Eastern U.S. most vulnerable to future harmful algal blooms

New modeling shows where global warming will increase cyanobacteria

Blue-green algae that sometimes produce toxins thrive as global warming heats up lakes, ponds and reservoirs. @bberwyn photo.

Staff Report

Scientists say it’s all but certain that global warming will increase potentially threatening outbreaks of freshwater algae that can produce toxins dangerous to people and animals.

A team lead by Tufts University researcher Steven C. Chapra has developed a modeling framework showing harmful algal blooms will increase the most in the northeastern region of the U.S. but that the biggest economic impact will be felt in the Southeast, where waters important for recreation will probably take a big hit.

The research, published in the journal Environmental Science & Technology, is part of larger, ongoing efforts among scientists to quantify and monetize the degree to which climate change will impact and damage various U.S. sectors.

“Some of the biggest CyanoHAB impacts will occur in more rural regions, such as those in the Southeast and Midwest – areas that don’t often come up in conversation about unavoidable effects of climate change,” said Chapra, Ph.D., lead author of the study and Louis Berger Chair of Civil and Environmental Engineering in the School of Engineering at Tufts. “The impact of climate change goes way beyond warmer air temperatures, rising sea levels and melting glaciers.”

“Our study shows that higher water temperature, changes in rainfall, and increased nutrient inputs will combine to cause more frequent occurrence of harmful algal blooms in the future,” he added.

Similar research also recently showed that the same factors will combine to worsen ocean dead zones. The blue-green algae, also known as cyanobacteria, are Earth’s oldest photosynthetic organisms. They’ve been around for 3.5 billion years and are resilient to climate change. As a result, some varieties show optimal growth and bloom potentials at high water temperatures relative to other aquatic plants. Therefore, global warming plays a key role in their expansion and persistence, said Chapra.

The new study used standard climate change projections, combined with two cyanobacterial growth scenarios. It is among the few studies to combine climate projections with a hydrologic/water quality network model of U.S. lakes and reservoirs. That involves computing a complex set of factors, including a rainfall model to simulate monthly rainfall and runoff in each of the 2,119 watersheds of the continental U.S.; and a water demand model, which projects water requirements of each watershed’s municipal, industrial, and agriculture sectors.

With those numbers, the scientists were able to project a time series of reservoir storage, release, and demand allocations (e.g., agriculture, environmental flows, and hydropower), all of which affect factors that control HABs.

Beyond the human health effects, CyanoHABs have a variety of negative consequences for aquatic ecosystems, including the creation of unsightly surface scums and a reduction in recreational use and access to shorelines. Also, because most cyanobacteria are inedible by zooplankton and planktivorous fish, they represent a “dead end” in the aquatic food chain – a scenario that ultimately hurts both commercial and recreational fishing industries.

Chapra said the research indicates that as water temperatures increase, more stringent and costly nutrient controls would be necessary in order to maintain current water quality.

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