5th iLEAPS Science Conference Abstracts - A3

Abstracts - Session A3

The role of soils in global environmental change

A301 - INVITED-KEYNOTE: International Soil Modelling Consortium: Improving soil models by connecting scientific disciplines

Anne Verhoef1, Michael H Young2, Kris Van Looy3, Harry Vereecken3, Martin van der Ploeg4

1University of Reading, Reading UK,  2Bureau of Economic Geology, The University of Texas at Austin, 3Agrosphere Institute, Forschungszentrum Jülich, 3Department of Soil Physics and Land Management, Wageningen University and Research

The International Soil Modeling Consortium (ISMC: https://soil-modelling.org) aims to integrate and advance soil systems modelling, data gathering, and observational capabilities through:

  • Bringing together leading experts in modelling soil processes within all major soil disciplines
  • Addressing major scientific gaps in describing key processes and their long term impacts with respect to the different functions and ecosystem services provided by soil
  • Promoting integration of soil modelling expertise in neighbouring disciplines (climate, land surface, eco, hydro, and other models)
  • Performing soil model intercomparison studies at local to global scales
  • Consolidating soil and other data platforms for modelling purposes
  • Integrating societal and environmental considerations into soil and ecosystem functioning

Our consortium will bring together modelers and experimental soil scientists at the forefront of new technologies and approaches to characterize soils. By addressing these aims, the consortium will contribute to improve the role of soil modelling and a knowledge dissemination instrument in addressing key global issues and stimulate the development of translational research activities.

A302 - ORAL-0073: Fluvial organic carbon losses from tropical peatland oil palm plantations, Sarawak, Southeast Asia

Sarah Cook1, Sue Page1, Mick Whelan1, Chris Evans2, Vincent Gauci3, Khoon Lip Kho4

1Centre for Landscape & Climate Research. University of Leicester, Leicester, United Kingdom 2Centre for Ecology & Hydrology, Bangor, United Kingdom 3Dept. of Environment, Earth and Ecosystems, The Open University, United Kingdom 4Tropical Peat Research Institute, Biological Research Division, Malaysian Palm Oil Board,, Selangor, Malaysia

Tropical peat swamp forests (TPSFs) are carbon dense ecosystems that are being increasingly converted to other land-uses within Southeast Asia. At present, only 6% of TPSFs remain intact with more than 25% now under oil palm plantations. This form of land-use requires significant peatland drainage as well as the felling and burning of trees. These disturbance regimes can lead to significant perturbations to the terrestrial carbon cycle through enhanced peat carbon mineralization and dissolved organic carbon (DOC) losses, which represents a carbon loss from the peat itself. Dependable peat-carbon loss estimates (both gaseous and fluvial) from oil palm plantations on tropical peat are few, with the aquatic component largely overlooked. Here, we present an annual (54 week) estimate of exported dissolved and particulate organic carbon from the drainage waters of two oil palm estates and nearby stands of TPSF in Sarawak, Malaysia, subjected to varying degrees of anthropogenic disturbance. We find the annual fluvial organic carbon flux from the oil palm plantations (107.0 ± 17.1 g C m-2 yr-1)  is about two thirds larger than that of an intact TPSF (63 g C m-2 yr-1; Moore et al., 2013) and comparable to fluxes from a degraded peat swamp forest site (97 g C m-2 yr-1; Moore et al., 2013). Furthermore, DOC accounted for 86% to 94% of the total organic carbon lost, within the plantations, most of which is in a bioavailable form. Wit et al (2015) estimate that 53 % of peat-derived DOC is decomposed and emitted as CO2, on a monthly basis. Based on these estimates our data suggests an additional 57 g CO2 m-2 may be emitted indirectly from DOC in degraded TPSFs per year. This could have regional implications on tropical peat carbon budgets, emphasizing the need to include aquatic carbon losses.

A303 - ORAL-0368: Tracing soil organic carbon isotopes and their response to grazing exclusion in a temperate grassland of northern China using Community Land model (CLM4.5)

Hui Tang1, Liping Zhou2, Frode Stordal1

1Department of Geosciences, University of Oslo, Oslo, Norway 2Department of Geography, Peking University, Beijing, China

Soil organic carbon (SOC) isotopes (i.e., 14C and 13C) are useful tracers for estimating decomposition and turnover of SOC, therefore can be applied to better validate and constrain model parameters in simulating SOC dynamics. In this study, we employ an isotope-enabled terrestrial ecosystem mode – Community Land Model with vertical explicit SOC dynamics (CLM4.5BGC) to simulate 14C and 13C contents of SOC in a temperate steppe site of Inner Mongolia, China. At this site, we measured 13C and 14C contents of bulk SOC and three density fractions (< 1.6 g cm-3, 1.6-2.2 g cm-3, > 2.2 g cm-3) from three enclosures with the durations of grazing exclusion of 2, 7 and 27 years. With the default setting, the CLM4.5BGC consistently underestimates gross primary production, SOC storage and 14C content. It well captures the linear decrease of 14C content with soil depth, but fails to capture the exponential increase of 13C content with depth in top soil. To better agree with the observed SOC isotopes and their vertical distribution, an increase of photosynthetic rate of grass, turnover of the recalcitrate SOC pool, and root input in surface soil are required in CLM4.5BGC. A comparison of the modelled SOC pools with measured density fractions of SOC indicates that the medium (1.6-2.2 g cm-3) and heavy fractions (> 2.2 g cm-3) are a combination of both fast and stable carbon pools. To simulate the observed response of SOC and its isotopes to grazing exclusion, a simple increase of carbon input from grass is insufficient. Parameter modification taking into account of changes in surface soil texture, turnover rate and vertical mixing due to grazing exclusion is needed. The improved CLM4.5BGC may lead to a more realistic projection of future climate and land-use change impacts on SOC in the temperate steppe region of China.

A304 - ORAL-0205: The influence of season and atmospheric N deposition on soil carbon dynamics in a subalpine grassland, illustrated by stable isotope analyses

Matthias Volk1, Seraina Bassin1, Christian Andersen2

1Agroscope Zürich, Air Pollution/Climate Group, Zürich, Switzerland 2US Environmental Protection Agency, Corvallis, Oregon, The United States of America

We followed belowground C dynamics in a subalpine grassland system exposed to increased atmospheric N deposition (4, 14 and 54 kg N ha-1 year-1) for 7 years. Bulk soil organic carbon (SOC) concentration and C stocks increased during the experiment. But the N-deposition treatment did not lead to consistent increases in SOC, despite a strong effect on plant growth.

Here we discuss whether N deposition had an impact on carbon isotope partitioning among different SOC pools. We also examined how N-deposition interacts with seasonal photosynthetic 13C discrimination and thus the isotopic signature of young organic matter (OM) by analysing the seasonal dynamics of soil respired δ13C (δ13CCO2), using gas wells buried in the soil.

In the control soils we found a strong, negative correlation between SOC concentrations and δ13C of soil density fractions (δ13COM). This correlation remained intact over the seven-year period as SOC increased. All of the fractions measured became more 13C depleted during the seven-year experiment. C concentration increased in bulk soil and the light density fractions, but not in the heavier fractions. Surprisingly, the strongest N effect on C concentration and δ13COM in the biologically most active soil fraction was not found at the highest level of N addition. Patterns of soil δ13CCO2 were affected by climate and canopy development. In the highest N treatment, δ13CCO2 was much less depleted than in the other N treatments, indicating an interaction between N deposition and soil δ13CCO2 dynamics.

The results show how soil C dynamics are affected by both climatic drivers and N deposition in alpine grassland systems. But the complex nature of C fluxes into and out of high elevation soils indicates that predicting the effects of climate change will be difficult without a better understanding of the underlying processes occurring in these large C sinks.

A305 -ORAL-0419: Soil physical and hydraulic properties of ‘forest islands’ and adjacent ecosystem types in West Africa

Amelie Baomalgre Bougma1, K. Ouatarra1, H Compaore1, N B Nacro2, V Logah3, J.O Azeez4, C Melenya3, S A Mesele5, G Saiz6, E Veenendaal7, J Lloyd6

1Institut de l’Environnement et de Recherches Agricoles (INERA), Burkina Faso, Burkina Faso 2Université Polytechnique de Bobo Dioulasso (UPB), , Burkina Faso, Burkina Faso 3Kwame Nkrumah University of Science and Technology (KNUST), , Ghana, Ghana 4Federal University of Agriculture of Abeokouta (FUNAAB), Nigeria, Nigeria 54 Federal University of Agriculture of Abeokouta (FUNAAB), Nigeria, Nigeria 6Department of Life Sciences, Imperial College, London, United Kingdom 7Nature Conservation and Plant Ecology Group, Wageningen University, Netherlands, The Netherlands

Understanding the functioning and soil dynamics of forest islands in West Africa should assist in the development of sustainable management of such ecosystems in the region. However, very little information exists on the physical and hydraulic properties of these ecosystems created through anthropogenic activities and preserved by local populations in an open savanna landscape. The objective of this study was therefore to evaluate the physical properties (aggregate stability, bulk density, etc.) and hydraulic properties (soil moisture, hydraulic conductivity, etc.) of forest islands in West Africa as compared to those of adjacent savannas and agroecosystems. The study was conducted in Ghana, Nigeria and Burkina Faso with three sites located in three different agro-ecological zones of the latter (Burkina Faso). Soil moisture was measured weekly using the neutron probe. Data on soil moisture in 2016 at the three sites (Dano, Houndé and Boromotenga) in Burkina Faso showed significant differences between sites. The highest soil moisture (75 m3m-3) was recorded at Dano whilst the lowest (43 m3 m-3) was observed at Houndé with a clear difference between the ecosystems types at all locations. Specifically, regardless of season, location or horizon, soil moisture was lower in forest islands compared to natural forests and croplands. Upper soil horizons in the upper 0.4 m are relatively depleted in soil moisture compared to the lower soil horizons.

A306 - POSTER-0402: Environmental impact assessment of artisanal small scale mining in Rwanda: prospect for soil rehabilitation

Francois Xavier Nshimiyimana1, Francois Gakwerere2, Sylvie Mucyo3, Gabriel Habiyaremye1, Francois Xavier Naramabuye4, Florien Nsanganwimana2

1University of Lay Adventists of Kigali, Kigali, Rwanda 2University of Rwanda – College of Education, Remera Campus, Kigali, Rwanda 3University of Rwanda – College of Agriculture and Veterinary Medicine, Busogo Campus, Musanze, Rwanda 4University of Rwanda – College of Agriculture and Veterinary Medicine, Huye Campus, Huye, Rwanda

The mining sector greatly contributes to national growth domestic production (GDP). The mining activities potentials leads to environmental and health risks. The accumulation of mining wastes on land surfaces could increase concentrations of heavy metals. These increase toxicity to all living organisms including humans. Nowadays, the main challenge is how to ensure environmental safety and minimizing its negative impact on various components of ecosystems. The purpose of the present baseline study was to assess the degree of soil physicochemical degradation as result of mining activities. The results concern mainly two artisanal mining sites: Gatumba coltan mining and Burera Gold mining, both located in highland zones. It was found out that the pH and cation exchange capacity (CEC) decreased in soil surface horizons. Regarding soil texture, these superficial soil horizons were dominated by sand fraction. However, the soil was not highly contaminated by major heavy metals, but mine tailings reveal relatively elevated concentrations of Li, Rb, Cr and Cs.  Overall, the results show that mined soil is no longer suitable for normal crop production. Moreover, apart from dusts which undoubtedly affect life of miners, there is a risk of metals to contaminate air water and soil, hence undermining the wellbeing of human populations working and/or living near sites. The physicochemical degradation of mining environment calls for an urgent for land rehabilitation. This could be done by considering the socio-economic needs of the areas in which farming activity is dominant. With this regard, phytoremediation using both ecologically and economically important crop would be an environmentally-friendly option.