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LEAFLET 20 • May 2010

Manitou StreamPhoto by Paul Zedler

Improving water quality: Newer, greener approaches Across the nation, 37,099 river-restoration projects cost their proponents and taxpayers an average of over $1 billion per year (Bernhardt et al. 2005). Most had the goal of improving water quality, but only a tiny minority had any monitoring data to allow comparison of benefits to costs—in either dollars or unintended impacts to the environment (ibid.). Among the most degraded rivers and streams are those that flow through urban areas. In Bernhardt’s terminology, urban streams are “disconnected from their floodplains and hyperconnected to their watersheds,” through drainage channels and stormwater pipes. The Arboretum’s Manitou Stream, near the intersection of Nakoma Road and Manitou Way, fits this description. Following are answers to three questions: How would ecologists restore Manitou Stream; how do engineers propose to control stormwater at Manitou Way; and what role will the public and regulators play in evaluating alternative approaches?

How would ecologists enhance ecosystem services in Manitou Stream?

Like many streams that receive pulsed runoff from watersheds covered with impervious concrete, asphalt and shingles, Manitou Stream has the “urban stream syndrome” exemplified by its downcut streambed and dewatered floodplain, caused by urbanization, which in turn alters hydrological conditions by increasing flood peaks and eroding streambeds and banks. Thanks to a grant from UW’s Women in Science and Engineering Leadership Institute, Dr. Emily Bernhardt spoke on campus (22 April 2010) about the nation’s costly and disappointing efforts to improve water quality by removing trees and grading streambanks. She offered her expertise on how best to manage the Arboretum’s Manitou Stream while visiting the

site with Arboretum staff on 23 April 2010. Accompanying her was another noted

stream ecologist, Dr. Bobbi Peckarsky, Emeritus Professor from Cornell U., now Honorary Fellow in Zoology at UW-Madison. How might Manitou Stream be rehabilitated? In North Carolina, Bernhardt’s data for engineered

approaches to abating the urban stream solution indicate an average cost of over $1 million per project, with minimal benefit

(ecosystem services) when they fail to reconnect the stream to its floodplain. Typical projects aim to remove obstructions to flow, grade the banks (which releases sediment during construction), then stabilize streambeds and banks with riprap and turf reinforcement matting. Environmental scientists offer newer, greener and less costly approaches. Dr. Bernhardt envisioned Manitou Stream being easily and cheaply cured of its syndrome. To rebuild the streambed and reconnect the stream to its now-elevated floodplain, she proposed mimicking the activity of beavers by felling trees near the bank, creating multiple dams along the 600-ft stream course, and allowing debris and sediment to accrete and raise the streambed, allowing water to overflow onto its elevated floodplain. That process had already begun behind a tree dam that developed on its own during 2009. A build-up of debris and sediment had elevated the streambed. Bernhardt and Peckarsky saw that the tree dam had been removed recently and predicted that the highly-functional debris deposit and its rich microbial community would be washed away by the next stormwater pulse (which likely happened during that evening’s rainfall). And the rocky riffle (potential habitat for stream invertebrates) that had formed downstream in eddies around the tree dam was likely covered in the released sediment.

How Best to Manage “UrBan streaM syndroMe”

Dr. Emily Bernhardt

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left to right across pages, 1904, 1937, and 2007 maps of Wingra Marsh, draft engineering plan superimposed on Manitou Stream.

Arb map and aerial view of Wingra Marsh

Arboretum staff have proposed similar green approaches for Manitou Stream (ARTF 2010), where the downcut streambed plus the accumulation of 1 to 4 feet of sediment (from inflows and some deliberate filling) has dewatered the floodplain and allowed box elder, cottonwood, and invasive exotic plants to become dominant where herbaceous plant cover (wet meadow?) was once dominant (Loheide Class web archive, Pathak 2009). Bernhardt’s proposed repair would not return the system to its historical condition—such a goal is no longer feasible in a watershed that is “hyperconnected” by drainage ditches and plagued with excess urban stormwater, nutrient discharges, and other human impacts. Her recommended course of action would, however, reverse the current trend of downcutting; it would reconnect the stream to its floodplain; and it would restore valued ecosystem services, such as the retention of sediment and phosphorus, the conversion of nitrates to harmless nitrogen gas, and the reestablishment of wetland vegetation in place of the more drought-tolerant garlic mustard.

How do engineers propose to control stormwater at Manitou Way?

Bernhardt’s vision for reconnecting all of Manitou Stream to its floodplain is not likely to be implemented, despite its “green” approach. Instead, the stream has been scheduled for major surgery under a new plan from Strand Engineering, called for by UW Facilities Planning and Management. Instead of elevating the streambed and reattaching the stream to a floodplain, Manitou Stream will be dammed to create a 2.43-acre retention basin. The principal reason is that the municipality responsible for runoff and low stormwater quality needs “credits” for managing stormwater and in an Intergovernmental Agreement signed in 2009, UW agreed to provide some of those credits by allowing the construction of large retention basins at the Arboretum. Two examples are already in place—a 6-acre basin

in Southeast Marsh and a 7.2-acre treatment system just east of Curtis Prairie. The price tags for retention basins are high--in dollars, as well as in lost conservation land and unintended impacts. Their potential for improving water quality is limited; they are designed primarily to allow suspended solids to settle out of the water column and to reduce and delay peak flood flows. The 2.43-acre retention basin that is planned for Manitou Way would settle out some of the phosphorus carried by the water, i.e., some of that associated with sediment particles, not necessarily the dissolved phosphorus or the phosphorus carried in floating matter, such as leaves from street trees, which add phosphorus to local lakes. Nor do retention ponds provide optimal conditions for nitrogen removal or treatment of other dissolved inorganic and organic contaminants. Taxpayers might wish to ask why, then, are large retention basins considered “best management practices” by WDNR, given their high cost and limited ability to restore ecosystem services? One appeal is that modelers can simulate the deposition of total suspended solids that should settle out and

hence assign “credits” that the City can be allocated towards their requirements under the new water-quality regulations. In other words, big basins make it cheap and easy to make big decisions, so long as no one considers the permanent impacts to Arboretum lands and the cost of perennial management of unintended consequences. High price tags do not guarantee high functionality; in fact, Bernhardt’s search for evidence that engineered streams outperform those restored using greener approaches has yet to turn up convincing evidence that benefits outweigh costs. The environmental costs of large retention basins are increasingly recognized. Building big basins requires big machines that make big messes. When trees are removed and soils disturbed, sediments are mobilized and flow downstream during and after construction. These suspended solids go unmeasured, but they create a debt that takes years to repay before there is a net removal of suspended solids by the big basin (EDF 2002; Bernhardt pers. comm.). The disruption of soil structure and its microbial functions also mobilizes leachates that are filled with nutrients (EDF 2002; Fruebrodt 2009, Virlee 2010) and contaminants, which, although unmeasured during

construction, contribute to the stormwater-treatment debt. The potential biological costs are equally alarming. Large impoundments attract invasive species and provide stepping stones for invaders to reach natural lakes (Johnson et al. 2008). Impounded water becomes anaerobic in the shallow water where cattails will invade. Soil phosphorus that is supposed to be trapped until the basin needs to be dredged can actually be taken up by invasive cattails (Boers and Zedler 2008). Once the phosphorus moves into the cattail leaves, it is free to move downstream as the vegetation breaks apart or forms buoyant litter. Warm, nutrient-rich water also supports algal blooms, some of which are toxic to native wildlife (Sonzoni et al. 1988), and standing water adds habitat for mosquitoes, some of which carry West Nile Virus (Hamer et al. 2009). Impoundments attract children and adults to explore and learn, and they can be marvelous venues for education and research. But impoundments can also be attractive nuisances where children can encounter the hazards associated with deep mud, thin ice, toxic algae, and disease organisms.

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Vertical streambank showing buried wetland soil. Photo: P. Zedler. Debris dam. Photo: P. Zedler.

Secret Pond was constructed in the mid 1980s, and it has collected sediment for ± 25 years.

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ARTF (Adaptive Restoration Task Force). 2010. Restoration of Ecosystem Services: A Plan for Manitou Stream. University of Wisconsin-Madison Arboretum. Madison, Wisconsin.

Bernhardt, E. M. A. Palmer, J. D.Allan, G.Alexander, K. Barnas, S. Brooks, J. Carr, S. Clayton, C. Dahm, J. Follstad-Shah, D. Galat, S. Gloss, P. Goodwin, D. Hart, B. Hassett, R. Jenkinson, S.Katz, G. M. Kondolf, P. S. Lake, R. Lave, J. L.Meyer, T.K. O’Donnell, L. Pagano, B. Powell, E. Sudduth. 2005. Synthesizing U.S. river restoration efforts. Science 308: 636-637.

Boers, A. M., and J. B. Zedler. 2008. Stabilized water levels and Typha invasiveness. Wetlands 28: 676-685.

EDF (Environmental Defense Fund). 2002. Amicus Brief No. 01-1243 filed to the Supreme Court the United States on the Borden Ranch Partnership, Angelo K. Psakopoulos, Petitioners, v. US Army Corps of Engineers, et al., Respondents. PDF available from J. Zedler.

Fruebrodt, Joe. 2009. Analysis of anaerobic topsoil in varying hydroperiods. Botany 699 Directed Study Report for J. Zedler. University of Wisconsin. Madison.

Hamer, G. L., U. D. Kitron, T.L. Goldberg, J. D. Brawn, S. Loss , M. O. Ruiz, D. B. Hayes , and E. D. Walker. 2009. Host selection by Culex pipiens mosquitoes and West Nile Virus amplification. Tropical Medicine and Hygiene 80: 268–278.

IGA (Intergovernmental Agreement). 2009. Intergovernmental agreement to fund a joint stormwater management construction & improvement program within watersheds draining to the University of Wisconsin – Madison Arboretum. UW-Madison Arboretum.

Johnson, P. T. J., J. D. Olden, and M. J. Vander Zanden. 2008. Dam invaders: Impoundments facilitate biological invasions into freshwaters. Frontiers in Ecology and the Environment 6: 357-363.

Loheide, S. 2008. Hydroecologic effects of stormwater inflow to Wingra Marsh. Civil and Environmental Engineering (CEE 619) web archive. University of Wisconsin. Madison. http://hydroecology.cee.wisc.edu/Stormwater/Introduction.html

Pathak, N. 2009. Assessment of the hydroecology of Wingra Marsh at the University of Wisconsin Arboretum. M.S. Thesis, University of Wisconsin. Madison.

Sonzoni, W., W. Repavich, J. Standridge, R. Wedepohl, and J. Vennie. 1988. A note on algal toxins in Wisconsin waters experiencing blue-green algal blooms. Lake and Reservoir Management 4: 281-285.

Virlee, C. 2010. Senior Thesis, Botany Dept., University of Wisconsin. Madison.

This leaflet was prepared by Joy B. Zedler, Aldo Leopold Chair of Restoration Ecology, UW-Madison, in consultation with Dr. Emily Bernhardt (Stream Ecologist and Biogeochemist, Duke University), and Dr. Bobbi Peckarsky (Stream Ecologist, UW-Madison). Funding for Dr. Bernhardt’s visit came from UW’s Women in Science and Engineering Leadership Institute. Layout by Kandis Elliot. The historical aerial photo analysis and research by Nayan Pathak and Dr. Stephen Loheide II is gratefully acknowledged.

References

What role will the public and regulators play in evaluating alternative approaches?

According to federal law (Clean Water Act, Section 404), the evaluation of plans to add “fill” to a water of the US begins with the following “sequencing process.”

• A project must first try to avoid filling that results in significant impacts, usually determined on the basis of the area filled.• If the project cannot avoid filling then it must minimize filling so that significant impacts are reduced to insignificance.• Only if filling cannot be avoided or minimized can filling be permitted. Impacts then need to be compensated with a mitigation plan.

The Arboretum’s Adaptive Restoration Task Force (ARTF 2009) developed a detailed and innovative plan that calls for Manitou Stream to be connected to a restored floodplain (accomplished by removing some of the accumulated sediment), with sandbar willows used to stabilize the streambed and banks and willow trees to stabilize the floodplain. This “green plan” does not require filling. The green plan, however, does not provide stormwater-treatment credits for the City. The fate of the green plan will likely depend on the wishes of the public. Is an environmentally-friendly, connected stream-floodplain system in the public’s best interest? Or is another big basin in the public’s best interest? Under the Clean Water Act, the public is welcome to provide comments and to call for an open hearing to ensure that the above issues are openly addressed.

Draft engineering plan 4/27/2010.

field stone

Tree removal,seedings and plantings

Erosion mat

section across streambed

retention basin

retention basin