Eutrophication, the over-enrichment of water bodies with nutrients, often leads to excessive plant and algal growth. Water pH, a measure of acidity or basicity, significantly impacts aquatic ecosystem health. While neutral pH is 7, natural waters range from 6.5 to 8.5. Eutrophication frequently increases water pH, especially during intense algal activity, which can affect the aquatic environment.
What is Eutrophication
Eutrophication is a process where water bodies become overly enriched with nutrients, primarily nitrogen and phosphorus. This nutrient overload stimulates excessive growth of aquatic plants and algae, often resulting in dense algal blooms. These nutrients commonly originate from human activities, such as agricultural runoff containing fertilizers and the discharge of wastewater.
The influx of these nutrients disrupts the natural balance of the aquatic ecosystem. The resulting overgrowth of algae and other simple plant life can cover the water surface, blocking sunlight from reaching submerged vegetation.
How Eutrophication Influences Water pH
Eutrophication directly influences water pH through the biological activity of the proliferating algae and aquatic plants. During daylight hours, these organisms actively perform photosynthesis. Photosynthesis is a process that consumes dissolved carbon dioxide (CO2) from the water.
Carbon dioxide dissolved in water forms carbonic acid (H2CO3), a weak acid that contributes to the water’s acidity. As algae and plants remove CO2 for photosynthesis, the concentration of carbonic acid in the water decreases. This reduction in carbonic acid leads to a decrease in hydrogen ions, consequently increasing the water’s pH and making it more alkaline. This effect is most pronounced during the day when photosynthetic activity is at its peak.
Ecological Impacts of pH Shift
The elevated pH levels resulting from eutrophication can have consequences for aquatic ecosystems. High pH can damage the outer surfaces, such as gills and skin, of aquatic organisms like fish and other invertebrates. This damage can impair their physiological processes, affecting their ability to regulate ion exchange, oxygen uptake, and overall health. Prolonged exposure to high pH can lead to decreased reproduction, reduced growth, and increased susceptibility to disease.
The shift in pH also alters the availability and toxicity of other substances in the water. For instance, as pH increases, the more toxic unionized form of ammonia (NH3) becomes more prevalent, posing a greater threat to aquatic life. This increased ammonia toxicity can be particularly harmful to fish, potentially causing convulsions and mortality.