Este estudo teve como objetivo conhecer a dinâmica do ciclo biogeoquímico do fósforo (P) (fases dissolvidas e particuladas) no Complexo estuarino-lagunar de Cananéia-Iguape considerando a influencia antrópica causada pela abertura do canal do Valo Grande e as possíveis diferenças no fluxo bêntico de PID. Foram observados valores de P dissolvido e particulado superiores no setor norte (Iguape) indicando a influência do aporte do Valo Grande ao estuário. As concentrações de P no sedimento foram maiores também no norte, sendo dominada pela fração inorgânica. Nas estações fixas de Cananéia (verão e inverno), a influência da maré foi evidente, enquanto em Iguape não foi observado sinal considerável. O fluxo do PID observado nas campânulas bênticas foi negativo indicando a remoção para o sedimento, consequente retenção do P neste compartimento. O Valo Grande influenciou o ciclo biogeoquímico do P na região, de forma mais acentuada ao norte do sistema e, a fração particulada em suspensão foi a forma que mostrou maior potencial para exportação de P para o oceano adjacente. O estudo do ciclo biogeoquímico do P em sistemas estuarinos constitui uma excelente ferramenta para o diagnóstico da qualidade ambiental, auxiliando também, os gestores ambientais em suas ações de preservação e manejo. / This study aims to know the dynamic of phosphorus biogeochemical cycle (P) (dissolved and particulate forms) in Cananéia-Iguape Estuarine-Lagoon Complex, considering the anthropogenic influence caused by the opening of Valo Grande channel and the possible differences in DIP benthic flux. Higher values of dissolved and particulate P were observed in the northern sector (Iguape), indicating the influence of the Valo Grande contribution to the estuary. P concentrations in sediment were also higher in the north, and the inorganic fraction prevailed. In Cananéia\'s fixed stations (summer and winter), the influence of the tide was evident, while in Iguape an extensive signal was not observed. The DIP flux observed in the benthic chambers was negative, indicating the removal to the sediment, and therefore the retention of P in this compartment. The Valo Grande influenced the P biogeochemical cycle in this region, the north of the system in a more sharply way. The suspended particulate P form showed the biggest potential to exportation of P to the adjacent ocean. The study of P biogeochemical cycle in estuarine systems is an excellent tool to diagnose environmental quality, also helping environmental managers in their actions of preservation and management.

Este estudo teve como objetivo conhecer a dinâmica do ciclo biogeoquímico do fósforo (P) (fases dissolvidas e particuladas) no Complexo estuarino-lagunar de Cananéia-Iguape considerando a influencia antrópica causada pela abertura do canal do Valo Grande e as possíveis diferenças no fluxo bêntico de PID. Foram observados valores de P dissolvido e particulado superiores no setor norte (Iguape) indicando a influência do aporte do Valo Grande ao estuário. As concentrações de P no sedimento foram maiores também no norte, sendo dominada pela fração inorgânica. Nas estações fixas de Cananéia (verão e inverno), a influência da maré foi evidente, enquanto em Iguape não foi observado sinal considerável. O fluxo do PID observado nas campânulas bênticas foi negativo indicando a remoção para o sedimento, consequente retenção do P neste compartimento. O Valo Grande influenciou o ciclo biogeoquímico do P na região, de forma mais acentuada ao norte do sistema e, a fração particulada em suspensão foi a forma que mostrou maior potencial para exportação de P para o oceano adjacente. O estudo do ciclo biogeoquímico do P em sistemas estuarinos constitui uma excelente ferramenta para o diagnóstico da qualidade ambiental, auxiliando também, os gestores ambientais em suas ações de preservação e manejo. / This study aims to know the dynamic of phosphorus biogeochemical cycle (P) (dissolved and particulate forms) in Cananéia-Iguape Estuarine-Lagoon Complex, considering the anthropogenic influence caused by the opening of Valo Grande channel and the possible differences in DIP benthic flux. Higher values of dissolved and particulate P were observed in the northern sector (Iguape), indicating the influence of the Valo Grande contribution to the estuary. P concentrations in sediment were also higher in the north, and the inorganic fraction prevailed. In Cananéia\'s fixed stations (summer and winter), the influence of the tide was evident, while in Iguape an extensive signal was not observed. The DIP flux observed in the benthic chambers was negative, indicating the removal to the sediment, and therefore the retention of P in this compartment. The Valo Grande influenced the P biogeochemical cycle in this region, the north of the system in a more sharply way. The suspended particulate P form showed the biggest potential to exportation of P to the adjacent ocean. The study of P biogeochemical cycle in estuarine systems is an excellent tool to diagnose environmental quality, also helping environmental managers in their actions of preservation and management.

Eutrophication is one of the greatest threats for the Baltic Sea, and one of its more critical consequences is bottom water hypoxia. Nutrient enrichment and oxygen-depletion affect both the deep central basins and a number of coastal areas, even though strategies for nutrient reduction have lately been implemented. In order to better understand why those threats are expanding and formulate more effective remediation strategies two main achievements are needed: (1) new data on benthic nutrient dynamics should be available in order to develop updated budgets for sensitive Baltic areas; (2) the main transformation processes and their regulation mechanisms (i.e. oxygen availability, presence of macrofauna, different organic loading scenarios) should be better constrained. Paper I was able to demonstrate that re-oxygenation of previously anoxic sediment has a positive effect on the ecosystem because of better retention of nutrients and efficient conversion of fixed nitrogen to nitrogen gas. Sediment colonization by the invasive genus Marenzelleria counteracts some of the positive aspects provided by benthic oxygenation (in particular, nutrient retention, N2 loss). A possible explanation for this reversal can be that Marenzelleria does stimulate anaerobic more that aerobic metabolism. Results from Paper II suggest that at the outermost stations of Himmerfjärden denitrification follows a pronounced seasonal pattern, primarily regulated by bottom water temperatures. At the innermost and impacted site oxygen level in the bottom water varies considerably during the year and causes denitrification/DNRA predominance to be the main nitrate reduction pathway. On an annual scale, the net amount of lost N2 is comparable at the four sampling sites and accounts for 96% of the total DIN discharged from the sewage treatment plant, suggesting that denitrification in the estuarine sediment acts as a major nitrogen sink for external N inputs.

Continental margin sediments play an important role in marine biogeochemical cycles, partly due to high primary production rates and efficient export of organic matter to sediments in margin environments. This thesis presents studies of solute exchange in fine-grained sediments representative of slope and rise environments, and carbon and nitrogen cycling in sandy sediments dominant in continental shelves worldwide. Results of these studies advance understanding of the role of benthic processes on marine ecosystems. In fine-grained sediments, solute exchange by diffusion, biological mixing and bioirrigation can be quantified using in situ flux chambers with inert tracer additions. Mechanistic models of chamber tracer transport across the seabed indicate that in organic-rich sediments, bioirrigation and mixing dominate over a wide range of bottom water oxygen levels, reflecting the patchiness and versatility of benthic macrofaunal communities. Positive correlations between benthic oxygen and tracer fluxes appear site-specific. Reliable chamber volume estimates derived from mechanistic models reveal that empirical fits to chamber tracer datasets may overestimate chamber volume and benthic solute fluxes. The biogeochemistry of sandy, highly permeable sediments that dominate continental shelves is largely unknown because of the difficulty in sampling and studying them under natural conditions. Novel sediment reactors were developed and used to mimic in situ porewater advection and natural sedimentary conditions. Compositional changes of natural seawater, with and without the addition of

No description available.