Lake Country Latitude(ºS)

Longitude(ºW)

Chungará Chile 18 69Capur Chile 23 67Miniques Chile 23 67Miscanti Chile 23 67Tuyajto Chile 23 67Chaxas Chile 23 68Gemelas Chile 23 68Verde Chile 23 68Tebenquiche Chile 23 68Santa Rosa Chile 27 69T. La Paloma Chile 30 61Antiñir Argentina 38 70Jabón Argentina 38 70L40-964 Argentina 39 70Blanca Argentina 39 70Burro Argentina 39 70Tero Argentina 39 70Verde Argentina 39 70Puyehue Chile 40 72Ranco Chile 40 72Rupanco Chile 40 72Clavos Argentina 41 71N.H. Puerto Blest Argentina 41 71Laguna 2 Chile 41 71Carrilauf. Chica Argentina 41 69Carrilauf. Grande Argentina 41 69Médanos Argentina 41 70Cántaros Argentina 41 71Escondido Argentina 41 71Ezquerra Argentina 41 71Frias Argentina 41 71Guillelmo Argentina 41 71Gutierrez Argentina 41 71Hess Argentina 41 71Los Moscos Argentina 41 71Martin Argentina 41 71Mascardi Argentina 41 71Morenito Argentina 41 71Moreno Este Argentina 41 71Moreno Oeste Argentina 41 71N.H. Bahía López Argentina 41 71N.H. Tristeza Argentina 41 71Roca Argentina 41 71Steffen Argentina 41 71Trébol Argentina 41 71T. Los Santos Chile 41 72Laguna 1 Chile 41 72Trapén Chile 41 73Esquel Argentina 42 71Cholila Argentina 42 71Futalaufquen Argentina 42 71Leleque 1 Argentina 42 71Leleque 2 Argentina 42 71Leleque 3 Argentina 42 71Mosquito Argentina 42 71Puelo Argentina 42 71Rivadavia Argentina 42 71Verde Argentina 42 71Willimanco Argentina 42 71Zeta Argentina 42 71Huillinco Chile 42 73Natri Chile 42 73Popetán Chile 42 73Tarahuín Chile 42 73Tepuhueco Chile 42 73Cucao Chile 42 74Langueño Argentina 43 70Quichaura Argentina 43 70Rosario Argentina 43 71Suñica Argentina 43 71Toro Argentina 44 70Musters Argentina 45 69Boeckella Antartica 63 57Chico Antartica 63 57Encantado Antartica 63 57Escondido Antartica 63 57Esperanza Antartica 63 57Flora Antartica 63 57Pingüi Antartica 63 57

UV attenuation and photolability of dissolved organic matter intemperate lakes of South America

Introduction UVR possesses a number of properties that combine to make it a potent environmental force. First, UV carries more energy per photon than any other wavelength reaching the Earth’s surface. Such highly energetic photons have the potential to damage many organic and biological molecules. In addition, they can initiate a series of redox reactions to form reactive oxygen species, which cause oxidative stress to cells and tissues. The second important characteristic of UV radiation is its ubiquity. Due to their dependence on light, primary producers and visual predators, such as fish, are also necessarily exposed to damaging levels of UVR. Third, the combined effect of UVR and other environmental factors may result in synergistic effects, such as the photoactivation of organic pollutants and photosensitization. A prerequisite to assess the environmental effects of UVR on freshwater ecosystems is the ability to measure and predict the amount of radiation to which the organisms are exposed. The concentration of dissolved organic matter (DOM) plays a major role in this regard, since it is the single most important factor controlling the penetration of UVR in freshwaters.

Objectives The primary objective of the Freshwater Sub-project is to provide an accurate description of the UV environment for a set of temperate lakes of South America. Such information will, in turn, be available for a series of ancillary projects looking at the biological effects of UVR in freshwaters.

Progress During the first two years, our efforts have been directed to the acquisition of relevant environmental information. We have conducted an extensive survey of lakes in three main regions: Argentina, Chile and the Antarctic Peninsula. For each lake, we collected the following information:

* ‘In situ’ extinction coefficients * Dissolved absorbance / Spectral slope* Dissolved organic carbon * Photobleaching rate constants* pH, alkalinity and conductance* N, P, Fe concentrations* Chlorophyll a concentration* Benthos, phyto- & zooplankton

1) Standardized inter-calibrated measure-ments of ground level UV irradiance, which may be used to produce a realistic picture of UV climatology in Southern South America. This information is being collected by the Atmospheric Sub-project (see poster by Vernet et al.)

2) The ability to measure and predict the penetration of UVR in South American lakes. For this purpose, we are building an extensive database looking at the relationship between underwater UV attenuation and the concentration and optical characteristics of DOM. In addition, for each lake we have performed a standardized UVR exposure assay aimed at assessing the photolability of DOM.

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Lake Ezquerra

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We are now in the process of analyzing data collected during the past two years. It is apparent already that our work has significantly expanded the information available for temperate lakes in South America. This is particularly true for high DOC lakes, for which there was virtually no information before the year 2000.

The figure of the right shows the results of one standard UV exposure assay, performed using water collected from Lake Ezquerra. The graph shows the absorption coefficients measured before and after UVR exposure, and the photobleaching rate constant (a measure of

U. Nac. del Comahue (Argentina)Dr. Horacio Zagarese, Co-PIDr. Diego Añón Suárez, InvestigatorLic. Vanina Rocco, PhD studentPatricia Pérez, Graduate studentMarcela Ferraro, TechnicianUniversidad Austral de Chile (Chile)Dr. Doris Soto, InvestigatorPatricio de Los Ríos, PhD studentJorge Jaramillo, PhD studentIvan Arismendi, TechnicianMarcos Ruiz, TechnicianLehigh University (USA)Dr. Bruce Hargreaves, InvestigatorDr. Donald Morris, Investigator

photolability) calculated assuming a first order kinetics model. The results from the remaining lakes are qualitatively similar to those portrayed for Lake Ezquerra: they show significant photobleaching within 250 and 500 nm, with a maximum rate between 330 and 350 nm in coincidence with the nominal maximum of the lamp emission spectrum. We are testing several optical properties of the DOM pool (spectral slope, carbon specific absorbance) to see if they are useful indices of DOM photolability.

Ancillary Projects The five year time frame of this study provided an excellent framework for the development of some additional projects aimed at studying various aspects of environmental effects of UVR in freshwaters. The proposals already approved include:

* The littoral community of Patagonian lakes: assessment of the effects of increasing ultraviolet radiation driven by current climatic changes. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina, PIP 02135)

* The effect of ultraviolet radiation on plankton communities on South Andean lakes. International Foundation for Science. (Grant A/2325-3F.

* Effects of solar radiation on reproduction and growth of early life history stages of fish in Andean lakes. Agencia Nacional de Promoción Científica y Tecnológica. PICT Nº 01/00002/00066 (Concluded).

Enhanced ultraviolet-B radiation in natural ecosystems as an added perturbation due to ozone depletion

The two main requirements to accomplish the above objective are:

Ultraviolet radiation monitoring site at Bariloche, Argentina

List of surveyed lakes.

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