redOrbit Staff & Wire Reports – Your Universe Online
Instead of being an isolated occurrence, a record-breaking 2011 algae bloom in Lake Erie could be a harbinger of things to come, researchers report in this week’s online early edition of the journal Proceedings of the National Academy of Sciences (PNAS).
The hazardous algae bloom — the largest in the recorded history of Lake Erie — was likely caused by long-term changes to farming practices in combination with weather conditions expected to become more common in the near future because of global climate change.
Those conditions include extreme precipitation, followed by weak lake circulation and warmer temperatures, according to the National Science Foundation (NSF), which funded the research through its Water, Sustainability and Climate (WSC) Program. Furthermore, scientists from the eight institutions involved in the study warn that unless those agricultural policies are changed, the lake will continue to experience extreme blooms.
“Intense spring rainstorms were a major contributing factor, and such storms are part of a long-term trend for this region that is projected to get worse in the future due to climate change,” University of Michigan aquatic ecologist Donald Scavia, one of the researchers involved in the study, said in a statement. “On top of that we have agricultural practices that provide the key nutrients that fuel large-scale blooms.”
“The factors that led to this explosion of algal blooms are all related to humans and our interaction with the environment,” added NSF program director Bruce Hamilton. “Population growth, changes in agricultural practices and climate change are all part of the equation. These findings show us where we need to focus our attention in the future.”
According to the Carnegie Institution for Science, which was also involved in the study, fresh water algal blooms result when excessive amounts of phosphorous and nitrogen are added to the water — often as runoff from fertilized agriculture. The increased amount of those nutrients spurs on unusual growth of algae and aquatic plants. When the plants and algae die, decomposers feed on them, using up oxygen in the process and dropping levels of the element to levels too low for aquatic-based life forms to thrive.
The researchers used both sampling, satellite-based observations of Lake Erie, and computer simulations to study the bloom, which began in the western region of the lake in mid-July. Initially it covered an area of 230 square miles and was comprised primarily of microcytsis, an organism which produces a liver toxin and can irritate the skin. It reached its peak in October when it covered more than 1900 square miles and was three-times more intense than any bloom previously recorded by scientists, the researchers added.
“The ‘perfect storm’ of weather events and agricultural practices that occurred in 2011 is unfortunately consistent with ongoing trends,” said Carnegie Institution scientist and lead author Anna Michalak. “That means that more huge algal blooms can be expected in the future, unless a scientifically-guided management plan is implemented for the region.”
The NSF said the researchers analyzed a number of different factors which could have contributed to the bloom, including land-use, agricultural practices, runoff, wind, temperature, precipitation and circulation. They discovered there were three agriculture management practices in the area can lead to increased nutrient runoff — autumn fertilization, broadcast fertilization (uniform distribution of fertilizer over an entire cropped field), and reduced tillage. All three practices have been used with increasing frequency in the region over the past 10 years.
The conditions in the fall of 2010 were found to be ideal for harvesting and preparing fields, as well as increasing fertilizer application for spring planting. However, the following spring a series of strong storms — including rainfall of more than 6.5 inches in May alone — caused sizable amounts of phosphorus to flow into Lake Erie.
Once the bloom began, warmer water and weak currents caused it to become more productive than in past years — helping to incubate it and allowing Microcystis to remain near the top of the water column. Those conditions also kept the nutrients from being flushed out of the system, the researchers added.
“They found that severe storms become more likely in the future, with a 50 percent increase in the frequency of precipitation events of .80 inch or more of rain,” the NSF said. “Stronger storms, with greater than 1.2 inch of rain, could be twice as frequent. The researchers believe that future calm conditions with weak lake circulation after a bloom’s onset are also likely to continue, since current trends show decreasing wind speeds across the United States. That would result in longer-lasting blooms and decreased mixing in the water column.”
“This event was caused by a complex combination of factors, and I think this paper really puts all the pieces together in a very clear and systematic way. We tried to think about this problem in a much more cross-disciplinary way than I think other people have thought about it before,” added atmospheric scientist Allison Steiner, one of 18 co-authors hailing from the University of Michigan. “The models do predict an increase in extreme springtime precipitation events, and that’s driven by an increase in greenhouse gases.”