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Hypertrophic or hypereutrophic lakes are very nutrient-rich lakes characterized by frequent and severe nuisance algal blooms and low transparency. Hypereutrophic lakes have a visibility depth of less than 3 feet (90 cm), they have greater than 40 micrograms/litre total chlorophyll and greater than 100 micrograms/litre phosphorus.
Phosphorus mainly enters a pond or lake through runoff from the watershed or by atmospheric deposition. Upon entering the system, a reactive form of phosphorus is usually taken up by algae and macrophytes, which release a non-reactive phosphorus compound as a byproduct of photosynthesis.
Increased plant growth within lakes changes the character of the substrate, which is sometimes a factor in biodiversity. Lakes with benthic feeding fish such as carp tend to have lower success at removing phosphorus. These species forage in lake sediments which disturbs the aluminum hydroxide flocs binding phosphorus to the lake bottom. [4]
Phosphorus is the limiting factor for plant growth in most freshwater ecosystems, [15] and because phosphate adheres tightly to soil particles and sinks in areas such as wetlands and lakes, [16] due to its prevalence nowadays more and more phosphorus is accumulating inside freshwater bodies.
As an example, the world’s fertilizer industry now recognizes the importance of phosphorus in lakes and reservoirs, 40 years after its importance was demonstrated at ELA. Regulatory actions have been supported by ELA research, and now there is action by the industry as a result of research and activities at ELA over several decades.
The Red River accounts for roughly 7,716 tonnes of phosphorus draining into Lake Winnipeg per year. [5] Approximately 2,500 tonnes of phosphorus flow out of the lake every year through the Nelson River. [7] It is estimated that incoming phosphorus levels are doubled by agriculture and waste waters from the northern United States.
Lake 226 was specifically studied over a four-year period, from 1973–1977 to test eutrophication. [5] Lake 226 itself is a 16.2 ha double basin lake located on highly metamorphosed granite known as Precambrian granite. [6] The depth of the lake was measured in 1994 to be 14.7 m for the northeast basin and 11.6 m for the southeast basin. [7]
Lake Ivanhoe receives this designation due to its in-lake phosphorus concentration which exceeds the water quality standards for oligotrophic lakes. The Lake Ivanhoe watershed is 455 acres (184 ha) and is 64% forested. The watershed is currently 17%, developed with 59% of the watershed being buildable area.