Millions of lakes worldwide are distributed at latitudes or elevations resulting in the formation of lake ice during winter. Lake ice affects the transfer of energy, heat, light, and material between lakes and their surroundings creating an environment dramatically different from open-water conditions. While this fundamental restructuring leads to distinct gradients in ions, dissolved gases, and nutrients throughout the water column, surprisingly little is known about the resulting effects on ecosystem processes and food webs, highlighting the lack of a general limnological framework that characterizes the structure and function of lakes under a gradient of ice cover. Drawing from the literature and three novel case studies, we present the Lake Ice Continuum Concept (LICC) as a model for understanding how key aspects of the physical, chemical, and ecological structure and function of lakes vary along a continuum of winter climate conditions mediated by ice and snow cover. We examine key differences in energy, redox, and ecological community structure and describe how they vary in response to shifts in physical mixing dynamics and light availability for lakes with ice and snow cover, lakes with clear ice alone, and lakes lacking winter ice altogether. Global change is driving ice covered lakes toward not only warmer annual average temperatures but also reduced, intermittent or no ice cover. The LICC highlights the wide range of responses of lakes to ongoing climate-driven changes in ice cover and serves as a reminder of the need to understand the role of winter in the annual aquatic cycle.

Sewage released from lakeside development can introduce nutrients and micropollutants that can restructure aquatic ecosystems. Lake Baikal, the world's most ancient, biodiverse, and voluminous freshwater lake, has been experiencing localized sewage pollution from lakeside settlements. Nearby increasing filamentous algal abundance suggests benthic communities are responding to localized pollution. We surveyed 40-km of Lake Baikal's southwestern shoreline from 19 to 23 August 2015 for sewage indicators, including pharmaceuticals, personal care products, and microplastics, with colocated periphyton, macroinvertebrate, stable isotope, and fatty acid samplings. The data are structured in a tidy format (a tabular arrangement familiar to limnologists) to encourage reuse. Unique identifiers corresponding to sampling locations are retained throughout all data files to facilitate interoperability among the dataset's 150+ variables. For Lake Baikal studies, these data can support continued monitoring and research efforts. For global studies of lakes, these data can help characterize sewage prevalence and ecological consequences of anthropogenic disturbance across spatial scales.

Grazing by microzooplankton has been shown to significantly impact freshwater cyanobacteria blooms; however, the contribution of rotifers to the overall effect of microzooplankton grazing is not well understood. We conducted monthly microzooplankton community grazing (dilution) experiments June-October 2019, concurrent with incubations of field-collected rotifers feeding upon the natural assemblage of microplankton prey < 75 mu m in Vancouver Lake (Washington State, USA), a lake annually affected by cyanobacteria blooms. Our results showed that just days after a large bloom, the microzooplankton community grazing impact on phytoplankton biomass was exceptionally high (> 1000% d(-1)), yet the impact by rotifers was low (< 1% d(-1)). As the bloom diminished in September and October, the grazing impact of rotifers increased dramatically, specifically consuming substantial dinoflagellate (<= 574%) and ciliate (<= 382%) biomass daily. Analysis of rotifers in Vancouver Lake during these months showed the presence of large, carnivorous Asplanchna spp., which indicates multi-trophic grazing dynamics within the rotifer assemblage. We conclude that non-rotifer micro-grazers (i.e., ciliates) were likely responsible for the initial dissipation of cyanobacteria just after the bloom peak, while rotifers primarily removed micro-grazers later in autumn. This study highlights the trophic roles of micro-grazers in controlling harmful cyanobacteria blooms and quantifies the specific grazing contributions of rotifers.

Mountain lakes experience interannual variability in spring snowpack and ice cover that can lead to differences in physical, chemical, and biological properties in the succeeding summer. Lake studies that capture extreme years of snow and ice would be useful to understand and anticipate effects of climate change, but such data are rare for remote mountain lakes. Monitoring of lakes in Olympic, North Cascades, and Mount Rainier National Parks from 2007 to 2018 allowed us to examine limnological differences along interannual and elevation-driven climate gradients that included unusually high (2011-2012) and 100-yr record low (2015) snowpack years. Years with lower spring snowpack had earlier ice-out. Across lakes, our analysis suggested an average of 0.075 degrees C lake warming per day of lost ice duration (0.525 degrees C per week), giving rise to other ecosystem changes linked to temperature such as lower dissolved oxygen, higher total dissolved N, higher chlorophyll, and higher abundance of cladoceran zooplankton. Conversely, in years with higher snowpack and a shorter ice-free season, lakes were colder and clearer (1 m deeper Secchi depth for every 1 m May snow water equivalent), with more dilute ions as well as lower algal biomass and zooplankton abundance. These results add to evidence that changes in snowpack or ice-out dates alter mountain lake ecology through multiple processes associated with hydrology, terrestrial-aquatic connection, water temperature, productivity, ion composition, and plankton communities.

Major and trace element and radiogenic isotopic characteristics of primitive mafic Pleistocene and Holocene lavas from Newberry Volcano, Oregon, define two groups. The first consists of dry tholeiitic high-alumina olivine basalts that are slightly enriched in highly incompatible elements. The second group consists of calc-alkaline basalts that contained 2-4 wt % H2O prior to eruption and shows strong enrichment in the light rare earth elements, Ba, and Sr, and deficits in Nb, Ta, Hf, and Zr. The tholeiitic basalts reflect 6-11% anhydrous adiabatic decompression melting of spinel peridotite. The calc-alkaline basalts derived from compositionally distinct sources with strong LIL enrichment and relative depletion in HFSE, but with Sr, Nd, Hf, and Pb isotopic composition only slightly distinct from the sources of the tholeiitic magmas. Radiogenic Os correlates with LREE enrichment in the calc-alkaline magmas, which indicates that their source materials include a contribution from a mafic component that was melted in the garnet stability field. The calc-alkaline magmas were derived by melting of peridotite metasomatized by a fluid/melt that originated by melting of a mixture of the sediment plus MORB basalt/mantle in the underlying subducting oceanic plate. While the trace element characteristics of the calc-alkaline magmas were determined by the subduction component, their isotopic characteristics were modified during transit through the mantle by interaction with the highly magmatically processed mantle wedge beneath Newberry Volcano that, without the slab component, serves as the source of the tholeiitic magmas.

In order to apply the vanadium (V) stable isotope system for studies of planetary accretion and evolution in the solar system and redox variations in terrestrial magmatic processes, the V isotope composition of the Bulk Silicate Earth (BSE) needs to be precisely constrained. Previous studies have shown that fertile peridotites have systematically higher V-51/V-50 ratios than MORB. This, however, is in conflict with the theoretical prediction that mantle melting residues should be enriched in V-50 rather than V-51. To address these issues, a more precise estimate of the V isotope composition of the BSE is required. This study presents delta V-51 data for eleven peridotite xenoliths from two late Cenozoic eruption centers at Tariat in central Mongolia, ten komatiites from five localities ranging in age between 3.48 and 2.41 Ga, and four 1.98 Ga picrites from the Onega Plateau in Fennoscandia. The mean delta V-51 for fertile spinel lherzolites is -0.91 +/- 0.06 parts per thousand (2SD, n = 8). They show no resolvable difference in V isotope compositions compared to three moderately to highly refractory peridotite xenoliths analyzed, with a mean 5 51 V of -0.93 +/- 0.01 parts per thousand (2SD, n = 3). The mean delta V-51 for the komatiites is -0.91 +/- 0.05 parts per thousand (2SD, n = 10), which is identical to that for the fertile peridotites. Based on the V isotope compositions of the peridotites and komatiites analyzed in this study, the mean delta V-51 of the BSE is estimated to be -0.91 +/- 0.09 parts per thousand (2SD, n = 18).