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Utah State University

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sediment, Bear River, Bear Lake, Mud Lake, shoreline, hydrology, water quality

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The overarching goal of this project was to compile and analyze a variety of existing datasets, and generate several new datasets, to advance our understanding of how the Bear River Mud Lake-Bear Lake system functions, how it has, or is expected to change, identify which components are degraded or vulnerable to degradation, and determine if/where critical data and/or knowledge gaps exist. We conducted a series of analyses to evaluate changes in hydrology and suspended sediment, collected sediment cores from nine locations in Mud Lake to evaluate how sedimentation rates, sediment sources and water quality have changed over time, and utilized historical air photos and satellite imagery to document changes in Bear Lake’s shoreline.

Hydrologic analyses indicate that low, median and high flows have not changed systematically at the Inlet Canal in terms of their long-term averages, since the 1940s. However, all three flow metrics have increased in terms of variability and have experienced longer duration wet and dry periods over the past three decades. We note a paucity of long-term hydrologic datasets for the Bear River-Dingle Marsh-Bear Lake system and additional monitoring would greatly help ensure that we are able to monitor trends throughout the system more carefully. We compiled suspended sediment data from all available sources and concluded, similar to previous studies, that Mud Lake appears to serve as a sediment sink for sediment, but the sediment trapping efficiency appears to vary considerably within and among years. Similar to the flow data, we note an unfortunate paucity of suspended sediment data and strongly recommend more rigorous and continuous monitoring of sediment in all parts of the Bear River-Mud Lake-Bear Lake system. Existing data and monitoring programs are insufficient to identify trends over time.

The nine sediment cores extracted from Mud Lake provide a longer-term perspective on sediment dynamics. Results demonstrate that Mud Lake has historically and continues to serve as a net sediment sink. Two of the six dated cores document continuous deposition over the past 120 years, while the other four cores show truncated profiles in the 1950s. Visual inspection of the cores, as well as analysis of organic, calcium carbonate and mineral fractions occurring in the cores demonstrate highly variable history of sediment sources and water quality conditions in Mud Lake. Analysis of diatom algae species provides more detailed information regarding water quality conditions, indicating that Mud Lake has changed from a planktonic glacial lake, to a cold water, low nutrient environment and has existed as a mesotrophic environment with moderate water quality over the past century. Given the detailed information that diatoms can provide regarding historical water quality, we suggest that a similar diatom study examining the past 150 years in Bear Lake’s history could be worthwhile. Elemental analysis of Mud Lake sediments indicate two significant shifts in sediment sources, one coincident with diversion of Bear River into Mud Lake approximately 100 years ago, and a recent shift, within the past 10 years as silver, mercury and rare earth elements have increased considerably.

Analysis of Bear Lake’s shoreline from historical imagery shows considerable amount of deposition has occurred in most areas around the lake in the past several decades. The shoreline at low water levels has moved lakeward by 30 to 50 meters (100 to 160 feet) in several locations and as much as 500 m (1600 feet) in the northwest corner of the lake, near St. Charles Creek. Notably, the only location where we document shoreline erosion (i.e., the shoreline moving landward for a given water elevation) is along the eastern edge of the lake, near Porcupine Hollow, Peterson Hollow and Bear Lake State Park. Further, we document that approximately 10% of the beach area in the northwest corner of the lake near St. Charles Creek has transitioned to vegetation cover between 2003 and 2016.