The influence of vegetation on oxygen and pH levels.

Plants influence (and are influenced by) many chemical compounds and nutrients. Two of the crucial chemical characteristics they influence are the levels oxygen and the pH (the acidity of the water).

Oxygen dissolved within the water are as important to aquatic creates as it is to us.  Like plants on land, aquatic plants photosynthesise which produces oxygen, only they emit oxygen into water as opposed to the atmosphere. However, a feature that is often overlooked is the fact that plants respire too. As a result, photosynthesis dominates during the hours of sunlight leading to higher oxygen levels. However, during the hours of darkness, respiration (of the plants and animals) removes oxygen from the water at night. This leads to a pattern like this:

Figure 1: The effect of plants on oxygen and pH of water.  (Jackson Bottom Wetlands Reserve, 2014).

Therefore, the introduction of plants in restoration schemes requires caution, for example plants introduced in shaded regions will reduce oxygen levels, not increase it! Furthermore, a process known as 'eutrophication' is one of the most significant pollution events that occurs within rivers. It is simply excessive plant growth which has been known to reduce oxygen levels to dangerously low levels and kill animals. 

Although changes in the oxygen and pH will change with the time of year, plant species and amount of vegetation, these patterns are easy to measure at home, as demonstrated by the home experiment 3.

This home experiment involves purchasing some form of aquatic vegetation and leaving this within a container filled with water. The amount of vegetation/water used is subjective and could be worth using different levels of each to see how this affects the results. The test kits are commercially available and many fish tank owners will already possess the equipment needed.

It involves simply taking readings of the oxygen and pH over a 24 hour period. The more often you collect measurements, the more reliable your data will be. It is useful for people who keep fish as a hobby to conduct this within the tank to see if oxygen levels are to a satisfactory level 24 hours a day (above 5mg/l as a minimum). 

Bibliography

ISECA (2013) 'What is eutrophication?' http://www.iseca.eu/en/science-for-all/what-is-eutrophication

Jackson Bottom Wetlands Reserve (2014) 'Aquatic chemistry overview' http://www.jacksonbottom.org/monitoring-restoration/aquatic-chemistry-overview/