Structure Of Diatom Assemblages Research Articles

Late spring bloom development of pelagic diatoms in Baffin Bay

The Arctic Ocean is particularly affected by climate change, with changes in sea ice cover expected to impact phytoplankton primary production. During the Green Edge expedition, the development of the late spring–early summer diatom bloom was studied in relation with the sea ice retreat by multiple transects across the marginal ice zone. Biogenic silica concentrations and uptake rates were measured. In addition, diatom assemblage structures and their associated carbon biomass were determined, along with taxon-specific contributions to total biogenic silica production using the fluorescent dye PDMPO. Results indicate that a diatom bloom developed in open waters close to the ice edge, following the alleviation of light limitation, and extended 20–30 km underneath the ice pack. This actively growing diatom bloom (up to 0.19 μmol Si L–1 d–1) was associated with high biogenic silica concentrations (up to 2.15 μmol L–1), and was dominated by colonial fast-growing centric (Chaetoceros spp. and Thalassiosira spp.) and ribbon-forming pennate species (Fragilariopsis spp./Fossula arctica). The bloom remained concentrated over the shallow Greenland shelf and slope, in Atlantic-influenced waters, and weakened as it moved westwards toward ice-free Pacific-influenced waters. The development resulted in a near depletion of all nutrients eastwards of the bay, which probably induced the formation of resting spores of Melosira arctica. In contrast, under the ice pack, nutrients had not yet been consumed. Biogenic silica and uptake rates were still low (respectively <0.5 μmol L–1 and <0.05 μmol L–1 d–1), although elevated specific Si uptake rates (up to 0.23 d–1) probably reflected early stages of the bloom. These diatoms were dominated by pennate species (Pseudo-nitzschia spp., Ceratoneis closterium, and Fragilariopsis spp./Fossula arctica). This study can contribute to predictions of the future response of Arctic diatoms in the context of climate change.

Diatom Assemblage Changes in Agricultural Alluvial Plain Streams and Application for Nutrient Management.

In large, alluvial floodplains dominated by agriculture, small streams have the potential to experience nutrient enrichment affecting algal assemblage structure and metabolism. Nutrient enrichment is largely driven by application of nutrients and altered hydrologic regimes. To inform stressor-response-based nutrient reduction goals for agricultural alluvial plain streams, diatom assemblages were sampled from 25 streams located within the Mississippi Alluvial Plain (MAP) with various land management practices and associated P and N inputs. From August through September 2015, epidendric diatom assemblage samples were collected from instream woody debris. Field nutrient gradients were skewed toward higher concentrations, and ranges of previously reported diatom assemblage response thresholds indicative of oligotrophic conditions were not well represented. Ordination analysis identified a gradient in species composition associated with increasing P and decreasing dissolved oxygen. A significant shift in diatom assemblage structure occurred when total P concentrations in the MAP streams exceeded 0.12 mg L-. Phosphorus-enriched systems were represented by a distinct set of indicator species, lower abundances of ubiquitous species, greater abundances of highly tolerant species, and greater abundances of high-P indicator species. No relationships were observed among diatom assemblage measures or traits with increasing N. Current results do not address potential criteria for identifying high-quality, oligotrophic streams. However, measures of diatom assemblage structure have potential for helping set benchmarks to reduce nutrient impacts and monitor effects of agricultural best management practices on MAP streams.

Diatoms from sediments of the Dagi geothermal system (Eastern Sakhalin)

Rich diatom flora, including 245 species and varieties belonging to 96 genera, was found in the sediments of the gassing field of the Dagi geothermal system on the coast of Nyisky Bay (Eastern Sakhalin).In the sediments of the gassing field of the Dagi geothermal system on the coast of Nyisky Bay (Eastern Sakhalin). The ecological structure of diatom assemblages indicates the predominant influence of lagoon waters on the formation of their host sediments.

Reconstructing the Trophic History of an Alpine Lake (High Tatra Mts.) Using Subfossil Diatoms: Disentangling the Effects of Climate and Human Influence

Diatom analysis was undertaken on a 200-year sediment record in an alpine lake (Popradské pleso, Tatra Mountains, Central Europe). Due to its remote character and well-documented human influence since the mid-nineteenth century, it allows a study of the relationship between anthropogenic pressures and diatom assemblages. Altogether, 122 diatom taxa of 40 genera were identified, and two major taxonomic shifts were revealed in the stratigraphic record. The timing of the first significant shift in ~ 1850 precludes the possibility of being caused by direct human activities, since according to historic documents there was neither continuous human presence nor grazing in the valley before that time. In addition, the direct effect of organic pollution early in the 1960s connected with the operation of a tourist hotel was not clearly reflected in the diatom signal. The diatom-inferred total phosphorus (DI-TP) reconstruction indicated the highest TP content well before the most direct wastewater pollution from a newly built hotel. There was a considerable effect of climate to diatom assemblage structure as well as diatom life forms. Our results suggest that direct organic pollution influenced the diatom communities less than expected, and the main driver of change was climate warming. We hypothesize that it is because of the short residence time of the lake, since it has both strong inlet and outlet, and it has been showed that the inlet had significant effect on benthic communities in the past. At the same time, fish manipulation could have been the reason for some fluctuation in DI-TP unrelated to climate and organic pollution.

Monitoring Phytoplankton and Nutrients in Tagus Estuary, Portugal, for 20 years

Monitoring Phytoplankton and Nutrients in Tagus Estuary, Portugal, for 20 years

Distribution of diatoms and geochemical features of holocene sediments from the Kuril Basin (Sea of Okhotsk)

Sediments from the Kuril Basin were collected during the Russian-German deep-sea expedition SokhoBio (Sea of Okhotsk Biodiversity Studies). Concentrations of biogenic and trace elements, quantitative content, and species composition of diatom assemblages in surface sediments and core samples were analyzed. Distribution in the surface sediments depending on different environmental conditions as well as changes in the diatom frustule content, the ratio of dominant diatom species, and the ecological structure of diatom assemblages were studied.The collected sediments were silt and clayey silt, with SiO2am and Corg contents ranging from 15.85% to 36.61% and 0.84–1.92%, respectively. The spatial distribution patterns of the elements studied and the diatoms, as well as vertical profiles of the sediment cores, revealed that the contents of biogenic components and trace elements, such as amorphous silica, organic carbon, barium and phosphorus, changed in parallel with the change in the number of diatoms and depended mainly on the biological productivity of the sea. The change in water mass parameters and in the hydrological regime also affected the chemical composition of the bottom sediments over time.A predominance of oceanic species is observed in the sediments at the bottom of the basin, and the mixed oceanic-neritic composition of diatoms is characteristic of slope deposits. Moreover, the assemblages reflect the influence of Pacific Ocean water masses at stations close to the Kuril Straits, as well as in the warm waters of the Sea of Japan at the station in the Soya Current zone.A nearly synchronous increase in the impact of Okhotsk water masses and the entry of the Sakhalin Current waters into the Kuril Basin as one moved deeper into the core at stations with different climatic conditions was observed.The productivity and species diversity of diatoms and the chemical composition of sediments are reflections of the regional features of climatic processes.

Diatom response to climatic warming over the last 200 years: A record from Gonghai Lake, North China

Annual monitoring data and centennial and millennial-scale paleolimnological records have revealed an increase in small-celled planktonic diatom species relative to heavier tycho-planktonic and small benthic diatoms in many high-altitude lakes, presumably in response to recent climatic warming. In addition to changes in the composition and structure of lacustrine diatom assemblages, there have also been changes in diatom biodiversity; however, these changes are not regionally consistent. In this study, we chose a temperate mid-latitude lake to explore the response of changes in diatom assemblages and biodiversity to recent climatic warming. The diatom record spans the past ca. 200years and reveals that since 1966 CE the small-celled Cyclotella ocellata+stelligera has replaced the previously dominant, large-celled phytoplankton Cyclotella schroeteri. These changes are in accordance with the increasing trend in global mean surface temperature. Biodiversity increased remarkably from 1966 CE, but began to decline after 1990 CE, presumably in response to rapid climatic warming. Our findings indicate that the response of diatom biodiversity to climate change was a nonlinear process.

Alta diversidad de especies (H´) de diatomeas bentónicas en una laguna costera ubicada dentro de un área natural protegida

The structure of benthic diatom assemblages (diversity, equitability, dominance) may be useful in assessing their ecological status in natural protected areas. Goals. To describe the structure of epipelic diatom assemblages from Laguna Guerrero Negro (LGN), a protected coastal lagoon, and test the hypothesis that H´diversity values would be higher for diatom assemblages in LGN sediments than in typical benthic diatom assemblages. Methods. Sediment samples were collected in the lagoon on November 2013, and January, March, and July 2014. Diatoms were mounted on permanent slides and examined at 1000× using phase contrast microscopy. In each slide, 500 valves were counted to compute relative abundances of each taxon, and species diversity, equitability, and dominance, using Shannon (H´), Pielou (J´), and Simpson (?) indices, respectively. Likewise, similarity between samples was measured. The calculated median value of H´ from LGN was compared to previously recorded median values to test the hypothesis that significant differences exist. Results. A total 225 diatom taxa were counted. With few exceptions, the similarity between samples was <60%. Relative abundances depict typical benthic diatom assemblages, with an average H´= 4.96 bits/taxon, and corresponding values of equitability and dominance. The median value of H´ (Md = 4.9) was significantly higher than the median value (Md = 3.7) found in previous studies. Conclusions. The structure of the epipelic diatom assemblages from LGN and their patchy distribution are similar to that of typical diatom assemblages, but with unusually high values of H´ that lead us to reject the statistical null hypothesis and thus sustain our research hypothesis.

River water quality assessment based on a multi-descriptor approach including chemistry, diatom assemblage structure, and non-taxonomical diatom metrics

In the present study, the ecological status of four major South Korean rivers flowing near industrial complexes is assessed using physico-chemical analyses and various descriptors based on benthic diatom assemblages. Principal component analysis conducted with physical and chemical variables singled-out four sites as more severely impacted (higher concentration of metals and total nitrogen, higher conductivity and biological oxygen demand), while the remaining 12 sites indicated less impacted conditions, although showing nutrient enrichment. Less-contaminated sites based on physico-chemical properties showed higher cell densities, higher richness and diversity, a larger proportion of live and healthy-looking diatoms, lower production of lipid bodies (in terms of number and size) and fewer teratologies than more-contaminated sites. Non-taxonomical metrics (cell heath status, cell size, lipid bodies and valve deformities) were in good agreement with traditional taxonomical metrics (assemblage structure, richness, diversity). Overall, water quality assessment based on diatom assemblages and diatom-based metrics had a good fit with the available physico-chemical data and agreed on the most impacted sites. However, additional sites showed signs of degradation based on the diatom metrics used. This suggests that the use of biotic indicators provides useful complementary information on the health status at the selected sites.

Development of a diatom-based multimetric index for acid mine drainage impacted depressional wetlands

Acid mine drainage (AMD) from coal mining in the Mpumalanga Highveld region of South Africa has caused severe chemical and biological degradation of aquatic habitats, specifically depressional wetlands, as mines use these wetlands for storage of AMD. Diatom-based multimetric indices (MMIs) to assess wetland condition have mostly been developed to assess agricultural and urban land use impacts. No diatom MMI of wetland condition has been developed to assess AMD impacts related to mining activities. Previous approaches to diatom-based MMI development in wetlands have not accounted for natural variability. Natural variability among depressional wetlands may influence the accuracy of MMIs. Epiphytic diatom MMIs sensitive to AMD were developed for a range of depressional wetland types to account for natural variation in biological metrics. For this, we classified wetland types based on diatom typologies. A range of 4–15 final metrics were selected from a pool of ~140 candidate metrics to develop the MMIs based on their: (1) broad range, (2) high separation power and (3) low correlation among metrics. Final metrics were selected from three categories: similarity to reference sites, functional groups, and taxonomic composition, which represent different aspects of diatom assemblage structure and function. MMI performances were evaluated according to their precision in distinguishing reference sites, responsiveness to discriminate reference and disturbed sites, sensitivity to human disturbances and relevancy to AMD-related stressors. Each MMI showed excellent discriminatory power, whether or not it accounted for natural variation. However, accounting for variation by grouping sites based on diatom typologies improved overall performance of MMIs. Our study highlights the usefulness of diatom-based metrics and provides a model for the biological assessment of depressional wetland condition in South Africa and elsewhere.

Impacts of late‐Holocene climate variability and watershed‐lake interactions on diatom communities in Lac Brûlé, Québec

AbstractA high‐resolution diatom analysis of a varved sediment sequence from Lac Brûlé, southwestern Québec, was used to study temporal patterns of environmental change in the late Holocene. Key periods of interest in the record included the Medieval Warm Period (~800–1300 CE), the Little Ice Age (~1450–1850 CE), and post‐European settlement (~1850–present). Subfossil diatom assemblages were compared to previously published pollen, cladocera, and sediment records from Lac Brûlé, revealing complex dynamics between terrestrial vegetation succession, nutrient fluxes, and trophic interactions. Generalized additive models showed a response to long‐term climate variability in the diatom record, although it was not the most influential driver of community changes at Lac Brûlé. Catchment‐mediated processes instead played the largest role in governing the structure of diatom assemblages in the lake. For example, nutrient loading following a local fire in the watershed at 1345 CE led to an abrupt and significant increase in Fragilaria spp. Human activity associated with deforestation and the Wallingford‐Back Mine (1924–1972 CE) also had strong impacts on the landscape, which triggered further responses in the aquatic communities of Lac Brûlé.

Late holocene environmental changes in the Southwestern Chukchi Sea inferred from diatom analysis

The environmental changes in the southern part of the Chukchi Sea over the last 2300 years (two warmings during the ~262 BC–630 AD and ~630–1300 periods AD and 1 cooling ~1300–1840 AD) were inferred from changes in the content of diatoms in sediments (per gram), the ratio of dominant species, and the ecological structure of diatom assemblages. The sediment age was determined based on the recent 210Pb sedimentation rates at the sampling point (0.43 mm/yr) and radiocarbon dating of mollusk shells. The environmental changes in the southern Chukchi Sea that were inferred from the diatom analysis correlate with global climate changes, viz., the warming events of the early (Roman) and the middle (Medieval) Subatlantic and the cooling of the late (Little Ice Age) Subatlantic.

How do abiotic environmental variables shape benthic diatom assemblages in subtropical streams?

Diatoms (Division Bacillariophyta) commonly dominate benthic algal communities in upland streams and are the major primary producers that sit at the base of food webs. Given their ecological importance, the aim of the present study was to investigate the spatial patterns of freshwater biofilm biomass and diatom assemblage composition in response to differences in physical and chemical variables in the Bremer, Logan and Albert catchments in south-east Queensland. Patterns in benthic diatom assemblage structure were examined during base flow conditions and the focus was on relating the spatial hierarchical interrelationships among ultimate (i.e. catchments and geology) and proximate (i.e. flow, nutrients, light, conductivity, pH and turbidity) environmental drivers. The spatial difference observed in the benthic diatom assemblages was predominantly driven by proximate environmental drivers, which, in turn, were affected by ultimate drivers. Flow played a critical role in controlling both biofilm biomass and affecting the occurrence of diatom taxa. Nutrients and light also played roles as limiting resources structuring biofilm biomass and the relative abundance of diatoms. Diatom growth form, cell size and attachment mode can be used to create a more quantitative and predictive approach to establishing relationships between diatoms and environmental gradients.

The structure and diversity of freshwater diatom assemblages from Franz Josef Land Archipelago: a northern outpost for freshwater diatoms.

We examined diatom assemblages from 18 stream and pond samples in the Franz Josef Land Archipelago (FJL), the most northern land of Eurasia. More than 216 taxa were observed, revealing a rich circumpolar diatom flora, including many undescribed taxa. Widely distributed taxa were the most abundant by cell densities, while circumpolar taxa were the most species rich. Stream and pond habitats hosted different assemblages, and varied along a pH gradient. Diatoma tenuis was the most abundant and ubiquitous taxon. However, several circumpolar taxa such as Chamaepinnularia gandrupii, Cymbella botellus, Psammothidium sp. and Humidophila laevissima were also found in relatively high abundances. Aerophilic taxa were an important component of FJL diatom assemblages (Humidophila spp., Caloneis spp. and Pinnularia spp.), reflecting the large and extreme seasonal changes in Arctic conditions. We predict a decrease in the abundance of circumpolar taxa, an increase in local (α-) freshwater diatom diversity, but a decrease in regional diversity (circumpolar homogenization) as a result of current warming trends and to a lesser extent the increasing human footprint in the region.

&lt;b&gt;Periphytic diatoms as bioindicators in a tropical stream: from urban to rural environments

Urbanization and agriculture alter expressively the physical and chemical variables of lotic habitats, especially streams, causing negative effects to the biota of these environments. This study aimed to (i) evaluate the spatial and seasonal variations in the structure of periphytic diatom assemblage in a stream under urban influence in its headwaters, and rural influence, in the rest of its course, and (ii) select diatom species as bioindicators of urban and rural stretches. Three sampling sites were set along the stream according to its longitudinal gradient. The structure of the periphytic diatom assemblage presented differences in spatial scale, differing substantially between the urban and rural habitats. There was a higher influence of nutrients (orthophosphate (PO 4 ) and total nitrogen (TN)) on the distribution of the assemblage. Therefore, the use of the assemblage of periphytic diatoms as environmental bioindicator indicated spatial differences along the riverine areas, from the agriculture environment to the urbanized environment.

Diatoms are better indicators of urban stream conditions: A case study in Beijing, China

Urbanization dramatically affects hydrology, water quality and aquatic ecosystem composition. Here we characterized changes in diatom assemblages along an urban-to-rural gradient to assess impacts of urbanization on stream conditions in Beijing, China. Diatoms, water chemistry, and physical variables were measured at 22 urban (6 in upstream and 16 in downstream) and 7 rural reference stream sites during July and August of 2013. One-way ANOVA showed that water physical and chemical variables were significantly different (p<0.05) between urban downstream and both reference and urban upstream sites, but not between reference and urban upstream sites (p>0.05). Similarly, structural metrics, including species richness (S), Shannon diversity (H′), species evenness (J′) and Simpson diversity (D′), were significantly different (p<0.05) between urban downstream and both reference and urban upstream sites, but not (p>0.05) between reference and urban upstream sites. However, diatom assemblages were very different among all sites. Achnanthidium minutissima was a consistent dominant species in reference sites; Staurosira construens var. venter and Pseudostaurosira brevistriata were the dominant species in urban upstream sites; and Nitzschia palea was the dominant species in urban downstream sites. Clustering analyses based on the relative abundance of diatom species, showed all the samples fit into three groups: reference sites, urban upstream sites, and urban downstream sites. Canonical correspondence analysis (CCA) and Monte Carlo permutation tests showed that concentration of K+, EC, TN, Cl− and pH were positively correlated with relative abundance of dominant diatom species in urban downstream samples; WT and F− were correlated with reference and urban stream diatom composition. Our results demonstrate that the composition of diatom species was more sensitive to urbanization than the water physical and chemical parameters, and that diatom assemblage structure metrics more accurately assessed water quality. Some species, such as Amphora pediculus and Cocconeis placentula were among the dominant species in low nutrients stream sites; however, they were considered to be high nutrient indicators in some streams in USA. We suggest using caution in applying indicator indices based on species composition from other regions. It is necessary to build a complete set of diatom species data and their co-ordinate environment data for specific regions.

Assessing the heavy metal pollution by the study of diatom assemblages from lacustrine sediments, European Russia

The taxonomic structure of diatom assemblages from the modern lacustrine sediments of the Kola Peninsula and Ni concentration in them are analyzed. It was found that the degree of negative transformation of structure of diatom assemblages from small (< 1 km2) and medium-sized (1–4 km2) lakes shows significant correlation with the Ni concentration in surface waters. A method of graphical analysis was applied to study the variations of taxonomic proportions in the diatom assemblages, which are proposed to use during integrated paleoecological investigations of bottom cores from weakly studied lakes of Caucasus. The prospects of application of the integrated analysis of bottom cores taken from lakes of different genesis are estimated. Obtained results have demonstrated that small closed lakes are the most promising objects for the assessment of heavy metal pollution caused by the transboundary transfer.

Diatom assemblages and their associated environmental drivers in isolated oceanic island streams (Azores archipelago as case study)

The identification of higher scale geographical processes (e.g., island location) that shape regional (catchment and landscape patterns) and local factors (e.g., water quality, microhabitat) is crucial to a correct understanding of diatom distribution, especially in isolated oceanic islands’. To assess the contribution of these processes in the composition of diatom assemblages in insular permanent streams, a total of 316 samples were studied from 37 sites along 14 permanent streams in Azores archipelago and related to environmental variables. Ordination techniques were used to identify the forcing factors that best explain the composition of diatom assemblages. The results revealed how individual and collective patterns emerging from local, regional, and geographic factors, and their shared variance, provided us with more detailed insight into what factors determine the structure of insular diatom assemblages in Azorean streams. The variance explained by local factors (24.3%) dominated over the regional (20.9%) and geographic fractions (18.5%). This result supports the notion that insular stream ecosystems and their communities are under strong abiotic control, as well as their continental counterparts. The results of this study provide support for current and future stream ecosystem research and baseline information for developing integrated freshwater management strategies for streams on the Azorean archipelago.

Flood disturbance effects on benthic diatom assemblage structure in a semiarid river network

Disturbances such as floods and droughts play a central role in determining the structure of riverine benthic biological assemblages. Extreme disturbances from flash floods are often restricted to part of the river network and the magnitude of the flood disturbance may lessen as floods propagate downstream. The present study aimed to characterize the impact of summer monsoonal floods on the resistance and resilience of the benthic diatom assemblage structure in nine river reaches of increasing drainage size within the Gila River in the southwestern United States. Monsoonal floods had a profound effect on the diatom assemblage in the Gila River, but the effects were not related to drainage size except for the response of algal biomass. During monsoons, algal biomass was effectively reduced in smaller and larger systems, but minor changes were observed in medium systems. Resistance and resilience of the diatom assemblage to floods were related to specific species traits, mainly to growth forms. Tightly adhered, adnate and prostrate species (Achnanthidium spp., Cocconeis spp.) exhibited high resistance to repeated scour disturbance. Loosely attached diatoms, such as Nitzschia spp. and Navicula spp., were most susceptible to drift and scour. However, recovery of the diatom assemblage was very quick indicating a high resilience, especially in terms of biomass and diversity. Regional hydroclimatic models predict greater precipitation variability, which will select for diatoms resilient to bed-mobilizing disturbances. The results of this study may help anticipate future benthic diatom assemblage patterns in the southwestern United States resulting from a more variable climate.

Variação da composição e estrutura da assembleia de diatomáceas do Páramo de Frontino (Cordilheira Ocidental dos Andes, Colômbia) durante o Holoceno

Neste trabalho é apresentada a variação temporal da composição e estrutura da assembleia de diatomáceas da Bacia Llano Grande, Páramo de Frontino, localizado a 3.460 m de altitude ao nordeste da Cordilheira Ocidental dos Andes, Colômbia. O material estudado é referente a um testemunho de 8,5 m perfurado na por- ção central da bacia, do qual 57 níveis holocênicos foram aleatoriamente amostrados para o estabelecimento da composição taxonômica da assembleia e sua densidade. Um total de 292 táxons foi reconhecido, incluindo 149 com nomenclatura taxonômica aberta, em nível de gênero. Estes últimos táxons podem correspondem a variações intraespecíficas de formas conhecidas ou novas espécies, demonstrando a riqueza biológica destes ambientes, sujeitos a condições particulares de estresse. Uma alta variabilidade na densidade, na composição e estrutura da assembleia de diatomáceas foi verificada ao longo do perfil sedimentar, com desaparecimento de 169 táxons, representando uma perda de 40,9 % da composição taxonômica. Os desaparecimentos são atribuídos a mudanças de temperatura, aportes externos de cinzas vulcânicas, desmineralização e diminuição da profundidade do corpo d’água. No trecho correspondente ao Holoceno inicial, as oscilações na composição, densidade e na estrutura da assembleia de diatomáceas são atribuídas a perturbações físicas e químicas da coluna d’água, que motivaram a diminuição da densidade e a substituição da maioria das espécies do intervalo por outras nos níveis correspondentes ao Holoceno médio e final. No Holoceno médio as variações são devidas às oscilações do volume e desmineralização do corpo d’água e ao aporte externo de cinzas dos vulcões. No final do Holoceno, as variações taxonômicas estão relacionadas à progressiva diminuição do nível d’água do ecossistema e colonização por macrófitas.