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Nutrients in the Nation's Streams and Groundwater

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Nutrient sources in both agricultural and urban areas contribute to elevated nutrient concentrations in streams and groundwater across the nation. A new USGS study shows that, despite efforts to control nutrient sources and transport, concentrations of nutrients that can damage aquatic ecosystems and affect drinking water have remained the same or increased in many streams and aquifers across the nation over the last two decades. We speak with Dr. Neil Dubrovsky, USGS hydrologist and lead scientist on the study.




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Kara Capelli:  Welcome to USGS CoreCast. I'm your host Kara Capelli. Concentrations of nutrients at levels that can negatively impact drinking water and aquatic ecosystems have either remained the same or increased in many streams and aquifers across the nation since the early 1990s according to a new study by the US Geological Survey. I'm joined today by Dr. Neil Dubrovsky, the USGS Hydrologist who led the study. Neil thanks for being here today.

Neil Dubrovsky:  Glad to be here Kara.

Kara Capelli:  So Neil why do a nationwide study on nutrients.

Neil Dubrovsky:  Well Kara during the last hundred years and particularly since 1950, there has been a very large increase in sources of nutrients like nitrogen and phosphorous applied to the landscape and discharged to streams. This increase corresponds to the nation's increasing population and agricultural development. The EPA reports that nutrient pollution remains one of the three top causes of degradation in US streams and rivers. And we know that nutrients can negatively affect drinking water.

01:04 Even though nutrients occur naturally in our waters and are need for plant growth and productive aquatic ecosystems, in high concentrations they often result in growth of large amounts of algae and other nuisance plants in streams, lakes and estuaries. This algae can interfere with recreational swimming and boating. Algae also causes areas of low dissolved oxygen known as hypoxic zones that stress or kill aquatic life. 

Hypoxia is a major issue in many other coastal areas around the nation as well as some Great Lakes. This USGS study, which includes more than 500 streams throughout the United States, is a way of objectively assessing and tracking the effectiveness of our efforts to manage nutrients. We anticipate nutrients will continue to be an issue well into the future.

Kara Capelli:  So since you started this study, what trends have you seen?

Neil Dubrovsky:  In general, what we're seeing is that despite local state and federal efforts to control and reduce nutrients across the nation, concentrations of nutrients have remained the same or increased in many streams and aquifers across the nation since the early 1990s.


For example, our sampling showed that concentrations of nitrogen and phosphorous remained two to ten times greater than nutrient criteria recommended by the US EPA in most agricultural and urban streams. We're also seeing increasing nutrient concentrations in groundwater. These findings suggest that continued reductions in nutrient sources and implementations of land strategies for reducing nutrient transport to streams are needed in most regions in order to meet recommended EPA criteria and achieve healthy ecosystems and safe drinking water.

Kara Capelli:  So you were just talking about broad trends across the entire nation, are nutrients a problem everywhere?

Neil Dubrovsky:  Well nutrients are not a problem everywhere but we do consistently see them elevated in certain landscapes across the United States.


The study showed clear regional patterns in nutrients in streams and groundwater that largely reflect areas of development whether agricultural or urban and residential. This is because nutrients can come from a variety of sources including fertilizers in farm lands and residential areas, manure, waste water treatment plants, septic systems, and even atmospheric deposition of nitrogen from combustion of fossil fuels. We found that concentrations in nitrogen generally are highest in agricultural streams in the northeast, the midwest, and the northwest, which have some of the most intense applications of fertilizer and manure in the nation.

The way nutrients are transported from land to surface water and ground water make some areas more vulnerable to contamination than others. For example, tile drains and artificial subsurface drainage in the upper midwest provide quick pathways fornutrient run off in this region resulting in elevated concentrations in streams.


If we move to the southeast part of the country, we see that streams and groundwater contain relatively low concentrations of nitrate partly because soil and hydrologic characteristics can naturally remove nitrate from waters in this area. We haven't talked much about phosphorous but total phosphorous concentrations are generally high in both agriculture and urban streams across the nation. 

Some of the sites with the highest concentrations are downstream from waste water treatment plants. This information about sources and transport is very useful because it can help decision makers anticipate sensitive areas of concern and also set priorities for monitoring streams, aquifers, and water sheds most vulnerable to nutrient contamination and implement effective strategies to track progress and protect water resources.

Kara Capelli:  A lot of groups are working to improve water quality and reduce nutrient concentrations, yet you didn't really see improvements in most streams nationwide. What does this mean?


Neil Dubrovsky:  Kara this is an incredibly complex issue and at least in part a political question. From our perspective, we did see water sheds with truly significant reductions in nutrients during our assessment period. But people need to have realistic expectations because in some areas, it may take some time before concentrations in streams change to reflect the changes on land surface. 

Also, if people want a more detailed understanding of where things are changing including how effective the conservation measures are, then we will need to have an expanded monitoring network as well as data on where and when these conservation measures are being used.

Kara Capelli:  Neil what are the primary human health effects related to elevated concentrations of nutrients?

Neil Dubrovsky:  As far as human health concerns go, the major findings from the studies that nitrate contamination is a continuing human health concern in some ground water use for drinking water.


This is especially true for shallow ground water in agricultural areas. The second important point to note is that nitrate concentrations are likely to increase in aquifers used for public drinking water supplies because this shallow ground water moves slowly and nitrate can persists in ground water for years and decades. Inevitably, the shallow ground water will move to the deeper drinking water supplies.

Kara Capelli:  So Neil just one more question. With a big nationwide assessment like this, how is this information eventually used?

Neil Dubrovsky:  As I mentioned previously, the findings help federal state and local managers and decision makers better anticipate which streams, aquifers, and water sheds maybe most vulnerable to nutrient contamination. This helps them set priorities for monitoring, assessment, and protection. This study is just one part of the USGS National Water Quality Assessment Program, which has been conducting water quality studies for the last two decades.


And it is producing a multitude of regional and national assessments. The goal is that through national assessments like this one we've been discussing today, we can assist those who set policy and write regulations, and together we can establish priorities and make sound decisions.

Kara Capelli:  Neil thank you so much for being here today.

Neil Dubrovsky:  Thank you Kara. It's been a pleasure sharing our findings with you.

Kara Capelli:  And you can find a link to this study as well as additional information related to the study at Don't forget to follow the USGS on Twitter at or visit our other social media channels at media. This CoreCast has been a product of the US Geological Survey Department of the Interior. Thanks for listening.


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