William Schlesinger - "New Perspectives on Biogeochemical Cycles"

>> Good afternoon, and welcome. Good afternoon. My name is Ross Virginia. I'm a member of the Environmental Studies program, and I'm also the Director of the Dickey Center's Institute for Arctic Studies. And today's seminar is sponsored by Arctic Studies, and it's also sponsored by the IGERT Polar Environmental Change Graduate Program. This is a contribution to a series we call "Dialogues in Polar Science, Engineering, and Society." It's really a wonderful opportunity for me personally to have someone here who is a friend and a colleague and a member of the Dartmouth community, and that Dr. William Schlesinger. Bill is internationally recognized as a leader in the fields of biogeochemistry and climate change. And he's built a career of connecting ecology to the Earth sciences in ways that creates new knowledge that's relevant to solving major environmental problems, problems such as desertification, nitrogen pollution, and human perturbation of the carbon cycle. And Bill is going to be talking about these issues today, what are the new challenges, the new perspectives around biogeochemistry. So if you don't know what biogeochemistry is yet, you will by the end of this talk, I can assure you. Bill is a member of Dartmouth's class of 1972, and that was a really special time at Dartmouth. It was a time at which ecosystem science was really becoming a science. It was a time when ecologists were beginning to actually work together and talk to Earth scientists around understanding how the environment works. And there were a lot of really great people at Dartmouth at that time that influenced bill, and he's carried forward with that work. Bormann, Likens, Johnson, Drake, there's other people in the room here, *** Holmes, and others that really had an influence on Bill in the evolution of this science. And so, what you're going to see today, in part, I think is a legacy of some of the things that Dartmouth has put forth and some of the good work that Bill has done is truly inspired by the faculty that he met here. At Dartmouth, Bill was a leader in the environmental movement at the time. There was the Environmental Studies Division of the Dartmouth Outing Club. And the very first Earth Day was 1970, right, so Bill was a student here. He was one of the principle organizers of Earth Day events at Dartmouth College. And so I tried to find out a little bit more on that, and I ran out of time today, but you have an assignment. If you go to the Rauner Library, Special Collections Library, there's a collection around the Dartmouth Outing Club. And if you pull box 6172, there's a hanging folder in there, and the title is, "William Schlesinger, Articles and Brochure circa 1971-'72." Now, Bill, I have no idea what's in there, if there's anything incriminating or not, but Bill's history is logged and it's recorded in Rauner. So from Dartmouth going on, he was stimulated by his interests in college in biogeochemistry to Cornell. He got his Ph.D. there. Then he took first faculty position at UC Santa Barbara. He was there for not too long. I think we learned last night that his sort of ivy tweed didn't fit in too well with the beach scene at Santa Barbara, and so he came east again. He came to Duke. And he spent 25 plus years at Duke as a faculty member, and then eventually becoming Dean of the School of the Environment, which, as most of us know, is one of the premiere programs in ecology and environmental science in the world. And there at Duke, Bill developed several lines of research that really I think are the hallmarks of his work. One line was around arid lands and the process of desertification and how humans interact with vegetation and soils and waste that accelerate change, change to great ecosystems and less in the ecosystems services that they provide to people. He also became involved as a leader in a very innovative experimental approach to release CO2 into the free atmosphere and look at the response of entire communities to elevated CO2. This was a major technological and scientific breakthrough, and Bill is a major player in this type of work. And all through this was another, the passion of Bill, and we share this, is he loves soil, he likes to dig holes and to collect things and analyze them. And Bill's been really, really a leader in understanding how soils influence the composition of the atmosphere. And this is becoming more and more a critical problem for the future, particularly with warming in the arctic regions. In 2007, Bill left Duke to come east, or left Duke to come north to the Institute, the Cary Institute of Ecosystem Studies. The Cary is a not-for-profit private research center and institute. It is a world center for ecosystem science, and it has been for quite a long time now. They have a 30-year history of doing this. And the Cary is known for its basic research used to solve applied problems. And the Cary provides information. It's an honest broker that provides information for decision makers and policy makers around issues such as clean water, air pollution, and more recently, I think some really neat work is coming out on the role of climate change and its impact on disease in the Northeast. One of the things that Bill has championed at Cary is he's greatly expanded their public outreach and their public education and their science education programs. And if you track Bill's career, you'll see that he's done this in a lot of different ways. He's been a frequent testifier to Congress on climate change-related issues. He's given testimony in various court cases. He's worked with a natural resource defense counsel and others that work hard to protect the environment, and it's always been a big part of Bill's career. His work has been recognized in many, many different ways. He's past president of the Ecological Society of America. He's a fellow of GSA, Geological Society of America, triple AS, the American Association for the Advancement of Sciences, and in 2003, he achieved really the highest honor that we can give to a scientist. He was elected as a member of the National Academy of Sciences. So Bill has, from his days here in organizing Earth Day, has done good. He's gone out into the world and he's advanced science, but he's also advanced the interface between science, education, and policy. So we have to thank him for that. Now, the last thing I want to mention is anyone who's been on one of my graduate committees, I'm always handing them Bill's book for their oral exams. I mean, he has the book. It's called, "Biogeochemistry and Analysis of Global Change." It was published in the late 90s, and it's been the standard for educating students and young scientists about this particular field. I learned last night that the third edition is coming out in January, completely rewritten. I wasn't paid to plug this book, but please pick up a copy. All my students, it'll be required reading, it'll be out in January. But Bill continues to freshen and lead in this synthesis between biogeochemistry and climate change. So Bill's presentation is up here today. It's "New Perspectives on Biogeochemical Cycles." So please join me in a very warm welcome for Bill Schlesinger. [ Applause ] >> Thank you. I think this is working. It's great to be back. I've known Ross for a long time, and that was a wonderful introduction, and he wonderfully stayed off the stories of being in the field together and such things. As Ross said, you know, I have a real fond spot for Dartmouth College for me. I was a birdwatcher when I arrived here, but entering the field of biogeochemistry really happened on the second floor of Gilman, which I sadly hear is going to be torn down or something, now that's going to be painful. But it was working in Bill Reiners' lab, and he really convinced me that, in fact, there was a career other than medicine, that one could make a living, have a good time, make a difference to society being a biogeochemist, and kind of the rest is history. I really caught that and took that to heart, and I've done it now for 40 years or something, so that's a little scary, that's why you're getting this kind of philosophical title today. That said, I would like to argue, and I'd like to have you come out of what I'm about to say today with the feeling that this subject of biogeochemistry, which I call the chemistry of the surface of the Earth, recognizing that biology has such an imprint on that, that as much as my geochemical colleagues would like to have pure geochemistry, if you're dealing with the surface of the Earth, you're really dealing with biogeochemistry. If you want to study the mantle, then you could be a pure geochemist. And beyond that, so many of our environmental problems today, nationally and around the world, deal with changes in the chemistry of our planet that affect biology and feedback on climate in ways that we're worried about, I think we should be very worried about, but in ways in which an understanding of the Earth's chemistry is absolutely essential. It's provided by science, it needs to be delivered to policy makers who hopefully we can entrain to listen to us, and hopefully we can get them to understand what we're saying and to use some of our science as they formulate responses to climate change and nitrogen pollution and the like. So I'm going to argue that biogeochemistry does not embrace, perhaps, all of ecology, but it underpins huge amount of what we're currently seeing happening to our natural systems today. Okay, that said, I want to give you a little bit of retrospective, at least, on how I think about biogeochemistry and hopefully some tools. I know there's a lot of students here that are interested in this field, or interested in incorporating this field interdisciplinarily with what they're doing. And so I want to give you a perspective on some, you know, just some ways in which over the years I have thought about this field and found it useful to progress there. And the first is to say, that if you're dealing with policy makers, the media, students, or your disbelieving colleagues, that if you're a biogeochemist, it doesn't do any harm to put together a cartoon for how the world is working with your particular element. It could be nitrogen, it could be sulfur, it could be phosphorus. I had a student do this for the boron cycle a few years ago, and you know, the individual cycle is not my point here. My point is that you see biology here. Boron is cycling on land and forests that take up boron as a trace element every year and use it biochemically. It's also cycling in the marine biology. There's also a release of boron, in this case, from rock weathering and it flows to the ocean and river flow. Boron returns to the land surface by movements through the atmosphere. And all of this is something that a policy maker can get a hold of. You know, even the most disbelieving of that can see that you've got some natural flows here, and then you've got this thing labeled industrial activity, and then get some idea of the comparison between the two and you can talk to them about that, and it gives you a common basis of communication. I would also say that it's really useful if you've been very carefully, you know, maybe in Antarctica, measuring the flux of something out of soil. And you've got this down to three decimal points per square meter on what the annual flux of nitrous oxide is coming out of the soil. That it's useful to stand back from your field measurements, your primary data, and actually say, well, if that's true, how does it fit into the global cycle for nitrogen. Does it make sense on that, and if it doesn't, then you've got two possibilities. Either you've discovered something really hot, or you might want to check your math, and both of those are worth pursuing. So, with these kinds of cartoons, I think it's interesting to see the effect of the biosphere on the surface of the Earth. I've taken a bunch of major elements here that are important to us. Most, but not all of them, are essential to life. Mercury is kind of an exception in that role. This is the flux in and out of the biosphere every year. That number is 10 to the 12 grams per year. That probably is not the point of this particular slide, except you can calculate the net primary production of the world's land and ocean plants, and calculate how much carbonate they take out of the abiotic environment and fix into plant tissue every year. Now, the important thing is, if you compare that to the sedimentary flux of materials on the surface of the Earth, which, in this case, includes the reaction of carbon dioxide in the atmosphere with rocks and the flow of bicarbonate to the ocean and river flow, so you can sort of compare how much is the biosphere cycling, and how much is moving and would move presumably on an abiotic Earth with no life, and that's what this comparison over here is. I simply took the cartoons, like the one you just saw for boron, and pulled the number for biological cycling off of it, and pulled the number for sedimentary flux off of it, and this really gives you a feeling for, you know, this is the "bio" in biogeochemistry. Life on Earth is dominant, hundreds of times more effective at cycling carbon, nitrogen, phosphorus, than the sedimentary cycle. It's important for sulfur, calcium, iron. It's interestingly important for copper. Copper is kind of a strange, you know, it's not as much as carbon, but it's surprisingly high. And then you look at an element like chlorine, and you see it less than one fraction there, and chlorine is sort of our, I used to call it our dud element, our conservative element. It's something that really, life isn't terribly interested in large quantities, and so it's mostly flowing in the sedimentary cycle as it would on a lifeless Earth. So I would look at this and say, you know, this is prime evidence of the role of biology, why we have a biogeochemistry at the surface of the Earth. Okay, now with that said, we can look at another aspect of this. Here's the same biospheric flux column here, but in addition to that, I've now got this calculation of the anthropogenic flux of the surface. That's the burning of fossil fuels, that's the [inaudible] that you and me and all of our activities that use coal, oil, and natural gas dig up and dig into the crust of the Earth and bring up carbon that would otherwise weather very slowly geologically. We bring it up and oxidize it and get it into the surface cycle. For nitrogen, it's the fixation of nitrogen N2 gas from the atmosphere and a nitrogen fertilizer purposely for the production of fertilizer and explosives. For phosphorus, it's mining. For sulfur, it's actually mostly the inadvertent release in the burning of coal and other sulfur-containing fuels. And so those are the anthropogenic fluxes, and this is an interesting ratio of anthropogenic to sedimentary. This is how much one species, not all of the biospheres as the previous slide, but how much one species, namely *** sapiens, has changed the flux at the surface of the Earth. And you can see for carbon and phosphorus and nitrogen, actually, the contribution is considerable. And, of course, our concern with climate changes all revolves around the fact is that the anthropogenic impact on digging up the crust of the Earth and putting carbon in the atmosphere some 36 times faster than that would happen naturally in a life -- well, in a world without, you know, it's kind of like that book, "The World Without Us." That's this column. This is the difference between a world without us and a world with us. And this last column, this is really *** sapiens versus all the rest of the biosphere. And so we're cycling about 8 percent of the carbon on the surface of the Earth right now. All of the basis of our concern about climate change is based on the fact that one species, namely *** sapiens, is now putting into the atmosphere, I guess advertently, 8 percent more carbon dioxide than would get there every year on a planet without us. And you can see the perturbations of all these cycles. Mercury is, you know, quite, it leaps out here, and of course, there's been a lot of work on mercury at Dartmouth, and that's the concern for it there. So I look at those, I guess my first message of the day today, is that if you're a biogeochemist and you want to participate in the policy arena, or have an effect on the improvement of environment, the cartoons are useful in that you can extract really interesting stuff out of those global pictures, such as in these slides about the human impact and the impact of life, and move forth in that way. They're also not bad if you're going back to your grandmother who wants to know what this field about geochemistry is, and, you know, you can use the cartoon to explain it. Okay, so I want to go into three points of view that illustrate things that I have found useful as a biogeochemist over the years, and all of these, I'll give you some examples of how they've been useful. And the first of these is the recognition that there's really a basic stoichiometry of life as seen in biomass, and it goes back into the 1800s. Robert Redfield looking at Redfield ratios in the ocean certainly, well, he got a name, a ratio named after him for recognizing that. Bill Reiners, shortly after he had left Dartmouth, actually has a huge contribution I'll show in a minute. Sterner and Elser have really been the ones that have articulated this the most broadly in the last few years. So what do we mean by the biogeochemistry of life? I think Reiners' paper here in '86 is one of the best examples of that. And what Bill gathered from the literature was basically the bulk living tissue composition of various taxa of bacteria down here to mammals. There's plants mixed in here. All these are ratioed against phosphorus, so if there was phosphorus here there would be an one in every slot in that column, and this is the amount of carbon per unit phosphorus in angiosperms. Here's carbon, hydrogen, nitrogen per unit phosphorus. And he found that there were fairly predictable ratios that differed between taxa depending on whether they were cellulose or living animal tissue, and whether it was animal tissue that had a lot of bone, or whether it was mostly protein. But you could extract fairly predictable ratios from those data. Now why is this kind of thing useful? Let me give you a hands-on example. Right now human beings are adding a whole lot of nitrogen to the -- this is a picture of global nitrogen cycle -- a whole lot of nitrogen is being added to that cycle on land. It's cycling -- it's always been -- plants have always been taking up nitrogen and incorporating in tissues and dropping it to the surface at the end of the year. Nitrogen has always been arriving in biological fixation. But humans have roughly doubled the amount of nitrogen available on the land surface by our production of nitrogen fertilizer. And it's a huge industry, it's worldwide now, and it's destined to increase as the world's population goes from 7 to 10 billion in the next four decades or so. And so we can ask, what happens to that. And one of the things that's been postulated as happening to that is that it fertilizes, inadvertently, parts of the biosphere word is not spread; in other words, it gets away from the farm fields where you put it and lands in other places where it stimulates the growth of plants. And a number of policy makers have latched onto that and said, that's great, you know, we've got all this fertilizer being used on farm fields. It's going to get to other places. It will stimulate the growth of plants in those other places. It'll take up carbon and solve the climate problem for it. And so you can say, what's the basis of that. I'm going to argue that some stoichiometry needs to be brought to bear on those kinds of arguments. So many of you have probably seen some of these maps. These are gathered by the National Atmospheric Deposition program, of the concentration, in this case, of ammonium in rain falling in the U.S. And you can see that it's highest out here -- so here's a scale of low to high -- highest out here in the Great Plains where a lot of ammonia and urea fertilizer is being used, and that volatilizes out of the soils. And when rain falls in those areas, it has a big concentration of ammonia. So that's almost like having a map of where fertilizer is used. And you can see the concentrations in the Eastern U.S. are much lower. Then you can ask, okay, where, what's the deposition of ammonia. And, of course, you still see a big concentration out here in the Midwest, but basically, as you go back and forth between these two, you can see that that cloud of ammonia has moved east and rained out where it had no intention of being distributed. And sometimes that amounts to about 30 percent of the fertilizer that's used in midwestern cornfields and the like, gets away, moves east, rains out in places like the Cary Institute and stimulates the growth of forests there. This has been used or noticed widely in Europe, as well as the U.S. It's been noticed by lots of people other than me. I have dabbled in various parts of this, but it's been fairly widely anticipated that this might stimulate the growth the plants and take up some carbon. Now, I want to give you an example of where stoichiometry could have been brought to bear in this problem. I'll pick on some Europeans today, because we're now comfortably in New Hampshire, and there may not be any of the coauthors of this paper in the room. But what they noted is that if you look at nitrogen deposition over forests in Europe -- so this was the amount falling from the atmosphere, and this was the amount of plant growth that was seen in those forests and tons of carbon per hectare per year, that there was this wonderful relationship, almost textbook -- in fact, I used to long for graduate students that would bring me .97 R squared to things. So not much response when you have a low amount of nitrogen falling from the atmosphere, and then nearly a linear response as you added more and more nitrogen. The problem, and where stoichiometry should have been brought to bear on this, is the slope of that line is about 500, 500 carbons per unit nitrogen. And that's way in excess, it's about 10 times higher than any value in Bill Reiners' or any other table for the C:N ratio in plant tissue. And so very early on, these workers -- that's why I say, if you find something that differs strongly from published compilations of things, you've got two possibilities -- either you're really onto something or you should check the math. And this paper was resoundingly criticized for ignoring the fact that that stoichiometry was just incompatible with anything we knew about a plant. It would be nice if plants stored 500 carbons to a nitrogen, we might have a policy option for climate change in that thing. But, you know, it should have had some stoichiometric principles brought to bear on it. Unfortunately, it didn't. It got resoundingly criticized in nature and global change biology. And we've now moved on, and what Christy Goodale and Thomas Quinn. Thomas used to be a student here a couple of years ago. Is that his name? Quinn Thomas. Just published a paper that I think brings more rational numbers to the carbon sink that is anticipated from nitrogen deposition. At least in the U.S. with a C:N ratio of, I think, 45, you know, is something that could be believable. Okay, second principle is this. I think biogeochemists need to remember some of the things about oxidation-reduction reactions that you learn in intro chemistry and intro microbiology; various players have been at this for a number of years. Paul Falkowski is one of my current favorites and is an articulate promoter of the importance of realizing that it's not just the content of biomass, which is a little bit static, but you can use the fact that electrons are being transferred in oxidation-reduction reactions to make some predictions about how biogeochemical cycles ought to behave. Okay, so what do I mean by that? This is actually out of the old edition of the book. Ross neglected to say that when the new one comes out, all of you need one for work and one for home, actually. But anyhow, in there you'll find a table like this of oxidation-reduction reactions that talk about each of these as coupled to the oxidation of carbon, so you can do that by aerobic respiration, you can do it by nitrate respiration, which we call denitrification, and that these default downward as the system gets more and more anaerobic. And so you can look at the redux potential there where you expect these to kick in. These are the kinds of things that Dr. Soderberg [phonetic] taught me 40 years ago in intro chemistry. And so there they are. And that's all transfers of electrons. In other words, you can really [inaudible] it out and say, you can't have denitrification where you're producing N2 gas unless it's coupled in an equivalent amount of oxidation and carbon. So what I did a few years ago is put these together in a chart where, across the top, these are things that are moving from oxidized form, for instance, carbon, that column is where carbon is moving from an oxidized form, like CO2 in the atmosphere, to a reduced form, which would be the carbon in cellulose. And so photosynthesis falls in that box. And over here, these are things that are moving from reduced oxidized form, and respiration is in that box. You and me are all in that box. It may not look that way, but we're taking carbon in reduced form that we ate and we're breathing out CO2. We're breathing in oxygen and exhaling and excreting water. And you can put almost all the metabolisms you can think about on that chart. I've now expanded this a little bit and added iron and manganese on this. It gets too complicated for a slide, but iron metabolism and manganese metabolism, and realize that they're coupled here. He's some critters that oxidize sulfur when they find it in reduced form in the environment and reduced nitrogen. You know, carbon is sort of a peripheral part of their life. They use it for building tissue, but the energy reactions are all a sulfur-nitrogen coupling. Jill Mikucki, who I found out last night has now left hallowed Dartmouth, pointed out, to at least a number of us, that many of these are not single organisms that do the coupling, but they can be consortiums of organisms. Here's one that's moving carbon from one form to another doing, coupling that with a redox reaction with sulfur. That is then connected to a redox reaction with iron, and Jill, quite nicely, showed that in a paper in science a few years ago. So you can use these kinds of things. And I want to go back to the nitrogen cycle here in a minute as an example of a problem facing policy makers, maybe slightly behind their concern with climate change right now, but I predict that nitrogen cycling will be the next carbon for us to think about here. Again, we're adding a whole lot of nitrogen to the Earth's land surface. Some of it we may think as being taken up by land plants, and we can make an estimate of that. But I was particularly interested, at this time, in what the change in the rate of denitrification might be globally. And the reason that that was of interest is that if microbes in wet, anaerobic places were converting a lot of the nitrogen that got away from farm fields and places where it's spread around, back to N2, nitrogen gas in the atmosphere, then it's much less of a problem for environmental scientists and managers than the nitrate that runs to the ocean and causes hypoxia in coastal zones. So I was curious. Could we get a global estimate of denitrification, and see what percent of the nitrogen fertilizer added might be going off to the atmosphere in any given year. So here's the denitrification reaction. If you're like me, it's good to have that refresher in front of us. So these organisms are taking up available carbon from the environment and nitrate. They're doing it in anaerobic conditions, and producing N2. That's what a textbook of microbiology will tell you is going on, okay. The interesting thing is that along the way, they produce some intermediates, particularly nitrous oxide. And they do that in a predictable ratio to the amount of nitrogen that's moving through the pathway, as well. And so I look looked at this and said, gee, we might be able to estimate -- it's very hard to estimate the denitrification rate anywhere, because if you put a chamber down, you're trying to measure an increase in nitrogen under that chamber when the background is 78 percent. And if you put it down and fill it with argon or helium or something so that you might be able to see the increase in nitrogen under there, just the slightest leak will mess up your measurement, because it's leaking in from an atmosphere of 78 percent. So it's really tough to get a direct measurement of that, and I was interested, could we estimate the global rate of the change in denitrification indirectly by recognizing that the metabolism is connected to N2O. Okay, so here's nitrous oxide in the atmosphere. It's been measured for a long time. These are actually reasonably old data, but it's increasing the atmosphere. It has an oscillation that looks somewhat like the increase in CO2 in the atmosphere, and it's increasing faster and has higher concentrations in the Northern Hemisphere than the Southern Hemisphere for reasons that have been speculated about all over the map. It's not because there's more dentists' offices in the Northern Hemisphere. This is, in fact, laughing gas, of the dentists' offices. But you know, there is this pattern, and we have a good data set for that. You can also find it in ice cores, and as my token slide for the IGERT Arctic Program here today, I wanted to say something about ice. But various people have drilled through Greenland and Antarctica, taking cores, analyze the bubbles of gas in those cores with depth, and gotten a historical sequence of N2 in the atmosphere from that. Fairly stable at about 290 parts per billion by volume for a long period of time, and then in the late 1800s, about the time we discovered nitrogen fertilizer, it began to increase rather rapidly, and, of course, you lose the top few layers of ice there. But that's an increase of about four teragrams of nitrogen per year in the global atmosphere. Park that number in the corner of your brain here for a second. We'll need to come back to that. And what I was thinking, okay, if we know the world is, world's atmosphere is increasing at that rate, and we know something about a ratio of N2O to the total production of N2 plus N2O and denitrification, could we back out an independent measure of the rise of denitrification. So here we are. This is the map behind it, expect I left a -- there should be one line there. So it's the change in N2 in the atmosphere divided by the ratio of N2O to the total production and denitrification globally, and that ought to give you total denitrification. Mathematicians might rough me around the edges for being that simple about it, but we'll operate that for the moment. I have a -- this is part of being in administration is that you have trouble going into the lab very often, but one thing that you can do easily as an administrator, any of you that go on in this and become department chair or dean or whatever, remember that you can always run to the library and, you know, spend the 15 minutes between appointments and grab a number out of the literature and compile a big, synthetic table of data and try to make something of it. So that's where these came from. These are -- I can show you the full data set if you wish, but these are average ratios with a standard error of the N2O to the total of the two gases, the ratio and production in different soils, ag soils, soils under upland, natural vegetation and wetlands. You'll see under wetlands the denitrification reaction mostly goes all the way to N2, and so only about 8 percent comes off as N2O. In ag and upland soils, you know, the textbooks say denitrification of product is N2, but in some cases, you know, half or more than half is coming off as N2O. And we were able to compile those ratios together, and then I kind of calculated a weighted average. This is the denitrification on land and the ratio in ag soils, plus the denitrification estimated for wetlands and the ratio on wetlands. So the total for land and the weighted average of the two to make the equation balanced. I asked you to remember four teragrams a minute ago, okay. So we had this, this is the weighted average global production of N2O to the total of N2 plus N2O, about .25 percent. Here's the rise in the atmosphere divided by the ratio would suggest that about 17 teragrams is the change, the human-induced change in denitrification globally. Where does that fit? We're currently putting about 150 teragrams on the land surface. We've roughly doubled the normal biological input from nitrogen fixation. And I'm suggesting that about 17 teragrams are now -- that's the delta of the human change in the denitrification rate on a background of about 100, okay. To me, that's relatively small. It means that there's a lot of potential for managing landscapes, particularly wet ones, and the runoff from farm fields to wetlands, to potentially increase denitrification and increase the loss by that pathway as opposed to the losses in some of these other pathways, like river flow and groundwater that create problems for us. So it allowed us, again, using that coupling of biogeochemistry, not just in stoichiometry, but the coupling in the actual reactions, allowed us to make a measurement of something that would be very difficult -- I call it an estimate, let's call it an estimate -- of something that would be very difficult to measure globally. And I put that out as the second of the tools to recommend for all of you. Now, a third aspect of biogeochemical cycles is to not underestimate the power of chelation. And I'm not going to give you an example of this in action, but I want to give you an example of a couple of places where chelation, which I look at as a greater affinity for an element of the periodic table for organic matter than for water, essentially that's my look at that. And a couple of examples. Here's a paper, it's quite old, 1978 out of the literature, that looked at the mean resonance time for elements in sea water as a -- well, this is a -- I got my ordinate and abscissa reserved mentally here. So the vertical axis is the ratio of these elements in seawater versus the ratio of the elemental content of sinking fecal pellets. I don't know who this guy that gathered those data, but it produces a very nice [inaudible]. If you look at elements that are highly concentrated in fecal pellets versus seawater, they have a relatively short resonance time in seawater; iron is a good example of that. If you look at elements that are not strongly adsorbed to fecal pellets or otherwise contained in zooplankton and fecal pellets, like strontium, they have a relatively long resonance time in seawater. And so you can look at that and say the whole transport of things out of the surface ocean to the deep ocean and the sedimentation, a major driver of that is the affinity of these elements to a biological material, in this case, the sinking fecal pellet that might have been produced on the surface. So I'm going to pick on Andy Friedland here. Not pick on you; I'm going to laud your work here. Here's another example of chelation. Of course, we had leaded gasoline. When I was at Dartmouth, my undergraduate project with Bill Reiners was looking at lead in rainfall, falling on Mount Moosilauke, and we're in an era of leaded gasoline, so there was a lot of it. Andy has been studying what happened to all that lead. Where did it accumulate in forests, and have these forests been flushing lead out ever since leaded gasoline stopped being used. So here is the fraction of loss of lead from forest floor. Andy told me if I get this right, fractional loss of lead from the forest floor is a function of over rise and thickness. How much organic matter you've got sitting on the ground in forests that are flushing a lot of lead have relatively low content of slow organic matter on the surface, and ones that have maybe not flushed any lead at all, it's all chelated, absorbed in those organic layers. So you could make a policy relevant prediction, how long will take lead to flush out of the system based on understanding its affinity to bind, adsorb or chelate to organic compounds. So I put that out as a third area that biogeochemists need to think about. Okay, I want to spend a little bit of time here closing up at looking at what we are calling more frequently geoengineering. I think this is something that policy makers are going to have to face. I'm not exactly comfortable with it myself, because I think our track record of big planetary scale manipulations is poor, and the things we might mess up are, you know, they'll take a long time to repair and they may be very distant from where we thought we were having an effect. But these are out there: fertilizing the ocean, putting sulfate aerosols in the stratosphere, you know, various other kinds of ways where we could -- let me be blunt about it -- where we could continue business as usual burning fossil fuels, which makes policy makers happy, and solve the climate warming problem by making the planet more reflective or getting the ocean to take up the CO2. They have a lot of appeal to people that really don't want to make the tough decision, which is stop burning so much fossil fuel and move to alternatives and renewables. But biogeochemists need -- this is a prime example of where we need to be at the table, come to the table, demand being at the table, however you want to do it. So here's a couple of examples. When I was at Duke, *** Barber, a colleague of mine down at the Duke Marine Lab, was very much involved with the ocean iron fertilization project. Here he took this picture off the back of their boat down in the southern ocean and just as winter was coming on. It looks miserable. I don't know, Ross, you probably identify with that kind of cold, gray water. But anyhow, there they are. Here's his result, you know, fertilized and unfertilized with iron, fertilized on the right. Those are the kind of data that I can appreciate, but I suppose you could have cells per cubic centimeter in there, as well. But here's a case where biogeochemists might weigh in on that, and it's interesting to see what we conclude. Suppose we wanted to sequester a billion metric tons of carbon dioxide from Earth's atmosphere, where it might otherwise cause climate change, and store that in the ocean. What would it take? Okay, so that's our goal, a billion metric tons to get into the ocean. Current marine net primary production, about 50 billion metric tons of carbon per year, that's the total photosynthesis of the world's oceans. That number is getting nicely refined from satellite measurements. I'd say that's plus or minus 10 right now, which is a whole lot better than when I was growing up as a biogeochemist. That's in the surface waters. About 15 percent of that sinks to the deep ocean, which is where you want to get it if you're going to store carbon, so that's seven-and-a-half billion metric tons of carbon that has the potential to sink down through the thermocline of the deep ocean. And so if you are sinking at that kind of ratio, and you want to store an extra billion metric tons, you need to transfer about 7 billion metric tons -- excuse me -- you'd need to stimulate a net primary production of about 7 billion metric tons. That's the goal. So some basic stoichiometry. That's the amount of stimulation of net primary production. Here's the iron-to-carbon ratios that have been measured in the lab and by field observations. That's the amount of iron, presumably, it would take, at minimum, to pull this off. And then you can say, well, gee, that's just a tiny fraction of the iron production globally. Maybe this looks pretty good. Don't write down that Schlesinger promoted this today, you know, there's all kinds of things that further need to be considered there. How much CO2 is released mining even this amount of iron and taking it out and spreading it into the ocean. You know, you might sink that much additional carbon to the deep sea, but you might, in the process, release even more CO2 to the atmosphere. And what are the other effects on the marine biosphere that we don't appreciate here in terms of trophic level changes and the like. Well, my point is, is that here's some basic stoichiometry in iron-to-carbon ratio that could be brought to bear, brought to the table in ways that I think are simple enough that policy makers can understand it and maybe deal with it a little bit. Here's one I've messed with more directly. I have done a lot of work, as Ross has said, on soils. I'd now like other people to dig the holes for me, though. That's one thing that happens with time. But I want to take the second question, there's a lot of policy makers who said, could we pay farmers to store carbon in the soil. And, you know, that might be an attractive policy option. To keep burning fossil fuels, we'll store carbon in agricultural soil. So this is a calculation, again, to store a billion tons of carbon in agricultural soils by fertilizing them. Not unreasonable a thing. Current terrestrial net primary production on the land surface, very similar to the ocean surface, about 50 billion metric tons of carbon. That number is even more refined. Preservation ratio is actually less than in the ocean. It's about 8/10 of 1 percent rather than 15. And so to store an extra billion metric tons of carbon in soil would require more than doubling terrestrial net primary production, because you're storing so little of it. Most of it decomposes. That is the result of the effectiveness of aerobic decomposition by fungi and bacteria. So we'd have to have from 50 to 125 billion metric tons of net primary production. Let's say we're not skeptical at this point, and we continue with the calculation. So here's 125 billion metric tons of carbon. Typical carbon and nitrogen ratio and plant matter, you could get that off of Reiners' table, about one nitrogen to 50 carbon requires 2.5 times 10 to the 15 grams of nitrogen as fertilizer every year just to pull it off. And that much -- that should be an N. We're moving that number down here. So 2.5 times 10 to the 15 grams of nitrogen multiplied by .857 grams of carbon released as CO2 per gram of nitrogen fertilizer produced means that you'd be releasing that much carbon dioxide to the atmosphere. Notice it's double what you set out to sequester from the atmosphere. This is a case where biogeochemists, provided they hadn't made this typo in here, could have had a very simple case saying that nitrogen fertilizer in ag lands maybe is not such a good approach to that. So my message today, or I guess there's been three or four of them, we have some tools, cartoons, stoichiometry, coupled biogeochemical reactions, appreciation of chelation, these are all ways in which we could help elucidate how elements move on the surface of the Earth, and we're moving a lot of them. And I said that I think the majority of our environmental problems are going to have some aspect of biogeochemistry impinging on them. We've got geoengineering facing us. I don't think there's a more ripe time for a young person to think about a scientific field than right now if you have a propensity to study this one. I've often said biogeochemistry has come of age in that process. And I think it's also ripe for those of you that want to make, you know, cross the threshold of doing really good science as scientists, but delivering that to the people that are -- I won't say they're demanding it, but they ought to be demanding it, and if they're not demanding it, we ought to deliver it to them whether they want it or not. And that's going to be a fun arena for the next, well, for the foreseeable future. Ross asked me to say a few philosophical words, you know, at this point. That's some of them. Here's a few others, for those of you that are just beginning this field. I would say that one of the premiums I've put on my scientific career is reading really widely. Finding a lot of ideas that we consider new are actually buried in the old literature, and for me, the old literature starts before 1975 in the web of science. And I'm just tickled when I find something, you know, published in 1957 that has the gem of things we're talking about now, because you can put that citation in your paper and it, you know, makes it look like this is this wonderful, scholarly review of things. So I would say read widely, because a lot of things that we consider new are actually old, and there's a huge amount of literature out there, and it's, of course, a really good place to get inspiration. The second one is that no matter what field you go into, there's a real premium on leaving a legacy of new primary measurements that you made. You can't do it all by computer modeling, by metaanalysis of somebody else's data. You know, measure something. Measure something that's never been measured before, and report that and compare it to other things that might have been measured similarly in places. And that leaves a legacy that will never go away. Sure, the analytical techniques will change and presumably get better, but nobody can erase that contribution to what you've done there. Third thing here. I would say if you're faced with a bunch of things to work on, you know, things that tear you in different directions, first of all, work on the thing that you think is the most important, that's a no-brainer. The second thing is to work on the thing that's closest to being finished. And I don't know how many students I've had that have messed up on that one. You know, they'll have five projects, five half-finished manuscripts, and they can't decide which one to finish. And so they work on the one that farthest from being finished, and as a result, nothing gets finished. And so the thing to do is to work on the one that's closest to being finished and move it out, and then start on the next one. Groups are fun. As I was talking to the group I had lunch with today, groups are fun. They can be productive, stimulating. But when I look back at what I've done, I actually have the greatest personal satisfaction on the things where I said, gee, I measured that, I analyzed that, I wrote that up. And you know, that's, if you need that kind of personal satisfaction, realize that that's probably a good way to get it. And my last message is that along the way, I think you need to have some fun in all of this. If you're not having fun, I would suggest even that you pick a different field where you can have fun. Life is too short to not have some fun doing what you're doing, and academics, maximally, allows you to do that, and so why not. And I would also argue that the work we do as biogeochemists is too important, and the time for our results is getting increasingly short. And so you want to make sure that you're fun and productive and deliver good things to what society needs from scientists, and you know, move along. And if you're not doing that, and you're not having fun and being productive and moving fast, then you probably ought to be doing something else. But the fun thing is the one not to forget, because a lot of people, in the course of being a graduate student, it all seems like such a huge labor that, you know, the idea that grad school was fun is often forgotten. I'm going to stop there and would be glad to take some questions. It's great to be back, and I've had the chance to chat with a number of people during the course of the day. What a great building this is, too. I mean, I have a fondness for Gilman, but, I mean, my god, this is just awesome. So, anyhow, great to be back. Thanks for having me. [ Applause ] Question, here we are. >> Yes. Well, you did a good job of closing the loop on chemical fertilizers and how much of a big net contributor to carbon dioxide in the atmosphere that actually is. I understand organic fertilizers and organic soils are much better to sequester carbon than chemical fertilized soils. Have you done the loop for that and what we would get in that gain of maintaining organic -- >> So this is manure. I'll repeat the question. The question is whether organic fertilizers, manures, presumably, are better at sequestering carbon in soils than artificial fertilizers. And you're absolutely right. If you take a pound of nitrogen delivered in manure and a pound of nitrogen delivered in urea produced in a petrochemical plant, the carbon, you know, from the organic fertilizer -- I mean you're adding carbon to start with as part of the manure, so you start ahead of the game that way. However, remember every cow poop has been through a cow, and a whole lot of carbon that, if it hadn't been eaten and passed through the cow that would enter the soil, got respired while it was in the cow. Okay, so I look at using organic fertilizers, that's a good way to dispose of fertilizer, but you've got to also include the carbon that was put into the atmosphere in cow respiration, and that pretty much levels the playing field and it makes inorganic fertilizer just about the same. We actually did some calculations of that a few years ago that I can point you to. Surprised me, actually. But as somebody wrote a letter to science [inaudible], and my response was, you know, as long as cows are heterotrophic, they're not going to be great sources of material to sequester carbon. Andy. >> Bill, twice now you've downplayed other greenhouse gases. In that answer there, you didn't mention methane, which I thought you would. But, my question [inaudible]. My question is about N2O, which you mentioned that denitrification is good. It can reduce nitrate in soil and nitrate in waterways, but you kind of downplayed that fact that N2O is the intermediate product of denitrification, hopefully getting to N2 gas, and lots of times it doesn't get all the way and you end up with increases in N2O and the atmosphere, which is a greenhouse gas. >> Let me add a codicil on my statement here about stimulating denitrification. You'd certainly want to do that in a wetlands where you have the maximum potential, the reaction being carried all the way to N2. If we do it in the kind of habitats that produce a lot of N2O, then we're going -- the N2O has enormous greenhouse warming potential and it will be problematic. So absolutely right, good point. And again, you know, our understanding of whether wetlands or uplands are better comes back to basic biogeochemistry of where the reaction goes most completely to N2. But absolutely right. And I could go on about methane too, but we'll spare you here a little bit. It's in the new edition of the book [laughing]. Other comments, yes, way back there. >> I appreciated that you were talking about conveying biogeochemical cycles to nonscientists and policy makers, and I wondered what advice you would give to early and mature scientists about how to enter that fray. How have you done that, you know, enter the fray of policy and bringing your science to policy. >> So the question, I'll repeat this question. How is it if you're a mid-career, early career scientist and you want to enter an arena where you're contributing to policy and policy makers. So I think there's a variety of ways to do that. And the first thing is to go public in local media -- Op-Eds in your newspaper is a great way to start -- and visits to some of the policy makers and decision makers at your local, state, and even the House Representatives level. They will meet with you, and you can walk in the door and say, we're doing this interesting research at Dartmouth that's relevant to climate change, and you ought to know about what's going on in your district. And so you can get rolling on that, and it requires sort of some momentum. And Op-Ed and local newspaper, most of the elected officials at all levels will read the local newspapers, they're usually looking for their name. But, you know, they'll look for your editorial. And say well, gee, that person over at, you know, biology at Dartmouth is doing some interesting work that I didn't know about, and maybe they could be a witness or something. So it requires a grassroots effort. I've always found it fun to do that, and then once you get on a roll, it begins to come a little bit more easily if people hear you at one thing and talk about it among their friends, provided you're good, you'll get more invitations and get on a roll about it. We were talking at lunch about whether this was a good or a bad thing to do, which is, of course a good question. I don't think there is, for a moment, a substitute of public outreach and policy for good, productive science. Okay, so the currency of the realm for me and for academics is still publication and productive, important, relevant science. The public outreach, I would say, is, it's on top of that, it's something you do because you want to do it for society, and that's kind of fun, and I think you can get a rush doing it. You know, I've been to a bunch of congressional hearings. I have to admit, you walk into the room and there's that table with the water pitchers and the microphones and the elected people are sitting up on high looking down at you and asking -- that's a rush. And the fact that you're there talking about your science makes it all the more fun. So that's kind of a rambling response, but, you know, go for it. And I think you'll find it rewarding, too. And if you don't, you know, then go to the lab and do important interesting things and nobody will complain. Other questions. Yes. >> So you mentioned nitrogen as possibly being the next carbon. And I was wondering how you think that falls into maybe some other essential uplands and, such as phosphorus, which arguably, because of the speed of the cycle, have, could also be [inaudible] and critical to [inaudible]. >> So nitrogen seems to -- we make a lot of artificial nitrogen fertilizer and spread it around, and because nitrate is so soluble, it gets away in places and causes problems where we don't anticipate it. Phosphorus is an interesting case, as well. I would say the problem looming with phosphorus is global supply. It's, you know, it's not clear whether we won't run through the global supply in this century. And most of it is in Morocco, overwhelming part is in Morocco, which means you've got the potential for another cartel, like OPEC, that, you know, it's bad enough to have control of energy, but there's some alternatives to oil. We don't like them and we don't use them very much, but phosphorus, you know, that's in there in essential biochemistry, and crop plants are not going to grow well without it. So if one country has control of it, or we run out, either way, that's a huge problem. I think we're beginning to see the [inaudible] refine the biogeochemical cycle of mercury much better than we had a few years ago, and we can appreciate what the human contribution of the mercury cycle and where that's going and what that's doing. There's a lot of aspects to that that scare me a little bit in terms of, you know, fish consumption of it. So, you know, that's kind of rambling down through the periodic table, but there's other elements that are out there that we need to be concerned about, either from adding too much to the environment or running out perspective. Copper is another one that is potentially in very short supply relative to use. Other comments? Yes. [ Inaudible question ] It was in lowest concentration, so all the other numbers were greater than one. He just picked that as something that produced no fractions. Or no less than, you know, less than one fraction. Yeah, it's just convenient. You could have used silicone or something, yeah. Actually, in a lot of ways, I wish that he had used silicone, but I wasn't in charge of that paper. Yes, back there. >> You said that all of this time, geoengineering, all of these ideas are scary. Do you think they're still worth, are they worth considering and thinking about, or does it just seem like, you know, we're just going to screw everything up. >> Okay, so is geoengineering scary, is it worth considering. You know, I -- in a lot of ways, I don't think we have that choice. I think if we don't consider it, other people are going to consider it, and we need to be ready to deliver the best science to help sort that out. So we may not have the luxury of that. I don't find -- I don't dismiss geoengineering right offhand. You know, adding calcium to watersheds as cleaned up runoff waters in some lakes without, at least seeming to have dramatic negative effects on some ecosystems. So you know, I guess my response to that is they're all worth talking about, but they all need to be evaluated with a full life cycle analysis of the costs and benefits, and in many cases, at that point, you back off and say, let's do something else. Let's -- my voice is about shot. >> What I'd like to say is you've inspired me, Bill. I'd like to offer the Schlesinger Prize to any graduate students. It's a free dinner if you can publish something in the Op-Ed Valley News related to biogeochemistry, I'll buy a dinner for you. So get out there [inaudible] and send those out to the Valley News. And I want to thank Bill very much for a fantastic talk and for a great time. Come back any time. >> It's been fun. [ Applause ]