Caracterização ecológica e estrutural de macrófitas em reservatórios no Estado de Pernambuco

Abstract

Aquatic macrophytes play an important role in the maintenance and equilibrium of aquatic environment, being considered as the main source that produces organic matter. They are shelter and/or food for many types of organisms and help cleaning aquatic environments, also acting on biomass production, water erosion control, soil physical and nutritional improvement and on nutrient cycling, among others. Despite the great occurrence of macrophytes on aquatic ecosystems, there are few researches dedicated to aquatic plants in Pernambuco, mainly under the taxonomic, floristic and ecological point of view. Pernambuco’s territory allows the existence of successive geographical landscapes, giving place to three well-defined phytogeografical zones: zona da mata/coast, agreste and sertão. This study aimed to: a) characterize the reservoirs of Apipucos, Prata, Tapacurá (zona da mata/coast), Jucazinho, Tabocas, Mundaú (agreste zone), Arcoverde e Jazigo (sertão zone) placed in the state of Pernambuco, by identifying the existent taxa and their respective biological forms; b) examine the existence of differences on reservoir’s richness between seasonal periods (rainy/dry); and c) coming from the floristic composition in eight reservoirs in the state of Pernambuco, and in different phytogeografical regions (zona da mata/coast, agreste and sertão) it is possible to identify which related abiotic variables (water transparence, air temperature, water temperature, dissolved oxygen, oxygen saturation, conductivity, turbidity, pH, total phosphorous, total dissolved phosphorous, orthophosphate and total nitrogen) can influence the distribution of macrophyte species. Aquatic macrophyte and water sample collections were performed for physic-chemical analyses in all reservoirs for both dry and rainy seasons in the period from April, 2008 to February, 2010. On the reservoir’s coastal margin 5 transects were established (perpendicular to the margin), each one with 10 m and 10 m distant from each other. The beginning of each transect was the coastal region (floodable margin) of the reservoir. Colections were performed alternately each 2m of the transect in PVC 50 x 50 cm parcels, totalizing 25 parcels in each reservoir for each seasonal period. A total of 65 species were identified, distributed in 29 families. The most representative families were: Poaceae (14 spp.), Cyperaceae (6 spp.), Fabaceae-Faboideae and Onagraceae, each one with 4 species. The most common biological form was the emergent (53 spp.), followed by free floating (6 spp.), submerjed (4 spp.) and rooted floating (2 spp.) The results showed that species richness was relatively high when compared to other researches in reservoirs. The highest Shannon diversity indexes were registered for the reservoirs of Apipucos (zona da mata/ coast), Tabocas and Mundaú (agreste zone), and Arcoverde and Jazigo (sertão zone). According to the trophic state index the reservoirs were classified as eutrophic. It was also observed that macrophytes are distributed in the different reservoirs in a distinct way and there is no species exclusivity for phytogeografical regions. However, the dry and rainy periods effectively influences species diversity. The Canonical Correspondence analysis (CCA) allowed the separation of species in the reservoirs based on the abiotic variables orthophosphate, turbidity, pH, water transparence and conductivity. However, no correlation was found among macrophyte species and abiotic factors.