Spatio-temporal variability in benthic silica cycling in two macrotidal estuaries: Causes and consequences for local to global studies

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• 作者：Mé ; lanie Raimonet^a ; ^{melanie.raimonet@univ-brest.fr} ; ^{melanie.raimonet@gmail.com} ; Olivier Ragueneau^a ; Franç ; oise Andrieux-Loyer^b ; Xavier Philippon^b ; Roger Kerouel^b ; Manon Le Goff^a ; Laurent Mé ; mery^a
• 关键词：heterogeneity ; season ; silicate ; sediment ; land&ndash ; sea interface ; upscaling
• 刊名：Estuarine, Coastal and Shelf Science
• 出版年：2013
• 出版时间：1 March, 2013
• 年：2013
• 卷：119
• 期：Complete
• 页码：31-43
• 全文大小：728 K

文摘

The high heterogeneity of silica cycling in coastal margins and the lack of silica data (compared to nitrogen and phosphorus) prevent the estimation of global silica retention in estuaries. In this study, the spatial and temporal variability of porewater silicic acid (Si(OH)₄) profiles - that integrate benthic transport and reaction processes - was investigated at different spatial (metre, longitudinal and cross-section, intra-estuary) and temporal (tidal, seasonal) scales in two macrotidal estuaries, very close geographically but essentially differing in their shape. Studying the spatial and temporal variability of Si(OH)₄ concentrations in porewaters provided evidence for the importance of transport processes, m>e.g.m> bio-irrigation, tidal pumping, resuspension and any combination of these processes, in affecting Si(OH)₄ concentrations and fluxes and therefore temporary or permanent retention along the land-ocean continuum. We confirm that aSiO₂ (amorphous silicate) transported by rivers and estuaries clearly needs to be better characterized as it provides an important source of reactive aSiO₂ to sediments. This study allows us to: (1) interrogate spatial and temporal scales, although both are most often in complete interaction; (2) design the most appropriate sampling schemes to be representative of any given system and to extrapolate at the scale of the whole estuary; (3) quantify uncertainty associated to the estimations of Si(OH)₄ stocks and fluxes in this type of ecosystem, essential for budget calculations. We showed that two adjacent small macrotidal estuaries, may exhibit different behaviours regarding Si retention. Temporary retention has been observed in the meanders of the Aulne Estuary and not along the more linear Elorn Estuary, demonstrating the importance of the morphology and hydrodynamic components of the estuarine filter. Research is needed in other systems and climatic zones, but our study suggests that the typology should not only account for the different types of land-ocean continuum (fjord, delta, mangrove¡­), but also incorporate the physical or biological attributes of the estuarine filter.