Using tracer based sediment budgets to assess redistribution of soil and organic material after severe bush fires

In the summer of 2001, a combination of severe wildfires and moderate intensity rainfall events swept through the catchment of Lake Burragorang, NSW, Australia. Beryllium-7 and 210Pbex budgets were used to assess the redistribution of soil and organic debris that occurred on hillslopes in this catchment after the wildfire. In the ?90-ha study site, 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 Be expected to be present with the balance, 35 � 6%, presumably being exported offsite. Construction of a 210Pbex budget showed a similar pattern of internal redistribution; some 28 � 6 % of the total amount was exported from the site. Analysis of litter, soil and sediment samples shows that both 7Be and 210Pbex were: (a) preferentially retained near the soil surface (due to their constant deposition in rainfall), and (b) exhibited an affinity with organic material. It appears that 210Pb and 7Be budgets can reveal much about the redistribution of soil, organic (and nutrient) material after fires in these systems.