Biota systems

The transfer of P from land to terrestrial biota (F23) represents the sum of terrestrial biological productivity. There is no significant gaseous form of P, nor is there a major transfer of living organisms between the freshwater-terrestrial system and the oceans. The terrestrial biota system is, therefore, essentially a closed system where the flux of P to the biota (p23) is balanced by the return of P to the land from the biota (F32) due to the decay of dead organic materials. 

Phosphorus cycling in soils. The cycling of P in soils (see Fig. 1) has received much attention, both in terms of fertilization and the natural development of ecosystems. Of the approximately 122,600 Tg P within the soil/biota system on the continents, nearly 98% is held in soils in a variety of forms. The exchange of P between biota and soils is relatively rapid, with an average residence time of 13 years, whereas the average residence time of... 

Fig. 8. Steady-state model for the earth s surface geochemical system. The kiteraction of water with rocks ki the presence of photosynthesized organic matter contkiuously produces reactive material of high surface area. This process provides nutrient supply to the biosphere and, along with biota, forms the array of small particles (sods). Weatheriag imparts solutes to the water, and erosion brings particles kito surface waters and oceans.

Contaminant transfer to bed sediments represents another significant transfer mechanism, especially in cases where contaminants are in the form of suspended solids or are dissolved hydrophobic substances that can become adsorbed by organic matter in bed sediments. For the purposes of this chapter, sediments and water are considered part of a single system because of their complex interassociation. Surface water-bed sediment transfer is reversible bed sediments often act as temporary repositories for contaminants and gradually rerelease contaminants to surface waters. Sorbed or settled contaminants are frequently transported with bed sediment migration or flow. Transfer of sorbed contaminants to bottomdwelling, edible biota represents a fate pathway potentially resulting in human exposure. Where this transfer mechanism appears likely, the biotic fate of contaminants should be assessed. 

In situations where Tobs is comparable in magnitude to tq, a more complex relation prevails between Q, S, and M. Atmospheric CO2 falls in this last category although its turnover time (3 years, cf. Fig. 4-3) is much shorter than Tobs (about 300 years). This is because the atmospheric CO2 reservoir is closely coupled to the carbon reservoir in the biota and in the surface layer of the oceans (Section 4.3). The effective turnover time of the combined system is actually several hundred years (Rodhe and Bjdrk-strom, 1979). 

The land biota reservoir (3) represents the phosphorus contained within all living terrestrial organisms. The dominant contributors are forest ecosystems with aquatic systems contributing only a minor amount. Phosphorus contained in dead and decaying organic materials is not included in this reservoir. It is important to note that although society most directly influences and interacts with the P in lakes and rivers, these reservoirs contain little P relative to soil and land biota and are not included in this representation of the global cycle. 

The most complex of the feedback systems are those in which biota are directly involved. Indeed, one feedback of climate on CH4 may well be an example microorganisms in soils are a known CH4 sink, and the rate at which they consume CH4 is temperature dependent. 

Ordinarily, the atmosphere is a self-cleansing system due to the abundance of O3, OH, NO2, and other reactive species. For example, hydrocarbon emissions from biota (such as terpenes) are oxidized in a matter of hours or days to CO and then on to CO2. Alternatively, carboxylic acids may be formed and then transferred to the hydrosphere or pedosphere by rain. The atmosphere acts much like a low-temperature flame, converting numerous reduced compounds to oxidized ones that are more readily removed from the air. The limit to the rate of oxidation can be defined by the concentration of OH... 

In most of the world s watercourses, dramatic modifications have occurred as a consequence of their intensive use by human societies [1]. Pollution, water abstraction, riparian simplification, bank alteration, straightening of watercourses, dam construction, and species introduction are widespread perturbations in river ecosystems. These human-driven alterations are part of global changes. The simplification of the channel network and the alteration of water fluxes reduce the capacity of fluvial systems to recover from namral disturbances. Hydrologic alterations affect the functional organisation of streams and rivers, and lead to a simplification and impoverishment of the biota within these ecosystems. 

The biota of long-distance dispersal. IV. Genetic systems in the flora of oceanic... 

P. Nannipieri, The potential use of soil enzymes as indicators of productivity, sustainability and pollution. Soil Biota Management in Sii.stainable Farming Systems (C. E. PankhursI, B. M. Doube. V. V. S. R. Gupta, and P. R. Grace, eds.), CSIRO, Adelaide, Australia, 1994, p. 238. 

For the purposes of these field studies, a test system is defined as a specific tract of land managed in part through use of pesticides. Test systems are normally limited to one crop or land use type and may include row crops, grains, fruits or golf courses. The tract of land, of course, has associated biota that are present naturally or as part of the management practices. These biota are also part of the test system and are normally described as test species or species of interest. Selection of test systems is critical to evaluate wildlife exposure scenarios in a sufficient number of sites within appropriate geographic regions. 

The symposium blended tutorial review papers with descriptions of field, laboratory, industrial, and regulatory problems that have been approached using chemical fate simulations. Authors presented current practices and practical questions such as material balance analysis, atmospheric processes influencing human exposure, aquatic system pathway analysis, movement in soil/groundwater media, and uptake or degradation in biota. 

Bioavailability of Metals, Nonmetals and Xenobiotics Immobilized on Soil Components, (4) Distribution and Activity of Biomolecules in Terrestrial Systems, (5) Interactions between Soil Microbial Biomass and Organic Matter/Nutrient Transformations, and (6) Impact of Interactions among Soil Mineral Colloids, Organic Matter and Biota on Risk Assessment and Restoration of Terrestrial Ecosystems. There were 2 plenary lectures, 9 invited speakers, 36 oral presentations and 45 posters. Dr. N. Senesi from University of Bari, Italy, presented an IUPAC lecture entitled Metal-Humic... 

---