Land management, water quality and sedimentation in subsurface karst conduits

Observations from several Tasmanian karsts suggest considerable changes have occurred underground following forest clearing for pasture and some commercial forestry practices. The changes include altered hydrological behaviour and water quality changes, together with the advent of sedimentation patterns that are (1) inconsistent with the stratigraphic record of cave sediment accumulation prior to human interference in the catchment, (2) at variance with what is happening beneath comparable undisturbed catchments, and (3) indicate the deposition of significantly greater volumes of sediment since catchment disturbance than was previously the case. Preliminary results from several Tasmanian caves suggest that the proportion of the anthropogenic isotope caesium-137 in cave sediments deposited during recent decades is inversely proportional to the broad degree to which the catchment overlying the caves has been disturbed. This is interpreted as being the result of the dilution of sediment eroded from the land surface by material derived from sub-surface sources. This seems most likely to be due to changed patterns of diffuse infiltration.