Navicula Gregaria Research Articles

Comparison of Metabarcoding and Microscopy Methodologies to Analyze Diatom Communities in Five Estuaries Along the Southern Coast of the Korean Peninsula

The study of microalgal communities is critical for understanding aquatic ecosystems. These communities primarily comprise diatoms (Heterokontophyta), with two methods commonly used to study them: Microscopy and metabarcoding. However, these two methods often deliver different results; thus, their suitability for analyzing diatom communities is frequently debated and evaluated. This study used these two methods to analyze the diatom communities in identical water samples and compare the results. The taxonomy of the species constituting the diatom communities was confirmed, and both methods showed that species belonging to the orders Bacillariales and Naviculales (class Bacillariophyceae) are the most diverse. In the lower taxonomic levels (family, genus, and species), microscopy tended to show a bias toward detecting diatom species (Nitzschia frustulum, Nitzschia inconspicua, Nitzschia intermedia, Navicula gregaria, Navicula perminuta, Navicula recens, Navicula sp.) belonging to the Bacillariaceae and Naviculaceae families. The results of the two methods differed in identifying diatom species in the communities and analyzing their structural characteristics. These results are consistent with the fact that diatoms belonging to the genera Nitzschia and Navicula are abundant in the communities; furthermore, only the Illumina MiSeq data showed the abundance of the Melosira and Entomoneis genera. The results obtained from microscopy were superior to those of Illumina MiSeq regarding species-level identification. Based on the results obtained via microscopy and Illumina MiSeq, it was revealed that neither method is perfect and that each has clear strengths and weaknesses. Therefore, to analyze diatom communities effectively and accurately, these two methods should be combined.

Benthic diatom diversity in microtidal mangrove estuaries

Mangrove habitats support taxonomically diverse benthic communities, yet their effects on microphytobenthos remain understudied. This study investigated the benthic diatom community structure of 17 microtidal mangrove estuaries situated along the east coast of South Africa. High sediment organic content (≤ 18.1 %) and clay fraction (≤ 17.5 %) measured in the Avicennia marina and Rhizophora mucronata habitats favoured diverse communities (H′ > 3) and the presence of unique benthic diatom species such as Gyrosigma balticum. The habitat complexity and stabilisation provided by the mangrove forests served as microrefugia for colonisation of benthic diatoms. Taxa displayed a broad range of nutrient tolerance, with some nutrient tolerant species (e.g., Halamphora acutiuscula, Navicula clausii, Navicula gregaria, and Navicula radiosa) dominating the communities in the Mbashe and Mnyameni estuaries. The presence of these nutrient tolerant taxa in relatively pristine systems serves as an early warning for possible anthropogenic nutrient enrichment.

Revealing Interactions between Temperature and Salinity and Their Effects on the Growth of Freshwater Diatoms by Empirical Modelling

Salinization and warming are of increasing concern for freshwater ecosystems. Interactive effects of stressors are often studied in bifactorial, two-level experimental setups. The shape of environmental reaction norms and the position of the “control” conditions along them, however, can influence the sign and magnitude of individual responses as well as interactive effects. We empirically model binary-stressor effects in the form of three-dimensional reaction norm surfaces. We monitored the growth of clonal cultures of six freshwater diatoms, Cymbella cf. incurvata, Nitzschia linearis, Cyclotella meneghiniana, Melosira varians, Ulnaria acus, and Navicula gregaria at various temperature (up to 28 °C) and salinity (until the growth ceased) shock treatments. Fitting a broad range of models and comparing them using the Akaike information criterion revealed a large heterogeneity of effects. A bell-shaped curve was often observed in the response of the diatoms to temperature changes, while their growth tended to decrease with increasing electrical conductivity. C. meneghiniana was more tolerant to temperature, whilst C. incurvata and C. meneghiniana were the most sensitive to salinity changes. Empirical modelling revealed interactive effects of temperature and salinity on the slope and the breadth of response curves. Contrasting types of interactions indicates uncertainties in the estimation by empirical modelling.

Diatom communities and ecological status classification in the upper Po River basin

One of the main challenges in river management is the setting of nutrient thresholds that support good ecological status, which is the main objective to achieve for the European member states. This is a complex process, which needs an accurate analysis of the data collected so far for the ecological classification of rivers belonging to different typologies. We analysed the data of the multiannual monitoring concerning diatoms and nutrients in the upper Po River (NW Italy) with the aim of exploring the response of diatom community in terms of species composition, ecological guilds and indices. We considered data of 390 samples, of which 2/3 belonging to the “Central macrotype” (i.e. lowland stretches) and 1/3 to “Alpine siliceous”. We performed a Principal Coordinate Analysis to detect community patterns with respect to water chemical classification and macrotypes highlighting species and ecological guilds characteristic of samples along a water quality gradient. We then performed a partial RDA to focus on the role of environmental and spatial factors in shaping the diatom community in each of the two macrotypes. Finally, we investigated the concordance between the Italian normative indices ICMi (for diatoms) and LIMECO (a chemical index of water quality). We found significant differences in the diatom communities of the two macrotypes and in their response to water quality and to spatial factors. Communities resulted as much more uniform in sites with a low water quality, with characteristic species such as Navicula gregaria, Nitzschia palea and Sellaphora nigri. On the other hands, moderately disturbed sites (in terms of trophic level) were characterised by the highest guild diversity. The RDA confirmed the importance of spatial factors in shaping the diatom assemblages, especially in Alpine streams where the physical barriers may condition species dispersion. The comparison between the two normative indices highlights that the correspondence in the classification is achieved in the 57% (Alpine macrotype) and 43% (Central macrotype) of samples. According to our findings, we suggest the revision of the ICMi, both class boundaries and reference value. In addition, we recommend to lower LIMECO threshold for total phosphorus: indeed, several studies have shown significant changes in the diatom community composition starting from very low values (below the current LIMECO threshold, i.e. 50 µgL-1). Moreover, the extension of our study to the whole Po River basin will complete our knowledge of species not yet included in the diatom indices and of the community response to nutrient levels also in other macrotypes.

Response of epilithic diatom assemblages to weir construction on the Nakdong River, Republic of Korea

In South Korea, sixteen multifunctional weirs were constructed on four major rivers (Han, Nakdong, Geum, Yeongsan) from 2009 to 2012. Hydrological changes resulting from weir construction altered the physical, chemical, and biological characteristics of natural large rivers. We aimed to investigate the variation in epilithic assemblages responding to changes in physicochemical, meteorological, and hydrological variables in the eight weir (lentic) sections of the Nakdong River, which is the longest river in South Korea. Sampling was conducted to determine the influence of environmental parameters on community composition, and to monitor the seasonality of environmental and biological patterns.A total of 173 taxa including 26 major epilithic diatom taxa were identified. Among them, nutrient-tolerant diatom species were characterized by Cyclostephanos dubius, Navicula gregaria, Fragilaria crotonensis, Aulacoseira granulata, Melosira varians, Navicula minima, Nitzschia amphibia, Amphora pediculus, and Nitzschia inconspicua. These species were primarily dominant in the midstream and downstream weir sections of the river adjacent to urban-industrial land use zones relating to nutrient enrichment. Moreover, preference for longer hydraulic retention time (HRT) was identified in C. dubius, N. gregaria, and F. crotonensis, in addition to its tolerance for high nutrition. Redundancy analysis based on the relative abundance of diatom taxa demonstrated that the diatom assemblage composition was closely related to total nitrogen (TN), total phosphorus (TP), phosphate phosphorus (PO4-P), electrical conductivity, precipitation, water discharge, and HRT. Variation partitioning analysis further revealed that hydrological-meteorological variables play a synergistic role in enhancing the function of physical and chemical variables in structuring diatom assemblage composition soon after weir construction. A generalized linear model using the Akaike’s information criterion also suggests that the trophic diatom index (TDI) could indicate the water quality status in the weir sections, as the TDI was positively correlated (p < 0.05) with nutrients (TN and PO4-P). Our findings inform the applicability of using the TDI for efficiently monitoring and managing the water quality of consecutive weir sections of the Nakdong River and the weir systems of other rivers in temperate regions.

Sezonske varijacije diverziteta i sastava silikatnih algi reke Crnice

The aim of this study was determining and comparing diatom diversity and dominant taxa in 4 seasons from the Crnica River. A total of 170 diatom taxa, 24 among them as dominant ones were recorded. The highest diversity expressed in number of taxa was observed in the spring (139) and the lowest in the autumn season (94). The most of 45 the best fitted taxa on the CCA ordination diagram are recorded in more than two seasons, often in all four seasons. One group of taxa (e.g. Hanaea arcus, Meridion constrictum, Navicula gregaria, N. lanceolata) was characteristic only for spring and other for winter season (e.g. Gomphonema innocens, G. lagenula, Stauroneis phoenicenteron, Nitzschia oligotraphenta). There were no taxa exclusively recorded only in summer and autumn.

Research into the Epipelic Diatoms of the Meriç and Tunca Rivers and the Application of the Biological Diatom Index in Water Quality Assessment

The Meric River is one of the longest rivers of the Balkans and the Tunca River is the most significant tributary of the Meric River. In the present study, the epipelic diatoms of the Meric and Tunca Rivers were investigated and the water quality was evaluated from a physicochemical and biological perspective. Epipelic (EPP) diatoms were collected from the middlestream of the Meric River (Edirne Province of Turkey) and from the downstream of the Tunca River (before emptying into the Meric River) and certain physicochemical parameters including dissolved oxygen (DO), oxygen saturation (OS), pH, electrical conductivity (EC), total dissolved solids (TDS), salinity, turbidity, nitrate (NO3), nitrite (NO2), ammonium (NH4), phosphate (PO4), sulphate (SO4), chemical oxygen demand (COD) and oxidation-reduction potential (ORP) were measured during the field studies. The Biological Diatom Index (IBD) was used to determine the trophic status of the Meric and Tunca Rivers in terms of EPP diatoms, and Cluster Analysis (CA) was applied to the detected biological data in order to classify the identified diatom taxa in terms of their dominance in the system. According to the results of the physicochemical analysis, the Meric and Tunca Rivers have I. – II. Class water quality in terms of dissolved oxygen, oxygen saturation, pH, EC, TDS, NO3, NH4, SO4 and COD parameters; and have III. – IV. Class water quality in terms of NO2 and PO4 parameters. 24 diatom species were recorded in the Meric River by counting a total of 403 valves and a total of 19 diatom species were identified by counting a total of 409 diatom valves in the Tunca River. Cyclotella atomus Hustedt, Navicula gregaria Donkin, Nitzschia palea (Kutzing) W.Smith and Nitzschia subacicularis Hustedt, were determined as the most dominant species in the Meric River and Navicula erifuga Lange-Bertalot, Navicula gregaria Donkin and Navicula rostellata Kutzing were recorded as the most dominant taxa in the Tunca River. According to the result of the IBD, the investigated rivers were found to be in a meso-eutrophic state and according to the results of CA, three statistical clusters were formed for both rivers, and were named as “dominant taxa”, “frequent taxa” and “rare taxa”.

Diatoms as an indicator for tile drainage flow in a German lowland catchment

BackgroundThe separation of runoff components within a model simulation is of great importance for a successful implementation of management measures. Diatoms could be a promising indicator for tile drainage flow due to their diverse preferences to different aquatic habitats. In this study, we collected diatom samples of 9 sites (4 tile drainage, TD, and 5 river sites, Ri) in a German lowland catchment at a weekly or biweekly time step from March to July 2013 with the aim of testing the suitability of diatoms for tile drainage flow, which is typical for lowland catchment.ResultsPlanothidium lanceolatum, Ulnaria biceps, and Navicula gregaria dominated in TD sites with relative abundances of 22.2, 21.5, and 10.9%, respectively. For Ri sites, the most abundant species was Navicula lanceolata (20.5%), followed by Ulnaria biceps (12.9%), Cyclotella meneghiniana (9.5%), and Planothidium lanceolatum (9.3%). Compared with Ri sites, TD had a lower diatom density, biomass, species richness, and percentage of Aquatic/Riparian diatoms (AqRi%). However, the proportion of Riparian diatoms (RiZo%) increased at TD. Indicator value method (IndVal) revealed that the two groups (Ri and TD) were characterized by different indicator species. Fifteen taxa, including Cocconeis placentula, Cyclotella meneghiniana, N. lanceolata, and U. biceps, were significant indicators for Ri sites. Planothidium lanceolatum, Achnanthidium minutissimum, and Navicula gregaria were significant indicators for TD sites.ConclusionA pronounced variation was found in the species lists of diatom community between Ri and TD water body types associated with different indicator species. With respect to hydrograph separation, these findings highlight the suitability of diatoms as an indicator for tile drainage flow. However, spatial and temporal variations of diatoms should be considered in future surveys.

Geothermal Diatoms: Seasonal Variability in the El Tatio Geothermal Field (Altiplano, Chile)

Diatom floras were examined in a high-altitude geothermal field, 4200 - 4500 m (29°19'S 68°W'), located in the Central Andean dry Puna ecoregion or southern Altiplano. These locations include hostile environments subjecting living organisms to extreme conditions. The aim of the present study was to investigate the spatial patterns and describe the response of diatom assemblages to differences in physical and chemical variables. Different shallow (<10 cm) aquatic systems with variable chemical and physical conditions (fumaroles, freshwater-saline rivers and swamps) were studied seasonally during 2011-2012. The conductivity exhibited high variability (360 to 18340 μS cm-1) among the systems studied, temperature was lower in rivers and swamps (6.8°C - 10°C) and high in fumaroles stations (30°C - 37.5°C), and pH was lower in fumaroles than freshwater systems (3.25 to 8.97). Statistical analyses suggest that the diatoms cluster into three major groups. The most common taxa include: Achnanthidium exiguum (Grunow) Czarnecki, Cocconeis placentula var. lineata (Ehrenberg) Van Heurck, Eolimna minima (Grunow) Lange-Bertalot, Staurosirella pinnata (Ehrenberg) Williams and Round, Navicula gregaria Donkin, Nitzschia inconspicua Grunow, Nitzschia palea (Kutzing) Smith, Nitzschia perminuta (Grunow) Peragallo, and Planothidium lanceolatum (Brebisson ex Kutzing) Lange-Bertalot. As expected, the 20 to 200 μm-size fraction contained the highest numbers of diatom taxa (53 species), although an unexpectedly high number (47 species) were also found in the smaller 5 to 20 μm-size fraction, more associated to fumaroles and saline systems. The 180 to 2000 μm size fraction contained only two species, including rosette-forming diatom Ulnaria ulna (Nitzsch) Compere, and the unicellular species Surirella chilensis Janisch, both species exclusively reported in freshwater systems. Canonical correspondence analysis (CCA) and Monte Carlo permutation tests showed clear correlations between species, conductivity, TP (total phosphorous), NO3- , HO3- , Mg2+, temperature and dissolved oxygen (DO). The gradient of ionic composition values explaining most variation in diatom assemblages ranged from waters dominated by Ca2+ and SO4- to waters with higher proportions of Na+, K+, F-, Li+, Mg2+ and Cl-. Other factors include substrate type, presence of macrophytes, current velocity and other local environmental conditions. The results presented here enhance our understanding of diatom richness/composition in hostile environments from a high-altitude arid and semi-arid geothermal region.

The use of diatoms to assess the water quality in the Wisłoka River in the town of Dębica and the surrounding area

Abstract The objective of this work was to examine the water quality using three diatom indices SPI, GDI and TDI. The material for the study was collected during four seasons from autumn 2010 to summer 2011, from four sampling sites located on the Wisłoka River, in the town of Dębica and the surrounding area. The Wisłoka at all selected sites was characterized by alkaline or close to neutral pH (pH 6.5-7.7). Electrolytic conductivity ranged from 364 to 480 µS cm-1. The Wisłoka at the selected sites in the urban area and in the surrounding areas was characterized by high diatom species richness. The total of 238 taxa from 53 genera were recorded, of which the most numerous were: Nitzschia (44), Navicula (33) and Gomphonema (12). Achnanthidium minutissimum var. minutissimum, Amphora pediculus, Navicula gregaria, N. lanceolata, and Nitzschia dissipata ssp. dissipata were usually the dominant species. Chemical parameters indicated very good quality of water. However, the diatom indices used to assess the water quality, classified the studied water into a group corresponding to quality class III or IV.

Diatom diversity and water quality of a suburban stream: a case study of the Rzeszów city in SE Poland

Abstract The aim of this work was to investigate the diversity of diatom assemblages developed in the Przyrwa stream, to assess water quality based on benthic diatoms and to make an attempt at the identification of physicochemical factors having the greatest impact on the differentiation of diatom assemblages. Studies were conducted in 2011-2012 on the Przyrwa stream, a left-side tributary of the Wisłok River flowing through the city of Rzeszów and with its spring section located on the borders of the city. A total of 259 diatom taxa were identified in the Przyrwa stream during three studied seasons. At all investigated sites, the most abundant population consisted of Ulnaria ulna (Nitzsch) Compère, Cocconeis pediculus Ehrenb., Achnanthidium minutissimum (Kütz.) Czarnecki var. minutissimum, Navicula gregaria Donkin, Planothidium frequentissimum (Lange-Bert.) Lange-Bert., P. lanceolatum (Brébisson) Lange-Bert., Navicula lanceolata (C. Agardh) Ehrenb., Amphora pediculus (Kütz.) Grunow, Eolimna minima, (Grunow) Lange-Bert., Melosira varians C. Agardh and Cyclotella meneghiniana Kütz. Based on IPS (Specific Pollution Sensitivity Index) and GDI (Generic Diatom Index) indices, the ecological status of the Przyrwa stream was assessed as moderate to poor (mostly III-IV class of water quality), while the TDI (Trophic Diatom Index) index indicated a poor to bad ecological status (mainly IV-V class of water quality).

Long term urban impacts on the ecological status of a lowland river as determined by diatom indices

This study determined changes in the ecological status of a lowland river under the impact of an urban agglomeration after modernizing the wastewater management. For 174 years the Ner River was loaded with pollution from expanding industry. Construction of the Group Sewage Treatment Plant (GOŚ) in 1994 and its subsequent modernization should have improved the water quality. After 20 years of proper sewage treatment the ecological status of the river hasn't improved. Study sites were established on the river above and below sewage disposal from GOŚ, and the ecological status was assessed on the basis of benthic diatoms. Diatom indices: IO, GDI, IPS were calculated in order to determine the ecological status and water quality. Hierarchical cluster analysis and multivariate analysis of diatom assemblages were used to reveal differences of the study sites. It was revealed that the river is divided into two sections: the first is above the sewage disposal and the second is below it. In the first section, domination of species sensitive to organic pollution Meridion circulare and Ulnaria ulna was noted, while in the second section species resistant and tolerant to organic pollution, Hippodonta capitata and Navicula gregaria, were noted. The ecological status at the first section was moderate to poor, while at the second it was poor to very poor. The division of the urban river into two sections with different ecological status stems from the history of water management. The present location of the GOŚ outflow served in the past as a dump of untreated sewage from the industry of the Łódź Agglomeration. Development of the city led to the degradation of the ecosystem. Modernization of wastewater management did not reverse the degradation of the river. The persistence of accumulated industrial pollution in sediments caused by the long-term impact of urban agglomeration almost completely destroyed the ecosystem of the river.

Aşağı Melet Irmağı (Ordu, Türkiye)’nda Su Kalitesinin Göstergesi Olan Epipelik Diyatomeler

Phytobenthos includes bioindicator species and is widely used in water ecology studies. Diatoms constitute one of the most important groups of phytobenthos in streams. In particular, these organisms are good indicators in investigations related with determining of water quality in medium and long time. In this study, the epipelic diatom flora of the lower part of River Melet were investigated, the most important source of drinking water in Ordu city. The examination was performed periodically in March-November 2012 and total of 56 taxa were identified. Cymbellales (14 taxa) and Naviculales (16 taxa) ordo constituted 54% of diatom diversity. These were followed by Fragilariales (16%, 9 taxa) Bacillariales (14%, 8 taxa) Surirellales (9%, 5 taxa) Achnanthales (3%, 2 taxa) Eunotiales (2%, 1 taxa) and Melosirales (2%, 1 taxa), respectively. Diatome vulgaris, Melosira varians, Navicula gregaria, N. tripunctata and Nitzschia sigmoidea species were recorded as widespread and intense in the epipelic communities. These species are usually tolerant to organic pollution and are found in β-α- mesosaprobic conditions. According to the obtained results, the lower part of the Melet River has character from pollution towards moderate pollution. In other words, it has II-III. class water quality.

Response of planktonic cyanobacteria and periphyton assemblages to physicochemical properties of stormwater in a shallow urban lake

The aim of this study was to determine the response of planktonic cyanobacteria and periphyton assemblages (periphytic algae in the separator pipes, epilithon and epiphyton) to lamella separator-treated stormwaters in urban Lake Jeziorak Maly in 1997-2003 and 2005. Relationships between periphyton and phytoplankton assemblage and water chemistry variables were analyzed by calculating the Spearman’s rank correlation coefficient, and then with canonical correspondence analysis (CCA). The basic factors favouring the cyanobacterial growth were water temperature and iron, while high chloride concentration limited their development. Cyanobacterial abundance recorded at the separators was half that of the pelagic zone because of a lower water temperature and higher Cl concentration, indicating high algal sensitivity to the considerable velocity and disturbances caused by stormwater effluents. Higher silicon and calcium concentrations at the separators and orthophosphates at sites with stones and gravel showed connection with the growth of diatoms, especially Fragilaria leptostauron var. martyi, Diatoma vulgaris and Navicula gregaria. The richness of the dominant cyanobacteria, Aphanizomenon gracile and Limnothrix redekei, was related with the water temperature, conductivity, pH, and TN. Similarities in the periphyton dynamics in separator pipes and epilithon between the years covered by the study suggest significant influence of separator-treated stormwater on these assemblages, in contrast to epiphyton and phytoplankton in the pelagial zone, where these waters had limited influence.

Establishment of equilibrium states and effect of disturbances on benthic diatom assemblages of the Torna-stream, Hungary

This paper analyses the establishment of equilibrium states in relation to natural disturbances in epilithic diatom assemblages. Sterilized limestone bricks were exposed between April 2008 and 2009 in the Torna-stream and were removed one by one on every third day in the first month and then weekly until May 2010. Physical and chemical parameters were measured on the field and in laboratory. Equilibrium states were restricted to three separate months: July 2008, May and January 2009 taking the consistence of biomass (chlorophyll-a) into consideration. Cocconeis placentula sensu lato, Fragilaria vaucheriae, Gomphonema parvulum, G. olivaceum, Navicula gregaria, N. lanceolata, Nitzschia linearis, and Surirella brebissonii took part in the equilibrium assemblages, two of which dominated by a single species. Analyses of environmental constancy during equilibrium phases allowed concluding that resilience of a developed equilibrium phase may ensure biotic constancy even though the underpinning environmental background fluctuates at higher amplitude. The conclusions of our study on attached stream diatom assemblages are similar to those found for temperate lakes: equilibrium states are rare, unpredictable, ephemeral, may occur both in relatively stable and strongly fluctuating environments, and are mostly characterized by monodominance, but contrary to phytoplankton, their establishment requires a longer time to develop corresponding to differences in generation times.

Tidal Channel Diatom Assemblages Reflect within Wetland Environmental Conditions and Land Use at Multiple Scales

We characterized regional patterns of the tidal channel benthic diatom community and examined the relative importance of local wetland and surrounding landscape level factors measured at multiple scales in structuring this assemblage. Surrounding land cover was characterized at the 100, 250, 1,000 m, and watershed buffer scales. Tidal channel benthic diatom communities were characterized by high species richness, abundance of rare species, and an abundance of species characterized as meso-eutraphentic and eutraphentic. The number of species per site ranged between 21 and 60 (mean ± standard deviation 43.5 ± 9.4). Abundant and frequently occurring taxa included Planothidium delicatulum, Navicula gregaria, and Amphora coffeaeformis. The tidal channel benthic diatom community was most strongly correlated with variables related to human disturbance at all scales surrounding the wetland and not with any tidal channel water quality parameter, including salinity. Furthermore, developed and impervious surface land covers within the 100 and 250 m buffers were more strongly correlated with the diatom assemblage than these covers at larger spatial scales. Species richness and Shannon diversity index were both negatively correlated with the amount of wetland and mudflat surrounding the sites. Of secondary importance in structuring the diatom assemblage were sediment nitrogen and phosphorus concentrations in wetlands immediately surrounding the tidal channels. The sensitivity of the tidal creek benthic diatom assemblage to both wetland and landscape level factors indicates that it might be a useful bioindicator of human disturbance to tidal wetland ecosystems.

Effects of varying pH on the growth and physiology of five marine microphytobenthic diatoms isolated from the Solthörn tidal flat (southern North Sea, Germany)

:Diatoms inhabiting intertidal flats are subject to strongly changing environmental conditions, which have a great influence on the oxygen, sulphide and pH gradients in the sediments. In previous studies, variations in pH in the range from 6.5 to 8.5 had only minor effects on the growth of benthic diatoms. In order to determine the physiological responses of marine benthic diatoms to pH changes, cultures of Amphora graeffii, Navicula gregaria, Navicula phyllepta, Nitzschia epithemoides and Pinnularia ambigua (=Biremis ambigua) isolated from the Solthörn tidal flat (lower Saxony, southern North Sea) were used to study the effect on growth rates and biochemical compositions at different pH values (7.25, 7.5, 7.75, 8.0, 8.25, 8.5 and 8.75). During short- (6 h) and long-term exposures (30 d), the composition of free amino acids and the accumulation of polyols, saccharides, quaternary ammonium compounds and β-dimethylsulphoniopropionate (DMSP) were determined. While growth rates of the five tested diatom taxa during short-term exposure to experimental pH were only hardly affected, long-term exposure to experimental pH led to decreasing growth rates in all tested species. Significant differences were found in physiological responses to pH treatments of the species tested. Growth in terms of chlorophyll a and protein contents showed decreasing values also after short-term exposure to experimental pH. Furthermore, at experimental short-term pH treatments, species accumulated higher levels of proline, glycerol, galactose and mannose, while only three out of the five tested taxa also accumulated high amounts of the quaternary ammonium compounds homarine and glycine betaine as well as DMSP. The physiological responses to long-term exposure to experimental pH showed distinct differences in the accumulation of proline, serine, taurine, glycerol and other compatible solutes. In conclusion, significant differences in osmolyte compositions were found in the five diatom species exposed to different pHs, suggesting specific intracellular acclimation processes. These responses provide a possible explanation for the insensitivity to short-term pH variations.

ECOLOGICAL CHARACTERIZATION OF DIATOM COMMUNITIES IN THE WISŁOK RIVER WITH APPLICATION OF THEIR INDICATORY ROLE TO THE EVALUATION OF WATER QUALITY

Research conducted in 2007–2008 on eight sites designated along the Wislok River showed great diatoms diversity – indicated a total of 401 diatom taxa. Achnathidium pyrenaicum, A. minutissimum var. minutissimum, Navicula gregaria, N. lanceolata, Amphora pediculus, Cyclotella meneghiniana, Gomphonema olivaceum var. olivaceum, Nitzschia dissipata ssp. dissipata were most frequent. Based on diatomaceous indices IPS, GDI and TDI has been shown that the upper part of Wislok had a high and good ecological status. However, the middle and lower section of river was characterized by moderate and poor ecological status, on the base of the IPS and GDI indices (III and IV class). TDI value indicated bad water quality (V class) in the middle and lower section.

Structure and diversity of intertidal benthic diatom assemblages in contrasting shores: a case study from the Tagus estuary(1).

The structure of intertidal benthic diatoms assemblages in the Tagus estuary was investigated during a 2-year survey, carried out in six stations with different sediment texture. Nonparametric multivariate analyses were used to characterize spatial and temporal patterns of the assemblages and to link them to the measured environmental variables. In addition, diversity and other features related to community physiognomy, such as size-class or life-form distributions, were used to describe the diatom assemblages. A total of 183 diatom taxa were identified during cell counts and their biovolume was determined. Differences between stations (analysis of similarity (ANOSIM), R=0.932) were more evident than temporal patterns (R=0.308) and mud content alone was the environmental variable most correlated to the biotic data (BEST, ρ=0.863). Mudflat stations were typically colonized by low diversity diatom assemblages (H'~1.9), mainly composed of medium-sized motile epipelic species (250-1,000μm(3) ), that showed species-specific seasonal blooms (e.g., Navicula gregaria Donkin). Sandy stations had more complex and diverse diatom assemblages (H'~3.2). They were mostly composed by a large set of minute epipsammic species (<250μm(3) ) that, generally, did not show temporal patterns. The structure of intertidal diatom assemblages was largely defined by the interplay between epipelon and epipsammon, and its diversity was explained within the framework of the Intermediate Disturbance Hypothesis. However, the spatial distribution of epipelic and epipsammic life-forms showed that the definition of both functional groups should not be over-simplified.

Sediment Diatom Species and Community Response to Nitrogen Addition in Oregon (USA) Estuarine Tidal Wetlands

Sediment microalgae play an important role in nutrient cycling and are important primary producers in the food web in Pacific Northwest estuaries. This study examines the effects of nitrogen addition to benthic microalgae in tidal wetlands of Yaquina Bay estuary on the Oregon coast, USA. Liquid nitrogen fertilizers (0, 0.2, 0.5, and 1.0 gN/m2/wk during the first year of the study, and increased to 0, 15.6, 62.5, and 156 gN/m2/wk during the second year of the study) were applied weekly to four salt marshes in Yaquina Bay for two summers (2009 and 2010). Diatom species and community parameters were analyzed in response to nitrogen addition in early and late summer 2010. Nitrogen addition (N) had a significant effect on species composition and community parameters. Amphora spp. and Nitzschia palea were more dominant with higher N, while Navicula gregaria and Navicula phyllepta were more dominant with lower N. Species diversity and richness were significantly higher (p < 0.05) with lower N (3.1 ± 0.1; 40.0 ± 3.3) compared with higher N (2.4 ± 0.5; 34.5 ± 3.0). NMDS ordination displayed shifts in overall diatom assemblage with time and with N. Results suggest the microalgal communities are limited by nitrogen levels and therefore may be susceptible to changes in nitrogen loading to these systems.