Restoring Fire-Impacted Lands with Biosolids
Previous research studies have demonstrated that land application of biosolids to fire-ravaged lands has positive impacts on the land’s ecosystem, soil quality, and runoff. In the aftermath of wildfires, erosion from fire-damaged lands poses a significant water quality concern. The reduction in vegetation intensifies runoff and increases exports of sediments and potential pollutants into surface water supplies. Applying wastewater-derived biosolids to these fire-ravaged lands has been shown to restimulate vegetation and enhance soil stability.
A successful research study was conducted in Colorado in 1996 where biosolids were land applied after the Buffalo Creek Fire. The promising results of this study inspired further trials in other parts of the United States, such as Southern California. Between 2019 and 2021, biosolids from the Las Virgenes Municipal Water District Composting Facility were applied to lands impacted by the Woolsey Fire. The Las Virgenes trial saw similar successful soil health results as shown in the Colorado 1996 study. With the unfortunate trend of California’s wildfires getting worse, this biosolids reuse application could be an important part of the solution to restoring fire-impacted lands.
Case Study - Biosolids Application to Colorado Buffalo Creek Fire Ravaged Lands
In May 1996, the Buffalo Creek Fire in Colorado burned 4,806 hectares of forest and wildlife in Pike National Forest, which later contributed to severe erosion and flooding events during the next wet weather season. In the spring of 1997, Meyer et al. applied Class A composted biosolids from the Denver Metro Wastewater District with the objective of determining impacts to revegetation and soil erodibility. The study experimented with 24 treatment plots (six treatments and four replicates each). Each plot was three meters wide and 100 to 300 meters long. The six treatments consisted of varied biosolids application rates ranging from 0 (control) up to 80 metric tons per hectare at a soil depth of 10 to 20 centimeters. The biosolids were tilled and the site was reseeded with a mixture of native grasses by the U.S. Forest Service. Plant biomass, plant cover information, and plant tissue samples were collected for four years after incorporation of biosolids.
The research study results found that plant biomass production increased with increasing application rates of biosolids in all four years of the study, which can be seen graphically in Figure 1 and visually in Figure 2. The year-to-year decline in biomass production was explained by below-average rainfall during the summer seasons after 1999.
Figure 1. Mean Annual Plant Production in Post-Fire study plots at Buffalo Creek fire site.
Figure 2. Images of treatment plots at 0, 40, and 80 mg/ha biosolids application.
The successful and promising revegetation results from this Colorado study increased interest in additional research for this biosolids application in other parts of the United States, such as in Southern California at the site of the Woolsey Fire.
Case Study – An Assessment of Runoff from Fire Damaged Lands Amended with Biosolids (Las Virgenes Municipal Water District Composting Facility)
In November 2018, the Woolsey Fire burned 39,000 hectares of California land starting in Los Angeles County and spreading north to Ventura County. Vegetative areas were completely burned, and some areas did not improve even after the wet weather season. The Las Virgenes Municipal Water District Composting Facility, located in the City of Calabasas, was also impacted by the Woolsey Fire which left significant burn scars on the property. Due to the convenient location of having biosolids onsite as well as burned vegetative engineered slopes on the property (shown in Figure 3), runoff experiments and chemical analyses were conducted after a single application of three types of biosolids to the fire damaged area. The three types of biosolids used in the experiment were: Class A compost (from Triunfo Sanitation District), Class B anaerobically digested cake (from Tapia WWTP), and Class A heat dried pellets (from City of Corona WWTP).
Figure 3. Vegetative Slopes (Treatment Plots) Used for Experiments. Source: CASA – An Assessment of Runoff from Fire Damaged Lands Amended with Biosolids.
In September 2019, the three types of biosolids were applied in a layer approximately 7.5 centimeters deep. Each treatment plot had three replicates for a total of 12 treatment plots (including three untreated control plots). Each plot was one meter wide and three meters long with an open-top pipe installed at the bottom of each plot to catch and collect the runoff water. Runoff was collected immediately after rain events over two years between 2019 and 2021. Runoff samples were analyzed for several water quality parameters by the City of Los Angeles Bureau of Sanitation (LA San) laboratory.
Based on visual observation, Class A compost and Class B cake encouraged rapid revegetation compared to Class A pellets and control plots. In addition, qualitative runoff results showed a dramatic decrease in runoff for Class A compost followed by Class B cake. It was reported that Class A heat-dried pellets had highly variable results, which may have been due to the observation that the pellets would roll off the sloped plots.
Both of these case studies demonstrate the benefits of using biosolids for revegetation and improving soil health in fire-impacted lands.
Additional links to fire-damaged land restoration trials are available in CASA’s biosolids resources page at https://casaweb.org/renewable-resources/biosolids/.
References
Meyer, V. F., Redente, E. F., Barbarick, K. A., Brobst, R. B., Paschke, M. W., & Miller, A. L. Plant and Soil Responses to Biosolids Application following Forest Fire. Journal of Environmental Quality, 33(3), 873–881. https://doi.org/10.2134/jeq2004.0873.
Meyer, V. F., Redente, E. F., Barbarick, K. A., & Brobst, R. (2001). Biosolids Applications Affect Runoff Water Quality following Forest Fire. Journal of Environmental Quality, 30(5), 1528–1532. https://doi.org/10.2134/jeq2001.3051528x
Kester, Greg (CASA); Allen, Harry (U.S. EPA); Crohn, David (UC Riverside); Hurtado, Veronica (Las Virgenes Municipal Water District); Change, Susan (Los Angeles City Bureau of Sanitation); Hutton, Matthew (Los Angeles County Sanitation District). California Association of Sanitation Agencies. An Assessment of Runoff from Fire Damaged Lands Amended with Biosolids. https://casaweb.org/wp-content/uploads/2024/09/9-11-24-Biosolids-Fire-Reclamation-Paper-FINAL.pdf