Doctoral defence: Sandeep Thayamkottu "Ecosystem scale modelling of carbon and nitrogen cycles in peatlands"

On the 26th of June at 14:15, Sandeep Thayamkottul will defend his doctoral thesis "Ecosystem scale modelling of carbon and nitrogen cycles in peatlands", to obtain the degree of Doctor philosophiae in physical geography .

Supervisors:
Assoc. Prof. Jaan Pärn, University of Tartu

Prof. Ülo Mander, University of Tartu

Dr. Thomas Luke Smallman, The University of Edinburgh (Scotland, UK)

Opponent:
Dr. Avni Malhotra, Pacific Northwest National Laboratory (Washington, USA)

Summary

Global warming and extreme climatic events are projected to increase in the future. It is expected to be driven by land-use and land-cover change (LULCC) and resulting greenhouse gas (GHG) emissions. Peatlands, play a crucial role in global carbon (C) and GHG budget by accumulating carbon (C) in soils (more than the global terrestrial vegetation). Soil water balance, movement of water in the soil-plant-atmosphere continuum, and meteorological drivers of gross primary production (GPP; shortwave radiation, vapour pressure deficit (VPD), air temperature, and precipitation) are of at most importance for ecosystem, regional, and global C and other GHG balance. Empirical knowledge of how soil moisture variations impact soil GHG emissions is essential for reducing the uncertainty around process-based understanding of peatland ecosystems. This doctoral thesis addresses the knowledge-gaps in C and N2O fluxes and its drivers at ecosystem scale. The study found that growing season chamber based GHG fluxes followed gaussian pattern to soil moisture variations and that CO2 was predominant in soil GHG exchange. Further studies on land-atmosphere exchange CO2 fluxes in sub-arctic fen peatland and drought affected temperate peatland delved into CO2 fertilisation effect and dual nature of VPD and soil moisture limitation of GPP respectively. This thesis investigated the drivers of GPP growth in the sub-Arctic using an intermediate complexity terrestrial ecosystem model of C calibrated by a Bayesian approach (model-data integration). The results also highlight the fractional allocation of photosynthate to different plant tissues and C residence times in the tissues. While soil moisture did not explain any variations in C fluxes in the high latitude site, it was a limiting factor of GPP as water table dropped below a threshold for the temperate site. This threshold is shallower than previously thought. This thesis helps to improve the hydroclimatic impact on GHG specifically C fluxes.