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Estudo do efeito da bioturbação na dinâmica de compostos de azoto em sedimentos costeiros
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Abstract(s)
Foi estudado O efeito da bioturbação na dinâmica dos compostos azotados em sedimentos costeiros. Para isso, O trabalho foi dividido em duas partes: a primeira, onde
foi estudado O efeito da bioturbação na estrutura da coluna sedimentar e nas taxas
reaccionáis causado pela amêijoa-boa (Ruditapes decussatus); e a segunda, onde se estudou o efeito da presença de diferentes espécies e densidades de bivalves nos fluxos de nutrientes e taxas de desnitrificação, nomeadamente, as espécies Cerastoderma sp (berbigão-comum) e Mya arenaria. Na primeira parte do trabalho, dois testemunhos verticais de 10 cm (cores) provenientes do mesmo bloco de sedimento incubado numa câmara experimental, foram analisados com uma precisão de micro-escala. Um dos cores serviu de controlo (CC) enquanto que O outro foi habitado por um exemplar de Raditapes decussatus. Em cada um foi determinado: porosidade, conteúdo orgânico, concentrações de NH4+, bactérias oxidadoras de l\lH4+ e taxas reais e potenciais de transformação de NH4+ líquida, de amonificação e de nitrificação. Todas estas determinações foram efectuadas em triplicado, em 13 sub-amostras de sedimento de cada camada de 2 cm. O efeito da bioturbação foi verificado com uma diminuição da concentração de NH4+ e teor em M.O., duplicação das taxas de nitrificação e um aumento de cerca de 12 vezes das taxas de nitrificação potencial. O número de bactérias oxidadoras de NH4+ foi mais elevado no CC, no entanto, a actividade específica de cada célula foi cerca de uma ordem de grandeza superior no CE. Na segunda parte do trabalho, foram medidos os fluxos de oxigénio, de nutrientes e taxas de desnitrificação em cores de sedimento (controlo), cores de sedimento habitados por duas espécies distintas de bivalves (DM) e cores habitados com uma densidade mais elevada (DE). Os fluxos de Oz e de nutrientes, bem como, as taxas de desnitrificação sofreram um aumento proporcional à densidade presente. As taxas de desnitrificação do NO3- proveniente do processo de nitrificação (dn) foram fortemente incentivadas nos cores habitados pela Mya arenaria enquanto que nos cores habitados pela Cerastoderma sp., foram as taxas de desnitrificação do NO3- proveniente da
coluna de água (dw) as mais incentivadas. Este facto é explicado pelo desempenho de
diferentes comportamentos e mecanismos de irrigação.
Effects of bioturbation on nitrogen compounds turnover were studied with coastal sediments. For this aim, the work was divided in two parts: first, the effect of bioturbation caused by the clam Ruditapes decnssatus on structure and reaction rates of sediment column was evaluated; second the effect of different bivalve species and densities on nutrient fluxes and denitrification rates was evaluated, namely Cerastoderma sp. and Mya arenaria. In the first part of the work two 10 cm cores from a unique sediment volume, subject to boundary layer flow and tidal simulation were analyzed in a smallscale. On one, a clam was present (CE) and the other, defaunated served as control (CC). On each of these, were measured: porosity, organic content, l\lH4+ concentrations, NH4+- oxidizing bacteria and actual and potential rates of NH4+ transformation, amonification and nitrification. These measurements where done in triplicate on thirteen sub-samples for each of five 2 cm deep layers. The effects of bioturbation were visible with lower NH4+ and O.M. content, doubled nitrification rates and potential nitrification rates (NH4+ enrichment) were enhanced by a factor of twelve. Highest number of ammoniumoxidizing bacteria was found in CC; however, specific bacterial cell activity was increased in CE. ln the second part of this work, Oxygen and nutrient fluxes and denitrification rates were measured in defaunated sediment cores (control), in sediment cores inhabited (DM) and in cores inhabited with a higher density (DE). This experiment was carried twice with two different bivalve species. Oxygen and nutrient fluxes as well as denitrification rates increased proportionally with density. Denitrification rates of NO3- from nitrification process (dn) were highly induced in Mya arenaria sediment cores, while sediment cores inhabited by Cerastoderma sp. showed higher denitrification rates of NO3- from water column (dw). These facts are explained by behavior and irrigation mechanisms performed by the two different bivalve species.
Effects of bioturbation on nitrogen compounds turnover were studied with coastal sediments. For this aim, the work was divided in two parts: first, the effect of bioturbation caused by the clam Ruditapes decnssatus on structure and reaction rates of sediment column was evaluated; second the effect of different bivalve species and densities on nutrient fluxes and denitrification rates was evaluated, namely Cerastoderma sp. and Mya arenaria. In the first part of the work two 10 cm cores from a unique sediment volume, subject to boundary layer flow and tidal simulation were analyzed in a smallscale. On one, a clam was present (CE) and the other, defaunated served as control (CC). On each of these, were measured: porosity, organic content, l\lH4+ concentrations, NH4+- oxidizing bacteria and actual and potential rates of NH4+ transformation, amonification and nitrification. These measurements where done in triplicate on thirteen sub-samples for each of five 2 cm deep layers. The effects of bioturbation were visible with lower NH4+ and O.M. content, doubled nitrification rates and potential nitrification rates (NH4+ enrichment) were enhanced by a factor of twelve. Highest number of ammoniumoxidizing bacteria was found in CC; however, specific bacterial cell activity was increased in CE. ln the second part of this work, Oxygen and nutrient fluxes and denitrification rates were measured in defaunated sediment cores (control), in sediment cores inhabited (DM) and in cores inhabited with a higher density (DE). This experiment was carried twice with two different bivalve species. Oxygen and nutrient fluxes as well as denitrification rates increased proportionally with density. Denitrification rates of NO3- from nitrification process (dn) were highly induced in Mya arenaria sediment cores, while sediment cores inhabited by Cerastoderma sp. showed higher denitrification rates of NO3- from water column (dw). These facts are explained by behavior and irrigation mechanisms performed by the two different bivalve species.