Organic carbon in the Caura River , Venezuela

A seasonal sequence of diel distribution patterns for the planktonic flagellate Ce-r&urn hirundinella in an eutrophic lake. Freshwater Biol. 14: 401-422. GLIWICZ, Z. M. 1984. Limnological study of Cahora Bassa reservoir with special regard to sardine fishery expansion. FAO, Rome.-. In press. A lunar cycle in zooplankton. Ecol-%Y. 198 1. Temperature dependence of growth and phosphorus uptake in two species of I/oZvox (Vol-vocales, Chlorophyta). Density dependent vertical migration in the freshwater dinoflagellate Peridinium penardii (Lemm.) Lemm. fo. californicum Javorn. J. Phy-col. 10: 475-477. SOMMER, U. 1982. Vertical niche separation between two closely related planktonic flagellate species (Rhodomonas lens and Rhodomonas minuta v. nannoplunktica). The underwater light climate as a controlling factor in the production ecology of freshwater phytoplankton. M. M. 1973. Diurnal periodicity in the phy-toplankton assemblage of a high mountain lake. Abstract-Samples were taken weekly over a 2-year period near the mouth of the Caura River, which drains a large watershed on Precambrian shield covered with tropical moist forest. The concentrations of dissolved organic carbon were essentially static despite a 1 O-fold seasonal change in discharge. Particulate carbon showed an unexpected but relatively weak inverse relationship to discharge. Yield of total organic carbon (12.3 g C m-2 yr-I) was higher than would have been expected from the literature. Yield can be predicted accurately from discharge because of the strong homeostasis in concentration of dissolved organic carbon. Information on concentrations of organic carbon in rivers throughout the world has become considerably richer over the last 10 years (Degens et al. 1984). Even so, detailedlan Ministerio de1 Ambiente y Recursos Naturales Re-novables. J. Meyer and an anonymous reviewer commented on the manuscript. information on organic carbon in large rivers draining tropical moist forest is still very scarce (Schlesinger and Melack 198 1). Our 2-year study of the Caura River, a tributary of the Orinoco, provides concurrent measurements of particulate organic carbon, dissolved organic carbon, and discharge for a large river draining undisturbed tropical moist forest. The Caura River watershed (47,500 km2) is located between 4 " and 8 " N lat within Venezuela. The watershed, which is virtually uninhabited, occupies a portion of the Guayana shield, a highly weathered Pre-cambrian formation. The vegetation of the watershed is a mixture of premontane rainforest (29%) with precipitation of about 6,000 mm yr-l, very humid tropical and premontane forest (42%; 3,000 mm yr-l), and humid tropical forest (29%; 2,200 mm yr-') (Ewe1 et al. …