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We examined the responses of suspended solids to forest thinning in steep small headwater catchments, PT (0.8 ha) and PR (0.7 ha), that drain a Korean pine (Pinus koraiensis) plantation forest. Based on a paired-catchment design, the relationship between total suspended solids (TSS) and the time differential of water runoff (dQ/dt) indicated a difference in the characteristics of TSS in the rising and falling stages within the initial two years after forest thinning. The relatively high initial TSS responded to the concentration-based first flush criterion in the early stage of the rainfall event concentrated in this initial period after the thinning. The rate of TSS event loads in the PT catchment was 4.3-fold greater than that in the PR catchment within the initial two years after forest thinning. This was induced by the low disturbance of soil surface by forest workers using chainsaws and non-heavy machinery. Three years later, the TSS event loads in the PT catchment appeared to decrease due to trapping and settling by protective vegetation. Therefore, mitigating accelerated TSS events during forest thinning requires appropriate site-specific land preparation, particularly for improving stream water quality in forested catchments. [ABSTRACT FROM AUTHOR]

Changes in water quality were examined during selected rainfall events in a headwater stream severely damaged by a forest fire on 21–23 February 2021. Seven water quality parameters were analyzed: pH, electrical conductivity, biochemical oxygen demand, chemical oxygen demand, total suspended solids (TSS), total nitrogen, and total phosphorous. First-flush effect and event mean concentration analyses were conducted in spring (dry season) and summer (wet season) immediately after the forest fire. In spring, the non-biodegradable organic matter concentrations increased along with pollutants related to ash-enhanced soil water repellency in water affected by first-flush effects. In summer, TSS and nutrient concentrations increased along with pollutants related to fire-induced soil surface disturbances after a series of rainfall events. First-flush analyses indicated that cumulative pollutant loads were greater in the spring than in the summer due to a higher concentration of forest fire ash in the early storm runoff immediately after the forest fire. The event mean concentrations revealed that pollutant loads were associated with both forest fire ash and storm events in the immediate post-fire period. Therefore, this study indicated that water quality along a headwater stream is affected by short-term effects of large and intense forest fires and rainfall seasonality. [ABSTRACT FROM AUTHOR]