Patterns and Potential Drivers of a Seasonal Glacial Sediment Plume derived from Landsat CDR Data, Lake Clark, Alaska

Abstract:

Lake Clark is large freshwater lake in Southcentral Alaska. Central to Lake Clark National Park and Preserve, Lake Clark is an important nursery lake for sockeye salmon (Oncorhynchus nerka) in the headwaters of Bristol Bay, Alaska, the most productive wild salmon fishery in the world. Lake Clark water clarity is seasonally influenced by a dynamic glacier fed sediment plume. We reconstructed lake-wide water clarity for Lake Clark using the Landsat TM and ETM+ Climate Data Record archive. Our study period consisted of May – October for 1985-2015. We found 151 (98 partial- and 53 whole-lake) Landsat scenes that captured the lake and/or sediment plume. Water clarity fluctuated on an annual basis with specific conditions common to certain months. Plume development and peak turbidity dates could be estimated for a number of years and mid-season gyres appear to represent wind-induced mixing of lake water. Our results showed short term (sub-decadal) trends in water clarity but little to no long term trend between 1991 and 2014. We did, however, detect interannual variation that exhibited a non-significant (r² = 0.20) but positive correlation (r = 0.20) with regional mean summer air temperature and found the month of May exhibited a significant positive trend (r² = 0.68, p-value = 0.02) in turbidity between 2000 and 2014. These results are important because reductions in water clarity within Alaska lake systems as a result of increased glacial runoff have been shown to reduce salmon production via reduced abundance of preferred prey items of juvenile salmon, such as zooplankton and macroinvertebrates.