Ocorrência de estados estáveis alternativos em reservatórios do semiárido e sua influência na dinâmica das comunidades aquáticas.

Abstract

This study aimed identify the occurrence of alternative stable states in the semiarid tropical reservoir and its regulatory factors. For better understanding the results were arranged in three complementary sections about: (i) the effects of climatic extremes of dry and rain on patterns of variation in submerged macrophyte community, (ii) effects bottom up and top down (predation by zooplankton) in variability of phytoplankton community, (iii) occurrence of alternative stable states in semiarid tropical reservoir and the triggers that determine the changes. During January to December 2011, sampled were colleted monthly, along 12 transects in the reservoir Camalaú (7° 53'33 .94" S 36° 50'39.16" W) located in the Brazilian semi-arid region. Were also considered monthly sampling conducted in Cordeiro reservoir (7°47'38.00" S 36°40'14.04" W). Changes in the hidrological level of the reservoir were the most importance in dinamic of aquatic communities, and regulate the occurence of alternative stable states in the ecosystems. Nutrient limitation was observed only during the rainy season and nitrogen is the limiting factor. Hydrological periods of dry (clear water) and rain (turbid waters) corresponded to alternative stable states and the changes caused by the hydrological cycle on the community of submersed macrophytes was the trigger of state changes, causing a positive feedback on phosphorus concentrations in the system