| Resumo: |
From November 1996 to October 1997, the river basins of five humic lakes on Chiloé Island were studied monthly: Lakes Natri, Tepuhueico, Tarahuín, Huillinco and Cucao. The objective of this study was to know the catchment area, river basin and the main physical, chemical and biological characteristics of these humic lakes. The trophic status, the actual loading, and the mass balances of phosphorus and nitrogen were determined in relation to anthropogenic activities. Lakes Cucao and Huillinco were characterized by a marine influence. All the lakes had brown coloured waters, caused by humic substances, which limit their transparency. Lake Natri was the deepest (58 m), whereas Lake Tepuhueico had the shallowest depth (25 m). Total phosphorus and nitrogen fluctuated between 23.5 and 35 µg L-1 and 197 and 380 mug L-1 (annual average) in lakes Natri, Tepuhueico and Tarahuín, respectively. Lakes Cucao and Huillinco showed extremely high concentrations of total nitrogen (annual average<FONT FACE=Symbol > or = </FONT> 3,000 mug L-1) and total phosphorus (= 223 and 497 mug L-1), and were classified as hyper-eutrophic. Lake Tarahuín registered the greatest diversity of phytoplankton, with 55 species, including Ceratium hirundinella which also occurred in lakes Cucao and Tarahuín. The diversity of the zooplankton community varied across these lakes. The presence of Diaptomus diabolicus (Tumeodiaptomus d. Dussart 1979) (Cucao, Huillinco and Tepuhueico) is noteworthy since this extends its geographical distribution to the south
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