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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.

33Discolouration of natural surface waters due to the humic component of dissolved organic carbon 34 (DOC) is a costly problem for water supply companies. This paper reviews what is known about 35 the impacts of prescribed moorland vegetation burning on water colour. Relevant research has taken 36 place at three scales: laboratory experiments on peat cores, plot scale sampling of soil waters and 37 catchment scale sampling of stream waters. While laboratory studies suggest burning increases 38 colour production, the evidence from catchment and plot studies is contradictory. Plot studies 39 suggest colour production may decrease or remain unchanged following burning although there is 40 evidence for some transient changes. Catchment studies suggest prescribed moorland burning 41 causes stream water colour to increase, although in most cases the evidence is not clear cut since 42 most studies could not clearly disentangle the effects of burning from those of vegetation cover. The 43 differences in findings between plot and catchment studies may be explained by: i) the short-term 44 nature of some studies which do not measure long-term response and recovery times to burning; ii) 45 the lack of colour measurements from shallow soil depths which contribute more to streamflow than 46 soil water from deeper in the peat; and iii) the possibility of hydrological interactions occurring 47

23Despite the fact that significant gaps remain in our understanding, it is known that 24 agricultural stewardship can be highly effective in controlling water pollution at the 25 plot and field scales. Knowledge at the catchment scale is, to a large extent, entirely 26 lacking though and this is of paramount concern given that the catchment is the