a ubiquitous estuarine-dependent species Rhabdosargus holubi (Steindachner, 1881) in the main vegetated and un-vegetated habitats in the Bushmans Estuary, South Africa, were interpreted along with published information on habitat complexity, relative abundance and behaviour of this species. Although the complexity of seagrass, together with the higher abundance and behaviour of R. holubi in seagrass suggests that this is the main nursery habitat (in terms of both feeding and protection from predation), the dominance of red filamentous algae and the presence of some invertebrates mainly in the diet of fish from un-vegetated habitats indicates that this species is using a mosaic of habitats, including un-vegetated areas, for foraging. Based on the above findings, and results from other studies, it is concluded that juvenile R. holubi in permanently open estuaries makes use of a range of habitats according to macrophyte shelter from predators, the availability of preferred food resources and physical drivers such as water depth and tidal phase. This study demonstrated that a multi-method approach, as opposed to a single method approach (diet alone) is useful to assess the nursery value of juvenile fish habitats.

The seasonal and spatial variations in diatom communities and the influence of environmental factors on three temperate reservoirs in Shandong province, China.

Diatoms play an important role as ecological indicators, and some species of diatoms can easily cause water blooms, thereby decreasing the production capacity of water treatment plants and endangering drinking water safety. Mastering the diatom community dynamics is crucial for water supply. In this study, diatom composition, spatial distribution and succession were investigated in Datun Reservoir, Donghu Reservoir and Shuangwangcheng Reservoir, which are important drinking water sources in Shandong province, China. Results showed that the three reservoirs could be classified as being between mesotrophic and moderately eutrophic. The diatom community in each of the three reservoirs exhibited no obvious seasonal succession. The diatom communities in the three reservoirs were relatively simple in composition, with Synedra and Cyclotella being the most dominant groups all year round. Synedra had a negative relationship with NO2-N. Cyclotella had a positive association with NO3-N, but was negatively associated with NH4-N and CODMn in the three reservoirs. Through the analysis of diatom and environmental factors, the three reservoirs have the potential of hosting diatom blooms in summer, when the higher temperature combines with reduced water flow.

Baltic Sea Coastal Eutrophication in a Thousand Year Perspective

Sediment cores from three sites along the east-coast of Sweden, north-western Baltic Proper, have been studied with respect to lithologies, geochemistry and diatom assemblages to trace and date early human impact with emphasis on nutrient discharge. The three sites Braviken, Himmerfjarden and Adfjarden, have been impacted to various degree during the last millennia by multiple stressors like excessive nutrient discharge and hazardous substances, leading to coastal hypoxia, eutrophication and pollution. These stressors are mainly caused by drivers in the drainage area as increased human population, changed land use and point sources as industries and a sewage treatment plant. Even though their detailed history differs, the results show similar general patterns for all three sites. We find no evidence in our data from the coastal zone supporting the hypothesis that the extensive areal distribution of hypoxia in the open Baltic Sea during the Medieval Climate Anomaly was caused by human impact. Timing of the onset of man-made eutrophication, as identified from δ15N and changes in diatom composition, differs between the three sites, reflecting the site specific geography and local environmental histories of these areas. The onset of eutrophication dates to ~1800 CE in Braviken and Himmerfjarden areas, and to ~1900 CE in the less urban area of Adfjarden. We conclude that the recorded environmental changes during the last centuries are unique in a thousand year perspective.

Water usage and seasonality as primary drivers of benthic diatom assemblages in a lowland reservoir

Abstract In general, reservoirs are multi-purpose objects and they often have to fulfil different tasks at the same time. The compliance with these different expectations is more manageable in reservoirs with well-separated heterogeneous basins than in homogenous ones. The Kiskore Reservoir is the second largest standing water in the Carpathian Basin. Its water level is artificially regulated which creates unique habitats with high nature conservation value. Furthermore, the Reservoir is also considered as an important recreation centre in the region. It consists of four basins with different protection degree and management strategy. Here, we tested whether spatial (usage-dependent) or seasonal (time-dependent) segregations characterized the benthic diatom composition in the Reservoir. We also tested the influence of different water usage of basins using diatom metrics and diversity indices. We hypothesized that spatial heterogeneity in diatom composition will be more pronounced than seasonal ones. We also supposed that composition and diversity of diatom assemblages as well as diatom based ecological status will clearly reflect to different management strategies in the basins, whereas we expected moderate ecological status and low diversity in basins with high level of human impact. Our first hypothesis was not confirmed by the results. While diatom composition was clearly heterogeneous in time, surprisingly no usage-dependent segregation was found. Furthermore, our second hypothesis was also only partially confirmed by the results. In early summer, diversity was significantly lower in basins with higher level of human impact, than in the other basins. In late summer, however, diversity was rather directly controlled by nutrients and light not by water usage. Moreover, diatom based ecological status positively correlated to the intensity of recreation activities and negatively to protection degree. Although these results were surprising at the first time, they clearly confirm that a balanced ecological-economical relation can be maintained with properly designed and performed strategies in artificial reservoirs. But protection strategies, because of their exclusive interest to habitat conservation of macroscopic not microscopic organisms, require careful revisions.

Micro-fossil analysis of Mesolithic human dental calculus, Motala, Sweden - Indications of health status and paleo-diet

We analysed microfossil remains in human dental calculus sampled from an individual of the Mesolithic burials at Strandvägen, Motala, central Sweden. The analysis was targeted on phytoliths, diatoms and fungal spores. The composition of the phytolith assemblage suggests that plant micro-fossils found in the dental calculus partially stem from reeds of Phragmites. This suggests that the studied individual was consuming and/or manipulating reeds with his teeth. Spherical fungal spores were abundant in the calculus, possibly indicating weak health status, although it cannot be excluded that they originate from natural long-term accumulations. The diatom composition in the dental calculus was dominated by Cyclotella distinguenda, a species which is strongly linked to waters of the nearby Lake Vättern. This suggests that the studied individual primarily used water, and/or aquatic flora/fauna, from Lake Vättern.

Latitudinal variations in &amp;lt;i&amp;gt;δ&amp;lt;/i&amp;gt;&amp;lt;sup&amp;gt;30&amp;lt;/sup&amp;gt;Si and &amp;lt;i&amp;gt;δ&amp;lt;/i&amp;gt;&amp;lt;sup&amp;gt;15&amp;lt;/sup&amp;gt;N signatures along the Peruvian shelf: quantifying the effects of nutrient utilization versus denitrification over the past 600 years

Abstract. The stable sedimentary nitrogen isotope compositions of bulk organic matter (δ15Nbulk) and the silicon isotope composition of diatoms (δ30SiBSi) both mainly reflect the degree of past nutrient utilization by primary producers. However, in ocean areas where anoxic and suboxic conditions prevail, the δ15Nbulk signal ultimately recorded within the sediments is also influenced by water column denitrification, causing an increase in the subsurface δ15N signature of dissolved nitrate (δ15NO3-) upwelled to the surface. Such conditions are found in the oxygen minimum zone off the coast of Peru, where, at present, an increase in subsurface δ15NO3- from north to south along the shelf is observed due to ongoing denitrification within the poleward-flowing subsurface waters, while the δ30Si signature of silicic acid (δ30Si(OH)4) at the same time remains unchanged. Here, we present three new δ30SiBSi records between 11 and 15∘ S and compare these to previously published δ30SiBSi and δ15Nbulk records from Peru covering the past 600 years. We present a new approach to calculate past subsurface δ15NO3- signatures based on the direct comparison of δ30SiBSi and δ15Nbulk signatures at a latitudinal resolution for different time periods. Our results show that, during the Current Warm Period (CWP, since 1800 CE) and prior short-term arid events, source water δ15NO3- compositions have been close to modern values, increasing southward from 7 to 10 ‰ (between 11 and 15∘ S). In contrast, during the Little Ice Age (LIA) we calculate low δ15NO3- values between 6 ‰ and 7.5 ‰. Furthermore, the direct δ30SiBSi versus δ15Nbulk comparison also enables us to relate the short-term variability in both isotope compositions to changes in the ratio of nutrients (NO3-:Si(OH)4) taken up by different dominating phytoplankton groups (diatoms and non-siliceous phytoplankton) under the variable climatic conditions of the past 600 years. Accordingly, we estimate a shift from a 1:1 (or 1:2) ratio during the CWP and a 2:1 (up to 15:1) ratio during the LIA, associated with a shift from overall high nutrient utilization to NO3--dominated (and thus non-siliceous phytoplankton) utilization.

Observation of Eunotia enigmatica (Bacillariophyta), a rare South-American diatom species, in the Congo Basin, tropical Africa

ABSTRACTIn material collected in the Losambila river, a small tributary of the Congo River at Yangambi (Tshopo Province, Democratic Republic of the Congo), an unusual Eunotia species was observed. The same taxon was also detected in material taken at the beginning of 2018 in a small tributary of the Luapula river in the Haut-Katanga Province in the South of DR Congo. We could identify it as Eunotia enigmatica, recently described from reservoirs in south-eastern Brazil. The valve morphology of the Congolese material is compared with the Brazilian. E. enigmatica was not observed frequently but was not rare either. In two samples of the Losambila river this taxon reached up to 5.6 and 5.4 % of the total diatom assemblage. It is not the only species with a distribution known from Africa and South-America observed in the Losambila River. Encyonopsis frequentis, also described from South America, was more common than E. enigmatica in samples collected in the Tshopo Province, and reached up to 16.8% of the total diatom composition in the Losambila river. However, Encyonopsis frequentis was not observed in the samples where E. enigmatica was present. The same applies to the material from the tributary of the Luapula river where Encyonopsis frequentis was not found in the sample where E. enigmatica was present.

Diatoms shape the biogeography of heterotrophic prokaryotes in early spring in the Southern Ocean.

The interplay among microorganisms profoundly impacts biogeochemical cycles in the ocean. Culture-based work has illustrated the diversity of diatom-prokaryote interactions, but the question of whether these associations can affect the spatial distribution of microbial communities is open. Here, we investigated the relationship between assemblages of diatoms and of heterotrophic prokaryotes in surface waters of the Indian sector of the Southern Ocean in early spring. The community composition of diatoms and that of total and active prokaryotes were different among the major ocean zones investigated. We found significant relationships between compositional changes of diatoms and of prokaryotes. In contrast, spatial changes in the prokaryotic community composition were not related to geographic distance and to environmental parameters when the effect of diatoms was accounted for. Diatoms explained 30% of the variance in both the total and the active prokaryotic community composition in early spring in the Southern Ocean. Using co-occurrence analyses, we identified a large number of highly significant correlations between abundant diatom species and prokaryotic taxa. Our results show that key diatom species of the Southern Ocean are each associated with a distinct prokaryotic community, suggesting that diatom assemblages contribute to shaping the habitat type for heterotrophic prokaryotes.

Hydrological fluctuations modulate phototrophic responses to nutrient fertilization in a large and shallow lake of Southwest China

Lake nutrient budgets and hydrology are being altered by human activities and climate change, yet little is known of how fertilization and hydrologic mechanisms interact to structure assemblages of primary producers. Here, we present sediment records from a large shallow lake in Southwest China to separate the relative importance of nutrients and hydrological fluctuation in regulating the abundance and composition of primary producers during the twentieth century, with a focus on their differential effects on diatoms and cyanobacteria. Shifts in sedimentary particle-size distribution were consistent with the documented events of hydrological regulation during ~ 1953–1971 and subsequent changes in water level associated with severe droughts. Nutrient enrichment since ~ 1965 resulted in a significant increase in the abundance of total phototrophs (pheophytin a, β-carotene) as inferred from pigment analyses, with stronger responses of cyanobacteria (echinenone, zeaxanthin) over siliceous algae (diatoxanthin). Fossil diatom assemblages revealed a pronounced replacement of benthic taxa by eutrophic and planktonic species (e.g., Fragilaria crotonensis) since ~ 1973, but we observed a significant increase of small benthic Fragilaria sensu lato taxa following ~ 2005, which generally corresponded with a moderate increase in fossil pigments. Although eutrophication was the paramount predictor of changes in phototrophs during the last century, variation in lake hydrology due to climate and water management also modulated phototroph abundances and, more recently, diatom assemblages. Specifically, our sediment evidence suggests that hydrological fluctuation has overridden fertilization by nutrients in structuring diatom composition, leading to a heterogeneous response of cyanobacteria and diatoms to external forcing of this shallow lake.

Environmental footprint of small-scale, historical mining and metallurgy in the Swedish boreal forest landscape: The Moshyttan blast furnace as microcosm

The history of mining and smelting and the associated pollution have been documented using lake sediments for decades, but the broader ecological implications are not well studied. We analyzed sediment profiles covering the past ~10,000 years from three lakes associated with an iron blast furnace in central Sweden, as an example of the many small-scale furnaces with historical roots in the medieval period. With a focus on long-term lake-water quality, we analyzed multiple proxies including geochemistry, pollen and charcoal, diatom composition and inferred pH, biogenic silica (bSi), visible near-infrared spectroscopy (VNIRS)-inferred lake-water total organic carbon (LW-TOC), and VNIRS-inferred sediment chlorophyll (sed-Chl). All three lakes had stable conditions during the middle Holocene (~5000 BCE to 1110 CE) typical of oligo-dystrophic lakes: pH 5.4–5.6, LW-TOC 15–18 mg L−1. The most important diatom taxa include, for example, Aulacoseira scalaris, Brachysira neoexilis, and Frustulia saxonica. From ~1150 CE, decreases in LW-TOC, bSi, and sed-Chl in all three lakes coincide with a suite of proxies indicating disturbance associated with local, small-scale agriculture, and the more widespread use of the landscape in the past (e.g. forest grazing, charcoal production). Most important was a decline in LW-TOC by 30–50% in the three lakes prior to the 20th century. In addition, the one lake (Fickeln) downstream of the smelter and main areas of cultivation experienced a shift in diatom composition (mainly increasing Asterionella formosa) and a 0.6 pH increase coinciding with increasing cereal pollen and signs of blast furnace activity. The pH did not change in the other two lakes in response to disturbance; however, these lakes show a slight increase (0.3–0.5 pH units) because of modern liming. LW-TOC has returned to background levels in the downstream lake and remains lower in the other two.

Physiology and iron modulate diverse responses of diatoms to a warming Southern Ocean

Climate change-mediated alteration of Southern Ocean primary productivity is projected to have biogeochemical ramifications regionally, and globally due to altered northward nutrient supply1,2. Laboratory manipulation studies that investigated the influence of the main drivers (CO2, light, nutrients, temperature and iron) on Southern Ocean diatoms revealed that temperature and iron exert major controls on growth under year 2100 conditions3,4. However, detailed physiological studies, targeting temperature and iron, are required to improve our mechanistic understanding of future diatom responses. Here, I show that thermal performance curves of bloom-forming polar species are more diverse than previously shown5, with the optimum temperature for growth (Topt) ranging from 5–16 °C (the annual temperature range is −1–8 °C). Furthermore, iron deficiency probably decreases polar diatom Topt and Tmax (the upper bound for growth), as recently revealed for macronutrients and temperate phytoplankton6. Together, this diversity of thermal performance curves and the physiological interplay between iron and temperature may alter the diatom community composition. Topt will be exceeded during 2100 summer low iron/warmer conditions, tipping some species close or beyond Tmax, but giving others a distinct physiological advantage. Future polar conditions will enhance primary productivity2–4, but will also probably cause floristic shifts, such that the biogeochemical roles and elemental stoichiometry of dominant diatom species will alter the polar biogeochemistry and northwards nutrient supply. Climate change will alter primary productivity in the Southern Ocean, and warming and iron limitation will influence the composition of diatoms in the region. Optimum growth temperatures are wider than expected, but limited iron will affect which species flourish.

Biological and geochemical changes in shallow lakes of the Hudson Bay Lowlands: a response to recent warming

The Hudson Bay Lowlands (HBL) region of the far north of Ontario (Canada) is expected to undergo considerable physical, chemical and biological change as a result of ongoing climatic change. Previous research in the region has shown marked limnological changes during the past ~ 20 years in relatively deep lakes that have been attributed to increased air temperatures and changes in sea ice phenology in Hudson Bay since the mid-1990s. Here, we present diatom assemblage, primary production and geochemical data from lake sediments documenting recent limnological change in two shallow sub-arctic lakes in the Sutton River region of the HBL. Both lakes recorded increased whole-lake production and diatom diversity changes that are consistent with a longer ice-free period and growing season. Changes in diatom composition at Wolfgang Lake were characterized by a response amongst benthic/periphytic taxa whereas a modest increase in planktonic diatoms was observed at Sam Lake. Geochemical changes (δ15N, C/N and %N) were temporally coherent with diatom assemblage changes, but showed different responses in the two study lakes. Thus, although the biological and geochemical changes were consistent with recent warming, differences in the nature and timing of these shifts illustrate the heterogeneous nature of shallow lakes, and suggest that local (catchment-specific) factors are important determinants of the trajectory of limnological change in these sensitive systems.

Efecto de la vegetación riparia sobre el fitoperifiton de humedales en la Orinoquía colombiana

La vegetación riparia es primordial para el funcionamiento de los ecosistemas acuáticos al aportar materia orgánica. Dado que el perifiton juega un rol indispensable en la dinámica de estos ecosistemas y existen pocos trabajos sobre su ecología en el Neotrópico, se planteó la pregunta: ¿Cómo afecta el tipo de cobertura vegetal de la zona riparia, la estructura del fitoperifiton de humedales de la Orinoquía? En noviembre de 2016 se estudiaron 15 humedales con cobertura boscosa y 15 humedales con vegetación herbácea en su zona riparia. Los humedales están ubicados en la zona periurbana de Villavicencio, Meta (Colombia). Se comparó la diversidad algal entre coberturas riparias y se realizaron análisis de Redundancia para determinar que variables ambientales explicaban la composición del fitoperifiton. Se encontraron 467 morfotipos de algas, el 36,2 % perteneció a la clase Zygnematophyceae, 35,3 % a Bacillariophyceae y 16 % a Chlorophyceae. En cuanto a las diatomeas, se encontraron 165 morfoespecies distribuidas en 30 géneros. Eunotia y Pinnularia fueron los más representativos. Los análisis multivariados indicaron que la composición de diatomeas se relacionó con la cobertura vegetal litoral y el carbono orgánico total. El resto del fitoperifiton fue explicado por la temperatura y la conductividad. Modelos de regresión lineal mostraron que la diversidad de diatomeas fue explicada por el número de sustratos, la temporalidad y la cobertura vegetal riparia. Los resultados permiten concluir que en humedales antropizados de la Orinoquía colombiana, el tipo de cobertura vegetal riparia afecta la composición y diversidad de las diatomeas.

The composition of diatoms in epiphyton of the Shchugor River (Urals, Russia)

In epiphyton of the Shchugor River 143 species (with varieties and forms) of diatoms from 49 genera, 21 families were identified. Families Fragilariaceae Achnanthidiaceae, Gomphonemataceae, Naviculaceae, Bacillariaceae, Eunotiaceae include 10 and more taxa. Genera Gomphonema (11), Eunotia, Nitzschia (10 species) are predominate. Diatoms on mosses are the most abundant and diverse. Common species on all macrophytes are Achnanthidium minutissimum (Kützing) Czarnecki, Cocconeis placentula Ehrenberg, Encyonema minutum (Hilse) Mann, Meridion circulare (Gréville) Agardh, Tabellaria flocculosa (Roth) Kützing, Ulnaria ulna (Nitzsch) Compère.