Linking land use, in-stream stressors, and biological condition to infer causes of regional ecological impairment in streams

Vander Laan, J.J., C.P. Hawkins, J.R. Olson, and R.A. Hill, 2013: “Linking land use, in-stream stressors, and biological condition to infer causes of regional ecological impairment in streams.” Freshwater Science, v. 32, pp. 801-820, doi: 10.1899/12-186.1.

We used field-derived data from streams in Nevada, USA, to quantify relationships between stream biological condition, in-stream stressors, and potential sources of stress (land use). We used 2 freshwater macroinvertebrate-based indices to measure biological condition: a multimetric index (MMI) and an observed to expected (O/E) index of taxonomic completeness. We considered 4 categories of potential stressors: dissolved metals, total dissolved solids, nutrients, and flow alteration. For physicochemical factors that varied predictably across natural environmental gradients, we quantified potential stress as the site-specific difference between observed (O) and expected (E) levels of each factor (O–Estress). We then used 2 sets of Random Forest models to quantify relationships between: 1) biological condition and potential stressors, and 2) stressor values and land uses. The 2 indices of biological condition were differentially responsive to stressors, indicating that no single measure of biological condition could fully characterize assemblage response to stress. Total dissolved solids (as measured by electrical conductivity [EC]) and metal contamination were the stressors most strongly associated with biological degradation. The most likely sources of these stressors were agriculture, urban development, and mining. Our findings highlight the need to develop EC criteria for streams. Measures of biological condition and stress that account for natural variability should reduce errors of inference and increase confidence in causal analyses. This approach will require development of robust models capable of predicting physical and chemical reference conditions. Causal analyses for individual sites require appropriate hypotheses about which stressors and what levels of stress can cause biological degradation. Our study demonstrates the usefulness of field data collected from multiple sites within a region for developing these hypotheses.

Subscription Required

Ecologically relevant geomorphic attributes of streams are impaired by even low levels of watershed effective imperviousness

Vietz, G.J., M.J. Sammonds, C.J. Walsh, T.D. Fletcher, I.D. Rutherfurd, and M.J. Stewardson, 2013: “Ecologically relevant geomorphic attributes of streams are impaired by even low levels of watershed effective imperviousness.” Geomorphology, doi: 10.1016/j.geomorph.2013.09.019.

Urbanization almost inevitably results in changes to stream morphology. Understanding the mechanisms for such impacts is a prerequisite to minimizing stream degradation and achieving restoration goals. However, investigations of urban-induced changes to stream morphology typically use indicators of watershed urbanization that may not adequately represent degrading mechanisms and that commonly focus on geomorphic attributes such as channel dimensions that may be of little significance to the ecological goals for restoration. We address these shortcomings by testing if a measure characterizing urban stormwater drainage system connections to streams (effective imperviousness, EI) is a better predictor of change to ecologically relevant geomorphic attributes than a more general measure of urban density (total imperviousness, TI). We test this for 17 sites in independent watersheds across a gradient of urbanization. We found that EI was a better predictor of all geomorphic variables tested than was TI. Bank instability was positively correlated with EI, while width/depth (a measure of channel incision), bedload sediment depth, and frequency of bars, benches, and large wood were negatively correlated. Large changes in all geomorphic variables were detected at very low levels of EI (< 2–3%). Excess urban stormwater runoff, as represented by EI, drives geomorphic change in urban streams, highlighting the dominant role of the stormwater drainage system in efficiently transferring stormwater runoff from impervious surfaces to the stream, as found for ecological indicators. It is likely that geomorphic condition of streams in urbanizing watersheds, particularly those attributes of ecological relevance, can only be maintained if excess urban stormwater flows are kept out of streams through retention and harvesting. The extent to which EI can be reduced within urban and urbanizing watersheds, through techniques such as distributed stormwater harvesting and infiltration, and the components of the hydrologic regime to be addressed, require further investigation.

Subscription Required

A decade of geomorphic and hydraulic response to the La Valle Dam Project, Baraboo River, Wisconsin

Greene, S.L., A.J. Krause, and J.C. Knox, 2013: “A decade of geomorphic and hydraulic response to the La Valle Dam Project, Baraboo River, Wisconsin.” Journal of the American Water Resources Association, doi: 10.1111/jawr.12100.

We investigate stream response to the La Valle Dam removal and channel reconstruction by estimating channel hydraulic parameter values and changes in sedimentation within the reservoir. The designed channel reconstruction after the dam removal included placement of a riffle structure at the former dam site. Stream surveys undertaken in 1984 by Federal Emergency Management Agency and in 2001 by Doyle et al. were supplemented with surveys in 2009 and 2011 to study the effects of the instream structure. We created a model in HEC-RAS IV and surface maps in Surfer© using the 1984, 2009, and 2011 surveys. The HEC-RAS IV model for 2009 channel conditions indicates that the riffle structure decreases upstream channel shear stress and velocity, causing renewed deposition of sediment within the former reservoir. We estimate by 2009, 61% of former reservoir sediments were removed during dam removal and channel reconstruction. Between 2009 and 2011 renewed sedimentation within the former reservoir represented approximately 7.85% of the original reservoir volume. The HEC-RAS IV models show the largest impacts of the dam and riffle structure occur at flood magnitudes at or below bankfull. Thus, the riffle and the dam similarly alter channel hydraulics and sediment transport. As such, our models indicate that the La Valle Dam project was a dam replacement rather than a removal. Our results confirm that channel reconstruction method can alter channel hydraulics, geomorphology, and sediment mobility.

Subscription Required

Restoring aquatic ecosystem connectivity requires expanding inventories of both dams and road crossings

Januchowski-Hartley, S.R., P.B. McIntyre, M. Diebel, P.J. Doran, D.M. Infante, C. Joseph, and J.D. Allan, 2013: “Restoring aquatic ecosystem connectivity requires expanding inventories of both dams and road crossings.” Frontiers in Ecology and the Environment, v. 11, pp. 211-217, doi: 10.1890/120168.

A key challenge in aquatic restoration efforts is documenting locations where ecological connectivity is disrupted in water bodies that are dammed or crossed by roads (road crossings). To prioritize actions aimed at restoring connectivity, we argue that there is a need for systematic inventories of these potential barriers at regional and national scales. Here, we address this limitation for the North American Great Lakes basin by compiling the best available spatial data on the locations of dams and road crossings. Our spatial database documents 38 times as many road crossings as dams in the Great Lakes basin, and case studies indicate that, on average, only 36% of road crossings in the area are fully passable to fish. It is therefore essential that decision makers account for both road crossings and dams when attempting to restore aquatic ecosystem connectivity. Given that road crossing structures are commonly upgraded as part of road maintenance, many opportunities exist to restore connections within aquatic ecosystems at minimal added cost by ensuring upgrade designs permit water flow and the passage of fish and other organisms. Our findings highlight the necessity for improved dam and road crossing inventories that traverse political boundaries to facilitate the restoration of aquatic ecosystem connectivity from local to global scales.

Subscription Required

Damned if you do, dammed if you don’t: Debates on dam removal in the Swedish media

Jørgensen, D., and B.M. Renöfält, 2013: “Damned if you do, dammed if you don’t: Debates on dam removal in the Swedish media.” Ecology and Society, v. 18, doi: 10.5751/ES-05364-180118.

Dam removal is an increasingly common practice. Dams are removed for various reasons, with safety, economics, and ecosystem restoration being the most common. However, dam removals often cause controversy. Riparian land owners and local communities often have a negative view of removal, and their reasons vary. It may be the loss of recreational benefits such as swimming and boating, loss of cultural and historical context tied to the dam, or fear that removal may have a negative effect on aesthetic values. Because controversies are often picked up by local media, and media in itself is an important channel to build support around a cause, the way in which dam removals are reported and discussed in the media is likely to influence the debate. Here, we examine the ways in which proponents and opponents of dam removal frame the services provided by two contrasting ecosystems, i.e., an existing dam and the potential stream without a dam, by performing a media discourse analysis of the reasons given for removal and the reasons presented for the dam to remain in place. Our source material includes Internet-based newspaper articles and their associated public comments in four dam removal controversies in Sweden. Our analysis indicates that public opposition is not based on knowledge deficiency, where more information will lead to better ecological decision-making, as is sometimes argued in dam removal science; it is instead a case of different understandings and valuation of the environment and the functions it provides.

Open Access

Selection, implementation and cost of restorations in lowland streams: A basis for identifying restoration priorities

Kristensen, E.A., A. Baattrup-Pedersen, P.N. Jensen, P. Wiberg-Larsen, and N. Friberg, 2012: “Selection, implementation and cost of restorations in lowland streams: A basis for identifying restoration priorities.” Environmental Science and Policy, v. 23, pp. 1-11, doi: 10.1016/j.envsci.2012.06.013.

Restorations have been conducted in Danish lowland streams for almost 30 years to combat the poor physical conditions resulting from decades of channelisation, flood plain drainage and other impacts. Despite this effort, the recently drafted River Basin Management Plans show that physical improvements are still required in more than 7000 km of stream in order to comply with the Water Framework Directive. In this study we used published studies and expert knowledge to describe the restoration approaches most likely to achieve the environmental goals. In addition, we collected information about the economic costs of the different restoration approaches based on Danish experiences. For heavily impacted lowland streams (channelised and deeply incised streams) we described only two different restoration methods, both of which are relatively expensive. For lesser impacted streams (channelised but not deeply incised streams) we described six different options for improving ecological quality, varying significantly in cost. Our analysis showed that the cost may increase dramatically if several remedial actions are required or if land owners are entitled to large monetary compensations. Consequently, stream managers face an important challenge in the future prioritisation of restoration efforts aimed to obtain ecological improvements within tight budgets. The information presented in this paper can help the decision-making of managers.

Subscription Required

Is urban stream restoration worth it?

Kenney, M.A., P.R. Wilcock, B.F. Hobbs, N.E. Flores, and D.C. Martínez, 2012: “Is urban stream restoration worth it?” Journal of the American Water Resources Association, v. 48, no. 3, pp. 603-615, doi: 10.1111/j.1752-1688.2011.00635.x.

Public investment in urban stream restoration is growing, yet little has been done to quantify whether its benefits outweigh its cost. The most common drivers of urban stream projects are water quality improvement and infrastructure protection, although recreational and aesthetic benefits are often important community goals. We use standard economic methods to show that these contributions of restoration can be quantified and compared to costs. The approach is demonstrated with a case study in Baltimore, Maryland, a city with a legal mandate to reduce its pollutant load. Typical urban stream restoration costs of US$500-1,200 per foot are larger than the cost of the least expensive alternatives for management of nitrogen loads from stormwater (here, detention ponds, equivalent to $30-120 per foot of restored stream) and for protecting infrastructure (rip-rap armoring of streambanks, at $0-120 per foot). However, the higher costs of stream restoration can in some cases be justified by its aesthetic and recreational benefits, valued using a contingent valuation survey at $560-1,100 per foot. We do not intend to provide a definitive answer regarding the worth of stream restoration, but demonstrate that questions of worth can be asked and answered. Broader application of economic analysis would provide a defensible basis for understanding restoration benefits and for making restoration decisions.

Subscription Required

Compensatory mitigation for streams under the Clean Water Act: Reassessing science and redirecting policy

Doyle, M.W., and F.D. Shields, 2012: “Compensatory mitigation for streams under the Clean Water Act: Reassessing science and redirecting policy.” Journal of the American Water Resources Association, v. 48, no. 3, pp. 494-509, doi: 10.1111/j.1752-1688.2011.00631.x.

Current stream restoration science is not adequate to assume high rates of success in recovering ecosystem functional integrity. The physical scale of most stream restoration projects is insufficient because watershed land use controls ambient water quality and hydrology, and land use surrounding many restoration projects at the time of their construction, or in the future, do not provide sufficient conditions for functional integrity recovery. Reach scale channel restoration or modification has limited benefits within the broader landscape context. Physical habitat variables are often the basis for indicating success, but are now increasingly seen as poor surrogates for actual biological function; the assumption “if you build it they will come” lacks support of empirical studies. If stream restoration is to play a continued role in compensatory mitigation under the United States Clean Water Act, then significant policy changes are needed to adapt to the limitations of restoration science and the social environment under which most projects are constructed. When used for compensatory mitigation, stream restoration should be held to effectiveness standards for actual and measurable physical, chemical, or biological functional improvement. To achieve improved mitigation results, greater flexibility may be required for the location and funding of restoration projects, the size of projects, and the restoration process itself.

Subscription Required