Environmental heterogeneity and community structure of the Kobuk River, Alaska, in response to climate change

Abstract

The Kobuk River runs west along the southern Brooks Range from Gates of the ArcticNational Park in Alaska, USA, to the Chukchi Sea. It is highly vulnerable to changes in climate due to itssub-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 predictingecosystem effects of climate change. We constructed a conceptual ecosystem model for the Kobuk Riversynthesizing surveyed baseline hydrologic, geomorphic and biotic conditions with literature on Arcticrivers. While the mainstem Kobuk has limited biological productivity, it provides spawning habitat andconnectivity 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, allowingperiods of late summer high productivity in off-channel habitat. Spring break-up and hill slope processesare critically important for maintaining habitat complexity and inter-connectivity. Climate change modelspredict the region will experience a disproportionate increase in average winter air temperature relative tosummer temperatures, in the number of ice-free days, and in annual rainfall. Our conceptual modelpredicts that changes to fish and invertebrate populations on the Kobuk River will result not fromphysiological 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) discontinuouspermafrost melt, resulting in widespread heterogeneous zones of active layer thickening andthermokarsting. The interaction of these two drivers offers four potential scenarios of geomorphic changein the system and four dramatically different biological outcomes. This model should help managers andscientists evaluate the magnitude and direction of ecosystem changes as they occur within the Kobuksystem and potentially other sub-Arctic river systems. © 2011 Durand et al.