How groundwater abstraction and tree management affect water levels and peat properties in a groundwater fed peatland

Groundwater-fed peatlands are a rare and vital ecosystem providing rich biodiversity, carbon storage and regulation of the hydrological cycle. Management of these species and carbon stores are essential for maintaining a healthy ecosystem. In parallel to this, groundwater aquifers are a common source of relatively clean drinking water, but they are under pressure from population growth and climate change. Groundwater abstraction can lead to a reduction in groundwater levels within groundwater-fed peatlands, affecting their condition, for example by facilitating tree encroachment. Therefore, sustainable water supply needs to balance water demand against other unintentional environmental impacts on these ecosystems. Greywell Fen is located in Southern England, situated above a chalk aquifer that is used to provide drinking water to the area. The fen has been designated a site of special scientific interest (SSSI) in recognition of its important flora. However, the significant fen vegetation species have been declining in recent decades in favour of extensive tree growth throughout the site. New management of the area has included the reintroduction of grazing and large areas of tree clearance. Our research concerns the impacts of groundwater abstraction and woodland management on the health of the fen. Extensive water level monitoring connected to areas with variable tree expansion and clearance is being used to determine if tree management is having an effect on water levels within the fen. In addition, peat cores have been sampled in the different areas to determine if tree management and/or water level changes are impacting peat properties, as an indication of drying and decline in fen health. Peat properties studied include pH, water content, C:N, and organic matter decomposition. The latter was performed using FTIR spectroscopy. The monitoring data have been fed into the Soil-Water-Atmosphere-Plant (SWAP) model to improve our understanding of the hydrology of the system and how the groundwater abstraction affects fen water levels. The model has also been used to determine how management can be optimised to enable sustainable abstraction. The results of the in-depth monitoring and modelling are presented here.