Available at: https://digitalcommons.calpoly.edu/theses/3251
Date of Award
3-2026
Degree Name
MS in Environmental Sciences and Management
Department/Program
Earth and Soil Sciences
College
College of Agriculture, Food, and Environmental Sciences
Advisor
Stewart Wilson
Advisor Department
Earth and Soil Sciences
Advisor College
College of Agriculture, Food, and Environmental Sciences
Abstract
Between 1992 and 2012, 84% of all documented wildfires were started by humans. These fires often start around high-risk locations such as power lines and roadsides where fuel loads are near these potential human-caused ignition sources. Point source ignition sites that are surrounded by shrubs or grasslands are especially important because fires that occur within these biomes are responsible for far more destruction of property than forest fires. One strategy that is effective at mitigating the spread of fires from ignition sites that are within grassland or shrub biomes are preventative fire-retardant products (PFRPs). These PFRPs differ from traditional fire-retardant products in that they are preventative measures and can be applied annually to potential ignition sources and vulnerable assets. While these PFRPs are an important tool in mitigating the risk of wildfires, the environmental repercussions of sustained PFRP applications remain poorly understood. Our study aims to investigate the impact of repeated PFRP applications on soil-water chemistry.
Our study examined the effects of applying two different PFRPs over the course of two consecutive summers on soil water chemistry. A MgCl2 and a NH4(PO3)n-based PFRP were applied at three rates: control, low (7.9 liters/ 9.3 m2) and high (15.8 liters/ 9.3 m2), across two sites, in a randomized complete block design . Lysimeters installed to a depth of 56 cm within each plot enabled the collection of water samples. Samples were collected every two weeks during the wet seasons of 2023-2024 and 2024-2025. Samples were analyzed for Mg2+, P, NO3-, NH4+, and electrical conductivity. Our research found that there was no significant effect on the cumulative concentrations of NO3- or NH4+ in soil water at either rate of application for both PFRPs for both years of the study. An increase in the cumulative concentration of P was found for plots treated with the high rate of the NH4(PO3)n-based PFRP after the second year of application. Mg2+ and electrical conductivity were elevated in plots treated with the high rate of the MgCl2-based PFRP after the first and second year of treatment.
Before committing to the widespread annual application of PRFP, stakeholders must grasp the potential environmental impacts. Our study aims to provide critical insights into sub-surface water and soil health, empowering stakeholders, policymakers, and regulators to make well-informed decisions regarding the utilization of these products.