The effect of water table depth on GHG emissions in an agricultural peatland with varying peat depth

Peatlands store around 30% of the world's soil organic carbon and therefore play a significant part in mitigating greenhouse gas (GHG) emissions. Some peatlands have been converted to agricultural use through artificial drainage and farming practices,leading to the accelerated release of carbon from the land to the atmosphere. However, the combination of soil characteristics, hydraulic properties and field management operations all play an important role in determining how much GHGs are emitted from the agricultural sites. The aim of this study is to 1) evaluate the applicability of the LandscapeDNDC model to cultivated peatlands by comparing the simulation outputs with the corresponding observations in the study site, and 2) assess the effects of the water table changes on GHG emissions. The LandscapeDNDC is a process-based model that can handle carbon and nitrogen cycling. The model can incorporate various input data, such as management, meteorological and water table data, and therefore provides a well-rounded framework for studying the effect of manipulating these input data on GHG emissions.

We performed the study at Luke Ruukki Research Station on the NorPeat platform, divided into 6 separate drainage blocks with varying peat depths (20 - 80 cm). Continuous flux measurements (June 2019 onwards) were collected at the site as well as block-specific dark chamber measurements of CO2 and N2O emissions. Each of the blocks had groundwater pipes equipped with pressure sensors to continuously measure the water table level. In addition, intensive measurements of soil properties and yield were carried out on the site during the study years 2019 - 2022, allowing us to establish a realistic site profile for our simulation runs.

The simulations were first validated with two meters: the satellite measurements of leaf area index and measurements of soil moisture. The model reproduced the observed variability in all blocks for both meters (R2 > 0.5) and was sufficiently able to simulate the observed CO2 and N2O fluxes. After analysing and ensuring that the model was able to reproduce the biochemical and hydraulic dynamics observed in the study site, we studied the three different water table scenarios and their effects on the GHG fluxes. In the scenarios the water table was raised on average to 15, 30, and 50 cm below the soil surface. These water table changes altered the soil respiration and nitrogen cycling, and provided insight into how peat thickness affects emissions. In addition, the study helped to quantify the mitigation effect of the raised water table, relieving the potential that water management could have on controlling GHG emissions.