How does afforestation affect the hydrology of a blanket peatland? A modelling study

Abstract

Over the last century, afforestation in Ireland has increased from 1% of the land area to 10%, with most plantations on upland drained blanket peatlands. This land use change is considered to have altered the hydrological response and water balance of upland catchments with implications for water resources. Because of the difficulty of observing these long-term changes in the field, the aim of this study was to utilize a hydrological model to simulate the rainfall runoff processes of an existing pristine blanket peatland and then to simulate the hydrology of the peatland if it were drained and afforested. The hydrological rainfall runoff model (GEOtop) was calibrated and validated for an existing small (76 ha) pristine blanket peatland in the southwest of Ireland for the 2-year period, 2007-2008. The current hydrological response of the pristine blanket peatland catchment with regard to streamflow and water table (WT) levels was captured well in the simulations. Two land use change scenarios of afforestation were also examined, (A) a young 10-year-old and (B) a semi-mature 15-year-old Sitka Spruce forest. Scenario A produced similar streamflow dynamics to the pristine peatland, whereas total annual streamflow from Scenario B was 20% lower. For Scenarios A and B, on an annual average basis, the WT was drawn down by 16 and 20 cm below that observed in the pristine peatland, respectively. The maximum WT draw down in Scenario B was 61 cm and occurred in the summer months, resulting in a significant decrease in summer streamflow. Occasionally in the winter (following rainfall), the WT for Scenario B was just 2 cm lower than the pristine peatland, which when coupled with the drainage networks associated with afforestation led to higher peak streamflows.

Simulating the spatio-temporal dynamics of soil erosion, deposition, and yield using a coupled sediment dynamics and 3D distributed hydrologic model

“…2). Given that groundwater and antecedent soil moisture have been found to play an important role on runoff generation (Lewis et al, 2013) and nutrient transport (Warner et al, 2009) in the catchment, the site serves as a good test case for validating the integrated model at catchment scale. The Dripsey catchment is located approximately 25 km northeast of Cork, and has an area of 15 km 2 .…”

GEOtop 2.0: simulating the combined energy and water balance at and below the land surface accounting for soil freezing, snow cover and terrain effects

“…Therefore, it makes possible the modelling of the interactions between several hydrological, cryospheric, ecological and geomorphological processes in an interdisciplinary research framework. For example, it has been applied to model geomorphological processes like landslide triggering (Simoni et al, 2008), ecohydrological processes (Bertoldi et al, 2010;Della Chiesa et al, 2014;Kunstmann et al, 2013) and peat hydrology (Lewis et al, 2012). However, this paper mainly focuses on the aspects related to the cryosphere.…”

Distributed hydrological modeling with channel network flow of a forestry drained peatland site

“…The effect of the underlying mineral soil with higher hydraulic conductivity in parts of the peatland catchment may also affect the drainage efficiency after rainfall events, probably increasing the variation shown in Figure 7. Also, the hydraulic conductivity of peat may vary spatially [Lewis et al, 2013;Rossi et al, 2014]. Compared to the spatial variability of soil properties, the distribution of stand characteristics may be more easily derivable, e.g., from Lidar data that have become openly available (National Land Survey of Finland).…”

“…Most hydrological modeling studies on drained forests are based on the simulation of water balance between parallel ditches in a two-dimensional profile [e.g., McCarthy et al, 1992;Amatya et al, 1997;Koivusalo et al, 2008]. Threedimensional distributed hydrological modeling of drained peatlands [e.g., Dunn and Mackay, 1996;Lewis et al, 2013] can potentially provide a more comprehensive understanding on the spatial variability of soil moisture conditions on forestry sites.…”