Trace metal biogeochemical cycling

We can see that the content of trace metals in water extraction is very low. This means that the direct involvement of these metals in biogeochemical cycles is very restricted. The significant increase of metal contents in acid-soluble form was shown only for Fe, Mn and, partly, for Zn. These data testify the importance of atmospheric deposition for the Arctic ecosystems as a source of nutrients. 

A high amount of various nutrients and trace metals is retained in peat and dead plant residues and thus temporarily eliminated from the biogeochemical cycles and pollutants exposure to human and ecosystem health. The period of this elimination depends on the solubility of these metals. It has been shown (Dobrovolsky, 1994) that... 

The different metal uptake by plants is accompanied by a different involvement of these trace metals and macronutrients in the biogeochemical cycles. A comparison of... 

The systematic removal of elements by runoff and the reimmobilization from solution by organic matter are continuously counterbalanced by the new input of chemical species, which maintain both biological and biogeochemical cycles. The main sources of water-soluble elements are oceanic aerosols deposited on the land surface and the weathering of rocks. The airborne input of the trace metals may be ranked as follows for the Spitzbergen island ecosystems (Table 4). 

We can compare these values with those characterizing the fluxes of trace metals in biogeochemical cycles. The biological productivity of the Polar Tundra ecosystem grown on the low terrace in the region of Barentsberg, Spitzbergen Island, is shown in Table 5. 

Amongst the ash elements the most abundant in biomass is calcium, which is accumulated in leaves, in trunk wood, and in twigs. Potassium is dominant in annual NPP. The masses of trace metals in biogeochemical cycling of this Oak Forest ecosystem are roughly in correspondence to their respective average values for the... 

We can see that the soluble and exchange forms of these metals are present in small amounts accounting merely for a few percent of the total metal content in soil. The content of organometal species is relatively high in the upper profile rich in humic species, whereas it drops sharply in the mineral horizons. Copper is extensively involved in the biogeochemical cycle in the Forest ecosystems and this is less profound for cobalt. It is noteworthy that a large part of metals (in particular, of copper) become bound to iron hydroxides. This is typical for various trace elements, including arsenic, zinc and other elements with variable valence. 

Martin, J.-M., Dai, M.-H. and Cauwet, G. (1995). Significance of colloids in the biogeochemical cycling of organic carbon and trace metals in the Venice Lagoon (Italy), Limnol. Oceanogr., 40, 119-131. 

Morel FMM, Price NM (2003) The biogeochemical cycles of trace metals in the oceans. Science 300 944-947... 

Lim B, Jickells TD. 1990. Dissolved, particulate and acid-leachable trace metal concentrations in North Atlantic precipitation collected on the Global Change expedition. Global Biogeochem Cycles 4 445-458. 

Benjamin, M.M., and Honeyman, B.D. (2000) Trace Metals. In Earth System Science—from Biogeochemical Cycles to Global Change (Jacobson, M.C., Charlson, R.J., Rodhe, H., and Orians, G.H., eds.), pp. 377-411, Academic Press, New York. 

Figure 3 -4 Export fluxes out of the mixed layer measured in unperturbed subAntarctic HNLC waters near New Zealand during the FeCycle experiment for (A) PFe, (B) PON, and (C) POP. Samples were collected at 80 and 120 m using two trace metal-clean drifting sediment trap arrays deployed for 7 days. Values are the means of four (PFe), two (PON), or one (POP) collection cylinders at each depth, after subtraction of procedural blank values (deployed but unopened cylinders). Error bars represent standard errors. PON samples were lost from the 80 m depth of Trap 1. Adapted from Frew et al. (2006), Global Biogeochemical Cycles 20 GB1S93.

EFFECTS OF TRACE METALS ON MARINE BIOGEOCHEMICAL CYCLES... 

At about the time that Honeyman and Santschi published their colloidal pumping hypothesis, lab and field studies showed that thorium and other metals in seawater are, indeed, associated with colloids (Baskaran et al., 1992 Moran and Buesseler, 1992 Moran and Moore, 1989 Niven and Moore, 1988). Subsequently, many more studies have demonstrated that colloids are abundant in seawater and that they play an important role in the marine biogeochemical cycles of organic carbon and of many trace elements (Guo and Santschi, 1997). 

The main removal process for oceanic components is via sedimentation and burial thus, the interaction of dissolved metals with particles in sea water is a major indication of their concentration and distribution in the world s oceans. In open ocean areas the particle cycle is driven by the biological production of particles in the surface layers, which after processes of mineralization and packaging reach the necessary size and density to fall to the ocean bottom. On the basis of this consideration, one can say that in the open ocean area the biogeochem-ical cycle of trace metals determining their distribution and speciation is frequently dominated by biological processes. In eoastal areas or particular geographical zones, other phenomena, e.g., inorganic precipitation, can take place. 

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