Abstract. In the UK, most large reservoirs constructed for public water
supply are in upland areas. Many are situated in catchments characterised by
organic-rich soils, including peatlands. Although these soils naturally
leach large amounts of dissolved organic matter (DOM) to water, the
widespread degradation of upland peat in the UK is believed to have
exacerbated rates of DOM loss. High and rising DOM concentrations in these
regions raise treatment challenges for the water industry. In the UK, water companies are increasingly considering whether upland-catchment peat restoration measures can slow down or even reverse rising
source water DOM concentrations and, thus, reduce the need for more costly and
complex engineering solutions. There remains considerable uncertainty around
the effectiveness of such measures, and a comprehensive overview of the
research in this area remains lacking. Here, we review the peer-reviewed
evidence of the effectiveness of four catchment management options in
controlling DOM release from peat soils: ditch blocking, revegetation,
reducing forest cover and cessation of managed burning. Results of plot-scale investigations into the effects of ditch blocking on DOM
leaching are currently largely equivocal, while there is a paucity of
information regarding impacts at spatial scales of more direct relevance to
water managers. There is some, although limited, evidence that the terrestrial
vegetation type may influence DOM concentrations and treatability. The
presence of plantation forestry on peat soils is generally associated with
elevated DOM concentrations, although reducing forest cover appears to have
little short-term benefit, and associated disturbance may even increase
concentrations further. Catchment management measures have rarely been monitored with downstream
water quality as the focus. To mitigate the uncertainty surrounding
restoration effects on DOM, measures should be undertaken on a site-specific
basis, where the scale, effect size and duration of the intervention are
considered in relation to subsequent biogeochemical processing that occurs
in the reservoir, the treatment capacity of the water treatment works and
future projected DOM trends.