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Horizontal and vertical gradients in sediment nutrients on mudflats in the Shannon estuary, Ireland
Wilson, J.G.; Brennan, M.; Brennan, B. (1993). Horizontal and vertical gradients in sediment nutrients on mudflats in the Shannon estuary, Ireland, in: Meire, P. et al. (Ed.) Marine and Estuarine Gradients: ECSA 21: Proceedings of the 21st Symposium of the Estuarine and Coastal Sciences Association held in Gent, 9-14 september 1991. Netherlands Journal of Aquatic Ecology, 27(2-4): pp. 173-180
In: Meire, P.; Vincx, M. (Ed.) (1993). Marine and Estuarine Gradients: ECSA 21: Proceedings of the 21st Symposium of the Estuarine and Coastal Sciences Association held in Gent, 9-14 september 1991. Netherlands Journal of Aquatic Ecology, 27(2-4). Netherlands Society of Aquatic Ecology: Bilthoven, The Netherlands. 496 pp., more
In: Netherlands Journal of Aquatic Ecology. Kluwer Academic Publishers/Netherlands Society of Aquatic Ecology: Bilthoven. ISSN 1380-8427, more
Peer reviewed article  

Also published as
  • Wilson, J.G.; Brennan, M.; Brennan, B. (1993). Horizontal and vertical gradients in sediment nutrients on mudflats in the Shannon estuary, Ireland. Neth. J. Aquat. Ecol. 27: 173-180, more

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Keywords
    Marine; Brackish water

Authors  Top 
  • Wilson, J.G.
  • Brennan, M.
  • Brennan, B.

Abstract
    Spatial variability in nutrient concentrations in the intertidal sediments and pore waters has been studied along downshore transects and in care profiles at three locations in the Shannon estuary on the west coast of Ireland. The parameters measured were N, as Kjeldahl N, NO3, NO2, and NH3, and P as total P and PO4 along with a range of other environmental variables such as salinity and sediment organic content. The concentrations of all nutrients varied with season, but winter values were generally low in comparison with polluted mainland European estuaries. There was a great deal of variation in nutrient concentrations along the transects, and coefficients of variability of up to 153% (NH3), 173% (NO3), 129% (NO2) and 117% (PO4) were found. Overall, there was little evidence of any trends in concentration in any of the nutrients from the top to the bottom of the transects, although it was occasionally possible to link particular instances to local conditions such as the presence of the channel or a stream. Sediment care profiles showed typical patterns, with NO3 concentrations for example being highest in surface sediments, while NH3 and PO4 concentrations increased with depth. Rather surprisingly perhaps, NO3 could still be detected on occasion at depths of up to 20 cm, well below the Redox Potential Discontinuity (RPD) and the limit of oxygen penetration which oxygen microelectrodes had measured as being within a few mm of the surface. This was ascribed to the activities of the macrofauna, in that the oxidised sediment which lined the burrows could clearly be seen in same cores. This study not only shows that nutrient distributions along estuarine gradients are linked to physico-chemical factors such as oxygenation and freshwater/marine influence, but also that sediment instability, through random physical events such as storms, and macrofaunal activity play an important role and that these latter factors deserve closer attention.

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