Benthic Chamber for Use in Rivers: Testing Against Oxygen Mass Balances

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Abstract
An in situ benthic chamber has been developed in order to measure rates of respiration and photosynthesis in rivers. Oxygen mass balances for three rivers show satisfactory agreement between chamber (24.7-52.3g⋅m-2⋅day-1) and calculated net (28.3-77.2g⋅m-2⋅day-1) benthic oxygen uptake rates (BUR) by matching chamber (0.25-0.35m⋅s-1) and river (0.25-0.40m⋅s-1) boundary velocities (each measured 0.05 m above bed). The BUR is a function of the flow velocity of the overlying water, with both sewage fungus biofilms and pumice sediments each showing a large positive response and approximately linear relationship to velocity over the range studied (0.06-0.35m⋅s-1). Measurements of the oxygen mass transfer coefficient for the air‐water interface of an inverted chamber showed that the response to flow velocity was not significantly different (P>0.05) from that predicted using the O'Connor‐Dobbins formula. Chamber devices must adequately simulate natural hydrodynamic conditions and future mathematical modelling sho...