Produtividade bacterioplanctônica e fitoplanctônica nos ecossistemas aquáticos do trecho médio da bacia do Rio Doce MG.
Resumen
This research had as major objective to quantify the existent relationships between
bacterioplankton and phytoplankton production rates, determining the importance of these
communities on the carbon fixation and organic matter transfer in rivers and lakes of the middle
stretch of the Rio Doce basin in Minas Gerais state (southeast Brazil) during dry and rainy
periods of the years 1999-2001. The concentrations of carbon, nitrogen and phosphorus and the
N/P ratios were used to evaluate possible relationships between productivity and trophic status
based in diel, seasonal, and annual patterns.
This thesis was divided into 5 chapters approaching mainly phytoplankton and bacterial
production rates in rivers and lakes of Rio Doce basin. The testing hypothesis is that production
rates varies seasonally (dry and rainy periods) thus resulting in changes of the BP/PP ratios, as a
consequence of changes in the inputs of allochthonous matter (nutrients) being also affected by
distinct internal loads during these periods. The study was conducted in 8 rivers of the middle
stretch of Rio Doce basin and in 7 lakes of the Rio Doce State Park and surrounding area, during
dry and rainy periods from 1999 to 2001. The ecosystems presented a wide trophic status (from
oligo to eutrophic), as well as bacterioplantonic (0.005 5.7 mg C.m-3.h-1) and phytoplanctonic
(0.01 747.5 mg C.m-3.h-1) production rates. For the lotic environments, seasonality and nutrient
concentration were considered the most important factors for productivity. Significant positive
correlations were obtained between phosphorus concentrations and bacterial production rates.
For the lentic environments seasonality was only evident for bacterial production rates with high
N/P ratios, suggesting phosphorus limitation in most of the lakes. Bacterial production in spite of
presenting lower values than the ones recorded for phytoplankton could be an important carbon
source mainly within deep layers and more eutrophic ecosystems.