This included wind and rain as well as land use and agricultural practices.
The bloom was “was triggered by long-term agricultural practices coupled with extreme precipitation, followed by weak lake circulation and warm temperatures,” says a report summary.
This created a “perfect storm” affecting the lake.
The blooms are created by excessive phosphorous and nitrogen as runoff from fertilizer.
When the algae die “the decomposers that feed on them use up oxygen, which can drop to levels too low for aquatic life to thrive.”
Three types of agriculture management practices are fingered: autumn fertilization, broadcast fertilization, and reduced tillage.
“These practices have increased in the region over the last decade,” the authors say.
Conditions in fall 2010 “were ideal” for field prep which included higher fertilizer application on land that is bare.
Come spring 2011 a series of major storms “caused large amounts” of phosphorous runoff.
In May there was almost seven inches of rainfall, more than 75 per cent above the previous 20 year average.
Weak lake circulation and warmer water “helped incubate the bloom.”
The researchers say that unless farming practices change “the lake will continue to experience extreme blooms.”
No-till farming ironically was designed as an environmentally-sound practice to prevent erosion.
However no-till, in which seeds are planted but the soil not plowed, keeps fertilizer in the upper soil and susceptible to runoff.
Lead researcher Anna Michalak told WON.com that her group said that practices like no-till – designed to reduce erosion and maintain nutrients – “can have unintended consequences.”
But she said her team is, ”in no way recommending that no-till be banned.”
Instead, she said, “we need to recognize the complexity of these systems, and work towards the development of scientifically-based management practices that are beneficial for both agriculture and lake ecology.”
Chitra Gowda, water quality specialist at the Essex Region Conservation Authority (ERCA), said the study indicates that there are “a number of factors not just no-till.”
Gowda said heavy rainstorms, for example, create the “transfer mechanism” for the chemicals to get into the lake.
“No-till is an excellent soil erosion control best management practice and we need to have more studies, longer term to show how tillage practices influence the transport of phosphorous,” she said.
Michalak said in the end both farmers and the environment can benefit.
“The point that I always try to make is that it is no more beneficial to the farmers than it is to the lake to have the fertilizer applied to the soil be flushed into the lake.”
Windsor Ontario News