A blank slate: revealing the eco-geomorphic dynamics of emergent reservoir landscapes using remote sensing data
Citation:
Kasprak, A., B. Bowen, M. DeHoff, C. Dott, G. Gianniny, C. Johnson, J. Sankey, AND M. Scott. A blank slate: revealing the eco-geomorphic dynamics of emergent reservoir landscapes using remote sensing data. Society for Freshwater Science Annual Meeting, Philadelphia, PA, June 02 - 06, 2024.
Impact/Purpose:
When reservoir water levels decline, what happens to the landscapes that emerge from the water? This research uses airborne and satellite data to document what species of vegetation colonize these new landscapes, and over what timescales that occurs.
Description:
As the world's reservoirs experience drawdowns from reduced precipitation and increased water demand, expanses of sediment are being exposed and colonized by both native and non-native vegetation. Within Lake Powell, the second largest reservoir in the U.S., drought in the Colorado River Basin has led to a rapid decrease in water level since ~2000. Here we use multispectral satellite and aerial imagery and airborne lidar to quantify vegetation dynamics across more than 400 km2 of backwater sediment between 2000-present. Our findings indicate that sediment deposits, which are up to 50 m thick and contain interbedded lacustrine, fluvial, and alluvial material, provide habitat for mesic (i.e., near-channel) riparian plants immediately following reservoir decline, but with progressive drawdown and exposure time, colonization shifts to drought-tolerant species, particularly the non-native shrub tamarisk (Tamarix spp.), which comprises approximately 20% of subaerial surfaces at present. With continued water recession, vegetation becomes disconnected from the water table, leading to nearly complete mortality and subsequent recolonization by xeric species. Finally, we compare current vegetation composition to the pre-reservoir ecosystem found along the Colorado and San Juan Rivers. Between dam closure and present, mesic riparian plan communities nearly doubled in area (91% increase), while more distal xeric communities increased by approximately 70%. Quantifying the dynamics of sediment exposure and vegetation provides opportunities for reservoir management to encourage the maintenance of native and/or culturally-valued ecosystems. The views expressed in this abstract are those of the authors and do not necessarily represent the views or policies of the US Government.