Sewage in
Freshwater Ecosystems
Effects of sewage in freshwater ecosystems
Dumping sewage into water bodies, such as rivers or lakes, creates a human health hazard but can also negatively disrupt the river and lake ecosystems.
The sewage contaminates the water, spreads disease, and leads to environmental degradation.
Here is a list of effects of untreated sewage disposal into freshwater ecosystems:
1. Increased organic matter (from the sewage) breaking down in the river reduces the amount of dissolved oxygen in the water body as the decomposition process uses up the available dissolved oxygen. Fish and other aquatic life need that dissolved oxygen in the water to live.
2. Sewage heightens the levels of nutrients, increasing the bioavailability of nutrients, which can increase productivity of plankton near the sewage outfall and increase the chance of algal blooms.
3. Contaminants present in the sewage might be toxic for some already existing phytoplankton.
4. Sewage can increase the turbidity and amount of suspended sediments. This effect reduces light available for plant growth, can smother in-stream habitats, and damage fish gills and respiratory structures of other species.
5. Sewage (and stormwater runoff) can introduce pesticides, other chemicals, and heavy metals into the water column. It may also introduce fine sediments, which have the potential to (bio)accumulate within animal tissues and have long-term toxic effects. Sewage and run off may increase acidity, such as from acid sulphate soils which kill fish and crustaceans, cause fish red-spot disease, damage or cause death of oysters, and interact with sediments to release heavy metals.
6. Industrial effluents (often a complex mixture of chemicals) can negatively affect fish by impairing growth and reproduction and by reducing immune competence. These effects have the potential to impact fish populations.
7. Microbial pathogens introduced by sewage into surface or groundwater can threaten public health, as well as affect ecosystem health and function.
8. Sewage can release water that is either warmer or cooler than the receiving water body. Because aquatic life has optimal temperature ranges within which it lives, too warm or too cool water temperatures can harm the aquatic life. For example, cold waters reduce ecosystem productivity, eliminate temperature-sensitive biota, and decrease survival of eggs, larvae of fish and aquatic insects.
9. Release of sewage can degrade vegetation and soil by depositing harmful chemicals in bottom sediment, for example.
10.With sewage comes water that has some degree of chlorine or similar agent. The chlorine or other disinfectant react with organic matter (such as what's in sewage) to create different end-products, such as chloroform or haloketons, which can be harmful in either the short or long term. These reactions happen faster in warmer water.
Release of untreated sewage into freshwater bodies is sometimes necessary. Yet, it not only creates a human health risk but damages the health of the receiving water bodies in over short or long time periods.
Our responsibility to ecosystems means we should have the capacity to deal with our own waste rather than expecting the rest of the ecosystem to do it for us.
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