Microbial layer uptake

Vertical distributions of dissolved Ba and total (dissolved+particulate) Pu, Am and Th in Framvaren Fjord all show increased concentrations with depth (Falkner etal., 1993 Roos etal., 1993). Ba cycling was dominated by its uptake into particulate matter associated with productivity in surface waters, followed by its regeneration at depth or in the sediments. Microbiological activity near the redox interface likely promotes the breakdown of settling particulate matter and the release of barite just above the 02/H2S interface (Falkner etal., 1993). Complex formation with dissolved organic carbon (DOC) is believed to be the main cause for the observed behavior of Pu, Am and Th (Roos etal., 1993). The distributions of these elements were not examined within the regions near the 02/H2S interface and the associated microbial layer. 

FIGURE 3-29 Diagram of a fully penetrated biofilm. The rate of uptake of a chemical is governed by the uptake capabilities of the microbial cells composing the biofilm as well as by Fickian transport limitations in both the biofilm and the stagnant boundary layer. In a partially penetrated biofilm, Cj would decrease to zero at some point in the bio film. In a shallow bio film, Cj would be approximately equal to C/s throughout the bio film. 

Studies carried out to evaluate the uptake of Fe by phytoplankton showed that only the dissolved metal is bioavailable and that a thermal or photochemical treatment is necessary for the colloidal Fe to become bioavailable (163). Moreover, the chemical form in which Fe is present can also affect its availability for plankton. The distribution of Fe(II) in the euphotic layer of the equatorial Pacific Ocean was examined by O Sullivan et al. (164). Its concentration is regulated by the balance between production and removal Fe(II) can be produced by microbial and chemical reduction, while the loss in surface water is controlled by biological uptake and by oxidation to Fe(III), subsequent hydrolysis, ageing and settling. The results showed maximum concentration near the surface and at the depths with higher chlorophyll a levels, the concentration ranging between 0.12 and 0.53 nM. Laboratory experiments carried out by the same authors showed that photoreduction can be an important source of Fe(II). Considering the different chemical speciation observed at various depths, different bioavailability can be expected in the examined zone. 

Ronov (1976) estimated the average CaO content in sedimentary layer of 15.91 %, and in granite layer, of 2.71 %. Accordingly, the calcium reservoir in sedimentary shell is 272.8 X 10 - tons, and in the granite pool is 222.8 x lO tons. The weathering and metamorphosis of deep-layer silicates is accompanied by the formation of clay minerals with release of calcium available for plant and microbial uptake. 

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