No abstract

River floodplains are subject to different inundation scenarios, mainly related to the flood pulse. Moreover, the ecology of floodplain lakes is modulated by exchanges of water with the main stream. On Amazonian floodplains, the water level fluctuates seasonally, with four distinct stages during the year: rising, high, falling, and low water. This study evaluated how/which three functional approaches to phytoplankton (FG, functional groups; MFG, morphofunctional groups; and MBFG, morphology-based functional groups) showed the largest relation to the environmental variations in response to rising and falling water periods, using data of the seven lakes sampled during rising and falling water periods, on the Curuaí Floodplain system, Pará state, Brazil. We used a Principal Coordinates Analysis to check for differences in phytoplankton species composition between the rising and falling water periods and a Redundancy Analysis to evaluate the relationship between functional approaches and environmental. Electrical conductivity, silica, and pH were the most important environmental variables to structuring the phytoplankton. The biological dissimilarity was computed using Bray-Curtis index for species biovolume and indicated greater similarity among the species compositions in the lakes during the falling water period. During rising water species is adapted in almost all lentic ecosystems (FG Y) and autotrophic organisms typical from the meroplanktonic that can be found in phytoplankton samples of the shallow lakes (FG MP); cryptomonads (MFG 2d), large centrics (MFG 6a), and large pennates (MFG 6b); and nonflagellated organisms with siliceous exoskeletons (MBFG VI) and unicellular flagellates of medium to large size (MBFG V) were predominant. During falling water, species that tolerate eutrophic to hypertrophic environments with low nitrogen content predominated all shallow lakes (FGs H1 and M; MFGs 5e and 5b; and MBFGs III and VII) and Dolichospermum spp. formed blooms. Morphology-based functional groups were the larger relation with the environmental variations than did functional groups and morphofunctional groups. MBFGs provides a relatively simple and objective classification and were the best in characterizing phytoplankton dynamics on the Curuaí floodplain. Therefore, we recommend using these groups to study phytoplankton ecology in shallow floodplain lakes.

Many trophic indices have been constructed for temperate aquatic environments, but few have proved reliable for tropical environments. Indices constructed on the basis of nutrients may not be effective for describing the trophic state because the fractions of nitrogen and phosphorus differ in their potential to predict the nutrient limitation in tropical aquatic environments. We developed an index based on the phytoplankton Reynolds functional groups for an Amazonian floodplain lake from samples collected during 2 contrasting hydrological periods (rising and flushing) and compared it with the index initially proposed by Carlson in 1977 and further adapted to tropical environments by Toledo in 1990. The functional group and Carlson indices matched only 37% and 56% of the sample units collected during the rising and flushing periods, respectively. Our study confirms the difficulty of assessing trophic states using only phosphorus and chlorophyll a in tropical floodplain lakes. In this environment (1) nitrogen may significantly limit phytoplankton growth and (2) complex phytoplankton-nutrient relationships occur during the hydrological cycle that cannot be accounted for through a simple phosphorus and chlorophyll a formula.

Este trabalho tem como objetivo investigar as variações da dureza da água captada através de poços no aquíferoBeberibe na zona urbana da cidade de João Pessoa, capital do estado da Paraíba. Foi desenvolvido a partir da análise dos perfis litológico-construtivos e dados da qualidade da água de poços tubulares profundos construídos para abastecimento de água na cidade. Os perfis geológicos elaborados, incluindo os poços, possibilitaram o estabelecimento de uma relação entre o valor do parâmetro dureza da água e a distância do topo do filtro do poço à superfície inferior da formação Gramame, esta constituída de rochas calcáreas. Os resultados obtidos permitiram inferir que quanto maior a distância entre o topo do filtro e a formação Gramame, menor a dureza da água captada. Conclui-se que a distância mínima de quarenta e cinco metros entre o topo do filtro e a base dessa formação deve ser obedecida no projeto de poços tubulares para se obter água subterrânea com dureza aceitável para o uso doméstico.