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Impacts of wildfires and retardants on surface water quality




Morgensen, Brent D., author
Omur-Ozbek, Pinar, advisor
Carlson, Ken, committee member
Stednick, John, committee member

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Wildfire retardant is one of the most beneficial tools used to prevent the spread of wildfire, yet its presence has been found to be of big concern when dropped into aquatic habitats. Many retardants are composed mainly of ammonium and phosphates, which can lead to troubles with eutrophication and fish kills at high doses. Iron is often included to help with the identification of retardant drops, but can result in aesthetic issues when gotten into waterways. Despite the risks associated with its use, retardant is still a needed tool to help reduce the spread of wildfire and the effects of wildfire on the increase of organics, nutrients, and metals into waters. This study aims to quantify the effects of wildfire and wildfire retardant on the quality of surface waters. A rainfall simulation was performed on soil plots to observe the influence of wildfire and wildfire retardant on the quality of runoff using Phos-Chek® LC-95A retardant. Soil plots were collected from a tallgrass prairie in Pingree, CO and plots were modified to simulate rainfall over unburned plots without retardant (Uwo), unburned plots with retardant (Uw), burned plots without retardant (Bwo), and burned plots with retardant (Bw). A Norton Ladder Type Rainfall Simulator was used to simulate rainfall over the plots at 165 mm/hr for 15 min and the runoff was collected and analyzed for ammonia, orthophosphate (Pi), Fe, and TOC immediately following the experiment. The experiment was performed on 3 consecutive days and the entire process of the experiment was performed on the same plots 2 months after the first set of runs. Retardant use showed a significant increase in nutrient and iron concentrations for unburned plots, while a significant increase was found for Pi concentrations in burned plots. Burned plots showed a noticeable increase in TOC compared to unburned plots, but retardant showed no influence on either. The second part of this study analyzed the leachate from soils collected from the burn area of the Royal Gorge on 3 separate occasions. Samples were collected from Uwo, Uw, Bwo, and Bw sites, as well as an unburned site with a high application of retardant (UwH). Nutrients and Fe were found to increase noticeably from Uwo to Uw + UwH soil, while ammonia was generally found to be higher in Bw than Bwo. Retardant was found to have no noticeable influence on TP and Fe in the first analysis, but Bw was found to show lesser concentrations than Bwo as the analyses carried on. Concentrations of Mn were generally less in Bw than Bwo for all of the analyses. These results show that concern is warranted when retardant is dropped near waterways.


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water quality


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