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Wildfires can pose environmental challenges in urban watersheds by altering the physical and chemical properties of soil. Further, invasive plant species in urban riparian systems may exacerbate changes in geomorphological and soil processes after fires. This research focuses on the 2018 Del Cerro fire, which burned upland and riparian areas surrounding Alvarado Creek, a tributary to the San Diego River in California. The study site has dense and highly flammable non-native vegetation cover (primarily Arundo donax) localized in the stream banks and has primarily native vegetation on the hillslopes. We estimated the post-fire organic matter and particle distributions for six time points during water years 2019 and 2020 at two soil depths, 0–15 cm and 15–30 cm, in upland and riparian areas. We observed some of the largest decreases in organic matter and particle-size distribution after the first post-fire rainfall event and a general return to initial conditions over time. Seasonal soil patterns were related to rainfall and variability in vegetation distribution. The riparian soils had higher variability in organic matter content and particle-size distributions, which was attributed to the presence of Arundo donax. The particle-size distributions were different between upland and riparian soils, where the riparian soils were more poorly graded. Overall, the greatest change occurred in the medium sands, while the fine sands appeared to be impacted the longest, which is a result of decreased vegetation that stabilized the soils. This research provides a better understanding of upland and riparian soil processes in an urban and Mediterranean system that was disturbed by non-native vegetation and fire.
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Assessing the Impact of Wildfire Intensity on Soil Hydrology and Stability: The Role of Soil Organic Matter and Mulching Strategies
Wildfires significantly impact hydrology and geomorphology by altering soil properties, which depend on the fire intensity, duration, and frequency. Soil organic matter (SOM) is vital for forest ecosystems, acting as fuel. In this study, unburnt and burnt soils were collected from nearby locations for a prescribed fire site. Additional samples were tested where unburnt soil was mixed with 25% volume of mulch and exposed to a temperature of 150°C and 650°C in a furnace to simulate the exposure to soil with organic matter to high temperatures experienced during wildfires. The variation of soil-water characteristic curves (SWCCs) for these different soil samples was evaluated to assess the impact of exposure to high temperature during wildfires. Results showed that low-intensity fires did not alter soil properties, while high-intensity fires resulted in a change in the soil property in terms of SWCC and physical and hydraulic characteristics, and posed greater erosion risks and disrupt soil stability, highlighting the need for better soil management strategies.
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- Award ID(s):
- 2327384
- PAR ID:
- 10663100
- Publisher / Repository:
- American Society of Civil Engineers
- Date Published:
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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