Efeitos da urbanização sobre a composição e estrutura das comunidades de macrófitas aquáticas ao longo do Rio Capibaribe - Pernambuco - Brasil

Abstract

It has been observed worldwide that the indiscriminate use of freshwater ecosystems by human activities alters the quality of water resources causing to a variety of environmental impacts. In Pernambuco state, the population increase, especially in more developed centres, is responsible for a marked urban pressure. At this condition are the municipalities located on the borders of the watershed of the Capibaribe River leading to numerous impacts on the river, which is a major river of the State. As a detrimental consequence of this intimate relationship between man and this resource eutrophication occurs, with increased productivity and the consequent proliferation of certain species of aquatic macrophytes. The present study aimed to analyze the effects of urbanization on the composition and community structure of aquatic macrophytes occurring in different areas of the Capibaribe River. The sampling sites were selected in four municipalities, two of them located in the Agreste zone (Santa Cruz do Capibaribe and Toritama) and two located in the metropolitan area (São Lourenço and Recife) considering urbanized and non-urbanized areas. These sites were visited bimonthly between January and July 2013 to observe the seasonal variation (wet and dry seasons). In the field, individuals of each species found were collected, pressed, identified and included in the collection of the Herbarium Professor Vasconcelos Sobrinho (PEUFR) of the Federal Rural University of Pernambuco. For the biomass analysis at each sampling site three transects measuring 9.75 m long each were plotted on the margins, spaced 10 meters from each other. The botanical material was collected at one meter from the margins along each transect, using three quadrats (0,25 m x 0,25 m), spaced three meters from each other. All plants within the quadrats were collected, placed in labelled plastic bags and transported to the Laboratory of Phycology (LABOFIC) of the Post-Graduation Program in Botany at the Federal Rural University of Pernambuco (PPGB/UFRPE). In the laboratory, the material was washed, sorted and taken to the oven (70° C) to obtain the average values of biomass (g.PS/m2). For the evaluation of the influence of environmental factors on the aquatic macrophytes community hydrological variables (transparency, temperature, turbidity, salinity and nutrients) were analyzed. Space-time distribution of plants and their frequency of occurrence was analyzed. For a better interpretation of the data, specific statistical tests were performed. 31 species of aquatic macrophytes were identified. The Division Monilophyta was represented by Salvinia auriculata and Azolla caroliniana, both belonging to the family Salviniaceae. Poaceae was the most abundant family of the Division Magnoliophyta, with four species, followed by Amaranthaceae, Araceae, Asteraceae, Cyperaceae, Nymphaeaceae, Onagraceae and Polygonaceae, with two species each. In the municipality of Santa Cruz do Capibaribe the urbanized area had a higher occurrence of species (five spp.) when compared to the non- urbanized area in the same city (one spp.). In the Metropolitan Region of Recife the number of species was similar between the non-urbanized area (11 spp.) and urban area (12 spp.). In Toritama the non urbanized area also showed a higher number of species (17 spp.) comparing to the urbanized area (three spp.). With respect to the frequency of occurrence only Ipomoea asarifolia (58.3 %), Eichhornia crassipes (54.2 %), and Paspalum sp1. (50%) were considered as being frequent. The species E. crassipes (637.39 g.PS/m2) and Paspalum sp2. (559.70 g.PS/m2) showed the highest biomass values. Multivariate analyzes based on biomass data indicated significant overall differences between urbanized and non-urbanized areas (R = 0.044, p = 0.001) and also between the dry and rainy seasons (R = 0.018, p = 0.019). Given the heterogeneity of the studied ecosystem, due to the large variation in physical, chemical and biological aspects between the urbanized and non-urbanized areas studied, it was observed that the urbanization factor influenced significantly on the floristic composition and structure of the macrophyte communities along the Capibaribe River.