THE TORRES-DEL-PAINE LAKE DISTRICT (CHILEAN PATAGONIA) - A CASE OF POTENTIALLY N-LIMITED LAKES AND PONDS

A wide range in ionic composition is found in the Torres del Paine lak es and ponds, all the conditions being naturally produced so far. The large lakes; Toro, Pehoe and Nordenskjold are the most oligotrophic an d they also seem to be N-limited. While smaller lakes and ponds are ri ch in nutrients, they can be very productive and often are P-limited. In most cases Chla content usually is lower than expected literature l evels for available nutrient concentrations. The typical correlation b etween phosphorus and Chla is rather poor. There is a greater slope in the N-Chla regression than in the P-Chla regression, suggesting that Nitrogen has an important influence on the Chla content. Phytoplankton abundance particularly in the lakes, however, is also controlled by o ther factors such as the wind conditions which may be responsible for the high temporal variability in nutrient content, and temperature, wh ich never exceeds 10-degrees-C. In these lakes Chla values are always lower than 1 mug/l although TP could reach up to 100 mug/l. Zooplankto n biomass appears to be a good predictor of Chla and of phytoplankton biovolume but mostly in fishless lakes. The study of these large, olig otrophic and polimictic lakes and these highly productive ponds can in crease the general limnological knowledge. As other pristine environme nts in the Southern hemisphere often they do not fit the models previo usly built for Northern hemisphere lakes.