Pedro Temporetti

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.

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.

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.