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Isotopic tracking of sources in coastal systems: special emphasis to Zostera noltii (Horneman) food web
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Advisor(s)
Abstract(s)
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.
Description
Tese dout., Ecologia, Universidade do Algarve, 2007
Keywords
Teses Ecologia Isótopos estáveis Zostera noltii Nutrientes Decomposição foliar Teia alimentar Algarve