Variation In Diatom Communities Research Articles

Temporal variation in diatom communities associated to sediments of impacted versus non-impacted seagrass meadows of an estuarine lagoon

Microphytobenthos play a key role as food resources at the base of the trophic web, particularly in sediments of highly productive seagrass meadows. Here, we investigated patterns of variation in microphytobenthic diatom communities and their driving factors in an impacted versus non-impacted meadow of Ruppia maritima in the Patos lagoon estuary (Brazil), across seasons in two consecutive years. We found higher taxa richness, diversity and equitability, together with lower dominance, at the non-impacted meadow. Seasonally, the same pattern was found in autumn and/or winter 2017 at both meadows, driven by the lower seawater temperature. Higher richness was related to lower river discharge and equitability to lower wind velocity. Diatom assemblages differed in species presence/absence and abundance between meadows, mostly due to higher phosphate at the impacted meadow, together with higher water transparency and sediment organic matter (2016) and with higher grain size (2017) for species presence/absence. Even diatom assemblages differed more in terms of species abundances than of presence/absence, Paralia sulcata and Tryblionela compressa (commonly reported as indicator of eutrophic conditions) were exclusively present at the impacted meadow, while Amphora charrua, Desikaneis howellii, D. simplex (commonly in undisturbed environments) did so at the non-impacted meadow. Often two species were responsible for more than half the dissimilarities in abundances, with Catenula adhaerens dominating at the impacted meadow and Ambo tenuissimus at the non-impacted meadow. Overall, the combination of natural and anthropogenic environmental factors acted together to determine between-meadow and seasonal patterns of variation in the presence and abundance of diatom species.

Intra-annual fluctuations dominating temporal dynamics of benthic diatom assemblages in a Chinese mountainous river

Understanding temporal dynamics of community may provide insights on biological responses under environmental changes. However, our knowledge on temporal dynamics of river organisms is still limited. In the present study, we employed a multivariate time-series modeling approach with a long-term dataset (i.e. 72 consecutive months) to investigate temporal dynamics of benthic diatom communities in four sites located in a Chinese mountainous river network. We hypothesized that: (1) there are multi-scale temporal dynamics within the diatom community; (2) intra-annual fluctuations dominate the community dynamics; (3) diatom species composing the community respond distinctly to environmental changes. We found that intra-annual fluctuations with periodicities <12 months explained 8.1–16.1% of community variation. In contrast, fluctuations with periodicities of 13–36 months and 37–72 months only accounted for 1.1–5.9% and 2.8–9.7% of variance in diatom community dynamics, respectively. Taxa correlating significantly to each significant RDA axis (namely, RDA taxa group) displayed distinct temporal dynamics. Conductivity, total nitrogen, and pH were important to most RDA taxa groups across the four sites while their effects were group-specific. We concluded that intra-annual dynamics dominated temporal variation in diatom communities due to community responses to local environmental fluctuations. We suggest that long-term monitoring data are valuable for identifying multiple-scale temporal dynamics within biological communities.

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.

Distance decay as a descriptor of the diatom compositional variation in tropical reservoirs

In the present study, distance decay was used as a descriptor of the compositional variation in diatom communities’ similarity between different habitats (phytoplankton and surface sediment) and seasons (summer and winter; only for phytoplankton) along a geographical gradient of ~64km over six reservoirs located in south-east Brazil. Whether rates of decay in similarity changed with distance in tropical biological communities was tested, and the degree to which dispersal (geographic distance) and niche (habitat association) processes explain variation in the diatom communities was estimated. In addition, whether the diatom assemblage captured in the surface sediment reflected the water column assemblage events was evaluated. Distance–decay curves were estimated using linear regressions. Partial Mantel tests were performed to examine the significance of relationships among the biological, environmental and spatial datasets. Similarity decreased significantly with distance between habitats and seasons, but the results were not statistically significant for surface sediment assemblages. All diatom communities were controlled more by limited dispersal than by environmental factors, probably as a result of the water quality and scale of the study area.

Diatom distribution in an alpine basin (central China) in relation to environmental factors and substrata

This study examines the habitat preferences of diatom species for bogs, ponds and streams, and explores the effects of environmental variables and substrata on diatom distribution in an alpine basin (Dajiuhu Basin, central China). Ponds and streams were characterized by high pH and high ionic strength, while bogs were acidic and heavy metal-rich habitats. Diatom samples of the epiphyton (attached to Sphagnum), the epipelon (associated with the mud) and the epilithon (attached to stones) were collected from bogs, ponds and streams, respectively. Diatom assemblages in bogs were characterized by acid-tolerant species, such as Eunotia paludosa, Eunotia seminulum and Frustulia rhomboides. In streams, the indicator species preferred circumneutral or alkaline conditions, and included Achnanthidium minutissimum, Nitzschia perminuta and Reimeria sinuata. The characteristic taxa in ponds included Achnanthidium catenatum, Aulacoseira ambigua and Discostella pseudostelligera. Canonical correspondence analysis (CCA) revealed that variations in diatom communities were significantly correlated with two environmental factors (i.e., concentrations of Si and ) and two substratum types (i.e., Sphagnum and stones). Substrata were found to influence diatom composition, probably through mediating the availability of microhabitats, moisture and nutrients. Our results point out the importance of substrata for diatom-based environmental monitoring. This study provides baseline information on diatom communities in the Dajiuhu Basin, for future comparisons, highlighting the utility of diatoms for monitoring environmental change in alpine landscapes.

How does water scarcity affect spatial and temporal patterns of diatom community assemblages in Mediterranean streams?

Abstract Mediterranean streams are mostly characterised by intermittent flow regime, with droughts in summer followed by floods in autumn. During droughts, the creation of lentic habitats (i.e. lentification process) and isolated pools in the riverbeds (i.e. fragmentation process) represents a strong selective pressure on biotic communities, which might be intensified by human‐induced water scarcity. In the highly heterogeneous habitat patches created by these processes, species sorting may be driven by stochastic mechanisms, as well as by environmental filtering. In this work, we investigated the spatial and temporal patterns in the assemblage of diatom communities during water scarcity periods in Mediterranean streams. Five oligotrophic streams, which were similar in terms of physical and chemical parameters, were sampled in the Ligurian Alps (NW Italy). Data were collected during moderate flow in April 2014 and then at least monthly during water scarcity, from June to September 2014, in: (1) lentic sites, where the water flow became slower but was permanent all year around, (2) fragmented sites, where the riverbed stretch dried out creating isolated pools. For each sampling site, we collected six benthic diatom samples from different microhabitats. We examined which type of factors, i.e. spatial or environmental, better explained the temporal and spatial variation in diatom communities. We then calculated the turnover and nestedness components of dissimilarity by comparing samples collected during moderate flow with samples obtained during a period of water scarcity. We further investigated if the idiosyncrasy of diatom species, i.e. a measure of their discrepancy from a nested pattern, could be explained by the ecological niche width of species and/or by species traits. Our results showed a contribution of both environmental and spatial factors in determining species composition during water scarcity, with the overall trends in community structure being driven by species turnover. The percentage of idiosyncratic species (those departing from the nested pattern) increased with increasing water scarcity, but showed no differences in terms of species traits. According to our results, species turnover, with replacement of sensitive species by tolerant species, seemed to be the dominating process in diatom benthic communities during water scarcity in the streams under investigation. A better evaluation of species autecology could improve the evaluation of water quality in Mediterranean streams.

Variations in diatom communities at genus and species levels in peatlands (central China) linked to microhabitats and environmental factors

Peatlands are a specialized type of organic wetlands, fulfilling essential roles as global carbon sinks, headwaters of rivers and biodiversity hotspots. Despite their importance, peatlands are being lost at an alarming rate due to human disturbance and climatic variability. Both the scientific and regulatory communities have focused considerable attention on developing tools for assessing environmental changes in peatlands. Diatoms are widely used in biomonitoring studies of lakes, rivers and streams as they have high abundance, specific ecological preferences and can respond rapidly to environmental change. However, diatom-based assessment studies in peatlands remain limited. The aims of this study were to identify indicator species and genus for three types of habitats (hummocks, hollows and ditch edges) in peatlands (central China), to examine the effects of physiochemical factors on diatom composition at genus and species levels, and to compare the efficiency of species- and genus-level identification in environmental assessment. Our results revealed that hummocks were characterized by drought-tolerant diatoms, while hollows were dominated by species and genus preferring wet conditions. Ditch edges were characterized by diatoms with different life strategies. Depth to water table, redox potential, conductivity and calcium were significant predictors of both genus- and species-level composition. According to ordination analyses, pH was not correlated with species composition while it was a significant factor associated with genus-level composition. Genus-level composition outperformed species composition in describing the response of diatoms to environmental variables. Our results indicate that diatoms can be useful environmental indicators of peatlands, and show that genus-level taxonomic analysis can be a potential tool for assessing environmental change in peatlands.

Metatranscriptomes reveal functional variation in diatom communities from the Antarctic Peninsula.

Functional genomics of diatom-dominated communities from the Antarctic Peninsula was studied using comparative metatranscriptomics. Samples obtained from diatom-rich communities in the Bransfield Strait, the western Weddell Sea and sea ice in the Bellingshausen Sea/Wilkins Ice Shelf yielded more than 500K pyrosequencing reads that were combined to produce a global metatranscriptome assembly. Multi-gene phylogenies recovered three distinct communities, and diatom-assigned contigs further indicated little read-sharing between communities, validating an assembly-based annotation and analysis approach. Although functional analysis recovered a core of abundant shared annotations that were expressed across the three diatom communities, over 40% of annotations (but accounting for <10% of sequences) were community-specific. The two pelagic communities differed in their expression of N-metabolism and acquisition genes, which was almost absent in post-bloom conditions in the Weddell Sea community, while enrichment of transporters for ammonia and urea in Bransfield Strait diatoms suggests a physiological stance towards acquisition of reduced N-sources. The depletion of carbohydrate and energy metabolism pathways in sea ice relative to pelagic communities, together with increased light energy dissipation (via LHCSR proteins), photorespiration, and NO3(-) uptake and utilization all pointed to irradiance stress and/or inorganic carbon limitation within sea ice. Ice-binding proteins and cold-shock transcription factors were also enriched in sea ice diatoms. Surprisingly, the abundance of gene transcripts for the translational machinery tracked decreasing environmental temperature across only a 4 °C range, possibly reflecting constraints on translational efficiency and protein production in cold environments.

The roles of environment and space in shaping stream diatom communities

Diatoms are widely used in stream quality assessment due to their response to the local environment. Diatoms are also influenced by many large-scale processes and so the diatom communities of boreal streams incorporate a strong spatial component at a regional level. What is not properly known yet is whether the variation in diatom communities between regions is larger than the variation in measured environmental variables. We studied the roles of environment and space in accounting for variability in stream diatom communities across four regions in Finland. According to canonical correspondence analysis, geographical coordinates, nutrient concentrations (total N and P), and water conductivity were the most important factors affecting variation in diatom community composition. Of physical factors, depth and current velocity were also significant. According to Mantel tests, both environmental and geographical distances were related to dissimilarity in diatom community composition. Analysis of Similarities indicated that the regional differences in diatom community composition were larger than the regional differences in environmental variables. We also found many indicator species confined to certain regions. Our results suggest that the four study regions differ in their diatom species composition more than in their environmental features and that diatoms are structured not only by the local environment but also by large-scale processes, possibly related to history, climate and dispersal. These results imply that, while diatom species composition reflects well the environmental differences between regions, future bioassessments would benefit from regional stratification. Otherwise, relationships with environmental variables may be masked by trans-regional differences in species pools caused by the large-scale processes.

Hydrologic processes influence diatom community composition in Dry Valley streams

AbstractOur paper describes the ecological controls on algal-mat diatom communities in the dynamic stream ecosystems of the McMurdo Dry Valleys in Antarctica. Dry Valley diatom communities are relatively diverse, and nearly ½ of the taxa found in these mats are considered endemic. Diatom community composition was examined in 5 streams in Taylor Valley during a 15-y cooling period that included a discrete flood event. Two hydrologic variables, total annual discharge and historical variation in discharge, gave the most parsimonious model of among-stream and interannual variation in diatom communities. Algal-mat biomass and chlorophyll a concentrations decreased after the flood, which occurred during the 2001/2002 summer season. Most algal-mat diatom communities recovered quickly after the flood. However, Green Creek, a relatively high-flow stream with low historical variation in discharge, appears to have experienced a persistent diatom community shift toward increased relative abundance of small, generalis...

Biofilm diatom community structure: Influence of temporal and substratum variability

Diatoms, which are early autotrophic colonisers, are an important constituent of the biofouling community in the marine environment. The effects of substratum and temporal variations on the fouling diatom community structure in a monsoon-influenced tropical estuary were studied. Fibreglass and glass coupons were exposed every month for a period of 4 days and the diatom population sampled at 24 h intervals, over a period of 14 months. The planktonic diatom community structure differed from the biofilm community. Pennate diatoms dominated the biofilms whilst centric diatoms were dominant in the water column. Among the biofilm diatoms, species belonging to the genera Navicula, Amphora, Nitzschia, Pleurosigma and Thalassionema were dominant. On certain occasions, the influence of planktonic blooms was also seen on the biofilm community. A comparative study of biofilms formed on the two substrata revealed significant differences in density and diversity. However species composition was almost constant. In addition to substratum variations, the biofilm diatom community structure also showed significant seasonal variations, which were attributed to physico-chemical and biological changes in both the water and substratum. Temporal variations in the tychopelagic diatoms of the water were also observed to exert an influence on the biofilm diatom community. Variations in diatom communities may determine the functional ecosystem of the benthic environment.

Effects of drought‐induced acidification on diatom communities in acid‐sensitive Ontario lakes

Chemical recovery of many acidified lakes in North America has been delayed or reversed as a result of interactions between climatic variability (alterations between drought and nondrought periods) and previously deposited acids stored in wetlands, but effects of this wetland‐mediated reacidification phenomenon on aquatic biota remain unknown. We compare changes in diatom assemblages in 200‐yr‐long sediment cores from two lakes with similar basin characteristics but different wetland area (4.4% of catchment at Chub Lake, 0% at Blue Chalk Lake) to evaluate the role of wetland‐mediated interactions among acid deposition and climatic variability on algal communities in acid‐sensitive lakes. Diatom assemblages were significantly more variable in Chub Lake than in Blue Chalk Lake. Variance partitioning analysis of approximately annually resolved sedimentary diatom analyses (1977–1997) identified that unique effects of water chemistry, independent of acid deposition and climatic factors, accounted for the greatest amount of variation (25%) in diatom assemblages at Chub Lake. Acid deposition (24%) and climatic factors (22%) accounted for similar, significant amounts of variation in diatom communities. Complex interactions among all three factors, which are attributable to wetland‐mediated drought‐induced reacidification, explained an additional 10% of the variation in diatoms at Chub Lake but only 1% at Blue Chalk Lake. Droughtrelated reacidification effects on water chemistry might thus cause important effects on algal communities in acid sensitive lakes with modest wetland coverage, but not in lakes without wetlands.

Distribution of Diatoms in a Forested Stream Containing a Series of Interconnected Lakes

We explored the spatial variation in diatom communities withinthe Turkey Lakes Watershed (TLW). The TLW is a single watershed in an old growth sugar maple forest that contains an alternatingseries of stream and lake embayments. Near the outlet of each lake, we sampled pools and riffles to determine abundance and diversity of diatom communities along this hydrologic system. Diatom diversity, measured by Shannon-Weaver Index, richness andevenness, increased steadily downstream before eventually decreasing near the watershed outlet. Canonical CorrespondenceAnalysis indicated that diatom genera were correlated with streamchemistry. Upper reaches were the least productive, characterizedby lower pH ( 7), lower N:P (71:1 to 90:1, dominated by simple forms of N, e.g., nitrate-N), and high mean relative abundances of Cymbella spp. and Brachysira spp. Achnanthesminutissima (Kutz.) Hustedt, the most abundant species, and Navicula spp., Nitzschia spp., Gomphonema spp., and Frustrulia spp. were represented at all stream sites. Thisstudy revealed that within the TLW, a hydrologic system of the same stream order, the diatom community was influenced by a nutrient gradient, where the stream and its intervening lakes contributed to a shift from acidic, inorganic N-poor upper reaches to a circum-neutral, inorganic N-richer outlet. By imparting genera-specific stresses, stream flow (i.e. pools vs. riffles) further shaped the diatom community.

Responses of Diatom Communities to Heavy Metals in Streams: The Influence of Longitudinal Variation

We investigated longitudinal variation (e.g., from upstream to downstream) in diatom community composition in an unpolluted stream (the Cache la Poudre River, Colorado, USA) and demonstrated how natural variation in community structure and morphological growth forms influence responses of diatoms in metal-polluted streams. Upstream communities in the Cache la Poudre River were physiognomically simple and dominated by small, adnate species (Achnanthes minutissima and Fragilaria vaucheriae), which decreased in relative abundance downstream. Responses of diatom communities to Zn in six metal-polluted streams were influenced by elevation and other variables correlated with the stream’s longitudinal gradient (pH, conductivity, alkalinity). Although clear community responses were observed at sites where Zn concentration exceeded 200 μg/L, effects of metals at moderately polluted sites were not significant. These field results were compared to responses of periphyton communities in experimental streams dosed with heavy metals. We hypothesized that communities collected from high elevation sites, which were dominated by early successional species (A. minutissima), would be more tolerant to metals than downstream communities. To test this hypothesis, diatom communities collected from a high elevation site (2340 m) and a low elevation site (1536 m) on the Cache la Poudre River were exposed to a mixture of Cd, Cu, and Zn in experimental streams. Small, adnate species (Achnanthes minutissima and Fragilaria vaucheriae) were tolerant to metals and increased in abundance in treated streams. In contrast, late successional species, which were found only at the low elevation site (Diatoma vulgare and Melosira varians), were highly sensitive to metals and were eliminated from treated streams after 24 h. These results indicate that natural variation in diatom communities may complicate interpretation of routine biomonitoring studies. We suggest that it may be useful to study periphyton community responses to pollutants in relation to ecological characteristics and morphological growth forms. Conducting research within this framework may improve the predictive ability of periphyton models and provide a theoretical basis for understanding the relationships between community patterns and the evolutionary processes that determine responses to disturbance.

RESPONSES OF DIATOM COMMUNITIES TO HEAVY METALS IN STREAMS: THE INFLUENCE OF LONGITUDINAL VARIATION

We investigated longitudinal variation (e.g., from upstream to downstream) in diatom community composition in an unpolluted stream (the Cache la Poudre River, Colorado, USA) and demonstrated how natural variation in community structure and mor- phological growth forms influence responses of diatoms in metal-polluted streams. Upstream communities in the Cache la Poudre River were physiognomically simple and dominated by small, adnate species (Achnanthes minutissima and Fragilaria vaucheriae), which de- creased in relative abundance downstream. Responses of diatom communities to Zn in six metal-polluted streams were influenced by elevation and other variables correlated with the stream's longitudinal gradient (pH, conductivity, alkalinity). Although clear community responses were observed at sites where Zn concentration exceeded 200 VLg/L, effects of metals at moderately polluted sites were not significant. These field results were compared to responses of periphyton communities in experi- mental streams dosed with heavy metals. We hypothesized that communities collected from high elevation sites, which were dominated by early successional species (A. minutissima), would be more tolerant to metals than downstream communities. To test this hypothesis, diatom communities collected from a high elevation site (2340 m) and a low elevation site (1536 m) on the Cache la Poudre River were exposed to a mixture of Cd, Cu, and Zn in experimental streams. Small, adnate species (Achnanthes minutissima and Fragilaria vau- cheriae) were tolerant to metals and increased in abundance in treated streams. In contrast, late successional species, which were found only at the low elevation site (Diatoma vulgare and Melosira varians), were highly sensitive to metals and were eliminated from treated streams after 24 h. These results indicate that natural variation in diatom communities may complicate interpretation of routine biomonitoring studies. We suggest that it may be useful to study periphyton community responses to pollutants in relation to ecological character- istics and morphological growth forms. Conducting research within this framework may improve the predictive ability of periphyton models and provide a theoretical basis for understanding the relationships between community patterns and the evolutionary processes that determine responses to disturbance.

Epiphytic and epilithic diatom communities along environmental gradients in the Nepalese Himalaya: implications for the assessment of biodiversity and water quality

Variations in diatom communities between river habitats might have ramifications for their use as bioindicators and for the assessment of their contribution to aquatic biodiversity. Diatoms therefore were sampled from similar surface areas of the epilithon and bryophytes in 24 hill-streams in the Nepalese Himalaya to assess whether communities varied more strongly between habitats or between streams. Some diatom species (e.g. Eunotia minor and Coccaneis placentula) were significantly more abundant on bryophytes than in the epilithon. In addition, bryophytes held, on average, a significantly larger proportion of the total species pool of diatoms at each site. However, neither diversity H' nor evenness E varied between habitats, suggesting no gross differences in community structure. Also, DECORANA ordination and TWINSPAN classification showed that communities were more similar between habitats within sites, than between sites. DECORANA scores from both epilithon and bryophytes showed the same linear relationships with water chemistry (acid-base status, sulphate concentration and conductivity), so that diatom samples from either habitat reflected the same chemical gradient. These results support previous conclusions that comprehensive sampling will be required in the assessment of diatom biodiversity, while samples from just one habitat may be sufficient for water quality monitoring.