Displays

In mountainous landscapes, rates of soil morphological and biogeochemical change during secondary forest succession (SFS) can vary widely with elevation due to gradients in water, energy, and mineral weathering status. Improved understanding of how elevation mediates the response of soils to SFS is critical not only for reducing the uncertainty of soil maps in complex terrain, but also for predicting the edaphic effects of SFS under future climatic conditions. Focusing on volcanic ash soils in Veracruz, Mexico, we sought to 1) quantify how elevation mediates the dynamics of soil organic carbon (SOC) and geochemistry during SFS and 2) disentangle the soil-forming processes responsible for altitudinal trends. We characterized 16 soil profiles (0-100 cm depth) at various stages of SFS after pasture abandonment at the lower and upper altitudinal limits of the cloud forest ecosystem (1350-1550 and 2050-2220 m) using a broad suite of analytical techniques. Elevation strongly affected the depth distributions of all measured inorganic elements and enhanced the rate of accumulation of biocycled elements (e.g., P, K, Ca, S, Mn) during SFS. Notwithstanding altitudinal differences in C inputs (namely, forest floor recovery rates), profile-level SOC composition and dynamics were more sensitive to mineral weathering status than to SFS stage or elevation per se. Differentiation of soil mineralogy and SOC dynamics contributed to variation of physical properties, consistent with local ‘folk’ soil taxonomy. Ongoing work addresses the interplay of climate, geology, and redistribution processes in determining the mineralogical properties and, ultimately, SOC dynamics of volcanic ash soils. Our findings underscore the importance of considering the complex environmental contingency of soil recovery rates during SFS.

How to cite: Looker, N., Margenot, A., McFarlane, K., Nater, E., Plante, A., and Kolka, R.: The chronosequence in context: Elevation-dependent dynamics of soil biogeochemistry during cloud forest succession, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12354, https://doi.org/10.5194/egusphere-egu2020-12354, 2020.

The content of organic carbon in forest is partitioned between organic carbon accumulated in aboveground biomass (AGB) and belowground biomass (BGB) and is impacted by various natural and human factors. Growing interest in estimates of global biomass (and organic carbon) pools require research on a local scale in the context of potential environmental factors affecting their spatial distribution. Therefore, our aim of the research was to both derive and evaluate the relationship between aboveground biomass consisting mainly of European beech (Fagus sylvatica L.), spruce (Picea abies L. Karst) and fir (Abies alba Mill.) and BGB with particular emphasis on fine root biomass (FRB) as the most dynamic part of the root system and soil organic matter stock (SOM). Data were collected at 32 national forest inventory plots in mountainous temperate forests with different history of forest management located across the Carpathian range in Poland. All study plots were characterized with very similar soil properties (Cambisols). Moreover, numerous environmental factors affecting biomass distribution were taken under consideration. The largest aboveground biomass occurred in beech-dominated stands (~40 Mg ha^-1 to over ~ 440 Mg ha^-1). In the sampled depth layer (0-40 cm) the highest SOM stock was identified in soils under beech-dominated stands (median ~158 Mg ha-1). FRB was the highest under fir-dominated stands (median ~3.7 Mg ha-1). The amount of SOM and FRB differed also in the analyzed soil depth layers (10 cm interval up to 40 cm) reaching mostly the highest values at soil depths of 0-10 cm. The highest amount of biomass (both aboveground and the belowground) has been identified in beech-dominated forests. We examined relationships between AGB, FRB, and SOM, but were not able to identify clear significant correlations based only on vegetation parameters. Derived results illustrate the complexity of identifying significant relationships between aboveground and belowground biomass stocks. Employing the same models may be an erroneous strategy for different study sites because of local environmental factors that strongly determine aboveground and belowground biomass stock. Accordingly, creating biomass and carbon models at larger scales in northern Carpathians based on forest aboveground data may cause an over- or underestimation due to the significant impact of both abiotic and biotic factors. 

This research study was funded by the Polish National Science Centre (RS4FOR Project: Forest change detection and monitoring using passive and active remote sensing data (No. 2015/19/B/ST10/02127) and via Project No. UJ/IGiGP/K/DSC/004779.

How to cite: Zielonka, A., Drewnik, M., Musielok, Ł., Struzik, D., Smułek, G., and Ostapowicz, K.: Relationships between aboveground and belowground biomass stock – a case study from mountain area temperate forests in the northern Carpathians, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20675, https://doi.org/10.5194/egusphere-egu2020-20675, 2020.

Soils are heterogeneous at all scales and so are the biogeochemical reactions driving the cycling of carbon (C) and nutrients in soils. While the microbial processes involved in these reactions occur at the pore scale, what we observe at the soil core or pedon scale depends on how micro-scale processes are integrated in space (and time). This integration step requires accounting for the inherent patchiness of soils, but models used to describe element cycling in soils typically assume that conditions are well-mixed and that kinetics laws developed for laboratory conditions hold. Similarly, the response functions used in models to capture the effects of environmental conditions on C and nutrient fluxes neglect the contribution of spatial heterogeneities, which might alter their shape. There is therefore a need to re-evaluate model structures to test whether they can account for micro-scale heterogeneities. Alternatively, one can ask why some models are clearly successful in capturing observations despite neglecting soil heterogeneities. In this contribution, we present examples of how soil heterogeneities – in particular the spatial placement of soil microorganisms and their substrate – may affect decomposition kinetics and microbial responses to soil drying. We show that the kinetics laws used in current models are different from the kinetics obtained by integrating microbial dynamics at the micro-scale, and that respiration responses to soil drying may vary depending on soil heterogeneity. These results thus highlight structural uncertainties in current models that we propose can be assessed using existing ‘scale-aware’ methods to derive macro-scale model formulations. Model advances will need to be supported by empirical evidence bridging the gap between pore and core (or larger) scales, but can also provide new theory-based hypotheses for novel experiments.

How to cite: Manzoni, S., Chakrawal, A., and Nunan, N.: Scaling up microbial dynamics for soil carbon cycling models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3739, https://doi.org/10.5194/egusphere-egu2020-3739, 2020.

In a warmer climate, regional and global climate models have projected Australia to experience an increase in the intensification of rainfall extremes, which range from heavy monsoon rains to long droughts. Here, we use a coupled carbon and nitrogen cycles mechanistic model (BAMS2) to investigate how the projected rainfall patterns affect carbon and nitrogen emissions, as well as the soil organic stocks in Australian grasslands located in different climatic regions.

                     The BAMS2 model (Tang et al., 2019) considers the depolymerization and mineralization of 11 soil organic matter (SOM) pools (i.e., lignin, cellulose, hemicellulose, peptidoglycans, monosaccharides, amino acids, amino sugars, organic acids, lipids, nucleotides, and phenols) and the transformation of inorganic nitrogen through fixation, nitrification, and denitrification. We explicitly model the growth, mortality, necromass decomposition, and water stress response of five microbial functional groups that mediate the carbon and nitrogen cycles. We include a simplified plant dynamics model to describe plant nutrient uptake, SOM inputs through root exudations and aboveground litter, and plant response to water stress. The BAMS2 reaction network is solved using a general-purpose multi-phase and multi-component bio-reactive transport simulator (BRTSim-v3.1a). We model the water flow along a vertical soil column using the Richards equation and the Brooks-Corey model for the water saturation-tension-permeability relationships, while the transport of dissolved chemicals is modeled using Darcy’s advection velocity and Fick’s diffusion. Aqueous complexation and gas dissolution are described using the mass action law, and SOM protection to soil is modeled using Langmuir’s kinetics.

                     Our multi-decadal simulations suggest a 30% increase in annual CO­₂ emissions in tropical grasslands with a 20% decrease in annual rainfall amount, while temperate and semi-arid grasslands have opposite trends. A decreasing annual rainfall amount also results in a decrease in annual N­_­2O emissions in the semi-arid grasslands, and a decrease in soil organic stocks in all grasslands. In tropical grasslands, a 20% decrease in annual rainfall results in approximately a 10% decrease in soil organic carbon stock and less than 1% decrease in soil organic nitrogen stock. Less frequent and more intense events in the semi-arid grasslands lead to increased soil moisture at greater depths where evapotranspiration rates are lower, hence reducing water loss to atmosphere and allowing the storage of water for plant growth. Our results show that changes in rainfall regimes alter both the emissions and the total amount of SOM. This study provides a modeling framework suitable for investigating SOM dynamics under various climatic and anthropogenic forcing.

Acknowledgement: This work is supported by SREI2020 EnviroSphere program, the University of Sydney.

Reference:

Tang, F. H.M., Riley, W. J., & Maggi, F. (2019). Hourly and daily rainfall intensification causes opposing effects on C and N emissions, storage, and leaching in dry and wet grasslands. Biogeochemistry, 1-18, https://doi.org/10.1007/s10533-019-00580-7.

How to cite: Tang, F., Riley, W., and Maggi, F.: Controls of rainfall patterns on C and N emissions and stocks in Australian grasslands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11724, https://doi.org/10.5194/egusphere-egu2020-11724, 2020.

Grazed alpine pastures have shaped landscapes of the European Alps for millennia. However, especially steep alpine areas have largely been abandoned since the 1950s, resulting in a fast re-forestation of mountain pastures in the last decades, which is accelerated by climate change. Re-grazing of abandoned pastures could preserve the cultural landscape of the European Alps with its high species diversity, but there is a lack of information on the response of the soil system to re-grazing. We investigated short-term effects of re-grazing of an abandoned pasture in the German Alps on soil organic carbon and nitrogen biochemistry, soil microbial communities, and water quality. In May 2018, we set up a pilot grazing experiment at Brunnenkopfalm (1500-1700 m a.s.l.), abandoned since 1955. Four ha were fenced and a herd of rustic, local and endangered breeds (ca 1/ha) was introduced. Two and five months after the beginning of grazing, we investigated the short-term re-grazing effects, considering grazing-induced heterogeneity, as well as the distribution of vegetation types. In order to gain a functional understanding of soil responses to re-grazing, we used a wide array of techniques to characterize soil biogeochemical properties (salt-extractable and total organic carbon, gross nitrogen turnover rates, soil mineral nitrogen availability), as well as the abundance and characteristics of microbial communities (microbial biomass, phospholipid-derived fatty acids analysis, abundance of nitrogen-related microbial communities). A few months after re-grazing started, extractable organic carbon, gross nitrogen mineralisation rates and inorganic nitrogen concentrations were increased only in intensively grazing-affected areas with bare soil. Bare soils represented a small fraction of the study area (~ 1 %), and the grazing effects on these areas could at least partially also be driven by the initial site heterogeneity (soil and vegetation) rather than solely by recent grazing activities. Re-grazing did not affect the microbial abundance, but induced a community shift towards a smaller proportion of fungi compared to bacteria and an increase of ammonia oxidizers (archaea/bacteria). Concentrations of dissolved organic carbon and nitrate in the draining creek remained very low. Overall, re-grazing of pastures in the first season had very limited effects on microbial communities and associated carbon and nitrogen turnover and concentrations, highlighting the initial resilience of alpine soils to extensive re-grazing. However, a slight increase in nitrifier abundances at bare soil spots, as well as the low organic carbon:nitrogen ratios of soils suggest that a future increase in inorganic nitrogen accumulation is possible at least at bare soil areas. This could possibly endanger some biodiverse grassland biotopes via eutrophication and result in environmental nitrogen losses along hydrological or gaseous pathways. Thus, long-term studies are needed to verify whether soils are also resilient to re-grazing in the long-term. On the short-term, undesired re-grazing effects can be avoided by extensive, guided grazing with adapted cattle breeds targeted to avoid trampling-induced bare soil areas.

How to cite: Vidal, A., Schucknecht, A., Toechterle, P., Andrade Linares, D. R., Garcia-Franco, N., von Heßberg, A., Krämer, A., Sierts, A., Fischer, A., Willibald, G., Fuetterer, S., Ewald, J., Baumert, V., Weiss, M., Schulz, S., Schloter, M., Bogacki, W., Wiesmeier, M., Mueller, C. W., and Dannenmann, M.: High resilience of soils to re-grazing in a long-term abandoned alpine pasture , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-244, https://doi.org/10.5194/egusphere-egu2020-244, 2020.

Coastal landscapes and their terrestrial-aquatic interface (TAI) will be increasingly exposed to short-term tidal inundation due to sea level rise and extreme weather events. These events can generate hot moments of biogeochemical activity and also alter ecosystem structure if occuring frequently. However, such responses of these vulnerable ecosystems to environmental perturbations are poorly understood, limiting our ability to evaluate the contribution of local processes on global scale carbon and nutrient budgets. Here, we evaluated whether and to what degree seawater inundation impacts biogeochemical responses in soils collected along a naturally variable salinity gradient in a first order tidal stream floodplain in the Pacific Northwest. A laboratory incubation experiment simulating episodic inundation was performed to detect the impacts on soil carbon chemistry. We characterized carbon before and after inundation using Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FTICR-MS), metabolite signatures via Liquid Chromatography-Mass Spectrometry (LC-MS), and high-frequency carbon dioxide (CO₂) and methane (CH₄) gas fluxes from intact soil cores. Following three inundation events, we observed significant decreases in the thermodynamic favorability of the remaining organic compounds in soils with high natural salinity as compared to low salinity soils. Low salinity soils showed higher average flux compared to high salinity soils following periodic inundation events. Seawater inundation led to distinct metabolite features in low salinity soils, with surficial soil preferentially getting enriched in phenolic compounds. Biogeochemical transformations inferred from FTICR-MS data showed an increase in total transformations with increasing salinity for soil cores from naturally low salinity exposure sites, likely suggesting higher microbial activity. In conclusion, ecosystem responses in a tidal landscape frequently experiencing seawater inundation preferentially influences terrestrial soils to behave as a carbon source. This response is likely a function of historical salinity gradient-driven molecular-level organic carbon characteristics.

How to cite: Sengupta, A., Bond-Lamberty, B., Rivas-Ubach, A., Zheng, J., Handakumbura, P., Yabusaki, S., Bailey, V., Ward, N., and Stegen, J.: Linking molecular properties of soil organic carbon to emergent ecosystem functions in a tidally influenced landscape of the Pacific Northwest, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22308, https://doi.org/10.5194/egusphere-egu2020-22308, 2020.

Soil organic carbon (SOC) is a valuable resource for mediating global climate change and securing food production. Despite an alarming rate of global plant diversity loss, uncertainties concerning the effects of plant diversity on SOC remain, because plant diversity not only stimulates litter inputs via increased productivity, thus enhancing SOC, but also stimulates microbial respiration, thus reducing SOC. By analysing 1001 paired observations of plant mixtures and corresponding monocultures from 121 publications, we show that both SOC content and stock are on average 5 and 8% higher in species mixtures than in monocultures. These positive mixture effects increase over time and are more pronounced in deeper soils. Microbial biomass carbon, an indicator of SOC release and formation, also increases, but the proportion of microbial biomass carbon in SOC is lower in mixtures. Moreover, these species‐mixture effects are consistent across forest, grassland, and cropland systems and are independent of background climates. Our results indicate that converting 50% of global forests from mixtures to monocultures would release an average of 2.70 Pg C from soil annually over a period of 20 years: about 30% of global annual fossil‐fuel emissions. Our study highlights the importance of plant diversity preservation for the maintenance of soil carbon sequestration in discussions of global climate change policy.

How to cite: Chen, H.: Effects of plant diversity on soil carbon in diverse ecosystems: a global meta-analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1425, https://doi.org/10.5194/egusphere-egu2020-1425, 2020.

Soils provide us with multiple essential services, such as food production, water flow regulation, and climate regulation. The loss of soil function endangers provision of these services, in turn endangering the local, regional and global societies and economies that rely on these. Soils, therefore, are in effect a critical infrastructure, which can be defined as an asset, system or process, the loss or compromise of which could result in a major detrimental impact on the availability, integrity or delivery of essential services, with significant economic or social impacts. Conceptualising soil as a critical infrastructure changes the way we as a society need to approach its management. For example, government authorities have a responsibility to reduce the vulnerability of critical infrastructure, and strengthen their security and resilience. To meet this responsibility there is a need to assess infrastructure resilience, identify critical vulnerabilities, and identify and implement strategies for increasing resilience. There has been growing interest and research on soil resilience, particularly drawing on ecological resilience concepts. In this contribution, we will consider our current understanding of soil system resilience from a critical infrastructure perspective and discuss where further science is needed.

How to cite: Davies, J., Batista, P., Janes-Bassett, V., O'Riordan, R., Quinton, J., and Yumashev, D.: Soil systems as critical infrastructure: do we know enough about soil system resilience and vulnerability to secure our soils?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20273, https://doi.org/10.5194/egusphere-egu2020-20273, 2020.

The study of anthropogenic soils is a growing area of interest, and as cities continue to expand, urban soils are heavily influenced by human activities. Urbanisation exhibits a wide range of impacts on soil, from buried horizons, compaction, sealing with impervious surfaces, additions of anthropogenic material to being largely man-made soils, or technosols. The properties of urban soil are further complicated by the addition of fertilisers, management strategies in greenspaces and the treatments of soil, including topsoil removal, during construction projects. Therefore, the properties and functions of anthropogenic soils differ notably to that of natural soils, and as such, there is a need to understand the dynamics of soil carbon in urban areas.

Research on urban soil carbon has been relatively limited, however there is recent growth in this area due to its importance, firstly, as a carbon store contributing to climate regulation, and secondly, in relation to the potential of urban soil to support numerous ecosystem services. Urban soils are highly heterogeneous and anthropogenic carbon additions can come from many current or historical sources, such as charcoal used in old roads, coal ash from power stations, carbon from car tyres, as well as inorganic carbonates in limestone road foundations. Understanding the current stores of carbon, as well as how stable it is, is important to understand likely carbon dynamics and storage potential.

This work presents a field study across Manchester (UK) where soil carbon data has been collected from soils across urban parks, greenspaces and from under sealed surfaces (roads and pavements). It provides carbon data for a variety of urban contexts and with high spatial variability. We will build on previous work from this field study by presenting i) a typology of urban soils according to anthropogenic content, ii) data for physical size fractionation to understand soil physical properties and texture, and iii) the carbon content of the size fractions to provide a proxy for understanding how labile or stable the carbon is. This will allow us to understand the impacts of soil sealing on the carbon content and build a picture of soil carbon stability across a range of urban situations.

This research will contribute to the much-needed understanding on how soil carbon behaves in urban areas, and the implications of this for carbon storage in both sealed and urban greenspace soils. 

How to cite: ORiordan, R., Davies, J., Stevens, C., Quinton, J., and Boyko, C.: The impacts of urbanisation on urban soil carbon – a study from Manchester, UK, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11818, https://doi.org/10.5194/egusphere-egu2020-11818, 2020.

Growing global demand of water use, and regional changes in precipitation in many regions, has resulted in increasing long-term irrigation of agricultural soils with post-treatment waste water. Overlaying this trend with the rising use of pharmaceuticals has created a new pathway for these pollutants, including biologically active compounds such as antibiotics, to enter the soil environment. We present results from a new interdisciplinary study of the response of an agroecosystem which was repeatedly contaminated with a typical combination of antibiotics at a representative concentration found in waste water effluent. Results from this experimental manipulation, show the impact of different concentrations of antibiotics in the soil and the unexpected repercussions throughout the agroecosystem. This includes effects on soil microbial communities, microbial function (anti-microbial resistance), abiotic soil condition, antibiotic persistence in the soil, ecosystem function (greenhouse gas exchange) and the effect on the arable crop itself. Implications of this study are relevant to fully understanding the impact of this land management technique on the sustainability of food production.

This study was funded through the UK’s N8AgriFood Programme.

How to cite: Stockdale, J., Sallach, B., Zealand, A., McCann, C., Bey, E., Ring-Hrubesh, F., Graham, D., Boxall, A., and Toet, S.: Impact of antibiotic pollution from wastewater irrigation on soils and agroecosystems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16870, https://doi.org/10.5194/egusphere-egu2020-16870, 2020.

The representation of soil carbon dynamics is a major source of uncertainty in Earth System Models (ESMs). The terrestrial carbon pool is more than twice the size of the atmospheric pool. Therefore, the role of soil carbon as a source or a sink of atmospheric carbon, and in feedback loops is important to quantify in a changing climate. Decomposition processes of organic matter in soil have often been represented by first order decay equations, which make comparison and validation against observations difficult. Therefore, quantification of the uncertainties  and validation of improved parameterizations are problematic. An emerging approach to tackle these challenges is to represent microbial soil processes explicitly in the models. Following this approach, we have built a process based module that represent the carbon fluxes during soil decomposition, from aboveground litter to soil organic matter (SOM). The role of saprotrophs and mycorrhizal fungi is explicitly represented with separate carbon pools with associated fluxes. On a site level, we compare initial results from the stand alone module with both existing models and observations of carbon pools and fluxes. The observations are from the Norwegian Dovre Mountains, with data from three different alpine communities. These geographic areas are important, because they are subject to changes due to shrubification. In addition, these ecosystems can store large amounts of carbon. By modeling these sites, we gain more insight in the most important processes in soil decomposition, and how different microbial communities affect the carbon dynamics. We will further refine the module by expanding our study with more sites. The long-term objective is to develop an improved module that can be used to represent soil processes in ESMs, and thereby reduce the uncertainty connected to the exchange of carbon between land and atmosphere.

How to cite: Ristorp Aas, E., Koren Berntsen, T., Eiler, A., and Hellevang, H.: Modeling of soil carbon dynamics, with focus on microbial activity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6875, https://doi.org/10.5194/egusphere-egu2020-6875, 2020.

In order to understand and model soil carbon (C) dynamics it is essential that we are able to partition net ecosystem C exchange by individual organic and inorganic fluxes under field conditions. Stable isotope methods provide a reliable means to separate fluxes from two sources, such as plant respiration and soil organic matter (SOM) mineralisation. In many soils, however, plant and soil respiration are not the only sources of C efflux, as breakdown of carbonate minerals provide a third, inorganic, C source. We currently lack methods and models to allow us to untangle plant, inorganic soil, and organic soil C fluxes in the field. This limits our ability to gather field-scale plant and soil C flux data to soils without inorganic carbonates, rendering calcareous soils a major gap in our understanding of, and ability to model, soil C dynamics.

To remedy this we have developed a novel three-way partitioning model to account for inorganic carbonate dissolution in a planted soil. Analysis of a mechanistic model of lime (CaCO₃) dissolution showed differences in CO₂ pressure in the soil, arising from differences in soil respiration as influenced by differences in temperature and moisture, to be a major control on dissolution rates. The thee-way partitioning model we have developed derives the CO₂ flux from CaCO₃ dissolution from SOM mineralisation and below-ground plant respiration fluxes.

To test this model we used cavity ring-down spectroscopy to measure CO₂ fluxes from soil mesocosms containing C3-origin SOM and planted with a C4 grass, both with and without CaCO₃, and unplanted soil mesocosms containing CaCO₃. As previously field measurements revealed temperature to be the strongest control on soil respiration this was carried out at four temperatures (15, 20, 25, and 30^oC). Using the distinct δ¹³C values for CaCO₃ dissolution, C4 grass respiration, and C3 SOM mineralisation, fluxes were partitioned from mesocosms containing two C fluxes to parameterise the model. The model was tested through application to flux data from mesocosms containing C fluxes from CaCO₃, SOM, and plants in order to assess its suitability for generating novel field datasets of C fluxes from calcareous soils.

How to cite: Kirk, G., McCloskey, C., Otten, W., and Paterson, E.: A model for three-way carbon flux partitioning in calcareous soils using stable isotope measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22627, https://doi.org/10.5194/egusphere-egu2020-22627, 2020.

In the northern ecosystems’ soils, the carbon stock is preserved in peat soils which includes frozen peat. It is vulnerable to any climate changes. The permafrost degradation can affect both the quantity and the composition of dissolved organic carbon of permafrost-affected soils, especially peat soils.

The main aim of our study was to determine the relationship among peat type, water regime and the quantity and composition of water borne carbon export. The research site was located in the discontinuous permafrost zone (N65º18’, E72º52’). Monoliths of various peat soils were collected in summer 2019 for a laboratory experiment.

The experiments were carried out with 6 types of monoliths (oligotrophic fibric peat; oligotrophic hemic peat with lichen debris; eutrophic hemic peat with reindeer moss debris; eutrophic sapric peat; eutrophic sapric peat with a burnt horizon; oligotrophic fibric peat, underlied with sand). We try to understand how organic matter is leached from peat soils with different constitution and different degree of decomposition. In the model experiment, we simulated 3 types of hydrological conditions. Soil monoliths were watered, and the contents of DOC and POC were determined in the collected soil waters.

1. Simulation of the moderate rainfall (70 mm) by adding distilled water during the week. DOC in this case ranged from 44,2±3.0 mg/l in oligotrophic peat to 80,6±28,7 mg/l in eutrophic peat.
2. The simultaneous flow of large quantities of water, simulating prolonged rainfall or spring snowmelt. In this case DOC content leaching from fibric oligotrophic peat didn`t change much while DOC leaching from sapric eutrophic peat decreased in comparison with moderate rainfall.
3. During modeling short stagnant regimen (spring conditions) we observed increase DOC, especially in sapric eutrophic peat (up to 291,0±11,3 mg/l). The mineral horizon under the peat layer reduced the rate of leaching of organic substances from the soil.

Our results indicate the significant role of both the peat constitution and hydrological regime of soils on the rate and amount of organic matter entering the hydrological basin from peat permafrost-affected soils. The data can be used to simulate the dynamics of permafrost ecosystems with changing climatic parameters or with the activation of anthropogenic load.

This research was supported by the Russian Foundation for Basic Research (Grant 18-04-00952)

How to cite: Timofeeva, M., Goncharova, O., and Matyshak, G.: Hydrological conditions and peat constitution effect on DOC leaching from permafrost-affected soils: model experiment (Western Siberia, Russia), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-590, https://doi.org/10.5194/egusphere-egu2020-590, 2020.

Freshwater flux transport large amount of carbon (dissolved and particulate, organic and inorganic) from the continent into the ocean, contributing significantly to the global carbon cycle. The present sources and sinks of natural as well as anthropogenically produced C compounds in the global carbon cycle remain enigmatic. Among the carbon sources in the river ecosystem, the dissolved inorganic carbon (DIC) constitutes a major component of carbon influx from land to ocean. These fluxes are significantly influenced by the terrestrial and estuary processes. The isotopic composition of DIC can be used to understand the sources and cycling of carbon in rivers and estuaries. In this study, δ¹³C values of DIC in river water of Ganga have been used to understand the sources of dissolved inorganic carbon into the river. The river Ganga (2500 km) is the largest river of the Indian subcontinent which originates from the Gangotri glacier and drains into the Bay of Bengal through its vast delta in the Sunderban. The Ganga river basin (GRB) covers an area of 10⁶ km² draining the carbon sources of the entire basin into the mainstream of river Ganga. The river transports nearly 0.2% of the global freshwater flux, 1% of global DIC flux and 5% of the global sediment flux into the ocean. Despite its significant importance to the global carbon transport, the understanding of the DIC sources in the complex Ganga river system remains enigmatic. Therefore to elucidate the carbon sources in the river Ganga, the δ¹³C DIC of river water were measured from source (Gomukh) to sink (Bay of Bengal) of the river Ganga for pre and late-monsoon period. The seasonal variation in the δ¹³C DIC shows enriched isotopic values in pre-monsoon compared to late-monsoon samples. The upper, middle and lower stretch of the river shows distinct enrichment factors for pre and late-monsoon samples. The variation in the δ¹³C DIC of river water might be indicating the DIC signature of the source water. The pre-monsoon samples show enrichment in the δ¹³C DIC values as we move downstream of the river, whereas the late-monsoon samples show a slight depletion trend. The difference between the pre and late- monsoon samples might be indicating the high input of soil CO₂ during the late-monsoon season which is characterized by lower δ¹³C values.

How to cite: Kumar, A. and Sanyal, P.: Decrypting the sources of dissolved inorganic carbon in river water: Isotopic study from river Ganga, India, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-724, https://doi.org/10.5194/egusphere-egu2020-724, 2020.

Studying the effects of droughts and heavy rain events on DOC in Scot pine in Belgium

Cristina Ariza-Carricondo(1,2), Marilyn Roland(1), Bert Gielen(1), Eric Struyf(1), Caroline Vincke(2) and Ivan Janssens(1).

(1) PLECO, University of Antwerp, Belgium. (2) Faculty of Bioscience Engineering & Earth and Life Institute, University of Louvain-la-Neuve, Louvain-la-Neuve, Belgium.

Climate extremes, including extreme rain events, are becoming more frequent and more extreme, and affect the carbon cycle of ecosystems. Very little is known about how Dissolved Organic Carbon (DOC) production and leaching are affected by such precipitation extremes while the relation between dissolved and gaseous exports of carbon under different precipitation regimes remains unexplored.

Hydrological conditions are the main driver of DOC leaching and alterations in precipitation patterns may cause large changes in the carbon balance of forests. To test the effects of precipitation extremes on DOC, we designed a manipulation experiment in a Scots pine forest in Belgium.

One of the challenges to estimate DOC export is the quantification of water drainage flow. In this study we used self-designed Zero Tension Lysimeters (ZTL) to capture leaching water and analyze its DOC-concentrations as well as other elements along profiles in the soil (up to 75cm depth), to study how DOC moves under different precipitation regimes. Different manipulation experiments were performed where we modified the precipitation regime simulating heavy rain events after different droughts as well as experiments where we modified the precipitation intensity over time. Leached water was collected at different depths at monthly intervals after natural rain events as well as after irrigations.

Preliminary results showed that drainage water transported DOC differently through the soil when different amounts of water were added. Furthermore, more frequent small rain events appear to favor the production of DOC as compared to less frequent high intensity rain events, while DOC production ceases during droughts.

How to cite: Ariza Carricondo, C.: Studying the effects of droughts and heavy rain events on DOC in Scot pine in Belgium, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5329, https://doi.org/10.5194/egusphere-egu2020-5329, 2020.

As climate change will cause a more pronounced rise of air temperature in northern high latitudes than in other parts of the world, it is expected that the strength of the boreal forest carbon sink will be altered. To better understand and quantify these changes, we studied the influence of different environmental controls (e.g., air and soil temperatures, soil water content, photosynthetically active radiation, normalized difference vegetation index) on the timing of the start and end of the boreal forest growing season and the net carbon uptake period in Canada. The influence of these factors on the growing season carbon exchanges between the atmosphere and the boreal forest were also evaluated. There is a need to improve the understanding of the role of the length of the growing season and the net carbon uptake period on the strength of the boreal forest carbon sink, as an extension of these periods might not necessarily result in a stronger carbon sink if other environmental factors are not optimal for carbon sequestration or enhance respiration.

Here, we used 31 site-years of observation over three Canadian boreal forest stands: Eastern, Northern and Southern Old Black Spruce in Québec, Manitoba and Saskatchewan, respectively. Redundancy analyses were used to highlight the environmental controls that correlate the most with the annual net ecosystem productivity and the start and end of the growing season and the net carbon uptake period. Preliminary results show that the timing at which the air temperature becomes positive correlates the most strongly with the start of the net carbon uptake period (r = 0.70, p < 0.001) and the start of the growing season (r = 0.55, p < 0.01). Although the increase of the normalized difference vegetation index also correlates with the start of these periods, a thorough examination of this result shows that the latter happens well before the former. No dependency between any environmental control and the end of the net carbon uptake period was identified. Also, the annual net ecosystem productivity is highly correlated with the length of the net carbon uptake period (r = 0.54, p < 0.01). Other environmental controls such as annual precipitations, the mean annual soil temperature or the maximum yearly normalized difference vegetation index have a smaller impact on the annual net ecosystem productivity. By extending the dataset to include forest stands that represent a wider climate and permafrost variability, we will examine the generalizability of these results.

How to cite: El-Amine, M., Roy, A., Legendre, P., and Sonnentag, O.: The relative importance of environmental factors on the interannual variability of carbon fluxes in the boreal forest, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12470, https://doi.org/10.5194/egusphere-egu2020-12470, 2020.

We investigate the edaphic, mineralogical and climatic controls of soil organic carbon (SOC) concentration utilising data from 147 primary forest soils (0-30 cm depth) sampled in eight different countries across the Amazon Basin. Sampling across 14 different World Reference Base soil groups our data suggest that stabilisation mechanism varies with pedogenetic level. Specifically, although SOC concentrations in Ferralsols and Acrisols were best explained by simple variations in clay content – this presumably being due to their relatively uniform kaolinitic mineralogy – this was not the case for less weathered soils such as Alisols, Cambisols and Plinthosols for which interactions between Al species, soil pH and litter quality are argued to be much more important. Although for more strongly weathered soils the majority of SOC is located within the aggregate fraction, for the less weathered soils most of the SOC is located within the silt and clay fractions. It thus seems that for highly weathered soils SOC storage is mostly influenced by surface area variations arising from clay content, with physical protection inside aggregates rendering an additional level of protection against decomposition. On the other hand, most of SOC in less weathered soils are associated with the precipitation of aluminium-carbon complexes within the fine soil fraction, with this mechanism enhanced by the presence of high levels of aromatic, carboxyl-rich organic matter compounds. Also examined as part of this study were a relatively small number of arenic soils (viz. Arenosols and Podzols) for which there was a small but significant influence of clay and silt content variations on SOM storage and with fractionation studies showing that particulate organic matter may accounting for up to 0.60 of arenic soil SOC. In contrast to what were in all cases strong influences of soil and/or litter quality properties, after accounting for these effects neither wood productivity, above ground biomass nor precipitation/temperature variations were found to exert any significant influence on SOC stocks. These results have important implications for our understanding of how Amazon forest soils are likely to respond to ongoing and future climate changes.

How to cite: Quesada, C. A., Paz, C., Oblitas, E., Phillips, O., Saiz, G., and Lloyd, J.: Variations in soil chemical and physical properties explain basin-wide Amazon forest soil carbon concentrations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6099, https://doi.org/10.5194/egusphere-egu2020-6099, 2020.

The main aim of this global review and systematic analysis was to investigate the impacts of previous land use system, climate zone and forest type and age on soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP), in the different soil layers (0-20, 20-60 and 60-100 cm), following afforestation. We collected 85 publications on SOC, TN and TP stock changes, covering different countries and climate zones. The data were classified into groups depending on these investigated parameters and analyzed using R version 3.6.1. We found that afforestation significantly increased SOC and TN stocks in the 0-20 and 20-60 soil layers, with values of 45% and 44% for SOC, 30% and 22% for TN, respectively, but had no impact on TP stock. Previous land use systems had the largest influence on SOC, TN and TP stocks, with greater accumulations on barren land compared to cropland and grassland. Climate zone influenced SOC, TN and TP stocks, with significant accumulations in the moist than in the dry climate zone. Afforestation with broadleaf deciduous and broadleaf evergreen forests led to greater SOC, TN and TP accumulations in each soil layer throughout the investigated profile (0-100 cm), compared to coniferous forests. Afforestation for <20 years had significantly increased SOC and TN stocks only at the soil surface (0-20 cm) whilst afforestation for ≥ 20 years had significantly accumulated them up to 100 cm soil depth. TP stock did not change with the forest age, suggesting that it may become a limiting factor for carbon sequestration under the older-age forest. Following afforestation, the change of soil bulk density had inverse relationships with SOC or TN stocks changes but had no effect on TP stock change.

How to cite: Guo, Y., Abdalla, M., Espenberg, M., Hastings, A., Hallett, P., and Smith, P.: A review of the impacts of land use change, climate zone, forest type and age on soil organic carbon and other soil quality indicators following afforestation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7370, https://doi.org/10.5194/egusphere-egu2020-7370, 2020.

The redistribution of soil by humans has been demonstrated to rival that of geologic events. Moreover, the impact of some conventional, agricultural techniques has been shown to redistribute a significant proportion of soil organic carbon. On the more erosive areas of hillslopes, the resulting thinning of soil could make deep soil carbon more accessible and, ultimately, more susceptible to destabilisation. However, downslope colluviation can thicken soil profiles such that subsoil carbon pools become inaccessible to microbial decomposition. The fate of soil thinning and thickening on soil organic carbon has not been studied in the UK until now. In this work, we studied the distribution of organic and inorganic carbon down profiles surveyed at three landscape positions (midslope, backslope, and toeslope) on Mountfield Farm, in Somerset, UK. In this poster, we present the results of thermogravimetric analysis and laser-induced fluorescence spectroscopy, both of which we used to investigate the stability of soil organic carbon down each profile. We explore the relationships between soil depth and the stocks and stability of soil organic carbon fractions at each position, and suggest the implications of continued upslope soil thinning and downslope soil thickening.

How to cite: Tye, A. and Evans, D.: Soil thinning and thickening: the fate of soil organic carbon, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22639, https://doi.org/10.5194/egusphere-egu2020-22639, 2020.

The study of different-aged fallow soils seems to be interesting from the point of view of changes in their conditions of genesis and functioning because a radical change of pedogenesis nature in time the removal of arable land to fallow leads to soil evolution. If the climax stages of postagrogenic successions are quite achievable, then the process of restoring the original climax vegetation should be associated with a reversible return of the soil to its original state. But pedogenesis is not limited only to the processes of converting organic residues into soil humus, binding it to mineral surfaces, humus, and biophilic elements accumulation. It also includes a slow chemical transformation of the parent rocks, due to the course of a number of reactions that rarely reach chemical equilibrium. And for soils that were once plowed, we can state with confidence that there is no identity between the component and phase compositions of fine mineral phases at the stages of involving virgin soil to cultivation and removing arable soil to fallow. Accordingly, the once homogeneous old-arable layer can be considered as a lithologically homogeneous soil-forming rock for the magnetic subprofile that is formed on it in the process of successional restoration of ecosystems. Therefore, the study of the magnetic properties of the upper part of the profile of different-aged fallow soils is appropriate in the aspect of the kinetic parameters of postagrogenic differentiation of the old-arable horizon. This work is devoted to studying magnetic properties of different-aged light-gray forest (30-35 years), dark grey forest (10-15 years) and sod-podzolic (12-17 years) fallow forest-steppe soils of the Republic of Tatarstan for the diagnosis of postagrogenic signs of differentiation of the old-arable horizon.

The work is performed according to the Russian Government Program of Competitive Growth of Kazan Federal University and with the support of the RFBR in the framework of the scientific project No. 19-35-50040.

How to cite: Fattakhova, L. and Kuzina, D.: Postagrogenic differentiation of the old-arable horizon of different-aged fallow soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21158, https://doi.org/10.5194/egusphere-egu2020-21158, 2020.

Soils are a critical component of the Earth system in regulating many ecological processes that provide fundamental ecosystem services (Adhikari and Hartemink, 2016). Soil formation factors may be operating at faster timescales than is typically considered in recently deglaciated alpine environments, yielding important implications for critical zone services (e.g., water retention, the preservation of carbon (C) and nutrients, and chemical weathering fluxes). It remains unclear how variation in these properties are linked to soil development and soil organic C pools and fluxes, in part because sites varying in these characteristics also typically vary in vegetation and climate.

Here we leveraged the high-altitude alpine pastures of the Nivolet Critical Zone and Ecosystem Observatory, Gran Paradiso National Park (Italy) to examine biotic and abiotic dynamics and controlling factors of organic C and weathering under different topographic positions and geologic substrates in a small localized mountainous region. Soil profiles were sampled across a range of parent materials deposited after the Last Glacial Maximum, including gneiss glacial till, carbonate and calcschist/gneiss colluvium, and gneiss/carbonate/calcschist alluvium across ridgetop, midslope and footslope topographic positions. Organic C, C stable isotopes, major and trace element content, particle size distribution, and pH reveal how parent material and landscape position govern soil C storage and development. Even under the cold climate, limited season with liquid water, young-age deglaciated context, soils have developed incipient spodic horizons and calcschist clasts appears completely weathered in place.

Alkali and alkaline earth elements exhibit chemical depletion throughout the profiles, whereas in some profiles phosphorus concentrations reflects nutrient uplift processes (i.e., accumulating at the top of the profile and depleted in mid-horizons) likely driven by “biotic” cycling. Phosphorus is relatively high in uppermost horizons at carbonate and glacial sites, but is quite low in gneiss, even though TOC is relatively high, suggesting that plants underlain by gneiss are able to generate organic compounds with lower P availability. Though rooting depth distributions exhibit linear declines with depth, contrary the typically observed exponential decay behavior, our data suggest that roots serve as important biotic weathering agents prompting rapid soil development. All profiles have high organic carbon content at the surface, but

are twice as high in the footslope Gneiss profile as in the midslope Glacier and Carbonate profiles and in the floodplain Alluvial profile.

These data, in conjunction with microbial analysis and geochemical variation, suggest that biota are key agents promoting the observed high degree of soil development in these high altitude ecosystems. We demonstrate how in the early stages of soil development abiotic and biotic factors influence soil weathering and C storage across different parent material and topography.

Adhikari, K. and Hartemink, A. E.: Linking soils to ecosystem services – A global review, Geoderma, 262, 101–111, 2016

How to cite: Baneschi, I., Dere, A., Aronson, E., Balint, R., Billings, S., Giamberini, S., Magnani, M., Mosca, P., Pennisi, M., Provenzale, A., Raco, B., Sullivan, P. L., and White, T.: The Nivolet CZ Ecosystem Observatory reveals rapid soil development in recently deglaciated alpine environments: Biotic weathering is the likely culprit, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16387, https://doi.org/10.5194/egusphere-egu2020-16387, 2020.

In this poster we will outline a new  ambitious cross-disciplinary project focused on detecting soil degradation and restoration through a novel multi-functional soil sensing platform that combines conventional and newly created sensors and a machine learning framework. Our work  aims to advance our understanding of dynamic soil processes that operate at different temporal/spatial scales. Through the creation of an innovative new approach to capturing and analyzing high frequency data from in-situ sensors, this project will predict the rate and direction of soil system functions for sites undergoing degradation or restoration. To do this, we will build and train a new mechanistically-informed machine learning system to turn high frequency data on multiple soil functions, such as water infiltration, CO2 production, and surface soil movement, into predictions of longer term changes in soil health including the status of microbial processes, soil organic matter (SOM) content, and other properties and processes. Such an approach could be transformative: a system that will allow short-term sensor data to be used to evaluate longer term soil transformations in key ecosystem functions. We will start our work with a suite of off-the-shelf sensors observing multiple soil functions that can be installed quickly. These data will allow us to rapidly initiate development and training of a novel mechanistically informed machine learning framework. In parallel we will develop two new soil health sensors focused on in-situ real time measurement of decomposition rates and transformation of soil color that reflects the accumulation or loss of SOM. We will then link these new sensors with a suite of conventional sensors in a novel data collection and networking system coupled to the Swarm satellite network to create a low cost sensor array that can be deployed in remote areas and used to support studies of soil degradation or progress toward restoration worldwide.

How to cite: Quinton, J., James, M., Davies, J., Whiting, G., Nemeth, C., Killick, R., Thomas, E., Bardgett, R., and Neff, J.: Detecting soil degradation and restoration through a novel coupled sensor and machine learning framework, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22591, https://doi.org/10.5194/egusphere-egu2020-22591, 2020.