Victor H. Conzonno

Dissolved organic matter in Chascomús Pond (Argentina). Influence of calcium carbonate on humic acid concentration

Water chemistry of the Chascomús Pond (Province of Buenos Aires, Argentina) was studied during a year characterized by low precipitation. Supersaturation of calcium carbonate up to a calcite saturation index of about 20 in spring and summer was observed, together with a diminution of the concentration of dissolved organic matter, in particular humic substances (HS). These results suggested an adsorption between organic matter and calcium carbonate which should influence the growth of calcium carbonate crystals. A preferential removal of higher molecular weight HS was observed by gel permeation chromatography experiments.

Physical and chemical characters, phytoplankton and primary production of Ezequiel Ramos Mexía Reservoir (Argentina)

We describe the distribution in space and time of a series of physical and chemical variables, phyto-plankton, and primary production in Ezequiel Ramos Mexía Reservoir (Argentina). Its waters are soft, poor in nutrients and with a low transparency that greatly depresses primary production. Phytoplankton data indicate the presence of 79 taxa with Bacillariophyceae, Cyanophyta and Chlorophyta alternatively dominant. Chlorophyll a was always low and never exceeded 3 mg m−3. Based on these results, the trophic status of this ecosystem is discussed.

Determination of seston alkalinity in natural waters

Seston alkalinity is a term introduced with the purpose of considering the acid base neutral capacity of the particles integrating it. It can be determined by a simple method, based on a volumetric titration. In alkaline waters, this variable is associated with the insoluble forms of carbonates of the seston.

Dissolved organic carbon in water fluxes of Eucalyptus grandis plantations in northeastern Entre Ríos Province, Argentina

Water fluxes in tree plantations and other ecosystems carry dissolved organic carbon (DOC) provided by atmospheric inputs, autotrophic and heterotrophic metabolisms and from the lysis of dead material. These compounds may be colorless or provide a yellow-to-brown color to water and may also absorb visible light due to the presence of chromophores in the chemical structure. Concentration and composition of DOC and DOC annual flux in water pathways of a Eucalyptus grandis plantation were studied in Entre Rios, Argentina. Samples of bulk precipitation, throughfall, stemflow, litter lixiviation, surface runoff and water table were analyzed for DOC concentration and color (optical density). Regression analyses for DOC concentration vs water fluxes intensity and for DOC concentration vs color were done. A DOC circulation model was calculated using available information on water budgets fluxes. Results showed that molecular features, values and range of DOC concentrations varied among fluxes, which may be explained by factors and processes influencing water gains and losses and by composition and availability of organic matter that may be dissolved in water in contact with biomass, necromass, soil and subsoil. Regression parameters from DOC concentration vs optical density were useful for DOC chemical composition analyses and interpretation of DOC changes. Annual circulation of DOC (in kg ha-1 year-1) showed that atmospheric contribution is low (ca. 30), aboveground biomass lixiviation is about 3-4 times the atmospheric input (126.7 to 101.4), and inputs to mineral soil (374.4 to 348.0) came mainly (74 to 78 %) from litter lixiviation.

Mechanisms involved in the proliferation and distribution of phytoplankton in the Patagonian Sea, Argentina, as revealed by remote sensing studies

Abstract Studies about the mechanisms that control the dynamics of phytoplankton in terms of surface chlorophyll patches by means of remote sensing information were encouraged in the Patagonian Sea (South Atlantic Ocean). Over this sea, circulation of the Patagonian Current and Malvinas Current, originated in the Circumpolar Antarctic Current, has much to do in the distribution of algal biomass. The study confirms the existence of three ecosystems: Coastal system, Shelf waters system and Shelf break. In the former, algal blooms are detected mostly between March and August. Later, the patches move inside the shelf area, the second ecosystem, towards NNE direction from approximately August to December under the influence of the Patagonian Current to reach the Malvinas Current, which circulates along the shelf break. The third ecosystem, Malvinas system, may be divided into the Malvinas Islands, where an intense algal bloom from December to January could be verified, and the Malvinas Current that shows a high concentration of algal pigment in the same period, although evidences support the hypothesis that the latter has mainly an allochthonous character. At about 37°S–39°S and 53°W–56°W, variable position, the confluence between Malvinas Current and Brazil Current takes place. As a result, the chlorophyll that functions as a tracer indicates that the impact has the characteristics of being an elastic collision, since the Malvinas Current identity was preserved afterwards. Special events, such as the climatic conditions that prompt changes in the annual behavior of the phytoplankton distribution, are discussed.

Interaction between humic substances and carbohydrates in a Pampasic pond (Argentina)

Interaction between humic substances from a Pampasic pond and carbohydrates was studied. Determinations were performed by gel chromatography using radiolabeled glucose. The results showed that upon lowering the pH the interaction decreases in relation to the steric arrangement that causes the diminution of the accessibility of the available sites. Results of displacement experiments carried out by addition of unlabeled glucose, galactose, saccharose and starch, confirmed that the interaction occurs mainly through labile non specific bonds and is, to a certain degree, independent of the carbohydrate molecular weight involved.