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Dam installation on a deep hydrologically open lake provides the experimental framework necessary to study the influence of outlet engineering and changing base levels on limnogeological processes. Here, high-resolution seismic reflection profiles, sediment cores, and historical water level elevation datasets were employed to assess the recent depositional history of Jackson Lake, a dammed glacial lake located adjacent to the Teton fault in western Wyoming (USA). Prograding clinoforms imaged in the shallow stratigraphy indicate a recent lake-wide episode of delta abandonment. Submerged ∼11–12 m below the lake surface, these Gilbert-type paleo-deltas represent extensive submerged coarse-grained deposits along the axial and lateral margins of Jackson Lake that resulted from shoreline transgression following dam construction in the early 20th century. Other paleo-lake margin environments, including delta plain, shoreline, and glacial (drumlins, moraines) landforms were likewise inundated following dam installation, and now form prominent features on the lake floor. In deepwater, a detailed chronology was established using 137 Cs, 210 Pb, and reservoir-corrected 14 C for a sediment core that spans ∼1654–2019 Common Era (CE). Dam emplacement (1908–1916 CE) correlates with a nearly five-fold acceleration in accumulation rates and a depositional shift towards carbonaceous sediments. Interbedded organic-rich black diatomaceous oozes and tan silts track changes in reservoir water level elevation, which oscillated in response to regional climate and downstream water needs between 1908 and 2019 CE. Chemostratigraphic patterns of carbon, phosphorus, and sulfur are consistent with a change in nutrient status and productivity, controlled initially by transgression-driven flooding of supralittoral soils and vegetation, and subsequently with water level changes. A thin gravity flow deposit punctuates the deepwater strata and provides a benchmark for turbidite characterization driven by hydroclimate change. Because the Teton fault is a major seismic hazard, end-member characterization of turbidites is a critical first step for accurate discrimination of mass transport deposits controlled by earthquakes in more ancient Jackson Lake strata. Results from this study illustrate the influence of dam installation on sublacustrine geomorphology and sedimentation, which has implications for lake management and ecosystem services. Further, this study demonstrates that Jackson Lake contains an expanded, untapped sedimentary archive recording environmental changes in the American West. 

The large population sizes and high dispersal potential of microbes suggests that a given microbial species should be found in all suitable habitats worldwide. Consequently, microbes should not exhibit the kinds of biogeographic patterns seen in macroorganisms. This paradigm is challenged by a growing list of exotic microbes with biogeographic disjunctions that instead promotes microbial dispersal as inherently limited. We sampled water bodies in the United States and compiled records from the literature and public databases to characterize the distribution of the freshwater planktonic diatom, Discostella asterocostata (Xie, Lin, and Cai) Houk and Klee. Discostella asterocostata was thought to be restricted to the Far East, but we report its presence in ecologically similar water bodies across the eastern United States. Populations from the U.S. and China are indistinguishable morphometrically, suggesting they may be recently separated—a hypothesis supported by paleolimnological data, which support an introduction of D. asterocostata into the U.S. as recently as the mid-1980s. The overlapping distributions of D. asterocostata and invasive carp species, in both their native and nonnative ranges, highlighted Asian carp as a possible vector for introduction of the diatom in the U.S. The existence of exotic diatoms underscores natural constraints on microbial dispersal, resulting in biogeographic distributions that can be upended through human activity.