Maria Helena Novais

Effect of riparian vegetation on diatom assemblages in headwater streams under different land uses.

Differences in the structure of diatom assemblages in headwaters with contrasting shading conditions and different land use in the buffer zone and upper catchment were studied in order to evaluate the influence of the lack of riparian vegetation on the biofilm. The objective was to ascertain whether a riparian buffer can mitigate the negative influence of human induced disturbance and pollution on diatom assemblages in headwaters. Four streams were selected in order to maximize the differences in the land cover and minimize other environmental gradients. Multivariate statistics, different comparative and permutation tests and correlations were applied to compare the diatom assemblages, the Specific Polluosensitivity Index (IPS) and the diatom ecological guilds (low profile, high profile and motile) among the sites studied and to evaluate their responses to disturbances. The analysis showed that low profile diatoms typically dominated in forested headwaters with limited resources, whilst assemblages at impacted sites showed a wider range of growth forms. In unimpacted streams, the diatom assemblages were influenced by temperature, pH, conductivity and calcium, as usually reported for oligotrophic streams with high natural disturbance due to fast current and shading. In both shaded and unshaded impacted streams, the importance of nutrients and land use disturbance, especially urbanization, prevailed. This trend was also reflected by the IPS index that showed consistently lower values at impacted sites, correlating most significantly with nutrients. The diatom species composition as well as diatom guilds at impacted sites were similar, regardless of the presence or absence of riparian vegetation, and were significantly influenced by seasonal changes. Our results indicate that diatoms react sensitively to alterations of the water environment in headwaters, induced by anthropogenic activities, and these impacts are not buffered by an intact riparian zone. Diatoms closely reflected land use practices in the upper catchment regardless of the buffer zone status.

Ecological assessment of Portuguese reservoirs based on littoral epilithic diatoms

The objective of this study was to evaluate whether biological methods based on epilithic littoral diatoms are a valuable complement to other biological elements for the assessment of the ecological potential of reservoirs in Portugal, in accordance with the requirements of the European Water Framework Directive. The statistical analysis performed (PCA, DCA, ANOSIM and SIMPER) based on the study of diatom communities of 18 reservoirs allowed the following results: (i) the separation of all the a priori defined types (North, Main Courses and South) was proved; (ii) there were no significant differences between reservoirs classified as reference and non-reference and (iii) the classification of the reservoirs as reference or non-reference based on the use of the diatom Specific Pollution sensitivity Index as a complementary variable allowed the definition of Maximum Ecological Potential reservoirs for the North and South types. Methods based on the use of epilithic littoral diatoms can therefore contribute, together with other biological elements, for the assessment of the ecological potential of aquatic lentic systems in Portugal, almost exclusively constituted by reservoirs.

Morphology and ecology of Achnanthidium caravelense (Bacillariophyceae), a new species from Portuguese rivers

A new benthic freshwater diatom species belonging to the genus Achnanthidium Kutz. has been recorded from several watercourses in the North of Portugal. Achnanthid- ium caravelense Novais et Ector is described as a new species based on light and scanning electron microscopic observations, as well as on its ecological preferences as reconstructed from field observations. The most characteristic morphological features of this species are the different outline of the raphe valve (narrowly elliptic with linear margins) and the ra- pheless valve (narrowly elliptic to narrowly rhombic with moderately convex margins), the non-protracted broadly rounded apices and the length/width ratio. Furthermore, the areolae of the single row along the mantle are elongated and are more or less widely open, which is a characteristic discernible in girdle view under light microscopy. The species that A. caravelense resembles most is A. eutrophilum (LaNgE-BErt.) LaNgE-BErt.; nevertheless it can be distinguished from the latter by the different raphe valve outline, its higher valve length/width ratio and autecology. A. caravelense is common and abundant in soft waters with low to moderate nutrient content in the North of Portugal.

Transfer of Staurosira grunowii to Staurosirella

The new combination Staurosirella grunowii (Pantocsek) E. Morales, Buczkó & Ector comb. nov. is presented based on a detailed analysis of fossil material from Lutila, Slovakia using light and scanning electron microscopy. The species is widely known as Staurosira harrisonii var. amphitetras Grunow. Striae bearing well-developed vimines delimiting typically long areolae, thick virgae-bearing spines, developed apical pore fields composed of simple round poroids and open girdle bands with valvocopula-bearing fimbriae are some of the features that link this taxon to species currently ascribed to Staurosirella D.M. Williams & Round. The taxon is readily distinguished by its tetra-angular shape, which is not seen in any other species within this genus. An analysis of the morphology of this taxon together with its nomenclatural history is presented herein.

EOLIMNA BECARESII SP. NOV., A NEW DIATOM TAXON FROM A SPANISH SHALLOW LAKE

In 2003 during a biological survey carried out on the shallow lakes located on the northern Iberian plateau, a diatom community dominated by an unknown Eolimna sp. was found as an epiphyte on Chara connivens in Lake Constanzana (Spain). Detailed light and scanning electron microscopy observations allowed the description of this new species. Differential diagnostic criteria with respect to similar taxa, especially E. archibaldii J.C. Taylor & Lange-Bertalot, together with ecological implications of this finding, are briefly discussed.

New species and combinations in the genus Geissleria (Bacillariophyceae)

Abstract Two new Geissleria species are described from Portugal based on their morphological and ultrastructural characteristics. Geissleria tagensis Novais et Ector sp. nov. has rhombic-elliptical valves with broadly rounded to slightly protracted apices and lacks an isolated pore. Geissleria lusitanica Novais et Ector sp. nov. has linear-elliptical to elliptical valves with slightly to markedly protracted ends and two isolated pores. The type analysis of similar species (Geissleria acceptata (Hustedt) Lange-Bertalot et Metzeltin, G. schoenfeldii (Hustedt) Lange-Bertalot et Metzeltin and Navicula modica Hustedt) allowed their better characterization and illustration, supporting the delimitation of the new Portuguese species. A new taxon present in the type material of G. schoenfeldii, G. hinziae Novais et Ector is also described. Three new combinations are also proposed: Geissleria capitata (H. Kobayasi in Kobayasi et Ando) Ector et Novais comb, nov., G. modica (Hustedt) C.E. Wetzel, Novais et Ector comb. nov. and G. taishanica (Y.Q. Guo et S.Q. Xie) Ector et Novais comb. nov. A checklist of the species and a thorough survey of the literature available on Geissleria are provided.

On the 3D reconstruction of diatom frustules: a novel method, applications, and limitations

Because of the importance of diatoms and the lack of information about their third dimension, a new method for the 3D reconstruction is explored, based on digital image correlation of several scanning electron microscope images. The accuracy of the method to reconstruct both centric and pennate (symmetrical and asymmetrical) diatoms was shown, independently of valve size and shape, and considering not only the general frustule morphology but also the intricate ornamentation. Several measurements were obtained, such as of the surface and projected areas and the valve volume. These results were validated by focused ion beam transverse cross section of one valve, and the quantitative results were compared with geometric models commonly applied. Furthermore, direct volume calculations based on 3D reconstructions have several advantages, such as it has higher taxonomic accuracy than the methods based on light microscopy; it solves the problems of the light halos; it allows the precise measurement of all linear dimensions, including the often neglected third dimension; natural samples can be measured directly; and it provides an exact estimate of cell volume, independently of its shape or alterations due to life cycle stage. This approach provides therefore a simple way to measure the morphological features of diatoms, even at a nanoscale, and can be applied to other microorganisms commonly illustrated by means of scanning electron microscopy.