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Abstract. The Kobuk River runs west along the southern Brooks Range from Gates of the Arctic National Park in Alaska, USA, to the Chukchi Sea. It is highly vulnerable to changes in climate due to its sub-Arctic location, unique geography, and permafrost foundation. Combined with its pristine condition, these qualities make the Kobuk an ideal system upon which to build a conceptual model for predicting ecosystem effects of climate change. We constructed a conceptual ecosystem model for the Kobuk River synthesizing surveyed baseline hydrologic, geomorphic and biotic conditions with literature on Arctic rivers. While the mainstem Kobuk has limited biological productivity, it provides spawning habitat and connectivity for large resident and migratory fish that rely upon off-channel habitat for food resources. System function is dependent largely on intermittent pulse flows that connect riverine habitats, allowing periods of late summer high productivity in off-channel habitat. Spring break-up and hill slope processes are critically important for maintaining habitat complexity and inter-connectivity. Climate change models predict the region will experience a disproportionate increase in average winter air temperature relative to summer temperatures, in the number of ice-free days, and in annual rainfall. Our conceptual model predicts that changes to fish and invertebrate populations on the Kobuk River will result not from physiological responses to increased temperatures, but rather to shifts in two main physical drivers: 1) spring break-up intensity, resulting in changes to scour rate and sediment deposition; and 2) discontinuous permafrost melt, resulting in widespread heterogeneous zones of active layer thickening and thermokarsting. The interaction of these two drivers offers four potential scenarios of geomorphic change in the system and four dramatically different biological outcomes. This model should help managers and scientists evaluate the magnitude and direction of ecosystem changes as they occur within the Kobuk system and potentially other sub-Arctic river systems.

The Sacramento-San Joaquin Delta (Delta) is in a state of inevitable transition. Physical and financial pressures are likely to transform parts of the Delta into open water within the next 100 years. Because flooded islands have different habitat, water quality, and hydrodynamic implications, depending on location, depth, orientation, and other physical factors, the state may decide to intentionally flood one or more Delta islands in an effort to better manage the Delta's ecosystem and valuable water supplies. This paper outlines three sets of near-term actions the state would have to take to begin transitioning toward intentional island flooding, and discusses legal and political challenges to those actions. Several key findings include the following: (1) amendments to California's water code and revisions to the Delta Land Use and Resource Management Plan may help the state ensure the legal authority to differentiate levee policies within the Delta; (2) permits for a first, experimental flooded island will likely require the State Water Resources Control Board to revise the Delta Water Quality Control Plan to allow for more short-term flexibility and deal with conflicting ecosystem and water supply uses; and (3) the state may want to prepare mitigation plans for private landowners on neighboring islands whose levees could face new threats of erosion and/or seepage from a nearby flooded island in order to avoid inverse condemnation lawsuits. If the state decides to shift its levee policies in the Delta, serious consideration will need to be given to these and additional common, regulatory, statutory, and constitutional laws.