Nutrient conserving mechanisms

It is not just small scale agriculture that is limited by the low fertility of Amazonian soils. In the past, almost all types of development that destroy the nutrient conserving mechanisms of the forest have suffered financially. Two examples are given here to illustrate. 

In summary, it is anticipated that decreasing litter production by green plants experiencing pollutant stress would result in a similar reduction in the inventory of nutrient elements held within the system, owing to the interruption of cycling pathways and mechanisms of nutrient conservation. ... 

Alcohol is an important factor in causing thiamin deficiency because it inhibits the active transport of thiamin across the gut and when abused it impairs the quality of the diet consumed. Diuretics accelerate the excretion of thiamin and appear to override the renal conservation mechanism. Their use is of potential concern in elderly people whose diet may be poor for other medical reasons and their physicians may be unaware of their need for supplemental nutrient. 

A model of the dynamics of phytoplankton populations based on the principle of conservation of mass has been presented. The growth and death kinetic formulations of the phytoplankton and zooplankton have been empirically determined by an analysis of existing experimental data. Mathematical expressions which are approximations to the biological mechanisms controlling the population are added to the mass transport terms of the conservation equation for phytoplankton, zooplankton, and nutrient mass in order to obtain the equations for the phytoplankton model. The resulting equations are compared with two years data from the tidal portion of the San Joaquin River, California. Similar comparisons have been made for the lower portion of Delta and are reported elsewhere (62). 

The dependence of resistance on the inverse of the fourth power of the pipe diameter makes resistance very sensitive to the size of the pipe. This property is important to biological organisms. For instance, a reduction in arteriolar diameter by 16% is sufficient to double resistance and thus halve blood flow. This mechanism is used in the body to direct blood from one pathway to another to bring oxygen to muscles, nutrients from the gut, or to conserve heat loss from the skin (Figure 2.9.3). On the other hand, a similar reduction in bronchiolar diameter during an asthma attack can cause extremely difficult breathing. 

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