Chemical

 

Both gases and salts have to some degree the ability to be dissolved in water, both have an impact up the lifeforms and the ability to sustain life within the water body. Lets deal with each individually.

Gases

The two most important gases are Oxygen and Carbon Dioxide, both of which dissolve quite readily in water.

Oxygen

The availability of oxygen for absorption is ever present but the ability for a given volume of water to absorb oxygen by diffusion is constant. As once the water becomes saturated with oxygen it is unable to absorb more. This is not all ways the case found though as it is reliant on the oxygen demand placed upon it by its inhabitants, the larger the biomass of population the faster the oxygen is consumed and consumption can far exceed the ability for diffusion. To make things even more complicated waters ability to absorb oxygen is decreased as the temperature rises. Water can hold about 9ml oxygen per litre at 4° C but only 7ml at 15° C so this also increases the fluctuation of oxygen levels present within the water body. So far we have only looked at the effect caused by atmospheric diffusion alone, these levels are also impacted by processes such as photosynthesis of plants which during the day can increase the oxygen levels to ones of supersaturation.

Carbon Dioxide

Although some carbon dioxide is absorbed by water the larger volumes created in solution are caused by the respiration of the ponds inhabitants, and the process of decay by bacteria, these quickly use up the available oxygen and replace it with carbon dioxide making the water unsuitable for the majority of inhabitants. When carbon dioxide is dissolved in water it forms a weak solution of carbonic acid, this has the ability to dissolve mineral salts.

Salts

When the carbonic acid produced by the solution of carbon dioxide comes in contact with calcium or magnesium it produces carbonate and bicarbonate salts, in areas which posses large quantities of calcium this can consume a large amount of the carbon dioxide from the water in the production of calcium carbonate. This produces an alkaline water with a high pH. This increase in dissolved salts encourages the production of molluscs and crustacia for use in production of there shell or exoskeletons and therefore make these water far more productive than a more acid water with less dissolved salts. Acidic waters such as those found which derive there source water from peat areas are low in salts content having a low pH. These waters are far less productive being unable to sustain the requirements of the lower food chain, therefore decay is slow and nutrients unavailable for plant growth which in turn effects animal numbers. The salts within a body of water are very much controlled by the available bedrock surrounding the water, we have looked at calcium but others may produce different volumes of dissolved salts such as nitrates and sulphates, all impacting the available resources for the possible species to be found within the water.