Stream Periphyton

Diatoms have become important organisms for monitoring freshwaters and their value has been recognised in Europe, American and African continents. If India is to include diatoms in the current suite of bioindicators, then thorough testing of diatom-based techniques is required. This paper provides guidance on methods through all stages of diatom collection from different habitats from streams and lakes, preparation and examination for the purposes of water quality assessment that can be adapted to most aquatic ecosystems in India.

The Island of Majorca (Spain) is characterized by a Mediterranean climate and a karstic geology that favors
the formation of numerous springs and spring–fed streams on the island’s Northwester zone. Water and epilithic diatom
samples were collected from two springs and four spring–fed streams, located at altitudes ranging from 0 to 756 m a.s.l.,
in different seasons between 2005 and 2008. Water chemistry in these systems is characterized by high concentrations of
dissolved calcium and pH values ranging from 6.6 to 8.4. A total of 111 diatom taxa belonging to 40 genera were found and
the most abundant taxa were illustrated with LM and SEM. The diatom communities of the studied sites were dominated by
species such as Achnanthidium minutissimum, A. pyrenaicum, Amphora pediculus, Cymbella vulgata, Diploneis separanda,
Encyonopsis minuta, Gomphonema lateripunctatum and Navicula cryptotenella, reflecting the calcareous geological nature
of Majorca Island. In the framework of the study 22 diatom taxa, which are new for Balearic Islands were recorded, such
as Achnanthidium straubianum, Amphora indistincta, Cymbella lange–bertalotii,Encyonopsis subminuta, Karayevia kolbei,
Navicula aff.margalithii, N. reichardtiana and N. subalpina. In addition, a new freshwater diatom species belonging to the
genus Cymbopleura,C. margalefii was found in the Torrente of Deià. Cymbopleura margalefiiis described as a new species
based on LM and SEM observations, and compared with similar taxa. A checklist of the 309 diatom taxa recorded so far from
the Balearic Islands is also presented.

Doñana temporary ponds (southwest Spain) form a system of water bodies of remarkable ecological singularity with a high protection status. However, its species composition, diversity, and distribution of algal communities are largely unknown. During a biological survey carried out in shallow temporary ponds in 2010, several unknown diatom taxa were found in various population densities in the epiphyton of these systems. Detailed light and scanning electron microscopy observations allowed the description of five of them (Eunotia vozmedianoi, Planothidium lacustre, Halamphora tharsis, G. undulans and Pinnularia acidophila var. baetica) as taxa new to science. Differential diagnostic criteria with respect to similar taxa, together with ecological and biogeographical implications of these findings, are briefly discussed. Our results support recent studies indicating that endemism in diatoms might be a widespread pattern.

"The Duero River Basin, with an area of 97290 km2 and more than 40000 km of streams, is the largest one in the Iberian Peninsula, and lies mainly under Mediterranean continentalized bioclimate. Aquatic ecosystems are endorheic and main watercourses are regulated and highly anthropized. As in every lotic environment, benthic algae play a key role in the structure and functioning of its ecosystems and, within this group, diatoms represent the most abundant and diversified component. Their biological features make them excellent water quality indicators, and this has promoted their study at international level. As a result of the implementation of the Water Framework Directive of the European Union, ecological status biomonitoring networks have been established in all Iberian basins, based on the use, among others, of diatom indices, which has led to the need of more detailed taxonomic and ecological studies on these organisms. Despite their relevancy, such works are still scarce in Spain. In the Duero Basin, up to date more than 500 diatom species have been recorded, a high floristic richness that contrasts with analogue regions, this being related to the large diversity of environmental conditions included within this zone.
The aim of the present work is to elaborate a practical identification guide in accordance with the needs of technicians and biologists evaluating water biological quality in the Duero Basin. This book gathers the 200 main diatom taxa in terms of abundance and occurrence, selected from more than 600 samples of river epilithon collected during annual surveys carried out between 2003 and 2007 in the Spanish part of the basin. Certain taxa that could not be identified to specific level are also presented. For every diatom species, the following information is provided: a mor-phometric and autoecological description, a selection of illustrated bibliographic references and an iconographic series illustrating the taxon’s morphological variability, with a total of 3110 photographs in light and scanning electron microscopy gathered into 109 plates. The nomenclature, taxonomy and systematic position of taxa follow the most recent phycological literature. 116 species new to the Duero Basin and 34 species new to the Iberian Peninsula are presented."

The terrestrial diatom Microcostatus schoemanii sp. nov. is described from dry soils of the Faan Meintjies Nature Reserve (North-West Province, South Africa). Microcostatus cholnokyi sp. nov. and Microcostatus angloensis  sp. nov. are described from sandy soils at a colliery near the town of Kriel (Mpumalanga Province, South Africa). The morphology of these taxa is examined using both light (LM) and scanning electron microscopy (SEM) and new taxa are compared with similar species. In M. schoemanii the density of the striae combined with the valve outline and the distance between the central raphe endings are the main distinguishing morphological features. M. cholnokyi is differentiated by the presence of a conopeum and the distinct structure of the microcostae. M. angloensis  is similar to M. schoemanii but differentiated by the shape of the cell and the apices, the angle of striation and the distance in between the proximal raphe endings.

"This work aims to analyse the response of epilithic diatom communities to environmental gradients in subtropical temperate
southern Brazilian rivers to contribute to the development of a widely applicable methodology for water-quality monitoring.
Samples for physical, chemical and biological determination were collected monthly, from December 2001 to November
2002 and from March 2003 to February 2004, at 9 stations along the rivers Pardo and Pardinho in the hydrographical basin
of Rio Pardo, State of Rio Grande do Sul (RS), Brazil. Physical and chemical variables (water temperature, pH, dissolved
oxygen, biochemical oxygen demand, chemical oxygen demand, nitrates, nitrites, phosphates and total dissolved solids) and
biological variables (epilithic diatom communities) were used as parameters for water-quality assessment. The data matrix
was examined by means of a multivariate ordination using Detrended Correspondence Analysis (DCA). In total, 270 taxa
were identied to specic or infra-specic levels. The results showed that of all the physical and chemical variables used, the
main gradient along the DCA rst axis was eutrophication, which was indicated by its signicant correlation with phosphates
( p < 0.001). Hence, the species’ scores on the DCA axis were used as an operational criterion for indicating their tolerance to
eutrophication. From this analysis, the 10 taxa that were the most tolerant to eutrophication were: Cyclotella meneghiniana,
Fallacia monoculata, Nitzschia acicularis, N. clausii, N. nana, N. palea, Nitzschia sp., Pinnularia sp., Sellaphora pupula
sensu lato and Ulnaria acus. The present study showed that epilithic diatom assemblages reect anthropogenic changes in
hydrographic basins in subtropical temperate streams, especially pollution by organic enrichment and eutrophication."

During a biological survey carried out in 2009, epiphytic and phytoplanktonic diatom assemblages of three  shallow saline lakes in the South of the Bolivian Altiplano (Lipez Area) (>4100 m asl), were studied.  Within the  identified taxa, Navicula pseudogracilis, Staurophora vilamae, Halamphora atacamana, Halamphora carvajaliana,  Halamphora atacamae, Denticula valida f. major and Surirella chilensis were studied in detail. For each of these, a  brief morphologic and morphometric description, a collection of bibliographic references where the taxon is cited or  illustrated in the scientific literature, and light and scanning electronic microscopy images are presented. S. vilamae  and D. valida f. major are cited for the first time out of their type localities, this last taxa observed for the first time  in the world since 1894. Besides, N. pseudogracilis is cited as a new species for Bolivia and the ultrastructure of this  taxon and D. valida f. major were illustrated for the first time.

"En este trabajo se ha realizado una aplicación que extrae automáticamente las principales características geométricas de las algas diatomeas. Estas algas resultan de gran utilidad en la monitorización de la calidad de las aguas, de ahí la importancia que la automatización de los procesos de análisis conlleva. La aplicación extrae 15 descriptores geométricos de
cada diatomea almacenando su valor tanto en píxeles como en micrómetros. Se obtiene también la presencia o no del estigma al ser éste un valor determinante en la clasificación. Para llegar a este resultado es necesario realizar con anterioridad una segmentación autónoma de las imágenes digitales obtenidas mediante fotografía digital. Dicha
segmentación autónoma requirió del desarrollo de un método específico basado en la combinación de dos técnicas: binarización por umbralización y detección de bordes utilizando el filtro de Canny. La separación de objetos solapados se resolvió mediante un método que combina binarizaciones, filtrados, adelgazamientos, operaciones morfológicas y el detector de bordes de Canny. Los valores
geométricos calculados se compararon con los resultados proporcionados por un experto, tras realizar las mediciones de forma manual. Los resultados son muy similares por lo que se considera correcto el desarrollo realizado."

In 2009, seventeen analysts participated in a pan-European diatom ring-test (intercalibration), analyzing nine samples from seven countries following the European standard EN 14407. The objective of this exercise was to agree on practical conventions on diatom identification to facilitate future intercalibration work and to assess the extent to which national differences in sample analysis (counting protocol and identification conventions) contribute to variability in EU-level comparisons of diatom-based methods. Differences in the reported taxa lists were large, but not a major source of variation in values of a common metric (the phytobenthos Intercalibration Common Metric, ICM). Therefore, every country can apply its own identification conventions for national assessments, and still be fairly confident that the ICM reflects the national classification of its streams. Part of the index variation was due to differences in counting protocols and care should be taken when handling broken valves, girdle views and small taxa. More work at both national and European level is needed to provide a harmonized way of using diatoms for ecological status assessments in the future.

"Hippodonta lange-bertalotii Van de Vijver, Mataloni & Vinocur sp. nov. is described from Crater
Lake, Deception Island (South Shetland Islands). Present paper reports a detailed morphological descrip-tion of this species by means of light and scanning electron microscopy. The main diagnostic criteria in-clude the rhombic outline of the valves, the comparatively narrow striae and the presence of two shortened
striae delimiting the central area. The adscription of this new species to the genus Hippodonta  and the
differences with related taxa are briefl y discussed. Additionally, the morphological variability of the similar
H. pseudacceptata  is examined analyzing the valvar ultrastructure of different populations collected from
Western Europe or published in the literature.  Hippodonta pumila  is presented as a heterotypic synonym
of H. pseudacceptata."

For bioassessment of freshwaters, diatom indices have been mainly used in streams although their applicability in shallow lakes has been demonstrated in several studies. However, the influence of sampling substrata on periphytic diatom communities and on the ecological quality inferred from them has been paid little attention. In this paper, we test the ‘neutral substrate hypothesis’, which predicts no relevant influence of host plant type on their epiphytic community. Nineteen shallow permanent lakes from north-west Spain were studied and classified into three trophic levels. Epiphytic diatom communities growing on three different macrophytes for each trophic level were sampled and analysed. We assess: (1) which of the most common diatom indices provides a reliable water quality assessment, (2) how different plant substrata influence the diatom communities growing on them and (3) how these differences affect water quality assessment. Similarity tests showed significant differences in the composition of diatom assemblages among nutrient concentrations and host macrophytes. In contrast, ANOVA results for selected diatom-based metrics showed significant differences among trophic levels but not between different plant substrata. This supports the use of epiphytic diatoms as biological indicators for shallow lakes irrespective of the dominant macrophyte.

During a biological survey carried out in five shallow, high-altitude saline lakes of the Bolivian Altiplano in 2009, six unknown diatom
taxa were found in various lake populations. Detailed light and scanning electron microscopy observations allowed the description of the
following new taxa: Navicula venetoides (distinguished from N. veneta Kützing by having coarser lineate striae), Pinnularia boliviana
(similar to P. rhombarea var. halophila Krammer but with coarser striae and a narrower central area), Nitzschia sansimoni (morphologically
close to N. supralitorea Lange-Bertalot, the latter having denser striae), Surirella striatula var. halophila (differing from the nominate and
other varieties in a distinctly heteropolar outline and the presence of denser fibulae) and S. moralesii (with large, strictly isopolar valves
and a deep pervalvar depression). Differential diagnostic criteria with respect to similar taxa, together with ecological and biogeographical
implications of these findings, are briefly discussed.