C H A P T E R

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Understanding EcosystemEffects of Dams

Emily H. StanleyUniversity of Wisconsin, Madison

As with most environmental problems, understanding the effects of dams on rivers,and how to manage these structures as they age, is a multifaceted challenge that moveswell beyond the traditional bounds of ecological research. My involvement with thisproblem began with a strictly academic curiosity about how rivers and streams work.In particular, I have had a long-standing interest in how nutrients are transported andtransformed as they move downstream, and saw dam removal as an opportunity to gainsome new insights into this question. But this path led me into far broader environmentalissues that included the practical challenges of dealing with dams that are getting oldand literally falling apart, environmental policy debates, and the reactions of individualsand communities faced with the prospect of removing a dam from a river. In the end, thecomplexities of dam removal provided me with a remarkable experience that updatedmy personal definition of ecosystem science.

When I arrived in Wisconsin in 1998, I learned about a plan to remove a series of damsfrom the Baraboo River, a mid-sized river that travels through farmlands and a series ofsmall towns and cities before flowing into the Wisconsin River. One dam had recently beenremoved, and the remaining three structures were to be taken out over the next three to fiveyears. At the time, my research interests were being influenced by the nutrient spiralingconcept (Webster and Patten 1979; Newbold et al. 1981; Box 5.2), which was the focus ofenormous research in stream ecology at the time (e.g., LINX), as well as my graduate workin Sycamore Creek, Arizona. As a desert stream, ecological dynamics of Sycamore Creek arestrongly affected by disturbances in the form of flash floods and drying (and later, we wereto learn, also by the presence of cattle; see Fisher et al. 1982; Stanley et al. 1997; Heffernan2008). As a recent arrival at University of Wisconsin and an “academic grandchild” of GeneLikens, I also had a strong appreciation for the power of whole-ecosystem experiments.

253Fundamentals of Ecosystem Science. © 2013 Elsevier Inc. All rights reserved.

Forest cutting at Hubbard Brook and food web manipulations in Peter, Paul, andTuesday Lakes were potent examples of simple but large-scale manipulations used toexamine and develop core concepts in ecosystem science (nutrient cycling and the smallwatershed concept in the first case, the trophic cascade in the latter). These various influ-ences came together in thinking about dam removal. I realized I could use the removal asa whole-ecosystem experiment to study disturbance and nutrient spiraling. My plan wasto test the nutrient retention hypothesis of Vitousek and Reiners (1975)—that nutrientretention increased, then decreased over time following disturbance in forests as a func-tion of changes in net biomass increment. This model had been successfully tested inSycamore Creek by Nancy Grimm (1987), and I wondered if it would be a robust modelthat could fit a vastly different sort of disturbance.

This is where I started—all business about ecosystem concepts and experiments.But this single motivation did not stand alone for long. I quickly learned that rather thanbeing a simple, elegant manipulation in a protected research setting, removing a damwas a complicated, emotional, and very public process. It became apparent that there wasa real problem at hand—what to do with these old dams that were falling apart. Therepair-or-remove decision needed to be informed by some knowledge of what happensfollowing a removal, and that information simply was not available. I started gettingphone calls from managers, advocacy groups, and concerned citizens asking me aboutthe best course of action and what to expect if a dam was removed. It is probably not sur-prising to report that callers were not terribly interested in nutrient spiraling. They hadmuch more practical questions about how the plants and animals in and around the riverwould be affected, and what the river would look like after the dam was extracted(Figure 14.1). At the same time, an adventurous graduate student from Purdue, MartinDoyle, who was also interested in dam removal as a whole-ecosystem experiment (in hiscase, for testing geomorphic concepts), called and asked if he could collaborate with meon planned removals in Wisconsin.

The collaboration between fluvial geomorphology and ecosystem science was, frankly,extremely fortuitous. The contribution of both perspectives was essential to the successof our research. Studying dam removal from a strictly ecological perspective would haveprovided an incomplete story, missing perhaps the most critical element: the fate of thesediments trapped in the reservoir and the changes in channel form above and belowthe dam. We learned that how the sediments moved not only determined the appearanceof the river, it also shaped a wide range of ecological patterns playing out in the weeksand years after the removal. And over the long term, biotic (in particular, plant establish-ment and growth) and geomorphic processes are inextricably linked (Doyle et al. 2003a)and mutually influential. Studying only the physical changes following dam removalwould have meant that many of the broader ecological changes of interest to managersand stakeholders would have been missed, and conversely, focusing purely on biologicalvariables would have severely limited our ability to understand why the changes weobserved were occurring.

While it is reasonable to say that my practice and perspective of ecosystem sciencematured substantially through this research to include interactions with other disciplinesand attention to questions driven by practical needs, the basic strategy of using damremovals as whole-ecosystem experiments proved to be successful. This management

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254 EMILY H. STANLEY

action provided us with the planned (and later, by studying more removals, replicated)opportunity to examine changes in nutrient retention, as well as channel form followingthe removal disturbance. But instead of focusing on the Vitousek and Reiners hypothesis,we developed and tested a new model that emphasized how changing geomorphic formand process alters nutrient retention (Figure 14.2; Stanley and Doyle 2002; Doyle et al.2003b; Orr et al. 2006). The geomorphology-nutrient retention relationship was massivelyamplified in the extreme case of dam removal, but we are learning that it also applies toless extreme cases, and can help explain differences in nutrient dynamics across differentsites (e.g., see Lewis et al. 2006; Kaushal et al. 2008). No doubt there are any number ofother similar whole-ecosystem “experiments” that are now under way that could providebasic ecological insights as well as practical information about ecosystem management.

Another concept from ecosystem science also provided us with important and unex-pected inspiration for our dam removal research. One of the earliest lessons I had learnedabout studying ecosystems was the simple importance of looking at the big picture andfiguring out what is and is not important. For example, in constructing nutrient budgets, we

(a) (b)

(c) (d)

FIGURE 14.1 Changes in the reservoir of Koshkonong Creek before (a) and 24 hours (b), 2 months (c), and8 months (d) after removal of the low-head dam. (Modified from Doyle et al. 2003b.)

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25514. UNDERSTANDING ECOSYSTEM EFFECTS OF DAMS

can safely ignore some pools and fluxes if they are small without losing track of the largerpicture of the budget. Put more generally, stepping back to look at the big picture leads usto ask the general question, how important is the process or phenomenon being studied?When we began our work, there was already a rich literature on the effects of dams on riv-ers, but the vast majority of these studies dealt with great huge dams, such as those thatpopulate virtually all the rivers in the western United States. Yet dams in the more topo-graphically challenged Midwest tend to be small structures, and these lesser dams and theirreservoirs have attracted little attention from aquatic researchers. This led me to begin to tryto figure out just how many dams there were in Wisconsin, where they were, how big theywere, and whether dam removal was affecting the population of dams in the state.

One of the first things I learned in answering this question was that the abundance ofwhat I now think of as “little dinky dams”—that is, small structures in small and midsizedrivers—vastly outnumber the larger, grossly conspicuous structures that reach theirextreme types in Hoover, Aswan, and Three Gorges dams. While there is no discounting

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Stage Process Channel form

A P removal Reservoir

B Dewatering Reservoir

C Incision Narrow, deep

D Degradation, mass wasting Wider, shallower

E Aggradation, widening Wide, shallow

F Quasi-equilibrium Complex, vegetated

A B C

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tion FIGURE 14.2 Conceptual model of

the stages of geomorphic adjustmentsin channel form within a reservoir fol-lowing dam removal (left). Stages ofchannel adjustment are associatedwith predictable changes in sedimenterosion and deposition (export) andcross-sectional channel form (wettedwidth; right). In turn, we hypothe-sized that these physical changes inprocess and form should dictate phos-phorus retention or transport as waterflows through the reservoir reach.Particulate phosphorus export shouldbe tightly tied to sediment export, andthe degree of sediment�water contactshould affect dissolved inorganicphosphorus removal from the watercolumn; i.e. phosphorus retention.(Modified from Doyle et al. 2003b andStanley and Doyle 2002.)

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256 EMILY H. STANLEY

of the immense consequences of these massive dams and their role in fundamentally alter-ing large rivers, the ubiquity of these smaller dams suggests an equally large impact onrunning waters that we are only just now beginning to quantify. Put another way, thisaccounting of the dams in Wisconsin waterways emphasized how effective human engi-neering has been at reconfiguring flowing water systems, and how we as ecologists arestill coming to terms with the actual structure of streams and rivers—not necessarily a lin-ear feature in the landscape, but an interrupted series of channels and pools connectedtogether to form complex networks that change shape over time. Doyle et al. (2008) tookthis analysis a step further to demonstrate that the amount of infrastructure across theUnited States, including dams and railroads, has grown rapidly since World War II, and isnow aging; these structures are increasingly in need of repair or removal. The intersectionof aging and environmental degradation may present an opportunity to kill two birdswith one stone—that is, strategic removal of aging infrastructure may provide an excellentopportunity for ecosystem restoration (Doyle et al. 2008).

I think much of our success in studying dam removal, and providing some usefulinformation to managers and stakeholders faced with the decision to keep or removea dam, reflects the openness of ecosystem science to include anything, and the practicallesson that ecosystems are often best studied by collaborations of researchers from differ-ent disciplines. Finally, despite the fact that our research was strongly influenced by theneed for practical answers to a pressing management problem, drawing on basic ecosys-tem concepts and blending physical and ecological perspectives provided the foundationfor our best successes.

References

Doyle, M.W., Selle, A.R., Stofleth, J.M., Stanley, E.H., Harbor, J.M., 2003a. Predicting the depth of erosion follow-ing dam removal using a bank stability model. Int. J. Sediment Res. 18, 128�134.

Doyle, M.W., Stanley, E.H., Harbor, J.M., 2003b. Hydrogeomorphic controls on phosphorus retention in streams.Water Resour. Res. 39, 1147. doi: 10.1029/2003WR002038.

Doyle, M.W., Stanley, E.H., Havlick, D., Kaiser, M.J., Steinbach, G., Graf, W., et al., 2008. Aging infrastructure andecosystem restoration. Science 319, 286�287.

Fisher, S.G., Gray, L.J., Grimm, N.B., Busch, D.E., 1982. Temporal succession in a desert stream ecosystem follow-ing flash flooding. Ecol. Monogr. 52, 93�110.

Grimm, N.B., 1987. Nitrogen dynamics during succession in a desert stream. Ecology 68, 1157�1170.Heffernan, J.B., 2008. Wetlands as alternative stable state in a desert stream. Ecology 88, 1261�1271.Kaushal, S.S., Groffman, P.M., Mayer, P.M., Striz, E., Gold, A.J., 2008. Effects of stream restoration on dentrifica-

tion in an urbanizing watershed. Ecol. Appls. 18, 789�804.Lewis, D.B., Schade, J.D., Huth, A.K., Grimm, N.B., 2006. The spatial structure of variability in a semi-arid, fluvial

ecosystem. Ecosystems 9, 386�397.Newbold, J.D., Elwood, J.W., O’Neill, R.V., Van Winkle, W., 1981. Measuring nutrient spiraling in streams. Can. J.

Fish. Aquat. Sci. 38, 860�863.Orr, C.H., Rogers, K.L., Stanley, E.H., 2006. Channel morphology and P uptake following removal of a small dam.

J. N. Am. Bentholog. Soc. 25, 556�568.Stanley, E.H., Fisher, S.G., Grimm, N.B., 1997. Ecosystem expansion and contraction in streams. BioScience 47,

427�435.Stanley, E.H., Doyle, M.W., 2002. A geomorphic perspective on nutrient retention following dam removal.

BioScience 52, 693�701.

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25714. UNDERSTANDING ECOSYSTEM EFFECTS OF DAMS

Vitousek, P.M., Reiners, W.A., 1975. Ecosystem succession and nutrient retention: A hypothesis. BioScience 25,376�381.

Webster, J.R., Patten, B.C., 1979. Effects of watershed perturbation on stream potassium and calcium dynamics.Ecol. Monogr. 49, 51�72.

258 EMILY H. STANLEY

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