The effect of drain blocking on the dissolved organic carbon (DOC) budget of an upland peat catchment in the UK

Extensive drainage of UK peatlands has been associated with dehydration of the peat, an increase in water colour and a loss of carbon storage. It has been considered that the blocking of these drainage channels represents a means of peat restoration and a way of reducing dissolved organic carbon (DOC) losses to surface waters. This study aimed to assess the effectiveness of drain blocking at both an individual drain scale and at a larger catchment scale (up to 1km2). A series of blocked and unblocked catchments were studied in Upper Teesdale, Northern England. A detailed sampling programme was undertaken in which a series of drains were studied in the 12months prior to and post blocking in comparison to a set of drains that were left unblocked and a catchment of similar scale where there had never been drainage. These stream networks were monitored for both their DOC concentration and export (flux per unit area). The results show that:(i)For DOC concentrations, a significant decline due to drain-blocking was only found at the first order scale when considered relative to control and relative to a pre-blocking period;(ii)drain blocking significantly reduces DOC export by reducing water yield in the drain and that the size of this DOC export reduction declines with increasing scale from 9.2% on zero order drains to 2.2% on first order drains;(iii)a linear relationship exists between DOC export and water yield at the zero order scale but this relationship becomes more complex at the first order scale as the relationship takes on the characteristics of a mixing model reflecting the effect of changing water sources with scale and providing evidence of the existence of flow bypassing drain blocks. The results suggest that effects of drain blocking decrease with increasing scale and that the presence of bypass flow around zero order blockages may limit the success of drain blocking as a method of reducing DOC loss as scale increases.