Effects of fire on the hydrology, biogeochemistry, and ecology of peatland river systems

Abstract

Peatlands are found around the world and cover ∼3.4% of the Earth's surface. In the UK, peatlands cover 17.2% or ∼1.58 Mha of the land surface and occur mainly in upland areas covering the headwaters of most major British rivers. However, large areas are now subject to prescribed vegetation burning despite policy guidance that recommends a strong presumption against burning on deep blanket peat. Wildfires occur sporadically but are forecast to increase in frequency in the future. This paper provides a synthesis of current knowledge about how UK peatland-dominated river catchments respond to fires caused by prescribed vegetation burning and uncontrolled wildfire. We provide insight into the effects of fire on the hydrology, biogeochemistry, and biota of peatland river ecosystems, and the peatland-soil-driven controls on these effects at the catchment scale. Burning increases the depth to water table and water-table variability, although some small-scale studies indicate shallower water table in some places. More work is needed on fire effects on peatland river flow, but recent results suggest a complex response with smaller flow peaks for burned systems associated with most rainfall events, but enhanced peaks compared to unburned systems for the top quintile of rainfall events with the largest total rain. Evidence from biogeochemical studies suggests that fire leads to increased dissolved organic C concentrations in rivers. River biota responses primarily include significant reductions in the density of grazing mayflies but increases among detritivores including Chironomidae and Baetis mayflies. We provide a conceptual synthesis that links the main responses of terrestrial and aquatic systems to fire, and we summarize some major research gaps that should be prioritized to inform future policy around peatland management.

Peatland carbon stocks and burn history: Blanket bog peat core evidence highlights charcoal impacts on peat physical properties and long‐term carbon storage

“…However, the plots offered comparable grazing impacts to this study with, for English uplands, representative low sheep grazing levels (see Section 2). As pointed out by Brown et al (2015), fires on such small experimental areas might not represent real burn rotation impacts (i.e., often burn patches are about 50 × 100 m and a 10-year burn rotation is considered very frequent). Therefore, a reassessment of this method is urgently required in a real grouse moor context to provide more evidence concerning long-term burn rotation impacts on peat C accumulation.…”

Sediment deposition from eroding peatlands alters headwater invertebrate biodiversity

“…In some areas, this enhanced erosion has been due to decay of the peatland through subsurface evacuation of sediment from large cavities (peat pipes) , a feature that appears to be exacerbated by installation of drainage ditches (Holden, 2006). In other areas, peat is extracted for use as fuel or in horticulture (Waddington, Plach, Cagampan, Lucchese, & Strack, 2009), and vegetation is removed to prevent wildfire, to promote grazing or to enhance game bird density for gun-sports leading to the exposure and erosion of soils (Brown et al, 2015). Disturbed and exposed organic soils are vulnerable to erosion due to their low density, which ultimately leads to enhanced delivery of particulate organic matter to rivers.…”

Forest clearfelling effects on dissolved oxygen and metabolism in peatland streams

“…However, benthic AFDM biomass did significantly increase following clearfelling supporting H 2 . Increases in benthic AFDM were also noted by Brown et al (2013) in peatland catchments subjected to burning and this was attributed to the increased vulnerability of organic soils to physical erosion. The emerging consensus is the effect of disturbance increases benthic organic matter in peatland stream systems (Brown et al, in press).…”

“…Studies have focused on sediment, and nutrient export and bio-indicators such as macroinvertebrates (e.g. Brown et al, 2013;Drinan et al, 2013;Ramchunder et al, 2011;Rodgers et al, 2010Rodgers et al, , 2011. This study has provided the first detailed insight into how instream metabolic rates respond to forest clearfelling on blanket peat.…”