Carbon balance of a grazed savanna grassland ecosystem in South Africa

Abstract. Tropical savannas and grasslands are estimated to contribute significantly to the total primary production of all terrestrial vegetation. Large parts of African savannas and grasslands are used for agriculture and cattle grazing, but the carbon flux data available from these areas is limited. This study explores carbon dioxide fluxes measured with the eddy covariance method for three years at a grazed savanna grassland in Welgegund, South Africa. The tree cover around the measurement site, grazed by cattle and sheep, was around 15 %. The night-time respiration was not significantly dependent on either soil moisture or soil temperature on a weekly temporal scale, whereas on an annual time scale higher respiration rates were observed when soil temperatures were higher. The yearly carbon dioxide balances of the growing seasons 2010–11, 2011–12 and 2012–13 were −85, 67 and 139 g C m−2 yr−1, respectively. The yearly variation was largely determined by the changes in the early wet season fluxes (September to November) and in the mid-growing season fluxes (December to January). Early rainfall enhanced the respiratory capacity of the ecosystem throughout the year, whereas during the mid-growing season high rainfall resulted in high carbon uptake. This study underlines the difficulty in establishing a functional relation between the total ecosystem respiration and the environmental drivers in savanna ecosystems. Furthermore, the high inter-annual variation of carbon balance in savanna ecosystems is difficult to relate to environmental drivers.

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Carbon balance of a grazed savanna grassland ecosystem in South Africa

Biogeosciences ◽

10.5194/bg-14-1039-2017 ◽

2017 ◽

Vol 14 (5) ◽

pp. 1039-1054 ◽

Cited By ~ 12

Author(s):

Matti Räsänen ◽

Mika Aurela ◽

Ville Vakkari ◽

Johan P. Beukes ◽

Juha-Pekka Tuovinen ◽

...

Keyword(s):

South Africa ◽

Carbon Dioxide ◽

Growing Season ◽

Tree Cover ◽

Terrestrial Vegetation ◽

Wet Season ◽

Night Time ◽

Yearly Variation ◽

Eddy Covariance Method ◽

Soil Temperatures

Abstract. Tropical savannas and grasslands are estimated to contribute significantly to the total primary production of all terrestrial vegetation. Large parts of African savannas and grasslands are used for agriculture and cattle grazing, but the carbon flux data available from these areas are limited. This study explores carbon dioxide fluxes measured with the eddy covariance method for 3 years at a grazed savanna grassland in Welgegund, South Africa. The tree cover around the measurement site, grazed by cattle and sheep, was around 15 %. The night-time respiration was not significantly dependent on either soil moisture or soil temperature on a weekly temporal scale, whereas on an annual timescale higher respiration rates were observed when soil temperatures were higher. The carbon dioxide balances of the years 2010–2011, 2011–2012 and 2012–2013 were −85 ± 16, 67 ± 20 and 139 ± 13 gC m−2 yr−1, respectively. The yearly variation was largely determined by the changes in the early wet season fluxes (September to November) and in the mid-growing season fluxes (December to January). Early rainfall enhanced the respiratory capacity of the ecosystem throughout the year, whereas during the mid-growing season high rainfall resulted in high carbon uptake.

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Carbon dioxide and methane exchange of a patterned subarctic fen during two contrasting growing seasons

10.5194/egusphere-egu21-2384 ◽

2021 ◽

Author(s):

Lauri Heiskanen ◽

Juha-Pekka Tuovinen ◽

Aleksi Räsänen ◽

Tarmo Virtanen ◽

Sari Juutinen ◽

...

Keyword(s):

Carbon Dioxide ◽

Global Warming ◽

Plant Community ◽

Carbon Balance ◽

Growing Season ◽

Drought Period ◽

Annual Carbon ◽

Ecosystem Level ◽

Community Types ◽

Annual Carbon Balance

AbstractNorthern mires have sequestered substantial amounts of atmospheric carbon since the last glacial period forming one of the largest carbon pools in the biosphere (Hugelius et al., 2020). Current global warming is causing the subarctic and arctic regions warm rapidly, two to three times as fast as the rest of the world (Masson-Delmotte et al., 2018), which will affect the carbon balance of these mires.In Kaamanen, northern Finland, we studied carbon dioxide (CO2) and methane (CH4) exchange between patterned mesotrophic fen and the atmosphere, both on ecosystem and plant community level. The ecosystem level measurements were conducted by utilizing eddy covariance method, while the fluxes on plant community scale were measured with flux chambers. The studied fen can be described as a mosaic of strings and flarks (or hummocks and hollows, respectively). The microtopography of the string-flark continuum form four main plant community types with varying water table conditions and vegetation composition. The measurements took place in 2017&#8211;2018. The two years in question were contrasting in their meteorological and environmental conditions. The 2017 growing season had average temperature, but high precipitation sum, while 2018 growing season was warm and dry. In July 2018 a north-western Europe-wide heatwave caused a month-long drought period at the site. Compared to 2017, the annual carbon balance of the Kaamanen fen was affected by earlier onset of photosynthesis in spring and the drought event during summer 2018.We found that the annual carbon balance of the fen did not differ markedly between the studied years, even though the meteorological and environmental conditions did. The earlier onset of growing season in 2018 strengthened the CO2 sink of the ecosystem, but this gain was counterbalanced by the later drought period. Additionally, we found strong spatial variation in CO2 and CH4 dynamics between the main plant communities. Most of the variation in ecosystem level carbon exchange could be explained by the variation in water table level, soil temperature and vegetation characteristics, which were also the environmental factors that varied between the plant community types.&#160;ReferencesHugelius, G., Loisel, J., Chadburn, S., Jackson, R. B., Jones, M., MacDonald, G., Marushchak, M., Olefeldt, D., Packalen, M., Siewert, M. B., Treat, C., Turetsky, M., Voigt, C. and Yu, Z.: Large stocks of peatland carbon and nitrogen are vulnerable to permafrost thaw, Proceedings of the National Academy of Sciences - PNAS, 117, 20438&#8211;20446, doi:10.1073/pnas.1916387117, 2020.Masson-Delmotte, V., Zhai, P., P&#246;rtner, H.-O., Roberts, D., Skea, J., Shukla, P. R., Pirani, A., Moufouma-Okia, W., P&#233;an, C., Pidcock, R., Connors, S., Matthews, J. B. R., Chen, Y., Zhou, X., Gomis, M. I., Lonnoy, E., Maycock, T., Tignor, M. and Waterfield T. (Eds.): Global Warming of 1.5&#176;C. An IPCC Special Report on the impacts of global warming of 1.5&#176;C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty, World Meteorological Organization, Geneva, Switzerland, 2018.

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The current state of CO2 flux chamber studies in the Arctic tundra

Progress in Physical Geography Earth and Environment ◽

10.1177/0309133317745784 ◽

2017 ◽

Vol 42 (2) ◽

pp. 162-184 ◽

Cited By ~ 15

Author(s):

Anna-Maria Virkkala ◽

Tarmo Virtanen ◽

Aleksi Lehtonen ◽

Janne Rinne ◽

Miska Luoto

Keyword(s):

Carbon Balance ◽

Ecosystem Respiration ◽

Vegetation Type ◽

Gross Primary Production ◽

Co2 Flux ◽

Arctic Tundra ◽

The Arctic ◽

Environmental Drivers ◽

Soil Conditions ◽

Flux Chamber

The Arctic tundra plays an important role in the carbon cycle as it stores 50% of global soil organic carbon reservoirs. The processes (fluxes) regulating these stocks are predicted to change due to direct and indirect effects of climate change. Understanding the current and future carbon balance calls for a summary of the level of knowledge regarding chamber-derived carbon dioxide (CO2) flux studies. Here, we describe progress from recently (2000–2016) published studies of growing-season CO2 flux chamber measurements, namely GPP (gross primary production), ER (ecosystem respiration), and NEE (net ecosystem exchange), in the tundra region. We review the study areas and designs along with the explanatory environmental drivers used. Most of the studies were conducted in Alaska and Fennoscandia, and we stress the need for measuring fluxes in other tundra regions, particularly in more extreme climatic, productivity, and soil conditions. Soil respiration and other greenhouse gas measurements were seldom included in the studies. Although most of the environmental drivers of CO2 fluxes have been relatively well investigated (such as the effect of vegetation type and soil microclimate on fluxes), soil nutrients, other greenhouse gases and disturbance regimes require more research as they might define the future carbon balance. Particular attention should be paid to the effects of shrubification, geomorphology, and other disturbance effects such as fire events, and disease and herbivore outbreaks. An improved conceptual framework and understanding of underlying processes of biosphere–atmosphere CO2 exchange will provide more information on carbon cycling in the tundra.

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Response of carbon fluxes to water relations in a savanna ecosystem in South Africa

Biogeosciences ◽

10.5194/bg-5-1797-2008 ◽

2008 ◽

Vol 5 (6) ◽

pp. 1797-1808 ◽

Cited By ~ 45

Author(s):

W. L. Kutsch ◽

N. Hanan ◽

B. Scholes ◽

I. McHugh ◽

W. Kubheka ◽

...

Keyword(s):

South Africa ◽

Water Relations ◽

Ecosystem Respiration ◽

Stomatal Closure ◽

Growing Season ◽

Carbon Fluxes ◽

Dry Season ◽

Canopy Conductance ◽

Wet Season ◽

Eddy Covariance Method

Abstract. The principal mechanisms that connect carbon fluxes with water relations in savanna ecosystems were studied by using eddy covariance method in a savanna ecosystem at Kruger National Park, South Africa. Since the annual drought and rewetting cycle is a major factor influencing the function of savanna ecosystems, this work focused on the close inter-connection between water relations and carbon fluxes. Data from a nine-month measuring campaign lasting from the early wet season to the late dry season were used. Total ecosystem respiration showed highest values at the onset of the growing season, a slightly lower plateau during the main part of the growing season and a continuous decrease during the transition towards the dry season. The regulation of canopy conductance was changed in two ways: changes due to phenology during the course of the growing season and short-term acclimation to soil water conditions. The most constant parameter was water use efficiency that was influenced by VPD during the day but the VPD response curve of water usage did change only slightly during the course of the growing season and decreased by about 30% during the transition from wet to dry season. The regulation of canopy conductance and photosynthetic capacity were closely related. This observation meets recent leaf-level findings that stomatal closure triggers down-regulation of Rubisco during drought. Our results may show the effects of these processes on the ecosystem scale.

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Annual carbon balance of a peatland 10 yr following restoration

Biogeosciences ◽

10.5194/bg-10-2885-2013 ◽

2013 ◽

Vol 10 (5) ◽

pp. 2885-2896 ◽

Cited By ~ 62

Author(s):

M. Strack ◽

Y. C. A. Zuback

Keyword(s):

Carbon Balance ◽

Ecosystem Respiration ◽

Carbon Sources ◽

Growing Season ◽

Photon Flux ◽

Photon Flux Density ◽

Winter Period ◽

Peat Extraction ◽

Annual Carbon ◽

Annual Carbon Balance

Abstract. Undisturbed peatlands represent long-term net sinks of carbon; however, peat extraction converts these systems into large and persistent sources of greenhouse gases. Although rewetting and restoration following peat extraction have taken place over the last several decades, very few studies have investigated the longer term impact of this restoration on peatland carbon balance. We determined the annual carbon balance of a former horticulturally-extracted peatland restored 10 yr prior to the study and compared these values to the carbon balance measured at neighboring unrestored and natural sites. Carbon dioxide (CO2) and methane (CH4) fluxes were measured using the chamber technique biweekly during the growing season from May to October 2010 and three times over the winter period. Dissolved organic carbon (DOC) export was measured from remnant ditches in the unrestored and restored sites. During the growing season the restored site had greater uptake of CO2 than the natural site when photon flux density was greater than 1000 μmol m−2 s−1, while the unrestored site remained a source of CO2. Ecosystem respiration was similar between natural and restored sites, which were both significantly lower than the unrestored site. Methane flux remained low at the restored site except from open water pools, created as part of restoration, and remnant ditches. Export of DOC during the growing season was 5.0 and 28.8 g m−2 from the restored and unrestored sites, respectively. Due to dry conditions during the study year all sites acted as net carbon sources with annual balance of the natural, restored and unrestored sites of 250.7, 148.0 and 546.6 g C m−2, respectively. Although hydrological conditions and vegetation community at the restored site remained intermediate between natural and unrestored conditions, peatland restoration resulted in a large reduction in annual carbon loss from the system resulting in a carbon balance more similar to a natural peatland.

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Seasonal variations in carbon dioxide exchange in an alpine wetland meadow on the Qinghai-Tibetan Plateau

Biogeosciences Discussions ◽

10.5194/bgd-6-9005-2009 ◽

2009 ◽

Vol 6 (5) ◽

pp. 9005-9044 ◽

Cited By ~ 3

Author(s):

L. Zhao ◽

J. Li ◽

S. Xu ◽

H. Zhou ◽

Y. Li ◽

...

Keyword(s):

Carbon Dioxide ◽

Tibetan Plateau ◽

Soil Temperature ◽

Ecosystem Respiration ◽

Growing Season ◽

Research Station ◽

Rain Event ◽

Area Index ◽

Alpine Wetland ◽

Yearly Average

Abstract. The unique climate of the alpine wetland meadow is characterized by long cold winters and short cool summers with relatively high precipitation. These factors shorten the growing season for vegetation to approximately 150 to 165 days and prolong the dormant period to almost 7 months. Understanding how environmental variables affect the processes that regulate carbon flux in alpine wetland meadow on the Qinghai-Tibetan plateau is critical important because alpine wetland meadow plays a key role in the carbon cycle of the entire plateau. To address this issue, Gross Primary Production (GPP), Ecosystem Respiration (Reco), and Net Ecosystem CO2 Exchange (NEE) were examined for an alpine wetland meadow at the Haibei Research Station of the Chinese Academy of Sciences. The measurements covered three years and were made using the eddy covariance method. Seasonal trends of both GPP and Reco, followed closely changes in Leaf Area Index (LAI). Reco, exhibited the same exponential variation as soil temperature with seasonally-dependent R10 (the ecosystem respiration rate (μmol CO2 m−2 s−1) at the soil temperature reach 283.16 K (10°C)). Yearly average GPP, Reco, and NEE (which were 575.7, 676.8 and 101.1 gCm−2, respectively, for 2004 year, and 682.9, 726.4 and 44.0 gCm−2 for 2005 year, and 630.97, 808.2 and 173.2 gCm−2 for 2006 year) values indicated that the alpine wetland meadow was a moderately important source of CO2. The observed carbon dioxide fluxes in this alpine wetland meadow plateau are high in comparison with other alpine meadow environments such as Kobresia humilis meadow and shrubland meadow located in similar areas. And the cumulative NEE data indicated that the alpine wetland meadow is a source of atmospheric CO2 during the study years. CO2 emissions are large on elevated microclimatology areas on the meadow floor regardless of temperature. Furthermore, relatively low Reco, levels occurred during the non-growing season after a late rain event. This result is contradicted observations in alpine shrubland meadow. The timing of rain events had more impact on ecosystem GPP and NEE.

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Carbon dioxide and methane exchange of a patterned subarctic fen during two contrasting growing seasons

Biogeosciences ◽

10.5194/bg-18-873-2021 ◽

2021 ◽

Vol 18 (3) ◽

pp. 873-896

Author(s):

Lauri Heiskanen ◽

Juha-Pekka Tuovinen ◽

Aleksi Räsänen ◽

Tarmo Virtanen ◽

Sari Juutinen ◽

...

Keyword(s):

Carbon Dioxide ◽

Ecosystem Respiration ◽

Growing Season ◽

Drought Event ◽

Flux Chamber ◽

Ch4 Emissions ◽

Growing Seasons ◽

Ecosystem Level ◽

Community Types ◽

Carbon Dioxide Co2

Abstract. The patterned microtopography of subarctic mires generates a variety of environmental conditions, and carbon dioxide (CO2) and methane (CH4) dynamics vary spatially among different plant community types (PCTs). We studied the CO2 and CH4 exchange between a subarctic fen and the atmosphere at Kaamanen in northern Finland based on flux chamber and eddy covariance measurements in 2017–2018. We observed strong spatial variation in carbon dynamics between the four main PCTs studied, which were largely controlled by water table level and differences in vegetation composition. The ecosystem respiration (ER) and gross primary productivity (GPP) increased gradually from the wettest PCT to the drier ones, and both ER and GPP were larger for all PCTs during the warmer and drier growing season 2018. We estimated that in 2017 the growing season CO2 balances of the PCTs ranged from −20 g C m−2 (Trichophorum tussock PCT) to 64 g C m−2 (string margin PCT), while in 2018 all PCTs were small CO2 sources (10–22 g C m−2). We observed small growing season CH4 emissions (< 1 g C m−2) from the driest PCT, while the other three PCTs had significantly larger emissions (mean 7.9, range 5.6–10.1 g C m−2) during the two growing seasons. Compared to the annual CO2 balance (−8.5 ± 4.0 g C m−2) of the fen in 2017, in 2018 the annual balance (−5.6 ± 3.7 g C m−2) was affected by an earlier onset of photosynthesis in spring, which increased the CO2 sink, and a drought event during summer, which decreased the sink. The CH4 emissions were also affected by the drought. The annual CH4 balance of the fen was 7.3 ± 0.2 g C m−2 in 2017 and 6.2 ± 0.1 g C m−2 in 2018. Thus, the carbon balance of the fen was close to zero in both years. The PCTs that were adapted to drier conditions provided ecosystem-level resilience to carbon loss due to water level drawdown.

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Carbon dioxide and methane exchange of a patterned subarctic fen during two contrasting growing seasons

10.5194/bg-2020-370 ◽

2020 ◽

Author(s):

Lauri Heiskanen ◽

Juha-Pekka Tuovinen ◽

Aleksi Räsänen ◽

Tarmo Virtanen ◽

Sari Juutinen ◽

...

Keyword(s):

Carbon Dioxide ◽

Plant Community ◽

Ecosystem Respiration ◽

Growing Season ◽

Vegetation Composition ◽

Flux Chamber ◽

Growing Seasons ◽

Community Types ◽

Eddy Covariance Measurements ◽

Carbon Dioxide Co2

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Inter-annual variation of carbon uptake by a plantation oak woodland in south-eastern England

Biogeosciences Discussions ◽

10.5194/bgd-9-9667-2012 ◽

2012 ◽

Vol 9 (7) ◽

pp. 9667-9710 ◽

Cited By ~ 5

Author(s):

M. Wilkinson ◽

E. L. Eaton ◽

M. S. J. Broadmeadow ◽

J. I. L. Morison

Keyword(s):

Carbon Balance ◽

Forest Canopy ◽

Annual Variation ◽

Ecosystem Respiration ◽

Growing Season ◽

Co2 Uptake ◽

Operophtera Brumata ◽

Area Index ◽

Growing Season Length ◽

Net Co2 Uptake

Abstract. The carbon balance of an 80 yr old deciduous oak plantation in the temperate oceanic climate of the south-east of Britain was measured by eddy covariance over 12 yr (1999–2010). The mean annual net ecosystem productivity (NEP) was 486 g C m−2 y−1 (95% CI of ±73 g C m−2 y−1), and this was partitioned into a Gross Primary Productivity (GPP) of 2034 ± 145 g C m−2 y−1, over a 165 (±6) day growing season, and an annual loss of carbon through respiration and decomposition (ecosystem respiration, Reco) of 1548 ± 122 g C m−2 y−1. The interannual variation of NEP was large (coefficient of variation (CV) 23%), although the variation for GPP and Reco was smaller (12%) and the ratio of Reco/GPP was relatively constant (0.76 ± 0.02 CI). Some anomalies in the annual patterns of the carbon balance could be linked to particular combinations of anomalous weather events, such as high summer air temperature and low soil moisture content. The Europe-wide heat-wave and drought of 2003 had little effect on the C balance of this woodland on a surface water gley soil. Annual variation in precipitation (CV 18%) was not a main factor in the variation in NEP. The inter-annual variation in estimated intercepted radiation only accounted for ~ 47% of the variation in GPP, although a significant relationship (p<0.001) was found between peak leaf area index and annual GPP which in turn played an important role in modifying the efficiency with which incident radiation was used in net CO2 uptake. Whilst the spring start and late autumn end of the net CO2 uptake period varied substantially (range of 24 and 27 days, respectively), annual GPP was not related to growing season length. Severe outbreaks of defoliating moth caterpillars, mostly Tortrix viridana L. and Operophtera brumata L., caused considerable damage to the forest canopy in 2009 and 2010, resulting in reduced GPP in these years.

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Response of carbon fluxes to water relations in a savanna ecosystem in South Africa

Biogeosciences Discussions ◽

10.5194/bgd-5-2197-2008 ◽

2008 ◽

Vol 5 (3) ◽

pp. 2197-2235 ◽

Cited By ~ 14

Author(s):

W. L. Kutsch ◽

N. Hanan ◽

R. J. Scholes ◽

I. McHugh ◽

W. Kubheka ◽

...

Keyword(s):

South Africa ◽

Water Relations ◽

Ecosystem Respiration ◽

Stomatal Closure ◽

Growing Season ◽

Carbon Fluxes ◽

Dry Season ◽

Canopy Conductance ◽

Wet Season ◽

Leaf Level

Abstract. The principal mechanisms that connect carbon fluxes with water relations in savanna ecosystems were studied by using eddy covariance in a savanna ecosystem at Kruger National Park, South Africa. Since the annual drought and rewetting cycle is a major factor influencing the function of savanna ecosystems, this work focused on the close inter-connection between water relations and carbon fluxes. Data from a nine-month measuring campaign lasting from the early wet season to the late dry season were used. Total ecosystem respiration showed highest values at the onset of the growing season, a slightly lower plateau during the main part of the growing season and a continuous decrease during the transition towards the dry season. The regulation of canopy conductance was changed in two ways: changes due to phenology during the course of the growing season and short-term acclimation to soil water conditions. The most constant parameter was water use efficiency that was influenced by VPD during the day but the VPD response curve of water usage did change only slightly during the course of the growing season and decreased by about 30% during the transition from wet to dry season. The regulation of canopy conductance and photosynthetic capacity were closely related. This observation meets recent leaf-level findings that stomatal closure triggers down-regulation of Rubisco during drought. Our results may show the effects of these processes on the ecosystem scale.

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