Efeito do regime hidroecológico sobre uma comunidade de macrófitas aquáticas na planície de inundação do alto rio Paraná.

• Autor(a) principal: Sousa, Wilson Treger Zydowicz de
• Data de Publicação: 2009
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Repositório Institucional da Universidade Estadual de Maringá (RI-UEM)
• Texto Completo: http://repositorio.uem.br:8080/jspui/handle/1/5012
• topic: Macrófitas aquáticas, Assembléia de; Planície de inundação; Alto rio Paraná; Diversidade de espécies; Regime hidrológico; Planície fluvial; Distúrbios de cheia; Macrófitas aquáticas; Facilitação; Fatores de força ecológica; Hydrocharitaceae; Biomassa; Regeneração; Brasil.; Aquatic macrophytes, Assemblage; Floodplain; Upper Paraná River; Riverine floodplain; Flood disturbances; Aquatic macrophytes; Facilitation; Ecological drivers; Hydrocharitaceae; Biomass; Regeneration; Brazil.; Ciências Biológicas; Ecologia

The present thesis comprises two scientific papers (represented by a chapter each) resulted from ecological studies about aquatic macrophytes in the Upper River Paraná floodplain. The first study focus on the plants community in a riverine lagoon, while the second leads with populations of two species of Hydrocharitaceae, Egeria najas (native) and Hydrilla verticillata (exotic), in habitats of the River Paraná. Both researches relate the spatio-temporal dynamics of plants with abiotic and biotic factors. The main focus of these studies is the effect evaluation of two distinct floods, which the second was an extreme flood (caused by the El Niño South Oscillation) comprised by the stronger flood pulse (in amplitude and duration) of the last twenty years in this ecosystem. In the first paper, we explore the hypothesis that flood events and connectivity (distance from the river) interact with local factors to drive changes in the structure of an aquatic plant community in a lagoon connected to the River Paraná. The lagoon vegetation was primarily structured by distance from the river. Total community abundance and emergent species diversity increased from the outer to the inner section of the lagoon while the opposite occurred for submersed and floating species. Spatial changes in the vegetation were strongly associated with gradients of depth, slope, water transparency, oxygen and phosphorus. A greater propagule flux brought by river water input into the lagoon favoured diversity in the entrance and middle lagoon, while the middle was also favoured by a greater area and spatial heterogeneity. The inner lagoon was probably more protected especially from short-term disturbances (e.g. water flow and wind dynamics) and was more susceptible to local biotic processes. Both flood events had different effects upon the macrophyte community depending on flood features (e.g. intensity, duration), location and vegetation state. In general, flood-pulses tended to reset the community, in terms of species abundance and richness, and disrupt competitive processes. Interactions among facilitation and competition processes are likely governed by flood disturbances. Connectivity and flood-pulses were the main factors responsible for sustaining high diversity of aquatic macrophytes in the lagoon, but these drivers interact, in both time and space, with local environmental and biotic drivers to structure the shifting mosaic of lagoon vegetation. In the second study, we carried monthly surveys, comprising two annual cycles, to two sampling stations in the River Paraná and two marginal lagoons, aiming to answer: (1) how do water level regimes and their associated changing environmental conditions, affect populations of E. najas and H. verticillata?; (2) how do native and exotic species respond to distinct flood disturbances and which species has the greater recovery potential?; (3) which environmental variables can best explain variations in E. najas and H. verticillata biomass?; and (4) is there vidence that either species is competitively superior in the habitats studied? Hydrilla verticillata did not develop in the lagoons, possibly due to the elevated proportion of organic matter in the sediment (~ 10 % DM). However the exotic species dominated the river sites apparently suppressing E. najas. Macrophyte biomass development was greatest during low-water periods, with clear water and high temperatures. Floods probably impacted submersed macrophytes through processes of sediment movement and plant scouring (uprooting), coupled with stress caused by low water transparency. Macrophyte recovery started soon after the 2006 flood (less intense) but the major flood of 2007 had a greater impact upon plants. In the river recovery started five months after the major flood, however in the lagoons water transparency did not improve so fast and no significant plant regeneration was found even nine months after the disturbance event. Egeria najas and H. verticillata started regeneration practically at the same time but H. verticillata had much higher rates of biomass increases.