Estuaries and Coasts

, Volume 38, Issue 3, pp 1016–1031 | Cite as

Factors Controlling Benthic Biogeochemistry in Urbanized Coastal Systems: an Example from Venice (Italy)

  • R. Azzoni
  • D. NizzoliEmail author
  • M. Bartoli
  • R. R. Christian
  • P. Viaroli


Benthic biogeochemical processes and their interactions are affected by multiple factors including organic matter load, season, and hydrology. We analyzed benthic biogeochemistry in two canals in the urban area of Venice (Italy), to assess the effects of contrasting tidal conditions on organic matter processing in the heavily modified lagoonal ecosystem. We measured sediment oxygen demand, bacterial sulfate reduction, denitrification, dissimilative nitrate reduction to ammonia, dissolved inorganic carbon, and inorganic nutrient fluxes across the sediment-water interface under different seasonal (late winter and summer) and tidal (spring and neap tide) conditions. Sediments were highly organic and strongly reduced. Organic matter mineralization was mainly driven by bacterial sulfate reduction, whereas denitrification was limited by both nitrate availability and competition with dissimilatory nitrate reduction to ammonium. While the elevated benthic metabolism can be largely explained by organic enrichment, contrasting tidal conditions can be a significant driver of intra-seasonal variability of benthic biogeochemistry. Under neap tide, dissolved inorganic carbon production increased up to threefold, sulfides attained up to 6.4 mM in porewater, denitrification became inefficient, and the ratio of nitrogen recycling to dissipation increased by ~70 % compared to spring tide. Additionally, increased efflux of inorganic nitrogen from sediments fed back to promote further eutrophication. We infer that human modifications to reduce fortnightly tidal flushing can impact benthic processes, impairing sediment functioning and water quality.


Organic enrichment Sulfate reduction Denitrification DNRA Nutrient fluxes Tidal regime Coastal urban ecosystems 



The authors are indebted with Drs. Roberta Carafa, Daniele Longhi, and Giulio Poiana for assistance during sampling activities. This study was supported by the research subcontract “Experimental studies of the metabolism of the canals of Venice,” within the INSULA SpA project directed by Prof. Antonio Marcomini (Department of Environmental Sciences, University Ca’ Foscari of Venice). We thank Prof. Iris Anderson for suggestions and comments to the early version of the manuscript.


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Copyright information

© Coastal and Estuarine Research Federation 2014

Authors and Affiliations

  • R. Azzoni
    • 1
  • D. Nizzoli
    • 1
    Email author
  • M. Bartoli
    • 1
  • R. R. Christian
    • 2
  • P. Viaroli
    • 1
    • 3
  1. 1.Department of Life SciencesUniversity of ParmaParmaItaly
  2. 2.Department of BiologyEast Carolina UniversityGreenvilleUSA
  3. 3.CNR-ISMARVeneziaItaly

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