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.

In the western USA, one legacy of historic mining is drainage of acidic, metal-rich water generated by exposure to oxygen of sulfide minerals in mine workings, referred to as acid mine drainage (AMD). Streams receiving AMD and natural acid rock drainage (ARD) have a low pH, high dissolved metal concentrations, and extensive streambed oxide deposits. Recently, enhanced ARD generation in the Snake River watershed in the Rocky Mountains has been shown to be associated with warmer summer air temperatures, which has been attributed to expanding weathering fronts that promote oxidation due to earlier drying of shallow soils. In mountain watersheds where complex orogeny disseminated minerals throughout the landscape, weathering processes may also mobilize rare earth elements (REEs). We report that in the Snake River REEs are currently distributed in streams at concentrations ranging from 1 to 100 μg/L. Further, analysis of archived sample indicates that REE increases over time are also associated with increased summer air temperatures. In downstream reaches where the Snake River discharges into a water supply reservoir, colloidal and particulate metal oxides are abundant and sorptive processes may influence REE speciation. We also show that REEs accumulate in benthic invertebrates at concentrations comparable to toxic metals associated with ARD.

During the week of 9–15 September 2013, about 44 cm of rain fell across Boulder County, Colorado, USA, representing a very rare precipitation event. The resultant streamflows corresponded to an extreme event not seen since the historical flood of 1894. For the Boulder Creek Critical Zone Observatory (BcCZO), this event provided an opportunity to study the effect of extreme rainfall on solute concentration‐discharge relationships and biogeochemical processes. We measured weathering‐derived lithologic solutes (Ca, Mg, Na, K, and Si) and dissolved organic carbon (DOC) concentrations at two sites on Boulder Creek during the recession of peak flow. We also isolated four distinct fractions of dissolved organic matter (DOM) for chemical characterization. At the upper and lower sites, all solutes had their highest concentration at peak flow. At the upper site, which represented a mostly forested catchment, the concentrations of lithologic solutes decreased slightly during flood recession. In contrast, DOC and K concentrations decreased by a factor of three. At the lower site within the urban corridor, concentration of lithologic solutes decreased substantially for a few days before rebounding, whereas the DOC and K concentrations continued to decrease. Additionally, we found spatiotemporal trends in the chemical quality of DOM that were consistent with a limited reservoir of soluble organic matter in surficial soils becoming depleted and deeper layers of the Critical Zone contributing DOM during the flood recession. Overall, these results suggest that despite the extreme flood event, concentration‐discharge relationships were similar to typical snowmelt periods in this Rocky Mountain region.

Few studies have comprehensively investigated the temporal variability in soil microbial communities despite widespread recognition that the belowground environment is dynamic. In part, this stems from the challenges associated with the high degree of spatial heterogeneity in soil microbial communities and because the presence of relic DNA (DNA from non-living cells) may dampen temporal signals. Here we disentangle the relationships among spatial, temporal, and relic DNA effects on bacterial, archaeal, and fungal communities in soils collected from contrasting hillslopes in Colorado, USA. We intensively sampled plots on each hillslope over six months to discriminate between temporal variability, intra-plot spatial heterogeneity, and relic DNA effects on the soil prokaryotic and fungal communities. We show that the intra-plot spatial variability in microbial community composition was strong and independent of relic DNA effects with these spatial patterns persisting throughout the study. When controlling for intra-plot spatial variability, we identified significant temporal variability in both plots over the six-month study. These microbial communities were more dissimilar over time after relic DNA was removed, suggesting that relic DNA hinders the detection of important temporal dynamics in belowground microbial communities. We identified microbial taxa that exhibited shared temporal responses and show these responses were often predictable from temporal changes in soil conditions. Our findings highlight approaches that can be used to better characterize temporal shifts in soil microbial communities, information that is critical for predicting the environmental preferences of individual soil microbial taxa and identifying linkages between soil microbial community composition and belowground processes. Importance Nearly all microbial communities are dynamic in time. Understanding how temporal dynamics in microbial community structure affect soil biogeochemistry and fertility are key to being able to predict the responses of the soil microbiome to environmental perturbations. Here we explain the effects of soil spatial structure and relic DNA on the determination of microbial community fluctuations over time. We found that intensive spatial sampling is required to identify temporal effects in microbial communities because of the high degree of spatial heterogeneity in soil and that DNA from non-living microbial cells masks important temporal patterns. We identified groups of microbes that display correlated behavior over time and show that these patterns are predictable from soil characteristics. These results provide insight into the environmental preferences and temporal relationships between individual microbial taxa and highlight the importance of considering relic DNA when trying to detect temporal dynamics in belowground communities.