Physical and chemical characteristics of ephemeral pond habitats in the Maracaibo basin and Llanos region of Venezuela

Jason E. Podrabsky, University of Colorado Boulder
Tomas Hrbek, Washington University in St. Louis
Steven C. Hand, University of Colorado Boulder


Physical and chemical variables of ephemeral rainwater pond habitats in the Maracaibo basin and Llanos region of Venezuela were investigated to assess environmental features important for future studies of the physiological ecology and bioenergetics of annual killifish. Dissolved oxygen, temperature, pH, Eh, and conductivity measurements were made in the field at each collection site. Water and filter samples were collected and analyzed for trace metals, cations, anions, and osmolality. Physical and chemical characteristics of rainwater ponds are highly variable both temporally and spatially. Large diurnal fluctuations occur in temperature and dissolved oxygen. Dissolved oxygen content, temperature, pH and conductivity values exhibit a high degree of interpool variation. All pools sampled have a high amount of suspended solids consistent with high turbidity. Pool sediments appear to be anoxic as indicated by measurement of Eh. Llanos region pools are dominated by calcium as the major cation, while Maracaibo basin pools are dominated by sodium as the major cation. Maracaibo pools can be further separated into two distinct regions, inland savanna and coastal desert, based on ionic composition. Annual killifish inhabiting ephemeral ponds may be exposed to extremes in dissolved oxygen concentration, temperature and pH values during adult, juvenile, and embryonic stages.