Connectivity of Aquatic Habitats in Space and Time

River systems have been extensively modified by human development of uplands and alterations in stream flows. These changes reduce the capacity of river floodplains to absorb natural geophysical and environmental changes and directly affect life-history adaptations that native species have developed over the millennia. For example, in western North America, changes in upslope processes (i.e., fire regimes, forest harvest and associated management) work in concert with alterations in natural flow and thermal regimes through dams, levees, and floodplain development to change inundation patterns of rivers and their floodplains. However, existing phenotypic (physical and life cycle) adaptation by native fish to environmental conditions may not be compatible with alterations to flow and thermal regimes. Climate change may compound this issue, both directly and indirectly, by pushing conditions toward what, in the past, would have been environmental extremes, thereby inhibiting the full expression of life-history diversity present in current populations.

Streams are organized as interconnected water networks. Fish and other aquatic-obligate species use habitats throughout a stream network. Patterns of occupancy for coho salmon in Canal Creek in the Oregon Coast Range expand and contract around a central core area that tends to be consistently used (Flitcroft 2007).

By analyzing streams as seasonal networks of connected and disconnected habitats, we have developed insights into patterns of habitat occupancy, as well as contextual links with broad-scale processes such as landslides and land management. The analysis also clarifies linkages between life stages and patterns of temperature and discharge with implications for future climate scenarios. This work examines multiple scales of processes to develop a synthetic understanding of patterns of aquatic habitat for fish and other aquatic biota.

Native fish are adapted to seasonal patterns of river discharge and temperature. Specific life stages can take advantage of available habitats as they change throughout the year. Age 1+ juveniles are last year’s hatch; age 0+ juveniles are this year’s hatch.

Restoration of floodplains provides an opportunity to affect multiple dimensions of connection in aquatic environments as rivers again interact laterally, vertically, and horizontally with the sediments, water, nutrients, and biota that occupy these dimensions of the river corridor. The goal of this type of restoration is to enable natural processes to develop complex habitat and resilient biological communities. Research into the effect of intense floodplain restoration is necessary to fully understand the effects of these new and revolutionary restoration actions. This work includes evaluation of the geomorphic, hydrologic, and biological changes that occur after intense restoration that modifies bedform configurations and local biological communities.

Log structures were placed in the floodplain of the South Fork McKenzie River as part of a restoration to Stage-0 project. Large wood is a critical element of surface roughness intended to contribute to hydraulic and geomorphic complexity. USDA Forest Service photo by Jay Munyon.

Interannual patterns in the distribution of juvenile coho salmon throughout river networks point to important core locations of consistent occupancy, as well as the response of the population to environmental conditions, and the size of the spawning population.

Sams Creek watershed in the Oregon Coast Range showing core locations of high juvenile coho salmon density over time. Some areas were occupied only in years of high population numbers, or when river discharge or adult population size facilitated expansion out of core areas (fig. 3 from Flitcroft et al. 2012).

By combining long-term records of stream flow, water temperature, and upstream fish passage in visualizations we call ichthyographs, we provide a strong empirical foundation for understanding upstream behavioral movement and tolerances of native fish. Using ichthyographs, we found that coho salmon in different watersheds will have varying vulnerability to future climate change.

Long-term data records of daily discharge, water temperature, and fish movement are combined in ichthyographs to assess current expressed behavioral variability of native fish, as well as their vulnerabilities to future climatic patterns (fig. 2 from Flitcroft et al. 2019).

Research into the effects of floodplain restoration is ongoing. Preliminary analysis suggests that there may be dramatic effects on the configuration of habitats and interactions with hydrologic processes. Efforts to quantify biological effects are underway, along with remotely sensed applications exploring stream evolution following restoration.

Network-based approaches have facilitated analysis of long-term monitoring datasets that contribute to adaptive management applications in the area covered by the Northwest Forest Plan as well as in other local or regional applications.

Analyses of phenological patterns of salmonid species demonstrate linkages between life-stage/habitat associations and patterns of stream flow and temperature at local and population scales. This information helps guide management on matters of water regulation, dam management, and fish-harvest timing.

Empirical as well as theoretical ichthyographs of expressed behavior of coho salmon in relation to river discharge and temperature allow for analysis of phenological variability and climate change. The amount of behavioral diversity is linked to the adaptive capacity of local populations as climate or land use alter patterns of temperature and discharge in streams, thus changing the cues for transitions between life stages. This information aids in the development of management goals that are intended to develop resilience to climate change in local salmon populations.

Restoration of floodplains for resilience is a high priority for recovery of imperiled species, and tracking effects of these projects on different seasonal assemblages of macroinvertebrates provides insights into the biological effectiveness of intensive restoration actions.

Researchers evaluate macroinvertebrate abundance and diversity in the South Fork McKenzie River, Oregon in spring and autumn to assess changes in assemblage diversity at different times of the year. The study took an unexpected turn when the restoration site burned in the Holiday Farm Fire in 2020. Here, technicians are taking macroinvertebrate samples shortly after the end of the wildfire season. USDA Forest Service photo by Jay Munyon.

Collaborators

• Mary Santelmann, Oregon State University

• Ivan Arismendi, Oregon State University

• Clint Epps, Oregon State University

• NOAA Fisheries

• University of Washington

• Oregon Department of Fish and Wildlife

• University of Oregon

• University of California at Merced