WHAT DO WE MEAN BY AN "UNHEALTHY AQUATIC ECOSYSTEM?"

Healthy aquatic ecosystems are those where human disturbances have not impaired the natural functioning (e.g., nutrient cycling), nor appreciably altered the structure (e.g., species composition) of the system. How do you know your creek is healthy? Here are some things to look for: cool, clear water with no smells, foam, or excessive algae; stable, gentle banks with deep-rooted plants to hold the soil; shade provided by healthy trees and shrubs, preferably native, to keep the water cool and to protect against erosion; no litter, yard waste, or dumped material. Natural debris, such as logs, is okay; healthy populations of insect larvae in the creek; birds, insects, and other wildlife around it; natural meanders and a varied bottom of pools, riffles, clean gravel, and cobbles rather than fine sediment.

On the opposite end of the spectrum, an unhealthy aquatic ecosystem is one where the natural state is out of balance. These disturbances can be physical (e.g., injection of abnormally hot water into a stream), chemical (e.g., introduction of toxic wastes at concentrations harmful to the organisms), or biological (e.g., introduction and propagation of non-native animal or plant species).

Symptoms of poor ecosystem health include the following:

1. The loss of species.
2. The accelerated proliferation of organisms. One example is algae blooms caused by an excess of phosphorous and nitrogen compounds in the water. This condition is called "eutrophication".
3. Increased incidences of tumors or deformities in animals.
4. A change in chemical properties. Perhaps one of the most significant has been a reduction of pH in water caused by acid rain.
5. The presence of certain organisms that indicate unsanitary conditions. Coliform bacteria, for example, are a sign that the system may contain organisms that cause a variety of human diseases such as diarrhea, typhoid, and cholera.
6. The loss of traditional aboriginal culture associated with the ecosystem. Many symptoms of poor ecosystem health occur simultaneously. For instance, increased lake acidity may kill certain species, thereby allowing the temporary proliferation of species more tolerant of acidity.

Water is elemental: it plays a major role in sustaining human life. Worldwide, freshwater supports about 40 percent of food-crop production via irrigation, supplies 12 percent of the fish people eat and accounts for some 20 percent of electrical power generation. Increasingly, however, it is becoming clear that without more attention to the sustainable management of this finite resource, emerging unhealthy aquatic ecosystem problems will only worsen -- with serious consequences for agriculture and food security, especially in the developing world.