As a child, one of my favorite things to do was go to the local nature preserve and look for turtles and fish in the ponds. However, it’s scary to think that the kids of the next generation might not get that opportunity because of eutrophication.
Eutrophication is the destruction of a pond ecosystem when algae growth skyrockets after a limiting factor for growth becomes readily available. All of this algae builds up on the surface of the water, practically turning the pond green. Clearly, eutrophied ponds are not a pretty sight to look at, but the ecological effects are far worse than just an eyesore.
When algae cover the surface of the pond, they block sunlight from reaching aquatic plants that need light for photosynthesis. Instead, the algae is doing photosynthesis and taking carbon dioxide from the water to do, causing the pond to get more basic. Most animals and plants have a very specific pH range that they can live in, so any changes in the pH of the water could be detrimental to aquatic life. Photosynthesis does produce oxygen, so you might think that the algal blooms would increase dissolved oxygen levels in the ponds. However, this is not the case because when the algae die, they sink to the bottom of the pond where they are decomposed by bacteria. These bacteria need oxygen, and consume enough of it to create anoxic environments. Areas like these are often referred to as “dead zones” because of the severely low oxygen levels that cannot support life. For example, the Gulf of Mexico has a dead zone that appears every year and has grown to be the size of Massachusetts. Anoxic environments also foster the growth of bacteria who can live in anaerobic condition that can produce toxic byproducts further threatening marine life in that area.
Eutrophication clearly destroys pond life, but it can also affect animals and humans living outside of the pond. Excessive algae growth not only looks displeasing, but also provides a barrier to recreation and fishing activities. Coastal economies and fisherman are increasingly threatened, such as in the Gulf of Mexico were 72% of U.S. harvested shrimp and 66% of oysters are caught. Algal blooms severely reduce water quality, and can change the taste of not just the water but also any fish raised in that water, so even if fishing practices can continue in the face of eutrophication, the fishermen can still struggle economically.
Beyond economic effects, there are health concerns as well. Some algae, like the red tide in Florida can cause respiratory irritation from just being near the eutrophied water. In the most severe cases, some types of algae produce toxins that can make anyone who drinks the water severely sick or even kill them. This happened as recently as 2014 when Toledo, Ohio had to shut down its public water supply because of an algal bloom in Lake Erie that was producing microcystin, a toxin that can damage the liver.
Obviously, this is a big issue that is not going away. Not surprisingly, humans are to blame. Fertilizers contain lots of nitrogen and phosphorus, since plants need it grow, but so do algae. Eventually, the nutrient rich fertilizer finds its way into a freshwater source and begins the process of eutrophication. Septic systems and animal waste (like manure) can also heavily contribute to algal blooms because of the nutrient dense organic material. Aquaculture, or freshwater farming of fish and shellfish, can also speed up eutrophication if not managed correctly. Both the food particles and fish excretion have large amounts of nutrients that contribute to algae growth.
There are natural causes to eutrophication as well. As lakes and ponds get older, they will naturally build up more sediment and nutrients, and events like storms or floods can bring outside nutrients into the system. However, this type of eutrophication happens very slowly over many years, so human activities are by far the leading contribution to the accelerated eutrophication seen all over the world.
Because humans are at fault for this issue, we are also able to mitigate the problem. The immediate step that needs to be taken is limiting the amount of nitrogen and phosphorus entering freshwater systems. Farmers should be encouraged by the government to use fewer fertilizers or time fertilizer application so that rain or storms will not wash runoff into a pond or lake. Animal waste products need to be managed better to keep them out of the water, and maintaining functional septic systems will eliminate a lot of excess nutrient inflow. As with many environmental problems, simply regulating pollution (especially by plants manufacturing and working with organic material in this case) will make all the difference in reversing the damage done.
There are also a few more complicated measures to try to reverse eutrophication. Wetlands are notoriously good at filtering water and removing pollutants and excess nutrients, but they are currently disappearing at an alarming rate. Restoration and conservation of coastal wetlands will be increasingly important in the upcoming years in limiting further eutrophication. Scientists are also looking into ways to target the algae themselves, and hope that ultrasonic radiation could be a tool to kill algae cells and reduce the algal blooms.
Eutrophication provides yet another example of the impact human activities have on the water system, but with hard work, it can be reversed and we can go back to clean and clear ponds.
Source: