Silicon is found in the marine environment under the forms: dissolved and particulate (biogenic and lithogenic). The biogeochemical cycle of this element is subject to seasonal influences and anthropogenic changes. This work aims to understand the relationship between different forms of silicon in response to processes of natural and anthropogenic origin in different environments ( Bransfield Strait , Antarctica ; Cananeia-Iguape Estuarine -Lagoon Complex, SP ; coastal region of Recife, PE) . The Bransfield Strait is, of the studied areas, the least impacted by man, because of its remote location.The northeastern Strait region showed lower silicate concentrations associated with lower phytoplankton diversity, consisting of diatoms of the genus Corethron that facilitate sinking af Si and remineralization of C and N. In the southwestern region of the Strait silicate concentration was higher, as well as the influence of thaw, which contributes to increased iron availability, indicated by Si* tracer, that increases phytoplankton diversity.In this region there was also the presence of species that facilitate the sinking of C and N and the remineralization of Si. Cananeia-Iguape Estuarine -Lagoon Complex, showed signs of anthropogenic impact especially in the northern sector (Iguape), showed by silicon different fractions, which were excellent indicators of erosion processes. In the southern sector, anthropogenic influence was not observed. Silicon indicated processes of natural origin, like sedimentation, evidenced by the removal of BSi and LSi, and resuspension where concentrations of particulate fractions was higher. The coastal region of Recife is under influence of fluvial inputs from Capibaribe and Beberibe rivers. The distribution of most parameters, including silicate and BSi, showed this influence coming from the west, reaching the barrier at the port exit and propagating toward northeast. Due to higher nutrient availability in the stations nearest to the coast, primary production was encouraged, evidenced by high values of chlorophyll-a and BSi. In the stations more distant to the coast, the parameters had values characteristic of oligotrophic areas , with the forms of silicon showing very low concentrations. Silicon proved to be an excellent indicator of continental natural and anthropogenic contributions. There are few studies that quantify the BSi and LSi in the aquatic environment, therefore this study is a starting point for understanding particulate silicon in Brazilian waters.

This study investigated the dispersal pattern of suspended sediment in the areas near the Stenhouse and Ajax glaciers, Visca Anchorage, Martel Inlet, King George Island, Antarctica. This study was conducted using visible band processing of Quickbird high-resolution spatial images obtained in October 2006. The methodology was also based on the collection and interpretation of data obtained from water samples collected in Admiralty Bay in December 2004. The digital processing of satellite images was performed using a classification method based on the reflectance characteristics of water. The classified images improved visual identification of the dispersion pattern of suspended sediments in the study area. These data were related to the interpretation of analyses conducted on suspended particulate matter (SPM) in the water. The sediment dispersal pattern observed may be associated with glacial erosion processes, their input of meltwater from the front of the glaciers into the study area, detritus flow processes and glaciomarine circulation in the region.

The urbanized areas mark its presence in the hydrological systems with some biogeochemical signs including silicon inputs. Natural influence of leaching and erosion is done by silicate contribution and sometimes, the agriculturally soil contains microphytoliths and contributes with biogenic silica. Once in the hydrological system, the silicon can integrate the biogeochemical cycles showing a balance or not between inorganic and biological forms that reveals a tendency of processes that occur in each sector of the estuarine-marine interface. This study aims to evaluate the impact of a heavily polluted/urbanized river, whose input can be evidenced by the contribution of different forms of silicon that can evidence the terrestrial contribution, erosion process, the presence of phytoplankton species with siliceous structures, mainly associated to diatoms and also, to study the river plume spreading on the coastal area by undertaking silicon profiles in the region adjacent to the river mouth. The coastal region of Recife is under influence of fluvial inputs from Capibaribe and Beberibe rivers verified by observed low salinity (min. 33.93). The distribution of silicon forms showed sectorial variation, and the maximum values were dissimilar. Dissolved silicate reached 14.40 µmol L-1, lithogenic silicon (LSi) maximum of 25.76 µmol L-1 and biogenic silica (BSi) reaching 7.39 µmol L-1 near the river mouth toward the sea, evidencing the river influence coming from the west, achieving the port barrier at the end and propagating in the sea toward northeast. Due to higher nutrient availability in the stations nearest to the coast, primary production was encouraged with evidencing by high values of chlorophyll-a associated to silicate (r=0.71) and to BSi (r=0.44). In the stations more distant to the coast, the forms of silicon showed very low concentrations and BSi/Chlorophyll-a showed negative correlation associated with chlorophyll-a concentrations evidencing the participation of non-silicon actors in the primary production in medium depth in oligotrophic tropical waters.