PRIMARY RESEARCH PAPER Phytoplankton seasonal and vertical variations in a tropical shallow reservoir with abundant macrophytes (Ninfe ´ias Pond, Brazil) Ba ´rbara M. Fonseca • Carlos E. de Mattos Bicudo Received: 30 November 2010 / Revised: 2 February 2011 / Accepted: 6 February 2011 / Published online: 22 February 2011 Ó Springer Science+Business Media B.V. 2011 Abstract This study aimed at analyzing the envi- ronmental factors which determine the structure and dynamic of phytoplankton in a shallow reservoir with abundant macrophyte flora, Ninfe ´ias Pond (Brazil). It is hypothesized that, although its shallowness, peri- odic stratifications play an important role on its phytoplankton community. Water samples were col- lected monthly, from January to December 1997, in four depths (sub-surface, 1 m, 2 m, and bottom) of pelagic zone (Z max = 3.6 m). Community seasonal and vertical variations followed a hot-rainy season with water column stratification (phase 1; Q index: medium), alternating with a cool-dry season with water column mixing (phase 2: Q index: excellent). Nanoplanktonic flagellates dominated, mainly mixo- trophic species. During phase 1, Chlamydomonas sp. (G) was the main species, dominating at the anoxic and nutrient-rich hypolimnion. At the same time, richness and diversity were relatively lower. During phase 2, lower water temperatures and higher dissolved oxygen concentrations favoured the pry- mnesiophyte Chrysochromulina cf. breviturrita (X2). Sequence of functional groups over phases 1 and 2 was: phase 1 = G ? transition = Y/P/E/D/F/W2/ X3 ? phase 2 = X2/Lo/X1; most of these groups have been associated to oligo-mesotrophic systems. Seasonal stratifications played a decisive role in determining the structure and dynamic of phyto- plankton in the Ninfe ´ias Pond. However, in such a complex and heterogeneous system, other compart- ments of the food web (macrophytes, zooplankton, fishes) may also act as relevant driving forces, in synergy with the physical and chemical environment. Keywords Community dynamic and structure Á Stratification Á Functional groups Introduction The search for driving factors of phytoplankton communities in individual lakes and reservoirs is a recurrent theme in the literature (Lopes et al., 2005; Fonseca & Bicudo, 2008; Becker et al., 2010). It is well recognized that mixing patterns and the avail- ability of light and nutrients act together providing the favorable habitat template for different algal assemblages (Reynolds, 1984). In the last years, phytoplankton studies have been improved by functional classification approaches that could be sensitive to environmental change. The Handling editor: Luigi Naselli-Flores B. M. Fonseca (&) Universidade Cato ´lica de Brası ´lia, Curso de Cie ˆncias Biolo ´gicas (Sala E-10), QS 07, Lote 1, A ´ guas Claras, 71966-700 Brası ´lia, DF, Brazil e-mail: bm_fonseca@yahoo.com.br C. E. de Mattos Bicudo Instituto de Bota ˆnica, Nu ´cleo de Pesquisa em Ecologia, Caixa Postal 3005, 01061-970, Sa ˜o Paulo, SP, Brazil 123 Hydrobiologia (2011) 665:229–245 DOI 10.1007/s10750-011-0626-3