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Making Waves: Hypoxia in U.S. Coastal Waters

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Earlier this month, a new interagency report was delivered to Congress that warns of the growing threat of low oxygen ‘dead zones’ in coastal waters around the U.S. This condition is known as hypoxia — where oxygen levels drop so low that creatures in the water are stressed or killed. In this episode, we hear from two of the scientists behind the report: Dr. Libby Jewett from NOAA and Herb Buxton from the US Geological Survey. They help us learn more about the extent of this problem, its causes, and how this trend might be reversed.

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Earlier this month, a new interagency report was delivered to Congress that warns of the growing threat of low oxygen “dead zones” in coastal waters around the U.S. This condition is known as hypoxia -- where oxygen levels drop so low that creatures in the water are stressed or killed. 

Today, we hear from two of the scientists behind the report – Dr. Libby Jewett from NOAA, and Herb Buxton from the US Geological Survey. They’re going to help us learn more about the extent of this problem, its causes, and how this trend might be reversed.

It’s Thursday, September 16, and you’re listening to Making Waves from NOAA’s National Ocean Service.

(Hypoxia Report)
Hypoxia isn’t a term that many people know, so let’s begin with an overview of what we’re talking about. To help us do that, we’re joined by Libby Jewett, Hypoxia Research Program Manager for NOAA and the lead author of the new report. We began by asking Libby to explain what exactly hypoxia is.

“Hypoxia is when the level of dissolved oxygen in the water gets too low to support most life and it’s a problem in coastal waters around the U.S. and in lakes. It’s been defined as when the level of oxygen falls below two parts per thousand or two milligrams per liter…”

And the biggest factor that leads to dissolved oxygen falling below this level is what’s known as nutrient pollution. We generally think of nutrients as good things because all organisms need nutrients to grow. The problem is that we humans are generating way too many of them. And these nutrients – mainly nitrogen and phosphorus – find their way into our waterways and end up in lakes, estuaries, and coastal waters.

Libby said that in most cases these excess nutrients are the main culprit behind the hypoxia problem.  What happens is that the nutrients become food for algae in the water, and this leads to unnaturally large algal blooms. In other words, it makes the algae grow like crazy, just like fertilizer boosts the growth of the grass on your lawn.  And then …

“As that algal bloom dies or is eaten by zooplankton, the organic matter falls down to the bottom waters and because the bottom waters are actually separated by the surface waters because they’re – in the case of an estuary – higher salinity, denser waters – as the bacteria is decomposing that organic matter in the bottom waters – it actually draws the oxygen level down. And so it’s through the nutrient supply of these systems that we actually see a growth in the frequency and intensity of hypoxia in many U.S. systems.”

How big of a problem is this in the U.S. today? That leads us back to the new interagency federal report, which was mandated by Congress in the Harmful Algal Bloom and Hypoxia Research and Control Act of 2004. We asked Libby what Congress is looking for in the report.

“So one of the requests by Congress is ‘update us,’ you know, ‘not only are we going to fund research,’ which is part of what that legislation does, but says ‘tell us how has the rate and intensity and frequency hypoxia changed in the last five years, because there was a report like this done in 2003, and what can be done? How much progress have we made and what are the next steps.”

She said that answering these questions is no easy task, mainly because the problem of hypoxia is so complex.

“In order to get at this, you really have to look at the whole watershed. And that doesn’t mean just NOAA, but NOAA plus the Department of Agriculture, plus the Environmental Protection Agency, plus the US Geological Survey, plus others as well…”

What this interagency group found by looking at the whole watershed is that there’s been a huge, 30-fold increase in hypoxia in U.S. waters since the1960s. Back then, there were only 12 documented hypoxic zones. Today, the report catalogues more than 300. 

The Oregon and Washington shelf off the West coast is now the site of the second largest seasonal hypoxic zone in the U.S. and third in the world – and the report finds that this may have more to do with climate change than nutrient pollution. The report also confirms that the northern Gulf of Mexico is home to the largest seasonal dead zone in the country and second largest in the world.

Overall, the report documents hypoxia on every coast and in around half of our estuaries.

“It wouldn’t matter if there was nothing living in those systems, but these are the most productive systems in the world along the coasts, and that’s where the fisheries are that our commercial fishermen and recreational fishermen rely on. And these are where marine mammals live that are eating the fish that are relying on the organisms that would have been living in those hypoxic zones. ”

Scientists are still trying to better understand what the long-term impacts might be to coastal ecosystems around the nation.  Some organisms – like fish -- have the capability of moving out of hypoxic areas, so Libby said it’s hard to figure out the effect on these fisheries.  But there are many other organisms like oysters and mussels that can’t move as fast, and when the hypoxia hits, they die.

“So you’re actually losing habitat substrate and nursery habitat. There are large swaths of Chesapeake Bay, for instance, and at the mouth of the Gulf of Mexico where there’s nothing living on the bottom for a good part of the year. And these were productive systems in the past. I mean, prior to the 1960s-1950s, you look at the amount of fish caught and those systems, for instance, the mouth of the Gulf of Mexico were the most productive in terms of fish caught and when they did abundance surveys where the fish lived. And now, if they do that mid-summer, there’s really nothing there.”

The northern Gulf of Mexico and the Chesapeake are two of eight in-depth case studies in the report that provide a representation of the many different types of hypoxia systems in the U.S. – those that are well-studied, those aren’t so well-studied, systems that are newer to hypoxia, and systems that have strong management interventions in place to reduce nitrogen and phosphorus pollution. Added to this:

“… one of the nice pieces to this report is the whole final appendix, which actually lists every system, no matter how small that experiences hypoxia. And that way, when we do the next report, we compare the difference over time, and whether we do have a beneficial impact through whatever nutrient reduction techniques or other control mechanisms that we put into place.”

This last point – measuring how well we’re doing at reducing the amount of nutrients running off the land into our waters – points to why so many different agencies are involved in this effort.  It’s a problem that needs to be tackled on many fronts.

NOAA’s main job is to focus on monitoring and understanding hypoxia and its impacts on coastal waters. The EPA is mainly focused on regulating nutrient inputs from sources like wastewater treatment plants. The Department of Agriculture is charged with leading strategies to reduce nutrient inputs to coastal waters from agricultural lands and urban ecosystems. And the US Geological Survey is the agency that measures and models how nutrients are delivered from freshwater systems to coastal waters throughout the nation.

To help us understand more about the complex flow of nutrients in our waterways that eventually lead to hypoxia along the coast, we’re now joined by Herb Buxton by phone from his office in New Jersey.  Herb is a co-author of the report, and chief of the US Geological Survey‘s Toxic Substances Hydrology Program. The USGS is a science agency in the Department of Interior that operates the largest federal water-monitoring program in the country. Herb said that one of the tasks of the USGS is to measure the quality and quantity of streamflow delivered to coastal ecosystems.

Streamflow is a term that simply refers to the amount of water flowing in rivers and stream. Most of this flow of freshwater ends up in the ocean. The main source for this water is from precipitation runoff. That may seem obvious to you, but what’s not so obvious is how human development impacts this flow.

“We make modification to the land surface, and we make modifications to river channels, and they all affect how the water runs over the land surface and down the rivers. Paving and development on land surfaces increases the amount of precipitation that runs off, vs. infiltrates into the ground, and that causes quicker runoff events. Also, channel modifications affect the way water flows down the streams. Channel modifications are sometimes made for navigation purposes, and this can reduce the amount of time that water spends in backwaters like in wetlands and other natural stream ecosystems and, basically combine these things, it can increase the amount of riverflow and also increase the peaks associated with storm events. ”

So in effect, the changes we make to the land often lead to water reaching the coastal ocean faster. This leaves less time for nutrients in the water to be absorbed in backwaters like wetlands. And, of course, our development of the land also means that there are less wetlands where the nutrients can be absorbed in the first place. So where are all of these nutrients in the water coming from?

“They enter the environment from the fertilizers that we apply to our agricultural lands or our commercial and residential properties; it enters the environment from agricultural lands that are used for animal production, particularly animal production that has large numbers of animals over relatively small areas. It enters the environment through the discharge of treated human waste waters. It even enters the environment through smokestack emissions that have nitrogen in it, and that ultimately retains to the land surface with atmospheric deposition and washes to rivers.  Nutrients are good in that they’re needed by living organisms to grow. The problem is when we have too much of them in the wrong place at the wrong time.”

So one of the main ways to reduce the problem of hypoxia is to reduce the amount of nutrients going into the streamflow. Herb said that improvements are being made on this front. For example, better wastewater treatment practices are decreasing nutrient loads that are put directly into streams. And new management practices are being implemented to reduce the amount of nutrient losses from fertilizer use on crop fields and from animal agriculture. Emission regulations have decreased the amount of nutrients entering our waterways from smokestacks. And wetlands are being restored.

Still, there’s lots still to be done. One of the biggest challenges in getting a handle on the nutrient pollution problem is that the U.S. is a big place and there’s a lot of streamflow that needs to be accounted for. Herb said that today the USGS monitoring of coastal delivery of nutrients is limited to about 18 major rivers. While that may not seem like much, he said that the streamflow from these rivers alone account for more than 80 percent of total nutrient delivery to our coastal waters.

“Although these are the largest 18, the National Hypoxia Report [lists] over 300 coastal ecosystems in the U.S. that are currently experiencing hypoxia, so we need to a better job in addressing many of the smaller watersheds, the smaller coastal ecosystems, and the only way to do that is to carefully increase monitoring in certain representative locations and also improving our modeling capabilities.”

“I think our ultimate goal with respect to managing our water quality and coastal hypoxia in particular is to have an adaptive management process in place that enables us to use scientific knowledge to guide the management actions we take and then to continually improve or correct those actions using continual feedback on what’s actually happening in the environment, and our improved understanding of the science related to what the cause-and-effect mechanisms are related to hypoxia.”

Well, that gives you a brief overview of what you’ll find in the new report. It’s called the ‘Scientific Assessment of Hypoxia in U.S. Coastal Waters,’ and it’s freely available online. We’ll provide a link to it in our show notes.  And it’s definitely worth a look to see what areas around the nation are affected by hypoxia, and it’ll give you a great overview of the scope of the problem, how things are changing through time, and how the Federal government is working together to tackle this serious issue.  Wondering what you can do to help? Here’s Herb with some simple steps we can all take to reduce the amount of nutrients we’re putting into our waters.

 “I think we can all do our part. Simple things like following the instructions on fertilizers that we use on our lawns or our golf courses or our gardens; taking the proper care of our septic systems to ensure that they don’t lose nutrients to our shallow groundwater systems which ultimately could get to local streams; keeping our pet wastes away from storm drains so that they don’t short-circuit into our streams; and even using household detergents that are low in phosphorus, which is a nutrient that is part of affecting nutrient enrichment, over-enrichment, and formation of hypoxia.”

And that’s all for this week. We’d like to thank Dr. Libby Jewett , Hypoxia Research Program Manager, with NOAA’s National Centers for Coastal Ocean Science … and Mr. Herb Buxton, chief of the US Geological Survey‘s Toxic Substances Hydrology Program.

Again, you’ll find a link to the ‘Scientific Assessment of Hypoxia in U.S. Coastal Waters’ in our show notes

If you have any questions about this week’s podcast, about the National Ocean Service, or about our ocean -- or if you have an ocean fact you’d like answered -- send us a note at And be sure to visit us online. We’re at

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This is Making Waves from NOAA’s National Ocean Service.

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