Phytoplankton productivity of tropical Lake Chapala, Mexico.

Phytoplankton productivity and other environmental variables were measured for one year (June 1983 - June 1984) at five stations on Lake Chapala, Mexico. Contrary to expectations, productivity in this shallow, tropical lake 14 was low. Phytoplankton productivity, estimated from C data, was 76.4 g C m”^ year”'' (209 mg C m”^ day”''). Phytoplankton productivity at the depth of optimum light intensity averaged 320 mg C m”^ day”'*', and always occured within the top 70 cm of the water column. Light extinction due to' inorganic turbidity was the principal limiting factor of areal phytoplankton productivity. Nutrient limitation was less important, although nitrogen may have become limiting during the dry season. Among stations, areal phytoplankton productivity varied inversely with turbidity and was decidedly seasonal. It was highest during the rainy season (June - September), when the water was most transparent.