The Effects of Fire on the Function of the 200-BP-1 Engineered Surface Barrier

Ward, Anderson L. ; Link, Steven O. ; Hasan, Nazmul ; Draper, Kathryn E.

Pacific Northwest National Laboratory (U.S.)

关键词: Plants;    Environmental Molecular Sciences Laboratory;    Soils;    Monitoring;    Disturbances;   

DOI  :  10.2172/1025100
RP-ID  :  PNNL-18934
RP-ID  :  AC05-76RL01830
RP-ID  :  1025100

美国|英语

来源: UNT Digital Library

【 摘 要 】

A critical unknown in use of barrier technology for long-term waste isolation is performance after a major disturbance especially when institutional controls are intact, but there are no resources to implement corrective actions. The objective of this study was to quantify the effects of wild fire on alterations the function of an engineered barrier. A controlled burn September 26, 2008 was used to remove all the vegetation from the north side of the barrier. Flame heights exceeded 9 m and temperatures ranged from 250 oC at 1.5 cm below the surface to over 700 oC at 1 m above the surface. Post-fire analysis of soil properties show significant decreases in wettability, hydraulic conductivity, air entry pressure, organic matter, and porosity relative to pre-fire conditions whereas dry bulk density increased. Decreases in hydraulic conductivity and wettabilty immediately after the fire are implicated in a surface runoff event that occurred in January 2009, the first in 13 years. There was a significant increase in macro-nutrients, pH, and electrical conductivity. After one year, hydrophobicity has returned to pre-burn levels with only 16% of samples still showing signs of decreased wettability. Over the same period, hydraulic conductivity and air entry pressure returned to pre-burn levels at one third of the locations but remained identical to values recorded immediately after the fire at the other two thirds. Soil nutrients, pH, and electrical conductivity remain elevated after 1 year. Species composition on the burned surface changed markedly from prior years and relative to the unburned surface and two analog sites. An increase in the proportion of annuals and biennials is characteristic of burned surfaces that have become dominated by ruderal species. Greenhouse seedling emergence tests conducted to assess the seed bank of pre- and post-burn soils and of two analog sites at the McGee Ranch show no difference in the number of species emerging from soils collected before and after the fire. However, there were fewer species emerging from the seed bank on the side slopes and more species emerging from two analog sites. Leaf area index measures confirmed the substantial differences in plant communities after fire. Xylem pressure potential were considerably higher on the burned half of the barrier in September 2009 suggesting that not all the water in the soil profile will be removed before the fall rains begin. The results of this study are expected to contribute to a better understanding of barrier performance after major disturbances in a post-institutional control environment. Such an understanding is needed to enhance stakeholder acceptance regarding the long-term efficacy of engineered barriers. This study will also support improvements in the design of evapotranspiration (ET) and hybrid (ET + capacitive) barriers and the performance monitoring systems.