Hydrodynamic characterization and performance of an autonomous benthic chamber for use in coastal systems

Sara Ferrón, Fernando Alonso-Pérez, Carmen G. Castro, Teodora Ortega, Fiz F. Pérez, Aída F. Ríos, Abelardo Gómez-Parra, Jesús M. Forja

Limnol. Oceanogr. Methods 6:558-571 (2008) | DOI: 10.4319/lom.2008.6.558

ABSTRACT: A benthic chamber (covering 5030 cm2 of seafloor) with real-time control of sampling and sensor data transmission has been developed for studying benthic fluxes in coastal sediments. Enclosed water is stirred by three submersible centrifugal pumps, which are connected to power circuits that regulate their input voltage, and thus, the current velocity inside the chamber. The complete mixing of the incubated water is achieved within 4 min. The 3-D velocity field and the distribution of the diffusive boundary layer (DBL) inside the chamber were characterized at different pump rates in a laboratory tank with a bottom layer of sediment or a false bottom supporting alabaster dissolution plates. Two different outlet devices from the pumps were tested. For the one finally selected, averaged tangential velocities at 5 cm above the bottom ranged from 2.0 cm s-1 to 4.8 cm s-1, depending on the voltage applied to the pumps, providing averaged DBL thicknesses that ranged from 125 µm to 279 µm. Average tangential velocity and average DBL thickness were found to correlate according to: VH = 615 × [DBL]-1.02 (R2 = 0.97). Successful field chamber measurements were performed in two shallow coastal systems: Ría de Vigo (NW Spain) and Bay of Cádiz (SW Spain).