Natural events and anthropogenic activities are the reasons of undesirable resuspension of contaminated sediments in aquatic environment. Uncontrolled resuspension could remobilize weakly bound heavy metals into overlying water and pose a potential risk to aquatic ecosystem. Shallow harbours, with contaminated sediments are subjected to the risk of uncontrolled resuspension. Remediation of sediments in these areas cannot be performed by conventional in situ methods (e.g. capping with or without reactive amendment). Ex situ remediation also requires dredging of sediment, which could increase the risk of spreading contaminants. Alternatively, the resuspension technique was introduced to address these issues. The concept of the resuspension method is that finer sediments have a greater tendency to adsorb the contamination. Therefore, finer sediments, believed carry more concentration of contaminants, were targeted for removal from aquatic environment by a suspension mechanism in a confined water column. The objective of this study was to evaluate the feasibility of the resuspension technique as a new approach for remediation of contaminated sediment and a viable option to reduce the risk of remobilization of contaminants in harbours due to an undesirable resuspension event. Unlike the common in situ techniques, the resuspension method could successfully reduce the total concentration of contaminants in almost all samples below the probable effect level (PEL) with no significant change in the quality of overlying water. The results indicated that removal efficiency could be drastically enhanced for metals in sediment with a higher enrichment factor. Moreover, availability of metals (e.g. Cd and Pb) with a high concentration in labile fractions was higher in finer sediments with a high enrichment factor. Consequently, removal of contaminants from sediment through the resuspension method could reduce the risk of mobility and availability of metals under changing environmental conditions. Potential dredging in harbours could be performed safer and more cost-effective afterward.

To evaluate the effects of diffuse contamination, biological measurements were applied in a scrap cargo harbour, a marina and an industrial area. Metal accumulation and biomarkers (survival in air, digestive gland and gonad histopathology, lysosomal membrane stability, intralysosomal metal accumulation, transcription of vitellogenin and MT20, peroxisome proliferation and micronuclei formation) were measured in transplanted mussels, together with metrics of benthic invertebrates. Benthic species were classified into ecological groups and univariate indexes were calculated. The marina showed high richness (16) and percentage of opportunistic species (55.1%) and low metal accumulation. Mussels in the scrap cargo harbour showed high metal accumulation, up-regulation of MT20 transcription, reduced health status (LP<6min) and increased micronuclei frequencies (up to 11.3‰). At the industrial area, low species richness (4) and badly organised assemblages were detected and chemical analyses indicated significant amounts of bioavailable metals. Overall, selected biological measurements showed potential for the assessment of diffuse contamination.

Susceptibility to pollution can be related to the flushing capacity of aquatic systems. Transport time scales constitute a useful tool for representing the water exchange and transport processes. A new transport time scale, recovery time, and a methodology to estimate it by means of numerical models is hereby developed. Recovery time, calculated in Gijon, Santander and Tarragona harbours, is significantly related to physical, chemical and biological water quality indicators. Susceptibility, assessed through recovery time values, provides spatial patterns of expected flushing capacity, being sensitive to physical and hydrodynamic characteristics. The developed method is appropriate to estimate recovery time and assess susceptibility against pollution in littoral waters having great potential to be applied to different disciplines. Recovery time could be used in littoral waters as a surrogate of water quality indicators, to establish efficient monitoring programs, to define and characterize modified water bodies or to improve the design of marine infrastructures.

Due to their close proximity to the point sources of pollution, estuaries and harbours are exposed to metals. Mussels are used worldwide to monitor marine pollution due to their ability to take up contaminants and the ease of transplantation. Mussels were collected from two reference sites and transplanted in Richards Bay Harbour (2006 and 2010) and in three harbours. Transplanted and resident mussels were removed after 6weeks exposure and metal concentrations were analysed using ICP-MS techniques. Transplanted mussels had higher metal concentrations than the resident mussels. This was attributed to regulation of metals by the resident mussels. Metal regulation was greater in mussels that are continuously submerged as opposed to those that undergo tidal influences. For monitoring it is essential that the reference population for transplantation is considered carefully as upwelling events in the pristine reference location results in significant increases in metal bioaccumulation.

Artificial habitats, such as harbours and marinas, are entry doors for the introduction and dispersal of species. Surveys on fouling community in these habitats help to understand preventing environmental impacts and management of invasive species. Thus, a survey on fouling bryozoan fauna was carried out along 17 artificial habitats (eight harbours and nine marinas) from three coastal stretches in Southwestern Atlantic. A total of 55 species were identified, including 13 non-native, 33 cryptogenic and nine native taxa. Only five bryozoan species were found in more than 75% of sampled sites. Our analysis revealed that bryozoan fouling communities in artificial habitats do not vary significantly between commercial and recreational localities. However, we also found that faunal assemblages varied significantly along Brazilian coastal stretches that are distinguished by environmental conditions, such as salinity and temperature.