Abstract
The Yukon-Kuskokwim Delta (YKD) is the largest delta in western North America and its productive coastal ecosystems support globally significant populations of breeding birds and a large indigenous population. To quantify past landscape changes as a guide to assessing future climate impacts to the YKD and how indigenous society may adapt to change, we photo-interpreted ecotypes at 600 points within 12 grids in a 2118 km2 area along the central YKD coast using a time-series of air photos from 1948–1955 and 1980 and satellite images from 2007–2008 (IKONOS) and 2013–2016 (WorldView). We found that ecotype classes changed 16.2% (342 km2) overall during the ~62 years. Ecotypes changed 6.0% during 1953–1980, 7.2% during 1980–2007 and 3.8% during 2007–2015. Lowland Moist Birch-Ericaceous Low Scrub (−5.0%) and Coastal Saline Flat Barrens (−2.3%) showed the greatest decreases in area, while Lowland Water Sedge Meadow (+1.7%) and Lacustrine Marestail Marsh (+1.3%) showed the largest increases. Dominant processes affecting change were permafrost degradation (5.3%), channel erosion (3.0%), channel deposition (2.2%), vegetation colonization (2.3%) and lake drainage (1.5%), while sedimentation, water-level fluctuations, permafrost aggradation and shoreline paludification each affected <0.5% of the area. Rates of change increased dramatically in the late interval for permafrost degradation (from 0.06 to 0.26%/year) and vegetation colonization (from 0.03 to 0.16%/year), while there was a small decrease in channel deposition (from 0.05 to 0.0%/year) due largely to barren mudflats being colonized by vegetation. In contrast, rates of channel erosion remained fairly constant. The increased permafrost degradation coincided with increasing storm frequency and air temperatures. We attribute increased permafrost degradation and vegetation colonization during the recent interval mostly to the effects of a large storm in 2005, which caused extensive salt-kill of vegetation along the margins of permafrost plateaus and burial of vegetation on active tidal flats by mud that was later recolonized. Due to the combination of extremely flat terrain, sea-level rise, sea-ice reduction that facilitates more storm flooding and accelerating permafrost degradation, we believe the YKD is the most vulnerable region in the Arctic to climate warming.
Highlights
The Yukon-Kuskokwim Delta (YKD) is the largest riverine delta in western North America and one of the most important breeding areas for migratory water birds in the world, with the highest population densities occurring in the central portion [1]
The drivers on landscape change associated with sea level rise, permafrost degradation, as well as other drivers, are active across the region so that our results provide an assessment that is roughly applicable across the coastal and coastal plain portions of the delta (Figure 1)
Assessing change trends is challenging, because different ecotypes respond to differing drivers in different areas at different times, with some drivers, such as sedimentation and salinization having short-term effects, while others, such as channel erosion and permafrost degradation having long-term effects
Summary
The Yukon-Kuskokwim Delta (YKD) is the largest riverine delta in western North America and one of the most important breeding areas for migratory water birds in the world, with the highest population densities occurring in the central portion [1]. The region has a large indigenous population because of the important subsistence resources in the surrounding Yukon Delta National Wildlife Refuge (YDNWR), with ~25,000 Yup’ik people in 35 villages, 17 of which are situated along the coast. The potential loss or alteration of habitat from sea-level rise, increased storm surges and permafrost degradation is a large concern to management of the YDNWR and to local communities. How fast ecosystems are changing in response to climate change, and what geomorphic and ecological processes are contributing to the changing landscape, are fundamental questions that need to be addressed to predict and adapt to future changes. To the need to understand complex changes in diverse ecosystems, and the processes driving change across heterogeneous landscapes, requires developing high-resolution spatial methodologies to adequately detect changes and trends at a level relevant to land managers and policy makers
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