Impacts on water quality by sediments and nutrients released during extreme bushfires:Report 2:Tracer assessment of post-fire sediment and nutrient redistribution on hillslopes:Nattai National Park, NSW.Sydney Catchment Authority - CSIRO Land and Water Collaborative Research Project

[摘要] Executive Summary:In the summer of 2001-2002, a combination of severe bushfires and moderate intensity rainfall events swept through Nattai National Park, in the catchment of Lake Burragorang, near Sydney, NSW.Soil eroded from hillslopes in the Nattai area in the post-fire period was carried downstream to Lake Burragorang, the Sydney Catchment Authority (SCA) reservoir.The series of events provided an opportunity to investigate fire-induced hydrogeomorphic changes in response to the episodic, but important, role of fires in the transfer of both sediment and accompanying nutrients from catchment slopes to waterbodies.Bule Gum Creek sub-catchment in Nattai National Park, located approximately 100 km southwest of Sydney, was selected for study.Typical of the lower Blue Mountains, the ~90 ha site is located within steeply dissected plateau terrain that supports native Eucalypt forest.The sub-catchment comprises five land units:plateau, steep hillslopes (11° slope angle), gentle lower slopes adjacent to the valley floor (11°) regions, depositional mounds, and post-fire outwash fans.The fallout nuclides Beryllium-7, Lead-210 and Caesium-137 (7Be, 210Pbex and 137Cs respectively) were used to construct tracer budgets to assess the redistribution of soil and organic debris that occurred within Blue Gum Creek catchment in the first 5 months after the bushfires.The budgets showed substantial losses of 7Be from the upper plateau (10 ± 2%) and side slopes (26 ± 5%), and deposition on the lower footslopes and alluvial fans (2 ± 4%).Overall, it was possible to account for ~65% of the initial amount of 7Be expected to be present with the balance, 35 ± 6%, presumably being exported offiste to downstream environments.Construction of a 210Pbex budget showed a similar pattern of internal redistribution iwth respective losses from the plateau and slopes of 4 ± 6% and 24 ± 15%, and some 28 ± 4% of the toal amount being exported from the headwater catchment system.The 137 Cs budget suggests that limited topsoil was eroded from the plateau in the initial months after the fires (4 ± 1%) and similarly negligible overall losses (4 ± 1%) from the system.

[发布机构] CSIRO

[学科分类] 地球科学(综合)