Internal wave effects on photosynthesis: Experiments, theory, and modeling

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109941/1/lno20085310339.pd

A Framework for Prioritization, Design and Coordination of Arctic Long-term Observing Networks: A Perspective from the U.S. SEARCH Program

Arctic observing networks exist in many countries and often cross international boundaries. We review their status and the development of networked long-term observations as part of a U.S. Arctic Observing System, highlighting major challenges and opportunities for prioritizing observations, designing a network, and increasing coordination. Most Arctic observing activities focus on specific themes and ecosystem services, resulting in a relatively narrow scope of observations for each network. Across all networks there is a need to improve national and international coordination to (1) reduce potential mismatch between identified science needs and outcomes desired by society, (2) link current observing networks to emerging agency and private-sector observing programs across disciplines, and (3) present a stable set of goals and priorities to increase network utility in view of the limited funding resources. We survey the landscape of observing activities and efforts to coordinate them internationally and present a framework for prioritization and coordination based on the activities of the U.S. Study of Environmental Arctic Change (SEARCH). This framework includes a hierarchy of interconnected activities involved in the design and implementation of observing networks. Across the hierarchy, definition of “actionable” science questions helps drive network design, with priorities set by the breadth and depth of the societal applications or policy requirements that these questions can inform. We present an example of applying this design hierarchy to observations that support policy and management decisions about offshore resource development in the Chukchi Sea.De nombreux pays sont dotés de réseaux d’observation de l’Arctique, et ces réseaux enjambent souvent des frontières internationales. Nous nous penchons sur ces réseaux de même que sur la réalisation d’observations à long terme au moyen d’un réseau américain d’observation de l’Arctique, en prenant soin d’aborder les principaux défis à relever et les possibilités à saisir pour établir les priorités en matière d’observations, pour concevoir le réseau et pour améliorer la coordination. La plupart des activités d’observation de l’Arctique portent sur des thèmes particuliers et des écoservices, ce qui produit une étendue d’observations relativement étroite pour chaque réseau. Dans le cas de tous les réseaux, il y a lieu d’améliorer la coordination nationale et internationale pour (1) réduire la possibilité d’écarts entre les besoins déterminés par la science et les résultats souhaités par la société, (2) lier les réseaux d’observation actuels aux programmes d’observation émergents du secteur public et du secteur privé dans les diverses disciplines, et (3) présenter une série d’objectifs et de priorités stables en vue de rehausser l’utilité des réseaux en fonction du financement restreint. Nous examinons les activités et les efforts d’observation afin d’en assurer la coordination à l’échelle internationale et de présenter un cadre de priorisation et de coordination fondé sur les activités de l’organisme américain Study of Environmental Arctic Change (SEARCH). Ce cadre comprend une hiérarchie d’activités interreliées se rapportant à la conception et à la mise en oeuvre de réseaux d’observation. Dans cette hiérarchie, la définition des questions de science « exploitable » guide la conception de réseaux, les priorités étant fixées par la portée et l’étendue des applications sociétales ou les exigences politiques que ces questions peuvent éclairer. Nous présentons un exemple d’application de cette hiérarchie de conception aux observations sur lesquelles reposent les décisions de politique et de gestion en matière de mise en valeur des ressources au large dans la mer des Tchouktches

Spatial‐temporal variability in surface layer deepening and lateral advection in an embayment of Lake Victoria, East Africa

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109913/1/lno20024730656.pd

Benthic community metabolism in deep and shallow Arctic lakes during 13 years of whole–lake fertilization

Benthic primary production and oxygen consumption are important components of lake biogeochemical cycling. We performed whole–lake nutrient manipulations in Arctic Alaska to assess the controls of lake morphometry, nutrients, and light on benthic community metabolism. One deep, stratified lake (Lake E5) and one shallow, well–mixed lake (Lake E6) in the Alaskan Arctic were fertilized with low levels of nitrogen (56 mg N m−3 yr−1) and phosphorus (8 mg P m−3 yr−1) from 2001 to 2013. Benthic primary production was not stimulated by fertilization in either lake. In the deep lake, decreased water clarity is consistent with an increase in phytoplankton biomass during fertilization. Benthic GPP decreased by 7–47 mg C m−2 d−1 (not statistically significant) and benthic respiration increased from 87 ± 20 to 167 ± 9 (SE) mg C m−2 d−1. The areal hypolimnetic oxygen deficit increased by 15 mg O2 m−2 d−1 each year during the 13 yr of monitoring, apparently driven by lower (more negative) benthic NEP. In the shallow lake, phytoplankton concentration did not change with fertilization. As a result, the light environment did not change and benthic GPP did not decrease. Overall the data suggest that (1) benthic algae are not nutrient limited in either the deep or shallow lake, (2) lake morphometry modulated the overall nutrient impact on benthic metabolism by controlling the response of phytoplankton, and by extension, light and organic carbon supply to the benthos, (3) year–to–year variability in light attenuation explains considerable variability in benthic GPP between lakes and years, (4) correlations between both dissolved organic carbon concentrations and light attenuation coefficients (kd) between lakes suggests a regional control on light attenuation, and (5) the dissolved oxygen concentrations in the deep experimental lake are highly sensitive to nutrient enrichment.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/113758/1/lno10120.pd

IMPLEMENTING DESKTOP COMPUTING, INFRASTRUCTURE, AND QUALITY OF WORKLIFE

This article presents preliminary findings from a three year longitudinal study on the role of desktop computing in the work of 38 work groups that have integrated computing significantly into their work lives. Both quantitative and qualitative data were collected from surveys and interviews. End-users\u27 participation in the process of implementing desktop computers in work groups is examined as a primary contributor to the quality of their work life, as is the available infrastructure (training, supplies, and consulting) to support computing in the work groups. Two primary implementation processes are examined: top-down and grass-roots: We discuss the quality of work life of computer users along five dimensions: participation in decisions about work, job complexity, expertise and involvement in computing, changes in job enrichment attributed to desktop computing, and changes in work effort attributed to desktop computing. The quality of working life is most improved in work groups that computerize with grass-roots processes and have adequate infrastructure to support their work with computing

Bottom‐up controls on bacterial production in tropical lowland rivers

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/110031/1/lno20034841466.pd

Long-term reliability of the figaro TGS 2600 solid-state methane sensor under low-Arctic conditions at Toolik Lake, Alaska

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Eugster, W., Laundre, J., Eugster, J., & Kling, G. W. Long-term reliability of the figaro TGS 2600 solid-state methane sensor under low-Arctic conditions at Toolik Lake, Alaska. Atmospheric Measurement Techniques, 13(5), (2020): 2681-2695, doi:10.5194/amt-13-2681-2020.The TGS 2600 was the first low-cost solid-state sensor that shows a response to ambient levels of CH4 (e.g., range ≈1.8–2.7 µmol mol−1). Here we present an empirical function to correct the TGS 2600 signal for temperature and (absolute) humidity effects and address the long-term reliability of two identical sensors deployed from 2012 to 2018. We assess the performance of the sensors at 30 min resolution and aggregated to weekly medians. Over the entire period the agreement between TGS-derived and reference CH4 mole fractions measured by a high-precision Los Gatos Research instrument was R2=0.42, with better results during summer (R2=0.65 in summer 2012). Using absolute instead of relative humidity for the correction of the TGS 2600 sensor signals reduced the typical deviation from the reference to less than ±0.1 µmol mol−1 over the full range of temperatures from −41 to 27 ∘C. At weekly resolution the two sensors showed a downward drift of signal voltages indicating that after 10–13 years a TGS 2600 may have reached its end of life. While the true trend in CH4 mole fractions measured by the high-quality reference instrument was 10.1 nmolmol−1yr−1 (2012–2018), part of the downward trend in sensor signal (ca. 40 %–60 %) may be due to the increase in CH4 mole fraction because the sensor voltage decreases with increasing CH4 mole fraction. Weekly median diel cycles tend to agree surprisingly well between the TGS 2600 and reference measurements during the snow-free season, but in winter the agreement is lower. We suggest developing separate functions for deducing CH4 mole fractions from TGS 2600 measurements under cold and warm conditions. We conclude that the TGS 2600 sensor can provide data of research-grade quality if it is adequately calibrated and placed in a suitable environment where cross-sensitivities to gases other than CH4 are of no concern.We acknowledge support received from Arctic LTER grants (grant nos. NSF-DEB-1637459, 1026843, 1754835, and NSF-PLR 1504006) and supplemental funding from the NSF-NEON and OPP-AON programs. Gaius R. Shaver (MBL) is acknowledged for initiating the study and supporting our activities in all aspects. ETH is acknowledge for supporting the purchase of the Fast Greenhouse Gas Analyzer that replaced the older Fast Methane Analyzer in 2016 (grant no. 0-43683-11)

Interannual, summer, and diel variability of CH4 and CO2 effluxes from Toolik Lake, Alaska, during the ice-free periods 2010-2015

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Eugster, W., DelSontro, T., Shaver, G. R., & Kling, G. W. Interannual, summer, and diel variability of CH4 and CO2 effluxes from Toolik Lake, Alaska, during the ice-free periods 2010-2015. Environmental Science: Processes & Impacts, 22(11), (2020): 2181-2198, doi: 10.1039/D0EM00125B.Accelerated warming in the Arctic has led to concern regarding the amount of carbon emission potential from Arctic water bodies. Yet, aquatic carbon dioxide (CO2) and methane (CH4) flux measurements remain scarce, particularly at high resolution and over long periods of time. Effluxes of methane (CH4) and carbon dioxide (CO2) from Toolik Lake, a deep glacial lake in northern Alaska, were measured for the first time with the direct eddy covariance (EC) flux technique during six ice-free lake periods (2010–2015). CO2 flux estimates from the lake (daily average efflux of 16.7 ± 5.3 mmol m−2 d−1) were in good agreement with earlier estimates from 1975–1989 using different methods. CH4 effluxes in 2010–2015 (averaging 0.13 ± 0.06 mmol m−2 d−1) showed an interannual variation that was 4.1 times greater than median diel variations, but mean fluxes were almost one order of magnitude lower than earlier estimates obtained from single water samples in 1990 and 2011–2012. The overall global warming potential (GWP) of Toolik Lake is thus governed mostly by CO2 effluxes, contributing 86–93% of the ice-free period GWP of 26–90 g CO2,eq m−2. Diel variation in fluxes was also important, with up to a 2-fold (CH4) to 4-fold (CO2) difference between the highest nighttime and lowest daytime effluxes. Within the summer ice-free period, on average, CH4 fluxes increased 2-fold during the first half of the summer, then remained almost constant, whereas CO2 effluxes remained almost constant over the entire summer, ending with a linear increase during the last 1–2 weeks of measurements. Due to the cold bottom temperatures of this 26 m deep lake, and the absence of ebullition and episodic flux events, Toolik Lake and other deep glacial lakes are likely not hot spots for greenhouse gas emissions, but they still contribute to the overall GWP of the Arctic.We acknowledge support received from the Arctic LTER grants NSF-DEB-1637459, 1026843, 1754835, NSF-PLR 1504006, and supplemental funding from the NSF-NEON and OPP-AON programs. W. E. acknowledges additional funding received from ETH Zurich scientific equipment grants 0-43350-07 and 0-43683-11. James Laundre is thanked for technical support, Jason Dobkowski for supervising deployment and removal of the float to and from the lake, and Randy Fulweber for his GIS support. Many thanks also go to Toolik Field Station staff members for support

Physical pathways of nutrient supply in a small, ultraoligotrophic arctic lake during summer stratification

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/110013/1/lno20065121107.pd

Seasonal and interannual variation of bacterial production in lowland rivers of the Orinoco basin

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71562/1/j.1365-2427.2004.01277.x.pd