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Historically, estimates of pelagic primary production in lake ecosystems were made by measuring the uptake of carbon‐14 (14C)‐labeled inorganic carbon in samples incubated under laboratory or in situ conditions. However, incubation approaches are increasingly being replaced by methods that analyze diel changes in high‐frequency in situ data such as free‐water dissolved oxygen (O2). While there is a rich literature on the comparison of approaches for estimating primary production using incubations (e.g., 14C and O2 bottle experiments), as well for approaches using high‐frequency data (e.g., diel O2 and CO2 metabolism models), there are few direct comparisons of 14C incubations and free‐water O2 approaches for estimating primary production. We used 20 lake‐years of concurrent measurements of primary production quantified from high‐frequency free‐water O2 data and 14C incubations in four different lakes (4–7 years per lake) to compare these different approaches. Across all lakes, 61% of the 14C production estimates were within the 95% credible intervals of the free‐water O2 production estimates. Error‐in‐variable regressions support the assumption that 14C methods estimate a production value between gross primary production and net primary production and the bottle effect is constant across the entire range of production values considered here. There was little evidence that daily pelagic, epilimnetic estimates of primary production differed substantially based on the selection of free‐water O2 or 14C approaches in these lakes during summer stratified conditions. [ABSTRACT FROM AUTHOR]

Repeated sampling of spatially distributed river chemistry can be used to assess the location, scale, and stability of carbon and nutrient contributions to watershed-scale exports. Here, we provide a comprehensive set of water chemistry measurements and secondary ecosystem metrics describing the biogeochemical conditions of permafrost-affected Arctic watershed networks. These data were collected in watershed-wide repeated synoptic campaigns across six rivers across northern Alaska. Three watersheds are associated with the Arctic Long-Term Ecological Research (ARC LTER) site at Toolik Field Station (TFS), which were sampled seasonally each June and August from 2016 to 2018. Three watersheds were associated with the National Park Service (NPS) of Alaska and the US. Geological Survey (USGS), and were sampled annually from 2015 to 2019. Extensive water chemistry characterization included carbon species, dissolved nutrients, and anions and cations. The objective of the sampling designs and data acquisition was to generate a dataset to support the estimation of ecosystem metrics that describe the dominant location, scale, and overall stability of ecosystem processes in the Arctic. These metrics are: (1) subcatchment leverage, (2) variance collapse, and (3) spatial stability. Both water chemistry concentrations and secondary metrics are available at the National Park Service Integrated Resource Management Application portal (https://doi.org/10.5066/P9SBK2DZ) and within the Environmental Data Initiative LTER Data Portal (https://doi.org/10.6073/pasta/258a44fb9055163dd4dd4371b9dce945). Plaintext Summary. Sampling various points in an entire river network over a short period of time (~a few hours) provides a synoptic "snapshot" in time of the water chemistry in a watershed. Here, we describe two unique datasets which captured river chemistry snapshots in six permafrost-impacted watersheds in northern Alaska. We present how these repeated snapshots can be used to inform predictions for carbon, nutrient, and other solutes in landscapes that are rapidly changing as a direct result of climate change. [ABSTRACT FROM AUTHOR]

Variation in resource supply can cause variation in temperature dependences of metabolic processes (e.g., photosynthesis and respiration). Understanding such divergence is particularly important when using metabolic theory to predict ecosystem responses to climate warming. Few studies, however, have assessed the effect of temperature-resource interactions on metabolic processes, particularly in cases where the supply of limiting resources exhibits temperature dependence. We investigated the responses of biomass accrual, gross primary production (GPP), community respiration (CR), and N2 fixation to warming during biofilm development in a streamside channel experiment. Areal rates of GPP, CR, biomass accrual, and N2 fixation scaled positively with temperature, showing a 32- to 71-fold range across the temperature gradient (~7°-24°C). Areal N2-fixation rates exhibited apparent activation energies (1.5-2.0 eV; 1 eV ¼ ;1.6 3 10-19 J) approximating the activation energy of the nitrogenase reaction. In contrast, mean apparent activation energies for areal rates of GPP (2.1-2.2 eV) and CR (1.6-1.9 eV) were 6.5- and 2.7-fold higher than estimates based on metabolic theory predictions (i.e., 0.32 and 0.65 eV, respectively) and did not significantly differ from the apparent activation energy observed for N2 fixation. Mass-specific activation energies for N2 fixation (1.4-1.6 eV), GPP (0.3-0.5 eV), and CR (no observed temperature relationship) were near or lower than theoretical predictions. We attribute the divergence of areal activation energies from those predicted by metabolic theory to increases in N2 fixation with temperature, leading to amplified temperature dependences of biomass accrual and areal rates of GPP and R. Such interactions between temperature dependences must be incorporated into metabolic models to improve predictions of ecosystem responses to climate change. [ABSTRACT FROM AUTHOR]