Physical regimes and nutrient limitation affecting phytoplankton growth in a meso-eutrophic water supply reservoir in southeastern Brazil

• Published in: Lakes & Reservoirs : Science, Policy and Management for Sustainable Use Vol. 14; no. 4; pp. 269 - 278
• Main Authors: Delazari-Barroso, Alessandra, Barroso, Gilberto Fonseca, De Moraes Huszar, Vera Lúcia, De Oliveira e Azevedo, Sandra Maria Feliciano
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01-12-2009
• Subjects: mixing regime; nutrient limitation; tropical reservoir; water supply
• ISSN: 1320-5331; 1440-1770
• DOI: 10.1111/j.1440-1770.2009.00409.x

The water‐mixing regime, light availability, nutrient limitation and trophic state were evaluated for the Duas Bocas Reservoir (DBR; Espírito Santo State, southeastern Brazil), a small (0.51 km2), shallow (zmax < 10 m) water supply reservoir located in a conservation area. Monthly water sampling was conducted for the lacustrine zone (zmax = 10 m) next to the water withdrawal tower, during one hydrological cycle (October 2002 to September 2003). Water samples were taken at four depths in this area, including subsurface, Secchi depth, euphotic/aphotic boundary and near the bottom of the lake. The variability of the reservoir’s limnological features defined two periods. Period 1, comprised of the summer months (October to April), was characterized by strong thermal stratification, nutrient limitation in the mixing layer, a metalimnetic biomass maximum and anoxia and high nutrient concentrations in the hypolimnion. Period 2, comprised of the winter months (May to September), was characterized by overturn events during which the phytoplankton population experienced light limitation. The observed water‐mixing regime was characteristic of warm monomictic system, presenting atelomixis, the incomplete vertical mixing of stratified water masses. The average total phosphorus and chlorophyll‐a concentrations suggested a meso‐eutrophic water system. The nutrient concentrations exhibited nitrogen and phosphorus limitation, suggesting that nutrients, rather than light, limit or regulate the phytoplankton biomass in the DBR for most of the year.