Structure Of Diatom Assemblages Research Articles

Regional patterns in periphyton accrual and diatom assemblage structure in a heterogeneous nutrient landscape

The effect of nutrient regime on periphyton community development in large rivers was examined (sites ranged from oligotrophic to eutrophic). Patterns in diatom community structure were examined at a large spatial scale (ultimate), whereas at the microhabitat scale (proximate), artificial nutrient-diffusing substrata were used to examine periphyton response to amendment with nitrogen, phosphorus, and N + P. Ratios of ambient dissolved inorganic nitrogen to total phosphorus were used to make predictions of nutrient limitation (molar total inorganic nitrogen (TIN) : total phosphorus (TP)), which matched experimental results in 8 of 12 sites. Two sites with highest ambient nutrient levels (mean NO3 + NO2 and TP, 1.49 and 0.081 mg·L–1, respectively) possessed the highest diatom richness and diversity (mean richness = 42). Lowest diatom taxa richness (19) occurred in an impounded system with low TP (0.008 mg·L–1). Principal components analysis (PCA) of diatom taxa structure among sites (control treatments only) and small-scale patterns among nutrient treatments using all sites and treatments combined indicated that sites were grouped according to drainage basin (r2 = 0.79) and that there was no unified response to enrichment (r2 = 0.43). Results suggest that large spatial scale factors are more important in determining the potential benthic diatom assemblage than small-scale, proximate variables provided by the diffusers.

Influence of Corophium volutator and Hydrobia ulvae on intertidal benthic diatom assemblages under different nutrient and temperature regimes

Epipelic diatoms dominate the microphytobenthos of estuarine sediments, where they play important roles in ecological processes such as primary production, secondary production and sediment stability. Grazing (top-down control) and nutrients (bottom-up control) regulate the bio- mass and species composition of intertidal benthic diatom assemblages. However, observations of grazing/predation effects on species richness differ under contrasting nutrient conditions. We inves- tigated the interactive effects of grazing, nutrients and temperature and compared the impacts of Corophium volutator and Hydrobia ulvae—2 species that differ in their feeding strategies and bio- turbation effects. Diatom assemblages were collected from 2 estuaries (Biezelingsche Ham, Wester- schelde, high nutrient, and Zandkreek, Oosterschelde, low nutrient) in The Netherlands that differ in their dominant macrofaunal grazer species. Assemblages were grown in the laboratory without (con- trol) and with grazing activity under different nutrient and temperature regimes. C. volutator exerted a strong regulatory influence on epipelic diatoms by reducing biomass, and preferentially consuming certain dominant taxa, thereby increasing species richness, evenness and diversity. The percentage of epipsammic species increased in the presence of C. volutator, at the expense of Navicula species. Biezelingsche Ham assemblages grazed by C. volutator were not influenced by nutrient or tempera- ture regime, while control assemblages were influenced by temperature. In contrast, differences in the structure of diatom assemblages between the treatments were far less pronounced for H. ulvae- grazed and control Zandkreek assemblages. H. ulvae appeared to be a general consumer, grazing subdominant species. Species richness was greater at low temperature, regardless of nutrient level. Macrofaunal grazing did not predictably increase or decrease species diversity, but could potentially do both, and it may mask the effects of environmental and bottom-up control.

Desalinization of running waters: III. Changes in the structure of diatom assemblages caused by a decreasing salt load and changing ion spectra in the river Wipper (Thuringia, Germany)

Salt-loaded effluents were introduced into the river Wipper during the mining period for almost a century. Beginning with the year 1990, the waste water load was strongly reduced due to the termination of the potash industry. Prior to 1990, monthly means of the chloride concentrations at times exceeded 6,000 mg l −1 in the strongly polluted sections. Maximum concentrations reached twice these values. Up to 1998, mean annual chloride concentrations decreased to values below 2,000 mg l −1. This led to more balanced fluctuations in salinity which had been pronounced before, depending on discharge and short-term changes in production. Similarly, the physiologically adverse ion conditions improved due to decrasing potassium and increasing calcium proportions. In 1963/64, 1986 and 1998, samples of epilithic, epiphytic and epipsammic diatoms were taken at locations of different salinities along the river and examined for the effects of the salinization on the structure of the diatom assemblages. These structures changed in dependence on salinity. Increasing salt concentrations coincided with decreasing oligohalophilic and increasing mesohalophilic and polyhalophilic species numbers. Above a chloride concentration of about 3,000 mg l −1, the proportion of the latter exceed that of the former (halobion index > 50). Corresponding to different conditions of salinization along the river, characteristic diatom assemblages occur differring from each other and which are specific for the river section. Spring and autumn aspects of the diatom assemblages show also salt-dependent differences. The assemblages found in 1998 after decrease of salinization have changed markedly in comparison to those from 1963/64 and 1986. Halobiontic species predominating formerly occurred only occasionally or not at all. They were replaced by oligohalobic-indifferent forms. An ecological assessment of the changes was performed based on the halobion index calculated from all the samples. For the strongly salinized section of the river Wipper, a shift from α-mesohalobic/polyhalobic conditions in 1963/64 and 1986 to α-oligohalobic/β-mesohalobic conditions in 1998 was found. However, constant α-oligohalobic conditions are still not given. With regard to the transition from α-oligohalobic (limnetic) to β-mesohalobic (brackish) conditions, a maximum chloride concentration of 600 mg l −1 was found. To guarantee α-oligohalobic conditions, a maximum chloride concentration of 400 mg l −1 should not be exceeded.

Distribution of benthic algae in the upper Illinois River basin in relation to geology and land use

SUMMARY 1 Benthic-algal distributions in the upper Illinois River basin, IL, U.S.A., were examined in relation to geology, land use, water chemistry and stream habitat using (detrended) (canonical) correspondence analysis, autecological metrics and indicator-species analysis in order to identify the major environmental gradients influencing community variation. 2 Ionic composition and major nutrient [i.e. nitrogen (N) and phosphorus (P)] concentration of surface waters, salinity (Na-Cl type), substratum type and physiognomic form of dominant species were primary factors contributing to variation in benthic-algal assemblages of the basin. Basin geology was a significant contributing factor, but the explained variance associated with this factor was less than that related to land use. 3 Proportions of algal biomass consisting of cyanophytes, filamentous chlorophytes, halophilic diatoms and diatoms which utilize nitrogen heterotrophically were greater in eutrophic river segments than in less nutrient-enriched segments. Composition of the benthic flora indicated meso-eutrophic or eutrophic conditions throughout the basin; there were few diatoms indicative of hypertrophic waters. Shifts in diatom-assemblage structure in response to nutrient loading provided an incomplete representation of the community-response curve. 4 A weighted-averages regression model based on total P and benthic-algal abundances (all divisions included) yielded a highly significant correlation (r2 = 0.83) between species-inferred [WA(tol)] and observed total P, with systematic bias (increased deviation of residuals) occurring only at concentrations greater than ∼ 1.0 mg L−1 total P. This result indicates that total P regression and calibration models can be predictable for a river basin receiving excessive loadings of phosphorus.

Structure of Benthic Diatom Assemblages from a Mangrove Environment in a Mexican Subtropical Lagoon1

'I'he taxonomic list and the structure of benthic diatom assemblages occurring in fine sediments (silt and sand) from the mangrove forest of the Balandra lagoon in Baja California Sur, Mkxico was determined based on seasonal samplings for one ycar. Assemblage structure was analyzed using several ecological indices for estimating diversity (H'), dominance (REDI), equitability, and similarity. A total of 230 diatom taxa were identified and include 109 new records for the Raja California peninsula coast. Taxa representative of highly productive and hypersaline environments were common. Assemblages were characterized by a few abundant species and many uncommon or rare taxa. High diatom diversity estimates at all sampling sites during all seasons suggest that diatom assemblages in sediments of the Balandra lagoon represent a quasi-pristine environment.

Structure of Benthic Diatom Assemblages from a Mangrove Environment in a Mexican Subtropical Lagoon

Structure of Benthic Diatom Assemblages from a Mangrove Environment in a Mexican Subtropical Lagoon

THE SEDIMENT DIATOM ASSOCIATION AND CHEMISTRY OF SURFACE SEDIMENTS OF LAKE BELAUER SEE, NORTHERN GERMANY

Within-lake variability in diatom associations deposited on the surface sediments (0–1 cm) of a hypereutrophic lake, Lake Belauer See, northern Germany, was compared with spatial variations in sediment composition, which were used to identify environmental gradients. Numerical analysis was used to explore the data for major patterns in order to interpret die complex diatom associations. Non-uniform hydrodynamics and sedimentary conditions related to the bipartite basin geometry and morphometry were found to have a major influence on surface sediment composition and explain the main trends in diatom assemblage structure. The planktonic diatoms Stephanodiscus spp (S. parvus, S. minutulus, S. neoastrae/rotula, S. hantzschii) and Cyclostephanos dubius were dominant in the majority of the surface samples. Non-planktonic forms, including very high frequencies of fragilarioid species (amongst these, especially Staurosira construens and Pseudo-staurosira brevistriata), were dominant only in shallow and/or marginal parts of the lake. Superimposed on this pattern of life-form categories is the influence of local pollution sources in die lake. While odierwise rare or absent, diatoms such as Amphora pediculus, Navicula scutelloides, N. cari, N. radiosa, N. gothlandica increase in abundance in those parts of the lake which receive the highest input of nutrients. Apart from düs large-scale pattern, marginal sites often have site-specific assemblages, which are believed to reflect direct or indirect influences of die erosional transport along shores and inwash from die catchment. To overcome die problems of spatial heterogeneity when dealing with communities of non-planktonic diatoms a multiple core strategy and higher diatom counts are advisable.

Epilithic diatoms of the St. Lawrence River and their relationships to water quality

Epilithic diatoms were sampled at 48 sites along the St. Lawrence River, from Salaberry de Valleyfield to Québec City, in an attempt to determine how diatom assemblages were related to measured water quality variables. Canonical correspondence analysis was used to explore the relationships between environmental variables and patterns in the epilithic diatom assemblages. "Distance downstream from Cornwall" was determined to be the strongest variable influencing the structure of epilithic diatom assemblages, likely due to the effect of tides (favouring aerophilic species) closer to the river outlet. Variables related to pollution (suspended solids, fecal coliforms, chlorophyll a) also explained significant (P < 0.05) amounts of variance in the diatom assemblages. The optima of common diatom species to suspended solids were explored further. Reconstructive models using weighted-averaging calibration and regression illustrated that "distance from Cornwall" and concentrations of suspended solids, fecal coliforms, and chlorophyll a, the most influential variables, could be inferred from the diatom assemblages. When compared with the inference models developed for pollution variables using epiphytic diatom assemblages (attached to macrophytes or Cladophora), the epilithon model appears to perform better.Key words: diatoms, rocks, epilithic, St. Lawrence River, water quality, calibration.

Short-Term Nutrient Influences on Algal Assemblages in Three Rivers of the Minnesota River Basin

ABSTRACT Periphyton accumulation variables and diatom assemblage structure were examined on nutrient diffusing pots placed in three rivers in the Minnesota River basin. The Minnesota River, which had the highest accrual of inorganic and organic matter, appeared to have phosphate and light limited algal accumulation. No nutrient effects were observed in the Blue Earth River although phosphate limitation was predicted by the N:P ratio. Cyclotella meneghiniana responded negatively and Gomphonema parvulum responded positively to ammonia diffusing pots in the Yellow Medicine River. Otherwise no release from nutrient limitation was observed in this stream. Diatom species composition varied independently of algal accumulation rates.

Relating Diatom Assemblage Structure to Stream Habitat Quality

Diatom assemblage structure on natural and artificial substrata was related to lotic physical habitat characteristics in an agricultural basin in Minnesota. We found 59 species across the basin, but species richness at individual sites ranged from 4 to 25 (median 16) on natural substrata and 9 to 23 (median 15) on artificial substrata. Most species were rare, with nearly half appearing at fewer than 3 sites. The most abundant taxa were biraphid diatoms (relative abundance >28% in most cases). Rank correlations of guild relative abundance from the artificial substrata (Achnanthes, biraphid, silt-tolerant) were strongest with% bank erosion and the Qualitative Habitat Evaluation Index riparian subscore, both of which were negatively correlated. Diatom assemblages from natural substrata showed strong rank correlations between% canopy coverage and the Achnanthes, biraphid, rheophilic, and silt tolerant guilds. Relative abundance of stalked diatoms and the width of the streams at flood were also strongly correl...

Predation of epipelic diatoms by the amphipod Corophium volutator and the polychaete Nereis diversicolor

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 145:53-61 (1996) - doi:10.3354/meps145053 Predation of epipelic diatoms by the amphipod Corophium volutator and the polychaete Nereis diversicolor Smith D, Hughes RG, Cox EJ The effects of Corophium volutator (Pallas) and Nereis diversicolor (O. F. Muller) on the densities and specific compositions of epipelic diatom assemblages were investigated experimentally, in the laboratory and in an estuary. In laboratory experiments cores containing no macrofauna had significantly higher densities of diatoms than cores with C. volutator and cores with N. diversicolor after 8 d. In field experiments the densities of diatoms increased where C. volutator were removed, by spraying with insecticide, and where N. diversicolor were prevented from surface deposit feeding, by the insertion of porous mats under the surface. The mean daily rates of consumption of diatoms by individual C. volutator and N. diversicolor in the field were estimated to be 2150 to 3767 and 5476 to 12184 cells respectively. In the laboratory the effects of C. volutator and N. diversicolor on the species composition of the diatom assemblage were similar. In the field the assemblages that developed where predation was reduced were different because of initial differences in diatom assemblage structure in the 2 experimental areas. The laboratory results showed that C. volutator and N. diversicolor may feed on the same species of diatoms when presented with the same diatom assemblage, indicating that interspecific competition for food may be important under some natural conditions. Corophium volutator · Nereis diversicolor · Epipelic diatoms · Predation Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 145. Publication date: December 31, 1996 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1996 Inter-Research.

DIATOM ASSEMBLAGES OF STREAMS INFLUENCED BY WILDFIRE1

ABSTRACTThe Greater Yellowstone Area ecosystem experienced major wildfires in 1988, resulting in a substantial number of catchments being burned. We studied diatom assemblage structure at 14 sites over 5 years in catchments ranging from 0 to over 90% burned. Coefficients of variation for selected physical measures provided a good assessment of the degree of disturbance experienced by the various sites and correlated highly with percentage of catchment burned. Principal components analysis quantitatively estimated the degree of temporal change in diatom assemblages at a site. The more extensively burned catchments showed the greatest amount of structural change in diatom taxa among years. Navicula permitis Hust. and Nitzschia inconspicua Grun. were predominant in the heavily disturbed systems, whereas Achnanthes minutissima Kuetz., A. lanceolata (Breb.) Grun., Rhoicosphenia curvata (Kuetz.) Grun. ex Rabh., and Diatoma hiemale var. mesodon (Ehr.) Grun. were common in less disturbed streams. The results demonstrate that recovery trajectories of lotic diatom assemblages following major landscape‐scale disturbances are a function of disturbance intensity resulting from differences in catchment characteristics.

DIATOMS AS INDICATORS OF LAKE TROPHIC STATUS IN CENTRAL ONTARIO, CANADA

Diatoms in surface sediment from 50 Canadian Precambrian Shield lakes in the Muskoka-Haliburton and central Ontario regions were analyzed in order to establish the relationship between lake trophic status and subfossil diatom assemblage structure. Distribution optima of the most abundant diatom taxa in 30 lakes were calculated by using a weighted average technique. The most commonly observed diatom taxa were classified into five trophic categories: O = oligotrophia OM = oligomesotrophic, M = mesotrophic, ME = mesoeutrophic and E = eutrophic. Abundance values of these diatom trophic groups were used to estimate corresponding values of total phosphorus (TP), chlorophyll-a (chl-a), Secchi depth (SD) and LTSI (a new lake trophic status index developed in this study) using multiple regression methods. The statistical equations obtained by both simple and multiple regression techniques were then applied to 20 newly sampled lakes to test the model. The transfer functions between diatom community structure and ea...

Resistance and Resilience of Lotic Algal Communities: Importance of Disturbance Timing and Current

We examined effects of disturbance timing on resistance and resilience of epilithic algal communities growing in fast— (29 cm/s) and slow— (12 cm/s) current outdoor experimental stream channels in Kentucky, USA that were either left undisturbed (control) over 33 d following a simulated spate, or were subjected to an additional spate after either 9, 18, 27, 33 d. On day 33, all channels were subjected to a final spate to assess effects of short—term disturbance history on resistance, independently of seasonal influences. Succession proceeded from a sparsely populated community dominated by a small, monoraphid diatom (Achnanthes minutissima) immediately after the initial spate, to dominance by dense floating mats of filamentous green algae (Zygnematales: Mougeotia and Spirogyra) and Synedra spp. by day 21—24. Resistance was generally lower in slow—current communities, both in terms of cell—density reduction and displacement of taxonomic structure, than in fast—current communities. Resistance in slow—current communities varied temporally, with communities least resistant on day 18, when community composition and physiognomy was changing rapidly, and on day 33, when green algal mats began to senesce. On day 33, slow—current communities that had not been recently disturbed (control, D9) exhibited greatest spate—induced loss of algal biomass. Additionally, slow—current communities with high pre—disturbance phaeophytin content (an indicator of algal senescence) also changed most in diatom assemblage structure across the final spate. No such relationship was noted in fast current, suggesting that autogenic factors influenced communities in slow current more than those in fast. Resilience was higher in slow—current communities than in fast current, with disturbed communities reaching biomass and taxonomic structure similar to controls after 3—9 d. High resilience in slow current resulted from enhanced reproduction in some populations following spate—induced biomass reduction and presumed release from nutrient and light limitation, and low shear stress relative to fast—current channels where biomass accrual was limited by current. Interactions between disturbance timing, successional state, and habitat affect the susceptibility of epilithic algal communities to disturbance and likely influence temporal and spatial heterogeneity in stream ecosystems.

Seasonal Changes in Epipelic Diatoms Along an Intertidal Shore, Berrow Flats, Somerset

Seasonal changes in the assemblage structure of dominant epipelic diatoms were studied along a transect crossing a salt marsh, sandflat, and mudflat of an estuarine intertidal shore at Berrow Flats, Somerset, UK. Seasonal changes in cell numbers displayed different patterns in the salt marsh and sandflat/mudflat. At salt marsh sites highest numbers of individuals were recorded in summer followed by a smaller autumn growth, while in the sandflat lower numbers showed no seasonal pattern. Repeated annual patterns in the succession of taxa were not observed as environmental conditions changed at the study site with time. Measurements of salinity, pH, interstitial water content, air and soil temperature were taken together with the diatom samples. A canonical correspondence analysis was employed to relate seasonal changes in assemblage structure to measured environmental variables. Total percentage variation in the first four axes of the species/site-environmental biplots ranged between 54 and 66°. In winter, sites and species separated most significantly along gradients of salinity and levels of organic matter. In spring and autumn, interstitial water content became a more significant environmental variable. By summer steep gradients in pH, levels of organic matter, and hypersaline conditions separated sites and assemblages into more discrete groups when compared to the more even spread of points in the other seasons. The results indicate that different combinations of environmental variables influence diatom assemblage structure seasonally.

Some factors affecting distribution of diatom assemblages in Pyrenean springs

SUMMARY. The composition and abundance of diatom assemblages were studied together with physiographical and physicochemical variables in twenty‐eight springs in the Central Pyrenees during the period 1987–88. Characteristic groupings of diatom taxa are revealed by Principal Components Analysis. One group, made up of assemblages of the taxa Navicula cincta, Caloncis spp. and Niizschia elliptica, is characteristic of springs with waters of high ionic strength. Certain diatom taxa are characteristic of hard water springs, either in quiet waters (Denticula tenuis, Achnanthes minutissima, Eunotia spp.) or fast flowing ones (Fragilaria spp., Diatoma hiemale). Other taxa are representative of relatively quiet, softwater springs: Anomoeoneis bracfiysira, Tabellaria flocculosa, Aulacoseira distans and Fragilaria vaucheriae. Five different spring types were identified, with respect to diatom assemblages, using discriminant analysis. The first consisted of high mountain springs with cold, fast waters and low ionic strength. The second group, distributed throughout the Pyrenees, had similar environmental characteristics to the first group but with intermediate water velocity and slightly higher mineral content. The third contained springs in calcareous regions of the Pyrenees, mainly slow‐flowing and with hard waters. The fourth was composed of softwater springs, whilst the fifth consisted of two springs which were subject to stressful conditions (limitation of light, abundance of nitrates or high salinity). Ionic strength and current velocity appeared to be the dominant environmental factors affecting diatom distribution in Pyrenean springs. These factors also seem to determine diatom communities in some other geographical areas. In some springs, however, peculiar environmental factors (dim light, salinity, and high temperature) affect the structure of diatom assemblages.

THE MIGRATORY BEHAVIOUR OF DIATOM ASSEMBLAGES IN A LABORATORY TIDAL MICRO-ECOSYSTEM EXAMINED BY LOW TEMPERATURE SCANNING ELECTRON MICROSCOPY

Low temperature scanning electron microscopy (LTSEM) was superior to freeze-drying and ambient SEM in preserving the fine structure of diatom assemblages inhabiting cohesive sediments. The accumulation of diatoms at the surface of the sediment, maintained in a tidal micro-ecosystem, was examined for the first time using LTSEM techniques. LTSEM revealed a low standing assemblage present on the sediment surface when exposed before dawn. There was a linear increase in the numbers of diatoms at the surface when photon flux densities increased above 0.5 μEm−2s−1. The first diatoms to migrate to the surface were species of Navicula and Nitzschia. After 4h there was a synchronous appearance of large numbers of Scoliopleura tumida at the surface. Data on the depth distribution of diatoms in the sediment, derived from sediment samples that had been frozen and then fractured, support the hypothesis that light is the factor controlling the onset of diatom migration and that different diatoms have different threshold...

The structure of benthic Diatom assemblages: A preliminary account of the use and evaluation of low-temperature scanning electron microscopy

Diatom assemblages on the surface of fine estuarine sediments have, for the first time, been examined undisturbed by a novel application of low-temperature SEM. The technique allows the visualization of surface diatoms and determination of the composition and orientation of the exposed assemblages at any one time. In a laboratory experiment, the total number of diatoms counted was similar to that obtained using the standard lens tissue technique. Although identification was more accurate using the light microscope, many different species could be readily distinguished with low-temperature SEM. An index of similarity analysis suggested a difference in the composition of the assemblages measured by the two techniques. This difference was considered to be due to the selectivity of the lens tissue technique. Further avenues of research in this subject using low-temperature SEM are briefly outlined.

Studies on Lake Erie's littoral algae; Host specificity and temporal periodicity of epiphytic diatoms

Substratum specificity and temporal periodicity of the attached diatom flora upon three aquatic vascular plants and an artificial substratum were examined in three Lake Erie marshes. No qualitative or quantitative specificity for substrata was observed. Variability of diatom assemblage structure within replicate samples of a particular substratum type was as great as, or greater than, variability between substrata. Diatom assemblages upon dowel rod displayed a mid to late summer density maximum. Variability of density maxima upon natural substrata was attributed to different growth rates of the host macrophytes. Diatom assemblages within each sampling site possessed a distinct temporal periodicity indicating that factors affecting diatom growth are heterogeneous in distribution throughout Lake Erie's littoral zone.

Effects of thermally elevated discharges on the structure and composition of estuarine periphyton diatom assemblages

Periphyton diatom assemblages in the saline cooling water canal system of the Oyster Creek Nuclear Generating Station were investigated for a twelve month period from December 1975 to December 1976. Uniform substrate samplers were placed in the intake canal water and the heated discharge canal water. These remained for 30 days before recovery to allow representative periphyton assemblages to develop. The structure and composition of the diatom assemblages in the two canals were compared. Thermal responses of individual taxa were difficult to identify; however, when the structure of the assemblages in the two canals were compared the effects of the thermally elevated effluent can be seen. In general, the assemblages in the heated effluent had fewer species, lower diversity indices, and greater redundancy. A degree of difference measure was used to show the differences between the assemblages at the two sites. Also, evidence is presented that thermal stress above a critical temperature for short periods is detrimental to the structure of the assemblages.