Summary: Seasonal and interannual variation of bacterial
production in lowland rivers of the Orinoco basin
MARIŽA M. CASTILLO,* J. DAVID ALLAN,* ROBERT L. SINSABAUGH
AND GEORGE W. KLING
*School of Natural Resources and Environment, The University of Michigan, Ann Arbor, MI, U.S.A.
Department of Biology, University of New Mexico, NM, U.S.A.
Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, U.S.A.
1. We examined the influence of hydrologic seasonality on temporal variation of
planktonic bacterial production (BP) in relatively undisturbed lowland rivers of the middle
Orinoco basin, Venezuela. We sampled two clearwater and two blackwater rivers over
2 years for dissolved organic carbon (DOC), chlorophyll, phosphorus and bacterial
abundance to determine their relationship to temporal variation in BP.
2. Dissolved organic carbon concentration was greater in blackwater (543664 lMM) than in
clearwater rivers (184240 lMM), and was generally higher during periods of rising and high
water compared with low water. Chlorophyll concentration peaked (3 lg L)1
) during the
first year of study when discharge was lowest, particularly in blackwater rivers. Soluble