Purpose Most of the information concerning the effects of contaminated sediments on estuarine organisms deals with the impacts of bed forming sediments. The ecotoxicological potential at the time of a dredging operation is more difficult to assess, and few studies have dealt specifically with resuspended contaminated sediments. The aim of this study was to determine whether release of contaminants through sediment resuspension during a dredging operation in the Itajaí-açu estuary (Brazil) changed the water quality classification and had an ecotoxicological impact on the near-field water column during the critical moment of this operation. Materials and methods Waters from two sites (control and dredged sites) were analyzed for physicochemical parameters before, during, and after a dredging operation. In parallel, a short-term, sensitive battery of biotests (bacteria, algae, and daphnids) was performed with water samples before and during this operation according to the ISO bioassay protocols.Results and discussion No short-term toxicity was observed with waters collected before or during the dredging operation. The results showed that desorption of contaminants from suspended particles of sediments with a low level of contamination during a dredging operation lowered the water quality in the near-field water column but that this did not promote significant acute toxicity effects on the organisms tested. Conclusions More detailed studies are needed (e.g., the question of the reliability of biotests under turbulent, particle-rich conditions) to fully understand this complex issue regarding water column ecotoxicity during the whole dredging operation and to support decisions on the management of dredging activities.

Pollution of surface freshwaters is one of the main environmental problems that result from antrophic activities. Comprehensive studies concerning water quality, however, demand a general understanding of the related aquatic ecosystems. In particular, water quality can be assessed by analyzing phytoplankton composition and diversity which tend to reflect extreme hydrological pertubations. The present study focus on the qualitative description of microphytoplankton, spatial variability of species composition and the creation of a reference collection of these algae in the Camboriu Watershed (Santa Catarina, Brazil) during summer 2005. Sampling was conducted in 9 stations along the basin. After taxonomic identication of the microphytoplankton, a similarity analysis was applied among all sampling stations. A total of 87 taxa of phytoplankton were identified distributed in classes Cyanophyceae (n= 14), Chlorophyceae (n= 19), Zygnematophyceae (n= 11), Euglenophyceae (n= 8), Bacillariophyceae (n= 34) and Crysophyceae (n= 1). Sampling stations located near the potamon environments showed highest values of total richness and those stations located near the rhithron environments the lowest richness values. The similarity analysis among stations revealed four dissimilar groups, separated into, urban, peri-urban, rural and naturial areas.

The waste dispoasal by human activities in these estuaries may result in poor water quality and even prevent its use for these activities. In order to evaluate the effects of the human activities upon the estuaries water quality, this study was carried out to evaluate and compare the surface water quality in both estuaries, using a toxicological bioassay to mesure the effect of these waters in growth of marine microalgae Skeletonema costatum (Bacillariophyceae). The samples were colletcted from august of 2003 to march of 2004 in every two weeks at CEPSUL/IBAMA pier (in Itajaí-Açú estuary) and turistic pier (in Camboriú estuary). The physical and chemical characteristics of the samples were determined in situ. The samples were taken to laboratory and frozen for further use. After conducing the bioassay, the results show an increase in algal growth due to excess of nutrients in the samples of both estuaries. This result indicates water eutrophication, as reported in other studies. No effect in the growth of the species was observed for the samples collected in summer months. The samples of march of 2004 from Camboriú estuary were toxic to S. costatum. This result may be due to the disposal of treated wastewater from Balneário Camboriú wastewater treatment plant in the surface river water. The observed concentration effect (CEO) obtained for the samples of march were almost 50%. The CE 50 calculated was 96,17% for one sample of march. In the present work, the use of microalgae toxicity test for mesure toxicity in environmental samples and its use as water eutrophication indicator were confirmed.