Potential effects of sea level rise on salmonid estuarine and freshwater habitat in Oregon, USA

Background/Question/Methods

Of the seven species of Pacific salmon, three are present in self-sustaining populations along the Oregon coast. Chinook (Oncorhynchus tshawytchta), steelhead (O. mykiss,), and coho salmon (O. kisutch) have complicated habitat requirements that include the continuum of freshwater, estuarine and marine habitats. Declining populations that appear resistant to current restoration efforts and strong popular support for restoration make these species of conservation interest. The primary objective of this study is to predict potential changes to salmon habitat in the estuarine and estuary-river ecotone with sea-level rise (SLR) associated with climate change. We used estuarine geomorphic conditions to organize our thinking about the effect of SLR on salmonid habitat. We analyzed five Oregon estuaries and calculated metrics that describe the physical and biological condition of the systems (total estuary area, perimeter, fractal dimension, ratio of watershed to estuary area, and length of upstream inundation by the estuary into current freshwater salmon habitat). Because elevation data was critical to this study, we evaluated the utility of different sources of elevation data for modeling the potential effects of sea-level rise on salmon habitat at the Salmon River estuary (comprehensive coast-wide LiDAR;  LiDAR flown specifically to capture low-tide conditions; and 10-m digital elevation models).

Results/Conclusions

In this study, we found that sea-level rise (SLR) has the potential to affect habitats critical in the life histories of imperiled populations of Pacific salmon. All estuaries showed considerable decreases in freshwater habitat for all three species of salmon explored in this study. The universal loss of freshwater habitat is of concern. A potential offset of freshwater habitat loss may be an expansion of estuarine habitat. Among the estuaries examined in our study, the potential of estuaries to develop additional complex habitats appeared greater in systems that are currently classified with a river- rather than a marine-dominated geomorphology. Further, the ability to predict effects of SLR on salmon habitat may depend on characteristics of the elevation data used for modeling. In essence, the coast-wide LiDAR at the Salmon River estuary yielded the most conservative estimate of the effect of SLR in terms of estuary area, sinuosity, salmonid freshwater habitat effects and river/marine classification because the base-level current condition that could be identified from the data is at high tide, rather than at the lower elevation of mean high tide.