Driving forces of the diel distribution of phytoplankton functional groups in a shallow tropical lake (Lake Monte Alegre, Southeast Brazil)

Lm Rangel,Ms Arcifa,Lhs Silva,A Perticarrari

doi:10.1590/s1519-69842009000100009

Abstract

Phytoplankton vertical and diel dynamics in a small shallow lake (Lake Monte Alegre, Ribeirão Preto, state of São Paulo) were investigated in two climatological periods: July 2001 (cool-dry season) and March 2002 (warm-rainy season). Monte Alegre is a eutrophic reservoir, with a warm polymictic discontinuous circulation pattern. The lake was thermally stratified in both periods, although dissolved oxygen varied less in the cool-dry period. Phytoplankton biomass was higher in the warm-rainy season and the vertical distribution was stratified in both seasons. Flagellate groups (L(m), Y, W(1) and W(2)) and functional groups typical of shallow eutrophic environments (J, X(1) and S(n)) were important throughout the study period. The lake's thermal pattern strongly influenced the vertical distribution of the phytoplankton community in both periods. Biomass, functional groups and size classes of phytoplankton also were determined by the presence of more efficient herbivores in the lake, especially during the cool-dry period when phytoplankton biomass decreased.

Highlights

Daily radiation input is mainly responsible for diel cycles of heat content and near-surface temperature
Lake Monte Alegre was stratified in both sampling periods (Figure 2)
Phytoplankton biomass in Lake Monte Alegre was related to the thermal structure in both seasons, especially during the warm-rainy period, when higher phytoplankton biomass coincided with the level of the metalimnion

Summary

Introduction

Daily radiation input is mainly responsible for diel cycles of heat content and near-surface temperature. Phytoplankton diel and vertical dynamics are driven by two main groups of factors: factors that produce small modifications in population growth rates, and factors that are responsible for population redistribution in the lake (George and Heavey, 1978; Reynolds, 2006). These dynamics are usually reported as dependent on: i) mixing patterns of the water body; ii) the presence of self-regulating populations by flagella or aerotopes; and iii) the occurrence of fast-growing species, which can fluctuate widely in numbers over a single diel cycle (Melo and Huszar, 2000; Melo et al, 2004). Larvae of Chaoboridae (Arcifa, 1997) and some species of fish such as Tilapia spp. (Arcifa and Meschiatti, 1996; Starling et al, 2002) are important plankton consumers

Methods

Results

Conclusion