Fernando Pedrozo

First results on the water chemistry, algae and trophic status of an Andean acidic lake system of volcanic origin in Patagonia (Lake Caviahue)

The acidic caldera lake Caviahue (Patagonia, Argentina) and its main tributaries were studied on two dates during September 1998. The main results are: The acidity of the Lake Caviahue (pH: 2.56, acidity: >5 mmol H+ l−1) is controlled by the extremely acidic Upper Rio Agrio (pH: 1.78, acidity: >20 mmol H+ l−1). The high sulphate contents of both the river and the lake can be attributed to sulphuric acid generated by the uptake of sulphurous gases in the crater lake of Copahue Volcano at approximately 2800 m a.s.l. The high concentrations of both Fe and trace metals (e.g. Cr, Ni, Zn) in Lake Caviahue originate from sulphur–acid interactions with the predominantly volcanic geology of the catchment area. The P-rich andesitic geology influences both the Upper and Lower Rio Agrio and Lake Caviahue. Both were found to have high phosphorus concentrations (300–500 μg P l−1) indicative of a high potential for eutrophication. The plankton community consisted of bacterioplankton, phytoplankton and rotifers. The phytoplankton was dominated by one green alga, Keratococcus raphidioides (>90% of total abundance) followed by a green sphaerical and Chlamydomonas sp. The total phytoplankton density was about 15 000 cells ml−1 in the upper 10 m of the water column. Rotifers were represented by one bdelloid species and their abundance was highly variable (360–4040 ind l−1) in the water columm. In the Upper and Lower Rio Agrio, the epilithic community was dominated by one chloroccocal species and two species of Ulothricales. According to trophic categories based on phytoplankton density and TP concentration, Lake Caviahue can be classified as mesotrophic/eutrophic. However, chlorophyll a concentrations observed were not in agreement with this state.

Phytoplankton of two Araucanian lakes of differing trophic status (Argentina)

The Araucanian lake district in southern South America encompasses many great lakes of glacial origin, as well as a large number of smaller lakes. In this study, we present data on two waterbodies, one large (Nahuel Huapi), and one shallow (Verde). The phytoplankton community structure and dynamics or either lake were monitored for a year, in relation to the physical and chemical fluctuation, as well as the morphometry of the respective basins. In the large lake, the phytoplankton biomass was strongly dominated by diatoms (Aulacoseira granulata, Rhizosolenia eriensis and Cyclotella stelligera) and by dinoflagellates (Gymnodinium and Peridinium spp.). In the small lake, Verde, the dominant algae were Trachelomonas spp. and Cosmarium punctulatum, during the summer biomass maximum, and Rhodomonas lacustris, Chrysochromulina parva and Navicula spp. during autumn. The maximum biomass value was 634 mg m-3 in Lake Nahuel Huapi in spring and 7800 mg m-3 in Lake Verde in summer. According to their phytoplankton and physical and chemical features, Lakes Nahuel Huapi and Verde are readily classifiable, as ultra-oligotrophic and mesotrophic, respectively.

Nutrient limitation of phytoplankton in a naturally acidic lake (Lake Caviahue, Argentina)

As a result of a low pH, the inorganic carbon of acidic lakes is present as CO2 at air-equilibrium concentration and is substantially lower than the inorganic carbon concentration in higher-pH waters with bicarbonate. This situation is quite common in artificially acidified lakes and where inorganic carbon is considered the limiting factor in phytoplankton growth. Apart from low inorganic carbon content, Lake Caviahue in Argentina has low nitrogen and high phosphorus content. The aim of this work was to assess the importance of inorganic carbon, phosphorus, and nitrogen, relating data on lake nutrients to phytoplankton species requirements. Lake samples taken in the 2004–2006 period did not show any particular trend in the vertical distribution of the water column of ammonium, inorganic carbon, and phosphorus with reference to either seasonality or depth. A decrease of some 15% in the lake’s phosphorus concentration was observed over the same period. Although the total phytoplankton biomass in Lake Caviahue was similar throughout the period, a seasonal variation was observed. Lab bioassays were carried out with solutions of bicarbonates, ammonium, nitrates, and phosphate. We worked with three species separately, namely, two chlorophytes, Keratococcus rhaphidioides and Watanabea sp.; and one euglenophyte, Euglena mutabilis. Answers to specific nutrient requirements differed for each algal species: both chlorophytes prefer ammonium or nitrates added on their own, whereas the euglenophyte registered a higher growth rate with the joint addition of ammonium and phosphorus. Even when the limiting nutrient(s) for phytoplankton yield and rate varied between species, we observed a tendency for nitrogen limitation in Lake Caviahue.

First record of the invasive algae Didymosphenia geminata in the Lake Nahuel Huapi: Argentina, Patagonia

Fil: Beamud, Sara Guadalupe. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Patagonia Norte. Instituto de Investigacion en Biodiversidad y Medioambiente; Argentina

The acidic waters of Rio Agrio and Lago Caviahue at Volcan Copahue, Argentina

Many active volcanoes are sources of highly acidic waters that originate from volatile mineral acids. Several crater Iakes and volcanic acid brines were chemically characterized (VAREKAMP et al. 200 l), showing a broad spectrum of dissolved elements, many heavy metals, and high temperatures (for more information on crater lakes and constraints in their physical and chemical properties see PASTERNACK & VAREKAMP 1997, VAREKAMP et al. 2000; for volcanoes and activities see JENSEN 2002). eopahue Volcano in Argentina has a crater lake near the summit at 2 700 m a.s.l. Ri o Agri o i s an acidic river emerging from a geothermic source below the crater lake at the flank of eopahue volcano (DE MooR et al. 2003). The 13-km Upper Ri o Agri o flows in to a glacial finger-lake, Lake eaviahue (l 600 m a. s. l.), the outflow o f which is the Lower Ri o Agri o. The system o f river stretches an d lakes ( Fig. l) shows an acidity gradient from p H O to 7 (PEDROZO et al. 200 I). The extreme chemistry along this gradient o f acidity was studied with an additional focus on microbiology and planktonic and epilithic algae.

Evaluation of native acidophilic algae species as potential indicators of polycyclic aromatic hydrocarbon (PAH) soil contamination

Polycyclic aromatic hydrocarbons (PAHs) are pollutants that are potentially carcinogenic, are widely distributed in the environment, and accumulate in soils. The peroxydisulfate anion strategy for the remediation of PAH-contaminated soils has attracted widespread interest, despite its negative effects on soil microbial activity as a result of oxidative stress and a decrease in pH of the soil caused by the treatment. The acidification caused by the process can itself affect the growth of the normal flora, regardless of the presence of PAHs. For this reason, it is necessary to identify microorganisms that are capable of developing in acidic environments and are sensitive to the presence of PAHs. The objective of the present study was to identify native acidophilic/acid-tolerant algae isolated from the Agrio River-Lake Caviahue system, Argentina, that could possibly be used as bioindicators of soil PAH contamination. Two of the three acidophilic species assayed were identified as potential bioindicator species. Cyanidium caldarium and Euglena mutabilis were responsive to PAH contamination in the tested soils, while the response of Keratococcus rhaphidioides was dependent on the type of soil. The use of acidophilic and cosmopolitan species, such as C. caldarium and E. mutabilis, as bioindicators is a promising first step for assays of PAH contamination in soils.

Utilisation of organic compounds by osmotrophic algae in an acidic lake of Patagonia (Argentina)

We investigated whether algal osmotrophy in naturally acidic Lake Caviahue is an important process for acquisition of organic carbon and organic nitrogen. To accomplish this, we quantified algal assimilation of organic compounds, measured the specific growth rate and biomass yield, and documented incorporation of organic compounds by phytoplankton in situ using microautoradiography. Substrate uptake quantification and microautoradiographic investigations were performed using 3H-leucine, 3H-glucose, 3H-thymidine, 14C-aspartic acid, 14C-acetic acid and 14C-bicarbonates. The results showed that the most important species of the phytoplankton community, Keratococcus rhaphidioides and Watanabea sp., took up various sources of organic carbon and nitrogen under both light and dark conditions. They were also able to assimilate leucine, thymidine, aspartic acid and acetate under high levels of inorganic nitrogen and phosphorus, while they could use leucine, arginine, glutamine and glucose under low levels of nitrogen and phosphorus. The assimilation rates were higher in light than in darkness, and the algal specific growth rates increased when organic sources were added. We proposed that osmotrophy complements the main photosynthetic process of the phytoplankton in Lake Caviahue, which helps to overcome the scarcity of light and inorganic nitrogen and carbon in the water column.

Photosynthetic performance associated with phosphorus availability in mats of Didymosphenia geminata (Bacillariophyceae) from Patagonia (Argentina and Chile)

Abstract: Recently reported blooms of Didymosphenia geminata from rivers in Argentinean and Chilean Patagonia, together with non-typical blooms reported from lake systems, have the potential to alter community and ecosystem dynamics of aquatic environments in the region. In an effort to quantify key aspects of ecosystem function of D. geminata mats in Patagonia, we describe for the first time photosynthesis–irradiance (P-E) curves of this species, associated P-E parameters (R, Pmax and α) and their relationship to other functional (alkaline phosphatase activity [APA] enzyme activity and chlorophyll a) and environmental variables (soluble reactive and organic phosphorous, electrical conductivity). Mats of D. geminata from lakes and rivers representing east and west sides of the Andes from 40°S to 46°S (i.e. much of current known distribution) varied mostly in the α and Pmax parameters of P-E curves. Southern systems showed a higher α and lower Pmax parameters than more northern sites on the east slope of the cordillera. None of the P-E curves showed photoinhibition. P-E parameters for the two lakes fell within the range of values for riverine mats; although, soluble reactive P was notably higher in the lakes. We used two different statistical approaches to evaluate associations across environmental, functional or P-E parameters, finding a strong relation between APA and Pmax and a weak one between soluble reactive phosphorus, pH, dissolved organic phosphorus and functional parameters. Our results do not contradict previous observations on the importance of P availability in communities of D. geminata; although the variability in response across P-E parameters suggests a more complex mechanism of regulation than implied in the existing literature.

Lake Caviahue: an extreme environment as a potential sentinel for nutrient deposition in Patagonia

The objective of this study was to determine if extreme acidic Lake Caviahue could be used as a sentinel of atmospheric deposition hypothesizing that the physiological state of algae will be the indicator parameter. The lake was sampled from 2000 to 2015 in order to determine chlorophyll concentration, algae abundance and phytoplankton in vivo fluorescence as a way to evaluate the physiological state of algae. Development and physiological state of phytoplankton in different seasons was related to concentration and dynamics of nutrients in the lake. Laboratory experiments of Keratococcus rhaphidiodes to nitrogen (N) enrichment confirmed that an increase in nutrient content enabled a better physiological state of algae (e.g. higher chlorophyll per cell). Therefore, under the projected scenarios of climate change, the increase of available N through the increase in deposition and the increase of dissolved inorganic carbon, as consequence of higher atmospheric CO2, will compensate the natural nutrient constraints observed in the phytoplankton of the lake. The effect that the atmospheric CO2 has on the DIC, and this on algal development, as well as the influence that N has on algal growth, make Lake Caviahue an interesting sentinel of nutrient deposition at regional level.