Sediment quality and resuspension rate in Mangueira Bay

RODRIGUEZ A; CORRAL M; ORONA C; HILLMAN G; PAGOT M; NIEMCHESKY F; SIERRA J

JOURNAL OF COASTAL RESEARCH

Coastal Education & Research Foundation

Lugar: Florida; Año: 2007 vol. 47 p. 68 - 74

0749-0208

Saco de Mangueira it is a bay located in the south of Brazil (between 30º and 32º south latitude). It constitutes a significant regional resource wich allows development of activities such as tourism and economic exploitation through fishing, fish- breeding and shellfish-breeding. Studies realized by FURG have demonstrated that due to its natural conditions, Saco de Mangueira is an area of shelter and feeding of the local biota ; that is why, the possibility of implementing an intensive breeding of shrimp is analyzed (Tagliani 2002). Hence, of this waterbody it is important to study the hydrodynamic, water quality and sediments.The spatial and temporal distribution  of heavy metals in sediments during the monitoring campaigns carried out under the framework of the ENCOSUD project of October 2002 and June 2003 are described in this work. In addition, it has been estimated the distribution of metals in the bed and the potential of resuspension due to the wave caused by a typical condition of storm similar to the one measured in the campaign of May 2003. This  sediment resuspension  process in the sea bed can be a source of re-pollution to a water column. Classic expressions have been made to estimate the wind induced water waves (USACE, 1984). The resuspension rate has been computed with the expressions proposed by Grant an Madsen (1979) and to estimate the concentration of suspended material, the functions proposed by Nielsen (1992) were applied. The results show a different spatial distribution between the two campaigns, highlighting in both cases that the south  of Saco de Mangueira is the proper area for aquiculture. Besides, in all the analyzed samples of sediments, the different metals quantized have presented concentrations under the limits stipulated by the Canadian Environmental Quality Guidelines of CEPA (Canadian Environmental Protection Agency). The calculation of resuspension of sediments have demonstrated that  in the south-west coast, under typical wind from the west, there are favorable conditions for shrimp-breeding, specially in the southern part of Mangueira Bay.