Catchment hydro-geomorphological responses to environmental change in the Southern Uplands of Scotland

Abstract

Lake sediment and geomorphic evidence from the Loch of the Lowes/St Mary's Loch basin in the central Southern Uplands of Scotland provide a multiproxy reconstruction of changing sediment availability and transmission through the catchment. Interrogation of magnetic, geochemical and grain size parameters for lake and catchment materials suggests it is possible to identify independent proxies that reflect both supply (availability) and discharge (capacity) controls on the sediment signal. Chronological control for the lake sediment record is proposed by linking a210Pb/137Cs chronology for the last c. 120 yr to an age/depth profile based on proposed temporal correlations between cyclic HIRM/χLF variability and the North Atlantic Oscillation. Geochronological studies on debris cones and alluvial fans yield evidence for episodic hillslope gullying ~2000—0 BC with more extensive region-wide slope instability AD 700—900, 1100—1300 and after AD 1450—1550 and gully stabilization over the last 150 years. The latter two episodes coincide with the lake sediment evidence for increased sediment supply from ~AD 1600 declining after ~AD 1870. The capacity-related lake proxies appear to identify phases of increased flooding ~AD 1625—1650, 1680—1700, 1730—1760, 1800—1815, 1850—1880, 1910—1930, 1960—1970 and possibly the 1990s. Close correspondence between the sediment `flood' archive and historical records of flooding in Scotland suggests that lake-catchment systems of this type have the potential to yield valuable information on past hydrological response.