Análise dos impactos das atividades antrópicas em lagoas costeiras: estudo de caso da Lagoa Grande em Paracuru - Ce

Abstract

This study was conducted in a coastal lagoon, Lagoa Grande. Located in the Northeastern State of Ceará, in the City of Paracuru, is a main water resources of the city. The Lagoa Grande provides raw water to CAGECE service water supply for the city of Paracuru, but also for Petrobras facilities. Thus arose the need for a more elaborate proposal for understanding the dynamics of this lagoon, Its main goal is to know the capacity of grant Lagoa Grande. Obtained data by topo-bathymetric survey of the pond, the basin contribution, precipitation, evaporation in the region, the flow surface, the water balance and diagnosis of water quality. It was selected three different collection points for the study of water quality, the first is located near the water catchment system, the second near the center of the pond and third close of the beginning of the pond. We carried out three collections of water. The physical, chemical and sanitary method followed APHA et al.(1998) and Lorenzo (1967). Bacteriological analysis showed the presence of coliform in all the samples. Marker for feacal contamination of E. coli, the values ranged from 1600 to 1160 NMP/100mL confirming faecal contamination above those permitted by CONAMA No. 357/05 Resolution. For the physical and chemical parameters, one can observe that the values of pH, alkalinity remained relatively low. The levels of nitrite and nitrate showed significant values, which may be related to pollution resulting from more distant regions that are coming to the pond, but the concentrations of sulfate were low, this indicates that there is no entry for industrial discharges. The results for turbidity and color, transparency and total solids were low, demonstrating that the presence of leaves and suspended material are not significant, and the waters are considered clear. BOD5 values were high in points 2 and 3, this shows that the lake has received a contribution of organic matter. Dissolved oxygen-DO varied in the three points, and may be related to the large amount of aquatic macrophytes in section 1, the depth and its placement near the center of the pond in 2, and, to the lowest values found in section 3 may be related to high primary productivity on high values of chlorophyll “a”, as also the lowest depth of this point. The results for the COD show a gradual increase of point 1 to point 3, this corroborates the reduced OD analyzed in pond water, indicating the presence of polluting material. Lagoa Grande showed EC and salinity values relatively low, although located in a region close to the sea, and was classified, according to CONAMA n ° 357/05, as freshwater. The water body has a great variation in their surface flow due to high evaporation process in the region. Although the lagoon presents a great demand for water for the CAGECE and Petrobras, its surface flow has been fueled by the dunes that are constantly around you, making that it can maintain its volume of water in drought periods.