Diane C. Whited

CLIMATE, HYDROLOGIC DISTURBANCE, AND SUCCESSION: DRIVERS OF FLOODPLAIN PATTERN

Floodplains are among the worlds most threatened ecosystems due to the pervasiveness of dams, levee systems, and other modifications to rivers. Few unaltered floodplains remain where we may examine their dynamics over decadal time scales. Our study provides a detailed examination of landscape change over a 60-year period (1945-2004) on the Nyack floodplain of the Middle Fork of the Flathead River, a free-flowing, gravel-bed river in northwest Montana, USA. We used historical aerial photographs and airborne and satellite imagery to delineate habitats (i.e., mature forest, regenerative forest, water, cobble) within the floodplain. We related changes in the distribution and size of these habitats to hydrologic disturbance and regional climate. Results show a relationship between changes in floodplain habitats and annual flood magnitude, as well as between hydrology and the cooling and warming phases of the Pacific Decadal Oscillation (PDO). Large magnitude floods and greater frequency of moderate floods were associated with the cooling phases of the PDO, resulting in a floodplain environment dominated by extensive restructuring and regeneration of floodplain habitats. Conversely, warming phases of the PDO corresponded with decreases in magnitude, duration, and frequency of critical flows, creating a floodplain environment dominated by late successional vegetation and low levels of physical restructuring. Over the 60-year time series, habitat change was widespread throughout the floodplain, though the relative abundances of the habitats did not change greatly. We conclude that the long- and short-term interactions of climate, floods, and plant succession produce a shifting habitat mosaic that is a fundamental attribute of natural floodplain ecosystems.

USING AIRBORNE MULTISPECTRAL IMAGERY TO EVALUATE GEOMORPHIC WORK ACROSS FLOODPLAINS OF GRAVEL‐BED RIVERS

Fluvial processes of cut and fill alluviation and channel abandonment or avulsion are essential for maintaining the ecological health of floodplain ecosystems char- acteristic of gravel-bed rivers. These dynamic processes shape the floodplain landscape, resulting in a shifting mosaic of habitats, both above and below ground. We present a new and innovative methodology to quantitatively assess the geomorphic work potential nec- essary to maintain a shifting habitat mosaic for gravel-bed river floodplains. This approach can be used to delineate critical habitats for preservation through land acquisition and conservation easements, often critical elements of river restoration plans worldwide. Spa- tially explicit modeling of water depth, flow velocity, shear stress, and stream power derived from surface hydraulic measurements was combined with airborne multispectral remote sensing for detailed modeling of floodplain water surfaces over tens to hundreds of square kilometers. The model results were then combined within a GIS framework to determine potential nodes of channel avulsion that delineate spatially explicit zones across the flood- plain where the potential for geomorphic work is the greatest. Results of this study dem- onstrate the utility of integrating existing multispectral remote sensing data coupled with time-lagged ground-based measures of flow hydraulics to model fluvial processes at rela- tively fine spatial resolutions but over broad regional extents.

Performance of salmon fishery portfolios across western North America

Summary Quantifying the variability in the delivery of ecosystem services across the landscape can be used to set appropriate management targets, evaluate resilience and target conservation efforts. Ecosystem functions and services may exhibit portfolio‐type dynamics, whereby diversity within lower levels promotes stability at more aggregated levels. Portfolio theory provides a framework to characterize the relative performance among ecosystems and the processes that drive differences in performance. We assessed Pacific salmon Oncorhynchus spp. portfolio performance across their native latitudinal range focusing on the reliability of salmon returns as a metric with which to assess the function of salmon ecosystems and their services to humans. We used the Sharpe ratio (e.g. the size of the total salmon return to the portfolio relative to its variability (risk)) to evaluate the performance of Chinook and sockeye salmon portfolios across the west coast of North America. We evaluated the effects on portfolio performance from the variance of and covariance among salmon returns within each portfolio, and the association between portfolio performance and watershed attributes. We found a positive latitudinal trend in the risk‐adjusted performance of Chinook and sockeye salmon portfolios that also correlated negatively with anthropogenic impact on watersheds (e.g. dams and land‐use change). High‐latitude Chinook salmon portfolios were on average 2·5 times more reliable, and their portfolio risk was mainly due to low variance in the individual assets. Sockeye salmon portfolios were also more reliable at higher latitudes, but sources of risk varied among the highest performing portfolios. Synthesis and applications. Portfolio theory provides a straightforward method for characterizing the resilience of salmon ecosystems and their services. Natural variability in portfolio performance among undeveloped watersheds provides a benchmark for restoration efforts. Locally and regionally, assessing the sources of portfolio risk can guide actions to maintain existing resilience (protect habitat and disturbance regimes that maintain response diversity; employ harvest strategies sensitive to different portfolio components) or improve restoration activities. Improving our understanding of portfolio reliability may allow for management of natural resources that is robust to ongoing environmental change.

Combining demographic and genetic factors to assess population vulnerability in stream species

Accelerating climate change and other cumulative stressors create an urgent need to understand the influence of environmental variation and landscape features on the connectivity and vulnerability of freshwater species. Here, we introduce a novel modeling framework for aquatic systems that integrates spatially explicit, individual-based, demographic and genetic (demogenetic) assessments with environmental variables. To show its potential utility, we simulated a hypothetical network of 19 migratory riverine populations (e.g., salmonids) using a riverscape connectivity and demogenetic model (CDFISH). We assessed how stream resistance to movement (a function of water temperature, fluvial distance, and physical barriers) might influence demogenetic connectivity, and hence, population vulnerability. We present demographic metrics (abundance, immigration, and change in abundance) and genetic metrics (diversity, differentiation, and change in differentiation), and combine them into a single vulnerability index for identifying populations at risk of extirpation. We considered four realistic scenarios that illustrate the relative sensitivity of these metrics for early detection of reduced connectivity: (1) maximum resistance due to high water temperatures throughout the network, (2) minimum resistance due to low water temperatures throughout the network, (3) increased resistance at a tributary junction caused by a partial barrier, and (4) complete isolation of a tributary, leaving resident individuals only. We then applied this demogenetic framework using empirical data for a bull trout (Salvelinus confluentus) metapopulation in the upper Flathead River system, Canada and USA, to assess how current and predicted future stream warming may influence population vulnerability. Results suggest that warmer water temperatures and associated barriers to movement (e.g., low flows, dewatering) are predicted to fragment suitable habitat for migratory salmonids, resulting in the loss of genetic diversity and reduced numbers in certain vulnerable populations. This demogenetic simulation framework, which is illustrated in a web-based interactive mapping prototype, should be useful for evaluating population vulnerability in a wide variety of dendritic and fragmented riverscapes, helping to guide conservation and management efforts for freshwater species.

A Riverscape Analysis Tool Developed to Assist Wild Salmon Conservation Across the North Pacific Rim

ABSTRACT A major constraint for management and conservation of wild salmon is the large geographic area and diversity of rivers that provide critical freshwater habitats for salmon production and sustainability. These habitats span lengths of entire river systems, crossing international borders and management jurisdictions, while encompassing a range of climate and landscape conditions and human impacts. We developed the Riverscape Analysis Project (RAP) to provide a consistent and comprehensive geospatial database to document, assess, and compare the physical habitats of large salmon rivers of the North Pacific Rim (NPR). Here, we introduce and summarize a web-based GIS and decision support system (DSS) to assist salmon conservation around the NPR. The foundation of the RAP database is a seamless mosaic of moderate (30 m) resolution, multispectral satellite imagery from the Landsat TM instrument series, mapped with coincident 90-m resolution digital terrain Digital Evaluation Model (DEM) information to a...

Climate variables explain neutral and adaptive variation within salmonid metapopulations: the importance of replication in landscape genetics

Understanding how environmental variation influences population genetic structure is important for conservation management because it can reveal how human stressors influence population connectivity, genetic diversity and persistence. We used riverscape genetics modelling to assess whether climatic and habitat variables were related to neutral and adaptive patterns of genetic differentiation (population‐specific and pairwise FST) within five metapopulations (79 populations, 4583 individuals) of steelhead trout (Oncorhynchus mykiss) in the Columbia River Basin, USA. Using 151 putatively neutral and 29 candidate adaptive SNP loci, we found that climate‐related variables (winter precipitation, summer maximum temperature, winter highest 5% flow events and summer mean flow) best explained neutral and adaptive patterns of genetic differentiation within metapopulations, suggesting that climatic variation likely influences both demography (neutral variation) and local adaptation (adaptive variation). However, we did not observe consistent relationships between climate variables and FST across all metapopulations, underscoring the need for replication when extrapolating results from one scale to another (e.g. basin‐wide to the metapopulation scale). Sensitivity analysis (leave‐one‐population‐out) revealed consistent relationships between climate variables and FST within three metapopulations; however, these patterns were not consistent in two metapopulations likely due to small sample sizes (N = 10). These results provide correlative evidence that climatic variation has shaped the genetic structure of steelhead populations and highlight the need for replication and sensitivity analyses in land and riverscape genetics.

The effects of riverine physical complexity on anadromy and genetic diversity in steelhead or rainbow trout Oncorhynchus mykiss around the Pacific Rim.

This study explored the relationship between riverine physical complexity, as determined from remotely sensed metrics, and anadromy and genetic diversity in steelhead or rainbow trout Oncorhynchus mykiss. The proportion of anadromy (estimated fraction of individuals within a drainage that are anadromous) was correlated with riverine complexity, but this correlation appeared to be driven largely by a confounding negative relationship between drainage area and the proportion of anadromy. Genetic diversity decreased with latitude, was lower in rivers with only non-anadromous individuals and also decreased with an increasing ratio of floodplain area to total drainage area. Anadromy may be less frequent in larger drainages due to the higher cost of migration associated with reaches farther from the ocean, and the negative relationship between genetic diversity and floodplain area may be due to lower effective population size resulting from greater population fluctuations associated with higher rates of habitat turnover. Ultimately, the relationships between riverine physical complexity and migratory life history or genetic diversity probably depend on the spatial scale of analysis.

Spatial and Temporal Dynamics of Invasive Freshwater Shrimp (Mysis diluviana): Long-Term Effects on Ecosystem Properties in a Large Oligotrophic Lake

Invasion of Mysis diluviana from upstream stockings drastically altered the food web of 480 km2 Flathead Lake, Montana (USA). Mysis increased exponentially after establishment in 1982, preying upon large zooplankters, thereby substantially altering zooplankton community composition, favoring small-sized species. In consequence, primary production increased by 21% owing to changes in zooplankton feeding efficiency. Moreover, the abundant Mysis provided forage for the nonnative lake trout that also rapidly expanded, causing concomitant extirpation of kokanee salmon and near loss of native fishes. This has become a case history of how introduced species can mediate trophic cascades. Here we examine the long-term (1982–2014) dynamics of Mysis in Flathead Lake and how distribution and abundance of this invasive species is related to chemical, physical, and biological factors. We show that Mysis is a strong interactor, regulating zooplankton and phytoplankton biomass interactively with nutrient (N and P) dynamics. Moreover, changes in life history and changing spatial dynamics are strengthening the regulatory role of the Mysis, despite seemingly strong top-down pressure via predation of the Mysis by lake trout. The Mysis are structuring nearly all interactions within and between the biota of Flathead Lake.

Chapter 1 – Riverscapes

Riverscapes (river ecosystems) are composed of catchment basins embedded within regional landscapes across the continents. The basic attributes of riverscapes are (1) the river, (2) its floodplains and other spatially heterogeneous and interconnected structures or habitats, and (3) the exchange of water, chemicals, and biota among those habitats. Hydrologic and biological connectivities from headwaters to the ocean occur in three spatial dimensions (longitudinal—upstream to downstream; lateral—channel to floodplain; and vertical—groundwater to channel) and are dynamic (ever changing) over time, as influenced or driven by a wide variety of natural biophysical and human-mediated (cultural) processes. In this chapter, tools that can be used to assess riverscapes at different scales of resolution are described in general terms to set the stage for detailed methods given in subsequent chapters of this book.

Application of airborne multi-spectral digital imagery to characterize the riverine habitat

Regional mapping of major habitats for river systems can provide a useful measure of the relative abundance and distriburion of aquatic plants and animals, since the type, condition and heterogeneity of channel habitats strongly influence nutrient exchanges, and associated plant and animal communities (BISSON & MoNTGOMERY 1996). Habitat characteristics change through time as floods and droughts alter hydrology, sediment transport and distributions of vegetation and other biota on daily, seasonal and interannual timescales. lntermediate levels of disturbance tend to promote biodiversity by maintaining environmental gradients and associated habitat complexity in space and time (WARD & STANFORD 1983, HusTON 1994). The spatial and temporal characterization of these features is therefore important for monitoring and management of river communities (TRISKA 1984, MosLEY 1987, HOWARD 1987, MONTGOMERY & BUFFINGTON 1993, BENCALA et al. 1993, HICKS 1996). However, traditional field-based survey techniques for assessing large river (i.e. ~4th order) and floodplain habitats are often slow, costly and subject to error because of the large areas involved and the spatially complex and temporally dynamic nature of these systems (PAINE 1981, NEwsoN 1994, PomE er al. 1997). Research and restoration efforts and associated management activities within large river systems would benefit from more efficient and consistent methods for multi-temporal, regional assessment of habitat conditions. In this investigation, the utiliry of airborne, digital multi-spectral remote sensing of river habitats was assessed within two large regulated and unregulated river systems. The Yakima study reach, in central Washington, USA, is a meandering channel system with a large degree o f lateral stability due to moderately confined and relatively srable bed geology and reduced sediment and water supplies from upstrearn river regulation and irrigation withdrawals. The Nyack study reach in north-west Montana is an active flood plain with a large degree oflateral channel instability and cut and fil! alluviation characteristic of unregulated montane rivers of the Rocky Mountains. The specific objective was to quantify the relative structure and spatial extent of major habitat features within these two systems as a basis for understanding differences in habitat characteristics associated with different management and land-use activities.