1. Abiotic Factors Affecting Aquatic Systems
What does abiotic mean?

2. Abiotic: a nonliving physical and chemical attribute of a system
What are some abiotic factors in a wetland?

3. When testing water samples, scientists measure and examine many abiotic factors including:
Dissolved oxygen
temperature pH
light
Dissolved solids

4. Dissolved Oxygen
With the exception of certain bacteria, all aquatic organisms need oxygen for cellular respiration (glucose + oxygen  carbon dioxide + water + energy)
According to Henry’s Law, a gas such as oxygen, when in contact with water, will dissolve in water.

5. The amount of oxygen dissolved in water is in equilibrium with oxygen in the atmosphere
And because atmospheric pressure changes with elevation, the amount of oxygen dissolved in water is less at higher elevations.

6. Temperature is another factor:
Solubility of oxygen in water is inversely proportional to temperature
Water at a higher temperature will hold less oxygen
Temperature (⁰C)
DO (mg/L) 1
14.19 5
12.75 10
11.27 15
10.07 20
9.07 25
8.24 30
7.54 35
6.93
DO = dissolved oxygen
Table 1:
Dissolved Oxygen & Temperature

7. The amount of oxygen in water can increase above the equilibrium either: - physically: by moving water
- or chemically: by photosynthesis

8. There are two patterns in oxygen concentration in water:
Diurnal variation: When oxygen is introduced to the water because of photosynthesis during the day and then oxygen levels are reduced due to aquatic organism’s respiration.

9. 2. Seasonal Variation: On an annual basis in Canadian water bodies, most photosynthesis takes place when the day length is longer and the lakes, rivers and ponds are ice free. How then, do you think water stays oxygenated during the winter months?

10. Exceptions:
Levels of Biomass (plant matter and animal waste): aquatic ecosystems with high levels of biomass to be decomposed have greater fluctuations in dissolved oxygen.
Decomposer organisms such as bacteria and fungi consume great amounts of oxygen as they breakdown organic matter.

11. We see this especially at the end of summer, when large amounts of dead plant and algal material to be decomposed produce hypoxic (inadequate oxygen) conditions. These hypoxic conditions are a stressor to aquatic animals and can lead to summer-kill of fish.

12. Dissolved Solids Water is considered to be a universal solvent.
As runoff water moves through and over the soil, it picks up small particles that become dissolved in the water.
Example solids that water dissolves are:
- calcium
- magnesium
- chloride
- sodium
Water also dissolves organic matter, giving it that brown/tea colour. Water can also dissolve metals such as iron. In SK there are salts in some soils which become dissolved in runoff water and accumulate in internal drainage lakes that have no surface outflow. Ex: Chaplin and Manitou.

13. Water also holds dissolved nutrients:
Nitrogen (N2) from the air and nitrogen ions in the form of ammonia (NH3), nitrite (NO2), nitrate (NO3),
And Phosphate (PO4)
Some of the nitrogen in the water is organic nitrogen in living and dead organisms.
**Some of these ions play a significant role in aquatic ecosystems and their absence can be a limiting factor to a population. Nitrogen and phosphorus are both needed by all organisms.

14. An excess of nitrogen from fertilizer runoff or sewage entering an aquatic ecosystem can cause increased growth of autotrophs (aquatic plants, protists, or cyanobacteria).

15. If excess phosphate is added to aquatic ecosystems it acts as a fertilizer stimulating the growth of autotrophs and increasing primary productivity of the ecosystem.
Runoff may carry phosphates from fertilizers into water bodies.
Sewage effluent has phosphate from soaps and organic wastes.

16. Eutrophication: a process in which bodies of water receive excess nutrients that stimulate growth of algae
Limiting factors are things that prevent a population from growing any larger. For example, 10 rabbits may live in a habitat that has enough water, cover and space to support 20 rabbits, but if there is only enough food for ten rabbits, the population will not grow any larger.