Exudates from Gracilaria chilensis stimulate settlement of epiphytic ulvoids

In the diatom communities of the Vanishing and Ornithologist Creek 74 taxa were found. Most of the taxa have a cosmopolitan range and are resistant to various environmental stresses. For example, Achnanthes lanceolata var. lanceolata, is found in all types of waters and in several ecological conditions. Achnanthes delicatula ssp. delicatula, Nitzschia frustulum, N. capitellata, Navicula mutica, and N. gregaria develop both in fresh and brackish waters. Some of the organisms also settle in terrestrial environments. Navicula atomus, N. mutica, Pinnularia borealis, and Hantzschia amphioxys are common soil algae. Navicula digitulus, N. contenta, N. cohnii and Achnanthes coarctata also live in an aerial environment. Navicula atomus is well developed in eutrophic waters and Nitzschia capitellata can tolerate a high level of pollution, while Nitzschia gracilis, Fragilaria capucina, and F. alpestris appear both in oligotrophic, and enriched waters. Stenotopic ecological features are shown by Achnanthes marginulata and Navicula digitulus — known from the Alps and the North, and Navicula muticopsis characteristic for Antarctic and Subantarctic.The index of diatom biomass, usually of low and medium value, was highest in the area of possible impact by a penguin colony.     

Structural changes in the benthic diatom community along a eutrophication gradient on a tidal flat

In the mud- and sandflat region of the outer Königshafen off List on Sylt, the effects of the outflow from a sewage treatment plant on the benthic diatom flora were investigated. The spectrum of shapes, biomass, and diversity was determined in relation to the concentrations of phosphate, silicate, and nitrogen compounds in the overlying and pore water. The biomass increased with the available quantities of nutrients, while the diversity reached a maximum at the intermediate concentrations. Every different set of nutrient concentrations is characterized by a different diatom community. Slight inputs of nutrients led to changes in the relative abundances of forms typical of the habitat. Moderate concentrations permitted the species that are normally present in winter to occur in summer as well. In the strongly eutrophic region, nutrient-loving species that are not locally present under normal conditions formed nearly monospecific populations. A relatively constant input of nutrients almost eliminated the seasonal variations. Navicula gregaria, Nitzschia sigma, and Nitzschia tryblionella proved to be tolerant of pollution, while the genera Achnanthes and Amphora were typical in the nutrient-poor regions. The nutrient budget, particularly that of the nitrogen compounds, was found to be predominant among the physical and chemical factors.     

The effects of dissolved heavy metals on attached diatoms in the Uintah Basin of Utah,U.S.A.

The relationships of diatom species to dissolved heavy metals in the streams of the Uintah Basin of Utah were studied through four seasons of 1977–1978. Niche center gradient analysis, cluster analysis and correlation analysis were performed.Achnanthes minutissima, Cyclotella meneghiniana, Cymbella minuta, Gomphonema parvulum, Navicula secreta var.apiculata, Nitzschia frustulum, Nitzschia frustulum var.perminuta, Nitzschia frustulum var.perpusilla, Nitzschia palea, andSynedra ulna appear to be indicator species of high or low heavy metal concentrations. Several other species also showed meaningful relationships to high or low heavy metal concentrations.Dept. of Physics and Astronomy, Brigham Young UniversityDept. of Physics and Astronomy, Brigham Young University     

Impact of Urban Pollution from the Hanoi Area on Benthic Diatom Communities Collected from the Red, Nhue and Tolich Rivers (Vietnam)

The effects of urban pollution from Hanoi city on the benthic diatom communities of the Nhue–Tolich river system were studied during the 2003 dry season. Benthic diatoms were allowed to grow on glass slides suspended in the water flow for 4 weeks. To reveal the relationship between water quality and diatom communities, Canonical correspondence analysis (CCA) was used on data concerning relative abundances of diatom species and environmental variables. Two diatom indices, IPS and DAIpo, were applied to evaluate water quality in the three rivers. A total of 291 diatom taxa were found in the Red, Nhue and Tolich Rivers. These were mainly cosmopolitan taxa, with some tropical, subtropical and endemic taxa. The most abundant taxa at the Red site were Aulacoseira granulata, Achnanthidium minutissimum, Encyonema minutum, Navicula recens and other halophilous taxa such as Nitzschia kurzii, Seminavis strigosa, Entomoneis paludosa, Bacillaria paradoxa. Diatom assemblages at the Tolich site consisted mainly of Nitzschia umbonata, Nitzschia palea and Eolimna minima. Diatom density ranged from 660 to 30,000 cells/cm². Environmental variables and diatom assemblage composition at all sites were significantly correlated. Two diatom indices gave similar results and indicate the Tolich River with the lowest values as a highly polluted site.     

Effects of water quality and season on diatom community structure in the Damour River,Lebanon

The diatom flora in the lower Damour River, a small coastal river in Lebanon, was studied during 1981. The study area included the Damour estuary and a tributary, the el-Hamam River. Achnanthes minutissima was the most abundant diatom in the flora. Other dominant taxa included Nitzschia dissipata and Navicula cryptocephala var. veneta in the spring and Anomoeoneis vitrea in the fall. The diatom community structure was characterized by 1 or 2 dominant taxa, a few common and many rare taxa, but the taxa in these categories varied according to season and locality. The freshwater flora had a group of 20 taxa which were widely distributed in the study area throughout the study period. These taxa, in addition to a few taxa of more restricted seasonal occurrence, were the major contributers to the flora and are characteristic of this river system. Certain aspects of the flora were resistant to change. Others were more sensitive to environmental conditions. The estuarine flora reflected brackish conditions beginning in June and extending through October.     

Can a benthic diatom community complement chemical analyses and discriminate between disturbed and undisturbed saline wetland habitats? A study of seven soda pans in Serbia

Soda pans are protected in the European Union as Natura 2000 areas in the category of “Pannonic saline steppes and marshes”. There are at least six soda pans of reference status in Serbia and only a half have strict legal protection. The number of similar, but disturbed (modified) habitats that could be reconstructed is still unknown. We conducted sampling in five natural and two disturbed soda pans aiming to compare a difference in physical and chemical water properties and benthic diatom communities. In addition, we tried to apply recently developed Diatom Index for Soda Pans (DISP) and Trait-based index (TBI) to test the applicability of taxonomic and trait-based approaches in ecological status assessment of soda pans in the southern part of the Carpathian Basin. In contrast to natural soda pans, lower pH and nutrients levels were recorded in disturbed pans. A total of 86 taxa of benthic diatoms, including 11 new for diatom flora of Serbia, were identified. A lower species richness and Shannon index was recorded in natural soda pans. Nitzschia austriaca, N. supralitorea, Navicula veneta and N. wiesneri were dominant diatoms in soda pans of the reference status. Both diatom indices were in average lower in disturbed pans, and this difference was statistically significant for DISP index. We concluded that two indices, supplemented with indicator values for some local diatom species, can be a promising tool for soda pan conservation in this part of the Carpathian Basin.

     

Diatoms as water quality indicators in the upper reaches of the Great Fish River,Eastern Cape,South Africa

This study focused on the spring-fed upper reaches of the economically important Great Fish River with the aim of determining if diatoms could be used for biomonitoring in semi-arid conditions in southern Africa. Five sites were monitored monthly from 2010 to 2012. Of the 269 diatom taxa belonging to 51 genera identified, the dominant taxa were mostly those considered to be pollution-tolerant: Amphora pediculus, Craticula buderi, Fragilaria biceps, Nitzschia frustulum, Nitzschia paleacea, Planothidium lanceolatum and Rhopalodia gibba. A number of diatom-based numerical indices were used to infer water quality, including the generic diatom index, the specific pollution sensitivity index, the biological diatom index, and percentage pollution-tolerant valves, which forms part of the UK trophic diatom index. All index scores showed the Great Fish River to be impacted, and showed significant correlations of diatom species abundance with pH, NO₃-N, electrical conductivity, NH4-N and CaCO_3. Analysis revealed EC and NO3-N as the main environmental drivers affecting diatom community composition, followed by pH and PO4-P. The percentage of diatom deformities at all sites was high, at 3.5%. Diatom indices showed the river to be impacted by decades of agricultural activity, which was confirmed by chemical water analysis. Thus diatom indices can be used for biomonitoring in semi-arid areas.     

Composition and dynamics of a highly diverse diatom assemblage in a limestone stream

The algal assemblages of a small limestone stream were studied for a year at monthly intervals. Algal standing crop was permanently high (mean concentration of 158 mg Chl-a · m^–2), but it reached the maximum values in spring and summer. Diatoms were dominant in the algal assemblages throughout this time, and more than one hundred species were recorded during the survey. Most of them are characteristic of hard waters, but others, mainly occurring in summer, have been observed elsewhere in moderately halophile waters.A striking succession was observed in the diatom assemblage in the stream in each season. This succession, with a maximum in summer, was mainly related with the lessening in flow and the increase in water mineralization. Moreover, the diversity of the samples increased sharply from April 1982 to July 1983. In fact, a progressive increase in salinity tolerant species could be observed from winter and spring to summer. Nitzschia sociabilis, Navicula gregaria, Navicula lanceolata and Gomphonema olivaceum were the most abundant species in winter, whereas Achnanthes minutissima reached its maximum in spring and Navicula schroeterii, Nitzschia thermaloides and Cyclotella meneghiniana were some of the most abundant in summer.     

上海市滩涂夏季底栖硅藻初步研究

报道了上海市夏季滩涂底栖硅藻的种类组成和生态分布的情况。样品于2005年8月从7个站点中采集,经处理、镜检观察,从中鉴定出硅藻98个分类单位,包括种、变种和变型,分别隶属于2纲7目10科31属。舟形藻属(Navicula)最多,共发现15个分类单位;其次为菱形藻属(Nitzschia),有10个分类单位。其中Cyclotella meneghiniana,Gyrosigma spencerii,Surirella ovata为优势种,Fragilaria capucina,Gyrosigma attenuatum,Naicula acceptata等为常见种,Melosira italica,Coscinodiscus wittianus,Navicula pygmaea等只在个别站点采到。数量分析表明,硅藻总细胞丰度变化为7.0×106-28.5×106 cells m-2,平均为17.39×106cellsm-2,在径流入海口处硅藻数量相对较多,其中淡水种比海生种多,这主要是因为长江口近岸河口水域是多种水系相混合的水体,淡水入海带来较多的淡水种类。     

扎龙湿地硅藻植物群落季节变化及其对环境的响应

扎龙湿地位于黑龙江省西部、松嫩平原乌裕尔河下游,是我国北方同纬度地区最完整的湿地。于2012年春、夏、秋3季,对扎龙湿地6个代表性区域进行硅藻标本采集,经观察鉴定,发现硅藻植物140个分类单位,包括121种19变种,隶属于2纲6目9科30属。羽纹纲物种较丰富,占总种类数的95%。硅藻植物群落呈现明显的季节演替,秋季硅藻种类丰富度及相对丰度明显高于春、夏两季,优势种多以淡水、半咸水、喜弱碱的种类为主,优势种与水体的盐度和酸碱度存在一定的响应关系。应用典范对应分析(Canonical Correspondence Analysis,CCA)探讨硅藻植物群落变化与环境因子之间的关系。CCA结果显示在扎龙湿地中,水温、电导率、pH、溶解氧是影响硅藻群落结构变化的主要因素,此外总氮、总磷也是硅藻群落季节演替的重要驱动因子。结合硅藻植物多样性指数和硅藻商对扎龙湿地水质进行综合评价,结果显示扎龙湿地整体为中-寡污带水体,部分水域水质较清洁,少数样点受人为因素影响,呈轻污染。     

Evaluating diatom community composition in the absence of marked limnological gradients in the high Arctic: a surface sediment calibration set from Cornwallis Island (Nunavut,Canada)

Fossil diatom assemblages preserved within the sedimentary record in Arctic lakes provide the potential to reconstruct past changes in important limnological variables. During the summers of 1992 and 1993, we examined previously unstudied freshwater ecosystems on Cornwallis Island, Arctic Canada, with the specific objectives of (1) documenting the limnology and modern diatom assemblages from this region, and (2) determining which environmental variables most influence diatom species distributions. The Cornwallis Island study sites displayed the least amount of variance in measured water chemistry variables in comparison to nearly all of our labs’ previous freshwater surveys in the Arctic. The small limnological gradients precluded the development of a statistically robust diatom inference model, but perhaps more importantly, allowed us to explore variations in diatom composition in the absence of marked variations in water chemistry. Diatom species turnover was minimal, with the most common diatom taxa being Achnanthidium minutissima, Nitzschia perminuta, N. frustulum, with lesser percent abundances of Chaemaepinnularia soehrensis, Navicula chiarae, Psammothidium marginulata, and A. kryophila. A small number of study sites differed from the majority with respect to water chemistry (e.g., coastal sites with high specific conductivities) and habitat availability (e.g., ephemeral ponds with extensive moss habitats), and these sites had markedly different diatom assemblages. These data reinforce previous observations that water chemistry and other climate-related factors are the primary environmental controls influencing diatom distributions at high latitudes. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Epiphytic diatom communities on intertidal seaweeds from Iceland

Epiphytic diatom communities on macroalgae from Iceland coastal waters were investigated during July 2005. Ten species of seaweeds have been collected belonging to brown, red and green algae. The analysis of epiphytic diatom community was carried out under scanning electron microscopy. The epiphytic diatom abundances varied from 7 ± 5 to 7524 ± 3491 cells mm⁻². Erect growth forms were the most abundant, representing on average 50% of the total diatoms (Achnanthes cf. brevipes var. parvula, Tabularia investiens, T. fasciculata, Hyalosira cf. delicatula, Gomphoseptatum aestuarii, Pseudogomphonema plinskii), followed by adnate (29%) (Cocconeis stauroneiformis, C. scutellum) and motile forms (21%) (Nitzschia cf. amphibia and Navicula perminuta). Highly branched seaweeds with articulated thallus surface, offering a number of microenvironments to be occupied by the epiphytes, showed a high level of colonization, mainly due to erect and motile diatoms. Flat thalli with smooth surface allowed for the growth of mainly erect diatoms.     

Changes in eicosapentaenoic acid content of Navicula saprophila, Rhodomonas salina and Nitzschia sp. under mixotrophic conditions

Three species of microalgae able to produce eicosapentaenoic acid(EPA) were collected from brackish and sea water around Japan. The species were identified as Navicula saprophila, Rhodomonassalina and Nitzschia sp. EPA as a proportion of total fatty acids increased in the presence of acetic acid for Rhodomonas salina and Nitzschia sp. However, Navicula saprophila displayed the greatest productivity of EPA and the EPA content of its biomass was enhanced under mixotrophic conditions in the presence of acetic acid. This revised version was published online in August 2006 with corrections to the Cover Date.     

Dynamics of diatom colonization process in some rivers influenced by urban pollution (Hanoi, Vietnam)

Periphytic diatom communities’ colonization patterns were studied at three sampling stations of the Red–Nhue–Tolich hydrosystem presenting different urban pollution levels by using artificial substrates for 6 weeks in dry season 2005. Structural characteristics of periphytic diatoms developed on glass substrates at each sampling site were followed and compared. This experiment showed, through various general criteria (total diatom density, dry weight biomass) and specific criteria (relative diatom abundances, indices) that the structure of benthic diatoms developed on these substrates was strongly affected by pollution as early as the second week of colonization. Communities exposed to heavily and moderately polluted sites contained species which are known to be saprophilous or tolerant to organic pollution such as Nitzschia umbonata, Nitzschia palea, Cyclotella meneghiniana, Eolimna minima. Growth inhibition of diatom communities at the heavily polluted site was mostly related to a strong increase of organic load rather than to low metallic input, though metallic (Cd and Zn) burdens have been successfully quantified in the biofilms developed at the three studied sites. Nevertheless, no significant difference in species richness and diversity index between colonization duration times was observed. Based on values of diatom indices Indice de Polluosensibilité (IPS) and diatom assemblage index to organic water pollution (DAIPo), water quality could be classified as medium quality at Red site, polluted at NT₂ and heavily polluted at TL. Thus, the use of diatoms as a tool for water assessment appears suitable for monitoring rivers in Vietnam, as it is in several other countries.     

Phosphate regime structures species composition in cultured phototrophic biofilms

1. The effect of phosphate on species composition in biofilms was studied under three different phosphate regimes (0.5, 5 and 50 μm ) in two different multi species communities: one composed of the four diatom species Melosira varians, Nitzschia perminuta, Navicula trivialis and Achnanthes lanceolata and one containing these diatom species plus the two cyanobacterial species Leptolyngbya foveolarum and Cylindrospermum stagnale. 2. Algal growth in monocultures and mixtures was measured as chlorophyll a and PAM fluorimetry was applied to document density and physiological condition of the two main groups of photosynthetic organisms in mixed cultures. 3. In phosphate‐replete communities, a single species dominated the community (N. perminuta in the diatom mixture and L. foveolarum in the all species mixture), while in the phosphate‐deprived communities several species persisted, in spite of severe phosphate limitation. 4. We conclude that high supply of phosphate enables the species L. foveolarum, and to a lesser extent N. perminuta, to overgrow biofilm consortia, facilitated by their filamentous growth form, motility or the excretion of inhibitors. The persistence of several species under a low phosphate regime is explained by a less intense interspecific interaction in low‐density biofilms. This clarifies field observations published previously.     

增江底栖硅藻种类多样性及分布特征

2010年1月和5月对东江水系重要支流增江进行底栖硅藻的采样调查,分析了增江流域底栖硅藻的多样性和时空分布特征,并探讨了硅藻优势种与环境因子的关系.结果表明,两次采样共检出底栖硅藻42属178种(包括亚种和变种),与1月份相比,由于5月份降雨量较大,硅藻的数量有所下降,种类组成也有所改变.在两次采样中,藻类分布从下游到...     

Diatom assemblages of the Cuyahoga river,N. E. Ohio (USA)

The Cuyahoga River is a heavily polluted tributary of Lake Erie located in N. E. Ohio (USA).One hundred seventy taxa of diatoms were identified from seven locations along the Cuyahoga River. The most frequently collected diatoms from each station were Cyclotella meneghiniana, Gomphonema parvulum, Navicula cryptocephala, N. cryptocephala var. veneta, N. lanceolata, N. menisculus, N. minima, N. minuscula, N. pelliculosa, Nitzschia amphibia, N. ovalis, N. palea, and Rhoicosphenia curvata.In the most heavily damaged region of the river these widely-distributed taxa were the only frequently collected diatoms.The relatively undamaged section of the river contained 94% more taxa than the most heavily damaged section. Chief among these additional taxa were Achnanthes lanceolata, A. lanceolata var. dubia, Cocconeisplacentula, Fragilaria vaucheriae, Melosira varians, Meridion circulare, Navicula mutica var. tropica, N. symetrica, Nitzschia dissipata, Stephanodiscus astraea, and Synedra rumpens.The degree of similarity between diatom assemblages along the Cuyahoga River as measured by a modification of Sørensen's index of similarity in species-frequency of occurrence composition was related to the degree of chemical-physical water quality similarities and to the extent of similarity between areas of geologic and biologic substrates. The most dissimilar diatom assemblages usually occurred between locations that were the most dissimilar with respect to chemical-physical water quality conditions rather than to dissimilarities with respect to sediment-substrate composition.     

Swamps,springs and diatoms: wetlands of the semi-arid Bogoria-Baringo Rift,Kenya

Lakes Bogoria and Baringo lie in a semi-arid part of the Kenya Rift Valley between 0° 15′–0° 30'N and 36° 02′–36° 05′E. Nevertheless, the area around these lakes contains numerous wetland systems that have been formed: along lake shorelines; along faults where hot, warm and cold springs have developed; and along river systems that cross the rift floor. Six major types of wetland are recognized: Proximal Hot Springs; Hot Spring Marshes; Blister Wetlands; Typha and Cyperus papyrus Swamps; Floodplain Marshes; Hypersaline Lake Littoral Wetlands; and Freshwater Lake Littoral Wetlands. These show significant variability in terms of geomorphic setting, water chemistry, temperature, plant communities and diatom floras. They are variously dominated by macrophytes, such as Cyperus laevigatus, Typha domingensis and Cyperus papyrus. In some cases macrophytes are absent. In hot spring settings and in hypersaline lake littoral zones bacterial mats are common. Although absent in some samples, diatoms occur in at least parts of all of the wetlands, varying in diversity, abundance and species composition. Canonical correspondence analysis indicates that diatom floras show a close relationship with pH, temperature, and specific conductivity, with other environmental variables such as Si and nitrate being of secondary importance. Common diatoms include: Anomoeoneis sphaerophora var. guntheri, Navicula tenella, N. cuspidata, and Nitzschia invisitata in hot springs, where diversity is generally low and abundance is variable. Other wetland types contain distinctive diatom floras that variously include: Fragilaria brevistriata, Gomphonema parvulum, Navicula tenelloides, Nitzschia communis, N. latens, N. sigma, Rhopalodia gibberula, and Stauroneis anceps.     

A review of diatoms found in highly acidic environments

A review is presented of 28 studies in the literature of diatoms in environments at pH 3.5, including natural and anthropogenic acid sources. A total of 124 diatom taxa have been reported, but many are likely to have been accidental occurrences, because only a few specimens were found. Approximately 19 taxa abundant in at least one study or common in several studies are considered true inhabitants of highly acidic waters. These include: Achnanthes minutissima, Eunotia exigua, E. tenella, E. septentrionalis, E. osoresanensis, E. arcus, E. glacialis, E. pectinalis, Frustulia rhomboides, F. rhomboides var. saxonica, Nitzschia capitellata/subcapitellata, Nitzschia communis, Nitzschia pusilla, Nitzschia vasta, Pinnularia acoricola, P. obscura, P. braunii var. amphicephala, P. subcapitata and P. terminitina. There are inconsistencies in the taxonomy of several of these species and possible synonymies could lower the number of taxa to less than 9. Compared to diatom species richness in environments at pH 4.5–5.0, there are many fewer taxa in environments pH 3.5, suggesting a threshold between pH 4.5 and 3.5 below which many species are unable to maintain a population.     

Distribution patterns of benthic diatoms in a Pampean river exposed to seasonal floods: the Cuarto River (Argentina)

The diatom community growing on cobbles and sand substrata along the Cuarto River (Córdoba, Argentina) was studied during 2000 and 2001. Multivariate analyses of the data (PCA and CCA) showed distinct differences in water chemistry and substrata types between the upstream sites (sites 1–10) and downstream sites (sites 11–19). Sites 1–10 supported an epilithic diatom community associated with low water conductivity and gravel substrata. This consisted of adnate Achnanthes (A. biasolettiana, A. minutissima), as well as stalked (Gomphonema aff. angustum, Reimeria uniseriata, Fragilaria capucina var. rumpens) or prostrate (Nitzschia lacuum) taxa. Downstream sites were associated with high conductivity, fast flowing waters and finer substrata (sand, silt), and were colonised by prostrate diatoms, including several species of Navicula (N. pupula, N. mutica, N. veneta, N. insociabilis) and Nitzschia (N. umbonata, N. palea). Variations in water flow caused significant changes in the diatom communities of the river. During periods of low flow (winter and autumn), chain forming (Diatoma vulgaris, D. moniliformis) or stalked (Synedra ulna) taxa partially replaced the former community of Navicula and Nitzschia in the downstream sites. High flow (in summer) led to diatoms of large size being replaced by smaller size diatoms, such as Achnanthes lanceolata, Navicula mutica, Hantzschia amphioxys and Amphora montana. The severe effect of floods in the lower part of the Cuarto led to these taxa having a much higher proportion in the lower stretch of the river, taking advantage of the subaerial conditions created by the floods. Local episodes of water pollution were associated with a transient shift towards the dominance of Navicula pupula, Synedra ulna, Nitzschia lacuum and Reimeria uniseriata during winter, when inputs were least diluted because of the low flow.