Hydrological Responses to Anthropogenic Disturbance in Peatlands: a Numerical Approach

Peatland ecosystems are complex mosaics and located often in low-lying transitional zones between terrestrial and aquatic ecosystems. Peatlands in its pristine state play a significant role in regulating the hydrological, biogeochemical and ecological functions and act as long-term storage for carbon. However, up to 20% of the global peatland resources have been disturbed for a variety of human land uses (e.g., forestry and agriculture) and lost their natural functions. In this research, we tested the effectiveness and applicability of a physically-based three-dimensional fully integrated surface-subsurface numerical model (HydroGeosphere, HGS) to study hydrological disturbances in peatlands. The model was specifically implemented to assess the impact of artificial drainage and subsequent restoration on the hydrological responses (runoff and water table) of a previously disturbed, now restored (ditches-blocked) peatland catchment (about 11.4 ha) located in Western Finland. The hydrological data included two years before restoration (drained condition) and one year after restoration (ditches-blocked) collected during frost-free periods. The model domain was discretized with seven vertical finite element layers of 146744 nodes and 255206 elements to represent the ditch networks (drained condition) and blocked ditches (restored condition) in the model realistically. The HGS model was run for the two disturbed conditions (drained and restored) using forcing weather data collected in 2016, 2017 and 2018. In all the years, simulated runoff in drained conditions was significantly higher than simulated at restored conditions. The simulated water table level in restored conditions was significantly closer to the ground surface than in drained conditions, which agreed with the observed water table data. The results indicated that three-dimensional models, such as the HGS can be implemented to evaluate the effect of restoration measures on the hydrological response of peatland catchments. Thus, high-resolution physically-based models have the potential to improve our understanding of the complex hydrology of disturbed habitats spatially. Understating the spatial dependence of peatlands to inputs from groundwater and surrounding upland areas could further help us improve restoration measures.