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Completion of Continent - Wide Soil Survey

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Detailed Description

The USGS recently completed sampling for the North American Soil Geochemical Landscapes Project on November 18, 2010. The last three samples of a total of 14,400 samples were collected at Bull Run Mountain in Virginia. During the multi-year project, about 20 students from a dozen different universities aided USGS employees and partners from Natural Resources Conservation Service (NRCS), the University of Nebraska's School of Natural Resources, Conservation and Survey Division (Nebraska Geological Survey), the Pennsylvania Geological Survey, and the Minnesota Geological Survey in the sample collection. The samples are currently being analyzed for 44 major and trace elements, including most of the macronutrients and micronutrients, most potentially toxic elements, and organic carbon.


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Completion of Continent - Wide Soil Survey

 Alex Demas:  Hello and thanks for joining us. I'm your host Alex Demas. Today we'll be discussing a North American Soil Geochemical Landscapes Project. It's just collected its last samples at Bull Run Mountain in Virginia. This was initially designed as a collaborative effort among the USGS Geological Survey of Canada and the Mexican Geological Survey to quantify the natural background variation of about 40 chemical elements and soils across all of North America.

Joining me today is the project chief of the USGS side of the project, Dave Smith. Dave thanks for joining me.

Dave Smith:  My pleasure Alex.

Alex Demas:  OK. So what was this study exactly? What were you looking for?

Dave Smith:  Alex, we refer to this entire endeavor as the North American Soil Geochemical Landscapes Project. It was initially designed as a collaborative effort among the USGS, the Geological Survey of Canada and the Mexican Geological Survey to quantify the natural background variation of about 40 chemical elements and soils across all of North America. The thrust of the project really boils down to the fact that we cannot recognize and understand changes in soil composition caused by human activities unless we understand the range of natural baseline levels for chemical elements in soil.01:10And this project will give us a big leap forward in that understanding. So the mission of the project is really threefold as we usually state it. Firstly is to establish a soil geochemical database and its representation in Math form for the continent of North America. Secondly, we will interpret those observed geochemical patterns in terms of the processes acting at the broad scale study. And last but not the least, we will establish an archive of soil samples for use by future investigators.

Alex Demas:  So how did such a major effort get it to start?

Dave Smith:  The project really had its origins back in a 2001 meeting of the directors of the three National Geological Surveys for North America. One of the outcomes of this meeting was the recognition that information on the chemical composition of soils and all three countries what was really woefully inadequate to meet the growing needs of government agencies that had a routine need to know about the background geochemistry of soils.02:11For example environmental regulatory agencies are regularly tasked with establishing soil screening levels or action levels for potentially toxic elements such as lead, arsenic or mercury. So as such, they need to know about the natural variation of these elements at various scales including the national and continental scales. These agencies also conduct risk based assessments of contaminated land and again in this process need information on the background variation of the contaminants in question. 

Now from a little bit different point of view public health agencies deal with soil pathways for toxic elements to enter the human body and they absolutely must have adequate information on the exposure levels of these elements in soil. So given the needs of this important client based, I think the directors recognized that the National Geological Surveys of the three countries where the logical organizations could tackle this continental sized issue.03:07Alex Demas:  So what are the next steps in the evolution of the project? Where did you go from there? 

Dave Smith:  Well after the directors gave their blessing to having their scientific staffs explore establishing a soil geochemical survey at a truly continental scale, a group of about 30 of us including representatives from all three geological surveys plus representatives from the USCPA, Department of Agriculture on the US side, also agriculture and AgriFood Canada and Health Canada, men in Denver in late 2002 to discuss how we might move forward to address this challenge that the directors had given us.

And we quickly agreed that our first step should be to formally engage our stakeholder community and get their input on how such a soil geochemical survey should be conducted. So in March 2003, we convened the soil geochemical workshop again in Denver. We attracted 112 attendees representing an addition to the three National Geological Surveys, I think it was nine federal government agencies from the US side, six state agencies, 11 universities, two federal agencies from Canada, six environmental consulting firms, a couple of medical institutes and one national laboratory the Lawrence Berkeley Lab was represented.04:21And we also had guests from the Geological Survey of Norway and the University of Essex in the UK. The primary outcome of the workshop was a set of recommendations on how to design a continental scale soil geochemical survey, in other words how to select the sample sites and also what the sampling protocols from the survey should be and what the analytical protocol should be.

Now the participants in the workshop also made some recommendations that really complicated our lives a little bit as well. They said as long as you guys are out collecting soils across the continent, why not look at the distribution of selected organic compounds such as pesticides.05:00They also recommended that we perform some level of microbial characterization of the soils because this type of characterization had never been done before at a continental scale. All of these were wonderful suggestions but we quickly realized that we couldn't just jump in to a full continental scale project trying to implement all of these recommendations that went far beyond our initial mandate of soil inorganic geochemistry.

So at that point in time we decided that that we would need a pilot phase to test and refine all of those recommended protocols before we embarked on the full sampling of the continent.

Alex Demas:  So how did you go about designing this pilot phase?

Dave Smith:  Well we had had yet another workshop. This time in Davis, California and we discussed this very issue on how to design our pilot studies. For this workshop, there were 26 attendees again representing all three countries and we came up with a plan that had really served us quite well. We decided that we would conduct our pilot studies at two very different scales. 06:00One pilot study was at a truly continental scale and involved sampling soils along two transects across he continent. We had a north-south transect which extended from Northern Manitoba in Canada on down to the US Mexico border near El Paso, Texas then on down to the Pacific Coast of Mexico just west to Acapulco. Then we had a west to east transect that ran right through the center of the US along the thirty eighth parallel from just north of San Francisco to the Atlantic Coast of Virginia.

Our sample sites were spaced about 40 kilometers apart along those transects and we collected four different sample types at each site. Those sample types included material from a depth of zero to five centimeters. Then we collected the organic rich soil O horizon where it was present we collected a composite of the soil A horizon which is the uppermost mineral soil. And we also collected a sample from the soil C horizon which is generally the weathered parent material07:05Now this work was conducted in the US and Canada in the summer and fall of 2004. The Mexicans were a little bit behind. They started their work the year after that. The analytical work involved inorganic geochemistry, quantitative mineralogy, microbial characterization and the determination of organochlorine pesticides sort of our as our contribution to the organic chemistry side of the equation.

Now in addition to this continental scale pilot study we also did a regional scale pilot study in about a 20,000 square kilometer area in Northern California. The study area extended from the Pacific Coast all the way to the California and Nevada border and Sacramento, it's at the very center just to give you an idea of where that is. This regional scale study was designed more to represent a higher resolution follow-up investigation of an area of interest that we might identify from the continental scale work.08:04Now this pilot phase was completed both the transects and the regional scale study in 2007 and we immediately applied some of the lessons learned and started the full continental scale sampling that same year.

Alex Demas:  So what were some of the lessons learned in the pilot phase of the project? How did that extrapolate on to the big project?

Dave Smith:  Well in particular we learned that we simply could not carry out all the recommendations from the 2003 workshop. There was just far too many and too complicated. It was far too expensive to analyze for organic compounds and also to conduct the extensive microbial characterization suggested by our 2003 workshop. So we eliminated those from our protocols with the exception of one bit of microbiology.

We're still collecting a sample at every site for the determination of selected soil pathogens particular anthrax. And we also decided to cut the number of samples collected at each site to three. 09:00For the full continental scale effort, we're only doing samples from zero to five centimeters then a composite of the soil A horizon and a sample from the soil C horizon at each site.

Alex Demas:  So how many sample sites do you have for the full continental study and how did you identify those sites?

Dave Smith:  We use something called a generalized random tessellation stratified design to identify 13,500 sites for the entire continent. That's a density of about one site per 1,600 square kilometers for the continents. So still a rather low density for sampling but such is the nature of these continental scale studies. Just over 4,800 of those sites are in the conterminous US and somewhere between 900 and 1,000 in Alaska.

This type of design ensured that each site was selected at random and it also ensured a uniform spatial distribution sites across the entire continent.

Alex Demas:  OK. So how did you go about collecting this large number of samples?

Dave Smith:  Well during our first year of the full continental scale sampling which is 2007, we had to add a pre-limited budget and we just simply used project scientist to go out and collect samples and the only territory we covered that first year was the sixth New England state and the state of New York.10:17Now our colleagues at the Geological Survey of Canada covered the maritime provinces at Nova Scotia, New Brunswick and Prince Edward Island and that was by design. We decided that the first year of the project, the Canadian Survey and the US Geological Survey would complete a slough across the two countries so we would have something in hand that we could use as evidence of international collaboration.

Now after that first year, we've had some terrific assistance from our partners and colleagues in the Department of Agriculture, the US Department of Agriculture particularly the National Resources Conservation Service NRCS and also State Geological Surveys. NRCS collected the entire state of North Dakota and South Dakota forest. The Nebraska Conservation and Survey Division which is in effect the Nebraska Geological Survey collected their state forest.11:07The Pennsylvania Geological Survey collected their state forest and the Minnesota Geological Survey collected large part of Minnesota forest and the rest of Minnesota was collected by USGS crew. So we really appreciate all the help we've had from those folks. Now from the rest of the sampling we've had tremendous success using students from all across the country.

Over the course of the last three years the project we hired about 20 students from Soil Science or Environmental Science Departments from about a dozen different universities and we brought on some truly outstanding young men and women. We would train them for a few days in our protocols and then send them out in groups of two to sample one or more assigned state. And they just worked their tails off for us and just doing an outstanding job.

So in this way we've been able to complete sampling and for the entire conterminous United States with the last sample actually being collected on November 18th, that Bull Run Mountain, Virginia.12:07We have collected now about 4800 sites and as we discussed three samples at each site so we now have in hand about 14,400 samples that will be analyzed both chemically and mineralogically over the next year or two as budget permits.

Alex Demas:  So given that it was taken about nine years to reach this milestone, how have kept in contact with the stakeholders during all of this?

Dave Smith:  Well that's been a real challenge. We've taken every opportunity that we could find to give updates on the project that various scientific and technical conferences throughout North America. And then once we completed the pilot phase and we actually had some hard data in hand then we've actually convened a quarter day or half day sessions at several scientific conferences. Our pilot study results were first presented at the International Conference on Soil, Sediments and Water which is an annual event held at the University of Massachusetts in Amherst and we were there in 2005 the year after we completed the sampling along the transects. 13:03Then we convened the session at the World Congress of Soil Science in Philadelphia in 2006 at the Geological Society of America, meeting in Houston in 2008. We had a session at the International Applied Geochemistry Symposium in Frederick, New Brunswick in 2009. And that same year we had a session at the National Environmental Public Health Symposium in Atlanta.

So we've been very active and reaching out and in that manner next year, we've been invited to convene a session at the National Environmental Monitoring Conference in Seattle. Now in addition to these sessions devoted strictly to the project, we've also given presentations at EPA Headquarters in Washington at the Department of Agriculture also in Washington and at the National Academy of Sciences in Washington.

We've given a couple of presentations to the American Association of State Geologists to keep them advised on the projects since we're working all of the other states throughout the course of the last four years. Now we're really proud of the fact that the results of our pilot studies that were published just last year as 21 papers and a special issue of the journal applied geochemistry. 14:10So we really tried our best to maintain our visibility and also our scientific output as best we could.

Alex Demas:  So what has been the reception of the stakeholders in the project?

Dave Smith:  Alex it's really been remarkable. Everywhere we talk about the project, the response has basically been wow we need this type of data yesterday but if we can have it yesterday, we'll be happy to have it in a couple of years. The centers for disease control and prevention in Atlanta sent a formal letter of support for the project to the USGS director back in 2004 just as we were starting our pilot phase. And just this year 2010, the EPA Homeland Security Research  Center in Cincinnati provided some funding to the project to support one of our students to help with sampling and also to assist with the determination of pathogens in soil.

Alex Demas:  So what's next?

Dave Smith:  Well now that we've completed our sampling for the conterminous US, we'll start releasing the data to the public probably via an online USGS data series report. And we hope to have that up and running during the first half of 2011. 15:13We'll update the report as data are received from the lab. The first version will have whatever data we have in hand at that time and then as more data come in, we'll add that to the website and hopefully have that fully stocked by 2012 or so. And then hopefully we can start providing some interpretive products so on, at least subsets of the data over the next year or so as well. So we're really to the point in the project where the fun stuff is just about ready to happen.

Alex Demas:  Well Dave thanks for joining me.

Dave Smith:  My pleasure Alex.

Alex Demas:  This podcast has been a product of the US Geological Survey Department of the Interior. For more information on this podcast or other podcast, please visit our website at Thank you for joining us.

Show Transcript