Hurricane Harvey more than doubled the acidity of Texas’ Galveston Bay, threatening oyster reefs

Most individuals affiliate hurricanes with excessive winds, intense rain and speedy flooding on land. But these storms may change the chemistry of coastal waters. Such shifts are much less seen than harm on land, however they’ll have dire penalties for marine life and coastal ocean ecosystems.

We are oceanographers who examine the effects of ocean acidification, together with on organisms like oysters and corals. In a latest examine printed in Communications Earth & Environment, we examined how stormwater runoff from Hurricane Harvey in 2017 affected the water chemistry of Galveston Bay and the well being of the bay’s oyster reefs. We wished to know how excessive rainfall and runoff from hurricanes influenced acidification of bay waters, and the way lengthy these adjustments may final.

Our findings have been startling. Hurricane Harvey, which generated large rainfall in the Houston metropolitan space, delivered an enormous pulse of contemporary water into Galveston Bay. As a outcome, the bay was two to 4 occasions more acidic than regular for at the very least three weeks after the storm.

This made bay water corrosive sufficient to break oyster shells in the estuary. Because oyster development and restoration depend on many components, it’s exhausting to tie particular adjustments to acidification. However, elevated acidification actually would have made it more durable for oyster reefs broken by Hurricane Harvey to get better. And whereas our examine centered on Galveston Bay, we suspect that related processes could also be occurring in different coastal areas.

Vast portions of water

Scientists predict that local weather change will make hurricanes stronger and increase the amount of rain they produce over the subsequent a number of a long time. Changes in ocean chemistry, attributable to runoff from these storms, have gotten an rising risk to many marine ecosystems, particularly coastal reefs constructed by oysters and corals.

Coastal estuaries like Galveston Bay, the place rivers meet the sea, are some of the most efficient ecosystems in the world. Galveston Bay is the largest bay on the Texas coast and one of the largest in the U.S.; it covers about 600 sq. miles, roughly half the measurement of Rhode Island. Its intensive oyster reefs present about 9% of the national oyster harvest.

Hurricane Harvey, the wettest tropical cyclone in U.S. historical past, made landfall on the Texas coast as a Category 4 hurricane on Aug. 26, 2017. Harvey stalled at the coast for 4 days, sitting over each land and ocean.

Maintaining contact with heat Gulf of Mexico waters fueled the storm with each vitality and rainfall, permitting it to persist and drop excessive quantities of rain instantly onto Houston and surrounding areas—as much as 50 inches in 4 days. All of that rain and floodwater needed to go someplace, and far of it flowed into Galveston Bay.

Climate change and ocean acidification

The ocean acidification points that we examine are a well known impact associated to local weather change. Human actions, primarily burning fossil gas, emit carbon dioxide into the ambiance. The ocean absorbs about one-third of these emissions, which alters ocean chemistry, making seawater more acidic.

Acidification can harm many forms of marine life. It is particularly harmful for animals that construct their shells and skeletons out of calcium carbonate, corresponding to oysters and corals. As seawater turns into more acidic, it makes these buildings more durable to construct and simpler to erode.

Oysters fuse collectively as they develop, creating giant rocklike underwater reefs that protect shorelines from wave erosion. These reefs provide habitat for different creatures, corresponding to barnacles, anemones and mussels, which in flip function meals sources for a lot of fish species.

Rising atmospheric CO₂ ranges are acidifying oceans worldwide. As our examine reveals, native occasions like tropical cyclones can add to world acidification.

Storm water from Harvey precipitated excessive coastal acidification

The essential trigger of the unprecedented acidification that occurred after Hurricane Harvey was the extreme quantity of rainfall and runoff that entered Galveston Bay. To assist handle large-scale flooding in the Houston space, the metropolis launched giant volumes of water from reservoirs for more than two months after Harvey. These releases prolonged the time throughout which storm water entered Galveston Bay and elevated its acidity.

Scientists use the pH scale to measure how acidic or primary (alkaline) water is. A pH worth of 7 is impartial; increased values are primary, and decrease values are acidic. The pH scale is logarithmic, so a lower of one full unit—say, from 8 to 7—represents a tenfold improve in acidity.

Rainwater is more acidic than both river water or seawater, which choose up minerals from soil which are barely primary and might steadiness out absorbed carbon dioxide from the ambiance. Rainwater’s pH is round 5.6, in contrast with between 6.5 and 8.2 for rivers and about 8.1 for seawater.

Galveston Bay incorporates a combination of contemporary water from rivers and salty seawater from the Gulf of Mexico—oysters’ most popular habitat. We collected water samples in the bay two weeks after Harvey and located that the bay was made up virtually completely of river water and rainwater from the storm.

Since rainwater, river water and seawater all have completely different chemistries, we have been in a position to calculate that rainwater made up virtually 50% of the water in the bay. This signifies that acidic rainwater from Harvey changed the primary seawater inside the bay after the storm. The common bay water pH had dropped from 8 to 7.6, a 2.5-fold improve in acidity. Some zones had pH even as little as 7.4—4 occasions more acidic than regular.

This excessive acidification lasted for more than three weeks. Bay waters turned corrosive not solely to more delicate larval and juvenile oyster shells, however to grownup oyster shells as nicely. Scientists had predicted that rising CO₂ may trigger this scale of coastal acidification however didn’t anticipate to see it till round the 12 months 2100.

The contemporary water from Harvey additionally precipitated a severe oyster die-off in the bay as a result of oysters want barely salty water to outlive. Harvey struck in the center of oyster spawning season, and acidification might have slowed reef restoration by making it more durable for younger oysters to type new shells. Officials at the Texas Parks and Wildlife Department have informed us that 4 years later, in late 2021, some Galveston Bay oyster reefs nonetheless confirmed very low additions of new oysters.

Other coastal areas in danger

Only a couple of research, together with ours, have analyzed how tropical cyclones have an effect on coastal acidification. In our view, nevertheless, it’s extremely doable that different storms have precipitated the form of excessive acidification that we detected in the wake of Harvey.

We reviewed the 10 wettest tropical cyclones in the U.S. since 1900 and located that 9, together with Harvey, precipitated giant quantities of rain and flooding in coastal areas with bay or estuary ecosystems. Other storms did not produce as a lot rainfall as Harvey, however some of the affected bays have been a lot smaller than Galveston Bay, so much less rain would have been wanted to interchange seawater in the bay and trigger an identical degree of acidification to what Harvey produced.

We suppose that this seemingly has already occurred in different places struck by hurricanes however went unrecorded as a result of scientists weren’t in a position to measure acidification earlier than and after the storms. As local weather change continues to make tropical cyclones bigger and wetter, we see storm-induced acidification as a big risk to coastal ecosystems.