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How Do Increased Phosphorus Levels Affect Aquatic Ecosystems?
If you've ever seen a pond, lake or river choked with green "seaweed" or covered in bright green algae, you've seen the results of phosphorus pollution. Even a small increase in phosphorus level can cause a dramatic increase in plant and algae growth.
Phosphorus is the limiting nutrient in shortest supply in freshwater ecosystems. Once the available phosphorus is used up, plants stop growing no matter how much nitrogen is available. If more phosphorus becomes available, the plants are again able to use more nitrogen and resume growing.
The fertilizing effect of phosphorus causes harm through a chain reaction of undesirable events. The added phosphorus encourages increased plant and algae growth followed by increased populations of bacteria. The bacterial decomposition of dead plant material lowers dissolved oxygen levels and can eventually result in the death of fish and invertebrates.
Problems caused by Increased Phosphorus Levels
- The increased growth and decay of floating algae causes water to smell and discolour. This interferes with recreational activities like swimming, fishing and boating.
- The increased growth of rooted aquatic plants can slow river currents, block river channels and interfere with boating, water skiing and swimming.
- Increased plant and algae growth can reduce dissolved oxygen levels every 24 hours. Plants stop photosynthesis in the dark and oxygen is not produced. Instead, plant respiration uses oxygen at night and lowers dissolved oxygen levels. Extreme changes in dissolved oxygen can kill fish before the sun rises.
- Dead plants and algae settle to the bottom. Decomposition leads to increased bacteria populations that remove oxygen from the water. Lowered oxygen levels may kill fish on hot days in late summer or under the ice during winter.
- Algae growing on the water surface may shade submerged plants and interfere with their photosynthesis.
- Algae can clog the filters in drinking water treatment plants and increase maintenance costs.
- Algae can be the cause of bad tasting drinking water.
- Phosphate levels greater than 1.0 mg/L interferes with the removal of organic material during the process of drinking water treatment. The result can be that bacteria on the organic particles may not be removed. Human health may be put at risk.
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Preventing Increased Phosphorus Levels
There are steps that will prevent storm water and snowmelt from transporting and increasing the phosphorus in a river:
- Storm water from streets should first enter a holding pond to settle before being sent on to a river.
- A buffer zone of trees along a river will prevent soil erosion and trap sediments with attached phosphorus.
- Feedlots should be operated on soils that will not leech or drain into rivers. Phosphorus-containing livestock waste can contaminate groundwater and surface run-off.
- Wastewater treatment plants can be upgraded to use bacteria in the biological nutrient removal of phosphorus.
- Consumers should purchase low phosphorus detergents for washing clothes and dishes.
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