Based on observation, dissolved oxygen exhibits an inverse proportionality with conductivity, primarily because both parameters are influenced by the presence of polluting substances in water.
While dissolved oxygen (DO) itself does not directly contribute significantly to the electrical conductivity of water in the way dissolved salts or ionic pollutants do, its level is often inversely correlated with conductivity in natural or treated water systems. The provided reference explains this relationship:
The inverse proportionality between conductivity and the dissolved oxygen (Fig. 3), can be explained by the increase of dissolved oxygen that takes place when polluting substances that cause turbidity are eliminated from water.
This suggests that rather than a direct effect of oxygen on conductivity, the observed relationship arises because both are indicators related to water quality and the presence of contaminants.
Understanding the Relationship
The inverse relationship described means:
- When dissolved oxygen levels are high, conductivity tends to be low.
- When dissolved oxygen levels are low, conductivity tends to be high.
Why does this pattern occur? The reference points to the role of polluting substances:
- Polluted Water: Contains dissolved or suspended contaminants, often ionic (like salts, acids, bases from industrial or agricultural runoff) or organic substances that decompose. These contaminants increase conductivity. At the same time, the decomposition of organic pollutants consumes dissolved oxygen, leading to lower DO levels.
- Clean Water: Has fewer dissolved ions and pollutants, resulting in lower conductivity. It also typically has higher dissolved oxygen levels, as oxygen is not being consumed by decomposition processes and water can hold more oxygen when pollutants affecting solubility are absent.
Therefore, as polluting substances are eliminated (e.g., through treatment or natural processes), dissolved oxygen increases (because there is less consumption), and conductivity decreases (because there are fewer ions/contaminants). This simultaneous change in opposite directions creates the observed inverse proportionality.
Practical Implications
This inverse relationship can be a useful indicator in water quality monitoring:
- Monitoring Water Quality: Observing both DO and conductivity can provide a more comprehensive picture. For instance, high conductivity paired with low DO strongly suggests pollution.
- Evaluating Treatment Effectiveness: A successful water treatment process aimed at removing pollutants would ideally show increasing DO and decreasing conductivity in the treated water.
In summary, while dissolved oxygen is crucial for aquatic life and water health, its observed effect on conductivity, as highlighted by the reference, is an indirect one, mediated by the presence and elimination of polluting substances.
