Cycles, biological

Natural water systems contain numerous minerals and often a gas phase (Fig. 1). They include a portion of the biosphere and organisms, and their abiotic environments are interrelated and interact with each other. The distribution of chemical species in waters is strongly influenced by an interaction of mixing cycles and biological cycles. 

Joly observed elevated "Ra activities in deep-sea sediments that he attributed to water column scavenging and removal processes. This hypothesis was later challenged with the hrst seawater °Th measurements (parent of "Ra), and these new results conhrmed that radium was instead actively migrating across the marine sediment-water interface. This seabed source stimulated much activity to use radium as a tracer for ocean circulation. Unfortunately, the utility of Ra as a deep ocean circulation tracer never came to full fruition as biological cycling has been repeatedly shown to have a strong and unpredictable effect on the vertical distribution of this isotope. 

The interactions of air pollutants with forests at low-dose concentrations result in imperceptible effects on the natural biological cycles of these species. In some instances, these interactions may be beneficial to the forest ecosystem. Forests, as well as other natural systems, act as sinks for the removal of trace gases from the atmosphere. 

The secondary biological cycles stem from the crucial roles that phosphates and particularly organophosphates play in all life processes. Thus organophosphates are incorporated into the backbone structures of DNA and RNA which regulate the reproductive processes of cells, and they... 

Between the emission of greenhouse gases and change in the climate are a range of climate and biological cycles that can influence the end result. Such outcome-modifier effects are called feedbacks or indirect effects in the climate change literature. 

Hitchcock, D. R. Wechsler, A E. Biological Cycling of Atmospherk Trace Gases Final Report NASA Contract NASA-CR-126663 1972 pp 117-154. 

The Earth s history, and its future, are shaped not by independent events but by an intricately linked series of feedbacks and responses spanning the spectrum of physical, chemical, and biological cycles, of which the hydrologic cycle is only a part, albeit a central one. 

Almost all elements in the periodic table are involved in at least one way or another in the biological cycle of the ocean. Many elements are essential or required nutrients. Others are carried along as passive participants. In either case the rates of biological processes need to be known. 

The superposition of the vertical biological cycle on the horizontal ocean circulation pattern leads to three general features in the distribution of the elements involved in this cycle. 

There are two important consequences of this superposition of biological cycling on the ocean circulation pattern that show up in the sediments. 

The global nitrogen cycle is often referred to as the nitrogen cycles, since we can view the overall process as the result of the interactions of various biological and abiotic processes. Each of these processes, to a first approximation, can be considered as a self-contained cycle. We have already considered the biological cycle from this perspective (Fig. 12-1), and now we will look at the other processes, the ammonia cycle, the cycle, and the fixation/denitrification cycle. 

The biological cycle of arsenic in the surface ocean involves the uptake of arsenate by plankton, the conversion of arsenate to a number of as yet unidentified organic compounds, and the release of arsenite and methylated species into the seawater. Biological demethylation of the methyl-arsenicals and the oxidation of arsenite by as yet... 

Wood, J. (1974). Biological cycles for toxic metals in the environment. Science 183,1049-1052. 

The precise role of melatonin in sleep and waking is uncertain but it seems to act as a go-between for the light and biological cycles and evidence suggests that it has a reciprocal relationship with the SCN (Fig. 22.3). Its actions are mediated by (MLi) receptors which are found predominantly in the SCN as well as thalamic nuclei and the anterior pituitary. These are G protein-coupled receptors, with seven transmembrane domains, that inhibit adenylyl cyclase. Their activation by melatonin, or an MLi agonist such as 2-iodomelatonin, restores the impaired circadian cycle in aged rats. 

The biological cycle — that may encompass processes of biological transformation, plant uptake, bioaccumulation, soil organisms transformations and others. 

From the pollutant and biological cycles the processes of advection, diffusion, volatilization (diffusion at the soil-air interface), adsorption or desorption (equilibrium), and degradation or decay, which are also the most important chemical processes in the soil zone. All other processes can be lumped together under the source or sink term of equation (3). 

In this cycle the reaction of H2 + C02 to give reduced carbon-based fuels such as sugar or oil with oxidation back to H20 and C02 could be useful. It is then precisely the same as the biological cycle. Note that at present mankind and organisms utilise... 

To what extent, and at what rate, do they become involved in the biological cycle, either... 

However, only the smallest part of soluble metals is involved in the biological cycle. Most of these are either lost to water runoff, or retained in the peat organic matter. The latter is the source of gradual remobilization but the whole mineralization may last up to 50 years or even more. The total accumulated retained amount of macro-or trace metals in organic matter of peat is tens and hundreds of time higher than the concentration of annually released soluble forms, which are available for plants. 

Table 2. Averaged fluxes and pools of biological cycling in Forest ecosystems (after Rodin and Bazilevich, 1965 Dobrovolsky, 1994).

Table 3. Averaged fluxes of trace elements in biological cycling of Boreal and Sub-Boreal Forest ecosystems (after Dobrovolsky, 1994).

The main soils of Forest Ecosystems are Podzols and Podzoluvisols. There are plenty of various soil subtypes, groups and families among these two main soil types. However, all forest soils have a number of common features originating in the similarity of processes occurring therein. The retarded biological cycle provides the organic materials for the build up of the covering layer on the soil surface. This layer consists... 

Rodin, L. E., Bazilevich, N. I. (1965). The dynamics of Organic Matter and Biological Cycling of Ash Elements and Nitrogen in Major Vegetation Type of the Earth. Moscow-Leningrad Nauka Publishing House, 321 pp. 

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