Lecture 8 Background

Ricklefs Ch. 2, pp22-29

Water has many properties favorable to life
- Exists in liquid state over most temperatures found on Earth
- Immense capacity to dissolve inorganic compounds

Water resists changes in temperature, therefore it remains liquid over a wide range of temperatures.
- It takes 500 times more energy to evaporate a quantity of water than to raise its temperature 1 C.
- Freezing requires the removal of 80 times more heat than is needed to lower a quantity of water by -1 C.

Water gets less dense as it cools below 4 C. Therefore, ice floats. This property of water prevents the bottoms of lakes and oceans from freezing, enabling aquatic plants and animals to seek refuge there in winter.

Water is viscous, meaning that it resists flow or the movement of a body through it.

Living organisms overcome the limitations of water by exploiting physical principals.
- For example, many fish species has a gas-filled swim bladder whose size can be adjusted to make the density of the fishes body equal that of the surrounding water.
- Some kelp have gas-filled bulbs that float their leaves to the sunlit surface waters.
- Fast-moving aquatic animals have evolved streamlined shapes to reduce drag from water

The solvent capacity of water
- Water has an impressive capacity to dissolve various substances, making them accessible to living systems and providing a medium within which they can react to form new compounds.
- The ocean functions like a large still, concentrating ions as mineral-laden water arrives via streams and rivers and as pure water evaporates from its surface.
- Some elements, such as calcium, have already reached the limits of solubility concentrations in the ocean. Others, such as sodium compounds, have not reached this limit and have been increasing over geologic time.

Hydrogen ions in ecological systems
- Among dissolved substances, Hydrogen is special because it is extremely reactive.
- The concentration of H in a solution is referred to as its acidity (pH).
- Highly reactive hydrogen ions enhance the natural solvent properties of water.

Ricklefs Ch. 24, pp 505-508

Weathering makes nutrients available in terrestrial ecosystems

Chemical elements can take on different forms as they cycle through ecosystems, but only some of those form are useful to organisms. (i.e. Nitrogen can exist in the form of nitrogen oxides, ammonium, or N2. However, plant life can only access the first two forms)

In terrestrial ecosystems, most nutrient elements cycle rapidly through three compartments: the soil, plant biomass, and detritus.

The major source of nutrients for terrestrial ecosystems is the formation of soil through the weathering of bedrock and other parent material. Typically, the weathering of bedrock provides only 10% of the soil nutrients taken up by vegetation each year (in other words, most nutrients in ecosystems are regenerated within those ecosystems).

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