Several researchers have proposed spectrophotometric modifications of the Winkler titrimetric method for measuring dissolved oxygen (DO). These modifications, although simple, are not widely used because of concern about accuracy, calibration, and possible sources of interference. Here we show, using natural samples from lakes and rivers as well as samples manipulated in the laboratory, that the spectrophotometric method can provide accurate and very precise measurements of DO over a wide range of concentrations (4 to ∼13 mg O2 liter−1). Further, interference from dissolved organic carbon (color) and turbidity are minor. We propose corrections for both color and turbidity, where necessary, that can be easily incorporated into the measurement design. Because of the speed and simplicity of the spectrophotometric method, it is easy to replicate measurements and thereby increase precision without greatly increasing analytical time. In 10 min of effort, we were able to achieve a coefficient of variation (CV) within one bottle of 0.09%, or 0.8% among different bottles. With n = 7 bottles, one can easily distinguish changes in DO of 0.05 mg liter−1 with this method, which makes it useful for metabolic studies in many environments. To achieve a comparable CV by conventional titration would require about 100 min of effort.

CoCr and UHSS rods have the ability to produce the highest correction forces, however, both can plastically deform in a very rigid curves. Therefore, it is critical to have sense of the quality of the bone fixation as well as the curve flexibility when selecting for appropriate rod size material and contouring the rod to the desired shape.

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Lake sedimentation rate represents a synthetic metric of ecosystem functioning. Many localized studies have reported a significant association between land use/land cover changes and lake sediment mass accumulation rates, with a few global syntheses echoing these findings at larger scales. In the literature, studies evaluating lead‐210 (210Pb) for establishing sediment chronologies will report at least one of three dating models, but the constant rate of supply (CRS) model is the most widely used. However, it is often unclear how or why this model is selected, despite its influence on the interpretation of many subsequent analyses about ecosystem dynamics and functioning. It would thus be advantageous to design an objective and semi‐automated way of choosing among dating models. We measured radioisotopic activities in 37 sediment cores across four ecozones of Eastern Canada and developed an approach to assess model fit for the three commonly applied dating models. The derived chronologies were then used to evaluate the spatial and temporal variation in sedimentation rates across four ecozones in Canada (covering a surface area of 2.2 × 106 km2). We observed a recent increase in lake sedimentation rates across most lakes, as has been observed globally, albeit with significant differences in the magnitude of sedimentation rates across ecozones. Across all lakes, we found that regional human population counts and mean annual air temperatures were significant temporal predictors of variation in mass accumulation rates. Overall, this analytical framework offers an objective approach for assessing fit and selecting among sediment age models, which contributes to a more robust quantification of sedimentation rates. With this first application, we provide a quantitative assessment of how lake sedimentation rates have varied across a northern lake‐rich region and have responded to environmental change.

Reservoirs are known to accelerate the mobilization and cycling of mercury and carbon as a result of flooding of terrestrial organic matter, which can lead to environmental concerns at local and broader spatial scales. We explored the covariation of mercury (Hg) and carbon (C) functional pools in natural and recently dammed portions of the aquatic network of the Romaine River watershed in Northern Quebec, Canada, to understand how the fate of these elements varies across systems with contrasting hydrology and environmental conditions. We found that total Hg (THg) concentrations in surface waters were relatively constant along the network, whereas both the concentrations and proportions of MeHg tended to increase in reservoirs compared to surrounding nonflooded systems, and along the cascade of reservoirs. Whereas THg was related to total and terrestrial pools of dissolved organic carbon (DOC), MeHg was weakly related to DOC but strongly linked to surface concentrations of CO 2 , as well as to concentrations of iron and manganese. The latter are proxies of cumulative organic matter processing within the network, presumably in anoxic portions of shallow bays, deep reservoir waters, and river sediments, as well as in prior seasons (e.g., under ice). Our results suggest that these deep boreal reservoirs acted more as transformation sites for Hg that was already present than as mobilizers of new Hg, and that under ice metabolism plays a role in MeHg production in these systems as we found strong dichotomies in MeHg patterns between spring and summer.

Lake sedimentation rate represents a synthetic metric of ecosystem functioning. Many localized studies have reported a significant association between land use/land cover changes and lake sediment mass accumulation rates, with a few global syntheses echoing these findings at larger scales. In the literature, studies evaluating lead-210 ( 210 Pb) for establishing sediment chronologies will report at least one of three dating models, but the constant rate of supply (CRS) model is the most widely used. However, it is often unclear how or why this model is selected, despite its influence on the interpretation of many subsequent analyses about ecosystem dynamics and functioning. It would thus be advantageous to design an objective and semi-automated way of

Freshwater ecosystems, including wetlands, lakes, and running waters, are estimated to contribute roughly 40% to global emissions of methane (CH4), a highly potent greenhouse gas. The emission of CH4 to the atmosphere entails the diffusive, ebullitive, and plant-mediated pathway. The latter, in particular, has been largely understudied and is neither well understood nor quantified. We have conducted a semi-quantitative literature review to (i) provide a synthesis of the different ways vegetated habitats can influence CH4 dynamics (i.e., production, consumption, and transport) in freshwater ecosystems, (ii) provide an overview of methods applied to study the fluxes from vegetated habitats, and (iii) summarize the existing data on CH4 fluxes associated to different types of vegetated habitats and their range of variation. Finally, we discuss the implications of CH4 fluxes associated with aquatic vegetated habitats for current estimates of aquatic CH4 emissions at the global scale. We identified 13 different aspects in which plants impact CH4 dynamics (three related to gaseous CH4 flux pathways) and ten approaches used to study and quantify fluxes from vegetated habitats. The variability of the fluxes from vegetated areas was very high, varying from -454.4 mg CH4 m-2 d-1 (uptake) to 2882.4 mg CH4 m-2 d-1 (emission). This synthesis highlights the need to incorporate vegetated habitats into CH4 emission budgets from natural freshwater ecosystems and further identifies understudied research aspects and relevant future research directions.