Benthic chambers

The exchange of solutes such as nutrients, dissolved organic substances, and metals and their associated processes at soil-floodwater interfaces are measured using laboratory-incubated cores or in situ pore water equilibrators as has been described. But these methods often underestimate fluxes because they do not account for processes such as bioturbation and bioirrigation at the soil-floodwater interface. To overcome these limitations, autonomous benthic chambers installed on top 

FIGURE 14.11 Pore water equilibrators used to determine in situ solute concentration gradients. 

FIGURE 14.12 Schematic showing benthic chamber used to measure in situ solute flux. 

---

Huettel, M., and Gust, G. (1992) Solute release mechanisms from confined sediment cores in stirred benthic chambers and flume flows. Mar. Ecol. Prog. Ser. 82, 187-197. 

Janssen, F., Faerber, P., Huettel, M., Meyer, V., and Witte, U. (2005a). Pore-water advection and solute fluxes in permeable marine sediments(I) Calibration and performance of the novel benthic chamber system Sandy. Limnol. Oceanogr. 50, 768—778. 

Table 8.5 Rates of nitrogen (N) release from sediment. Rates were quantified by measuring concentration changes (CC) in either sediment cores (SC) or benthic chambers (BC)... 

Measurements of Diffusive Fluxes. Benthic chamber experiments were carried out by using an automatic flux chamber (sediment lander). Our lander followed closely the design of Devol (43). The two benthic flux chambers have an area of 400 cm2 each. They penetrated the sediment to a... 

In situ measurements of Mn fluxes with benthic chambers and dialysis samplers confirmed the seasonal variability of the Mn redox cycle. They indicated that the reduction of particulate Mn oxides is a fast process that occurs close to the sediment surface within a time scale similar to that of Mn(II) oxidation. A maximum release rate of 5.5 mmol/m2 per day was measured in July. This rate indicates a close coupling between the oxidation of Mn(II) in the bottom waters and the reduction of Mn02 at the sediment surface. 

Benthic Chamber Results - Santa Monica Basin Oct 87 ROSE 2... 

Jahnke, R.A. and Christiansen, M.B., 1989. A free-vehicle benthic chamber instrument for sea floor studies. Deep-Sea Research, 36 625-637. 

S., Nuppenau, V., Pfannkuche, O., Reimers, C., Rowe, G, Sahami, A., Sayles, F., Schurter, M., Smallman, D., Wehrli, B. and De Wilde, P., 1995. Benthic chamber and profiling landers in oceanography - A review of design, technical solutions and function. Progress in Oceanography, 35 253-292. 

Fig. 6.15 Concentration versus time plots of different solutes measured with benthic chambers in the central equatorial Pacific (from Hammond et al. 1996). Black vertical bars indicate bottom water values.

The determination of in-situ fluxes of nitrate is comparatively limited. Although there are electrodes for the determination of microconcentration profiles in form of biosensors (Larsen et al. 1996), they are not yet snitable to be nsed on lander systems in the deep sea. The measurement of total nitrate flnxes by benthic chambers in continental slope sediments off California is shown in Figure 3.24 (Jahnke and Christiansen 1989). At this site, nitrate flnxes are directed into the sediment indicating strong denitrification snpported by very low oxygen concentrations in the overlying bottom water. 

Fig. 6.24 Model results of Soetaert et al. (1996) for a site in the abyssal Pacific. The curve of mineralization rates (oxygen fluxes) is smoother and shows a slight shift compared to the sedimentary carbon flux caused by the effective reaction kinetics. Squares indicate oxygen fluxes determined on the basis of benthic chamber and box corer data.

In the last decade, however, in-situ techniques have been developed to overcome these problems. Profiling lander systems were deployed to record the pore water microprofiles of oxygen, pH and pCOj, and Ca whereas benthic chambers were deployed to measure solute fluxes across the sediment-water interface directly. Very often, reactive-transport models are used to explain the interrelation between measured microprofiles, to predict overall calcite dissolution rates by defining the dissolution rate constants, and to distinguish between dissolution driven by organic matter oxidation and by the undersaturation of the bottom water. 

This study (Benth. Camb.) O Benthic Chamber A Pore Water Model... 

Benthic chambers are constructed in various sizes. For example, benthic chambers used by Fisher and Reddy (2001) were constructed of 6.35 mm (0.25 in.) thick acrylic and enclosed a soil surface area of 0.5 m (Figure 14.12). Each of the chambers was equipped with a recirculation pump and ports for installing electrodes and other related sensors. 

---