Part Two: Eutrophication
Eutrophication is the second cause of cloudy water in ponds like the Coves. Essentially, eutrophication is the overgrowth of algae (and sometimes aquatic plants) as a result of excess inputs of nutrients like nitrogen (N) or phosphorus (P). Lakes that have undergone a significant amount of eutrophication are said to be eutrophic. Eutrophication can either be natural or cultural (i.e. human-caused).
Many of you may remember when P-containing phosphates were banned from detergents by the International Joint Commission in the 70s. This ban was to protect our Great Lakes from cultural eutrophication. Since the banning of phosphates in detergents, the main driver of eutrophication is the runoff of N- and P-containing fertilizers from farms. The same chemicals used to increase yields of crops also allow algae to grow and reproduce more rapidly, leading to a larger algae population. In some cases, the algae population grows so rapidly that a bloom or mat forms on top of the water. This bloom of algae disrupts normal ecosystem functioning and causes many problems within the lake.
The most common symptoms of eutrophication are decreasing concentrations of dissolved oxygen (DO), leading to aquatic death; and increases in turbidity. As you may remember from Part One of this series, increases in turbidity can lead to a number of additional problems, including fish kills. In severe cases, the algae blooms can produce a toxic compound that is harmful to humans and wildlife. This is why Great Lakes beaches are sometimes closed in the summertime.
It is important to remember that many lakes, particularly in temperate zones like London, and in heavily industrialized areas like Western Europe, have always been eutrophic – even before human settlement. Eutrophic lakes can also undergo eutrophication. In fact, they can become extremely eutrophic, or “hyper-eutrophic.” Because so many lakes in our climate zone have always been eutrophic, it is likely that water in the Coves was never clear. We should continue to be concerned about excess nutrients entering the Coves, however, because even lakes that have always been eutrophic can experience the detrimental symptoms listed above.