Ninth International Conference on Permafrost ... - IARC Research

Retrogressive Thaw Slump Impacts on Inconnu Spawning Habitat in theSelawik River, AlaskaRaymond HanderU.S. Fish and Wildlife Service, Fairbanks Fish and Wildlife Field Office, Fairbanks, AK, USAKenji YoshikawaInstitute of Northern Engineering, Water and Environmental Research Center, University of Alaska Fairbanks, USANathan OlsonU.S. Fish and Wildlife Service, Selawik National Wildlife Refuge, Kotzebue, AK, USAIntroductionOne of the most dramatic changes and concerns of climatewarming is the increased rate of thawing permafrost andits related environmental shifting, such as changing thehydrological regime of river systems. The Kotzebue Soundarea of northwestern Alaska is widely recognized as oneof the most ice-rich and thaw-sensitive areas in Alaska(Fig. 1). In particular, glaciated areas are prone to developretrogressive thaw slumps (RTS) by the thawing of buriedglacial ice bodies.In the spring of 2004, a large RTS occurred in the upperSelawik River drainage above important inconnu Stenodusleucichthys spawning habitat within the Selawik NationalWildlife Refuge (Refuge) (Fig. 2). This event changed thewater from a clear to a glacial-colored river that was noticedby Refuge personnel and persons from Selawik. The SelawikRiver is habitat for a number of whitefish species, including inconnuthat support an important subsistence fishery and occupyan important ecological role in the Kotzebue, Alaska area.Little is known about the physical spawning habitatrequirements for inconnu, especially sensitivity to theaccretion of sediments. There is potential that sedimentcould fill interstitial spaces between the gravel and cobblesubstrate where fertilized eggs need to settle, overwinter,and mature.Since 2004, the RTS has continued to erode and influencethe river with no apparent end in sight. The RTS is causedby ice-rich permafrost degradation resulting in slope failure(Jorgenson & Osterkamp 2005). Also, increasing thermokarstactivity has been identified in a 5,000 km 2 survey area in theadjacent Noatak National Preserve by Bowden et al. (2007).Preliminary RTS analysisWe attempted to provide an estimate of the volume ofsediment/ground ice that has eroded into the Selawik Riverfrom the RTS since 2004 using stereophotogrammetricanalysis methods of aerial remote sensed imagery (Fig. 3).This analysis indicated that approximately 25,000,000 to60,000,000 kg of sediment were released from the RTS in the2007 melting season. Since 2004, the RTS was discharging267 g/L of suspended sediments and discharging more than100 L/sec from thawing permafrost during the meltingseason. At the inconnu spawning area in August 2007,deposited sediment was observed, and suspended sedimentswere measured to be at least 375 mg/L.Figure 1. Map of the Selawik River, inconnu spawning area, andthe retrogressive thaw slump location.Figure 2. Selawik River retrogressive thaw slump, 2005. Whitecircle is around a person and provides a slump-size scale.Inconnu habitat and RTS monitoring and researchImpacts to the Selawik River inconnu population maynot be known until the age cohorts from eggs depositedduring sediment discharge years reach maturity and returnto spawn in about 7 to 12 years (Brown 2000). Work isplanned to assess the spawning habitat area for silt accretionon the spawning ground. Also, assessment of inconnu eggdistribution relative to stream substrate characteristics willbe explored to gain an understanding of specific habitat(s)where eggs reside for overwintering and maturation.Continued RTS analysis in 2007 will include assessing the91