Navicula Cryptocephala Research Articles

First diatom-based assessment of Lower Hari Rud River (a transboundary system) in Afghanistan.

It is essential to determine the dominant/indicator species and their ecological preferences to develop a comprehensive bioassessment strategy for rivers. The objective of this work was to provide dependable ecological evaluation techniques for ecosystems that experience significant human-induced disruptions, with the Hari Rud River (a transboundary water resource) serving as a case study during the May (wet) and July (dry) periods of 2023. Canonical correspondence analysis revealed that electrical conductivity (EC), dissolved oxygen, ortho-phosphate (P ), and nitrate (N ) had substantial impacts on the spatial distribution of diatom species in the basin. Relatively pollution-tolerant species, including Nitzschia brevissima, N. capitellata, N. umbonata, N. palea, N. dissipata, and Navicula cryptocephala, had close relationships with EC and P , integrated with Joi Injil and Karbar streams. Of the sampling stations, especially Hari Rud River1 and Hari Rud River2, exhibited pollution-sensitive diatom species, Cymbella excisa, Achnanthidium minutissimum, Diatoma moniliformis, Cymbella affinis, and Meridion circulare. Various eco-regional diatom metrics exhibited distinct scores, indicating a range of ecological status from high to bad in the Lower Hari Rud River basin. European diatom indices revealed good ecological status for Hari Rud River 1 and 4, but poor or bad ecological statuses for Joi Injil and Karbar streams. The findings of the current study emphasize the requirements of autecological studies to understand the regional diatom compositions and their ideal survival ranges in different locations before considering using non-regional diatom indices to evaluate the ecological status of lotic systems.

Relationship of Modern Diatoms with Lake Acidification and Water Quality in Nsonji Lake of Nagaland, North-East India

Understanding the relationship of diatoms and water quality is of paramount importance to link it to Holocene Climate Change. Since diatoms are extremely sensitive to environmental changes, they are the obvious choice to study diatom inferred water quality and climate changes. Therefore, sediment samples along with water samples were collected during pre monsoon seasons from the Nsonji Lake of the Nagaland, India to establish the relationship between the diatom and water quality. The Nsonji Lake has circum-neutral pH (around 7) indicating gradual degradation of organic matter leading to acidification of the lake. The surface sediments of the Nsonji Lake revealed the dominance of Discostella stelligera, Achnanthidium sp., Navicula cryptocephala, Navicula radiosa and Nitzschia palea. These diatom species could be used to unravel the acidification history of lake caused by natural and anthropogenic activities. Understanding the past climate dynamics need modern analogue in order to evaluate the important processes relative to Earth's history and built future scenario. Keywords: Diatoms, Water Quality, Acidification, pH, Organic Matter, Nsonji Lake, Nagaland

Relationship of Modern Diatoms with Lake Acidification and Water Quality in Nsonji Lake of Nagaland, North-East India

Understanding the relationship of diatoms and water quality is of paramount importance to link it to Holocene Climate Change. Since diatoms are extremely sensitive to environmental changes, they are the obvious choice to study diatom inferred water quality and climate changes. Therefore, sediment samples along with water samples were collected during pre monsoon seasons from the Nsonji Lake of the Nagaland, India to establish the relationship between the diatom and water quality. The Nsonji Lake has circum-neutral pH (around 7) indicating gradual degradation of organic matter leading to acidification of the lake. The surface sediments of the Nsonji Lake revealed the dominance of Discostella stelligera, Achnanthidium sp., Navicula cryptocephala, Navicula radiosa and Nitzschia palea. These diatom species could be used to unravel the acidification history of lake caused by natural and anthropogenic activities. Understanding the past climate dynamics need modern analogue in order to evaluate the important processes relative to Earth's history and built future scenario. Keywords: Diatoms, Water Quality, Acidification, pH, Organic Matter, Nsonji Lake, Nagaland

Distribution of the Diatoms and Water Quality Assessment of the Thamirabarani River, Tamil Nadu, South India


 
 
 
 
 
 The diatoms are one of the most significant organisms beneficial for biomonitoring investigations. The present study deals with the diatom and water samples collected from 10 different localities in the Thamirabarani River, Southern India. Diatom samples were collected by scraping stones with a toothbrush and squeezing macrophytes. Study of diatom valve morphology and measurements of diatoms were carried out using an optical miccroscope. The present study recorded 58 diatom taxa belonging to 25 genera. Among the diatoms, the taxonomical characters of 20 abundant diatom taxa viz. Aulacoseira granulata, Discostella stelligera, Navicula cryptocephala, Encyonema minutum, Gomphonema gandhii, Eunotia asterionelloides, Gomphonema parvulum, Brachysira neglectissima, Aulacoseira ambigua, Diadesmis confervacea, Nitzschia palea, Nitzschia amphibia, Sellaphora Americana, Staurosirella pinnata, Gomphonema affine, Fragilaria pararumpens, Eunotia incisa, Navicula erifuga, Navicula cryptotenella and Navicula rostellata are described and illustrated. In the present study abundant diatom genera were observed such as Aulacoseira, Discostella, Navicula, Encyonema, Gomphonema, Brachysira, Nitzschia, Sellaphora, Staurosirella, Fragilaria and Euno- tia. In abundant diatom taxa such as Aulacoseira granulate, Discostella stelligera, Gomphonema gandhii, Fragilaria pararumpens, Navicula cryptocephala, Navicula rostellata, Staurosirella pinnata water quality index values between 21-42 were recorded at Sites 1-9, which indicates unpolluted water. The abundant diatom taxa Diadesmis confervacea, Nitzschia palea, and Gomphonema parvulum were present at Site 10 and a water quality index value of 101 was recorded, indicating water polluted due to anthropogenic activity. The diatom assemblage of the present study was compared with various river systems to understand the environmental condition assessment. The water samples were analysed for assessment of the water quality.
 
 
 
 
 
 
 

Characterization of Spatiotemporal Variations in Mert Stream Water Quality by Phytoplankton Community and Biological Indices

In order to determine the water quality of the Mert Stream, algal indicators and some biological indices (TDI, IDG, PTI, Palmer, DAIpo) based on phytoplankton species were used. Phytoplankton samples were performed monthly from six different sites at a depth of 0.5 meter using a one-litre water sampler between July 2011 and June 2012. After phytoplankton samples were placed in 250-mL dark bottles and fixed with Lugol’s solution until processed in the laboratory, they were identified and counted in the tubular plankton counting chambers using an inverted microscope according to Utermöhl method. Bacillariophyta members became the dominant division in the phytoplankton with an abundance rate of 83.3% and 71 taxa. Lindavia glomerata, Navicula cryptocephala, Cyclotella planctonica, and Navicula veneta were determined as the most dominant species among phytoplanktonic taxa of Mert Stream. Trophic diatom index (TDI) and Generic diatom index (IDG) based on planktonic diatoms were used to determine the trophic status of the Mert Stream. Pollution tolerance index (PTI), Diatom assemblage index (DAIPo) and Palmer index were also included to assess the organic load-based sabrobity level of the Mert Stream. According to the results of mean TDI and IDG (55 and 13, respectively), the trophic status of the Mert Stream is a mesotrophic structure with moderate nutrients and good water transparency. According to the average PTI result (2.7), Mert Stream is in the β-mesosaprobic class, which corresponds to moderate pollution. Considering DAIpo indice, the saprobity of Mert stream is α-oligosaprobic level and the stream is not exposed to a serious organic-based pollution. However, according to the Palmer index, all stations of the Mert Stream except the 6th station are under the threat of high organic pollution. In present study, it was seen that the best biological index that reflects the station-based trophic structure of the stream is IDG, and the best biological index that reflects the station-based organic pollution of the stream is PTI.

河流着生藻类多样性对城镇化的响应-以深圳市为例

PDF HTML阅读 XML下载 导出引用 引用提醒 河流着生藻类多样性对城镇化的响应——以深圳市为例 DOI: 10.5846/stxb202105271393 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 深圳市主要河流水生态监测与评价项目（NO.2019-07-233） Response of stream benthic algal diversity to urbanization: A case study in Shenzhen Author: Affiliation: 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:着生藻类是河流生态状况的重要指示生物，然而关于城镇化对着生藻类多样性影响的研究还较缺乏。基于深圳市9条主要河流74个样点2020年雨、旱季的调查数据，对比了城区、郊区河流样点的着生藻类α、β多样性。两次调查共鉴定出着生藻类301个分类单元，其中硅藻门种类最多。谷皮菱形藻（Nitzschia palea）、隐头舟形藻（Navicula cryptocephala）、平庸菱形藻（Nitzschia inconspicua）等污染指示种在城区组相对丰度更高，而清洁指示种微小曲丝藻（Achnanthidium minutissimum）在郊区组相对丰度更高。城镇化对着生藻类物种丰富度、香农维纳多样性指数、Pielou均匀度指数等α多样性指数均无显著影响，但对着生藻类群落结构有显著影响。城区组样点的着生藻类β多样性（用主坐标分析质心指示）低于郊区组，城区组与郊区组藻类β多样性差异在旱季更为显著。两组样点的藻类β多样性差异主要来源于物种周转组分。与城区组着生藻类群落显著相关的环境因子包括总氮、高锰酸钾指数、电导率、pH、浊度和水深，而与郊区组着生藻类群落显著相关的是总氮、溶解性无机磷和电导率。研究发现，城市人类活动导致的总氮、溶解性无机磷、高锰酸钾指数、电导率等指标的显著增高导致着生藻类β多样性的降低。为了保护河流生物多样性，建议有效控制城区生产生活污水排放，减少人类活动对河流的干扰。 Abstract:Benthic algae are important indicators for ecological conditions of streams and rivers, but studies on effects of urbanization on benthic algal diversity is still sparse. In this study, we surveyed 74 sites from nine rivers located in Shenzhen City in the wet and dry season of 2020, and compared differences of α- and β- diversity of lotic benthic algal assemblages between urban and suburban groups. A total of 301 algal taxa were identified in the two seasons, among which the most taxa belonging to diatoms. The relative abundance of pollution indicator species such as Nitzschia palea, Navicula cryptocephala and Nitzschia inconspicua was higher in the urban groups, while the suburban groups with higher relative abundance of Achnanthidium minutissimum, which is an indicator species of clean water. We found that urbanization had no significant effects on algal α-diversity indices including richness, Shannon-Wiener's diversity index, and Pielou's index; while, algal community compositions in urban sites were significantly different from that of suburban sites. β-diversity of benthic algae, represented by centroids of the principal coordinate analysis, was lower for the urban sites than that of the suburban sites, with more significant difference in the dry season. The difference of benthic algal assemblages between the two groups mainly came from species turnover components. Total nitrogen, CODMn, conductivity, pH, turbidity and water depth were identified by the Mantel test as the environmental factors that were significantly correlated with algal community compositions in the urban group; while, TN, Dissolved inorganic Phosphorus (PO4-P) and conductivity were significantly correlated with the community compositions of benthic algae in the suburban group. We found that levels of TN, PO4-P, CODMn and conductivity were significantly increased in the urban group, which decreased β-diversity of benthic algae communities in Shenzhen rivers. To protect biodiversity of Shenzhen rivers, we therefore suggest to effectively control domestic and industrial sewage in urban areas to reduce human disturbance to rivers. 参考文献 相似文献 引证文献

Relations between Benthic Diatom Community and Characteristics of Karst Ponds in the Alpine Region of Slovenia

The aim of this research was to investigate the structure of the benthic diatom community and its relations to selected environmental parameters. We collected samples in 16 karst ponds in the alpine region of Slovenia, where the Alpine karst is found. Since the predominating substrate in these ponds was clay, the epipelic community was analyzed. Hydromorphological characteristics, and physical and chemical conditions were also measured at each site. We found 105 species of diatoms, which belonged to 32 genera. The most frequent taxa were Gomphonema parvulum (Kützing) Kützing, Navicula cryptocephala Kützing, Sellaphora pupula (Kützing) Mereschkowsky (species group) and Achnanthidium pyrenaicum (Hustedt) Kobayasi. The pond with the lowest diversity was found at the highest altitude, while, on the other hand, the most species-rich pond was found at the lowest altitude. Regarding the ecological types, the most common were motile species. We confirmed a positive correlation between the number of diatom species and the saturation of water with oxygen, while correlation between species richness and NH4-N was negative. The content of NO3-N and NH4-N explained almost 20% of the total variability of diatom community. Unlike our expectations, we calculated a negative correlation between the diversity of macroinvertebrates and diatoms, which is probably a consequence of different responses to environmental conditions.

Seasonal variation of phytoplankton community structure in the Tianhe Reservoir of the Daluoshan Mountain in southern Zhejiang Province, China and its indication to water quality

To explore the association between phytoplankton community structure and water quality of the Tianhe Reservoir in Wenzhou, Zhejiang, we examined the phytoplankton and physico-chemical factors in the Tianhe Reservoir from February 2019 to January 2020. A total of 89 phytoplankton species belonging to 60 genera and 7 phyla were identified. The annual average abundance and biomass of phytoplankton were 2.02×105 cells·L-1 and 0.26 mg·L-1 respectively. Bacillariophyta was dominant in the whole year. Chlorophyta was dominant in spring and autumn. Cyanophyta was dominant in summer. Both Euglenophyta and Pyrrophyta appeared in the whole year. Cryptophyta appeared in autumn and winter. However, none of them was dominant due to their low abundance. The dominant species throughout the year were Melosira granulata, Synedra acus, Navicula cryptocephala, Asterionella formosa, Pseudoanabaena, Closterlum venus, Pediastrum duplex, Peridinium bipes, Dinobryon cylindricum and Cryptomonas ovata. Results of redundancy analysis (RDA) showed that water temperature, total nitrogen, CODMn and pH value were the main factors driving phytoplankton community structure in the whole year. According to the evaluation based on diversity indices, including Shannon index, Pielou evenness index, Margalef richness index and comprehensive trophic status index (TLI), water quality of Tianhe Reservoir is between oligotrophication and mesotrophication.

Epipelic Algae in Hemren Reservoir , Iraq

The study includes the epipelic algae in Hemren reservoir, for the period between Januarys to October 2000 .The samples were collected from three selected sites at north, middle and south of reservoir. A total of 96 taxa of epipelic algae were identified. The diatoms were the dominated by 82 taxa represented 85.4% of the total identified species, followed by blue-green algae (cyanophyta) of 6.3 taxa (6%), and then green algae (chlorophyta) of 5.2 taxa (5%). One species was recorded for each crysophyta, euglenophyta and pyrrophyta. The seasonal variation for the cell density showed two peaks during spring and autumn seasons. Few species were dominated during the most studied period such as Achnanthes minutissima, Navicula cryptocephala, N. cryptocephala var . veneta and Nitzschia palea .

<p><strong>Re-examination of the type materials of <em>Navicula exilis</em> and <em>Navicula cryptocephala</em> (Naviculaceae, Bacillariophyceae)</strong></p>

Type material of Navicula exilis and Navicula cryptocephala from the Kützing collection at the Natural History Museum, London, was re-investigated in light and electron microscopy. The morphology of these species was studied in detail using original materials and the nomenclature and previous studies of type material summarized. Navicula exilis is compared with Navicula cryptocephala, Navicula cryptocephala var. exilis, Navicula lothargeitleri and Navicula adversa.

Sedimentary Diatom Records Reveal the Succession of Ecosystem in Lake Xihu, Dali over the Past 50 Years

In recent decades, intense human activities have caused a decline in many lake ecosystems in Yunnan Province, rendering the transformation of the lake from a clear macrophyte-dominated state to a turbid phytoplankton-dominated state. Improved understanding of the ecological changes in lake ecosystem has significant implications for management. In this study, a small lake in Dali Prefecture of Yunnan Province, i.e., Lake Xihu, was selected. Combined with diatom records and physicochemical proxies from the lake sediments, this paper focuses on the long-term ecological changes in Lake Xihu, Dali since the mid-1960s. The results show that the Lake Xihu, Dali has undergone a significant shift in stable states over the past 50 years. Prior to 2000, the benthic-epiphytic species (i.e., Cocconeis placentula, Staurosira construens, Gomphonema angustum, and Achnanthidium minutissimum) dominated in diatom assemblages, indicating oligotrophic conditions; since 2000, benthic-epiphytic species (i.e., Encyonopsis microcephala and Navicula cryptocephala) and planktonic species (i.e., Cyclotella atomus, Cyclotella meneghiniana, Stephanodiscus hantzschii, and Aulacoseira granulata) dominated successively, indicating mesotrophic to eutrophic conditions. Principal component analysis based on the diatom assemblages in temporal scale showed the response of diatoms succession to nutrients. Redundancy analysis also confirmed that nutrient enrichment was the main driving force for the succession of diatom assemblages in Lake Xihu, Dali. In the past 50 years, climate change and human activities (i.e., agricultural reclamation, fertilization, animal husbandry, and fishery) have enhanced the accumulation of nutrients in the lake. The continuous loading of nutrients promoted the propagation of planktonic algae, and also the productivity of the lake, rendering the transformation to a turbid phytoplankton-dominated state.

Bioassessing ecological status of surface waters in the Araban-Yavuzeli catchment (Turkey): application of diatom indices

Within the scope of the European Union Water Framework Directive, diatom assemblages as biological quality components were used to evaluate the ecological status of 12 surface waters in the Araban-Yavuzeli catchment between October 2013 and October 2014. A total of 75 diatom species were identified during the study period. Amphora ovalis, Denticula elegans, Gomphonema parvulum,Gomphonema truncatum, and Navicula cryptocephala were commonly observed. The relationship between diatom assemblages and environmental factors was assessed by canonical correspondence analysis and weighted average regression. Dissolved oxygen, tem-perature, nitrate, biological oxygen demand, lead, and copper played significant roles in the distribution and composition of diatom assemblages (P < 0.05). The ecological status of the stations in Araban and Yavuzeli was characterized using the trophic index-Turkey (TIT), trophic index (TI), and eutrophication and/or pollution index-diatom (EPI-D) indices. According to the TIT, Ardıl Creek1 had very good ecological conditions and was characterized by the occurrence of pollution-sensitive diatom taxa (e.g., Cymbella affinis, En-cyonema silesiacum, Navicula radiosa), indicated by multivariate analyses. The significant positive correlation of the TIT (P < 0.01, r = 0.789) with logPO4 indicated that TIT may be used as an appropriate diatom metric to assess the ecological status of surface waters in the Araban-Yavuzeli catchment.

Limno-ecological assessment of Aras River surface waters in Turkey: application of diatom indices.

This study is the first attempt to evaluate the limno-ecological status of freshwater ecosystems in Aras River system (Turkey) using diatom metrics and multivariate analyses according to the European Union Water Framework Directive requirements. Samples were collected using the standard protocols from 17 sampling stations in August and October of 2014, and June of 2015. Deterioration of water quality in the Aras River catchment was remarked from the downstream of Karakoyunlu, Sarısu, and Bozkuş creeks, which showed higher values of trophic index Turkey (TIT), trophic index (TI), and eutrophication and/or pollution index-diatom (EPI-D). These sites were also characterized by pollution tolerant taxa e.g., Cocconeis placentula, Gomphonema parvulum, Navicula cryptocephala, Navicula trivialis, and Tryblionella angustata. Sites S14-S17 had high ecological status according to TIT, supported by the score of EPI-D which indicated a good ecological condition for S14. The occurrence of pollution-sensitive species (e.g., Hannaea arcus, Cymbella affinis, Didymosphenia geminata, Meridion circulare, and Encyonema silesiacum) and the low nutrients like total phosphorus, orthophosphate and nitrate, conductivity, and BOD5 supported the high ecological status of S14-S17. The relationships between diatom assemblages and environmental variables were also illustrated by multivariate analyses. Spearman correlation analysis revealed that TIT had positive important correlations with total phosphorus (p < 0.01, r = 0.768). Trophic index and EPI-D had also significant correlations with environmental variables, but they had lower correlation coefficient than that of TIT. It seems that TIT could be a suitable diatom metric for assessing the ecological status of sampling stations in Aras River system and Mediterranean region. Our findings showed also that ecological statuses of surface waters should be evaluated due to the indices developed in their ecoregions.

Ecological quality assessment of running waters in the North Aegean catchment with diatom metrics and multivariate approach

Assessing ecological quality of surface waters is getting more important to achieve environmental sustainability since the implementation of EU Water Framework Directive. This study was designed to assess ecological quality of freshwater bodies in the North Aegean catchment using the trophic index Turkey (TIT), recently developed for Turkish running water assessment. This first work attempts to evaluate rivers water quality in the Northern Aegean catchment, a touristic region based on the diatom index dedicated to the Anatolia region. Data were taken from 18 sampling stations in the Northern Aegean catchment (Turkey) from August 2014 to August 2015. A canonical correspondence analysis (CCA) performed to evaluate the relationship between diatom assemblages and environmental variables especially nutrients, temperature, electrical conductivity, and biochemical oxygen demand played important roles in the distribution of diatom species. CCA explained 12.5% of the cumulative percentage variance of diatom assemblage’s data with 92.8% of the species-environment correlations. In related to the water ecological status, the lowest TIT (1.57) values was recorded in Geyikli creek, whereas the highest TIT (2.82) was calculated in Bakırçay stream. The ecological quality ratio changed between 0.58 (Bakırçay stream with moderate status) and 0.99 (Geyikli, Kar and Kemer creeks with high status). Pollution tolerant species such as Gomphonema parvulum, Navicula recens, Navicula cryptocephala, Navicula cryptotenella, Navicula trivialis, and Cyclotella meneghiniana characterized the moderate ecological status water bodies were, while the high and good ecological status sites were characterized by nutrient sensitive species such Navicula radiosa, Didymosphenia geminata, Cymbella excisa, and Hannaea arcus. The ecological status the water bodies indicated exactly the state of deterioration of these watercourses due to human activities in the catchment. A significant positive correlation between TIT values and logTP confirmed that this index as a metric is a useful biological tool for the bioassessment of regional water quality.

Microbial mats as shelter microhabitat for amphipods in an intermittent karstic spring

Microbial mats represent complex communities where cyanobacteria and diatoms as key organisms provide shelter for diverse assemblages of aquatic invertebrates, like the small stygophilous amphipodSynurella ambulans. Studies addressing such communities in the karst springs have rarely examined springheads, and have ignored intermittent springs. During high flow conditions the stygophilic crustaceans are flushed to the surface of a temporary stream Krčić where microbial mats prevent their drift and enables their successful retreat into underground in the periods of drought. The objective of this study was to characterize the microbial mat community of the Krčić Spring as a shelter forS.ambulansduring strong current and high water level. Representative samples for diatom and cyanobacterial species identification and composition, as well as the fresh mat material for potential animal activity and cyanobacterial phylogenetic analysis were collected. The most dominant diatom wasAchnanthidiumminutissimum, whilstFragilariacapucina,Meridioncirculare,NaviculacryptocephalaandNitzschiapaleahad abundance greater than 0.5%. Morphological observations of cyanobacteria revealed thatPhormidiumfavosumwas the most dominant, withHydrocoleummuscicolaas a subdominant. Cyanobacterial phylogenetic relationship revealed two distinct clusters: (i) "Phormidiumcluster", confirming morphological observations in both winter and spring samples, and (ii) "Wilmottiacluster", a first report for Croatia and found exclusively in the winter sample. Laboratory observations revealed a small stygophilic amphipodS.ambulans, hiding and feeding inside the pockets of fresh microbial mat. The intermittent Krčić Spring as a predator-free and competitor-free ecosystem provides a spatiotemporal conformity between microbial mat and stygophilous amphipod.

Factors driving diversity and succession of diatom assemblages in a Neotropical rainforest stream

This study assessed short-term succession and related changes in diversity and succession of benthic diatom assemblages in a tropical rainforest stream in the biogeographic region of Chocó, Colombia. Diatom colonizationin situwas studied over a 60-day period, in which we analyzed the number of valves and the taxonomic changes. The Shannon index ranged from 2.06 to 3.02 bits. A total of 127 species were identified and the most abundant were acidophilic species such asEunotia intermedia,E. veneris,E. bilunaris var. mucophila,E. pirlaandE. bilunaris. A Detrended Canonical Correspondence Analysis (DCCA) was used to explore the succession of diatom assemblages and its driving environmental factors. The DCCA explained 74.1% of the correlation between environmental variables and diatom species and 16.2% of the data variance. The species fell into four groups, the first group (Eunotia incisa,Frustulia saxonica,Fragilaria capucina var. acatu, among others) was related to lower nitrate concentrations, acidic pH and lower water temperature. The second group (Fragilaria capensis,Gomphonema olivaceum,Cymbella gracilis, among others) was associated to higher alkalinity and lower solar radiation availability. The third group (Nitzschia obtusa,N. amphibia,Naviculadicta vitabunda,Navicula cryptocephala, among others) was related to lower phosphate, higher nitrate concentrations, lower pH, and higher temperatures. The fourth group (Eunotia soleirolli,Frustulia vulgarisandF. rhomboides)was associated with higher solar radiation and lower alkalinity. These results underscore the importance of diatom diversity in Neotropical streams and the relevance of small variations in environmental factors on the composition of reference assemblages of Neotropical fluvial systems.

Periphytic Diatoms in the Polluted Linggi (sensu stricto) and Kundor Rivers, Negeri Sembilan, Malaysia

The investigation in this paper aimed to describe periphytic diatom assemblage, species composition and distribution in tropical polluted Linggi (sensu stricto or s.s.) and Kundor rivers in Negeri Sembilan, Malaysia. Regardless of ecological and environmental conditions, diatoms were the numerically dominant flora among periphytic algae collected monthly over a period of 13 months at nine stations in the Linggi (s.s.) and Kundor rivers. The freshwater periphytic diatom samples were collected mainly using artificial substrates and supplemented with natural substrates. The periphytic diatoms thus collected from both natural and artificial substrates comprised 86 taxa (82 pennate and 4 centric forms) belonging to 21 genera. Of the 86 species, 71 species were found colonized in artificial substrates while the remaining 15 species were recorded exclusively on natural substrates. On the whole, the most common diatoms in both rivers combined were Eunotia vanheurckii, Gomphonema parvulum, Nitzschia palea, Pinnularia braunii, Navicula cryptocephala, Achnanthes saxonica, Achnanthes minutissima and Pinnularia microstauron. The most abundant species were E. vanheurckii, N. palea, A. saxonica, G. parvulum and A. minutissima.

Ecología del fitoplancton primaveral de superficie en el lago de Tequesquitengo, Morelos, México

Physical and chemical data including temperature and transparency of the water, pH, dissolved oxygen, hardness and alcalinity, as well as primary production and details of the phytoplankton structure in the lake of Tequesquitengo, Morelos, Mexico between March 7 and May 22, 1981 are presented here. Fifteen species were identified: 13 in bottle samples and 2 in one series taken with net, five taxa could be identified to genus level; all taxa belong to five algal lasses; the diatom Navicula cryptocephala and the dinoflagellate Peridinium cinctum were the most abundant species. During this study, while dominance decreased by one single species the diversity and eveness indices were increasing. At the end of May the green and the blue-green algae increase in numerical importance. Gross primary produ ction and phytoplankton biornass were significantly related. Influence by stratification and mixed periods over the variation of some variables and phytoplankton species succession is discussed.

ESTUDIO DEL VALOR INDICADOR DE LAS COMUNIDADES DE ALGAS BENTÓNICAS: UNA PROPUESTA DE EVALUACIÓN Y APLICACIÓN EN EL RÍO MAGDALENA, CIUDAD DE MÉXICO

The application and development of environmental laws governing watershed management requires identification of biological indicators, parameters and measures to establish its ecological status, for which the present study aims to characterize the ecological indicator value of stream benthic algae in an urban area of Mexico City. Six sites of the Magdalena river were studied in the most contrasting seasons: dry-warm, rainy and dry-cold. At each site the physicochemical parameters of water were recorded and 10 samples were collected: Five with visible algal growths and five with diatoms. The environmental quality of each site was determined by the trophic status and its confirmation with the richness and benthic algal diversity, through a canonical correspondence analysis and the calculation of the indicator value of species (IndVal). According to the trophic status, three groups of sites were recognized. The first group (G1) was assessed as reference of the oligotrophic conditions and presented 11 species with the highest IndVal, protruding: Encyonema silesiacum, Gomphonema parvulum, Navicula cryptocephala, Planothidium lanceolatum, Vaucheria bursata, Placoma regulare and Nostoc parmelioides. A second group (G2) was associated with 15 species considered detectors, which were tolerant to increased nutrients in at least one season, such as Diatoma mesodon and Prasiola mexicana. The third group (G3) included sites with species that had a wide range of tolerance to pollution: Fistulifera saprophila , Nitzschia minuta , Nitzschia palea , Nitzschia recta and Phormidium autumnale. The species IndVal of Magdalena River has established reference sites of good environmental quality and those that are altered by human activities, therefore they are recommended as the first step in a methodological proposal for a long-term biomonitoring through a biological index.

Are diatoms a reliable and valuable bio-indicator to assess sub-tropical river ecosystem health?

The use of diatoms as bio-indicators of water quality is common in temperate regions worldwide. However, less attention has been accorded to sub-tropical regions, particularly in Australia. This study assessed the value of diatom communities to infer water quality in a sub-tropical riverine system. Epilithic diatom and water samples were collected monthly from an east Australian river. Principal components analysis showed that the Lower Catchment sites were more strongly influenced by the measured environmental variables differentiating them from the Upper Catchment sites. Canonical Correspondence Analysis showed electrical conductivity and total phosphorus strongly influenced the diatom community distribution. The study revealed diatom species that are robust bio-indicators of water quality in this sub-tropical catchment. Cocconeis placentula, C. placentula var lineata, Gomphonema spec 2 and Tabellaria flocculosa were identified as indicators of moderate water quality. Bacillaria paradoxa, Navicula cryptocephala, Navicula mutica var mutica and Achnanthes fogedii were identified as indicators of poor water quality. This study identified that diatoms are effective indicators of water quality. Further research is required to develop a diatom biological index applicable to sub-tropical east Australian river systems to improve the effectiveness of environmental monitoring and sustainable river management.