Oxygen photosynthetic production

The photobiological production of H2 by oxygenic, photosynthetic organisms occurs in four major sequential steps ... 

Figure 15.6. Photosynthesis and respiration, (a) A well-balanced ecosystem may be characterized by a stationary state between photosynthetic production, P (rate of production of organic material) and heterotrophic respiration, R (rate of destruction of organic matter). Photosynthetic functions and respiratory functions may become vertically segregated in a lake or in the sea. In the surface waters the nutrients become exhausted by photosynthesis, (b) The subsequent destruction (respiration) of organism-produced particles after settling leads to enrichment of the deeper water layers with these nutrient elements and a depletion of dissolved oxygen. The relative compositional constancy of the aquatic biomass and the uptake (P) and release (R) of nutritional elements in relatively constant proportions (see equation 3) are responsible for a co-variance of carbon, nitrate, and phosphate in lakes (during stagnation period) and in the ocean an increase in the concentration of these elements is accompanied by a decrease in dissolved oxygen, (c, d) The constant proportions AC/AN/AP/AO2 typically observed in these waters are caused by the stoichiometry of the P-R processes.

In the lower part of the metalimnion, this compensation point is attained and surpassed. Respiration is still present but oxygen production decreases due to the decreasing amount of oxygenic photosynthetic microorganisms. Finally, oxygen is totally consumed and the anoxic zone starts. 

Prior to simulating stream conditions and determining responses to imposed organic loads, it is desirable to investigate the individual factors that influence oxygen balance, namely atmospheric reaeration, photosynthetic production, respiration, and benthic uptake of oxygen. The aerobic or anaerobic conditions of a stream may drastically influence transport of ions, but the effect of reaeration may be difficult to monitor in a stream. 

This flux was greater in the distant past, due to higher heat flow (Turcotte 1980). Therefore, for the pre-oxygenic-photosynthetic biosphere, it is assumed that global primary productivity scaled with the square of heat flow, and thus was estimated to have been in the range (2 to 20) x 10 mol yr (Fig. 7). 

The Kaapvaal Craton, South Africa has preserved a remarkably complete sediment package that records coastal environments seaward to deeper water facies (e.g Klein and Beukes 1989). For example, the Kaapvaal includes the earliest known example of an extensive carbonate platform that resembles modern platforms in remarkable detail (Grotzinger and Kasting 1993). The extent and diversity of associated stromatolitic carbonate reefs are fully consistent with the existence at that time of highly productive, cyanobacterial (oxygenic photosynthetic) communities (Grotzinger 1989 Des Marais 2000). 

Solar conversion efficiency and H2 production tests in wild type and tlal transformant Scale-up tests were initiated under field conditions (in the University of California Berkeley [UCB] greenhouse) where photosynthetic productivity of wild type and tlal strains is conducted under mass culture conditions. Preliminary measurements of biomass accumulation and gas production (so far oxygen) support the notion of a better performance for the tlal versus the wild type strain. 

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