Hierarchical Ecosystem Classification for the Columbia River Estuary: Applications to Long-Term Monitoring and Salmon Recovery

Classification of diverse scale-dependent and scale-independent ecosystem structures and processes can be a valuable tool for research, monitoring and management of across complex estuarine gradients and process scales. Current estuarine classification approaches often do not address tidal-freshwater ecosystems or lack sufficient resolution to distinguish landscape and geomorphic features that influence ecosystem development. We have developed a hierarchical framework that classifies the diversity in ecosystem structure and processes across the euhaline to oligohaline continuum in the Columbia River estuary (CRE). The CRE Ecosystem Classification (“Classification”) aggregates land and aquatic cover classes according to the ecosystem processes that structure landscapes at different spatial scales. Of the six hierarchical levels (Ecosystem Province, Ecoregion, Hydrogeomorphic Reach, Ecosystem Complex, Geomorphic Catena, Primary Cover Class), the first three are based on the US Environmental Protection Agency’s ecoregions and the last level on remotely-sensed land cover class data. The intermediate levels—Ecosystem Complex and Geomorphic Catena—are derived from bathymetric, topographic, geomorphic, geologic and other higher-resolution datasets and are the most challenging scales to capture the dynamic nature of estuarine ecosystems for research, monitoring and management. The overall morphology of the CRE—attributes defining the eight hydrogeomorphic reaches—is chiefly attributable to Neocene and Quaternary geologic events of the last 50 Ma, whereas the character of the distribution of channel and floodplain areas constituting ecosystem complexes and geomorphic catena mostly derives from processes and events of the Holocene epoch, encompassing the last 15-10,000 yr since the last glacial maximum; but the greatest change to CRE ecosystem processes that shape the structure of complexes and catena derives from the hydrologic and floodplain development of the last 100 yr. With the support of the federal action agencies on the Columbia River estuary, we have recently been able to acquire and incorporate the most recent bathymetric, topographic (LiDAR) and land cover/land use datasets into the Classification. Although just emerging as a complete geospatial data catalog for the entire 235 km estuary, the Classification has already proven its potential utility as a template for environmental monitoring and juvenile salmon habitat restoration planning: the Hydrogeomorphic Reach and Ecosystem Complex levels provide a coarse-scale template for allocating chemical and biological samples, and the Geomorphic Catena are proving useful in developing fish habitat priorities for restoration and conservation. Although data specific to the CRE, the Classification may offer insights toward more effective frameworks for research and monitoring of ecosystems in other large flood plain estuaries.