Abstract
Landscape geomorphic instability is common in tectonically active regions, but the ecological consequences of mass wasting are rarely considered. The Late-Holocene sediment from Lake Crescent (USA) exhibits a remarkable record of repeated catastrophic mass wasting events, each of which led to deposition of meter-scale mass transport deposits on the lake floor. We used high temporal resolution diatom analysis of selected intervals of a 14C-dated sediment core to assess the effect of two disturbance events on the lake at different period in its development state. The two disturbance events produced mass transport deposit I (MTD-I) and mass transport deposit II (MTD-II) at 3100 ± 100 and 4000 ± 100 cal year BP, respectively. The MTD-II event dammed the lake and increased water levels, but also blocked the migration of spawning salmon, reducing marine-derived nutrient inputs. These changes resulted in a more oligotrophic lake environment. Following the MTD-II event, diatom assemblages were dominated by benthic species and exhibited low rates of compositional change. In contrast, the MTD-I event favored nutrient-demanding planktonic diatoms (e. g.
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