The annual cycle of primary productivity in Laguna de Río Cuarto, a volcanic lake (maar) in Costa Rica

Abstract

The annual cycle of primary productivity of Laguna de Río Cuarto, a tropical lake formed by volcanic activity (maar) in Costa Rica, was measured using the oxygen method. Gross and net primary productivity amounted to 470 and 163 g C m-2 y -1 respectively. A distinct seasonal variation was observed. Maxma occurred in March / April and September / October, whereas minima were found in July and from December to February. The peak in primary productivity during March and April took place after a' period of deeper circulation by which nutrients from the upper part of the hypolimnion were mixed into the photic zone. The carbon budget of the lake is imbalanced since the autochthonous primary productivity does not deliver the amount of organic material necessary to match the heterotrophic processes. The missing quantity, which amounts to at least 110 kg C per day for the whole lake, is transported mainly by leaves and litter from the densely forested rims of the lake.