Strategies for Restoring River Ecosystems: Sources of Variability and Uncertainty in Natural and Managed Systems

<em>Abstract</em>.—River ecosystem integrity is evaluated within a variety of landscape scales. We examine influences of variations in natural processes and human actions on river ecosystems and propose a concept for restoring impaired systems. The ecological structure and function of rivers vary across a hierarchy of landscape scales with different spatial and temporal dimensions. The major linkages within river systems include exchange of water and materials along longitudinal connections from streams to rivers, lateral connections between river and floodplain systems, and vertical surface and subsurface (hyporheic) water exchanges. Strong longitudinal linkages dominate confined river reaches while unconfined floodplain reaches show strong affinities for lateral and vertical exchange. A landscape concept, “the shifting habitat mosaic” (SHM), provides a framework for understanding how these interactions create and maintain the physical and ecological diversity of habitats, biotic communities, and ecosystem integrity. While each river system has unique physical and ecological characteristics, many human actions and ecological effects can be expressed within the SHM concept. For example, societal needs for power generation, transportation, water management, and land uses (e.g., urban and agricultural) often alter natural processes of hydrologic regimes and material transport and deposition. These factors affect interactions between the river channel and the surrounding river–riparian corridor. Restoration strategies can apply the SHM concept by focusing on restoring normative variations to processes (e.g., hydrologic regimes) that contribute to ecosystem integrity. Management practices (e.g., dam hydrologic regimes, flood control facilities, levees, land uses) can be modified to restore natural physical and ecological processes (e.g., thermal regimes, water exchange, and animal migrations).

Strategies for Restoring River Ecosystems: Sources of Variability and Uncertainty in Natural and Managed Systems

<em>Abstract</em>.—Decisions about watershed restoration projects often are complicated by competing interests and goals, gaps in scientific knowledge, and constraints on time and resources. Under these circumstances, there is no best approach to decision making and problem solving. Appropriate decision processes need not always be analytically complex, but instead depend on the characteristics of the external social context, the decision makers, and the decision problem itself. Because social concerns so often prevail in restoration decisions, we begin with a discussion of issues characterizing the social context. Next, in three increasingly broad contexts for watershed restoration, we discuss the application of several methods for facilitating decisions and solving problems involving uncertainty: Bayesian decision analysis, active adaptive management, passive adaptive management, and evolutionary problem solving.

Strategies for Restoring River Ecosystems: Sources of Variability and Uncertainty in Natural and Managed Systems

<em>Abstract</em>.—Productivity and biodiversity of stream and river ecosystems vary at multiple spatial and temporal scales. Spatial variation in productivity of salmonid fishes varies over two orders of magnitude worldwide and shows lesser, but still considerable, variation at the regional and watershed level. Spatial variation in production and diversity is related to variation in physical, chemical, and biological attributes of watersheds and channels. Channel constraint, gradient, and size are key factors in determining productivity and diversity. Constrained reaches generally support different species and lower productivity than lower-gradient, unconstrained channels. Variation in the condition of stream reaches is greatly influenced by disturbances. Severe disturbances fundamentally change the functional and structural properties of stream ecosystems and alter the way in which the surrounding watershed interacts with the stream. Periodic occurrence of disturbances and the process of recovery play a key role in maintaining spatial and temporal variability in stream conditions and thereby contribute to the productivity and diversity of stream biota. Land use by humans alters the frequency and characteristics of disturbances. As a result, human-altered disturbance patterns often homogenize channel conditions across a watershed rather than introducing diversity. Watershed restoration plans need to recognize the role variability and disturbance play in maintaining the productivity and diversity of stream biota. Incorporating this understanding into watershed management and restoration will require scientists, managers, and policy makers to view watersheds at much longer temporal and larger spatial scales than is currently done.

Strategies for Restoring River Ecosystems: Sources of Variability and Uncertainty in Natural and Managed Systems

<em>Abstract</em>.—We examine decision-support models designed to help recover salmon <em>Oncorhynchus </em>spp. in the Columbia River Basin as a case study for the use of models to help resolve scientific uncertainty and select management options. The models all have somewhat different objectives, use different data, and deal with a variety of salmon-related issues. Divergence of model outputs has, in the past, been used to justify different policy positions, leading some to conclude that science has failed to provide clarity to salmon recovery planning. Three distinct approaches are represented in the models: decision analysis, statistical, and expert system. Of the three approaches, decision analysis provides the clearest management advice and the most formal method for treating uncertainty. Its success depends on the engagement of decision makers in framing questions, identifying management options under consideration, and assigning values to possible outcomes. However, decision analysis could be very difficult to perform. As an alternative, the statistical model is the traditional scientific approach and it can operate with a large degree of detachment from policy. Statistical models proceed by testing hypotheses and estimating life-cycle parameters with available data. They have the advantage of scientific clarity, rigor, and empirical objectivity. The limitation of a statistical model is that the scope of the questions and their answers are restricted by availability of data, and in a domain that is data-poor, many pressing questions go unanswered. Expert system approaches fill gaps in data with expert opinion. In the context of salmon recovery, expert opinion allows consideration of the most concrete menu of specific options for salmon management. Expert opinion is a weaker basis for scientific prediction than is a mathematical relationship validated with empirical data. However, at the level of spatial resolution and environmental detail required to make salmon management decisions affecting the entire Columbia River Basin, there are no validated mathematical formulae for predicting the effects of management actions on salmon, and no adequate data archive exists for deriving such relationships. Communication between scientists and managers is improved when there is a formal institutional mechanism for summarizing scientific results and clarifying the interpretation of models for policy makers. If a modeling effort is driven by a desire to contribute to a particular decision, it is helpful to initially invest in enough communication to ensure that the model really is addressing the right question. Scientists can help managers craft decision rules that are formalized <em>before </em>analyses are undertaken. Decision rules define what measurements will be made, what statistical operations will be performed, and what threshold magnitudes of estimated quantities at specified levels of certainty will serve as criteria for the decision. Such specifications ensure that model results are properly used in the decision process. Committing to these specifications in advance helps dispel suspicions that analyses may be manipulated to achieve a particular outcome.

Strategies for Restoring River Ecosystems: Sources of Variability and Uncertainty in Natural and Managed Systems

<em>Abstract</em>.—Hydrogeomorphic processes play key roles in creating, modifying, or destroying aquatic habitat and act as ecological disturbances that shape ecosystem characteristics and dynamics. Within the broad regional context set by general patterns of climate, physiography (geology and topography), and vegetation, the combined influences of the hydrologic, geomorphic, and vegetation regimes dominate the variability of river systems. Interactions among these regimes can strongly influence river ecosystems, and an understanding of the nature of these regimes and disturbance histories is crucial for setting restoration targets and interpreting the long-term ecological influences of hydrogeomorphic processes. It is difficult to design effective stream and channel restoration measures, or evaluate project performance, without an understanding of the pertinent geomorphic context, habitat-forming processes, and disturbance history. Of particular relevance are the main processes that transport and store water, sediment, and wood, and how differences in current and potential conditions are related to local conditions, basin-wide contexts, and the influences of human activities. Because stream and channel processes and characteristics vary regionally and throughout a drainage basin, there is no universal template for guiding restoration efforts. In designing restoration measures, it is essential to address trends and differences between current and potential conditions to ensure that restoration efforts are neither futile nor poorly matched to the site or system in question.

Strategies for Restoring River Ecosystems: Sources of Variability and Uncertainty in Natural and Managed Systems

<em>Abstract</em>.—Genetic considerations can be crucially important to the success of reintroductions of lotic species. Current paradigms for conservation and population genetics provide guidance for reducing uncertainties in genetic issues and for increasing the likelihood of achieving restoration. Effective restoration is facilitated through specific goals and objectives developed from the definition that a restored or healthy population is (i) genetically adapted to the local environment, (ii) self-sustaining at abundances consistent with the carrying capacity of the river system, (iii) genetically compatible with neighboring populations so that substantial out-breeding depression does not result from straying and interbreeding between populations, and (iv) sufficiently diverse genetically to accommodate environmental variability over many decades. Genetic principles reveal the importance of describing and adhering to the ancestral lineages for the species to be restored and enabling genetic processes to maintain diversity and fitness in the populations under restoration. Newly established populations should be protected from unnecessary human sources of mortality, gene flow from maladapted (e.g., hatchery) or exotic populations, and inadvertent selection by fisheries or other human activities. Such protection facilitates initial, rapid adaptation of the population to its environment and should enhance the chances for persistence. Various uncertainties about specific restoration actions must be addressed on a case-by-case basis. Such uncertainties include whether to allow natural colonization or to introduce fish, which populations are suitable as sources for reintroduction, appropriate levels of gene flow from other populations, appropriate levels of artificial production, appropriate minimum numbers of individuals released or maintained in the population, and the best developmental stages for releasing fish into the restored stream. Rigorous evaluation or experimental management is necessary to reduce uncertainty in our knowledge so that future conservation and restoration activities can be more effective.

Strategies for Restoring River Ecosystems: Sources of Variability and Uncertainty in Natural and Managed Systems

<em>Abstract</em>.—River ecosystems are naturally variable in time and space and this variability is largely determined by climate, geology, and topography. We explore how variability in climate influences rivers. Our specific goals are to discuss (1) the major natural drivers of global-scale climate; (2) variability in temperature, precipitation, and streamflow patterns and how they relate to natural climate oscillations, such as El Niño/Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and Arctic Oscillation/North Atlantic Oscillation (AO/NAO); (3) how human activities influence climate variability; (4) how climate variability influences river systems; and (5) the need to account for climate variability in river restoration activities. Three regional-scale river drainages are explored in detail: the Columbia River in the Pacific Northwest; the Colorado River in the Rocky Mountains and the Southwestern USA; and the Kissimmee–Okeechobee–Everglades drainage in South Florida. As is true for many river drainages, humans have strongly influenced the hydrologic cycle in the three aforementioned basins through land-use practices. Clearing forests, creating urban environments, building dams, irrigating fields, and straightening rivers all contribute to hydrologic change, especially river flooding. Rates of climate change and climate variability are now being influenced by human activities. Restoring the connectivity between river channels and floodplains, and “naturalization” of flow regimes of many large river drainages could be a major management action for ameliorating changes due to increased climate variability.

Strategies for Restoring River Ecosystems: Sources of Variability and Uncertainty in Natural and Managed Systems

<em>Abstract</em>.—Formulating effective restoration goals and strategies for riparian ecosystems requires knowledge of the sources of variability at local and broad landscape scales. We examine sources and influences of natural and human-induced variability in riparian ecosystems and discuss their implications for restoration actions and recovery. We recommend that the development of restoration strategies should apply landscape perspectives that emphasize the connectivity of riparian systems to associated terrestrial and aquatic ecosystems. Particularly important are processes that involve the exchange of surface–subsurface waters, sediments, organic matter, and organisms between riparian and other ecosystems. Furthermore, the development of strategies should be based on understanding how past natural disturbances and human alterations and uses alter the connectivity and processes of riverine habitats throughout a drainage. Historical or retrospective information increases our understanding of how riparian and aquatic ecosystems function and provides insights on how to conserve and restore these resources. Although many restoration initiatives strive to repair ecosystem damage caused by humans, more recent views maintain that restoration efforts should facilitate the self-sustaining occurrence of natural processes and linkages among riparian, terrestrial, and aquatic ecosystems. Three general restoration strategies are presented: conservation, passive restoration (riparian reserves and buffer zones), and active restoration (flow and floodplain manipulations, restoring cottonwood/willow communities, and reducing invasive and exotic plants). Regardless of the strategy employed, restoration objectives should recognize that different portions of a riparian system can exhibit an array of recovery patterns as well as failure scenarios. Thus, objectives and strategies should enable us to evaluate the success of restoration activities as well as possibilities for continued degradation.

Strategies for Restoring River Ecosystems: Sources of Variability and Uncertainty in Natural and Managed Systems

<em>Abstract</em>.—Development of effective restoration strategies for river systems requires the use of scientific concepts about sources of variability and uncertainty. Most of these concepts are based on physical and biological properties, their processes and variability, and human-induced uncertainties within river drainages and their differences across regions. Important natural properties include climate; hydrology; geology; geomorphology; disturbance regimes like floods and fires; connectivity between river channels and floodplains; plant and animal population and community characteristics; and trophic dynamics. A major question when developing restoration strategies is, “How can we use information about variations in natural properties and anthropogenic actions to assist policy makers by reducing the uncertainty of decisions and to better manage river ecosystems?” We evaluate several concepts of variability in river ecosystems that are presented in this book: spatial and temporal scales, connectivity, and disturbance. Case studies of fish responses to temperature and hydrologic variability are used to show how this information can be applied to restoration plans. We also focus on the need to incorporate concepts of “recovery” into restoration strategies, and present several examples of recovery processes that occur following disturbances and potential restorative actions. Finally, we explore alternatives for evaluating and treating uncertainty in societal and policy arenas.