Biogeochemical fluxes

The other output from watershed and slope landscapes positions is related to the surface and subsurface runoff of trace metals. The ecosystems of waterlogged glacial valleys, geochemically subordinate to the above mentioned landscape, can receive with surface runoff an additional amount of various chemical species. This results in 3 1-fold increase of plant productivity in comparison with elevated landscapes and in corresponding increase of all biogeochemical fluxes of elements, which are shown in Table 6. For instance, the accumulation of trace metals in dead peat organic matter of waterlogged valley was assessed as the follows Fe, n x 101 kg/ha, Mn, 1-2 kg/ha, Zn, 0.1-0.3 kg/ha, Cu, Pb, Ni, n x 10-2 kg/ha. 

Box 2. Biogeochemical fluxes of elements in Oak Forest ecosystem (after Jakucs, 1985)... 

In may be of interest to compare the fluxes of elements in biogeochemical cycles of Oak Forest ecosystem with exposure to airborne deposition input. The latter were (inkg/ha/yr)forN, 17.7 forCa, 14.7 forMg, 1.8 for K, 4.2 for Na, 1.4 forP, 1.1 for Fe, 0.07 and for Zn, 0.14. The deposition input of these elements fall into a range of 20% (calcium) to 4.5% (potassium) relative to the respective biogeochemical fluxes (see Table 9). The airborne Fe input accounts for a mere 2.5%. Simultaneously, for some heavy metals, like zinc, the deposition input is commensurate with the fluxes of biogeochemical cycle. 

BIOGEOCHEMICAL FLUXES AND EXPOSURE PATHWAYS IN SOIL-WATER SYSTEM OF BOREAL AND SUB-BOREAL ZONES... 

Table 1. The annual biogeochemical fluxes and pools in Steppe and Desert natural ecosystems (after Rodin et al., 1975).

The ash content of Arid Steppe and Desert ecosystem vegetation is about 2 times higher than that of forest species. Accordingly, the biogeochemical fluxes of elements are similar to those in the forest ecosystems, in spite the smaller biomass (see above). The compartments of biogeochemical turnover in Steppe and Desert ecosystems are shown in Table 1. 

The annual biogeochemical fluxes of various elements are shown in Table 10. 

In plain autonomous ecosystems the fluxes of sodium are less 40 g/ha/yr and those of Mg are less than 10 g/ha/yr. For iron these values are close to 1 g/ha/yr, and for all heavy metals, are between 0.01 and 0.04 g/ha/yr. In the geochemically subordinate landscapes (Naloxylon ammodendron and Ephedra przewalskii ecosystems) which receive additional moisture and chemical elements, the biogeochemical exposure fluxes are 360-912 g/ha/yr for Mg and Na, and from 0.44 to 6.65 g/ha/yr for heavy metals. In the periphery of the Gobi desert, Anabasis brevifloria and Graminaceae Dry Desert ecosystems show the overall increase of biogeochemical fluxes. The turnover for some elements (Mg, V, Cr) rises but slightly in comparison to their turnover in Extra-Dry ecosystems, whereas the turnover for other elements (Sr, Zn, Cu) increases several times. 

The biogeochemical fluxes and exposure to various chemical species are shown in Table 11. 

The biogeochemical fluxes and exposure pathways of various macro- and microelements are different from those shown for Tropical Rain Forest ecosystems. The chemical composition of leaves of tree species in Mangrove Forest ecosystems is connected with higher content of Mg, Cl and S-SO4- and lesser content of K and Si as compared to the leaves of trees from Tropical Rain Forest ecosystems. The content of A1 is 3-4 times higher than that of Si and this can be related to the values of hydrogenic accumulation of these elements in soils (Figure 3). 

The comparison of biogeochemical fluxes and relevant exposure rates of heavy metals in the Mangrove and Tropical Rain Forest ecosystems shows that the total mass of ash elements per unit area is similar. However, the proportion of various elements is markedly different. The Mangrove plant uptake of Fe and Mn is less and that of Sr is higher than the uptake of these elements in Tropical Rain Forest ecosystems. 

The Mangrove ecosystems perform a role of biogeochemical barrier, which decreases significantly the runoff of chemical species from the coast to the ocean waters. This is correlated with the major biogeochemical parameters of these ecosystems such as high productivity and high values of annual biogeochemical fluxes and relevant exposure rates. 

Value of Isotopic Labeling. The experiments described demonstrate the usefulness of stable-isotope additions in understanding trophic interactions and biogeochemical fluxes in whole ecosystems. Using stable isotopes as chemical tracers in natural, undisturbed systems is especially helpful in interpreting the results of perturbation experiments. 

Because of the high area of solid surfaces covered with biofilms, these biofilms dominate the heterotrophic metabolism in many aquatic ecosystems. In streams, rivers, and shallow lakes, bacterial activity in epilithic and epiphytic biofilms may be several times higher on an areal basis than the activity of free living bacteria. By the differential use of specific DOM fractions, biofilm bacteria influence the biogeochemical composition of DOM in these ecosystems. Biofilms thus can control biogeochemical fluxes of DOM and are important sinks of organic matter. 

Ducklow, H. W. (1995). Ocean biogeochemical fluxes New production and export of organic matter from the upper ocean. Rev. Geophys., Suppl. 1271-1276. 

Testa, J. M., and Kemp, W. M. (2005). Stoichiometry of Biogeochemical Fluxes in the Patuxent River Estuary, USA. Presentation at American Society of Limnology Oceanography, Santiago de Compostela, Spain. 

Cho B. C. and Azam F. (1988) Major role of bacterial in biogeochemical fluxes in the ocean s interior. Nature 332, 441-443. 

Nuttle, W.K. Hemond, H.F.(1988) Salt marsh hydrology implications for biogeochemical fluxes to the atmosphere and estuaries. Global Biogeochem. Cycl. 2, 91-114. 

These reasons are connected with S biogeochemical fluxes and pools in biosphere, atmosphere and hydrosphere. However, the main reservoirs are related to lithosphere. According to Ronov (1976) and Dobrovolsky (1994), the average concentration of sulfide sulfur in sedimentary shell is 0.183% and the total amount of sulfur is 9.3 x 10 tons. In addition, the granite crustal layer contains 8.6 x 10 - tons of S. Totally in the Earth s crust there is around 94% of the global S mass (Table 24). 

Table 25. Annual global biogeochemical fluxes of sulfur, IQrtonsS/yr. (Modified from Charlson el al, 1992).

Discuss the global biogeochemical cycle of calcium. Draw your attention to the most important fluxes and pools. Explain the importance of calcinm biogeochemical fluxes in terrestrial ecosystems for the global budget of this element. 

Biogeochemical Fluxes of Zinc Zinc in plant-soil system... 

Discuss biogeochemical fluxes and pools of copper and the global mass balance of this trace metal. 

Describe the biogeochemical fluxes of zinc in various soil-plant systems of the World. Present the quantitative estimates of these fluxes. 

Table 17. The biogeochemical fluxes and pools In the Oak Forest ecosystem of Central Europe.

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