What do Zebra Mussels have to do with Phosphorus?
In the soil it becomes a nutrient essential for the growth of plants. Ontario soils contain a lot of phosphorus, as much as 2,000 lbs per acre. Most of this phosphorus is fixed in soil particles and is unavailable for plant growth. Wind and water erosion have the ability to move particulate phosphorus into water courses.
In the water phosphorus is considered a limiting nutrient. The addition of phosphorus will cause increased growth of water plants and algae. This increased growth removes dissolved oxygen from the water making it unavailable to fish.
Phosphorus levels in the Great Lakes have decreased significantly over time, from highs around 12 ug/l in the early 80's to todays level of between 4 and 6 ug/L. This decrease can be partially attributed to increased soil erosion management on farms, improved sewage treatment and reduced phosphates in detergents. So why is phosphorus loading still and issue in the Great Lakes?
In two words, Zebra Mussels.
Mussels are filter feeders meaning they take in particulates and strip them of their nutrients. The mussels have been taking bound phosphorus and releasing it as soluble phosphorus in the near shore areas of the lake. This excess of soluble phosphorus has lead to an excess of aquatic plant growth in the near shore areas. The plants interfere with boating, get caught in anglers lines, and detract from the recreational swimming experience. Some municipalities have incurred great expense to remove this excessive plant growth.
Some of these nuisances have refocused the attention back to phosphorus loading into streams, tributaries and eventually the lakes. There are several contributors of phosphorus into the lakes, only one of which is agriculture. The others include construction, sewage treatment plant discharge and overflows, storm water run-off form urban areas and septic systems.
These multiple source however will not take away continued pressure on farmers to reduce wind and soil erosion. Fortunately there is a large suite of management practices available to producers. These include soil testing, vegetated buffer strips, windbreaks, grassed waterways, sediment control basins, stream bank stabilization and cover crops. With a history of successfully implementing these practices, farmers are well positioned in a society that is once again focusing on phosphorus management.
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