More Like this

1. Pond methane dynamics, from microbial communities to ecosystem budget, during summer in Alaska

   https://doi.org/10.1002/lno.12003  

   Vizza, Carmella ; Jones, Stuart E. ; Hart, Julia A. ; West, William E. ; Lamberti, Gary A. ( December 2021 , Limnology and Oceanography)

   Ponds play a larger role in the global freshwater methane (CH₄) budget than predicted from surface area alone. To improve our understanding of pond CH₄dynamics, we measured summer CH₄production, concentrations, and emissions to the atmosphere in nine Alaskan wetland ponds along with potential physical, chemical, and biological regulators. Pond CH₄production (0.64, 0.086–1.3 mmol m⁻²d⁻¹; median, interquartile range), as assessed with slurry incubations, was positively related to water‐column temperature and chlorophylla(Chla), negatively influenced by oxygen levels, and varied with microbial community structure. Average water‐column CH₄concentrations (0.39, 0.21–0.87 μmol L⁻¹) were lower in deeper ponds and at higher oxygen levels, and as expected, they were correlated with diffusive emissions (0.055, 0.024–0.20 mmol m⁻²d⁻¹) assessed with flux chambers. Based on a mass balance approach, 39–99% of CH₄produced in ponds was oxidized. Pond ebullition (3.7, 0.60–24 mmol m⁻²d⁻¹) was higher and more variable than diffusive emissions. Additionally, pond ebullition rates were better correlated with production rates from the previous month. We also systematically compared the ratio of ebullition to diffusive CH₄emissions in our ponds and other northern lakes, which was negatively related to water depth (n = 71), but positively related to Chla (n = 28). Our study sheds light on the factors that influence pond CH₄dynamics and demonstrates that pond ebullition is a significant CH₄source worthy of continued study.

    

   more » « less
2. Variability and drivers of CO 2 , CH 4 , and N 2 O concentrations in streams across the United States

   https://doi.org/10.1002/lno.12281  

   DelVecchia, Amanda G. ; Rhea, Spencer ; Aho, Kelly S. ; Stanley, Emily H. ; Hotchkiss, Erin R. ; Carter, Alice ; Bernhardt, Emily S. ( December 2022 , Limnology and Oceanography)

   Streams and rivers are major sources of greenhouse gases (GHGs) to the atmosphere, as carbon and nitrogen are converted and outgassed during transport. Although our understanding of drivers of individual GHG fluxes has improved with numerous site‐specific studies and global‐scale compilations, our ability to parse out interrelated physical and biogeochemical drivers of gas concentrations is limited by a lack of consistently collected, temporally continuous samples of GHGs and their associated drivers. We present a first analysis of such a dataset collected by the National Ecological Observatory Network across 27 streams and rivers across ecoclimatic domains of the United States. Average concentrations of CO₂ranged from 36.9 ± 0.88 to 404 ± 33 μmol L⁻¹, CH₄from 0.003 ± 0.0003 to 4.99 ± 0.72 μmol L⁻¹, and N₂O from 0.015 to 0.04 μmol L⁻¹and spanned ranges of previous global compilations. Both CO₂and CH₄were strongly affected by physical drivers including mean air temperature and stream slope, as well as by dissolved oxygen and total nitrogen concentrations. N₂O was exclusively correlated with total nitrogen concentrations. Results suggested that potential for gas exchange dominated patterns in gas concentrations at the site level, but contributions of in‐stream aerobic and anaerobic metabolism, and groundwater also likely varied across sites. The highest gas concentrations as well as highest variability occurred in low‐gradient, warmer, and nonperennial systems. These results are a first step in providing unprecedented, continuous estimates of GHG flux constrained by temporally variable physical and biogeochemical drivers of GHG production.

    

   more » « less
3. Integrating Ecosystem Patch Contributions to Stream Corridor Carbon Dioxide and Methane Fluxes

   https://doi.org/10.1029/2021JG006313  

   Bretz, Kristen A. ; Jackson, Alexis R. ; Rahman, Sumaiya ; Monroe, Jonathon M. ; Hotchkiss, Erin R. ( September 2021 , Journal of Geophysical Research: Biogeosciences)

   The heterogeneity of carbon dioxide (CO₂) and methane (CH₄) sources within and across watersheds presents a challenge to understanding the contributions of different ecosystem patch types to stream corridor and watershed carbon cycling. Changing hydrologic connections between corridor patches (e.g., streams, vernal pools, hillslopes) can influence stream corridor greenhouse gas emissions, but the spatiotemporal dynamics of emissions within and among corridor patches are not well‐quantified. To identify patterns and sources of carbon emissions across stream corridors, we measured gas concentrations and fluxes over two summers at Coweeta Hydrologic Laboratory, NC. We sampled CO₂and CH₄along four stream channels (including flowing and dry reaches), adjacent vernal pools, and riparian hillslopes. Stream CO₂and CH₄emissions were spatially heterogeneous. All streams were sources of CO₂to the atmosphere (median = 97.2 mmol m⁻²d⁻¹) but were sources or sinks of CH₄depending on location (−0.19 to 4.57 mmol m⁻²d⁻¹). CO₂emissions were lower during the drier of two sampling years but were stable from month to month in the drier summer. CO₂and CH₄emissions also varied by both corridor and patch type; the presence of a vernal pool in the corridor had the strongest impact on emissions. Vernal pool patches emitted more CO₂and CH₄(246 and 1.95 mmol m⁻²d⁻¹, respectively) than their adjacent streams. High resolution sampling of carbon fluxes from patches within and among stream corridors improves our understanding of the connections between terrestrial, riparian, and aquatic zones in a watershed and their contributions to overall catchment carbon emissions.

    

   more » « less
4. Effects of filtration timing and pore size on measured nutrient concentrations in environmental water samples

   https://doi.org/10.1002/lom3.10529  

   Reed, Megan H. ; Strope, Erica K. ; Cremona, Fabien ; Myers, Justin A. ; Newell, Silvia E. ; McCarthy, Mark J. ( December 2022 , Limnology and Oceanography: Methods)

   Nutrient monitoring is important for informing management decisions to mitigate eutrophication in aquatic systems. Many nutrient monitoring programs use filter pore sizes that allow microorganisms to pass into samples and/or wait extended times between sample collection and filtration/preservation, allowing microbial processes to alter nutrient concentrations. Here, 34 sites were sampled to determine how filter pore size and filtration timing affected measured ammonium (NH₄⁺) and orthophosphate (ortho‐P) concentrations. Three filter pore sizes (0.22, 0.45, and 0.70 μm) were used to filter water immediately upon collection and after 5 and 22 h in a bottle. NH₄⁺and ortho‐P concentrations varied relative to “baseline” measurements (i.e., 0.22 μm, field‐filtered samples), both over time and with different filter pore sizes, and showed no predictable direction of change based on ambient nutrient concentration or trophic status. As expected, larger relative changes occurred with lower ambient concentrations; however, for the entire dataset, samples with > 1 μmol L⁻¹ortho‐P and > 3 μmol L⁻¹NH₄⁺were lower by 11 and 33%, respectively, which would result in reported nutrient concentrations that were not representative of in situ conditions. Whole‐water samples filtered after 22 h varied up to 3070% for NH₄⁺and 480% for ortho‐P from baseline concentrations. Filtering water samples with a 0.22 filter (or 0.45 μm, at worst), immediately upon collection, should be adopted as standard practice to ensure that reported nutrient concentrations represent the most accurate measurement possible. Inconsistent and/or insufficient sampling and sample handling procedures can lead to poorly calibrated models and misinformed management and legislative decisions.

    

   more » « less
5. Carbon dioxide supersaturation in high‐elevation oligotrophic lakes and reservoirs in the Sierra Nevada, California

   https://doi.org/10.1002/lno.11330  

   Cohen, Adam P. ; Melack, John M. ( October 2019 , Limnology and Oceanography)

   To better understand the contribution of alpine lakes to global CO₂emissions, carbon dioxide concentrations and fluxes to the atmosphere were measured in five high‐elevation lakes and five reservoirs in the Sierra Nevada, California. Median summer surface concentrations of dissolved CO₂(reservoirs: 21.1μM, lakes: 23.7μM) were supersaturated for most of the ice‐free season. Median diffusive flux of CO₂was low as compared to other inland waters (lakes: 260 mg CO₂m⁻²d⁻¹, reservoirs: 192 mg CO₂m⁻²d⁻¹). Linear mixed modeling demonstrated that the length of ice cover, persisting for 5–9 months and allowing for accumulation of under‐ice CO₂, was a strong predictor of summer surface CO₂. During the ice‐free period, surface evasion of CO₂was highest for the first 40 d after ice‐off when carbon dioxide that had accumulated during winter was released, although supersaturation and evasion continued until fall at most sites despite low rates of ecosystem metabolism. This study suggests that the contribution of high‐elevation, oligotrophic lakes and reservoirs in the Sierra to global CO₂emissions are small despite persistent supersaturation, and are primarily driven by the duration of ice cover.

    

   more » « less