DOI: 10.5285/a81c6520-c116-4e99-810d-23eba79b9b3f
title: Modelled soil carbon and nitrogen pools and soil respiration, under control and drought conditions, related to the climate change experimental fieldsite in Clocaenog forest, UK, using ECOSSE

description: Soil organic carbon pools, soil water content, and soil respiration were modelled throughout the soil profile under both control and drought conditions, as well as various drought scenarios, utilizing the ECOSSE model (Estimate Carbon in Organic Soils - Sequestration and Emissions). Data collected from climate change experimental plots (control and drought) at Clocaenog forest in North Wales (UK) were employed to parameterize the model. Information from the experimental site spanning from 2009 to 2014 was used to calibrate the process-based model, which simulated four drought scenarios with durations of 12, 24, 48, and 96 years of drought and subsequent recoveries. The ECOSSE model facilitates the modelling of carbon pools, including: 1) decomposable plant material (DPM), 2) resistant plant material (RPM), 3) microbial biomass (BIO), and 4) humified organic matter (HUM). These pools were analysed for their responses to drought conditions, particularly in relation to soil water availability. Both carbon and nitrogen pools were modelled, along with respiration rates. By integrating field observations with process-based modelling, the study used these data to investigate how the frequency of drought influences the ability of organo-mineral soils to sequester carbon.
description: Continuous meteorological field observations (precipitation and air temperature), soil moisture, vegetation biomass, litter inputs, and soil respiration were collected from control and experimental drought treatments between January 2009 and December 2014 using datasets published as part of the Clocaenog climate change experiment data collection.

Total soil respiration was partitioned into autotrophic and heterotrophic components using seasonally varying fractions of respiration which were derived from published literature for comparable heathland systems. 

Field data were used as inputs to the ECOSSE soil carbon and nitrogen model v6.3.4. ECOSSE stands for Estimate Carbon in Organic Soils - Sequestration and Emissions.

Model initialization was carried out assuming steady-state soil carbon conditions prior to experimental manipulation. This steady state was established using long-term monthly climate data (1957-2000) together with measured soil carbon stocks. The forward simulations then explicitly used the 2009-2014 experimental observations to drive the control and drought scenarios. Long-term drought scenarios were imposed for 12-, 24-, 48- and 96-year intervals, each followed by equivalent post-drought recovery phases.

ECOSSE was parameterized with site-specific inputs for soil texture, bulk density, soil carbon stocks, vegetation productivity, and hydrology. Plant input quality was related to the high lignin content of heathland vegetation. Soil moisture dynamics were simulated using the ECOSSE tipping-bucket hydrology module adapted from the SUNDIAL model, driven by measured precipitation and Thornthwaite-derived potential evapotranspiration.

Multiple QA and validation steps were applied: 1) heterotrophic respiration (Rh) was evaluated against partitioned chamber measurements from the field experiment; 2) a sensitivity analysis was carried out for the seasonal partitioning of respiration into autotrophic and heterotrophic; 3) uncertainty in model simulations was quantified by propagating uncertainty in the most influential climate and soil parameters; 4) the steady-state was validated by checking initial soil carbon pools for equilibrium before the forward drought simulations were initiated.