Any Way the Wind Blows: Dynamics of Greenhouse Gas Exchange in Northeastern Siberian Tundra

Dolman, A.J. [Promotor]Huissteden, J. van [Copromotor

Longer growing seasons do not increase net carbon uptake in Northeastern Siberian tundra

With global warming, snowmelt is occurring earlier and growing seasons are becoming longer around the Arctic. It has been suggested that this would lead to more uptake of carbon due to a lengthening of the period in which plants photosynthesize. To investigate this suggestion, 8 consecutive years of eddy covariance measurements at a northeastern Siberian graminoid tundra site were investigated for patterns in net ecosystem exchange, gross primary production (GPP) and ecosystem respiration (Reco). While GPP showed no clear increase with longer growing seasons, it was significantly increased in warmer summers. Due to these warmer temperatures however, the increase in uptake was mostly offset by an increase in Reco. Therefore, overall variability in net carbon uptake was low, and no relationship with growing season length was found. Furthermore, the highest net uptake of carbon occurred with the shortest and the coldest growing season. Low uptake of carbon mostly occurred with longer or warmer growing seasons. We thus conclude that the net carbon uptake of this ecosystem is more likely to decrease rather than to increase under a warmer climate. These results contradict previous research that has showed more net carbon uptake with longer growing seasons. We hypothesize that this difference is due to site-specific differences, such as climate type and soil, and that changes in the carbon cycle with longer growing seasons will not be uniform around the Arcti

The role of endophytic methane oxidizing bacteria in submerged Sphagnum in determining methane emissions of Northeastern Siberian tundra

Contains fulltext : 83833.pdf (publisher's version ) (Open Access)31 p

The growing season greenhouse gas balance of a continental tundra site in the Indigirka lowlands, NE Siberia.

Carbon dioxide and methane fluxes were measured at a tundra site near Chokurdakh, in the lowlands of the Indigirka river in north-east Siberia. This site is one of the few stations on Russian tundra and it is different from most other tundra flux stations in its continentality. A suite of methods was applied to determine the fluxes of NEE, GPP, <i>R</i><sub>eco</sub> and methane, including eddy covariance, chambers and leaf cuvettes. Net carbon dioxide fluxes were high compared with other tundra sites, with NEE=−92 g C m<sup>−2</sup> yr<sup>−1</sup>, which is composed of an <i>R</i><sub>eco</sub>=+141 g C m<sup>−2</sup> yr<sup>−1</sup> and GPP=−232 g C m<sup>−2</sup> yr<sup>−1</sup>. This large carbon dioxide sink may be explained by the continental climate, that is reflected in low winter soil temperatures (−14°C), reducing the respiration rates, and short, relatively warm summers, stimulating high photosynthesis rates. Interannual variability in GPP was dominated by the frequency of light limitation (<i>R<sub>g</sub></i><200 W m<sup>−2</sup>), whereas <i>R</i><sub>eco</sub> depends most directly on soil temperature and time in the growing season, which serves as a proxy of the combined effects of active layer depth, leaf area index, soil moisture and substrate availability. The methane flux, in units of global warming potential, was +28 g C-CO<sub>2</sub>e m<sup>−2</sup> yr<sup>−1</sup>, so that the greenhouse gas balance was −64 g C-CO<sub>2</sub>e m<sup>−2</sup> yr<sup>−1</sup>. Methane fluxes depended only slightly on soil temperature and were highly sensitive to hydrological conditions and vegetation composition

CO2 fluxes and evaporation on a peatland in the Netherlands appear not affected by water table fluctuations, Agricultural and Forest Meteorology

The effect of shallow water table fluctuations on the evaporation and C

Methane producing and oxidizing microorganisms display a high resilience to drought in a Swedish hemi‐boreal mire

An increased frequency of droughts due to anthropogenic climate change can lead to considerable stress for soil microorganisms and their functioning within northern peatlands. A better understanding of the diversity and relative abundance of methane producing and oxidizing taxa, and their functional genes, can help predict the functional potential of peatlands and how the microorganisms respond to disturbances such as drought. To address knowledge gaps in the understanding of how functional genetic diversity shifts under drought conditions, we investigated a hemi boreal mire in Southern Sweden. Environmental parameters, including soil and air temperature, precipitation, and water table depth, as well as methane flux data were collected during the summer of 2017 under typical growing conditions, and in 2018 during a drought. In addition, the diversity and composition of genes encoding for methane metabolism were determined using the captured metagenomics technique. During drought we observed a substantial increase in air and soil temperature, reduced precipitation, and a lower water table depth. Taxonomic and functional gene composition significantly changed during the drought, while diversity indices, such as alpha and beta diversity, remained similar. These results indicate that methane producing and oxidizing microbial communities, and their functional genes, displayed a resilience to drought with specific genera having the ability to outcompete others under stress. Furthermore, our results show that although methane emissions are substantially reduced during drought, we can expect to see a shift toward more resilient methanogens and methanotrophs under future climate conditions

The Cooling Capacity of Mosses: Controls on Water and Energy Fluxes in a Siberian Tundra Site

Arctic tundra vegetation composition is expected to undergo rapid changes during the coming decades because of changes in climate. Higher air temperatures generally favor growth of deciduous shrubs, often at the cost of moss growth. Mosses are considered to be very important to critical tundra ecosystem processes involved in water and energy exchange, but very little empirical data are available. Here, we studied the effect of experimental moss removal on both understory evapotranspiration and ground heat flux in plots with either a thin or a dense low shrub canopy in a tundra site with continuous permafrost in Northeast Siberia. Understory evapotranspiration increased with removal of the green moss layer, suggesting that most of the understory evapotranspiration originated from the organic soil layer underlying the green moss layer. Ground heat flux partitioning also increased with green moss removal indicating the strong insulating effect of moss. No significant effect of shrub canopy density on understory evapotranspiration was measured, but ground heat flux partitioning was reduced by a denser shrub canopy. In summary, our results show that mosses may exert strong controls on understory water and heat fluxes. Changes in moss or shrub cover may have important consequences for summer permafrost thaw and concomitant soil carbon release in Arctic tundra ecosystems. Key words: moss; evaporation; ground heat flux; shrub; permafrost; tundra; Arctic; climate change

Evidence for past variations in methane availability in a Siberian thermokarst lake based on b13C of chitinous invertebrate remains

Understanding past methane dynamics in arctic wetlands and lakes is crucial for estimating future methane release. Methane fluxes from lake ecosystems have increasingly been studied, yet only few reconstructions of past methane emissions from lakes are available. In this study, we develop an approach to assess changes in methane availability in lakes based on ?13C of chitinous invertebrate remains and apply this to a sediment record from a Siberian thermokarst lake. Diffusive methane fluxes from the surface of ten newly sampled Siberian lakes and seven previously studied Swedish lakes were compared to taxon-specific ?13C values of invertebrate remains from lake surface sediments to investigate whether these invertebrates assimilated 13C-depleted carbon typical for methane. Remains of chironomid larvae of the tribe Orthocladiinae that, in the study lakes, mainly assimilate plant-derived carbon had higher ?13C than other invertebrate groups. ?13C of other invertebrates such as several chironomid groups (Chironomus, Chironomini, Tanytarsini, and Tanypodinae), cladocerans (Daphnia), and ostracods were generally lower. ?13C of Chironomini and Daphnia, and to a lesser extent Tanytarsini was variable in the lakes and lower at sites with higher diffusive methane fluxes. ?13C of Chironomini, Tanytarsini, and Daphnia were correlated significantly with diffusive methane flux in the combined Siberian and Swedish dataset (r = ?0.72, p = 0.001, r = ?0.53, p = 0.03, and r = ?0.81, p < 0.001, respectively), suggesting that ?13C in these invertebrates was affected by methane availability. In a second step, we measured ?13C of invertebrate remains from a sediment record of Lake S1, a shallow thermokarst lake in northeast Siberia. In this record, covering the past ca 1000 years, ?13C of taxa most sensitive to methane availability (Chironomini, Tanytarsini, and Daphnia) was lowest in sediments deposited from ca AD 1250 to ca AD 1500, and after AD 1970, coinciding with warmer climate as indicated by an independent local temperature record. As a consequence the offset in ?13C between methane-sensitive taxa and bulk organic matter was higher in these sections than in other parts of the core. In contrast, ?13C of other invertebrate taxa did not show this trend. Our results suggest higher methane availability in the study lake during warmer periods and that thermokarst lakes can respond dynamically in their methane output to changing environmental conditions

Correction to "Spatial and temporal dynamics in eddy covariance observations of methane fluxes at a tundra site in Northeastern Siberia" (Journal of Geophysical Research G: Biogeosciences (2011) 116 (G03016) DOI: 10.1029/2010JG001637)

[1] In the paper “Spatial and temporal dynamics in eddy covariance observations of methane fluxes at a tundra site in northeastern Siberia” by F. J. W. Parmentier et al. (Journal of Geophysical Research, 116, G03016, doi:10.1029/2010JG001637, 2011), a few typographical errors have been brought to our attention which have unfortunately slipped through, and we apologize for any inconvenience they may have caused. [2] In equation (1), the conditions of L > 0 and L 1.” [4] We'd like to thank Bernard Heinesch and students for bringing these typographical errors to our attention

Longer growing seasons do not appear to increase net carbon uptake in Northeastern Siberian tundra

With global warming, snowmelt is occurring earlier and growing seasons are becoming longer around the Arctic. It has been suggested that this would lead to more uptake of carbon due to a lengthening of the period in which plants photosynthesize. To investigate this suggestion, 8 consecutive years of eddy covariance measurements at a northeastern Siberian graminoid tundra site were investigated for patterns in net ecosystem exchange, gross primary production (GPP) and ecosystem respiration (R<inf>eco</inf>). While GPP showed no clear increase with longer growing seasons, it was significantly increased in warmer summers. Due to these warmer temperatures however, the increase in uptake was mostly offset by an increase in R<inf>eco</inf>. Therefore, overall variability in net carbon uptake was low, and no relationship with growing season length was found. Furthermore, the highest net uptake of carbon occurred with the shortest and the coldest growing season. Low uptake of carbon mostly occurred with longer or warmer growing seasons. We thus conclude that the net carbon uptake of this ecosystem is more likely to decrease rather than to increase under a warmer climate. These results contradict previous research that has showed more net carbon uptake with longer growing seasons. We hypothesize that this difference is due to site-specific differences, such as climate type and soil, and that changes in the carbon cycle with longer growing seasons will not be uniform around the Arctic. Copyright 2011 by the American Geophysical Union