Intro: Urbanism has become a pervasive and ubiquitous presence within the environment and this development coincides with an increase in concentrations of different types of pollutants, as well as a reduction in absorptive surfaces. These toxic substances make their way into our waterways and riparian buffers, carrying their effects through a chain of organisms and disrupting the balance of these essentially open and dissipative networks. In addition, drastic changes in hydrology and sediment load can result from the increase in quantity and peak rate of storm water runoff (Roznowski). These changes further disrupt the biological community by altering in stream habitat structure.
In the context of urban impacts on the environment our rivers and waterways are particularly inundated. Development within close proximity to riparian areas or stream channels can be particularly detrimental to stream communities (Wang and Kanehl). Furthermore, riparian areas and their connected water bodies represent low-lying points in the landscape and thus act as a catchment for all the pollutants we leave across their path, so in the context of a degraded matrix, they represent areas of even greater degradation due to their high toxic concentrations.
In recent years the fields of engineering and ecology have formed and overdue alliance by which their common integration has allowed them to address more effectively some of our most troubling environment related problems. Ecology is in a position to meet global environmental problems through ecosystem design. The core issue to be addressed is how do we achieve sustainable development? Ecosystem engineering uses the functionality and structural characteristics of the worlds ecosystems as a model for restoring our environment and optimizing human made systems. Yet we have only begun to understand the biological integrity of such systems.
Recognition of the important role of riparian systems within the landscape has led to legislation requiring compensatory replacement or restoration of all wetlands lost through the practice of ecological engineering. The trouble is we may not understand functional equivalency and therefore rather than mitigation we have allowed for an even greater loss.
Brief History of Environmental Management in the U.S.
Like change in ecosystems themselves, the recognition of our deleterious effects on the environment has been incremental. The first wave of the ‘green movement’ began in the late 60’s with the invention of environmental technology to solve point-source pollution problems. From there we began to use ecological models to assess ecosystems self-purification capacities and establish emissions standards. In the early 70’s the U.S. Congress established the Clean Water Act and we then began to initiate a strategy for environmental management that persists today. However, with the rise of global environmental problems, the complexity of the situation has increased. Today’s management strategy involves a simultaneous application of environmental technology, cleaner technology, environmental legislation, ecological engineering and ecosystem restoration. Even still, trillions of dollars have been spent in pollution abatement on a global scale and yet pollution problems continue to grow (Mitsch, Jorgenson).
The task of environmental management remains a complicated issue. The need remains for us to evaluated the current application of management strategies to determine whether or not they have actually been successful in accomplishing set goals. While the value in modeling after ecosystems has the potential to be quite effective we must focus our efforts on working order, rather than form.
Review: A review of studies evaluating design implementation outcomes of river restoration efforts, as well an evaluation of the criterion itself used to determine functionality, and an evaluation of legislative success will hopefully bring us closer to an understanding of whether our efforts are being realized and how to proceed with future projects.
CASE 1: In a study examining the success of urban stream restoration projects to enhance habitat structure and support characteristic stream biota of undisturbed systems, a comparison analysis was conducted between urban degraded, urban restored and forested streams in the Piedmont region of North Carolina. This study was based upon the assumption that if habitat is restored sufficiently then biological recovery at the site will follow. It was judged on the parameters that effective restoration should recapture the habitat structure and biological communities of an undisturbed reference site (forested site), and thereby show a greater degree of similarity to forested sites than to their urban degraded equivalent (Violin, et al.).
Previous work has demonstrated that taxonomic richness for macro-invertebrate communities are positively correlated with spatial heterogeneity (Gorman and Karr, Angermeier and Winston, Vinson and Hawkins, Brown). In response the design of stream restoration efforts often deploy habitat provision as the primary objective in overall structure of a project. This occurs in spite of the fact that the common theoretical concepts in ecological engineering emphasize the need for a systems approach (Perrow and Davy). Ecological objectives should form a hierarchal gradient, restoration of lower order objectives such as native species is unlikely to be sustained without attention to the upper orders, natural water and sediment regime and hydrological connectivity to the floodplain (Ward, et al.).
The restoration techniques of sites in this study were the reconfiguration of pattern, profile, and dimensions of the degraded channel to emulate an undisturbed site. Heavy machinery was used to regrade the channel, hard structures to control grade, root wads for bank stabilization and coarse bed materials were used to create riffles. Vegetation was also added in newly created riparian areas. Sampling efforts began in as little as 1-7 years after completion of the newly regraded sites and involved habitat surveys, hydrological surveys measuring velocity and depth values, nutrient load and organic matter dynamics were measured and macroinvertebrate communities were sampled.
The results of this study conclude that the urban restored channels did not have a higher index of sensitive macro-invertebrate species richness, suggesting that natural channel design alone is not sufficient in mitigating factors causing loss in these sensitive species (Violin, et al.).
CASE 2: In a second and separate study the effectiveness of large woody debris in urban stream rehabilitation projects were examined in the Puget Sound lowland of Washington. This study operated under the same assumption that if physical channel characteristics are addressed then biological conditions will improve. Large woody debris (LWD) is believed to play a prominent role in influencing bank stability pool and bar formation, sediment retention, and grade in the Pacific Northwest (Montgomery, et al.; Beechie and Sibley; Nelson) and additionally, enhancement of habitat structures. Under this study, in-stream log placement was the primary strategy for achieving rehabilitation goals and effectiveness of LWD placement was evaluated on physical improvements and biological response. This study, in addition to the one above, had a very short incubation time, only 4 years had passed between when the project had been put in place and the study was conducted.
The categories for stream morphology evaluation were residual pool depths, average pool spacing, pool formation, in-channel sediment storage, grade control. Biological conditions were assessed using the benthic index of biological integrity (B-IBI) (Karr and Chu, 1999).
In a similar manner to the study above, the addition of LWD improved some parameters of physical geomorphology of the river system but had little demonstrable effect on biological condition.
Evaluation of Criterion to Judge Success
In a book titled Ecological Engineering and Ecosystem Restoration, the authors Mitsch and Jorgensen outline the three most determining factors in the failure of riparian zone remediation projects are:
- insufficient time for development
- lack of recognition or underestimation of self-design capacity of nature (Mitsch and Wilson).
- little understanding of ecosystem function
Given these parameters we can begin to assess how evaluation methods have been used to gauge the success of restoration efforts and whether these measures are appropriate. The first of these conditions (time) seems to indicate an obvious limitation in the assessment and given the failure to address this criterion properly undermines the other two categories as well. Ecosystems are complicated matrices of interwoven interactions between numerous organisms and yet we often take a very linear approach to the way we describe them, A leads to B, etc. Change in these systems is incremental and cumulative. Understanding the long-term change in stream ecosystems is fundamental to determining their long-term biogeochemistry. As watershed ecosystems change with time, the relative importance, and the magnitude of interplay between stream ecosystems and upland drainage areas change in a myriad of complicated ways (Bernhardt, et al.). Mitsch and Jorgensen suggest the appropriate time for restoration to be achieved is on a scale closet to 15-20 years. Yet the standard time frame in the U.S. is much closer to <5 years (Mitsch, Jorgensen), which leads to the question, has enough time passed to truly evaluate these systems given the varying rates of ecosystem processes and disturbance legacies?
Self design can be understood as a form of “self organization [which] manifests itself in microcosms of newly created ecosystems showing that after the first period of competitive colonization, the species prevailing are those that reinforce other species through nutrient cycles, aids to reproduction, control of spatial diversity, population regulation and other means (Odum). Once an ecosystem is constructed it should be able to sustain itself through self design, however in the context of urban systems fragmentation plays a key role in an ecosystems ability to reestablish itself. Fragmented landscapes isolate populations of species, removing them from source populations makes rescue of such populations increasingly more difficult coincident with their degree of disconnection. Fragmented landscapes also have an increased edge effect which creates an area subjective to generalist species and one non-suitable to more specialized or sensitive ones that formed under the original matrix (Knight).
The third parameter given is lack of understanding of ecosystem function; this seems to be a significant issue in our evaluation of restored sites. In both the studies above habitat structure was assumed to form a direct relationship to biotic integrity. Biodiversity has been shown to decline in situ with the homogenization of benthic habitats (Violin, et al) and macroinvertebrate communities are strongly affected (Lenat & Crawford). Furthermore, studies assessing the representativeness of one or a few benthic macroinvertebrate samples taken from the Cache la Poudre River compared to long-term averages have shown that short-term data still provide a relatively accurate picture of stream health, within this regional context, relative to a reference site (Voelz, et al.), indicating that despite the short incubation time of these studies, biotic index may still be a valuable tool in assessing short-term recovery of urban streams, and yet neither of the above studies produced significant changes in the ability to foster sensitive species based upon production of habitat. The question then turns into: Was insufficient time given between project implementation and the conduction of the study, or Do these studies ignore larger forcing factors that overshadow the importance of habitat heterogeneity for supporting macroinvertebrate communities? For instance, it is possible the location of these mitigated sites in the context of an urban degrade watershed has a larger impact on biotic index than any other factor.
Another example of an incomplete understanding of ecosystem function and the relations between its components is that of the use of vegetation alone as a measure of ecosystem health. Vegetation is commonly used as an indicator of ecological function in wetlands, (Turner, et al.), ignoring other more comprehensive approaches such as flood storage, and water quality improvement. The reason for this is that vegetation is easy to measure, and establishes itself quickly in a wet environment. However, vegetation is a poor indicator of underlying functionality (J.A. Reinaetz) and can lead to inaccurate evaluations. In a study conducted by the National Research Council’s Committee on mitigating wetland losses it was found that while plant cover and plant community health between mitigation sites and reference sites were similar, species composition differed significantly, and use by amphibians, mammals and birds were much lower in mitigated sites (Turner, et al.). This example demonstrates how ecological functionality based upon the wrong parameters can lead to invalid findings. Criterion based at the species level ignores the forcing functions operating at higher levels.
Evaluation of Legislative Success
In the 1990’s the U.S. Army Corps of Engineers and the Environmental Protection Agency outlined a mitigation strategy aimed to halt the devastating loss of wetlands in the U.S. This policy was termed No-Net-Loss and would require a 2:1 offset of wetlands created or remediated for every hectare of wetland permitted for loss (Turner, et al.). However, in the time since the enactment of this code, it has become clear that the requirement of mitigation does not guarantee that the effort is achieved or that it will even be attempted.
In a comprehensive literature review by the National Research Council Committee on the performance of wetland mitigation under the No-Net-Loss goal, section 404 of the Clean Water Act, it was revealed that many mitigation projects were never initiated, while others still were never completed, or the goals never realized. This study asked if mitigation projects has resulted in a net gain, as outlined by the 2:1 proposal, or a net loss of wetland function and found that the average area of mitigation implemented was only .69 hectares for every hectare lost and additionally, only 21 percent of the mitigation sites, under various tests of ecological equivalency of function met the standards. Furthermore, the ecological criteria used in setting permit requirements were often based on vegetation alone, which has shown to be inadequate for estimating soil, nutrient, and habitat trajectories in disturbed sites. The study concluded that the fundamental reason for insufficient ecological performance was the inability to create or restore the necessary hydrological conditions. This study informs us that a systems approach in ecological engineering must be inherent in our mitigation efforts.
Discussion: The shared assumption in the first two studies, that effective restoration should recapture the habitat structure and biological communities of an undisturbed reference site, led to a design approach based on the establishment of physical structure alone. This strategy while addressing the river habitat complexity fails to recognize that structural habitat may be only one of the numerous conditions that are lacking for the survival of macroinvertebrate and other aquatic species communities. Because these sites are situated in disturbed urban settings, they are removed from areas of source populations; their increased fragmentation and edge effect, further inhibits their recovery. Insufficient time was also a factor in these studies, considering biological food webs may need a longer time to restore themselves.
A third condition not taken into account in these studies is that biological integrity is strongly influenced by overall watershed disturbance and directly relates to the level of development in the upstream watershed. If the matrix is primarily urban, then there are implications toward the quality of this habitat that come with its urban setting and may not be offset on a localized scale. Urban streams feature increased concentrations of pollutants due to their hyper-connectivity to their urban environment; urban development creates impervious surfaces that prohibit infiltration and act as sluice channels for contaminants into urban waterways, particularly during big storm events. Impacted riparian zones compound this toxicity by their reduced removal efficiency (Violin, et al). The dynamic interaction between rivers and their floodplain is primary in the understanding of watershed restoration. If either is altered the result will cause a change in both systems over time (Mitsch, Jorgensen).
Analysis: Legislation has abstracted riparian ecosystems and their attached waterways into functional categories, this blurs the understanding of the cumulative effects of their interwoven components that contribute to the overall health of these ecosystems. In addition these abstracted categories isolate services from the performance of the watershed impairing our ability to make informed decisions about management strategies regarding these systems. The policy of No-Net-Loss allows for the exchange of categorical values, we permit the destruction of intact wetlands for replacement of manmade “equivalents” based on the categorical function that we designate, however, the criterion used to evaluate ecological function has been shown to be a poor tool for truly assessing ecological working order. While the wetlands destroyed under Section 404 were of diverse functional classes, the vast majority of mitigations were classified as a single type, (Robertson, 2000) disregarding the array of services provided across unique sites. Furthermore, given our inability to recapture working order, it seems we do not fully understand fully the material character of these systems. This has led to an estimated 80 percent loss in our nations wetlands and riparian zones. Mitigation efforts could be dramatically improved through the use of appropriate ecological criteria in evaluating success and in setting permit requirements for section 404. A more broadly defined narrative classifying wetlands into their unique types and functional classes and situating mitigation sites within the context of watershed management plans could significantly improve efforts as well.
Conclusion: Wetlands and riparian zones are embedded features within the landscape, they host a multitude of links to hydrology, floral dispersal and fauna corridors that extend beyond their hydric soil boundaries. In our conception of them, however, we view them as admixtures of functional values to which we designate and assign value. We have have permitted the loss of intact working systems in exchange for fully engineered or partially restored ‘equivalents’ that do not necessarily perform. Our assessment methodologies to evaluate ecological characteristics have allowed us a means to abstract them towards qualities of socio-economic value. Ecosystems consist of a multitude of material linkages within the landscape but we tend to view them in a linear fashion in isolation from these other networks. It is important that we understand their function in relation to their landscape position.
For centuries man has made huge modifications to the environment and in the process we have disrupted thousands of functional characteristics of ecosystems and their interwoven elements. Humanity has a long relationship with viewing the environment as the medium through which we construct our markets. We are however, approaching an age of diminishing resources where the growth of human population continues. In this retrospective moment we begin to see the inherent merit in ecological function and its relation to our own wellbeing, as well as the cost of restoring those systems which, as a result of our modifications, have ceased to function. Mitigation is ecologically possible and modeling our own networks of growth after such dynamically functioning systems as nature has provided is a step in the right direction. In this moment of pause in human history we must evaluate the effectiveness of our engineering to determine whether the practice of development will proceed as it has done in the past, or whether we can conceive of a more ecologically in tune form of expansion, a paradigm shift that imitates and restores natures functions while keeping in mind our own presence in them.
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