Assessment of the Decadal Impact of Wildfire on Water Quality in Forested Catchments

Mengran Yu,Floris Van Ogtrop,Thomas Bishop

doi:10.3390/w11030533

Abstract

Wildfire can have significant impacts on hydrological processes in forested catchments, and a key area of concern is the impact upon water quality, particularly in catchments that supply drinking water. Wildfire effects runoff, erosion, and increases the influx of other pollutants into catchment waterways. Research suggests that suspended sediment and nutrient levels increase following wildfire. However, past studies on catchment water quality change have generally focused on the short term (1–3 years) effects of wildfire. For appropriate catchment management, it is important to know the long-term effect of wildfire on catchment water quality and the recovery process. In this study, a statistical analysis was performed to examine the effect of 2001/2002 Sydney wildfire on catchment water quality. This research is particularly important, since the catchments studied provide drinking water to Sydney. Linear mixed models were used in this study in an analysis of covariance (ANCOVA)-type change detection approach to assess the effect of wildfire. We used both burnt and unburnt catchments to aid the interpretation of the results and to help disentangle the effects of natural climate variation, as well as of the wildfire. The results of this study showed persistent long-term (10-year) effects of wildfire, including increases in total suspended sediment concentrations (64% higher than in unburnt catchments), total nitrogen concentrations (48% higher), and total phosphorus (40% higher).

Highlights

Wildfire can have a significant impact on the hydrologic cycle of forested catchments due to changes in the surface vegetation and canopy cover, combined with ash sealing of soil pores [1,2].This is of particular concern for water quality (WQ) in forested catchments [3,4], as in many cases these catchments supply drinking water to urban communities [5]
The number of observations for WQ data is limited to around one per month; 200–300 observations are available for each catchment during both the pre-wildfire and post-wildfire period
For catchment B1, because most available data were collected before 2007, this might have resulted in a higher maximum and mean total suspended sediment (TSS) value in this catchment because the catchment has had less time to recover during the post-wildfire period

Summary

Introduction

Wildfire can have a significant impact on the hydrologic cycle of forested catchments due to changes in the surface vegetation and canopy cover, combined with ash sealing of soil pores [1,2]. This is of particular concern for water quality (WQ) in forested catchments [3,4], as in many cases these catchments supply drinking water to urban communities [5]. Suspended sediment and nutrients (phosphorus and nitrogen) are two important measures of catchment water quality [10]. Increases in total phosphorus (TP) and total nitrogen (TN) levels can result in excessive algal growth [12]

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Conclusion