The Blurred Line Between Form and Process: A Comparison of Stream Channel Classification Frameworks

Stream classification provides a means to understand the diversity and distribution of channels and floodplains that occur across a landscape while identifying links between geomorphic form and process. Accordingly, stream classification is frequently employed as a watershed planning, management, and restoration tool. At the same time, there has been intense debate and criticism of particular frameworks, on the grounds that these frameworks classify stream reaches based largely on their physical form, rather than direct measurements of their component hydrogeomorphic processes. Despite this debate surrounding stream classifications, and their ongoing use in watershed management, direct comparisons of channel classification frameworks are rare. Here we implement four stream classification frameworks and explore the degree to which each make inferences about hydrogeomorphic process from channel form within the Middle Fork John Day Basin, a watershed of high conservation interest within the Columbia River Basin, U.S.A. We compare the results of the River Styles Framework, Natural Channel Classification, Rosgen Classification System, and a channel form-based statistical classification at 33 field-monitored sites. We found that the four frameworks consistently classified reach types into similar groups based on each reach or segment’s dominant hydrogeomorphic elements. Where classified channel types diverged, differences could be attributed to the (a) spatial scale of input data used, (b) the requisite metrics and their order in completing a framework’s decision tree and/or, (c) whether the framework attempts to classify current or historic channel form. Divergence in framework agreement was also observed at reaches where channel planform was decoupled from valley setting. Overall, the relative agreement between frameworks indicates that criticism of individual classifications for their use of form in grouping stream channels may be overstated. These form-based criticisms may also ignore the geomorphic tenet that channel form reflects formative hydrogeomorphic processes across a given landscape

Puget sound habitat status and trends monitoring program: nearshore and large river delta geospatial data and habitat status and trends monitoring metrics

The Puget Sound Habitat Status and Trends Monitoring (PSHSTM) program was developed to provide consistent salmon habitat status and trends data to support status reviews of Endangered Species Act (ESA) listed salmon populations across Puget Sound’s major population groups. Our approach primarily relies on readily available and regularly updated aerial imagery to consistently map key habitat features at a regional scale. We have developed a census-based approach to map key habitat features throughout the nearshore, large river delta, large river, and floodplain environments across Puget Sound. This presentation will focus on our mapping efforts in Puget Sound’s nearshore and large river delta environments, and the habitat status and trends metrics that will be derived from these efforts to support ESA listing reviews. In the nearshore environment, we are mapping overwater structures (e.g., docks, piers, bridges, buoys/floats, booms, aquaculture, and boat ramps), forested shoreline, and small embayment habitat features (e.g., lagoons, pocket estuaries, and blind tidal channels) for all ≈4,000 km of Puget Sound’s shoreline. In the large river delta environment, we are mapping tidal wetland areas, geomorphic delta boundaries, and channel features (e.g., distributaries and tidal channels) for all 17 large river deltas that drain into the Puget Sound, Hood Canal, and the Strait of Juan de Fuca. This census-based approach will provide a unique opportunity to develop consistent habitat status and trends metrics for habitat quantity and quality at a regional scale that can be used to inform ESA status reviews of listed salmon populations. We anticipate that the consistent regional-scale geospatial data sets developed from these efforts can be used to support a variety of other research and management needs

Glacier retreat creating new Pacific salmon habitat in western North America

Glacier retreat poses risks and benefits for species of cultural and economic importance. One example is Pacific salmon (Oncorhynchus spp.), supporting subsistence harvests, and commercial and recreational fisheries worth billions of dollars annually. Although decreases in summer streamflow and warming freshwater is reducing salmon habitat quality in parts of their range, glacier retreat is creating new streams and lakes that salmon can colonize. However, potential gains in future salmon habitat associated with glacier loss have yet to be quantified across the range of Pacific salmon. Here we project future gains in Pacific salmon freshwater habitat by linking a model of glacier mass change for 315 glaciers, forced by five different Global Climate Models, with a simple model of salmon stream habitat potential throughout the Pacific Mountain ranges of western North America. We project that by the year 2100 glacier retreat will create 6,146 (±1,619) km of new streams accessible for colonization by Pacific salmon, of which 1,930 (±569) km have the potential to be used for spawning and juvenile rearing, representing 0 to 27% gains within the 18 sub-regions we studied. These findings can inform proactive management and conservation of Pacific salmon in this era of rapid climate change.Ye

Evolutionary History, Habitat Disturbance Regimes, and Anthropogenic Changes: What Do These Mean for Resilience of Pacific Salmon Populations?

Because resilience of a biological system is a product of its evolutionary history, the historical template that describes the relationships between species and their dynamic habitats is an important point of reference. Habitats used by Pacific salmon have been quite variable throughout their evolutionary history, and these habitats can be characterized by four key attributes of disturbance regimes: frequency, magnitude, duration, and predictability. Over the past two centuries, major anthropogenic changes to salmon ecosystems have dramatically altered disturbance regimes that the species experience. To the extent that these disturbance regimes assume characteristics outside the range of the historical template, resilience of salmon populations might be compromised. We discuss anthropogenic changes that are particularly likely to compromise resilience of Pacific salmon and management actions that could help bring the current patterns of disturbance regimes more in line with the historical template

Process-based principles for restoring river ecosystems

Process-based restoration aims to re-establish natural rates and magnitudes of physical, chemical, and biological processes that sustain river and floodplain ecosystems, thereby moving ecosystem conditions (physical, chemical, and biological) into the range of natural potential conditions at any site. Ecosystem conditions at any site are governed by hierarchical regional, watershed, and reach-scale processes, identifying restoration actions that are necessary to restore ecosystem function should include analyses that answer two main questions: (1) How have changes in riverine habitats affected biota?, and (2) What are the ultimate causes of changes in riverine habitats? Answers to these questions identify habitat types or areas that are most in need of restoration or will contribute most to biological recovery, as well as the causes of degradation that must be addressed to achieve restoration goals. Watershed analyses therefore include assessments of processes controlling hydrologic and sediment regimes, floodplain and aquatic habitat dynamics, and riparian and aquatic biota. Four process-based principles help guide river restoration toward sustainable actions: (1) address root causes of degradation, (2) make sure actions are consistent with the physical and biological potential of the site, (3) the scale of restoration should match the scale of environmental problems, and (4) restoration actions should have clearly articulated expected outcomes for ecosystem dynamics. Applying these principles will help avoid common pitfalls in river restoration, such as creating habitat types that are outside the range of a site’s natural potential, attempting to build static habitats in dynamic environments, or constructing habitat features that are ultimately overwhelmed by untreated system drivers

A life-table model estimation of the parr capacity of a late 19th century Puget Sound steelhead population

An age-structured life-cycle model of steelhead (Oncorhynchus mykiss) for the Stillaguamish River in Puget Sound, Washington, USA, was employed to estimate the number of age-1 steelhead parr that could have produced the estimated adult return of 69 000 in 1895. We then divided the estimated parr numbers by the estimated area of steelhead rearing habitat in the Stillaguamish River basin in 1895 and under current conditions to estimate density of rearing steelhead then and now. Scaled to estimates of total wetted area of tributary and mainstem shallow shoreline habitat, our historic estimates averaged 0.39–0.49 parr·m−2, and ranged from 0.24 to 0.7 parr·m−2. These values are significantly greater than current densities in the Stillaguamish (mainstem average: 0.15 parr·m−2, tributaries: 0.07 parr·m−2), but well within the range of recent estimates of steelhead parr rearing densities in high-quality habitats. Our results indicate that modest improvement in the capacity of mainstem and tributary rearing habitat in Puget Sound rivers will yield large recovery benefits if realized in a large proportion of the area of river basins currently accessible to steelhead

A multispecies assessment of climate change threats to salmonids across their life cycle

During their life cycle, salmonids experience conditions in freshwater, estuarine, and marine habitats, exposing them to numerous climate change threats. The extent to which different species utilize different habitat types and habitat-specific climate change risks should result in differential overall vulnerability of these species to climate change, but most previous vulnerability assessments have focused only on particular life stages for particular species, hampering our ability to protect, restore stocks and their habitats to maximize species portfolios in river systems. We performed a life cycle-based risk assessment of climate change threats for nine species of salmonids (species within Oncorhynchus, Salvelinus, and Prosopium genera) inhabiting the Skagit River system, which is vulnerable to the panoply of climate impacts forecasted for the Pacific Northwest. The risk assessment integrated both species-specific intensity and exposure and incorporated uncertainty. We found that while climate change threats existed across all habitats inhabited by these species, the greatest threats to all species were associated with projected changes in the extremes of freshwater flow (high incubation flows, low summer flows). These results suggest that restoration strategies targeting restoration of floodplain function will be most effective for reducing the most serious threats for a broad portfolio of salmonids inhabiting the Skagit River, although other climate adaptation strategies may provide additional benefits to other suites of species

A systematic review of ecological attributes that confer resilience to climate change in environmental restoration

<div><p>Ecological restoration is widely practiced as a means of rehabilitating ecosystems and habitats that have been degraded or impaired through human use or other causes. Restoration practices now are confronted by climate change, which has the potential to influence long-term restoration outcomes. Concepts and attributes from the resilience literature can help improve restoration and monitoring efforts under changing climate conditions. We systematically examined the published literature on ecological resilience to identify biological, chemical, and physical attributes that confer resilience to climate change. We identified 45 attributes explicitly related to climate change and classified them as individual- (9), population- (6), community- (7), ecosystem- (7), or process-level attributes (16). Individual studies defined resilience as resistance to change or recovery from disturbance, and only a few studies explicitly included both concepts in their definition of resilience. We found that individual and population attributes generally are suited to species- or habitat-specific restoration actions and applicable at the population scale. Community attributes are better suited to habitat-specific restoration at the site scale, or system-wide restoration at the ecosystem scale. Ecosystem and process attributes vary considerably in their type and applicability. We summarize these relationships in a decision support table and provide three example applications to illustrate how these classifications can be used to prioritize climate change resilience attributes for specific restoration actions. We suggest that (1) including resilience as an explicit planning objective could increase the success of restoration projects, (2) considering the ecological context and focal scale of a restoration action is essential in choosing appropriate resilience attributes, and (3) certain ecological attributes, such as diversity and connectivity, are more commonly considered to confer resilience because they apply to a wide variety of species and ecosystems. We propose that identifying sources of ecological resilience is a critical step in restoring ecosystems in a changing climate.</p></div