Salomé F. P. Almeida

Heavy metal pollution downstream the abandoned Coval da Mó mine (Portugal) and associated effects on epilithic diatom communities.

This study examined trace-element concentrations in 39 sediment samples collected in the vicinity of the abandoned Coval da Mó mine, and evaluated the anthropogenic contaminant effects and other environmental variables in the taxonomic composition, structure and morphological changes of benthic diatom communities. The results show the existence of extremely high contamination in Pb, Zn and Cd (the mean values exceed the background values 376, 96 and 19 times, respectively) on the first 2.5 km in the water flow direction. Also Co, Cu, Mn and Ni are present in high concentrations. Dilution by relatively uncontaminated sediment reduces metal concentrations downstream, but Zn concentrations increase downstream Fílvida stream, as a result of several factors such as sewage and agriculture. To evaluate the biological effects caused by Pb, Cd and Zn, three sites were selected. In the stressed environment, near the mining area (C232), diatoms were extremely rare, however there was a slight recovery at site C79 located 2km downstream. Fragilaria capucina var. rumpens, Fragilaria cf. crotonensis and Achnanthidium minutissimum showed abnormal valves which may be related to high levels of metals. Six km downstream, in Fílvida stream (C85), an increase in species richness and diversity was registered while the relative percentage of valve teratologies was lower. In the absence of OM, nutrients and low pH the diatom community patterns must be attributed to the metal concentration at some sites. Considering that community diversity can be affected by abiotic and biotic variables and valve deformations are caused by a small number of variables, basically metals, and acid conditions, we consider the presence of teratologies as an indication of the presence of metals.

Diatoms and macroinvertebrates provide consistent and complementary information on environmental quality

Predictive models based on invertebrate assemblages are a powerful tool for assessing water quality. Yet, few attempts have been made to build predictive models with diatoms although they are widely used in freshwater assessment and are among the mandatory biological monitoring elements indicated in the European Water Framework Directive. We built two predictive models for central Portugal, one for macroinvertebrates and the other for diatoms, using data sampled simultaneously from 43 sites in the Spring of 2004 and 2005. Our objective was to test the performance of models based on the diatom community and compare the assessments made by the two indicator communities for the same sites. Each model was tested with 17 sites. Both models showed good performance in predicting reference sites to the correct group: 76 % for the macroinvertebrate model using the discriminant variables longitude, distance to source, alkalinity, depth, number of riffles and channel substrate diversity; 85 % for the diatoms model using latitude, runoff, mineralization, distance to source, slope, discharge and hardness. The water quality assessments of test sites produced by the two models were similar in 76 % of the cases. According to the predictive models, invertebrates were more sensitive to morphological alterations of the channel and habitat conditions (presence of dams and artificial walls, destruction of riparian corridor) while diatoms were more sensitive to changes in water chemistry. Moreover, in lowland streams, where the habitat and substrate heterogeneity are naturally low, assessment by diatoms was more useful than evaluations using invertebrates. We concluded that invertebrates and algae provide consistent and in some cases complementary information on environmental quality and recommend their simultaneous use for bioassessment.

Sensitivity of biochemical markers to evaluate cadmium stress in the freshwater diatom Nitzschia palea (Kützing) W. Smith.

Human activities have been increasing the cadmium levels in soils and waters, disturbing many organisms in the primary trophic levels such as microalgae. Toxic metal pollution is a focus point of serious concern and the examination and monitoring water quality are becoming essential procedures. Diatoms are important bioindicators to monitor the metal concentrations in diverse habitats. The present study was planned to determine the biochemical mechanisms used by freshwater diatoms to cope with cadmium stress and to identify biomarkers of metal stress. For this, Nitzschia palea (Kützing) W. Smith was grown under different concentrations of Cd (0.01-0.1 mg l(-1)) and the IC(50) determined. Three concentrations (0.1, 0.2 and 0.3 mg Cd l(-1)) and a control (no cadmium) were used to undergo the experimental assays which allowed the determination of cadmium accumulation and several biochemical markers currently used to assess metal stress. N. palea was sensitive to cadmium, as the IC(50) calculated was 0.0276 mg Cd l(-1). Cadmium accumulation increased sharply and was mainly associated to the frustule. Total protein content increased with cadmium exposure, inducing increases and decreases in polypeptide expression, indicating an attempt of N. palea cells to adjust to the new prevailing conditions induced by metal stress. In order to cope with cadmium stress, cells induced the synthesis of chelating molecules such as phytochelatins (PCs). The enzymatic (SOD and CAT) and non-enzymatic (glutathione and proline) ROS scavenging mechanisms were also induced. Our results indicate the existence of diverse metal stress-mediated mechanisms in order to lessen metal damages to the cell. PCs showed to be a suitable biomarker of metal stress; besides being metal specific and concentration respondent it also allows to infer about the level of stress imposed to cells, constituting a useful tool to complement the evaluation of diatom communities when accessing aquatic metal toxicity.

Identification versus counting protocols as sources of uncertainty in diatom-based ecological status assessments

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.

Water quality assessment of rivers using diatom metrics across Mediterranean Europe: A methods intercalibration exercise

The European Water Framework Directive establishes a framework for the protection of water resources. However, common water management tools demand common understanding of assessment methods, so quality goals are equally met. Intercalibration of methods ensures the comparability of biological elements across similar geographical areas. Many aspects can influence the outcome of intercalibration: data sampling, treatment methods, taxonomic reliability of databases, choice of metrics for ecological quality status classification, and criteria for selecting reference sites. This study describes the potentials and constraints of the intercalibration of indices using diatoms for assessment of Mediterranean rivers. Harmonisation of diatom taxonomy and nomenclature was based on a previous ring test which took place at the European level. Four diatom indices (Indice de Polluosensibilité Spécifique-IPS, Indice Biologique Diatomées-IBD 2007, Intercalibration Common Metric Italy-ICMi and Slovenian Ecological Status assessment system) were intercalibrated using data from six European Mediterranean countries (Cyprus, France, Italy, Portugal, Slovenia and Spain). Boundaries between High/Good and Good/Moderate quality classes were harmonised by means of the Intercalibration Common Metric (ICM). Comparability between countries was assured through boundary bias and class agreement. The national boundaries were adjusted when they deviated more than a quarter of a class equivalent (0.25) from the global mean. All national methods correlated well with the ICM, which was sensitive to water quality (negatively correlated to nutrients). Achnanthidium minutissimum sensu lato was the most discriminative species of Good ecological status class. Planothidium frequentissimum, Gomphonema parvulum and Nitzschia palea were the most contributive to Moderate ecological status class. Some taxa were discriminative for both Good and Moderate ecological status classes due to low indication and ecological discriminative power but also due to differences in taxonomy between countries. This intercalibration exercise allowed establishment of common water quality goals across Mediterranean Europe, which is substantiated with the ICM.

Ecology of freshwater diatoms from the central region of Portugal

Abstract Tychoplanktonic and epilithic diatom samples were taken monthly during one year at 18 sites in small lowland rivers in the northern central region of Portugal. Canonical correspondence analysis was used to explore the relationships between measured environmental variables and patterns in the diatom assemblages. Conductivity, HCO3−, and chemical oxygen demand (COD) were the most significant environmental variables influencing the structure of the tychoplankton and of the epilithon. Other less important variables, such as K+, Fe, N(NO3−), and Na+ also explained significant (P 600 μS·cm−1), alkaline pH, HCO3− concentrations equal or higher than 150 mg·l−1, the first group includes Achnanthes hungarica Grunow, Amphora pediculus (Kutzing) Grunow, Bacillaria paxillifera (O. F. Muller) Hendey, Cymatopleura solea (Brebisson) W. Smith, Navicula accomoda Hustedt, Navicula lanceolata (Agardh) Ehrenberg, Navicula trivialis Lange-Bertalot, Nitzschia hungarica Grunow. In waters of lower conductivity (varying between 72 and 262 μS·cm−1) slightly acid pH (6 to 6.5) and HCO3−1 lower than 46 mg·l−1 the following species were common: Achnanthes oblongella Ostrup, Achnanthes subatomoides (Hustedt) Lange-Bertalot, et Archibald, Cymbella gracilis (Ehrenberg) Kutzing, Cymbella naviculiformis Auerswald, Diatoma mesodon (Ehrenberg) Kutzing, and Eunotia exigua (Brebisson) Rabenhorst. Considering COD, two further groups were distinguished. At high values (> 40 mg·l−1) the following taxa were observed: Achnanthes delicatula (Kutzing) Grunow, Navicula capitata Ehrenberg var. hungarica (Grunow) Ross, Nitzschia nana Grunow, Pinnularia interrupta W. Smith, Thalassiosira pseudonana Hasle & Heimdal, Thalassiosira weisflogii (Grunow) Fryxell et Hasle. For lower values than 19 mg·l−1, we found Cymbella naviculiformis Auerswald, Diatoma mesodon (Ehrenberg) Kutzing, Eunotia exigua (Brebisson) Rabenhorst, Fragilaria arcus (Ehrenberg) Cleve, and Nitzschia epithemioides Grumow var. disputata (Carter) Lange-Bertalot.

Use of biological indicators to assess water quality of the Ul River (Portugal).

Diatoms and macroinvertebrates have been extensively used as water quality indicators in Europe for the last two decades. In Portugal, the use of biological indicators to assess water quality in rivers has increased greatly. The aim of this work was to assess the water quality and ecological status of the Ul River in order to evaluate its ability for the establishment of a fluvial beach, using periphytic diatoms and macroinvertebrates as indicators. Four sites were selected along the Ul River. At each site, biological, physical, and chemical parameters were investigated. Epilithic diatoms and macroinvertebrates were sampled. The Specific Polluosensitivity Index and the Biological Diatom Index were applied to diatom data, while for macroinvertebrates, the Iberian Biological Monitoring Working Party (IBMWP) was used. According to the results obtained, it was possible to conclude that up to now, this river does not possess the ideal conditions for the establishment of a fluvial beach. We concluded that epilithic diatoms and macroinvertebrates provided consistent information on water quality assessment and can be used as biological indicators of the water quality in Ul River.

Diatom assemblages of thermal and mineral waters from volcanic environments in São Miguel Island, Azores

Volcanic areas are hostile environments where the release of toxic gases is added to the low pH and high temperature, subjecting living organisms to extreme conditions. High-temperature environments, particularly those associated with volcanic activity have been evolving on earth throughout time. The aim of this study is to contribute to increasing knowledge of these high-temperature events and describe their associated diatom assemblages. The fumarolic fields of São Miguel Island in the Azores Archipelago were selected as a case study due to its particular characteristics and were studied seasonally during 2007. Temperature, pH and conductivity variables were measured in situ. Other environmental data were available in the literature. Diatom diversity, assessed using the Shannon–Wiener Index (H′), ranged between 0.02 and 4. Statistical analyses revealed that temperature is a significant driver for the distribution of diatom species. Achnanthidium exiguum Grunow, Nitzschia cf. thermalis var. minor (Hilse) Grunow, Pinnularia joculata (Manguin) Krammer, P. trivialiformis Lange-Bertalot & Metzeltin and P. subcapitata Gregory were prominent with relative abundance above 40% of diatom assemblages. Some diatom taxa with high relative abundance, such as N. cf. thermalis and P. joculata may be considered representative of thermal springs and may be considered important biological indicators of geochemical changes induced by volcanic activity.

Integrating geochemical (surface waters, stream sediments) and biological (diatoms) approaches to assess AMD environmental impact in a pyritic mining area: Aljustrel (Alentejo, Portugal)

Aljustrel mines were classified as having high environmental hazard due to their large tailings volume and high metal concentrations in waters and sediments. To assess acid mine drainage impacted systems whose environmental conditions change quickly, the use of biological indicators with short generation time such as diatoms is advantageous. This study combined geochemical and diatom data, whose results were highlighted in 3 groups: Group 1, with low pH (1.9-5.1) and high metal/metalloid (Al, As, Cd, Co, Cu, Fe, Mn, Ni, Pb, Zn; 0.65-1032 mg/L) and SO4 (405-39124 mg/L) concentrations. An acidophilic species, Pinnularia aljustrelica, was perfectly adapted to the adverse conditions; in contrast, teratological forms of Eunotia exigua were found, showing that metal toxicity affected this species. The low availability of metals/metalloids in sediments of this group indicates that metals/metalloids of the exchangeable fractions had been solubilized, which in fact enables metal/metalloid diatom uptake and consequently the occurrence of teratologies; Group 2, with sites of near neutral pH (5.0-6.8) and intermediate metal/metalloid (0.002-6 mg/L) and SO4 (302-2179 mg/L) concentrations; this enabled the existence of typical species of uncontaminated streams (Brachysira neglectissima, Achnanthidium minutissimum); Group 3, with samples from unimpacted sites, showing low metal/metalloid (0-0.8 mg/L) and SO4 (10-315 mg/L) concentrations, high pH (7.0-8.4) and Cl contents (10-2119 mg/L) and the presence of brackish to marine species (Entomoneis paludosa). For similar conditions of acidity, differences in diversity, abundance and teratologies of diatoms can be explained by the levels of metals/metalloids.

From perennial to temporary streams: an extreme drought as a driving force of freshwater communities

Alterations in trait proportions of diatom and aquatic macroinvertebrate communities were used to evaluate the consequences of the drying of temperate perennial streams due to an uncommon drought event. Four Atlantic-temperate Portuguese streams were sampled on three occasions; spring before the drought, 2 weeks after the return of water to the streambed, and spring after the drought. The traits from diatom and macroinvertebrate communities from temperate streams were also compared with those from Mediterranean systems to assess possible shifts in traits. The effects from stream drying were long-lasting for macroinvertebrates; however, only the diatom trait proportions shifted towards proportions similar to those occurring in Mediterranean streams. There was a significant reduction of macroinvertebrates with the ability to produce cocoons, to disperse actively by flight and passively disperse in the water and of swimmers following the return of water. A decrease in stalked species immediately after drought was evident in diatom communities. In contrast to temperate communities, Mediterranean ones were characterised by larger and less mobile diatoms, and smaller-bodied macroinvertebrates with shorter life cycles. Additional studies are required to determine the long-term effect of uncharacteristic drought events on biological traits and their ecosystem functions in typically perennial streams.