Phosphorous (P) is the key limiting nutrient in freshwater, a part of plant and animal remains, by-products and life. When phosphorus is the limiting nutrient, there is a direct relationship between the algae growing in the lake and the amount of phosphorus in a lake. As phosphorus levels increase, the amount of algae increases too. Phosphorous levels in the lake can be natural and man-made. Excess phosphorous causes Eutrophication, combined with low flows; pressure & Abstraction, reducing base flows and climate change, this massively increases algal growth.
There are different types of P Sources:
- Diffuse – Land agriculture flow dependant sources washes from the soil.
- Point – Waste water effluent flow independent.
How can these P Sources be controlled? Point Source Mitigation has had a great success in reducing P Concentration. With Agricultural Mitigation succeeding in reducing P in edge-of-field run off. Despite this success in lowering P levels, P mitigation over decades has not yet delivered expected long lasting ecological improvements. This is because there are also P legacy stores to take into account; this is stored in flood plains, soil/hill slope, riparian buffer and wetlands. Lag time can occur before Legacy P is delivered. In a free flowing river it may not have so much legacy P lag time but in a typical lake there can be 5 – 30 years of legacy P lag time, meaning a continued release of P from legacy stores may mean a long wait for downstream water quality improvements. Therefore lake recovery phases and processes take longer to internally recycle.
On the other hand, lakes are unique, and phosphorous can support diversity in a lake environment. It is said lowered phosphorous levels improves water quality, but for who? It is good for drinking water and industrial use for humans, what about the lake’s inhabitants? When Phosphorous levels are lowered too much it can cause top down controls. Changing flow velocity, temperature and shading leading to change in the natural habitat.
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I can see the dilemma here, too much phosphorous can cause damage but not enough can lower the quality. I was interested in the last part of your blog when you refer to who the quality is increased for. I found that there are different types of phosphorous that affect our lakes in different ways. It has been found that orthophosphate causes blooms in cynobacteria which decreases the transparency of the water. I have found a document by the environmental services, which gives information on how we can manage the phosphorous levels in our water systems, I have attached a link below.
Click to access bb-20.pdf
Having next to no knowledge on how the phosphorous (P) levels can have such a massive effect on the ecosystem found within bodies of water, I found this blog very interesting. It would seem that aquatic plant life is dependent on the P levels in water although the author also describes P as something that can help avert climate change with the process of Eutrophication. As well as describing the combining effects that causes algal growth.
The man-made effects on P in agriculture completely escaped me but I found the lake section very interesting. The question of who would benefit from lowering P levels was raised, as would it be an ecological benefit or industrial? As although altering the P levels may be beneficial towards humans there is little describing on what effects this might have on the environment.