US scientists, speaking at the annual meeting of the American Association for the Advancement of Science (AAAS) in Washington Saturday, said climate change could increase exposure to water-borne diseases originating in the world’s oceans, lakes and coastal ecosystems, adding that the impact will most likely be felt within the next 30 years, and as early as the next 10 years.
Numerous studies have shown that shifts from climate change make ocean and freshwater ecosystems more susceptible to toxic algae blooms and allow harmful microbes and bacteria to rapidly grow and multiply, said researchers from the National Oceanic and Atmospheric Administration (NOAA).
“These studies and others like it will better equip officials with the necessary information and tools they need to prepare for and prevent risks associated with changing oceans and coasts,” said Jane Lubchenco, Ph.D., undersecretary of commerce for oceans and atmosphere and NOAA administrator.
In one study, NOAA researchers modeled future ocean and weather patterns to predict the effect on blooms of Alexandrium catenella, most commonly known as toxic “red tide,” which builds up in shellfish and can be fatal to humans who eat the contaminated seafood.
“Our projections indicate that by the end of the 21st century, blooms may begin up to two months earlier in the year and persist for one month later compared to the present-day time period of July to October,” Stephanie Moore, one of the scientists who worked on the study, told AFP.
Prolonged harmful algal bloom seasons could mean more days the shellfish fishery is closed, threatening the vitality of the shellfish industry.
“Changes in the harmful algal bloom season appear to be imminent and we expect a significant increase in Puget Sound and similar at-risk environments within 30 years, possibly by the next decade,” said Moore.
Natural climate variability also plays a role in the length of the bloom season from one year to the next. Therefore, in any given year, the change in the bloom season could be more or less severe than implied by the long-term warming trend due to climate change.
In another study, NOAA scientists found that desert dust that gets deposited into oceans from the atmosphere could also lead to increases of harmful bacteria in seawater and seafood.
Researchers from the University of Georgia found that adding desert dust to seawater significantly stimulated the growth of Vibrios — a group of ocean bacteria that can cause gastroenteritis and infectious diseases in humans.
“It is possible this additional input of iron, along with rising sea surface temperatures, will affect these bacterial populations and may help to explain both current and future increases in human illnesses from exposure to contaminated seafood and seawater,” said the researchers.
“Within 24 hours of mixing weathered desert dust from Morocco with seawater samples, we saw a huge growth in Vibrios, including one strain that could cause eye, ear and open wound infections, and another strain that could cause cholera,” Erin Lipp, who worked on the study, told the French news agency.
The amount of iron-rich dust that has fallen into the sea has increased over the past 30 years and is expected to continue to rise, based on precipitation trends in western Africa which are causing desertification.
Since 1996, Vibrios cases have increased 85 percent in the United States based on reports that primarily track seafood-illnesses. It is possible this additional input of iron, along with rising sea surface temperatures, will affect these bacterial populations and may help to explain both current and future increases in human illnesses from exposure to contaminated seafood and seawater.
And researchers at the University of Wisconsin-Milwaukee warned that an increase in rainfall could also cause more sewage overflows, which would release disease-causing bacteria, viruses and protozoa into drinking water and onto beaches.
Spring rains are expected to increase over the next 50 years, and with that increase, aging sewer systems are more likely to overflow because the ground is frozen and rainwater cannot be absorbed, said Sandra McLellan, Ph.D., at the University of Wisconsin-Milwaukee School of Freshwater Sciences.
As little as 1.7 inches of rain in a 24-hour period can cause an overflow in spring, and the combination of increased temperatures with increased rainfall can magnify the impact.
McLellan and colleagues showed that under worst case scenarios there could be an average 20 percent increase in volume of overflows, and the overflows could last longer.
In Milwaukee, infrastructure investments have reduced sewage overflows to an average of three times per year, but other cities around the Great Lakes still experience overflows up to 40 times per year.
“Hundreds of millions of dollars are spent on urban infrastructure, and these investments need to be directed to problems that have the largest impact on our water quality,” said McLellan. “Our research can shed light on this dilemma for cities with aging sewer systems throughout the Great Lakes and even around the world.”
In the past 10 years there have been more severe storms that trigger sewage overflows. While there is some question whether this is due to natural variability or to climate change, these events provide another example as to how vulnerable urban areas are to climate.
“Understanding climate change on a local level and what it means to county beach managers or water quality safety officers has been a struggle,” said Juli Trtanj, director of NOAA’s Oceans and Human Health Initiative and co-author of the interagency report A Human Health Perspective on Climate Change.
“These new studies and models enable managers to better cope and prepare for real and anticipated changes in their cities, and keep their citizens, seafood and economy safe.”
Image 1: Herrold family harvesting oysters in Willapa Bay, Washington. Credit: Bill Dewey, Taylor Shellfish Farms, Inc.
Image 2: Aerosolized dust is clearly visible in the satellite image and stretches across the Atlantic Ocean nearly continuously from Western Africa into the Caribbean and Gulf of Mexico. Credit: SeaWIFS Project, NASA/Goddard Space Flight Center and ORBIMAGE
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