Nearly 240 square miles of Lake Okeechobee, the largest freshwater lake in Florida, are covered in a scum of blue-green algae that has also traveled down nearby waterways and out to the coastline. The stinking sludge has impacted local ecosystems and the tourism industry and caused Gov. Rick Scott to declare a state of emergency in the affected counties.
The algae bloom is the result of a combination of factors, including the abundant nutrients washed in from surrounding agricultural lands, heavy winter rains and hot, calm summer weather. In the future, such blooms could become more common as Earth’s rising temperature heats up lakes and oceans, providing a more favorable home for algae and other potentially toxic microorganisms in the water.
Algae Goes Bloom
The Okeechobee bloom began in May, when it was only about 33 square miles in area. Nutrients that the algae need to flourish are plentiful in the lake, primarily coming from fertilizers used in agricultural land. But those nutrients are not enough on their own to fuel a bloom; normally the lake is too turbid, with sediment in the water blocking the light that the algae need to drive photosynthesis.
But in May, calm weather led to stiller water that let light through its upper layers, allowing the algae (a type called Microcystis) to go wild.
Added to that recipe were very heavy winter rains (due largely to a strong El Niño) that led to high water levels in the lake, taxing an old, ailing dike. To ease the pressure on the dike, the U.S. Army Corps of Engineers released water from the lake, which took the algae down the St. Lucie River and out to coastal waters, along with enough freshwater for them to thrive in the normally saline estuary.
The algae are a major concern because of the potential harm they can do both to the local ecosystems and human health. They can release toxins that can cause respiratory problems in humans and can be deadly to local fish and other aquatic species. As they die, the algae also use up the available oxygen in the water, creating so-called dead zones. Dying algae also release a pungent odor that can mean tourists stay well away, hitting the local economy.
Warmer Waters, More Algae
Lakes and oceans are warming up as they absorb some of the excess heat trapped by greenhouse gases accumulating in the atmosphere. According to the most recent report of the Intergovernmental Panel on Climate Change, the oceans around Florida could warm by 1.8° to 5.4°F (1° to 3°C) by the end of the century depending on emissions levels.
A 2015 study that Havens co-authored found that 70 percent of 235 freshwater lakes around the world were warming faster than the oceans. On average, they have warmed by 0.61°F (0.34°C) per decade over the last 25 years. In some cases, lakes were warming even faster than the local air temperature. Florida is a spot where lakes have been warming more slowly, though why is unclear, Havens said.
Warmer water temperatures could provide a more favorable environment for algae to grow and affect where they occur, how quickly they grow and how toxic they are. The 2015 study found that such blooms should be expected to increase by 20 percent in lakes.
Algae, of course, aren’t the only potentially harmful microorganisms lurking in the water that could benefit from warmer temperatures.
— source climatecentral.org By Andrea Thompson