Avaliação ambiental de igarapés influenciados pela Criação de matrinxã (brycon amazonicus) e por peixes Ornamentais em Manaus – AM

Abstract

Fish culture is an activity closely monitored concerning its environmental impact, mainly due to its effluents, rich in nutrients that are discharged into natural water bodies. On the other hand, there are many benefits resulting from fish production. In the Amazonas State, the production using igarape (perennial stream) channels has gotten attention due to its economical and social positive aspects. In order to evaluate the environmental impacts of fish production on the igarape water quality, water samples from three properties were collected: Sítio São Carlos and Sítio do Borrachinha, and an ornamental-fish exporter facility (aquarium), located in Manaus. The water physicochemical parameters assessed were: total ammonium, nitrite, phosphate, total alkalinity, hardness, electric conductivity, sodium and potassium ions, carbon dioxide, dissolved oxygen, chemical oxygen demands, biochemical oxygen demand, temperature and pH. Simultaneously, as biological indicators aquatic macroinvertebrates were collected at the same sites. Four collections were made, two in the rainy season and two in the dry season. Three collection points in each of the igarapes were used: upstream, in the fish production area and downstream. In order to evaluate the physicochemical parameters, the analyses of variance with repeated measures in time, the Tukey test at 5% level of significance and the ordination analysis PCA were applied. The macro invertebrate community was itemized applying NMDS analysis. Finally, an interaction was made among the most significant PCA axis and the bidimensional NMDS axis, including the two kind of analysis. The results obtained from the igarape at Sítio São Carlos showed that the production of fish could be harmful to the environment. ANOVA analyses did not point out differences between the sampled points and the collection seasons (p>0.05), except for dissolved oxygen, alkalinity and potassium. However, PCA grouped the points discriminating the variables that indicate euthrophization. Accordingly, the NMDS ordination suggested an influence of fish farming in the course of the igarape. In the aquarium, the variance analysis did not show difference among the collection points and season (p>0.05). Only alkalinity and conductivity presented a seasonal difference. On the other hand, the ordination analyses grouped the points in accordance with the fish farming, although it indicated a subsequent improvement in the igarape water quality. At the Sítio do Borrachinha, analyses based on water physical and chemical variables did not show statistical differences (p>0.05). PCA distinguished the points according to the season. The macro invertebrate community showed to be influenced by fish production, a punctual and non-persistent disturbance was found along the igarape, suggesting its good resilience. The fish production using igarape channels has shown to be a promising economical alternative. The production system adopted at the Sítio do Borrachinha indicated to be an appropriate set up for that area due to its low-level of impact on the water quality and on the hydrology of the igarape. However, there is a lack of information on the impact of fish farming on this kind of environment. The establishment of an economical-ecological zoning of these areas become necessary in order to reduce the environmental degradation and to guide the rural producers on the best options for land use.