Eukaryotic Community Distribution and Its Relationship to Water Physicochemical Parameters in an Extreme Acidic Environment, Río Tinto (Southwestern Spain)

The correlation between water physicochemical parameters and eukaryotic benthic composition was examined in Río Tinto. Principal component analysis showed a high inverse relationship between pH and most of the heavy metals analyzed as well as Dunaliella sp., while Chlamydomonas sp. abundance was positively related. Zn, Cu, and Ni clustered together and showed a strong inverse correlation with the diversity coefficient and most of the species analyzed. These eukaryotic communities seem to be more influenced by the presence of heavy metals than by the pH

Eukaryotic community distribution and its relationship to water physicochemical parameters in an extreme acidic environment, Rio Tinto (Southwestern

The correlation between water physicochemical parameters and eukaryotic benthic composition was examined in Río Tinto. Principal component analysis showed a high inverse relationship between pH and most of the heavy metals analyzed as well as Dunaliella sp., while Chlamydomonas sp. abundance was positively related. Zn, Cu, and Ni clustered together and showed a strong inverse correlation with the diversity coefficient and most of the species analyzed. These eukaryotic communities seem to be more influenced by the presence of heavy metals than by the pH. Natural extreme acidic rivers are scarce worldwide (18). Extreme acidic environments, characterized by a pH of Ͻ3, are often the consequence of anthropogenic influences (e.g., mining activity or acid rain) (14). Thus, most ecological studies of acidic waters have been focused on environments affected by human activity. In addition, most of the information available about acidophilic communities in aquatic environments is focused on bacterial communities, although microbial eukaryotes are also present and could also play a critical role in these places. There have been few reports on eukaryotes, and most of them are related to acid mine drainages instead of naturally acidic locations In this regard, the Río Tinto (southwestern Spain), a 92-kmlong river, is one of the most extensive examples of a naturally extreme acidic environment. The river springs up in the core of the Iberian Pyritic Belt, one of the largest bodies of iron and copper sulfide deposits in the world (5). Ferric iron and sulfuric acid are the most common components found in this acidic environment, establishing a buffer system at pH values of approximately 2.3. Ferric iron is produced by the metabolism of ironoxidizing microorganisms, which are very active in the aerobic part of the river; sulfuric acid originates from sulfides by chemical oxidation or the activity of sulfur-oxidizing microorganisms, depending on the sulfide mineral substrate (15). The result is a strongly acidic solution of ferric iron which brings into solution other heavy metals, increasing their concentrations in relation to neighboring rivers with higher pH (12). It is usually assumed that high metal concentrations in acidic habitats limit eukaryotic growth and diversity due to their toxicity. It has been also proposed that metal hydroxide deposition could change the physicochemical conditions of surfaces, resulting in a reduction of epiphytic growth on rocks (8). However, what makes Río Tinto a unique acidic extreme environment is that eukaryotic organisms are the principal contributors of biomass in the river, over 65% of the total biomass, as well as the unexpected degree of eukaryotic diversity found in its waters (1, 21, 28). Members of the Bacillariophyta, Chlorophyta, and Euglenophyta phyla as well as ciliates, cercomonads, amoebae, stramenopiles, fungi, and yeast have been detected. The main purpose of the current investigation was to study the seasonal dynamics of the epiphytic eukaryotic community as well as to evaluate the influences of different physicochemical characteristics of water in the biodiversity structure and population abundance. Although chemistry and microbiology should be linked, there have been few reports in which both have been described in detail for acidic environments. MATERIALS AND METHODS Sample collection and in situ measurements. Twelve sites along the Río Tinto (between 0 and 50 km from its source) were selected for in situ measurements, water sampling, and epilithon collection Chemical analysis. Water samples were filtered through 0.45-m Millipore membranes. The total concentrations of eight recoverable metals (Zn, Cu, Fe, Co, Ni, As, Cd, and Cr) were measured for each water sample using X-ray fluorescence reflection and inductively coupled plasma-mass spectrometry. These metals were used to calculate the toxicity index (TI). This index was used as a measure of relative heavy metal presence in each sampling station following the equation previously proposed (11). Distances between sampling sites based on biodiversity and water physicochemical parameters. Two different measures of distance have been defined. In order to compare biodiversity, we calculated first the relative frequency of each species at each site with the equation f i ␣ ϭ n i ␣ /N ␣ , where the subindex i represent

Hacemos ciencia en la escuela : experiencias y descubrimientos

Resumen basado en el de la publicaciónSe aborda la enseñanza y aprendizaje de las ciencias y el método científico al alumnado de educación primaria y secundaria de una manera distinta a la establecida tradicionalmente. La primera parte es un bloque introductorio de reflexiones que se centran en la necesidad de cambiar el paradigma didáctico y curricular de las ciencias. En la segunda parte se muestran experiencias de diversa índole y temática, agrupadas en educación infantil y primaria, y educación secundaria.CataluñaBiblioteca de Educación del Ministerio de Educación, Cultura y Deporte; Calle San Agustín 5 -3 Planta; 28014 Madrid; Tel. +34917748000; [email protected]