Biogeochemical availability

Trace element speciation analysis is a base for the description of forms and compounds in which they occur in soils. Other definitions are also used to define properties of trace elements in soils. In fact, the general term availability has been recently defined as geoavailability, geochemical availability, biogeochemical availability and bioavailability (Wolt 1994, Smith and Huyck 1999) ... 

Biogeochemical availability is defined as the quantity-intensity factor calculated as a ratio of total content to the concentration of a trace element in soil solution. 

In most cases models describing biogeochemical cycles are used to estimate the concentration (or total mass) in the various reservoirs based on information about source and sink processes, as in the examples given in Section 4.4. This is often called forward modeling. If direct measurements of the concentration are available, they can be compared to the model estimates. This process is referred to as model testing. If there are significant differences between observations and model simulations, improvements in the model are necessary. A natural step is then to reconsider the specification of the sources and/or the sinks and perform additional simulations. 

The availability of a metal describes one aspect of its potential to cycle among biogeochemical reservoirs. The initiation of the cycling process is called mobilization. Metals may be mobilized, that is, made available for transport away from their region of deposition, when the geochemi-... 

The evolution of life on Earfh has depended on a sustained supply of nutrients provided by the physical environment. Life, in turn, has profoundly influenced the availability and cycling of these nutrients hence the inclusion of bio in biogeochemical cycles. The involvement of the biosphere with biogeochemical cycles has been determined by the evolution of life s biochemical properties in the context of the physical and chemical properties of planet Earth. 

Hamilton SK, Bunn SE, Thoms MC et al (2005) Persistence of aquatic refugia between flow pulses in a dryland river system (Cooper Creek, Australia). Lirrmol Oceanogr 50 743-754 Bernal S, Butturini A, Sabater E (2002) Variability of DOC and nitrate responses to storms in a small Mediterranean forested catchment. Hydrol Earth Syst Sci 6 1031-1041 Romani AM, Vazquez E, Butturini A (2006) Microbial availability and size fractionation of dissolved organic carbon after drought in an intermittent stream biogeochemical link across the Stream-Riparian interface. Microb Ecol 52 501-512... 

The bioavailability of trace elements in soil-water-plant ecosystems of arid zones is largely determined by their partitioning between solution and solid-phase components. The redistribution and transformation of trace elements among solid-phase components under various biogeochemical conditions strongly adjust their lability and bioavailability. Soluble, exchangeable and organically bound forms are bioavailable to plants. The carbonate bound fraction represents a reservoir of potentially bio-available trace elements to plants. In paddy soils, the amorphous Fe/Al oxide fraction contributes to trace element availability as well. 

Zinc has only been measured accurately in open ocean by a few investigators [239,604-607]. Few data are available because of very low zinc concentrations in seawater and the ubiquitous sources of zinc contamination. The uncertainty of all zinc measurements prior to these investigations, and the paucity of reliable data since, have left little information for the environmental chemist to unravel the biogeochemical behaviour of zinc or to detect waters perturbed by anthropogenic inputs. 

Bouwman AF, Boumans LJM, Batjes NH (2002) Emissions of N20 and NO from fertilised fields summary of available measurement data. Glob Biogeochem Cycles 16 1058 Christensen S, Simkins S, Tiedje JM (1990) Spatial variation in denitrification dependency of activity centers on the soil environment. Soil Sci Soc Am J 54 1608-1613 CONCAWE (2006) Well-to-wheels analyses of future automotive fuels and powertrains in the European context. Study of European Council for Automotive R D, EUCAR, European Commission, Brussels... 

This book is aimed at generalizing the modem ideas of both biogeochemical and environmental risk assessment during recent years. Only a few books are available for... 

Risks and Trends (Modelling and Mapping Manual, 2004)3. Moreover, many research groups engaged in biogeochemical model development make them available as freeware . Annual reports published by the National Focal Centers of the LRTAP Convention as provides insights on methodologies and partially input data for the CLL calculations. 

The regulation of biogeochemical cycles by microbial populations is of most direct importance in the cycling of N, S, P, and C. Most of the ecosystem pool of these elements resides as organic forms in forest floor and mineral soil compartments. These organic complexes are subjected to microbial transformations, which regulate nitrate, sulfate and phosphate ions dynamics and availability. In turn, this influences indirectly... 

Information from surveys conducted decades ago can now be viewed in light of subsequent exploration activities, and the value of biogeochemical surveys (when and where to use the techniques) can be more accurately assessed and applied using the rapidly-advancing analytical methodologies (e.g. ICP-MS) that are now widely available. 

The rivers play a major role in the transfert of carbon and mineral nutrients from land to the sea and influence significantly the biogeochemical processes operating in coastal waters. Quantification of the material transport, both in the dissolved and particulate forms, has been attempted by several authors in the past (Clarke, 1924 Holeman, 1968 Garrels McKenzie, 1971 Martin et al., 1980 Meybeck, 1982 Milliman Meade, 1983). Depending on the type of sampling techniques and methods of calculations employed there are differences in the reported fluxes. A major problem in such calculations is the paucity of reliable data from some of the major rivers of the world especially of Asia (see e.g. Milliman Meade, 1983). Additionally the difficulty of obtaining representative samples from the rivers will adversely affect flux calculations. Most of the inferences drawn on the nature and transport of riverine materials rest on data collected randomly - at different points in time and space. Seasonal variations in the transport of materials are very common in some of the major world rivers, and in some cases more than 60 % of the material transport occurs within a very short period of time. Furthermore, available data are not always comparable since the analytical techniques used differ from river to river. 

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