Abstract
Abstract. Peatlands store substantial amounts of carbon and are vulnerable to climate change. We present a modified version of the Organising Carbon and Hydrology In Dynamic Ecosystems (ORCHIDEE) land surface model for simulating the hydrology, surface energy, and CO2 fluxes of peatlands on daily to annual timescales. The model includes a separate soil tile in each 0.5° grid cell, defined from a global peatland map and identified with peat-specific soil hydraulic properties. Runoff from non-peat vegetation within a grid cell containing a fraction of peat is routed to this peat soil tile, which maintains shallow water tables. The water table position separates oxic from anoxic decomposition. The model was evaluated against eddy-covariance (EC) observations from 30 northern peatland sites, with the maximum rate of carboxylation (Vcmax) being optimized at each site. Regarding short-term day-to-day variations, the model performance was good for gross primary production (GPP) (r2 = 0.76; Nash–Sutcliffe modeling efficiency, MEF = 0.76) and ecosystem respiration (ER, r2 = 0.78, MEF = 0.75), with lesser accuracy for latent heat fluxes (LE, r2 = 0.42, MEF = 0.14) and and net ecosystem CO2 exchange (NEE, r2 = 0.38, MEF = 0.26). Seasonal variations in GPP, ER, NEE, and energy fluxes on monthly scales showed moderate to high r2 values (0.57–0.86). For spatial across-site gradients of annual mean GPP, ER, NEE, and LE, r2 values of 0.93, 0.89, 0.27, and 0.71 were achieved, respectively. Water table (WT) variation was not well predicted (r2 < 0.1), likely due to the uncertain water input to the peat from surrounding areas. However, the poor performance of WT simulation did not greatly affect predictions of ER and NEE. We found a significant relationship between optimized Vcmax and latitude (temperature), which better reflects the spatial gradients of annual NEE than using an average Vcmax value.
Highlights
Peatlands cover only 3–5 % of the Earth’s land area but store large amounts of soil organic carbon (SOC)
We present the development of a multilayer peat hydrology and carbon model in the Organising Carbon and Hydrology In Dynamic Ecosystems (ORCHIDEE) land surface scheme, with a focus on the water table dynamics and its effects on the energy budgets, and on carbon decomposition occurring within the oxic and the water-saturated parts of the peat profile
Wania et al (2009b) separated floodtolerant C3 graminoids and Sphagnum moss in LPJ-WHy to represent peatland-specific vegetation, with peatland extent defined from an organic soil map and the fractional cover of plant functional types (PFTs) determined by bioclimatic conditions including temperature, water table depth, inundation stress, etc
Summary
Peatlands cover only 3–5 % of the Earth’s land area but store large amounts of soil organic carbon (SOC). Chaudhary et al (2017a, b) included a dynamic multilayer peat accumulation functionality in a customized Arctic version of the Lund–Potsdam–Jena General Ecosystem Simulator (LPJ-GUESS) In their approach, new layers of litter were added at the top of the soil every year, and the remaining litter mass, after decomposition, was treated as a new individual peat layer from the first day of the following year. CH4 fluxes and DOC loss through runoff are important components of the carbon balance of a peatland (Chu et al, 2014; Olefeldt et al, 2012) but are not included in this study This new peat model is incorporated consistently into the land surface scheme in order to conserve water, carbon, and energy at scales from local sites to grid-based largescale applications in an Earth system modeling context
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