ANÁLISE DE ISOTOPOS ESTÁVEIS DE CARBONO, ENXOFRE E AZOTO PARA O ESTUDO DO FLUXO DE MATÉRIA ORGÂNICA DE DOIS SISTEMAS COSTEIROS, RIA FORMOSA E ESTUÁRIO DO GUADIANA

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Publications

Isotopic tracking of sources in coastal systems: special emphasis to Zostera noltii (Horneman) food web

Publication . Machás, Maria Raquel de Assunção Gonçalves; Santos, Rui; Peterson, Bruce Jon

The main objectives of this research were 1) to review the isotopic tracking of anthropogenic N sources 2) to trace the distribution of the urban effluent in Ria Formosa lagoon and to reveal its biological uptake and impact, 3) to assess the changes in stable isotope contents of Zostera noltii leaves during the early phases of decomposition and 4) to investigate the trophic interactions in Z. noltii meadows. When evaluated with care, the δ15Ν values can provide valuable information on qualitative and quantitative changes in the nitrogen status of aquatic systems. For this evaluation it is important to characterize the nutrient δ15N values in the different compartment. Our study of the distribution of the urban effluent in Ria Formosa lagoon revealed that the seasonal variation of the Waste Water Treatment Works (WWTW) internal metabolism was reflected in the δ13CDIC and δ15NNH4 of its effluent. The WWTW isotopic signal was most evident in the isotopic signature of the particulate organic matter, rather than in the sediment organic matter or in Zostera noltii. The overall results show that the effluent discharge is likely to impact the clam cultivations areas that are as close as about 300 m from the WWTW. The δ13C and δ15N values of Zostera noltii do not change during the breakdown of the biomass into finer particulate material. Stable isotope studies to assess the contribution of this species to secondary production can thus consider the natural δ13C and δ15N abundances of living tissues without any correction to account for decomposition. On the other hand, the use of δ34S values of Z. noltii detritus should be done with caution due to the contamination of the samples with pyrite, which has a depleted δ34S signal. The δ13C, δ15N and δ34S values of primary producer, organic matter, detritus and consumers provided unique insights into trophic relationships within the Z. noltii meadows. δ-values indicate that animals, excluding the gastropod Elysia sp., are dependent to varying degrees upon seagrass and/or seagrass epiphytes and green algae for their C, N and S sources.

2007Doctoral thesis

Open Access