AVALIAÇÃO DA QUALIDADE AMBIENTAL DA BACIA HIDROGRÁFICA DO BACANGA (SÃO LUÍS MA) COM BASE EM VARIÁVEIS FÍSICO-QUÍMICAS, BIOLÓGICAS E POPULACIONAIS: SUBSÍDIOS PARA UM MANEJO SUSTENTÁVEL

Abstract

Pressures happened of the urbanization s increase have caused serious damages to the environment. Because of this, the present study objectified to evaluate the environmental quality of the Bacanga River Basin, that represents one of the most degraded basins of the São Luís Island (Maranhão). The work consisted in analyses of the physical-chemistries, biological and population indicators. For it accomplishment, bimonthly collections of water were effected in six points, between Octuber/2007 and June/2008, in order to characterize the following hydrological variables: depth, transparency, temperature, salinity, pH, dissolved oxygen, material in suspension and nutrients (ammonia, nitrate and phosphate). Fish communities were used as environmental quality bioindicators, being realized catches in five points in the same sampling period of hydrological variables. Questionnaires were applied to the living population and the fishermen of the basin, for social, economical and environmental characterization of the area. It was observed that the depth is higher next Barragem, while the pH s values were reduced during the rainy period. Transparency and material in suspension didn t disclose any standard of variation. Temperature was probably related to the collect s time, while the salinity was more raised in the estuary s mouth points. Ammonia and phosphate presented high concentrations in the Bicas river, while the dissolved oxygen disclosed the values lowest for this point, which consist in depositary of sewage of the São Luís Island. Four groups were formed by principal components analyses, being that ammonia, nitrate, pH, salinity, depth and phosphate were the most representative variables. Ichthyofaunistic community was represented by 3.682 individuals distributed in 36 species, which were grouped, for similarity, in three groups, defined possibly in function of the water s salinity gradient. The diversity didn t demonstrate defined standard, and it didn t allow inferring about the environmental stress, even reduced values had occurred for it. The ABC method classified the environment as without disturbance (Coelho narrow river), moderately disturbed (Barragem and Gapara) and disturbed (Jambeiro and Mamão narrow river), while biotic integrity index classified the environment between very poor and poor categories. Profile of the inhabitants of the basin disclosed the precariousness of the sanitary exhaustion and collection of the garbage services, being that the more cited problems were: garbage, sewage, forest fires and deforestation of mangrove. With regard to the characterization of the area s fishing, the fishes more captured are prata, tainha, bagre, sardinha and tilápia. The majority obtains till 5 kg of fish per day of fishery, being these destined to sale and consumption. Gains obtained with the activity by mostly of the interviewed is between R$ 200,00 and R$ 400,00. According to majority of them, fishery got worse in recent years, being the pollution and the barrage the most harmful problems to it. As suggestion for improvement of the fishing activity, it was distinguished inspection of the barrage floodgates opening. Although the reduced environmental quality in the Bacanga, this basin still discloses importance for the fishery. The scenes considered for fisheries indicate an investment directed to the sustainability as more viable alternative to the place.