Long-term changes in hydrological pathways in an upland peat catchment—recovery from severe drought?

Abstract

This study analyses long-term water quality data from an upland peat catchment in order to understand long-term changes in hydrological flowpaths and how they relate to recovery from severe drought and control the release of DOC. The study examined comparative records from rainfall, soil and stream samples over a 9-year period, which included an approximately 1 in 30-year drought 2 years into the period. The study examined single tracers and utilised multivariate statistics to examine changing sources and routes of runoff. The study shows that the severe drought is part of dry period not restricted to a single summer and this extended dry period may give rise to the extent of the chemical changes observed in the stream chemistry. During this period of drought there is no evidence for substantive new flowpaths being generated during the drought, instead the residence time of the water in the upper peat horizon (<10 cm depth) increases and that this increase is reflected in the chemistry of runoff. The soil waters deeper in the peat profile (approx. 50 cm) show increased influence of rainwater compositions and that during drought the residence times at depth increase. There is an offset between the severe drought and maximums in concentrations of Fe, DOC and Al are related to the hydrophobic nature of the peat matrix. The effects of a 30-year drought persisted for no more than 3 years ending with the end of the dry period, and at least the effects of severe drought lasted only a year. The study suggests that in peat catchments summer's are hydrologically independent of the winters and this fact limits the consequences of severe drought.