Turbidity limits gas exchange in a large macrotidal estuary

• Published in: Estuarine, coastal and shelf science coastal and shelf science, 2009-07, Vol.83 (3), p.342-348
• Main Authors: Abril, Gwenaël, Commarieu, Marc-Vincent, Sottolichio, Aldo, Bretel, Patrice, Guérin, Frédéric
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Brackish; Brackish water ecosystems; current; Fundamental and applied biological sciences. Psychology; gas exchange; Marine; Synecology; turbidity; turbulence; wind
• ISSN: 0272-7714; 1096-0015
• DOI: 10.1016/j.ecss.2009.03.006

In estuaries, the gas transfer velocity ( k) is driven by a combination of two major physical drivers, wind and water current. The k values for CO 2 in the macrotidal Gironde Estuary were obtained from 159 simultaneous pCO 2 and floating chamber flux measurements. Values of k increased with wind speed and were significantly greater when water currents and wind were in opposing directions. At low wind speeds ( 0.2 g L −1) had a significant role in attenuating turbulence and therefore gas exchange. This result has important consequences for modeling water oxygenation in estuarine turbidity maxima. For seven low turbidity estuaries previously described in the literature, the slope of the linear regression between k and wind speed correlates very well with the estuary surface area due to a fetch effect. In the Gironde Estuary, this slope follows the same trend at low turbidity (TSS < 0.2 g L −1), but is on average significantly lower than in other large estuaries and decreases linearly with the TSS concentration. A new generic equation for estuaries is proposed that gives k as a function of water current velocity, wind speed, estuarine surface area and TSS concentration.