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Diving Deeper : Episode 1 (Jan. 26, 2009) —
What is Eutrophication?

HOST: Welcome to Diving Deeper where we interview National Ocean Service scientists on the ocean topics and information that are important to you! I’m your host Kate Nielsen.

Today’s question is….What is Eutrophication?

Eutrophication is also known as nutrient pollution. Eutrophication is the process where nutrients, mainly nitrogen and phosphorus, are added to bodies of water and can act like fertilizer causing the growth of algae. Excessive amounts of nutrients can lead to more serious problems such as low levels of oxygen dissolved in the water. This can kill fish, crabs, oysters, and other aquatic animals.

To help us dive a little deeper into this question, we will talk with Dr. Suzanne Bricker about eutrophication – what it is, what it means, and what scientists are doing about it. Suzanne is a Physical Scientist from the National Centers for Coastal Ocean Science. Hi, Suzanne, welcome to our show.

SUZANNE BRICKER: Hi Kate, thanks for having me today. I’m looking forward to talking about eutrophication and some of the studies that we’ve done to understand nutrient pollution in our nation’s estuaries.

HOST: Thanks Suzanne. First, can you explain to us a little bit more about the difference between eutrophication and nutrient pollution?

SUZANNE BRICKER: Essentially, eutrophication and nutrient pollution are the same thing. Nitrogen and phosphorus are nutrients that plants need to grow. The problem occurs when an excess amount of these nutrients are delivered to a water body and that causes an excessive growth of algae that clouds the water. This may cause other more serious problems such as low levels of dissolved oxygen as the algae decomposes.

HOST: Ok, so what can cause these increased levels of nutrients and where do nutrients come from?

SUZANNE BRICKER: Nutrients come from a variety of different sources. They can occur naturally, and always have, as a result of weathering of rocks and soil in the watershed and they can also come from the ocean due to mixing of water currents.

But, we are most interested in the nutrients that are related to people living on and in the coastal zone because human-related impacts are much greater than natural inputs. Basically, more people living in the coastal zone means more nutrients entering our coastal waters from wastewater treatment facilities, runoff from land in urban areas during rains and from farming. When fertilizers are applied to crops, the excess nutrients that aren’t taken up by the plants wash away in runoff typically during a rain storm. This also happens in urban areas where lawn fertilizers are used and, interestingly, pet and wildlife wastes can also be a nutrient source.

I should also mention here that it’s not just the coastal zone, but upstream sources that can impact water bodies. And so, it’s important not only to focus on the coastal zone, but also those upstream sources of nutrients as well.

HOST: Can eutrophication happen anywhere or only in coastal areas where there is runoff?

SUZANNE BRICKER: Actually, eutrophication can happen anywhere. It can happen in lakes, streams, or estuaries - basically any body of water where nutrients can enter. We mostly work in estuaries or bays, which is where rivers meet the sea. Estuaries are of particular interest to us because of our interest in using them, for instance, for recreational and commercial fishing. These are supported because estuaries are typically full of fish populations. And since eutrophication can cause low dissolved oxygen which kills fish, fisheries are in danger from nutrient pollution.

HOST: We’ve talked about excessive algal growth as the first stage of eutrophication but, other than the fact that it looks bad, why is excess algal growth a bad thing?

SUZANNE BRICKER: Well Kate, you may have noticed green masses of algae growing on a pond or a lake or in an embayment, a coastal embayment. This is the first sign of eutrophication. And basically, this layer of algae blocks light that is needed for seagrasses to grow. Seagrasses are plants that grow in shallow waters and they’re basically living rooted at the bottom of the pond or in shallow coastal areas and in extreme cases the lack of light will kill them. When algae and seagrass die, they decay. And in the process of decay, the oxygen in the water is used up and this leads to low levels of dissolved oxygen called hypoxia and anoxia. Hypoxia is just a little bit of oxygen and anoxia is a total lack of oxygen in the water. This can kill aquatic organisms like fish. And especially if the smaller fish are killed, then you also lose the larger fish.

HOST: Thanks Suzanne, I have actually noticed these green masses of algae before and I had no idea that the light they block can result then in hypoxic or anoxic situations which can ultimately kill fish. Are there other negative impacts of eutrophication?

SUZANNE BRICKER: Yes, there are other negative impacts. The increase of nutrients to a water body can change how the entire system functions. It not only affects the organisms that live there, but it can alter the habitat that they live in.

For example, the seagrasses that we were just talking about are important feeding and nursery grounds for fish and other aquatic organisms. If you lose those bottom plants, if they die from lack of light, the fish lose their home or their habitat, and will have to move to a new location. This will impact the success that you might have if you’re fishing in that area. You won’t catch any fish since they will have moved away somewhere else or they actually may have died.

HOST: And besides the green algal masses, are there other changes that we can see because of eutrophication?

SUZANNE BRICKER: Yes, eutrophication can cause a range of changes that we can see, but also some that we cannot. Sometimes the algae that blooms on account of the increased nutrients will discolor the water, like the green algae that we’ve talked about, but in coastal areas the blooms can also appear red or brown in color. In some areas, floating algae will wash up on a beach and really smell as it decays making the beach an undesirable place to go. And there are lots of estuaries that actually have a place called “stinky beach,” that is very characteristic thing with those decaying algal mats. These things may make the water body look murky and smell unhealthy. These changes can also impact the health of organisms and humans. For instance if the algal blooms are toxic, they can decrease fishing success and can cause losses of tourism, and also of real estate values.

HOST: Suzanne, how do scientists study or learn about eutrophication in the first place to know if it is a problem in an area?

SUZANNE BRICKER: Well, this is a simplificiation because the research can be quite complicated to understand eutrophication. But, there are essentially two main things that scientists look for in order to understand nutrient pollution better, one is how much nutrient is reaching the estuary and the other is the water quality within the estuary. By measuring the amount of nutrients that reach the estuary and the water quality, scientists can determine the level of nutrient that causes undesirable conditions in that specific place.

Because each estuary has a different source of nutrients, for example one estuary may get most nutrients from agricultural fields while another may receive most nutrients from urban runoff, these measurements have to be made at a local level. But when the data for the individual estuaries are looked at by grouping results, in for instance into regional or even by looking at national data (all the data together for the U.S.), then scientists can look for patterns that will help the managers to develop management plans to prevent further eutrophication.

HOST: So, since data needs to be collected at the local level and analyzed, is there a national study for the U.S. that ties this all together for a lot of different regions?

SUZANNE BRICKER: Yes, eutrophication has been a concern of many scientists during the past maybe 20 or 30 years and because of that NOAA conducted a national study of eutrophication looking at conditions in the early 1990s. This study looked at nutrient-related conditions and showed that more than half of the U.S. estuaries that were studied, and there were 141, more than half of those had significant nutrient-related problems. The report also suggested that conditions in most estuaries were at risk of becoming worse in the future due to expected increases in population in coastal areas. That was in early 1990s. In 2007, NOAA released an update to that original report to look at conditions in the early 2000s and how things have changed since the early 1990s.

HOST: How did you get the data that you needed for this particular study?

SUZANNE BRICKER: For both those studies, the one looking at early 1990s and the more recent looking at the early 2000s, we needed data for 141 estuaries. And we relied on, and I am extremely grateful to the local experts who are monitoring these estuaries and who provided us with their data so that we could do this study. These investigators take measurements of algae, dissolved oxygen, and seagrasses, as well as other things, several times a year in their particular, or specific, estuary. By looking at the changes that occur over time, those scientists can examine how the estuary is doing and whether things are changing in an undesirable way.

HOST: It sounds like a lot of data to combine and analyze to determine national trends. What did this national study show?

SUZANNE BRICKER: Overall, the national results showed that since the early 1990s we are maintaining or basically holding the line against further eutrophication problems. There were improvements in some estuaries, which is good news, but in about an equal number of estuaries conditions have worsened since the early 1990s. For most, though, conditions were about the same.

HOST: Were there any smaller, maybe local or regional trends that you can expand on as well as this broader, national look?

SUZANNE BRICKER: Yes, and actually, the regional trends were really interesting. We divided the U.S. into five regions - the North Atlantic, Mid-Atlantic, South Atlantic, Gulf of Mexico, and the Pacific Coast.

And what we found was that the least impacted estuaries, nationally speaking, occurred or are located in the North Atlantic region, which includes the coastline from Cape Cod to Maine. And these systems are different from most other regions because they have fewer people living in the watershed and also, the tidal range is very high so there is very good exchange with the ocean for most of the systems that occur there. By contrast, the most impacted systems we found were in the Middle Atlantic, which is from Cape Cod down to Chesapeake Bay. And unlike the North Atlantic, the Middle Atlantic region has probably the highest density of people living in the region and many of the estuaries in the Middle Atlantic have a smaller tidal range and not very good exchange with the ocean. So they’re, by contrast, they’re more susceptible or more vulnerable to development of problems for those reasons.

But the majority of U.S. estuaries that we studied were highly impacted by human-related activities, in fact more than half, just like in the early 1990s. Human activities that impacted the systems included agriculture and that includes both the use of fertilizers and the animal operations, also wastewater treatment plants, and urban runoff. The results also show that eutrophication is not just a problem in the United States, it is a problem that impacts estuaries on a global level. Some of the consequences that we’ve seen globally of eutrophication are losses of seagrasses, loss of fish habitat, low levels of dissolved oxygen, and longer-lasting or first-time blooms of nuisance or toxic algal.

HOST: Suzanne, is there any good news in all of this?

SUZANNE BRICKER: Yes, actually, the good news is that conditions in some estuaries improved and they improved as a direct result of changes in human behaviors and of successful management measures that were implemented. But the overall message from the most recent study is that conditions are still expected to worsen in many estuaries, in the future they will worsen if appropriate management actions are not taken right now.

HOST: You mentioned that the report indicated that eutrophication is a global problem. What are some of the other countries experiencing this?

SUZANNE BRICKER: We have worked with and have strong, close relationships with Chinese and European scientists and we know that there are serious problems with eutrophication in estuaries and coastal water bodies in both places. What we’ve tried to do is share our methods and to learn from other scientists in other places about management measures that have been successful in reducing eutrophication. It’s a global problem and we can all benefit from working together.

HOST: Is there a way to reverse trends of eutrophication or the damage caused to an estuary?

SUZANNE BRICKER: Yes Kate, there is, but the only way to reverse or limit the impacts of eutrophication is to reduce the amount of nutrients that are added to a water body. This can be done by decreasing or more efficiently using fertilizer or, for example, by adding buffer strips at the edge of farm fields so that the nutrients don’t actually reach the water body.

An alternative complimentary way to reduce algal growth within the water body is to have large populations of oysters or clams. And as an example in Chesapeake Bay, there use to be very large, thriving populations of oysters which filtered the water body and kept the Chesapeake Bay waters clearer. When those oysters died, that’s when the Chesapeake Bay started having problems, in addition to the fact that there were more nutrients entering the system. But, an alternative method, or complimentary to the usual way of reducing nutrients, is to promote the growth by shellfish farming maybe or encouraging natural populations and in this way the water can become more clear even though you’re not actually reducing the nutrient load.

HOST: Suzanne, can you highlight an example of where these methods have been successful to help us understand this a little better?

SUZANNE BRICKER: Yes, there are actually several examples of where local management actions have improved the health of impacted systems such as Long Island Sound, the Neuse River Estuary, and the Patuxent River Estuary, but probably the best example of where local management actions have been successful is Tampa Bay, Florida, where elevated nutrient levels caused significant losses of seagrasses.

Seagrass as we’ve mentioned is an important habitat for fish, but it also provides human benefits. For instance, seagrass beds can act as storm buffers that protect us from flooding during coastal storm and they also, as we know, support commercial fisheries.

So Tampa Bay, between 1950 and 1980, half of the acres of seagrass beds were lost as a result of the murkiness of the water due to those algae blooms. So starting in the 1980s, local officials worked on various actions to reduce nutrients that would then reduce those algal blooms. Wastewater treatment plants were required to provide advanced treatment. Stormwater discharges were regulated. And, the phosphate industry changed their practices to reduce fertilizer spills from port facilities from which fertilizer products were shipped. The combination of these actions reduced nutrient loads resulting in less algal growth and the waters cleared up. Seagrasses started growing again and in 2004, researchers observed the highest level of seagrass acreage since 1950. Local officials in Tampa Bay continue to try to find ways to reduce nutrient loads and are working to restore seagrass beds in the area.

HOST: Suzanne, this is great news and a wonderful story to show that through increased effort on our part, we can reverse this trend. What is the National Ocean Service doing to better understand eutrophication and improve the health of our nation’s estuaries?

SUZANNE BRICKER: Kate, the National Ocean Service has developed partnerships with local, state, federal, and international partners to study eutrophication. Many of these relationships are not short-term, but rather have developed over the last 15 or 20 years. While most research and assessment studies and management measures happen at the local level, these partnerships play a very important role. By sharing our data and our methods and information, we can develop smart solutions to nutrient related problems both here in the U.S. and elsewhere. The results from our scientific studies will help to develop management measures and those management measures will restore and protect our valuable coastal resources from eutrophication.

HOST: Thanks Suzanne for joining us on today’s episode of Diving Deeper and exploring what eutrophication is, its impacts, and what scientists are doing to learn more about it. To download a copy of the national report that Suzanne talked about today, please visit

That’s all for this week’s show, please tune in on February 9th for our next episode on marine protected areas.