PROFILE

Profile of Stephen R. Carpenter hether you are a fisher- man, a kayaker, or just a lover of the outdoors, the sight—and smell—of a scummy,W algae-covered lake may not be particularly appealing. For Stephen R. Carpenter, who is all of the above as well as a renowned lake ecologist, the problems associated with this algae buildup, or eutrophication, go far deeper than simple aesthetics. ‘‘Eu- trophication is a significant environmen- tal problem that can impact humans on a recreational, economic, and even pub- lic health level,’’ says Carpenter, ‘‘and it’s likely to intensify in the coming decades due to increases in human pop- ulation, demand for more food, land conversion, and fertilizer use.’’ Carpenter, the S. A. Forbes Professor of Zoology and Halverson Professor of Limnology at the University of Wiscon- sin–Madison (Madison, WI), has studied freshwater for over 30 years. Stephen R. Carpenter and algae on Lake Mendota, WI. His multitude of research interests in- clude eutrophication, aquatic food webs, nutrient cycling, and ecological econom- outdoors at an early age. Carpenter was an aquatic systems ecologist, and ics. Beyond his research and teaching, spent most of his youth in Bethesda, that field really captured my imagination.’’ Carpenter also has, among other activi- MD. ‘‘It was a much smaller place back Carpenter performed undergraduate ties, served on numerous National Sci- then,’’ he says. ‘‘Bethesda was at the research for Fisher, who specialized in ence Foundation (NSF) advisory panels, urban fringe of DC. Everything beyond stream ecology, and Carpenter pub- been President of the Ecological Society that was rural.’’ His father, Richard, was lished his first paper on the primary of America (2001–2002), and served as a chemist, so there was always a lot of production of macrophytes (rooted the Chair of the Beijer Institute of Eco- science discussion in the household. Af- aquatic plants) in the Fort River of logical Economics Board of Directors ter his father became a staff member Massachusetts (2). Carpenter’s work in (2003–2005). In addition, he works on on the National Academies’ Board on Fisher’s laboratory convinced him to the editorial board of multiple scientific further his ecological research in gradu- journals, including PNAS. Carpenter Environmental Studies and Toxicology, ecology and the environment became a ate school, and after receiving his B.A. was elected to the National Academy of in biology in 1974, Carpenter entered regular part of their conversations. Sciences in 2001. the graduate programs in Botany and Growing up, Carpenter spent many Recently, Carpenter has become in- & Limnology at the summers on his grandfather’s farm in terested in the capabilities and limits of University of Wisconsin–Madison. He forecasting. In his Inaugural Missouri. In between helping with the joined Michael Adams’ laboratory to Article published in this issue of PNAS farm work, he and his cousins found study the role of macrophytes in the (1), he forecasts the long-term impact of time to enjoy the nearby wilderness, phosphorus cycle of lakes. the primary human contributor to lake whether fishing, camping, or just frolick- Graduate research gave Carpenter eutrophication: nonpoint phosphorus ing: ‘‘Boys who are roaming free in a his first exposure to the three fields he pollution. Using Wisconsin’s Lake Men- farm environment find all kinds of inter- would continue to study over the course dota as a model, Carpenter projects the esting things to do.’’ Carpenter thinks of his career: lake science, phosphorus phosphorus concentrations in the water, his transition to an ecologist just cycling, and the emerging field of eco- sediment, and surrounding soils over the stemmed naturally from his youth. ‘‘Hik- . ‘‘My project was part of course of a millennium. The scenarios ing, camping, fishing, and hunting all the follow-on grants to the International predict a need for dramatic change be- come together in ecology,’’ he says. ‘‘I Biological Program,’’ says Carpenter. cause moderate reductions in agricul- was really excited when I discovered ‘‘The [International Biological Program] tural phosphorus will only delay, and there was a way to get paid for being a was, I think it’s fair to say, the first big not prevent, eutrophication. The results scientist outdoors.’’ ecosystem research program funded in also demonstrate the persistence of eu- the United States.’’ trophication. ‘‘In theory, eutrophication Carpenter’s interest in ecology blos- Graduate school also proved to be is reversible,’’ says Carpenter, ‘‘but from somed during his undergraduate educa- personally rewarding for Carpenter. He the perspective of a human lifetime, tion at Amherst College (Amherst, met fellow student Susan Moths, whom once you push a lake over that thresh- MA), where he met a pair of dynamic old, eutrophication is a one-way trip.’’ teachers: Stuart Fisher and Lincoln Brower. ‘‘Fisher and Brower . . . were This is a Profile of a member of the National Academy of From Streams to Lakes very influential and made me think Sciences to accompany the member’s Inaugural Article on Born in Kansas City, MO, in 1952, Car- ecology was just a great thing to do,’’ page 10002. penter was immersed in science and the says Carpenter. ‘‘Fisher, in particular, © 2005 by The National Academy of Sciences of the USA

www.pnas.org͞cgi͞doi͞10.1073͞pnas.0504706102 PNAS ͉ July 19, 2005 ͉ vol. 102 ͉ no. 29 ͉ 9999–10001 Downloaded by guest on September 24, 2021 he married in1979, the same year he from the land.’’ The researchers found investigations began to branch into de- defended his doctoral dissertation. Car- labeled C-13 throughout the food vising strategies to manage the phospho- penter did not take much time to cele- web—in bacteria, plankton, and even rus cycle. This expansion brought him to brate, though—soon after graduation, fish. These findings helped strengthen the interdisciplinary field of ecological he drove from Wisconsin down to South the concept that neighboring economics, which seeks to quantify the Bend, IN, to begin teaching at Notre are interconnected and dependent on relative value of ecosystem services: Dame University. each other. ‘‘Ecosystem services can be defined The case may not be entirely closed, broadly as the valuable things people get Untangling the however. ‘‘One of the big questions in from nature.’’ In terms of lakes, such Carpenter did not leave Wisconsin com- this study is whether the findings hold services include irrigation, fishing, hunt- pletely behind, however. He continued for bigger lakes,’’ Carpenter points out. ing, swimming, and drinking water. to work on lake research at Notre Dame ‘‘These isotope experiments are very Carpenter thus began examining the and carried out most of his studies at expensive, so the lake we studied is only economics of eutrophication. He com- the university’s field station near Land about 2 hectares. We are now doing an pared the benefits lakes provide if they O’ Lakes in Wisconsin. He shifted his experiment in a 30-hectare lake, which remain clean and clear versus the bene- research focus to include plants and ani- is about the largest we can afford.’’ fit factories or farms receive by causing mals, as he began studying how the food eutrophication. The goal of this compar- web structure controls lake ecosystems. Returning to His Roots ison is to find a level of phosphorus in- In 1982, he began collaborating with While Carpenter continued working on put that maximizes benefits to both Jim Hodgson and James Kitchell, two the Trophic Cascades Project after his sides (8). other scientists interested in the dynam- return to the University of Wisconsin in Most recently, Carpenter has devel- ics of lake ecosystems, on the Trophic 1989, Madison’s location and strong lim- oped an interest in ecological forecast- Cascades Project. nology program allowed him to pursue ing, another interdisciplinary field that The goal of this project was to under- other interests. Some of that research seeks to project ecosystem dynamics by stand the dynamics of food webs included examining the accumulation of building models based on past and fu- through large-scale manipulations of polychlorinated biphenyls (PCBs) in fish ture trends. ‘‘Many ecologists are getting entire lakes. One of the early studies and invertebrates in Lake Michigan (7), interested in ecological forecasting involved physically exchanging the bass but a majority involved studying Madi- because it’s a really exciting research and minnow between two son’s Lake Mendota, a 40-km2 body of frontier,’’ says Carpenter. ‘‘Ecologists lakes, creating altered environments water that is one of the most extensively have been talking about it since the late with contrasting top predators. Through studied lakes in the world. One of Car- 1990s, but some of the new tools for these manipulations, the researchers penter’s many projects at Lake Mendota statistical acquisition and modeling open could test the theory that altering the was a renewed interest in the phospho- up whole new opportunities to tackle of the higher levels of a food rus cycle and its role in eutrophication. forecasting-type problems.’’ web could regulate the biomass and pro- Carpenter particularly focused on ‘‘However, the most important chal- ductivity of the plankton (3). nonpoint phosphorus pollution, or pollu- lenge of ecological forecasting is not After 10 years at Notre Dame, Car- tion that does not originate from a spe- the projections themselves,’’ Carpenter penter returned to Madison for a faculty cific source, such as a factory. Most adds. ‘‘They are intellectually interest- position opening in the Department of ing, but they are only part of the job.’’ Zoology. Carpenter was curious about Rather, he believes, accurate assess- the respective contributions of aquatic ‘‘The food web ments of the uncertainties and limits of and terrestrial carbon in supporting a ecological forecasts are the critical chal- lake’s food web. The prevailing theory, of a small lake is lenges facing ecologists. ‘‘Many features first proposed by Stephen Forbes in of change are fundamentally unpredict- 1887, was that lakes were self-sufficient strongly dominated able,’’ he says, ‘‘so a big part of dealing ecosystems. Many ecologists had begun with change is building resilience against to question that theory but could not by the terrestrial the unpredictable and retaining the ca- actually test it because aquatic and ter- pacity to adapt when surprising things restrial carbon are virtually identical in ecosystem.’’ happen.’’ isotopic composition. In his Inaugural Article (1), Carpenter The Trophic Cascades experiments projects the phosphorus levels in the suggested that big fish can regulate car- nonpoint pollution, Carpenter says, water, sediment, and soil around Lake bon fixation and determine whether a comes from agriculture. ‘‘In agricultural Mendota over 1,000 years and how lake acts as a source or a sink of atmo- or dairy watersheds, there’s a tendency these levels would affect eutrophication spheric carbon (4). Together with to import a lot of phosphorus, mostly in status of the lake. He then proposes two Michael Pace, Jonathan Cole, and col- the form of chemical fertilizers or ani- possible management plans that would laborators in Sweden, Carpenter and mal feed,’’ he explains. ‘‘While some reduce the input of soil phosphorus to Kitchell tested the importance of terres- phosphorus does leave the watershed, potentially improve the lake’s condition. trial carbon for lake food webs (5, 6). such as in the form of food, most of it The first plan Carpenter puts forth As it turned out, lakes were not isolated builds up in the soils. And then a small involves balancing the phosphorus bud- communities and were in fact strongly amount runs off to surface water, but it get, such that no more phosphorus is linked to the surrounding environment. doesn’t take very much to cause a lot of introduced into fertilizer than leaves in ‘‘Our results showed that the conven- damage.’’ the form of food products such as meat tional wisdom is inaccurate, and that Carpenter studied how elevated phos- or grain. Although balancing the phos- the food web of a small lake is strongly phorus impacted the Lake Mendota phorus budget may seem like a simple dominated by the terrestrial ecosystem,’’ ecosystem, including its effect on phyto- solution, ‘‘the simulation shows that so says Carpenter. ‘‘Up to 50% of the plankton production, food web struc- much phosphorus is stored in the up- organic carbon in the water comes ture, and water clarity. Carpenter’s land soils that eventually the lake will be

10000 ͉ www.pnas.org͞cgi͞doi͞10.1073͞pnas.0504706102 Zagorski Downloaded by guest on September 24, 2021 driven over a threshold,’’ he explains. In the past decade since receiving the duced a mixed bag of results; although ‘‘This could take as long as 150 years, Pew Fellowship, Carpenter has lent his they concluded that the environment on but once the lake is driven over the voice as a lake expert to bring attention Earth was deteriorating, it was still threshold, water quality is substantially to various ecological issues. In 2001, he treatable (11). ‘‘There are a number of worse and persistently so.’’ helped author a viewpoint paper, along policies that could improve ecosystem In his article, Carpenter also explores with James Clark of Duke University services,’’ says Carpenter, ‘‘and all of a second, more dramatic policy shift for and other prominent scientists, address- them are being practiced somewhere at effectively stopping phosphorus imports. ing the role of ecological forecasting in a large enough scale that you can tell ‘‘Under that more severe scenario [of the decision-making process (9). The that they work. Unfortunately none of stopping agricultural import],’’ says Car- same year, he and other international the policies are being practiced at the penter, ‘‘the lake gets no worse and scientists coauthored another paper scale needed to improve global ecosys- begins to make a smooth recovery, al- highlighting the dangerous losses of re- tem services by 2050.’’ though it does take a long time.’’ silience that make ecosystems vulnerable Carpenter plans to do what he can to Carpenter adds that his simulations to rapid and severe degradation (10). help implement some of those policies, only considered agricultural phosphorus Carpenter points out that lakes often do and he also plans to remain active in input. In practice, humans could take not undergo a steady progression from ecosystem forecasting and ecosystem other measures, such as installing buffer clear to eutrophic, and instead they can strips to absorb phosphorus or erecting exist in two stable states, clear or turbid, management. ‘‘I think that ecologists structures to retard erosion, which could separated by an unstable intermediate. have a tremendous role in understand- speed up the recovery process. Although Currently, many lakes are stressed to ing change,’’ he says. ‘‘We are on the he does not know how many of these levels near the unstable point. ‘‘A big brink of some very big changes in the measures are feasible, he says that at a runoff event, like an extremely wet sum- way ecosystems function and in the way minimum some change is needed: ‘‘We mer or a big thunderstorm, could come people relate to ecosystems.’’ He notes can’t simply continue with the status along and quickly tip the balance,’’ he that findings from the Millennium Eco- quo. That basically writes off water says ‘‘It’s essentially an accident waiting system Assessment showed that recent quality.’’ to happen.’’ environmental changes influenced by In June 2001, Carpenter undertook humans are some of the fastest seen in A Call for Change his largest ecological forecasting project history, and future changes might be Although his Inaugural Article and by taking part in the Millennium Eco- faster still. ‘‘While some of these other recent projects focus on Lake system Assessment, an international, changes may be beneficial, many others Mendota, Carpenter believes his models multipartner-funded program launched can be potentially threatening.’’ are applicable to lakes around the by the United Nations. ‘‘The goal of this ‘‘We simply have to change the way world: ‘‘I became quite active in study- program was to understand globally the we do business in managing ecosys- ing eutrophication globally, and that status, trends, and plausible futures of tems,’’ he adds, ‘‘and in that regard sparked my interest in global phospho- ecosystem services,’’ he says. Carpenter ecosystem ecologists have an opportu- rus cycles and the ways that large-scale served as cochair for the Scenarios nity and responsibility to work with poli- management of phosphorus is affecting Working Group: ‘‘We were charged cymakers and scientists from other lakes.’’ In 1995, he had an opportunity with looking up to 50 years in the future disciplines to make those changes as to pursue this interest when he received and projecting what the situation for constructive as possible. We’re either a Pew Fellowship in Conservation and ecosystem services might be under going to make changes on our own or the Environment. ‘‘That fellowship al- various assumptions about changes in get some hard ones forced on us by lowed me to look very broadly at lake global policy, demographics, [and] nature, and the former is much more degradation and causes of environmen- global governance.’’ preferable, in my opinion.’’ tal problems,’’ he says, ‘‘and it was a After 5 years of information gathering real switch point in my career.’’ and research, the Scenarios team pro- Nick Zagorski, Science Writer

1. Carpenter, S. R. (2005) Proc. Natl. Acad. Sci. USA 5. Pace, M. L., Cole, J. J., Carpenter, S. R., Kitchell, 8. Carpenter, S. R., Ludwig, D. & Brock, W. A. 102, 10002–10005. J. F., Hodgson, J. R., Van de Bogert, M., Bade, (1999) Ecol. Appl. 9, 751–771. 2. Fisher, S. G. & Carpenter, S. R. (1976) Hydrobio- D. L., Kritzberg, E. S. & Bastviken, D. (2004) 9. Clark, J. S., Carpenter, S. R., Barber, M., Collins, logia 47, 175–187. Nature 427, 240–243. S., Dobson, A., Foley, J., Lodge, D., Pascual, M., 3. Carpenter, S. R., Kitchell, J. F, Hodgson, J. R., 6. Carpenter, S. R., Cole, J. J., Pace, M. L., Van de Pielke, R., Jr., Pizer, W., et al. (2001) Science 293, Cochran, P. A, Elser, J. J., Elser, M. M., Lodge, Bogert, M., Bade, D. L., Bastviken, D., Gille, C., 657–660. D. M., Kretchmer, D., He, X. & von Ende, C. M. Hodgson, J. R., Kitchell, J. F. & Kritzberg, E. S. 10. Scheffer, M., Carpenter, S., Foley, J., Folke, C. & (1987) Ecology 68, 1863–1876. (2005) Ecology, in press. Walker, B. (2001) Nature 413, 591–596. 4. Schindler, D. E., Carpenter, S. R., Cole, J. J., 7. Stow, C. A., Carpenter, S. R., Eby, L. A., Amrhein, 11. Millennium Ecosystem Assessment (2003) Ecosys- Kitchell, J. F. & Pace, M. L. (1997) Science 277, J. F. & Hesselberg, R. J. (1995) Ecol. Appl. 5, tems and Human Well-Being: A Framework for 248–251. 248–260. Assessment (Island Press, Washington, DC).

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