BG2

In the last years, several studies were published evaluating aerosol-cloud-precipitation interactions. These studies improved the knowledge and reduced the uncertainties in the quantification of the aerosol aerosol-cloud interactions. However, there were only very few attempts to describe how clouds modify the aerosol properties. The main goal of this study is to evaluate the effect of weather events on the Particle Size Distribution (PSD) at the Amazon Tall Tower Observatory (ATTO). This research combines different types of datasets, all co-located at the ATTO towers. Basically, the data were obtained from the new generation of GOES satellites, GOES-16, the SIPAM S Band radar and two Scanning Mobility Particle Sizers (SMPS) installed at the heights of 60 and 325 m from 2017 to 2020. In addition, the LAP 3000 radar wind profile recently installed at the ATTO- Campina site was employed to evaluate the vertical distribution of the vertical velocity. The combination of these datasets allows to explore changes in PSD due to the different meteorological processes. The diurnal cycle shows an increase of nucleation particles and decrease in Aitken and accumulation modes during the night. The early morning is the time of minimum mass concentration. From the early morning to the middle of the afternoon, a contrary behaviour is observed, where the concentration of nucleation particles decreases and Aitken and accumulation mode increase, characterizing a typical particle growth process. In the late afternoon, when rain starts, PSD begin to have the night behaviour described above. Composite studies were computed to evaluate how the PSD evolve during rainfall events. The composite from lighting density shows a large increase in nucleation particles from around 100 minutes before the maximum lighting density, reaching maximum values nearly 200 minutes later. The nucleation particles growth rate increases exponentially with the thunderstorm intensity. Aitken and accumulation modes have a different behaviour, with decreasing number concentration from around 100 minutes before the maximum lighting activity and reaching the minimum concentration at the time of maximum lighting activity. This effect could be related to the more intense downdraft in thunderstorms that intensify the transport of ultrafine particles from the upper atmosphere as described in recent studies using GoAmazon and ACRIDICON-CHUVA data. Another possibility could be the transport of O₃ and NO₂ column densities during thunderstorms events, helping the oxidation of volatile organic component forming secondary organic aerosol at the surface. This is an open question and needs further studies specifically designed to understand the chemical processes occurring near-surface during intense rainfall events. The first data from the radar wind profile installed at the ATTO-Campina site was employed to compute the vertical distribution of the vertical velocity. The downdrafts are mainly located below 10km, but the layer of maximum concentration of ultrafine particles is mainly above 10km. In addition, the number concentration of nucleation particles at 60m is around twice the value at 325 m, in contrast to former studies showing an increase in ultrafine particles with height. CAFE-Brazil, scheduled for 2022, will be an opportunity to study these open questions.

How to cite: T. Machado, L. A., Pöhlker, M., Artaxo, P., Cecchini, M., Ditas, F., M. Franco, M. A., Kremper, L., Andreae, M. O., Saraiva, I., Pöschl, U., and Pöhlker, C.: How Weather Events Modify Amazonian Surface Aerosol Particle Size Distributions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11283, https://doi.org/10.5194/egusphere-egu21-11283, 2021.

The vegetated canopy plays a key role in regulating the surface fluxes and, therefore, the global energy, water and carbon cycles. In particular, vulnerable ecosystems like the Amazonia basin can be very sensitive to changes in vegetation that exert subsequent shifts in the partition of the energy, water and carbon in and above the canopy. Despite this relevance, most 3D atmospheric models represent the vegetated canopy as a flat 2D layer with, at most, a rough imitation of its effect in the atmospheric boundary layer through a modified roughness length. Thus, the representations often describe quite crudely the surface fluxes. In this work, particular emphasis is placed in the biophysical processes that take place within the canopy and its impact above. Our approach is to represent the coupling of the flow between the canopy and the atmosphere including the following processes: radiative transfer, photosynthesis, soil evaporation and CO2 respiration, combined with the mostly explicit atmospheric turbulence within and above the canopy. To this end, we implemented in LES a detailed multi-layer canopy model that solves the leaf energy balance for sunlit and shaded leaves independently, regulating the exchange of heat, moisture and carbon between the leaves and the air around. This allows us to connect the mechanistically represented processes occurring at the leaf level and strongly regulated by the transfer of diffuse and direct radiation within the canopy to the turbulent mixing explicitly resolved at the meter scale.

We test and validate this combined photosynthesis-turbulence-canopy model by simulating a representative clear day transitioning to shallow cumulus. We based our evaluation on observations by the GoAmazon2014/5 campaign in Brazil in 2014. More specifically, we systematically validate the in-canopy radiation profiles; sources, sinks and turbulent fluxes of moisture, heat and CO2, and main state variables within the canopy, and also study the effects of these in the air above. Preliminary results show an encouraging satisfactory match to the observed evolution of the profiles. As a first exploration and demonstration of the capabilities of the model, we test the effects of a coarser in-canopy resolution, a different radiation scheme and the use of a more simple 2D canopy representation.

How to cite: Pedruzo-Bagazgoitia, X., Moene, A. F., Ouwersloot, H., Gerken, T., Machado, L. A. T., Martin, S. T., Patton, E. G., Sörgel, M., Stoy, P. C., Yamasoe, M. A., and Vilà-Guerau de Arellano, J.: Understanding in and above canopy-atmosphere interactions by combining large-eddy simulations with a comprehensive observational set, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12869, https://doi.org/10.5194/egusphere-egu21-12869, 2021.

How to cite: van Asperen, H., Warneke, T., C De Araújo, A., Forsberg, B., Ramos de Oliveira, L., de Lima Xavier, T., Sá, M., Teixeira, P., Azevedo de Oliveira, R., Leal, L., Moura, V., Rafael Alves-Oliveira, J., Botia, S., Lavrič, J., Komiya, S., Frumau, A., Hensen, A., van Dinther, D., van den Bulk, P., and Notholt, J.: Tropical forest CH4: from termite mounds to tower  measurements, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13468, https://doi.org/10.5194/egusphere-egu21-13468, 2021.

Mauritia flexuosa palm swamp, the prevailing Peruvian Amazon peatland ecosystem, is

extensively threatened by degradation. The unsustainable practice of cutting whole

palms for fruit extraction modifies forest's structure and composition and eventually

alters peat-derived greenhouse gas (GHG) emissions. We evaluated the spatio-temporal

variability of soil N₂O and CH₄ fluxes and environmental controls along a palm swamp

degradation gradient formed by one undegraded site (Intact), one moderately degraded

site (mDeg) and one heavily degraded site (hDeg). Microscale variability differentiated

hummocks supporting live or cut palms from surrounding hollows. Macroscale analysis

considered structural changes in vegetation and soil microtopography as impacted

by degradation. Variables were monitored monthly over 3 years to evaluate intra- and

inter-annual variability. Degradation induced microscale changes in N₂O and CH₄ emission

trends and controls. Site-scale average annual CH₄ emissions were similar along the

degradation gradient (225.6 ± 50.7, 160.5 ± 65.9 and 169.4 ± 20.7 kg C ha⁻¹ year⁻¹ at

the Intact, mDeg and hDeg sites, respectively). Site-scale average annual N₂O emissions

(kg N ha⁻¹ year⁻¹) were lower at the mDeg site (0.5 ± 0.1) than at the Intact (1.3 ± 0.6) and

hDeg sites (1.1 ± 0.4), but the difference seemed linked to heterogeneous fluctuations

in soil water-filled pore space (WFPS) along the forest complex rather than to degradation.

Monthly and annual emissions were mainly controlled by variations in WFPS, water

table level (WT) and net nitrification for N₂O; WT, air temperature and net nitrification

for CH₄. Site-scale N₂O emissions remained steady over years, whereas CH₄ emissions

rose exponentially with increased precipitation. While the minor impact of degradation

on palm swamp peatland N₂O and CH₄ fluxes should be tested elsewhere, the evidenced

large and variable CH₄ emissions and significant N₂O emissions call for improved modeling

of GHG dynamics in tropical peatlands to test their response to climate changes.

How to cite: Hergoualc’h, K., Dezzeo, N., Verchot, L., Martius, C., van Lent, J., Del Aguila Pasquel, J., and Lopez, M.: Spatial and temporal variability of soil N2O and CH4 fluxes along a degradation gradient in a palm swamp peat forest in the Peruvian Amazon, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-831, https://doi.org/10.5194/egusphere-egu21-831, 2021.

During extreme drought events, aboveground biomass (AGB) dynamics in Amazonian forests are altered through reduced productivity and increased tree mortality and carbon loss. Tree adaptations developed in response to historical drought may reduce the severity of carbon loss. Past droughts were likely associated with fire, which produced Pyrogenic Carbon (PyC), a form of carbon formed by the incomplete combustion of biomass burn and fossil fuel. PyC has specific properties that improve soil fertility and water holding capacity and decrease aluminium toxicity, among others. PyC can be found in different concentrations across the Amazon Basin, since it can be produced by local fires and aerosol deposition. It is unknown whether PyC could explain tree adaptations or contributes to Amazon forest dynamics, especially for extreme drought events. We hypothesize that PyC in soil can serve as a proxy of fire history and fire/drought adaptations and also support the forest during drought events because of its properties, decreasing mortality rates and maintaining rates of AGB gain equivalent to a non-extreme drought year. To evaluate this hypothesis, we used a dataset with more than 70 plots with repeat censuses distributed across the Amazon Basin and classified extreme drought events using maximum cumulative water deficit (MCWD) analysis. Soil samples were collected from the same plots during an intensive fieldwork campaign and PyC was quantified by hydrogen pyrolysis (HyPy). Forest plots were classified into high and low PyC based on the median across the whole dataset. Our preliminary results show that during extreme drought events, plots that have a greater concentration of PyC had significantly higher rates of AGB gain when compared with plots with lower concentrations of PyC (t-test, p < 0.05). During non-extreme drought years there was no significant difference in rates of AGB gain between plots with different concentrations of PyC. When we focus on plots with lower concentrations of PyC there is a significant decrease in rates of AGB gain during drought years compared to non-extreme drought years (t-test, p < 0.05). However, in plots with high concentrations of PyC there is no significant difference in rates of AGB gain, showing trees are able to maintain normal forest dynamics during extreme drought years. We conclude that PyC has an important role in mediating drought resistance and productivity in Amazonian forests.

How to cite: Vedovato, L., Carvalho, L., Aragão, L., and Feldpausch, T.: Pyrogenic carbon and forest dynamics during drought in Amazonian forests, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13194, https://doi.org/10.5194/egusphere-egu21-13194, 2021.

Overall, global forests are expected to contribute about a quarter of pledged mitigation under the Paris Agreement, by limiting deforestation and by encouraging forest regrowth.

Secondary Forests in the Neo-tropics have a large climate mitigation potential, given their ability to sequester carbon up to 20 times faster than old-growth forests. However, this rate does not account for the spatial patterns in secondary forest regrowth influenced by regional and local-scale environmental and anthropogenic disturbance drivers.

Secondary Forests in the Brazilian Amazon are expected to play a key role in achieving the goals of the Paris Agreement, however, the Amazon is a large and geographically complex region such that regrowth rates are not uniform across the biome.

To understand the impact of key drivers we used a multi-satellite data approach with the aim of understanding the spatial variations in secondary forest regrowth in the Brazilian Amazon. We mapped secondary forest area and age using a land-use-land-cover dataset – MapBiomas – and, combined with the European Space Agency Aboveground Carbon dataset, constructed regional regrowth curves for the year 2017.

We found large variations in the regrowth rates across the Brazilian Amazon due to large-scale environmental drivers such as rainfall and shortwave-radiation. Regrowth rates are similar to previous pan-Amazonian estimates in the North-West (3 ±1.0 MgC ha^-1 yr^-1), which are double than those in the North-East Amazon (1.3 ±0.3 MgC ha^-1 yr^-1). The impact of anthropogenic disturbances, namely fire and repeated deforestation prior to the most recent regrowth only reduces the regrowth by 20% in the North-West (2.4 ±0.8 MgC ha^-1 yr^-1) compared to 55% in the North-East (0.8 ±0.8 MgC ha^-1 yr^-1). Overall, secondary forest carbon stock of 294 TgC in the year 2017, could have been 8% higher with avoided fires and repeat deforestation. We found that the 2017 area of secondary forest, which occupies only ~4% of the Brazilian Amazon biome, can contribute significantly (~5.5%) to Brazil’s net emissions reduction targets, accumulating ~19.0 TgC yr^-1until 2030 if the current area of secondary forest is maintained (13.8 Mha). However,this value reduces rapidly to less than 1% if only secondary forests older than 20 years are preserved (2.2 Mha).

Preserving the remaining old-growth forest carbon stock and implementing legal mechanisms to protect and expand secondary forest areas are key to realising the potential of secondary forest as a nature-based climate change mitigation solution.

How to cite: Heinrich, V., Dalagnol, R., Cassol, H., Rosan, T., Torres de Almeida, C., Silva Junior, C., Campanharo, W., House, J., Sitch, S., Hales, T., Adami, M., Anderson, L., and Aragão, L.: Quantifying the spatial patterns of Secondary Forest carbon sequestration potential in the Brazilian Amazon, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7956, https://doi.org/10.5194/egusphere-egu21-7956, 2021.

Forest - savanna transition is the most widespread and perhaps more dynamic ecotone in the tropics, and extremely sensitive to climate and environmental change. Both kinds of tropical ecosystems are globally strategic and their presence and dynamics have important ecological, climatic and biogeochemical implications, even at the global scale. However, the processes and mechanisms that control this transition vary among regions and remain not fully understood. In general, this transition is influenced by multiple interactions between vegetation and environmental factors such as climate, soil properties, fire, and herbivory. However, the magnitude of these effects can vary substantially across continents, which can result in different responses to environmental change. For this reason, more regional studies are needed to describe and understand the factors and interactions that control forest - savanna transition, particularly in Northern South America, where climate alone has failed to explain this transition. Based on a combination of LiDAR and satellite-derived data, we developed a statistical analysis on the interactive effects of rainfall, soil properties, and fire on the forest - savanna transition in Northern South America, in the savanna region between Colombia and Venezuela, using tree cover as an indicator variable that differentiates forest from savanna. Specifically, we analyze the relationships of tree cover (from GEDI) with soil sand content (from SoilGrids), fire frequency (from Fire_CCI v5.1) as well as three rainfall variability components (from CHIRPS): mean dry-season rainfall, length of the dry season, and frequency of rainy days within the dry season. Our results show that tree cover increased with mean dry-season rainfall and frequency of rainy days within the dry season, whereas it decreased with increased fire frequency. In particular, mean dry-season rainfall followed by fire frequency are the most important predictors of tree cover gradient in the transition. Importantly, our results also suggest that areas with high annual rainfall (2000 to 2800 mm) have low tree cover (i.e. savanna) if the local rainfall climatology consists of infrequent (< 0.35) and low total rainfall (< 650 mm) in the dry season. This highlights the role of water availability and fire disturbance in determining the limits between forest and the second largest area of savanna in South America. Further, our results support that future projections for forest - savanna transition should include not only changes in mean annual rainfall but also changes in rainfall variability, which is expected to be more impacted by climate change. 

How to cite: Valencia, S., Villegas, J. C., and Salazar, J. F.: Analysis of determinants of forest - savanna transition in the northern South America, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8937, https://doi.org/10.5194/egusphere-egu21-8937, 2021.

Tropospheric ozone is a greenhouse gas, and high tropospheric ozone levels can directly impact plant growth and human health. In the Congo basin, simulations predict high ozone concentrations, induced by high ozone precursor (VOC and NOx) concentrations and high solar irradiation, which trigger the chemical reactions that form ozone. Additionally, biomass burning activities are widespread on the African continent, playing a crucial role in ozone precursor production. How these potentially high ozone levels impact tropical forest primary productivity remains poorly understood, and field-based ozone monitoring is completely lacking from the Congo basin. This study intends to show preliminary results from the first full year of in situ measurements of ozone concentration in the Congo Basin (i.e., Yangambi, Democratic Republic of the Congo). We show the relationships between meteorological variables (temperature, precipitation, radiation, wind direction and speed), fire occurrence (derived from remote sensing products) and ozone concentrations at a new continuous monitoring station in the heart of the Congo Basin. First results show higher daily mean ozone levels (e.g. 43 ppb registered in January 2020) during dry season months (December-February). We identify a strong diurnal cycle, where minimum values of ozone (almost near zero) are registered during night hours, and maximum values (near 100 ppb) are registered during the daytime. We also verify that around 2.5% of the ozone measurements exceeds a toxicity level (potential for ozone to damage vegetation) of 40 ppb. In the longer term, these measurements should improve the accuracy of future model simulations in the Congo Basin and will be used to assess the impact of ozone on the tropical forest’s primary productivity.

How to cite: Vieira, I., Verbeeck, H., Meunier, F., Peaucelle, M., Lefevre, L., Cheesman, A., Sitch, S., Mbifo, J., Boeckx, P., and Bauters, M.: Meteorological and fire impacts on tropospheric ozone concentration over tropical forest in the Congo Basin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13301, https://doi.org/10.5194/egusphere-egu21-13301, 2021.

Oil palm (Elaeis guineensis) is the most important oil crop in the world, with more than 85% of the global production coming from Indonesia and Malaysia. However, knowledge of country-wide past, current and likely future greenhouse gas (GHG) footprints from palm oil production remains largely incomplete. Over the past year, first studies reporting measurements of net ecosystem carbon dioxide (CO₂) fluxes in oil palm plantations of different ages and on different soil types became available. Combining the recent CO₂ flux estimates with existing measurements on methane and nitrous oxide fluxes allows for a refined quantification of the GHG footprint of palm oil production over the whole plantation life cycle.

To derive country-wide GHG emissions from palm oil production for both Indonesia and Malaysia, we applied the refined GHG footprint estimates to oil palm area extents. Therein, we differentiated between mineral and peat soils, second- and first-generation plantations and within the latter category also among previous land-use systems from which conversion to oil palm likely occurred. For deriving the current (2020) proportions for each category, we combined FAO data with existing remotely sensed maps on oil palm extent and tree density as well as peatland and intact forest layers. These area proportions were then applied to available historic (1970 – 2010) and future (2030 – 2050) oil palm extent estimates as a business-as-usual scenario (BAU), complemented by alternative scenarios. GHG footprint estimates comprise all GHG emissions from palm oil production, i.e. from land-use change, cultivation, milling and use.

Our refined approach estimates the 2020 GHG emissions from palm oil production at 1011 Tg CO₂-eq. yr^-1 for Indonesia and at 261 Tg CO₂-eq. yr^-1 for Malaysia. Our results show that while plantations on peatland only represented 17% and 15% of the total plantation area in 2020 for Indonesia and Malaysia, they accounted for 73% and 72% of the total GHG emissions from palm oil production. Emissions in 1980 and 2000 were estimated to be only 1% and 14% of the 2020 palm oil emissions for Indonesia, but already 24% and 96% for Malaysia due to the earlier oil palm expansion. Projected emissions for 2050, assuming further oil palm expansion on suitable land and constant yields from 2020 on, represent 64% of the 2020 value for Indonesia and 97% for Malaysia under a BAU expansion scenario. These lower or constant GHG emissions for future scenarios despite assumed increases in cultivated area are the consequence of lower GHG emissions in second and subsequent rotation cycles. For both countries, the 2050 BAU emissions could be reduced by more than 50% by halting all conversion of peatlands and forests to oil palm from 2020 on, and by more than 75% when additionally restoring all peatlands currently under oil palm to forest until 2050. Closing yield gaps could potentially lead to further emissions savings.   

How to cite: Meijide, A., de la Rúa, C., Ehbrecht, M., and Röll, A.: Refined past, current and future greenhouse gas footprints of palm oil production, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15996, https://doi.org/10.5194/egusphere-egu21-15996, 2021.

The impact of soil age on geochemical properties and carbon cycling has been studied via chronosequences. However, only few studies have addressed how land-use and soil age might interactively shape properties of Andosols and in turn their capability to retain organic carbon (OC). Geochemical soil analyses and laboratory incubation experiments were carried out to assess soil characteristics and mineralization of soil organic carbon (SOC) in Indonesian soils with two contrasting land uses, viz. pine forest and horticulture. Both of these land uses are the results of conversion of primary forest which had similar parent materials, soil age, as well as weathering intensity. Results showed that intensive agricultural practices (+ 40-50 years) did not result in a significant loss of SOC or the increase of bulk density compared to forest. On the other hand, they were found to increase pH, exchangeable cations, base saturation, and most strikingly non-crystalline materials (i.e. Al_o + ½ Fe_o) leading to phenotype formation in agricultural soils. Positive correlations were found between non-crystalline materials with properties such as soil specific surface area and micropores volume, and it was also positively correlated with SOC, particularly in the subsoil. This study highlighted the resilience of Andosols to soil degradation under agricultural practices and its ability to stabilize SOC.

How to cite: Anindita, S., Sleutel, S., and Finke, P.: Agriculture effects on geochemical soil properties and stability of soil organic carbon on tropical Andosols, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11776, https://doi.org/10.5194/egusphere-egu21-11776, 2021.

The Philippines is one of the world’s leading producers of pineapples, wherein production is comprised mostly of small family farms that are less than 2 hectares in size. As by-product, they generate a large amount of plant residues (e.g., crowns and stems) that are commonly left at the edge of the field. This practice releases substantial amount of greenhouse gas (GHG) emissions and neglects the potential value of pineapple residue. Enabling a waste treatment by returning them to the field through incorporation or mulching holds the potential to maintain soil fertility, reduce climate impact, secure yield stability, and achieving a high resource efficiency by closing material cycles locally. It may also increase soil organic carbon stock (SOC) and reduce greenhouse gas (GHG) emissions. To date, however, the knowledge about this is still very sparse.

The rePRISING project aims to demonstrate that returning pineapple residue either through mulching or incorporation to the field may help promote the closing of nutrient-cycles (C/N/P/K) locally, thus helping to increase soil fertility and soil C sequestration, while reducing GHG emissions. Within the project, the recycling of pineapple residue together with various local organic and inorganic amendments will be studied during a two-year field experiment using the manual closed chamber method. The field study will be supplemented by pot-scale greenhouse and incubation experiments, used inter alia to determine baseline GHG emissions and carbon budgets of pineapple cultivation systems and residue treatments.

Here we present first results of a pot experiment performed during winter 2020-2021 used to develop a suitable procedure for the in-situ determination of dynamic net ecosystem C balances (NECB) for pineapple cultivation systems. This will be further utilized for upcoming field study. This is challenging in so far as pineapple plants use the Crassulacean acid metabolism (CAM photosynthesis) and the manual closed chamber method has not yet been applied to determine NECB from CAM plants.

Keywords: nutrient-cycling, carbon sequestration, greenhouse gas (GHG) emissions, pineapple residue, climate change mitigation

How to cite: Macagga, R., Vaidya, S., Antonijevic, D., Schmidt, M., Lueck, M., Jancsó, M., Augustin, J., Sanchez, P., and Hoffmann, M.: Reuse of Pineapple Residue in Philippine Agriculture: determination of the net ecosystem C balance for a CAM plant in a pot-scale experiment, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8240, https://doi.org/10.5194/egusphere-egu21-8240, 2021.

The carbon fluxes in rivers plays a critical role in the global carbon cycle but its role is always understated. The tropical rivers alone accounts for about 70% of global riverine carbon fluxes due to their large areal extent, varying climatic conditions and land use. Studies on the dissolved carbon fluxes in non-perennial tropical rivers are limited, but it holds much importance as that of perennial rivers. Hence, the present study was carried out with an objective to understand about the inorganic and organic carbon fluxes in a large non-perennial tropical river of Southern India. The samples were collected from 28 locations along the river thrice in a year from 2013-2020 and were analysed for major ions, DIC and DOC. The concentration of DIC in the river water in most of the locations is greater than that of DOC. The DOC concentration is greater at pristine locations thereby decreasing along the flow direction of the river, whereas the DIC concentration increases along the flow direction. The spatial and temporal variability in DOC and DIC concentrations is attributed due to the changes in the rainfall, river flow, climate, lithology, land use patterns, in the catchment. The DIC concentration was found to be majorly governed by silicate and carbonate weathering along with biogenic process, mineralisation and other river process, whereas the primary production, microbial process along with soil organic carbon influences the DOC concentration in the rivers. Thus, this study identifies the sources of DIC and DOC in rivers and the processes which influences the carbon export to the sea.

How to cite: Ramesh, R. and Lakshmanan, E.: Assessment of the dissolved inorganic and organic carbon flux in Cauvery, a tropical river of Southern India., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16162, https://doi.org/10.5194/egusphere-egu21-16162, 2021.

To mitigate global warming, a noticeable research effort is being devoted to NCS (Natural Climate Solutions) as means to reduce greenhouse gas emissions or sequester carbon within the oceans or terrestrial environments by exploiting natural processes. Enhanced weathering is a NCS that aims to increase the weathering reaction rates of silicate minerals, by amending soils with crushed reactive minerals. Various studies have shown that this technique is favored by hot and humid climates (i.e., tropical ecosystems), since weathering reactions are mostly effective under high temperature and soil moisture. Despite olivine dissolution dynamics in laboratory conditions are quite well known, understanding and modeling them in field is still a challenge. Indeed, apart from some pot experiments involving soils of agricultural fields, only few weathering models are available. Given the urgency of the problem, models play a very important role for extrapolating results of laboratory and field experiments in both time and space, as well as for quantifying the impact of hydroclimatic fluctuations on the involved biogeochemical processes.

The present study explores the role of hydrological processes on long-term Forsterite dissolution, a highly reactive silicate mineral also known as Mg-olivine or simply olivine. Toward this goal, we present a novel dynamic mass balance model coupling ecohydrological and biogeochemical dynamics, including mineral dissolution. Results under different climate scenarios highlight that hydrological fluctuations lead to hysteretic patterns of weathering rate with soil moisture, meaning that the process maintains a memory of past events (i.e., dry or wet periods). The model allows to explore the twofold role of organic matter on enhanced weathering; indeed, while its decomposition is a source of CO₂, organic matter also increases the soil CEC, thus buffering changes in soil pH. Carbon sequestration and nutrients availability due to enhanced weathering are quantified, in this study, as a function of MAP (Mean Annual Precipitation). Average CO₂ that reacts with olivine can exceed 40 t ha^-1 y^-1 for MAP higher than 2000 mm, condition that is always reached in the tropics. This CO₂ can be found as dissolved in soil water in the form of bicarbonate (HCO₃^-) and carbonate (CO₃^2-) ions and will be leached away from the domain, eventually reaching the ocean. In presence of tropical climate olivine application also leads to an increase of soil pH and nutrients availability, especially calcium and magnesium, which in turn can enhance plant productivity. This study paves the way for a potential integration of enhanced weathering in agroecosystem management practices, especially in humid tropical regions since these are characterized by high MAP and temperature.

How to cite: Cipolla, G., Calabrese, S., Noto, L. V., and Porporato, A.: The role of hydrological processes on enhanced weathering for carbon sequestration in soils in tropical areas, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4075, https://doi.org/10.5194/egusphere-egu21-4075, 2021.