Nitzschia Acicularis Research Articles

TAXONOMIC STUDIES OF FRESH WATER ALGAE FROM CHISHTIAN CITY, DISTRICT BHAWALNAGAR

Chishtian city was being explored for the collection of fresh water algae in the present study and for those purpose 12 samples of fresh algae from different areas was being collected. From those samples total 28 species was being collected that belong to 16 genera, 11 families, 7 orders and total 4 phylum including, Cyanophycota, Volvocophycota, Bacillariophycota and Chlorophycota. Those samples were being collected from September 2019 to December 2019. After they were classified and identified taxonomically upto species level by using Shameel classification [25,26]. Those 28 species that are being obtained in the total research work: Kingdom Monera has been acknowledged with phylum one; Cyanophycota that omits two classes, two orders, two families four genera and eight species that were following; Chroococus turgidus, Merismopedia punctate, Oscillatoria rubescens, O. priencp, O. tenuis, O. ornate, Spirulina gigantea and Arthospira platensis. Kingdom Protista has been identified with two phylum; Volvocophycota and Bacillariophycota with three classes, four orders, eight families, 11 genera and 18 species which were following; Hydrodictyon reticulatum, Scenedesmus armatus, S. dimorphus, S. bijuga, Cosmerium botrytis, C. microsphinctum, C. pseudopyramiolatum, Closterium turgidum, Fragilaria ulna, F. crotonensis, Ghomphonemia ghosea, Navicula exigua, Nitzschia acicularis, Gyrosigma acuminatum, G. scalproides, Cymbella ventricosa, Cyclotella operculata, C. meneghiniana. Kingdom protoctista have one phylum; Chlorophycota that have 1 class, one order, one family and two species that are following, Spirogyra pratensis and S. acquinoctialis.

Characteristic of phytoplankton and water quality assessment in the Amur River at Khabarovsk in the ice-free period of 2018–2019

Species composition and taxonomic structure of phytoplankton communities in the main channel of the Amur at Khabarovsk (Russia) were monitored from spring to autumn of 2018–2019. In total, 187 species, varieties and forms of algae and cyanobacteria were found belonged to 8 phyla (Cyanobacteria, Bacillariophyta, Charophyta, Chlorophyta, Heterokontophyta, Rhodophyta, Euglenozoa, and Miozoa) and 75 genera. Diatoms formed the basis of the algal flora (94.7 % of the total species number). Mass vegetations of the diatoms and charophytes were observed with dominance of Asterionella formosa, Aulacoseira islandica, A. ambigua, A. granulata var. granulata, A. granulata var. angustissima, Ulnaria ulna, Diatoma tenue, Nitzschia acicularis, Stephanodiscus sp., Tabellaria flocculosa, Hannaea arcus var. rectus, Melosira varians, Fragilaria capucina var. vaucheriae, F. crotonensis, and Mougeotia sp. ster. Total number and biomass of plankton algae and cyanobacteria varied in the ranges of 1.74–5724.39 million cells/L and 2.5–2648.5 mg/L in spring-summer and 0.07–0.62 million cells/L and 0.2–1.4 mg/L in autumn. The water quality was evaluated by Pantle-Buck method modified by Sládeček as the betamezosaprobic III class (slightly polluted).

Munzur Çayı (Tunceli-Türkiye)‘nın Algal Florasının ve Su Kalitesi Değişimi

Şubat 2015-Ocak 2016 tarihleri arasında aylık olarak Munzur Çayı‘nda belirlenen iki istasyonda gerçekleştirilen çalışmada fitoplankton dağılımı ile fiziko-kimyasal parametreler belirlenmeye çalışılmıştır. Yerüstü Su Kalitesi Yönetmeliği‘ne göre suyun kalitesi, sıcaklık, pH, oksijen, amonyum nitrat I. Sınıf özelliği; nitrit ise II. Sınıf özelliği niteliğinde değerlendirilmiştir. Ayrıca II. İstasyon evsel atık sebebiyle organik kirlenme tehdidi altında olduğu belirlenmiş ve bu duruma markerleri olarak bölgedeki fitoplankton dağılımı incelenmiştir. Elde edilen sonuçlar göstermiştir ki: Munzur Çayı‘nda Chlorophyta (6), Bacillariophyta (54), Cyanobacteria (15), Rhodophyta (1), Ochrophyta (1), Euglenophyta (2), Charophyta (3), Miozoa (2) sınıflarına ait toplam 84 takson tespit edilmiştir. Fitoplanktonda organizma sayısı bakımından iki istasyon içinde Bacillariophyta divizyosunun dominant, Cyanobacteria ise subdominant olduğu gözlenmiştir. Fitoplanktonda Bacillariophyta‘dan Ulnaria ulna, Nitzschia palea, Bacillaria paradoxa ,Encyonema sp., Navicula sp. ve Nitzschia acicularis türlerinin çoğunlukla bulunduğu; Cyanobacteria üyelerinden Lyngbya sp., Spirulina labyrinthiformis, Oscillatoria labyrinthiformis ve Oscillatoria mougeotii türlerinin ise önem açısından ikinci sırada yer aldığı raporlanmıştır. Chlorophyta, Charophyta ve Euglenophyta türleri ise önemli sayılara ulaşamamışlardır.

EPILITHIC DIATOM-BASED ECOLOGICAL ASSESSMENT IN TAŞMANLI POND (SINOP, TURKEY)

The common goal of the Water Framework Directive (WFD) published by The European Parliament and European Council and the Regulation on the Management of Surface Water Quality Directive (RMSWQ) published by the Republic of Turkey, Ministry of Forestry and Water Affairs, is to provide all water bodies to achieve a fine ecological status. These directives require the use of relevant biological quality elements and diatoms constitute an important group within these elements. The use of diatom based indices for assessing ecological conditions in inland water systems is increasing day by day. The current study was performed with the aim of determination of the ecological status of the Taşmanlı Pond based on epilithic diatoms, physico-chemical parameters and to estimate pond water quality using diatom indices. For this purpose, epilithic diatom and water samples were collected from 3 stations in the pond in monthly intervals from March 2008 to March 2009. The identifications of the sampled revealed presence of a total of 46 taxa in the sampled stations. Achnanthidium minutissimum (Kützing) Czarnecki, Nitzschia acicularis (Kützing) W. Smith, Navicula cincta (Ehrenberg) Ralfs in Pritchard and Navicula cryptocephala Kützing were the dominant taxa in all stations. According to Regulation on the Management of Surface Water Quality directive, the pond water was classified as III-IV quality class and trophic status changed from mesotrophic to eutrophic. Significant correlation was determined between LTDI (Lake Trophic Diatom Index) and EQR (Ecological Quality Ratio). The values of LTDI and EQR indicate that, pond water has class III (poor, moderately polluted site) water quality.

Mikroalga Divisi Bacillariophyta yang Ditemukan di Danau Aur Kabupaten Musi Rawas

Lake Aur has many aquatic biota as well as become one of the mainstay attractions in Musi Rawas Regency. Community activities and lack of awareness of tourists on the cleanliness and importance of maintaining the lake environment have an impact on water pollution. One of the organisms that can be used as an indicator of river water quality is microalgae. The purpose of this study is to determine the types of microalgae Bacillariophyta divisions that exist in the lake Aur, Musi Rawas.The type of research used is survey research. Bacillariophyta Division consists of two classes, 6 orders, 7 families, 8 genera and 11 species. Observed environmental factors: temperature: 290C, pH: 6.7, Brightness: 115 cm and dissolved oxygen amount of: 38 mg / L. Based on the results of research and discussion, we can conclude that: the type of microalgae division bacillariophyta were found in Lake Aur namely: Cylotella sp, Eunotia sp, Eunotia pectinalis, Fragilaria croronensis, Synedra acus, Nitzschia sp, Nitzschia acicularis, Surirella sp, Surirella elegans, Pinnularia sp and Stauroneis sp.

水质对东江流域附生硅藻群落的影响研究

PDF HTML阅读 XML下载 导出引用 引用提醒 水质对东江流域附生硅藻群落的影响 DOI: 10.5846/stxb201305201124 作者: 作者单位: 华南师范大学化学与环境学院,珠江流域水环境监测中心,珠江流域水环境监测中心 作者简介: 通讯作者: 中图分类号: 基金项目: 公益性行业科研专项(201001021,201301047) The effects of water quality on epilithic diatoms communities of Dongjiang river basin Author: Affiliation: School of Chemistry and Environment，South China Normal University，Guangzhou 510631，China,Water Environment Monitoring Center of Pearl River Basin,Water Environment Monitoring Center of Pearl River Basin Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:运用相关分析(CA),典型对应分析(CCA),加权平均分析(WA)研究了影响东江流域附生硅藻的主要水质因子及对应的最适生态范围。CA显示,13项水质指标中溶解氧(Dissolved Oxygen,DO)、氨氮(NH4-N)、亚硝氮(NO2-N)、氯化物(Cl)、五日生化需氧量(BOD5)、磷酸盐(PO4-P)与其它指标间的相关性较强(P < 0.05),其余指标间相关性较低(P < 0.05)。以相关性较弱的pH、电导率(Cond.)、硅酸盐(SiO2)、总磷(TP)、总氮(TN)、硝氮(NO3-N)、化学需氧量(CODKMnO4)进行CCA分析,排序显示影响附生硅藻的水质因子依次为Cond.、NO3-N、CODKMnO4、TP、TN,对应的生态最适范围分别为39.20-642.00μs/cm、0.46-2.77mg/L、1.0-5.5mg/L、0.02-0.64mg/L、0.48-3.43mg/L。研究表明,Cond、NO3-N、CODKMnO4、TP、TN是影响东江附生硅藻分布的主要水质因子,Cyclostephanos invisitatus、Gomphonema olivaceum、Nitzschia acicularis、N. capitellata、N. intermedia可以指示东江较高的电导率,Aulacoseira ambigua、A. lirata、Cyclotella meneghiniana、Cyclostephanos invisitatus、Eunotia minor、Nitzschia acicularis、N. Clausii、Pinnularia subcapitata是东江TN、TP污染的指示种。Nitzschia acicularis对TN、TP的耐受性最高,Navicula eidrigiana对TN、TP敏感性最强。 Abstract:The effects of thirteen water quality parameters(Conductivity, pH, Dissolved Oxygen, Biochemistry Oxygen Demand, Chemistry Oxygen Demand, Total Nitrogen, NH4-N, NO3-N, NO2-N, Total Phosphorus, PO4-P, SiO2 and Cl) on the distribution of epilithic diatoms in the Dongjiang basin were investigated by correlation analysis (CA), canonical correspondence analysis (CCA) and weighted average (WA). Correlation analysis showed that NH4-N, NO2-N, PO4-P, Cl, DO and BOD5 had significant correlations with the other seven water quality parameters, while CCA analysis revealed that the impacts level of the five environmental variables. Cond., CODKMnO4, NO3-N, TN and TP on the variation in community composition of epilithic diatoms were in the order of Cond.> NO3-N > CODKMnO4 > TP > TN. Furthermore, the optimum ecological values of Cond., NO3-N, CODKMnO4, TP and TN for epilithic diatoms were calculated using weighted average regression method to be 39.20-642.00μs/cm, 0.46-2.77mg/L, 1.0-5.5mg/L, 0.02-0.64 mg/L and 0.48-3.43mg/L, respectively. The results indicated that Cond., CODKMnO4, NO3-N, TN and TP were the major water quality parameters affecting the distribution of diatom assemblages. Cyclostephanos invisitatus, Nitzschia acicularis, N. capitellata and N. intermedia could be used as bioindicators for the higher conductivity in the Dongjiang river basin. Aulacoseira ambigua, A. lirata, Cyclotella meneghiniana, Cyclostephanos invisitatus, Eunotia minor, Nitzschia acicularis, N. clausii and Pinnularia subcapitata were indicative species for TN and TP in the Dongjiang river basin. Moreover, Nitzschia acicularis is the best bioindicator for TN and TP in the Dongjiang basin, while Navicula eidrigiana is the least sensitive bioindicator for TN and TP. 参考文献 相似文献 引证文献

OCENA STANU TROFICZNEGO WÓD ZBIORNIKA ZAPOROWEGO WAPIENICA

In this publication the trophy level of Wapienica dam reservoir, based on the composition species of planktonic algae and their biomass, and concentrations of chlorophyll a, was defined. The research was conducted during the vegetative season in 2013 year; the samples were taken from two research points (W1 – the part of river Wapienica inflow to reservoir and W2 – the part of the reservoir dam) by using bathometer. The whole biomass of planktonic algae and concentration of chlorophyll a from two research areas were low and it allowed to classify water of this reservoir to oligo-/ mesotrophic. Only in the part of the reservoir dam, in summer season, an increased trophy level was observed (Heinonen 1980). A similar trophic character (oligo-/ mesotrophic) of the water reservoir was also indicated by algae species: Achnanthes lanceolata (Breb.) Grun. in Cl. and Grun., Chrysoccoccus minutus (Fritsch) Nygaard. For a temporary increase of the trophy level, the diatom Nitzschia acicularis (Kutz.) W. Sm. could indicate, because it is a typical species in poorly eutrophic water. The green algae (Pediastrum and Coelastrum, which were observed in summer season) could also indicate for a rise of the trophic state, because they are typical for eutrophic water.

Feeding selectivity of wild and pond-cultured Nile tilapia Oreochromis niloticus in the Lake Victoria basin in Mara, Tanzania

A comparison of feeding selectivity of wild and pond-cultured Nile tilapia Oreochromis niloticus was conducted in 2008. Water and fish samples were collected in Shirati Bay, Lake Victoria, and from fish ponds in Tarime district using a La Motte water sampler and seine nets, respectively. Cyanophytes were abundant and were the major diet component of fish in both habitats. Chlorophytes were selected by pond fish. Bacillariophytes were selected by fish in both habitats, despite their low abundance in pond water. Astrionella sp. and Rhopalodia vermicularis (bacillariophytes) and Peridinium sp. (dinophyte) were selected by fish in both habitats. Astrionella sp., Aulacoseira nyassensis, Navicula sp. and Rhopalodia vermicularis (bacillariophytes) were the species most selected by lake fish, whereas Ankistrodesmus falcatus (chlorophyte), Lyngbya circumcreta (cyanophyte) and Nitzschia acicularis (bacillariophyte) were the species most selected by pond fish. These results suggest that Nile tilapia is a selective feeder. It is therefore recommended that nutrient enrichment should be controlled to prevent excessive growth of cyanophytes, which form excessive blooms and thereby prevent growth of other algae such as diatoms, which were selected by fish in both habitats.

A Preliminary Checklist of Epilithic Algaeof Kahuzi-Biega National Park, Democratic Republic of the Congo

In this study, the epilithic algae of Kahuzi-Biega National Park were investigated at the first time. The samples were collected from 10 streams in between 1900 and 2400 m asl during dry season (July-August 2007). Altogether, some 170 species have been encountered and identified, belonging to 61 genera were observed. Bacillariophyceae formed the most abundant group making up 61 species from 20 genera. This was followed by the Cyanophyceae with 47 species from 12 genera, the Chlorophyceae with 30 species from 15 genera, the Desmidiaceae with 17 species from 7 genera, the Euglenophyceae with 10 species from 4 genera and the Dinophyceae represented by 5 species from 2 genera. This algal community is very diversified and balanced (Shannon Weiner index varied between 4.44-4.67, Species Diversity between 15.81-13.31 and Equitability between 0.97-0.99). Frustulia rhomboides, Gomphonema angustatum, Melosira nyassensis, Navicula cuspidata, Nitzschia acicularis, Nitzschia filiformis, Synedra pulchella, Cladophora aeragrophila, Crucigenia cuneiformis, Mougeotia planctonica, Penium jenneri, Anabaena flos-aquae, Coelosphaerium nagelianum, Microcystis aeruginosa, Oscillatoria geminate, Synechocistis elongatum, Closterium aciculare, Cosmarium moniliferum, Ceratium hirundinella, Euglena acus and Phacus longicauda were more abundant and present in all stations surveyed. Comparatively, a higher number of species, 114 species was recorded at Mushuva River (station 4) and a lesser number, 91 species at Mugaba River (station 6).

Spatial heterogeneity of diatom silicification and growth in a eutrophic reservoir

Summary Diatoms are one of the most important phytoplankton groups. As they grow, diatoms use silicon to produce a siliceous frustule, which protects the cell. During April–November 2011, at 1–3 week intervals, we estimated diatom silicification rates at two distinct sites along the longitudinal profile of the canyon‐shaped eutrophic Římov Reservoir (Czech Republic): (i) a nutrient‐depleted lacustrine zone near the dam and (ii) a nutrient‐rich transition zone upstream near the river inflow. Diatom silicification was estimated using the 24‐h in situ incubation of natural phytoplankton assemblage with a fluorophore 2‐(4‐pyridyl)‐5‐{[4‐(2‐dimethylaminoethyl‐aminocarbamoyl)methoxy]phenyl}oxazole (PDMPO) which fluorescently stains the newly synthesised diatom frustules. Diatoms contributed an average c. 40% to the total phytoplankton biovolume in the lacustrine zone, but only c. 20% in the transition zone where a cyanobacterial bloom developed during summer. Asterionella formosa and Fragilaria crotonensis were the most abundant diatom species, while Aulacoseira italica, Nitzschia acicularis, Synedra acus and Stephanodiscus sp. were less important. Silicification rates of all diatom species were significantly higher in the transition zone than at the dam. The intensity of PDMPO fluorescence per diatom cell was tightly related to the growth rates of three diatom species calculated from changes in cell counts during the incubation. The PDMPO technique can thus be used as a proxy for diatom growth. Growth rates of the two most abundant diatom species were positively correlated with daily light exposure but not with nutrient concentrations.

Temperature and photoperiod effects on phytoplankton growing under simulated mixed layer light fluctuations

We measured specific growth rates of Stephanodiscus minutulus, Nitzschia acicularis (diatoms), and Limnothrix redekei (cyanobacterium) under fluctuating and constant light in semi‐continuous culture at 10°C, 15°C, and 20°C and under photoperiods of 6 h d−1 and 12 h d−1. Fluctuating light regimes simulated regular vertical mixing in lakes with a ratio of euphotic to mixed depth (zeu : zmix) of 1 and 0.5 on a cloudless day. Light fluctuations at zeu : zmix = 1 decreased the growth rates of S. minutulus, N. acicularis, and L. redekei by 18%, 33%, and 29%, respectively, compared to constant light at the same daily light supply. Temperature had no effect on this decrease. Halving zeu : zmix (simulating deep mixing) had the same effect on growth as halving the photoperiod, demonstrating that these factors are cumulative. We introduce a simple empirical factor to adjust growth rates measured under constant light to account for fluctuating light. This factor is independent of temperature and photoperiod, applies over a range of zeu : zmix, and accurately describes present and published growth rates of several species. We show how to account for temporal variability of the light supply at different temperatures and photoperiods when predicting growth rates of phytoplankton.

Spatial and temporal patterns of phytoplankton abundance and composition in three ecological zones in the Tanzanian waters of Lake Victoria

Phytoplankton abundance and composition in relation to physico-chemical parameters were investigated from September 2005 to October 2007 at 51 stations of various depths in the nearshore, intermediate and deep offshore waters of Lake Victoria. Shallow nearshore waters had the highest abundance of phytoplankton (mean 2.12 × 108 ind. l−1), compared to the intermediate (1.96 × 108 ind. l−1) and deep offshore waters (7.59 × 107 ind. l−1). Bacillariophyta was the most abundant group (48.17% of total phytoplankton) and was uniformly distributed in all waters, followed by Cyanobacteria (33.33%), which decreased with distance offshore. Chlorophyta, the third highest in abundance (15.5%), increased with distance offshore. A total of 92 phytoplankton species were recorded. The most diverse phyla were Chlorophyta with 37 species, of which Staurastrum sp. and Siphonctosiphon polymorphus were the most abundant species, followed by Bacillariophyta with 25 species and Cyanobacteria with 21 species. In general, the phytoplankton community was dominated by the less nutritious species Nitzschia acicularis (Bacillariophyta), Lyngbya circumcreta and Microcystis flos aquae (Cyanobacteria). These findings contrast with those of most studies from before 1990, but agree with many thereafter. Eutrophication, affecting availability of nutrients etc., and pollution, affecting transparency and water pH, were the forces responsible for the observed spatial and temporal variability in phytoplankton abundance patterns and composition.

Analysis and modelling of the interactive effects of temperature and light on phytoplankton growth and relevance for the spring bloom

Global climate change alters the relationship between temperature and light in aquatic ecosystems, which is expected to affect the success of different phytoplankton species. To examine this, the interactions between temperature, photoperiod and light exposure (LE) (integral daily light supply) on specific growth rates were analysed for Limnothrix redekei, Planktothrix agardhii (cyanobacteria), Nitzschia acicularis and Stephanodiscus minutulus (diatoms). A model of factor interactions was developed based on new (P. agardhii and St. minutulus) and previously published laboratory studies. It describes the measured data with high precision. Temperature and photoperiod affect the parameters of the light-growth response curve differently, but these effects are the same for all species. The link between functions for temperature and photoperiod is more species-specific. Using meteorological data, the model developed here was used to study the interplay of these factors during a spring bloom in Lake Muggelsee (Berlin). It was found that while all three factors influenced phytoplankton growth, temperature and photoperiod were more important than LE. Both the intensities of the factors and the interactions between them influenced each species to a different degree. The results may help improve our understanding and ability to predict shifts in phytoplankton communities caused by weather patterns and climate change.

Microcystin production by cyanobacteria in the Mwanza Gulf (Lake Victoria, Tanzania)

In order to investigate the potential for microcystin (MC) production by cyanobacteria in the Mwanza Gulf (Lake Victoria, Tanzania), nutrients, phytoplankton and microcystins were sampled inshore (3 m depth) and offshore (18 m depth) from May to August 2002. Significant differences in soluble reactive phosphorus (SRP) and nitrate concentrations between offshore and inshore indicated eutrophication via terrestrial runoff. Though the concentrations of SRP and nitrate ranged between 36–127 and 35–726 l gl )1 each, the phytoplankton biovolume was generally low. The phytoplankton community was dominated by diatoms (Nitzschia acicularis), a number of cyanobacterial species (Aphanocapsa sp., Anabaena sp., Planktolyngbya spp., Microcystis sp.) and cryptomonads. The water column was completely mixed and Nitzschia peaked in abundance during July. All cyanobacteria were low in abundance during the entire study period (0.1–1.6 mm 3 l )1 ). Microcystins were analysed using high performance liquid chromatography coupled with diode array detection High Performance Liquid Chromatography with Diode Array Detection (HPLC-DAD) and in most samples no microcystins were detected. The highest concentration of [Asp 3 ]MC-RR was found in open water at the surface on July 2nd, 2002 (1 l gl )1 ). MC concentrations did not pose a potential health risk in the Mwanza Gulf during the study period, however, it is possible that the period of higher cyanobacterial biovolumes has been missed during the sampling period of this study.

Epiphytic Diatoms of the Reed Plants in Lake Gocheonam

A great portion of the marginal zone in Lake Gocheonam was covered with reed plants. Algae attached to the reed stems were exclusively composed of diatoms. Sixty-six species of diatoms were encountered in a floral survey. The important species were Nitzschia liebetruthii Rabh., Nitzschia acicularis (Ku¨tz.) W. Sm., Navicula gregaria Donk., Cocconeis placentula var. lineata (Ehr.) V.H. etc. Among the diatom flora, six species - Navicula nivalis Ehr., Navicula recens Lange-B., Nitzschia angustatula Lange-B., Nitzschia compressa (Bail.) Boyer, Nitzschia lanceola var. minutula Grin. and Surirella crumena Bre´b. - were recorded in Korea for the first times. Life forms of the reed-attached diatoms were simply prostrate. The biomass of epiphytic algae ranged from 0.05㎍ chl- cm to 2.32g chl- cm. The algal biomass of dead stems was higher than that of the living stems, and their flora were rich. The algal biomass reached a maximum in the spring after the death of the reed plants. The reed plants exhibited rich diatom flora and significantly high algal biomass on their stems to have taxonomical and ecological importance in the freshwater.

Differential dissolution of Lake Baikal diatoms: correction factors and implications for palaeoclimatic reconstruction

In order to assess how faithfully the composition of diatom assemblages in the recent sediments of Lake Baikal represents the composition of the planktonic diatom populations in the lake, we have compared the flux of diatoms from the water column (i.e., “expected” in the sediment) with the accumulation rates of the same diatom taxa (i.e., “observed” in the sediment) from BAIK 38, a sediment core collected in the south basin of the lake. Whilst there are many uncertainties, the results indicate that only approximately 1% of the phytoplankton crop is preserved in the sediment and some species are more affected by dissolution than others. These findings are comparable to similar studies undertaken in the marine environment. In terms of differential dissolution, our studies suggest that the endemic taxa (e.g., Cyclotella minuta and Aulacoseira baicalensis) are the most resilient, whereas cosmopolitan taxa such as Nitzschia acicularis and Synedra acus are the least resilient. N. acicularis dissolves in the water column, but for other taxa, most dissolution takes place at the surface sediment–water interface. We use the data to develop a series of species-specific correction factors that allow the composition of the source populations to be reconstituted, and we argue that failure to take these processes into account can undermine the use of the diatom and biogenic silica record in Lake Baikal for palaeo-productivity and palaeoclimate reconstruction.

Quantitative and qualitative relationships between planktonic diatom communities and diatom assemblages in sedimenting material and surface sediments in Lake Baikal, Siberia

Endemic planktonic diatoms are a major component of Lake Baikal sediments during interglacial periods. To investigate how these diatom assemblages are altered during sediment formation, quantitative plankton monitoring (1995–1998) was integrated with sediment trapping over 2 yr (1996–1997) in Baikal's southern basin (depth ~1,400 m). The traps consisted of both open (~6 monthly) and sequential (~2 weekly) collectors deployed throughout the water column. Sedimentation was seasonal, with diatom species composition, valve abundance, and total dry massreflecting changes in the planktonic communities. Sedimented assemblages were transmitted largely intact to the deepest traps (~1,300–1,390 m); some compositional blurring occurred from differential sinking rates and dissolution of diatom valves. A rapid mass flux event of Aulacoseira skvortzowii and A. baicalensis was recorded in summer 1997 with particle sinking rates between 60 and 100 m d−1 and dry mass fluxes &gt;5 g m−2 d−1. Although dissolution was evident for all species, more delicate taxa were preferentially affected (e.g., A. skvortzowii vegetative cells and fine Synedra species), whereas Nitzschia acicularis valves were almost entirely dissolved within the water column. Comparing trap and plankton diatom assemblages with those in nearby core tops demonstrated that a fundamental taphonomic change occurs in the surface sediment, with sedimentary diatom accumulation rates being only about 1% of trap deposition and plankton production rates. Dissolution was significant in explaining 5–30%

Diatom and thecamoebian signatures of Red River (Manitoba and North Dakota) floods: Data collected from the 1997 and 1999 spring freshets

Overbank deposits that aggraded during the severe and moderate Red River, Manitoba and North Dakota floods of 1997 and 1999 were examined to characterize the typical diatom and thecamoebian flood assemblages. The deposits contain diatom assemblages dominated by Nitzschia spp., Stephanodiscus spp. and Navicula spp. as well as large quantities of Hantzschia amphioxys, Luticolaimbricata and L. mutica and lesser amounts of Aulacoseira italica, A. granulata, A. ambigua, Cyclotella meneghiniana, Amphora montana and Synedra ulna. Samples collected from the Red River in late summer are dominated by the plankton Cyclotella atomus, species of Stephanodiscus, Cyclostephanos sp. 1 (cf. delicatus), Cyclotella meneghiniana, Nitzschia reversa and Nitzschia acicularis. Late summer, floodplain lake plankton are dominated by Fragilaria capucina, Cocconeis placentula, Stephanodiscus parvus/minutulus and Cyclotella atomus. Red River thecamoebian flood assemblages are dominated by Cyclopyxis spp., with lesser amounts of Centropyxis aculeata and Arcella vulgaris. Late summer water samples from the Red River contain very few thecamoebian remains. The majority of the taxa present are Centropyxis aculeata, Arcella vulgaris and Cyclopyxis spp. Floodplain lakes are dominated by benthic thecamoebians, especially Difflugia oblonga and Cucurbitella tricuspis, a eutrophic indicator. The results of this baseline study suggest that diatom and thecamoebian assemblages can characterize flood deposits, within floodplain lake basins, during both very high and moderately high flood years, and that these assemblages are inherently different from those typically found in lakes along the Red River.

Finding new diatoms for intensive rearing of the pacific oyster ( Crassostrea gigas): energy budget as a selective tool

Intensive shellfish rearing in the polders of Bourgneuf Bay on the French Atlantic coast (46–47°N, 1–2°W) relies on the diatom Skeletonema costatum (Grev.) Cleve produced in nutrient-rich saline ground water. An episodic reduction in biomass production caused by an unidentified protozoon stressed the need to find new microalgal species as substitutes for S. costatum and diversify the microalgae used by the bivalve industry. Three species met the requirements for year-round availability in Bourgneuf Bay coastal waters and growth potential in saline ground water: Nitzschia acicularis (Kützing), Nitzschia closterium (Ehrenberg) Wm Smith and Nitzschia gandersheimiensis Krasske= Nitzschia tubicola Grunow. These microalgae were tested as food sources for adult Pacific oysters ( Crassostrea gigas) by comparing short-term bivalve physiological responses with those obtained with S. costatum as reference. Suspended particulate matter concentrations in experimental diets ranged from 9.3 to 18.6 mg l −1 and particulate organic matter concentrations from 3.3 to 5.7 mg l −1. Significant differences were observed, with clearance rates ranging from 4.0 l h −1 g −1 for N. acicularis to 7.3 l h −1 g −1 for N. gandersheimiensis. The filtration rate for organic matter was significantly higher for N. gandersheimiensis than the other species, but this algae was also significantly more rejected in pseudofaeces. No differences were found among the four mean faeces production rates. Net energy balance differed significantly among the four microalgae tested, ranging from 282 J h −1 g −1 for S. costatum to 27 J h −1 g −1 for N. closterium. However, no differences were found between S. costatum, N. acicularis and N. gandersheimiensis. These results suggest that N. acicularis and N. gandersheimiensis could be tested on a larger scale involving the production of microalgae in 50-m 3 outdoor tanks in association with Pacific oyster growth experiments.

Distribution of algae in the San Joaquin River, California, in relation to nutrient supply, salinity and other environmental factors

1. The taxonomic composition and biomass of the phytoplankton and the taxonomic composition of the phytobenthos of the San Joaquin River and its major tributaries were examined in relation to water chemistry, habitat and flow regime. Agricultural drainage and subsurface flow contribute to a complex gradient of salinity and nutrients in this eutrophic, ‘lowland type’ river.2. Because of light‐limiting conditions for growth, maintenance demands of the algae exceed production during summer and autumn in the San Joaquin River where there is no inflow from tributaries. In contrast to substantial gains in concentration of inorganic nitrogen and soluble reactive phosphorus during the summer of normal‐flow years, net losses of algal biomass (2–4 μg L−1 day−1 chlorophyll a) occurred in a mid‐river segment with no significant tributary inflow. However, downstream of a large tributary draining the Sierra Nevada, a substantial net gain in algal biomass (6–11 μg L−1 day−1) occurred in the summer, but not in the spring (loss of 1–6 μg L−1 day−1) or autumn (loss of 2–5 μg L−1 day−1).3. The phytoplankton was dominated in summer by ‘r‐selected’ centric diatoms (Thalassiosirales), species both tolerant of variable salinity and widely distributed in the San Joaquin River. Pennate diatoms were proportionally more abundant (in biomass) in the winter, spring and autumn. Abundant taxa included the diatoms Cyclotella meneghiniana, Skeletonema cf. potamos, Cyclostephanos invisitatus, Thalassiosira weissflogii, Nitzschia acicularis, N. palea and N. reversa, and the chlorophytes Chlamydomonas sp. and Scenesdesmus quadricauda. Patterns in the abundance of species indicated that assembly of the phytoplankton is limited more by light and flow regime than by nutrient supply.4. The phytobenthos was dominated by larger, more slowly reproducing pennate diatoms. Few of the abundant species are euryhaline. The diatoms Navicula recens and Nitzschia inconspicua and cyanophytes, Oscillatoria spp., were the principal late‐summer benthic species upstream in the mainstem and in drainages of the San Joaquin Valley. Many of the other abundant diatoms (Amphora veneta, Bacillaria paxillifer, Navicula symmetrica, Nitzschia amphibia, N. fonticola, N. palea, Pleurosigma salinarum) of late‐summer assemblages in these segments also are motile species. While many of these species also were abundant in segments downstream of confluences with rivers draining the Sierra Nevada, the relative abundance of prostrate (Cocconeis placentula var. euglypta, Navicula minima) and erect or stalked (Achnanthidium deflexum, Achnanthes lanceolata, Gomphonema kobayasii, G. parvulum var. lagenula) diatoms and Stigeoclonium sp. was greater in these lower San Joaquin River segments.5. A weighted‐averaging regression model, based on salinity and benthic‐algal abundance in the San Joaquin River and segments of its major tributaries within the San Joaquin Valley, yielded a highly significant coefficient‐of‐determination (r2=0.84) and low prediction error between salinity inferred from the species and that observed, indicating that salinity tolerance is a primary constraint on growth and assembly of the phytobenthos. The same measures of predictability indicated poor performance of a model based on inorganic nitrogen. However, with a greater representation of tributaries (including segments within the Sierra Nevada foothills) in the sample set, an inorganic nitrogen model also yielded a highly significant coefficient‐of‐determination (r2=0.87) and low prediction error between the species‐inferred and the observed concentration. As with the salinity model (r2=0.94) for the enlarged data set, a systematic difference (increased deviation of residuals) existed at high inorganic nitrogen concentrations. These results indicate substantial interaction between salinity and inorganic nitrogen as constraints on the structure of benthic‐algal communities of the San Joaquin River basin.