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

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

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

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

Production and export of dissolved C in arctic tundra mesocosms: the roles of vegetation and water flow

To better understand carbon (C) cycling in arctic tundra we measureddissolved C production and export rates in mesocosms of three tundra vegetationtypes: tussock, inter-tussock and wet sedge. Three flushing frequencies wereused to simulate storm events and determine potential mass export of dissolved Cunder increased soil water flow scenarios. Dissolved C production and exportrates differed between vegetation types (inter-tussock < tussock < wetsedge). In the absence of flushing, dissolved organic C (DOC) dominatedproduction in tussock and inter-tussock soils but was consumed in wet sedgesoils (8.3, 32.7, and −0.4 μg C g soil −1 day −1 ). Soil water dissolved C concentrations declined over time when flushedat high and medium frequencies but were variable at low flushing frequency.Total yield of dissolved C and DOC increased with increased flushing frequency.The ratio of DOC to dissolved inorganic C exported dropped with increasedflushing under tussock but not inter-tussock or wet sedge vegetation. Massexport per liter of water added declined as flushing frequency increased intussock and inter-tussock mesocosms. Export and production of dissolved C werestrongly correlated with above ground biomass, but not with photosynthetic ratesor below ground biomass. DOC quality was examined by measuring production ofToolik Lake bacteria fed mesocosm soil water. When normalized for DOCconcentration, wet sedge soil water supported significantly higher bacterialproduction. Our results indicate that arctic tundra soils have high potentialsfor dissolved C export, that water flow and vegetation type mainly controldissolved C export, and that responses of aquatic microbes to terrestrial inputsdepend on the vegetation type in the watershed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42476/1/10533_2004_Article_360520.pd

Biogeography of bacterioplankton in lakes and streams of an arctic tundra catchment

Author Posting. © Ecological Society of America, 2007. This article is posted here by permission of Ecological Society of America for personal use, not for redistribution. The definitive version was published in Ecology 88 (2007): 1365–1378, doi:10.1890/06-0387Bacterioplankton community composition was compared across 10 lakes and 14 streams within the catchment of Toolik Lake, a tundra lake in Arctic Alaska, during seven surveys conducted over three years using denaturing gradient gel electrophoresis (DGGE) of PCR-amplified rDNA. Bacterioplankton communities in streams draining tundra were very different than those in streams draining lakes. Communities in streams draining lakes were similar to communities in lakes. In a connected series of lakes and streams, the stream communities changed with distance from the upstream lake and with changes in water chemistry, suggesting inoculation and dilution with bacteria from soil waters or hyporheic zones. In the same system, lakes shared similar bacterioplankton communities (78% similar) that shifted gradually down the catchment. In contrast, unconnected lakes contained somewhat different communities (67% similar). We found evidence that dispersal influences bacterioplankton communities via advection and dilution (mass effects) in streams, and via inoculation and subsequent growth in lakes. The spatial pattern of bacterioplankton community composition was strongly influenced by interactions among soil water, stream, and lake environments. Our results reveal large differences in lake-specific and stream-specific bacterial community composition over restricted spatial scales (<10 km) and suggest that geographic distance and connectivity influence the distribution of bacterioplankton communities across a landscape.This research was supported in part by the University of Michigan and University of Maryland, and by National Science Foundation grants OPP-0408371, OPP-9911681, OPP- 9911278, DEB-0423385, DEB-9810222, and ATM-0423385

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