BG3.19

Tropical peat swamp forests are major global carbon (C) stores that are particularly vulnerable to human intervention. In the Peruvian Amazonia they have been severely degraded through recurrent cutting of Mauritia flexuosa palms for fruit harvesting, and potentially been transformed from a CO₂ sink into a significant source. To estimate emissions associated with degradation, we combined C stock changes in aboveground biomass with peat C losses along a gradient comprising undegraded (Intact), moderately degraded (mDeg) and heavily degraded (hDeg) palm swamps. Temporal and spatial dynamics of the main components of the peat C budget (heterotrophic soil respiration (Rh) and litterfall) were investigated (bi)monthly over three years, while annual site-specific root C inputs and default dissolved organic C exports were taken from the literature. Variables measured at tree or microtopographic level were site-scaled considering forest structural changes from degradation. Site-scale litterfall (Mg C ha⁻¹ year⁻¹) at the hDeg site (2.3 ± 0.5) was less than half the rate at the Intact and mDeg sites (5.2 ± 0.9 and 6.0 ± 1.6, respectively). Conversely, site-scale Rh (Mg C ha⁻¹ year⁻¹) was higher at the hDeg site (9.6 ± 0.6) than at the Intact and mDeg sites (7.5 ± 1.1 and 6.1 ± 0.5, respectively). The peat carbon budget (Mg C ha⁻¹ year⁻¹) indicated that medium degradation reduced the sink capacity of the soil (from -1.8 ± 1.8 at the Intact site to -0.3 ± 0.7 at the mDeg site) while high degradation turned the soil into a high C source (6.0 ± 0.6 at the hDeg site). The large total C stock loss rates of 23.5 ± 14.3 and 57.7 ± 14.3 Mg CO₂ ha⁻¹ year⁻¹ at the mDeg and hDeg sites, respectively, which originated 94 and 77% from aboveground biomass changes clearly highlight the need for sustainable management of these peatlands.

How to cite: Kristell, H., Jeffrey, V. L., Nelda, D., Louis Vincent, V., Jan Willem, V. G., Mariela, L., and Julio, G.-R.: Major CO2 losses from degradation of Mauritia flexuosa peat swamp forests in western Amazonia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13155, https://doi.org/10.5194/egusphere-egu22-13155, 2022.

The megadiverse Andean mountain rain forests in southern Ecuador are threatened by climate and land use change, which are expected to alter biodiversity and thus functional traits impacting ecosystem processes. However, the high biodiversity of tropical mountain forests is still poorly represented in Land Surface Models (LSMs). We developed a biodversity-informed LSM entitled HUMBOL-TD (Hydroatmo Unified Model of Biotic interactions and Local Trait Diversity) to analzye the impact of climate and land-use change on carbon- and water fluxes. HUMBOL-TD consists of three coupled submodels specialized to represent different processes at the land surface. As such, energy- and water fluxes between land surface and atmosphere (LSMatmo) are simulated by the Community Land Model (CLM), vegetation dynamics including C, N and P cycling (LSMbio) are simulated by the Lund-Potsdam-Jena General Ecosystem Simulator (LPJ-GUESS), while the soil hydrology (LSMhydro) is represented by the Catchment Modeling Framework (CMF). A first test towards the simulation of the mountain forests and their replacement systems is conducted for a pasture site at 2000 m elevation. The model is parameterized and validated using a year of local site data. The first runs of the model enable the investigation of the differences in accuracy of modeled changes in the carbon- and water fluxes between coupled, partially coupled (LSMatmo – LSMbio, LSMatmo – LSMhydro, LSMbio – LSMhydro) and the fully coupled model (LSMatmo – LSMbio – LSMhydro).

How to cite: Limberger, O., Dantas De Paula, M., Windhorst, D., Trachte, K., Breuer, L., Hickler, T., and Bendix, J.: The new coupled land surface model HUMBOL-TD - Concept and performance, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12150, https://doi.org/10.5194/egusphere-egu22-12150, 2022.

Knowledge about microclimatological conditions strongly contributes to our understanding of land surface – atmosphere interactions as drivers of the Earth’s surface energy budget. Particularly the radiative fluxes are major determinants providing energy for vital climate processes and are crucial for climate warming, water availability, primary productivity and ecosystem services. The partitioning into sensible and latent heat fluxes are highly dependent on the land coverage and represent feedback effects affecting the cycling of heat and water in the vegetation-atmosphere continuum. In the Reserva Biologica San Francisco (RBSF) on the eastern escarpment of the South Ecuadorian Andes on 2000m elevation above sea level (a.s.l.) two eddy-covariance measurement stations have been installed over natural rain forest and pasture ecosystem to observe atmospheric water and carbon fluxes. The aim is to assess net-ecosystem exchange (NEE) and evapotranspiration (ET) in order to estimate the impact of deforestation on the carbon sink function and the water availability. Additionally, microclimatological conditions in terms of e.g. radiative fluxes and soil conditions are supposed to further disentangle effects of the respective land surface properties on the environmental conditions. Over the last three years generally higher water fluxes could be observed during daytime over the forest ecosystem compared to pasture. Concerning NEE a clear carbon sink was revealed for both ecosystems indicated by a mean gross primary productivity (GPP) of 12.7 gC/m²day (forest) and 6.5 gC/m²day (pasture), while a mean ecosystem respiration (Reco) of 10.6 gC/m²day (forest) and 5.9 gC/m²day (pasture) was obtained. However, a mean NEE of 2.1 gC/m²day (forest) and 0.6 gC/m²day (pasture) clearly shows the stronger productivity of the forest ecosystem and thus, a higher carbon sink as a contribution to climate change mitigation.

How to cite: Trachte, K., Pucha Cofrep, F., Raffelsbauer, V., Limberger, O., Fries, A., Carillo-Rojas, G., and Bendix, J.: Microclimatological conditions along a land use gradient in the tropical Andes of South Ecuador, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11987, https://doi.org/10.5194/egusphere-egu22-11987, 2022.

Conventional intensive management, such as high fertilizer and herbicide applications, are common practice in large-scale oil palm plantations. One of the proposed solutions to lessen its environmental impact is to reduce fertilization and employ mechanical weeding without sacrificing yield and profit. A full factorial experiment with two fertilization rates (260 N, 50 P, 220 K kg ha^-1 yr^-1 as conventional practice, and 136 N, 17 P, 187 K kg ha^-1 yr^-1, equal to harvest export, as reduced management) and two weeding methods (conventional herbicide application, and mechanical weeding as reduced management) was established in 2016 at a large-scale oil palm plantation (planted in 1998-2002) on a sandy clay loam Acrisol soil in Jambi, Indonesia. Soil CO₂, N₂O, and CH₄ fluxes were measured monthly from July 2019 to June 2020, using vented static chambers. At each plot, the measurements were conducted on two randomly selected subplots, and in each subplot, we measured at three management zones (palm circle, inter-row, and frond-stacked area). During 2017-2020, fruit yield did not differ among treatments (fertilization: P=0.35; weeding control: P=0.11). Soil CO₂, N₂O, and CH₄ fluxes also did not differ among treatments (fertilization: P>0.81; weeding control: P>0.28). Area-weighted from the three management zones, soil CO₂ fluxes (mg C m^-2 h^-1) were 61±2 for conventional and 65±4 for reduced fertilization and 64±4 for herbicide and 62±2 for mechanical weeding. Soil N₂O fluxes (µg N m^-2 h^-1) were 46±12 for conventional and 45±16 for reduced fertilization and 57±15 for herbicide and 34±12 for mechanical weeding. Soil CH₄ fluxes (µg C m^-2 h^-1) were -17±2 for conventional and -17±3 for reduced fertilization and -17±3 for herbicide and -17±2 for mechanical weeding. Distinct differences were observed among the three management zones. Frond-stacked area, with high soil organic carbon and low soil bulk density, had the highest soil CO₂ emission and soil CH₄ uptake (P≤0.01). Palm circle, with fertilizer application and high soil bulk density, had the highest soil N₂O emission and lowest soil CH₄ uptake (P≤0.01). Inter-row area, with low soil organic carbon and no direct fertilizer application, had the lowest soil CO₂ and N₂O emission (P≤0.01). Soil CO₂ (rho=0.64, P≤0.05) and N₂O (rho=0.53, P≤0.05) fluxes were positively correlated with total mineral N. Soil CH₄ flux was negatively correlated with total mineral N (rho=-0.30, P≤0.05) and positively correlated with water-filled pore space (rho=0.66, P≤0.05). Although the frond-stacked area only accounted for 15% of the oil palm plantation area, it contributed 30% of soil CO₂ emission and 41% of soil CH₄ uptake. The palm circle accounted for 18% of the oil palm plantation area and contributed 79% of soil N₂O emissions. Our results indicated that the inherent management zones in oil palm plantations should be spatially represented for accurate quantification of soil greenhouse gas fluxes. Our findings showed that reduced management maintained yield whereas soil greenhouse gas fluxes remained high at least during the 3-4 years of this management experiment, which signified the legacy effect of more than a decade-long conventional management in this mature oil palm plantation.

How to cite: Chen, G., Veldkamp, E., Tjoa, A., Damris, M., Irawan, B., and Corre, M. D.: Soil greenhouse gas fluxes from large-scale oil palm plantation under conventional and reduced management systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2664, https://doi.org/10.5194/egusphere-egu22-2664, 2022.

Oil palm (OP) plantations have replaced large areas of forest in the tropical landscape of Southeast Asia and are major emitters of greenhouse gases (GHGs). However, within established plantations there are management options which may reduce these emissions, including altered management practices within plantations and restoring forest within the landscape. Managing the vegetation within and around plantations could potentially minimise environmental damage and maximise co-benefits such as soil protection, pest control and support for biodiversity. Such practices include relaxed management, passive restoration, and active restoration. The impact of these management practices is uncertain, and there is a real need for an evidence-base to guide improvements in the environmental sustainability of OP management.

Here we present GHG fluxes from two long-term experiments as part of ‘The Biodiversity and Ecosystem Function in Tropical Agriculture’ (BEFTA) Project. The first experiment is investigating the impact of three alternative understory management treatments on biodiversity, ecosystem functioning and yield in Sumatra, Indonesia:

• Normal biodiversity complexity: standard industry practice, intermediate level of herbicide use in harvest circles around the palms.
• Reduced biodiversity complexity: spraying/removing all understory vegetation with herbicides.
• Enhanced biodiversity complexity: reduced-input management with no herbicide application and limited understory cutting.

The second experiment focusses on riparian restoration options (‘Riparian Ecosystem Restoration in Tropical Agriculture’ (RERTA) Project). The experimental site began as a mature OP plantation, followed by felling in April 2019 and replanting and riparian restoration in October 2019. Four management strategies were applied on both sides of a river to create 50 m riparian buffers, 400 m in length:

• A control treatment of no restoration, the removal of mature OP and replanting of young OP to the river margin.
• Passive restoration: Little to no agricultural management of mature OP.
• Active restoration A: Clearance of mature OP and enrichment planting with native forest trees.
• Active restoration B: Little or no agricultural management of mature OP and additional enrichment planting with native forest trees.

For both experiments, we measured the GHGs nitrous oxide (N₂O), methane (CH₄) and ecosystem respiration/carbon dioxide (CO₂) from static chambers and analysis by gas chromatography (GC-µECD/FID). Additionally, meteorological and basic soil parameters were measured as potential variables or drivers of measured fluxes that might be greater than any ‘treatment’ or ecological management effect. Measurements were carried out monthly from the understory treatments, taken from 54 static chambers for the duration of one year starting in October 2018. For the riparian restoration project, monthly background measurements were taken between January and April 2019 and then approximately monthly after replanting from 6 chambers in each riparian treatment and 16 in the actual OP plantation resulting in 40 chambers in total.

We investigated whether the observed ecological benefits of alternative management and restoration options such as introducing native tree species in riparian buffers and allowing the natural regrowth of understory in plantations may be associated with an additional or reduced GHG burden; thereby assessing the overall environmental impact.

How to cite: Drewer, J., Sionita, R., White, S., Luke, S., Turner, E., Raine, B., Banin, L., Skiba, U., Advento, A. D., Ketut Aryawan, A. A., Caliman, J.-P., and Pujianto, P.: Diversifying understory vegetation and riparian restoration as ecological management options to regulate greenhouse gas fluxes in oil palm plantations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13120, https://doi.org/10.5194/egusphere-egu22-13120, 2022.

Mangrove and other coastal wetlands such as saltmarsh and seagrass are termed ‘blue carbon’ ecosystems due to their substantial capacity for carbon storage and sequestration over a long-term time scale. Policymakers and stakeholders are currently promoting mangroves into national carbon management as part of nature-based climate change mitigation and adaptation strategy. Unfortunately, global mangroves area with particularly in the tropics is decreasing at a rapid rate due to land-use and land-cover change (LULCC). Yet, there has been limited study of carbon emissions impacted by multiple mangrove conversions at the landscape scale. Here we assessed spatio-temporal patterns of soil CO₂ and CH₄ effluxes across six land uses, namely mangroves converted to 15 yrs oil palm, 20 yrs coconut, and 20 yrs aquaculture (pond wall and water surface), as well as newly logged mangrove, 10 yrs planted mangrove, and undisturbed mangrove forests reference in North Sumatra, Indonesia. Direct measurement of soil CO₂ and CH₄ effluxes were performed by using an ultra-portable LGR gas analyser during low tide condition between 08.00 and 16.00, with triplicated PVC 10-inch diameter and 25 cm height opaque static chambers (closed system) were installed at each land use in September-October 2021 -- representing wet season in the study site. The soil CO₂ and CH₄ effluxes were collected three times for each chamber and 3 days of measurement during this field campaign with a total of 193 measurements were performed. We observed that the top three highest soil CO₂ and CH₄ effluxes were among aquaculture pond wall soils (591±104 mgCO₂ m² h^-1 and 0.40±0.17 mgCH₄ m² h^-1), logged mangroves (480±104 mgCO₂ m² h^-1 and 3.21±1.34 mgCH₄ m² h^-1), and natural mangroves (274±71 mgCO₂ m² h^-1 and 0.58±0.28 mgCH₄ m² h^-1). By contrast, relatively low effluxes (< 200 mgCO₂ m² h^-1 and < 0.1 mgCH₄ m² h^-1) were observed across other land-use types. Our preliminary results suggest that the variation of soil CO₂ and CH₄ in our study sites may be controlled by the duration of the disturbances, particularly we observed the highest CO₂ and CH₄ effluxes at newly (occurred at the same year with our measurement) constructed pond wall and logged mangrove locations. On the other hand, low CO₂ and CH₄ effluxes were observed at both oil palm and coconut plantations. These new land uses were constructed more than 10 years ago with the application of drainage and tidal blocking. Our current limited data constraint further essential factors that commonly control CO₂ and CH₄ in the coastal wetlands, such as tidal elevation, bioturbation, seasonal variation, and soil properties. Overall, our dataset will be essential to guide policymakers in related to the improvement of land-based low carbon development and climate change mitigation strategies for Indonesia to meet the targeted 29% of unconditional carbon emissions reduction by 2030 as outlined in the Nationally Determined Contributions (NDCs) as part of the Paris Agreement.

How to cite: Sasmito, S., Arriyadi, D., Bimantara, Y., Amelia, R., Saragi-Sasmito, M., Darusman, T., Basyuni, M., Maher, D., Hutley, L., and Murdiyarso, D.: CO2 and CH4 effluxes across six land uses in coastal wetlands of North Sumatra, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13486, https://doi.org/10.5194/egusphere-egu22-13486, 2022.

Tropical forest plays a fundamental role in the ecosystem services maintenance. Amazon forests have been subject to intense land use and cover changes (LUCC), mainly in the Southeast portion. Like many tropical countries, more than 70% of Brazilian greenhouse gasses emissions come from LUCC. Under the framework of the CARBAM Project, atmospheric CO₂ measurements in four sites of the Amazon, show that there is a reduction in the Amazon forest capacity to absorb C in the proximities of previous deforested and degraded forest areas, such as the well-known “Deforestation Arc” in the Southeast amazon. There are many LUCC databases now available that allow to assess the deforestation, degradation and second forest dynamics and contribute to a better understanding of the carbon dynamics of nine years of in situ atmospheric CO₂ measurements. Nevertheless, in order to know how much CO₂ is released to the atmosphere due to LUCC, it is necessary to quantify how much carbon is stored in the forest biomass and to assess the biomass variability along the different datasets. Here we compared the forest biomass quantity of three biomass maps: the fourth national communication of Brazil map (official), a global map (Baccini et al. 2012) and a regional map for the Brazilian Amazon (EBA project). We found significant differences for the Brazilian Amazon: between the official biomass map and the regional map 27%, between the global and regional map 25% and the smallest difference was between the official and the global map (3%). Even though the official and the regional maps were obtained using the same data inputs, the official map refers to a potential biomass for 2010 and the regional map reflects the real biomass in 2016, this could explain the difference. The official and global maps represent the potential biomass, and as we used the mean forest area, the biomass content is similar. When comparing these maps at a deforested pixel level the differences could be larger. The spatial and temporal scale of biomass maps make it hard to estimate the CO₂ emissions of degradation and secondary forest loss and growth which are fundamental to understand the Amazon C balance under climate change and LUCC pressures.  

Key words: Amazon, CO₂ emissions, forest biomass, land use and cover change, carbon balance

How to cite: Tejada, G., V. Gatti, L., S. Basso, L., A. V. Mataveli, G., L.G. Cassol, H., and Von Randow, C.: Forest biomass - an uncertainty source of land use and land cover change related carbon emissions in the Amazon, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10410, https://doi.org/10.5194/egusphere-egu22-10410, 2022.

Application of mineral nitrogen (N) fertilizer and water management are two very essential farming practices, used to optimize potential yields in sub-Sahara African rice cultivation. Differences in both practices, however, might affect the patterns of climate relevant gaseous carbon (C) emissions (CO₂ and CH₄) and soil C losses, thus contributing to global climate change. To date, knowledge about the combined effects of different N fertilizer rates together with different water management practices on the gaseous C emissions and soil C losses are very limited. This is even more the case for arable lands in sub-Sahara Africa. Our study aims to identify the best combination of water management and N fertilizer amount to reduce gaseous C emissions and limit soil C losses for an irrigated rice production in Benin. We hypothesize that especially a combination of alternate wetting and drying (AWD) as water management and an optimum amount of N fertilizer reduce gaseous C emissions and might help to enhance C sequestration by reducing soil C losses from irrigated rice production in Benin. To test this hypothesis, a field experiment was established at Koussin lélé, Cove district, southern Benin using a full factorial, split-plot experimental design. Within the experiment the combination of three levels of water management and two levels of N fertilizer amount are tested. The water management technologies include continuous flooding (CF) and two alternate wetting and drying (AWD) methods (AWD15 and AWD25) of irrigation. Nitrogen fertilizer levels is 90 kg/ha (farmer’s practice) and 120 kg/ha (high amount of fertilizer). To measure gaseous C emissions (CO₂ and CH₄) and estimate dynamics in soil C losses, an innovative, customized low cost dynamic NFT-NSS closed chamber system is used. The system consists of CO₂/CH₄ NDIR sensors connected to a microcontroller for data storage and transparent (NEE measurements) polycarbonate chambers (40 cm x 40 cm x 100 cm). To measure R_eco, transparent chambers where covered with an opaque hood. Chamber measurements for diurnal variability in CH₄ and CO₂ fluxes are performed biweekly at all plots. In addition, agronomy and crop growth indices such as the Normalized difference vegetation index (NDVI) are measured weekly. Here we present CO₂ and NECB balances for the first crop growth period.

Key words: Water management, N fertilizer, CO₂ emission, net ecosystem carbon balance (NECB), rice

How to cite: Sossa, L. G., Naab, J., Augustin, J., Sintondji, L., Sanogo, S., and Hoffmann, M.: Effect of N fertilizer amount and water management on CO2 exchange and net ecosystem C balance of rice cultivation in Southern Benin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-232, https://doi.org/10.5194/egusphere-egu22-232, 2022.

Degradation, conversion and drainage of tropical peatlands generate sizeable emissions of greenhouse gases (GHG). Current IPCC default emission factors (EF) for drained tropical peatlands are based on a very limited number of observations, thereby resulting in large uncertainties in emissions estimates. Impacts of disturbance on peat GHG emissions in undrained tropical peatlands can also be substantial but are not well characterized and not considered by IPCC guidelines. Research is critically needed to support development of more accurate EF for national GHG accounting for both drained and undrained degraded tropical peatlands. To explore the potential of process-based modelling to refine tropical peat EF, we used the DeNitrification DeComposition (DNDC) model to simulate peat GHG emissions and biogeophysical variables in oil palm plantations and undrained primary and secondary peat swamp forests of Central Kalimantan, Indonesia.

The simulated magnitude of C inputs (litterfall and root mortality) and dynamics of annual heterotrophic respiration and peat decomposition N₂O fluxes in oil palm plantations were generally consistent with field observations. The modelled onsite oil palm peat CO₂ EF was lower than the IPCC default (11 Mg CO₂-C ha^-1 yr^-1) and decreased from 7.7 ± 0.4 Mg C ha^-1 yr^-1 in the first decade to 3.0 ± 0.2 and 1.8 ± 0.3 Mg C ha^-1 yr^-1 in the second and third decades of the rotation. The modelled N₂O EF from peat decomposition was higher than the IPCC default (1.2 kg N ha^-1 yr^-1) and increased from 3.5 ± 0.3 kg N ha^-1 yr^-1 in the first decade to 4.6 ± 0.5 kg N ha^-1 yr^-1 in the following ones. Modelled fertilizer-induced N₂O emissions were minimal and much less than 1.6% of N inputs indicated by the IPCC EF in wet climates regardless of soil type. Temporal variations in oil palm EF were strongly linked to soil C:N ratio and mineral N content for CO₂ and fertilizer-induced N₂O emissions, and to precipitation, water table level, and soil NH₄⁺ content for peat decomposition N₂O emissions. These results suggest that current IPCC EF for oil palm on organic soil could over-estimate onsite CO₂ emissions and underestimate peat decomposition N₂O emissions and that decadal-scale temporal variation in emissions should be considered for further improvement of EF. Simulations allowed the generation of oil palm EF disaggregated by plantation age and emission source (decomposition, fertilizer-induced), a practical and useful application for GHG inventories in tropical peatlands.

In unconverted land uses, the GHG budget (Mg CO₂-equivalent ha^-1 yr^-1) was ten times higher in the secondary forest (10.2 ± 4.5) than in the primary forests (0.9 ± 3.9) on the account of a larger peat C budget and N₂O emission rate. Preliminary modelling results suggest increased peat C outputs from heterotrophic respiration and decreased C inputs from litterfall and root mortality in secondary forest compared to primary forest. Our study highlights the disastrous atmospheric impact associated with not only conversion to oil palm but also forest degradation in tropical peatlands and stresses the need to investigate GHG fluxes in disturbed undrained lands.

How to cite: Swails, E., Hergoualc'h, K., Deng, J., and Frolking, S.: How can process-based modelling improve tropical peat greenhouse gas emission factors?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5145, https://doi.org/10.5194/egusphere-egu22-5145, 2022.