Changing Arctic River Deltas

Wednesday, December 12, 2018 - 08:00
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Deltas connect rivers to the coastal ocean and buffer or filter the delivery of water, sediment, and nutrients to the coast. The potential filtering effect of deltas depends on the spatial patterns of channels and lakes, which is likely to change as Arctic deltas respond to sea level rise, changing hydrology, permafrost thaw, and retreating sea ice. We conducted an analysis of Landsat imagery for six high-latitude deltas (Colville, Kolyma, Lena, Mackenzie, Yenisei, Yukon) to determine the change in patterns and types of water bodies on decadal timescales. We utilized the oldest available cloud-free Landsat image(s) for each delta and a modern-day image (ca. 2014). Image classifications were done using eCognition and image objects were classified as either channel, land, lake, or other small water (≤ 4 pixels in width). Change on each delta was determined using two methods: (1) detecting change in the classification type of each individual pixel and (2) using the Spatially Continuous Riverbank Erosion and Accretion Measurements program to detect shifts in the planform channel network. Results suggest drying of the Yenisei delta over the period measured, while the other deltas have become wetter. The most notable change on the Yenisei was the disappearance or shrinking of small water bodies and lakes, as many seem to have dried up or contracted between 1990 and 2013, indicating a possible decrease in water storage on the delta plain over time. The Yukon and the Kolyma, on the other hand, showed many areas of lake expansion and new lake development, suggesting that these systems may be able to store more fine sediment and/or increase the residence time of water traveling through the deltas. Channels on the Yukon delta had the lowest erosion rates and some of the highest accretion rates overall, which may be due to the more rapid colonization of in-channel bars in the warmer climate of the Yukon compared to the other deltas. Channel erosion rates were highest on the Lena and Kolyma deltas, while channel accretion rates were highest on the Lena and Yukon. Future work aims to unravel the influences of local climate, hydrology, ice, and marine forcings on rates of channel bank migration and landscape change in Arctic river deltas.

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