Research Assistant Professor Nathan Hall with the UNC Institute of Marine Sciences in Morehead City. COASTAL REVIEW ONLINE

NC - Study of estuaries finds lower acidification than in oceans

MOREHEAD CITY — A study of the country’s two largest estuaries reveals that inshore coastal waters are not necessarily experiencing what scientists say is a worrisome global trend of increasingly acidic oceans.

The recently published paper is the latest in a small collection of studies highlighting the complexities of coastal zones onshore.

In this case, researchers looked at trends from data collected more than 20 years within the Neuse River Estuary-Pamlico Sound waters and Chesapeake Bay and found that things like nutrient pollution and algal blooms play a role in how carbon dioxide is dissolved in inland coastal waters.

Research Assistant Professor Nathan Hall with the UNC Institute of Marine Sciences in Morehead City and co-author of the study explained that eutrophication is effectively causing, in some cases, estuarine waters to have lower acidification than that of the ocean.

Eutrophication happens in waters that become overloaded by nutrient runoff, leading to harmful algal blooms, fish kills and areas of low oxygen where aquatic life cannot survive.

“We think of ocean acidification as bad, eutrophication as bad,” Hall said. “But eutrophication also in these estuaries can prevent, at least in the surface layers, the effects of ocean acidification from showing up. So, it adds a lot of complexity in the coastal zone.

“It’s not just as simple as gauges going down everywhere because we’re pumping CO2 into the air. In a lot of cases estuaries, because we load them with so much organic matter and the rivers feeding into them usually have more CO2 than they can take to begin with, they usually are releasing CO2 back into the atmosphere.”

The release of that CO2 into the atmosphere means that the carbon dioxide does not often have the same influence on the pH — or measure of how acidic or basic water is — alkalinity, in an estuary.

The measure of pH ranges from 0-14. A measurement of 7 is neutral, while those less than 7 indicate acidity and those greater than 7 indicate a base.

Scientists say increased levels of CO2 in the atmosphere driven by human activity is causing the ocean to absorb more carbon dioxide, which decreases pH, causing the ocean to become more acidic.

Increasingly acidic seas are threatening species like oysters, corals and some calcifying planktons. Threats to these species, scientists say, will create a rippling effect up the ocean food chain.

The Neuse River Estuary-Pamlico Sound and Chesapeake Bay study corroborates previous findings of how production of phytoplankton, or microalgae that float in the upper layer of fresh and marine waters, swamp out from estuaries signals that detect acidification in the ocean.

But the study also found something Hall was not expecting.

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