Premium
Limnological Studies in a Tropical Man‐Made Lake (Lagartijo Reservoir) Venezuela
Author(s) -
De Infante Aida Gonzáles,
Infante Otto
Publication year - 1994
Publication title -
internationale revue der gesamten hydrobiologie und hydrographie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.524
H-Index - 52
eISSN - 1522-2632
pISSN - 0020-9309
DOI - 10.1002/iroh.19940790105
Subject(s) - hypolimnion , photic zone , thermocline , phytoplankton , zooplankton , environmental science , tributary , biomass (ecology) , plankton , chlorophyll a , dry season , hydrology (agriculture) , photosynthesis , oceanography , trophic state index , ecology , eutrophication , biology , nutrient , geology , geography , botany , cartography , geotechnical engineering
Abstract The purpose of this study was to evaluate the present limnological conditions of Lagartijo reservoir (North central Venezuela) and to compare them with conditions reported in early studies. Lagartijo reservoir supplies an important part of the water demand for Caracas city and wide fluctuations on water volume occur annually. Relevant physical, chemical and biological data were obtained from three sampling stations between July 1990 and April 1992. The reservoir was permanently stratified with a well defined thermocline. The main tributary (Lagartijo river), with a temperature about 6° C colder than the surface temperature of the reservoir, flows through the hypolimnion producing distinct chemical and biological properties. The average of the daily integral phytoplankton photosynthesis was 1550 mg C m −2 d −1 . The present annual average of the net photosynthetic activity is about 40% lower than the reported for 1970 and corresponds to an apparent decrease in phytoplankton biomass and to the reduction of the euphotic zone. Photosynthetic activity was higher for the wet season than for the dry season. Actual chlorophyll a concentration in the euphotic zone averages 4.9 μg l −1 . Abundance of zooplankton was significantly decreased in comparison to 1976. Mean zooplankton biomass (dry weight) for the upper 10 m layer was 596 μg l −1 . Copepods accounted for most of this biomass, followed by cladocerans and rotifers. For the first time, a freshwater medusa (probably Craspedacusta sowerbyi ) was collected from Venezuelan waters.