Interactions Between Physical and Biological Processes in Riverine Landscapes II: Spatial Heterogeneity and Scales of Interactions A
Presiding: J M Buffington, USDA Forest Service; C V Baxter, Colorado State University; A E Rosenberger, University of Idaho and USDA Forest Service
B41A-01 08:30h
Integration of Biological and Physical Sciences to Advance Ecological Understanding of Aquatic Ecosystems
Conservation and restoration of freshwater stream and river habitats are important goals for land management and natural resources research. Several examples of research have emerged showing that many species are adapted to temporary habitat disruptions, but that these adaptations are sensitive to the spatial grain and extent of disturbance as well as to its duration. When viewed from this perspective, questions of timing, spatial pattern, and relevant scales emerge as critical issues. In contrast, much regulation, management, and research remains tied to pollutant loading paradigms that are insensitive to either time or space scales. It is becoming clear that research is needed to examine questions and hypotheses about how physical processes affect ecological processes. Two overarching questions concisely frame the scientific issues: 1) How do we quantify physical watershed processes in a way that is meaningful to biological and ecological processes, and 2) how does the answer to that question vary with changing spatial and temporal scales? A joint understanding of scaling characteristics of physical process and the plasticity of aquatic species will be needed to accomplish this research; hence a strong need exists for integrative and collaborative development. Considering conservation biology problems in this fashion can lead to creative and non-obvious solutions because the integrated system has important non-linearities and feedbacks related to a biological system that has responded to substantial natural variability in the past. We propose that research beginning with ecological theories and principles followed with a structured examination of each physical process as related to the specific ecological theories is a strong approach to developing the necessary science, and such an approach may form a basis for development of scaling theories of hydrologic and geomorphic process. We illustrate the approach with several examples.
http://www.fs.fed.us/rm/boise/
B41A-02 INVITED 08:45h
The Interdependence of Surface and Subsurface Habitat Diversity
Geomorphic structures and hydrologic dynamics shape the physical template of lotic ecosystems, both on the surface and within the hyporheic zone. While recent studies have described the importance of surface and subsurface habitat diversity, our ongoing field and modeling research projects are documenting the interdependence of channel and hyporheic habitat diversity along with the role of biological processes in responding and contributing to hydrologic complexity and habitat diversity in fluvial landscapes. Patterns of variation in both hydrologic flow paths and water temperature can be used to illustrate the interdependence of complexity and diversity in lotic and hyporheic environments, both of which are mediated by variation in stream geomorphology and discharge regime. For instance, our data suggest that flood-plain topography interacts with the discharge regime to determine the complexity of surface and hyporheic hydrology, which influences and is influenced by seasonal growth and senescence of vegetation. Flood-plain hydrology, in turn, drives patterns of surface water temperature, in both main-channel and lateral aquatic habitats. These results lead us to conclude that simplification of surface habitat can have substantive effects on subsurface habitat diversity, and vise versa.
B41A-03 09:00h
Geomorphic Heterogeneity at the Valley Segment Scale: Effects on Habitat Structure, Aquatic Organisms, and Stream-Riparian Food Web Linkages
A distinct domain of heterogeneity at the valley segment scale has long been recognized by geomorphologists, but its implications for stream ecology have received less attention. As opposed to sampling discrete points, stream ecologists' efforts to make maps have generally been applied at only at very large or small spatial scales. We have found mapping of valley segment types a powerful tool for detecting patterns at an intermediate scale, which then sets the stage for interpreting patterns observed at both smaller and larger scales. We report results from a series of studies that describe how valley segment types and their arrangements within river networks affect the expression of habitat structure, the distribution and abundance of species, the makeup of communities, and the flux of resources between aquatic and terrestrial food webs. Study tools such as valley segment mapping provide a more spatially continuous perspective on biophysical heterogeneity in riverine landscapes. In turn, increasing the spatial extent and resolution of data improves the scope of a study, which enhances power to detect patterns and investigate scaling relationships in river networks.
B41A-04 09:15h
A Spatially Explicit Approach for Evaluating Relationships among Coastal Cutthroat, Habitat, and Disturbance in Headwater Streams
Headwater stream systems are complex networks that form a physicochemical template governing the persistence of aquatic species such as coastal cutthroat trout. Individual portions of the network can function as conduits or receptacles for sediments, wood, and nutrients from terrestrial areas. Temporal and spatial changes in the delivery of these constituents can substantially alter the habitat template and its ability to support this native fish. Our study of 40 mid-sized watersheds (500 - 1,500 ha) in western Oregon is providing new insights into the factors affecting the distribution of coastal cutthroat trout within, and among, headwater stream networks. For example, data suggest that coastal cutthroat trout move throughout the accessible portions of headwater streams for reproductive, feeding, and refuge purposes. Fish congregate in these areas and form local populations that may exhibit unique phenotypic and genetic attributes. At times, coastal cutthroat trout move into larger downstream portions of the network where they may contribute to the persistence and genetic character of anadromous or local potamodromous assemblages. Variation in distribution patterns among watersheds reflects diverse environments and selective factors, such as geology, geomorphology, climate, and land-management history. Our research findings suggest that human activities that impede movement among suitable habitat patches can have lasting consequences for local assemblages of coastal cutthroat trout and may ultimately affect persistence.
B41A-05 09:30h
Hydrogeomorphic Classification and Functional Composition of Benthic Communities in the Pacific Northwest Mountains
We examine variation in insect species traits in the context of a multi-scale hydrogeomorphic classification of streams in mountainous regions of the Pacific Northwest. Using insect data from over 250 streams in Oregon and Washington, we focus on key species traits that explain significant variation in community trait composition across a gradient of hydrogeomorphic disturbance regimes. Site-specific predictions of flow regime, valley setting, geomorphic type, and substrate characteristics derived exclusively from common geospatial data are used individually and in combination to construct a priori and a posteriori physical classifications that are geographically independent. The relative strengths of the classification schemes are assessed by the extent to which within-class similarity in functional composition exceeds the similarity between classes. Given the fundamental role of interactions between flow regime and geomorphic context in structuring insect communities, process-based classifications that integrate hydrologic and geomorphic characteristics offer an attractive means for understanding how environmental drivers vary with landscape context and stratifying bioassessment sites within heterogeneous regions.
B41A-06 09:45h
Spatially Explicit, Individual-Based Models Can Predict Fish Population Responses to Spatio-Temporal Variation in Physical Processes
Spatially explicit, individual-based models of fish populations can provide insights into the interactions of physical and biological processes in rivers. These models can include virtual environments with many of the complexities of real river habitat, including spatial and temporal variation in hydraulic conditions, cover, predation risk, and competition for resources. Model fish can use realistic behaviors to adapt to their physical environment, especially by moving to habitats that offer relatively high fitness potential. We used an individual-based model of stream trout with a daily time step to estimate responses to variation in physical conditions and processes at various spatial scales. Within simulated reaches, greater physical heterogeneity at the habitat-cell scale produced populations with greater variation in size and age distributions and less variable overall abundance. Realistic variation in reach-scale physical factors such as turbidity and redd scour probability had strong consequences for fish abundance and biomass. However, time lags in some biological responses reached several years. Sensitivity analyses of the model highlight the need for greater understanding of abiotically driven spatial and temporal variation in key biological processes.