- Nitrates from fertilizers in surface runoff (agriculture)
- Insecticides and herbicides (agriculture)
- Bacteria from sewage (population)
- Heavy metals (mining)
- Plant debris (logging)
- Silt (land clearing, logging)
- Chemical waste (industry)
- Acids (industry)
The effects of pollutants on an aquatic ecosystem depend on the nature of the pollutant.
- Insecticides, herbicides, chemical waste, and heavy metals can work their way into the food chain. Through the process of biomagnification, they are concentrated in higher and higher levels in the food chain until they reach dangerous concentrations. For example:
- 1. Each plankton absorbs one unit of mercury (1 unit mercury)
- 2. Each small fish eats twenty plankton (20 units mercury)
- 3. Each medium fish eats ten small fish (200 units mercury)
- 4. Each large fish eats five medium fish (1000 units mercury)
- 5. Each human eats two large fish (2000 units mercury)
- 6. The high mercury concentration causes sickness or even death.
- Plant debris and silt will increase the turbidity (cloudiness) of the water. This can make it difficult for fish to see, which makes it harder for them to catch their food. It also increases the water temperature, often killing off the native population.
- Acids lower the pH of aquatic ecosystems. Aquatic organisms live in a very narrow pH range, so acids have the power to deform or kill entire populations.
- Nitrates are used in fertilizers to encourage plant growth. The excess nitrates accumulate in surface runoff and are carried to local streams and ponds. Once in the water, the nitrates make the aquatic plants and algae grow out of control. They soon run out of nitrates and die. Bacteria decompose them and, in the process, deplete the oxygen in the water. The area becomes a “dead zone” in which living things can no longer survive. This process is called eutrophication..
A Common Resource
As with air, most water is considered a common resource. Unfortunately, shared water can lead to shared pollution. Rivers flow from country to country without discrimination, gathering local pollution along the way. By the end of the journey, the river is often worse for wear. Countries situated at the end of a river are at the mercy of those upstream, be they big-time polluters or environmental saints.
The Amur River in east Russia is one such unwilling carrier of pollution. Upstream lies the Sungari River, which flows from northeastern China. The Sungari transfers tons of poisonous industrial sludge from China’s Jilin province to the Amur.
The 4 million Russians on the Amur have traditionally made their living from fishing. Now the fish are as toxic as the river, and the villages have fallen into poverty. Additionally, many local residents now suffer from diarrhea, rashes, and other health issues.Goto the top of this page.