Eutrophication

The literal meaning of the word eutrophication is "well-nourished."

When eutrophication is used in the context of an ecosystem—for example, in Greenwich Bay—it means that there is an increase in the amount of organic matter (or molecules that come from living things) entering the system.

What this usually means, in simplified terms, is that plants, such as phytoplankton, in the bay are photosynthesizing, growing, and reproducing at a greater rate than they were before. It may also mean that the same thing is happening in a tributary, such as a river, and the increased organic matter is flowing into the bay.

In most cases, this happens because nutrients, such as nitrogen, are being added to the water from sources such as septic systems, fertilizers, and the atmosphere (nitrogen in the atmosphere comes from high-temperature burning of fossil fuels). These nutrients have the same effect as plant food that contains nitrogen and phosphorus: They cause plants to grow.

Often, an increase in nutrients flowing into an ecosystem results in eutrophication.

What does this mean for the health of an ecosystem such as Greenwich Bay? Eutrophication is not necessarily a good or a bad thing. However, an increase in plant life can result in some problems.

When plants die, they are decomposed by bacteria. The greater the number of dead plants, the more bacteria there will be. The problem is that these bacteria, like people, need oxygen. The more bacteria there are, the more oxygen they will use. The more oxygen the bacteria use, the less oxygen will be available for other aquatic life, such as fish. Sometimes this can lead to low levels of oxygen in the water and even to fish kills, in which large numbers of fish die off at once.

For this reason, it is important for scientists to understand where nutrients are entering Greenwich Bay, where they come from, and whether they are affecting oxygen levels in the bay's waters.

Ground Water

Ground water can be a source of pollution to Greenwich Bay because anything that is put on or in the ground can end up in the water that flows underground. When septic systems that treat sewage leak, bacteria and nutrients often flow into ground water. Nutrients from fertilizer can leach through soil into ground water. In many places, ground water eventually flows into the bay.