Variability Of Carbon Dioxide Flux Research Articles

High‐frequency variability of carbon dioxide fluxes in tidal water over a temperate salt marsh

AbstractExisting analyses of salt marsh carbon budgets rarely quantify carbon loss as CO2 through the air–water interface in inundated marshes. This study estimates the variability of partial pressure of CO2 (pCO2) and air–water CO2 fluxes over summer and fall of 2014 and 2015 using high‐frequency measurements of tidal water pCO2 in a salt marsh of the U.S. northeast region. Monthly mean CO2 effluxes varied in the range of 5.4–25.6 mmol m−2 marsh d−1 (monthly median: 4.8–24.7 mmol m−2 marsh d−1) during July to November from the tidal creek and tidally‐inundated vegetated platform. The source of CO2 effluxes was partitioned between the marsh and estuary using a mixing model. The monthly mean marsh‐contributed CO2 effluxes accounted for a dominant portion (69%) of total CO2 effluxes in the inundated marsh, which was 3–23% (mean 13%) of the corresponding lateral flux rate of dissolved inorganic carbon (DIC) from marsh to estuary. Photosynthesis in tidal water substantially reduced the CO2 evasion, accounting for 1–86% (mean 31%) of potential CO2 evasion and 2–26% (mean 11%) of corresponding lateral transport DIC fluxes, indicating the important role of photosynthesis in controlling the air–water CO2 evasion in the inundated salt marsh. This study demonstrates that CO2 evasion from inundated salt marshes is a significant loss term for carbon that is fixed within marshes.

Spatial and temporal variability of carbon dioxide fluxes in the Alpine Critical Zone: The case of the Nivolet Plain, Gran Paradiso National Park, Italy.

The dynamics of carbon dioxide fluxes in the high-altitude Alpine Critical Zone is only partially understood. The complex geomorphology induces significant spatial heterogeneity, and a strong interannual variability is present in the often-extreme climatic and environmental conditions of Alpine ecosystems. To explore the relative importance of the spatial and temporal variability of CO2 fluxes, we analysed a set of in-situ measurements obtained during the summers from 2018 to 2021 in four sampling plots, characterised by soils with different underlying bedrock within the same watershed in the Nivolet plain, in the Gran Paradiso National Park, western Italian Alps. Multi-regression models of CO2 emission and uptake were built using measured meteo-climatic and environmental variables considering either individual years (aggregating over plots) or individual plots (aggregating over years). We observed a significant variability of the model parameters across the different years, while such variability was much smaller across different plots. Significant changes between the different years mainly concerned the temperature dependence of respiration (CO2 emission) and the light dependence of photosynthesis (CO2 uptake). These results suggest that spatial upscaling can be obtained from site measurements, but long-term flux monitoring is required to properly capture the temporal variability at interannual scales.

Strong diurnal variability of carbon dioxide flux over algae-shellfish aquaculture ponds revealed by eddy covariance measurements

Aquaculture ponds represent a biogeochemical hotspot of the global carbon cycle. However, accurate estimations of their carbon budgets are hindered by a limited understanding of the temporal variability of carbon fluxes across time scales. In this study, the eddy covariance (EC) approach was applied to quantify net ecosystem CO2 exchange (NEE) over algae-shellfish aquaculture ponds (razor clam cultivation) in Zhangjiang Estuary of Southeast China from January 2020 to June 2022, aiming to assess the diurnal variability of NEE during various management periods. The EC-based NEE over the ponds showed strong diurnal variations with daytime sink and nighttime source, mainly controlled by photosynthetically active radiation and air temperature, respectively. The ponds acted as a net sink system during razor clam (daily mean flux of −0.42 μmol m−2 s−1) and shrimp-crab (−0.50 μmol m−2 s−1) farming periods with a stronger daytime sink than a nighttime source, while it was the opposite during the drainage period acting as a net source (0.40 μmol m−2 s−1). The strength of sink/source also differed between the early and late stages of the razor clam farming period, with much larger (∼ 16 times) net carbon uptake in the late stage as a result of the strong daytime sink and near-neutral nighttime flux. The diurnal variability of NEE over the ponds was overall larger than other aquatic ecosystems and tended to increase with air temperature. Previous estimates of daily NEE from discrete daytime-only samplings might have biased the actual carbon budgets if no diurnal correction was applied in the temporal aggregation. The confirmed strong temporal variability of NEE across time scales highlighted the importance and necessity of continuous and high-frequency flux measurements in assessing the carbon budgets of algae-shellfish aquaculture ponds.

Investigation of the intensity of carbon dioxide emissions by steppe soil when introducing fallow lands into circulation

The paper reflects the results of studying the temporal variability of carbon dioxide fluxes by the soils of deposits when they are introduced into agricultural circulation. The purpose of the research is to study the change in carbon dioxide emissions by the soils of fallow lands in the conditions of the steppe of Western Siberia. In 2022, research was conducted in the Omsk Region at key sites. The soils of the site are solodic, malodorous medium low-sodium columnar heavy loamy meadow-chernozem; cortical columnar heavy loamy saline meadow-chernozem, fine-grained low-humus heavy loamy meadow malt. Seasonal changes in carbon dioxide fluxes by soils on deposits when introduced into circulation using agrotechnical technology are significant (Figure 2) with a maximum in July (67.7 g CO2/m2/day) and a minimum in September (16.7 g CO2/m2/day); on deposits with combined technology, respectively, 54.4 and 14.1 g CO2/m2/day. Agrotechnical technology contributed to a greater emission of carbon dioxide from the soils of the deposit than combined. The system of agrotechnical techniques when introducing fallow soils into agricultural circulation has a significant impact on the release of carbon dioxide by the soil surface. Of the soil level of the deposit without treatment, it was 162% with agrotechnical technology (tillage), and with combined (tillage + herbicide application) 133%.

Quantification of water stress induced within-field variability of carbon dioxide fluxes in a sugar beet stand

Net ecosystem exchange of carbon dioxide (NEE) and soil respiration at field scale can exhibit considerable spatial variability linked to the heterogeneity of soil properties and state variables. In this study, we measured NEE with the eddy covariance (EC) method in a sugar beet field characterized by high spatial variability in soil physical properties. We further measured NEE and soil respiration by chambers as well as soil water content and temperature at 18 locations within the field.Spatially averaged chamber-measured NEE showed good agreement to the EC-based data. During a dry period high spatial variation of within-field NEE was detected with the chamber method. The coefficient of variation was on average 0.57 during the dry period, with a maximum of 0.72. Based on the depth-specific soil water content measurements the AgroC ecosystem model was inverted for soil hydraulic properties at each of the 18 locations, where soil water content was measured. Analyzing the model results revealed that root water uptake stress was the main driver of spatial and temporal variability in crop development and NEE, whereby the soil coarse material fraction (gravel content) and thickness of the layer above a gravel dominated soil layer were identified as the main influencing soil properties.The chamber-measured NEE and the flux footprint analysis showed that particularly during periods of severe root water uptake stress EC-based measurements would be prone to biases. A combination of the footprint model with the AgroC ecosystem model estimated a bias of 14 % for the dry period and a vegetation period bias of 6 % in relation to the average CO2 flux.

Contribution of unvegetated tidal flats to coastal carbon flux.

Unvegetated flats occupy a large area in the intertidal zone. However, compared to vegetated areas, the carbon sequestration of unvegetated tidal flats is rarely quantified, even though these areas are highly threatened by human development and climate change. We determined benthic maximum gross primary production (GPPm ), net primary production (NPP) and total respiration (TR) during emersion on seven tidal flats along a latitudinal gradient (from 22.48°N to 40.60°N) in winter and summer from 2012 to 2016 to assess the spatial and temporal variability of carbon dioxide flux. In winter, these processes decreased by 89%-104% towards higher latitudes. In summer, however, no clear trend was detected across the latitudinal gradient. Quadratic relationships between GPPm , NPP and TR and sediment temperature can be described along the latitudinal gradient. These curves showed maximum values of GPPm and NPP when the sediment temperatures reached 28.7 and 26.6°C respectively. TR increased almost linearly from 0 to 45°C. The maximum daily NPP across the latitudinal gradient averaged 0.24±0.28gCm-2 day-1 , which was only 10%-20% of the global average of NPP of vegetated coastal habitats. Multiplying with the global area of unvegetated tidal flats, our results suggest that the contribution of NPP on unvegetated tidal flats to the coastal carbon cycle is small (11.04±13.32TgC/year). If the land cover of vegetated habitats is continuously degraded to unvegetated tidal flats, the carbon sequestration capacity in the intertidal zone is expected to reduce by at least 13.10TgC/year, equivalent to 1% of global carbon emissions from land-use change.

Carbon dioxide fluxes in the city centre of Arnhem, A middle-sized Dutch city

This paper reports on the temporal variability of carbon dioxide fluxes in the city centre of Arnhem, a middle-sized Dutch city. The fluxes were continuously measured during four years (2012–2016) using the eddy-covariance method. Additionally, continuous meteorological measurements were carried out. We also analysed data from 30-minute traffic counts performed during those years. Results indicate that the city centre of Arnhem is a strong emission source of CO2 compared to many other cities. The measured annual CO2 flux equals about 8.0kgCm−2yr−1. Heterogeneity within the footprint of the EC tower appeared to have no or only a small influence on the estimated annual and seasonal carbon fluxes. Sector analysis shows that CO2 fluxes are consistently higher in sectors with the highest built-up surface fraction. However, no statistically significant relationship could be determined. Traffic and space-heating related burning of natural gas are the main emission sources. Weekly and diurnal variations in CO2 flux are clearly correlated with traffic intensity, whereas seasonal variation can largely be explained by space heating demand. Partitioning of the total flux into a heating-related and traffic-related flux revealed that space heating accounts for up to 60% to the total flux during winter. Traffic intensity remains more or less constant throughout the year. In summer, when space heating is absent, CO2 emission is almost entirely related to traffic intensity. However, our estimations suggest that human respiration could have a non-negligible share in this. The contribution of the small fraction of urban green in the city centre is probably minimal. The annual emissions for the city centre estimated from our EC measurements are 20–25% lower than those reported for the whole city by the official emission inventory. Climate projections for the Netherlands suggest that in 2050 Heating Degree Days would be reduced by 27% resulting into a 32% reduction of the heating-related emission flux, without a change in fossil fuel use.

On the controlling factors for the variability of carbon dioxide flux in a heterogeneous urban environment

ABSTRACTLocal heterogeneity of CO2 sources and sinks is a key factor for the variability of carbon dioxide flux (FC) in urban areas. Information on the urban structure around a site, especially the related emission characteristics, is thus of great importance to the understanding of observed FC. Strong spatially confined sources like major roads inhibit a direct correlation of FC to area‐averaged features of the urban structure and may lead to a heavily biased signal.Four years of FC measured at Basel Aeschenplatz, Switzerland, are analysed with respect to the controlling factors and the cause for variability on different time scales. The source area is segregated into equal sectors to address heterogeneous emission patterns. Residential areas to the east are bordered by business areas and major roads to the west, which leads to a fundamental dependence of FC on wind direction. Besides, its diurnal course is explainable with traffic emissions while its annual course follows heating‐related combustion emissions. Vegetation fraction is rather considered to be an indicator for urban land use types (residential/business) and the attributable emission characteristics than to be a measure for biological sink effects. Inter‐annual variability occurs as a result of anomalies in wind direction patterns or air temperature. Average yearly FC is 16.4 µmol m–2s–1 with slight variations (±0.55 µmol m–2s–1) over the 4 years. It likely originates from an average of 70% traffic and 30% heating‐related emissions with significant sectoral differences.As a continuous measure for the emissions of each sector, the expected CO2 flux (eFC) per sector is introduced, leading to an enhanced comparability. Relating sectoral eFC instead of FC to urban surface fractions of buildings and vegetation results in a better agreement (also with data from other studies).

Relationship between Distance Sampling and Carbon Dioxide Emission under Oil Palm Plantation

Relationship between Distance Sampling and Carbon Dioxide Emission under Oil Palm Plantation

Carbon dioxide flux in the centre of Łódź, Poland—analysis of a 2‐year eddy covariance measurement data set

AbstractContinuous measurements of carbon dioxide turbulent flux F carried out with the eddy covariance method have been made in Łódź since F July 2006. The measurement point (Lipowa Station) is located in the west part of the densely built‐up city centre, where artificial surfaces clearly prevail over natural terrain. The measurement system includes a Kipp and Zonen's (Delft, Holland) CNR1 net radiometer, RMYoung (Traverse City, Michigamn, USA) 81000 sonic anemometer and Li‐cor (Lincoln, Nebraska, USA) 7500 open path H2O/CO2 infrared gas analyser. Sensors are installed on the high tower 20 m above the roof of the building and 37 m above the ground, so the measurement height exceeded the urban canopy layer more than twice. The diurnal and annual variability of carbon dioxide flux for the period July 2006 to August 2008 is analysed in the article. The results show the characteristic features in diurnal and annual courses of F. Independently from the season, positive (upward) fluxes of the order of 0–15 µmol m−2 s−1 prevail in the data. During the cold season, an increase in turbulent CO2 exchange is observed (F quite often exceeded 30 µmol m−2 s−1). This can be attributed to anthropogenic CO2 emissions, which are particularly strong in winter due to, among other things, mineral fuel combustion during domestic heating. The average monthly fluxes are positive in all seasons, which means that emission of CO2 in the surroundings of the measurement point prevails over its uptake. Apart from the season, the maximum flux occurred during the day and the minimum during the second part of the night. Wintertime monthly averaged fluxes are much higher than summertime ones. The observed increase in CO2 exchange during weekdays in comparison with weekends can be caused by the weekly rhythm of traffic in the surroundings of Lipowa Station. Copyright © 2010 Royal Meteorological Society

Climatic and phenological controls on coherent regional interannual variability of carbon dioxide flux in a heterogeneous landscape

The climate sensitivity of plant seasonal life cycles, or phenology, may impart significant carbon cycle feedbacks on climatic change. Analysis of interannual ecosystem carbon exchange provides one way to assess this climate sensitivity. Multiyear eddy covariance carbon dioxide flux observations from five different ecosystems (deciduous forest, northern hardwood mixed forest, old‐growth forest, shrub wetland, and mixed wetland‐forest) in the Upper Great Lakes, United States, located within 400 km of each other and exhibiting coherent interannual variability, were used to parameterize a simple ecosystem model. The model, when properly constrained with an interannual sensitive cost function, was able to explain a significant proportion of the interannual variation of carbon fluxes in all ecosystems except the old‐growth forest. The results reveal that spring or autumn climate thresholds impact annual carbon uptake, though the magnitude and strength varied by site. When the model was forced to maintain the same climate‐phenology relationship across the five sites, most of the interannual variability could still be explained except at the old‐growth forest and the forest farthest in distance from the others. These results suggest that at least for this region, coarse spatial resolution carbon‐climate models could likely specify general climate‐phenological relationships at grid scales on order of 100 km without appreciably sacrificing ability to model interannual carbon cycling.

Variability of carbon dioxide flux from tropical (Cerrado) hydroelectric reservoirs

Hydroelectric reservoirs generate energy without significant combustion of fossil fuels. However, these systems can, potentially, emit greenhouse gases (GHG’s) at a rate which may be significant at the global scale, and, possible, co-equal, per kilowatt-hour, to that from conventional coal or oil-fired systems. Although much of the new construction of hydroelectric reservoirs is in the tropics, most of the data on GHG emissions comes from temperate regions. Further, much of the existing data on reservoir gas emissions comes from single sites, usually near the terminal dams. Large tropical reservoirs often involve the impoundments of river systems with complex morphology which in turn can cause spatial heterogeneity in gas flux. We evaluated spatial and seasonal variability in CO2 concentrations and gas flux for five large (50–1,400 km2) reservoirs in the Cerrado region of Brazil. Most of data set (87% of all measurements) showed CO2 supersaturation and net efflux to the atmosphere. There was as much or more variation in pCO2 over space and among seasons. The large studied reservoirs showed different zones in terms of CO2 emission because those fluxes are dependent on flooded biomass, watershed input of organic matter and dam operation regime. Here we demonstrate that the reservoirs in the Brazilian Cerrado have low rates of CO2 emissions compared to existing global comparisons. Our results suggest that ignoring the spatial variability can lead to more than 25% error in total system gas flux.