EUTROPHICATION IN WATER

Eutrophication is a condition in an aquatic ecosystem where high nutrient concentrations stimulate blooms of algae (e.g., phytoplankton).

Why Should We Be Concerned? Although eutrophication is a natural process in the aging of lakes and some estuaries, human activities can greatly accelerate eutrophication by increasing the rate at which nutrients and organic substances enter aquatic ecosystems from their surrounding watersheds. Agricultural runoff, urban runoff, leaking septic systems, sewage discharges, eroded streambanks, and similar sources can increase the flow of nutrients and organic substances into aquatic systems.

These substances can overstimulate the growth of algae, creating conditions that interfere with the recreational use of lakes and estuaries, and the health and diversity of indigenous fish, plant, and animal populations. Algal blooms hurt the system in two ways.

• First, they cloud the water and block sunlight, causing underwater grasses to die. Because these grasses provide food and shelter for aquatic creatures (such as the blue crab and summer flounder), spawning and nursery habitat is destroyed and waterfowl have less to eat when grasses die off.
• Second, when the algae die and decompose, oxygen is used up. Dissolved oxygen in the water is essential to most organisms living in the water, such as fish and crabs. Increased eutrophication from nutrient enrichment due to human activities is one of the leading problems facing some estuaries in the mid-Atlantic.

Federal and state agencies have joined together to monitor the natural resources and report upon their condition. The data are being summarized into reports that tell the percent of ecological resources in good, fair, or poor condition for a wide variety of stressors.

What are the trophic states and effects?

• Oligotrophic: Clear waters with little organic matter or sediment and minimum biological activity.


• Mesotrophic: Waters with more nutrients, and therefore, more biological productivity.


• Eutrophic: Waters extremely rich in nutrients, with high biological productivity. Some species may be choked out.


• Hypereutrophic: Murky, highly productive waters, closest to the wetland status. Many clearwater species cannot survive.


• Dystrophi: Low in nutrients, highly colored with dissolved humic organic material. (Not necessarily a part of the natural trophic progression.)