Assessment of the impact of soil heating on soil cations using the degree-hours method .

Abstract

Important factors in the evaluation of fire severity are the duration of the soil exposition to a certain temperature as well as the factors that determine the thermal transmissivity on the soil (moisture, texture, organic matter content, etc.). The aim of this work was to apply the degree-hours method (DH) to characterize the thermal impact of forest fires in soils. Thermal treatments in the laboratory were conducted using soil samples in order to study the effects in the soil exchange complex. The results showed the effect of the supplied degree-hour (DH) on the cation exchange capacity (CEC), which was expressed by a continuous exponential decrease in the CEC. This function may better explain the process of the decreasing of CEC than only the maximum temperature values. The sum of cations extracted in relation to the thermal treatment gradually increased with temperature or DH, and tended to stabilize at high values. The concentration of the different cations extracted increased gradually with the intensity of heating, and when related to the DH appeared to fit an equation of the type y=a+bx<sup>c </sup>with a high degree of confidence. Analyses of the results show that the measurement of the heat supplied to the soil is a useful parameter with which to interpret pedologic changes, especially when those changes happen continuously over time.

A review of simulation experiment techniques used to analyze wildfire effects on water quality and supply

“…Following are the definitions for wildfire intensity and wildfire severity as used in this review, as well as other relevant wildfire and rainfall simulation terms. Wildfire Intensity: is typically a quantitative characterization of energy, such as the amount of fuel burned (e.g., units of g), the rate of fuel burned (e.g., units of g/s or W/m2) 22,51 , or peak temperature (e.g., units of °C) 24,48,49,[52][53][54] . This allows for explicit…”

“…Propane torches typically produce peak soil surface temperatures of 500-600°C 54,61 whereas heat lamps produce peak temperatures of 200-400°C 90 from 5 to up to 220 minutes of exposure 54,61 , representing a range in burn intensities. The temperature gradient extending down through the soil surface in these experiments is typically measured using thermocouples placed 0-15 cm below the soil surface 22,24,29,54,61,103 . Studies reported a wide range of significant responses to burning: soil and water chemical constituents increased or decreased ~10-700% and hydraulic and water repellent properties changed by ~60-200% at ~1-3 increments of burn intensities each 62,89,121 .…”

“…Control over duration of heating (WP6) is an attribute of propane torches and heat lamps, as well as muffle furnaces. This allows for further control and precision of burn intensitysometimes characterized by burn duration 24 . Incremental control over burn intensity (WP7) is a benefit unique to muffle furnaces.…”

“…Limited information exists about post-wildfire water quality response, in particular, with most studies primarily focusing on DOM and nutrients-leaving the responses of microbial constituents and more novel contaminants largely unknown 23 . Laboratory-and plot-scale simulation experiments which replicate burning and combustion mechanisms present in natural wildfires, as well as raindrop kinetic energies and leaching effects similar to post-wildfire precipitation, offer an alternative analytical technique for estimating wildfire effects on water quality and supply 2,7,[24][25][26][27][28] . Hereafter, these two types of simulation experiments will be referred to as wildfire and rainfall simulators, respectively.…”

“…The controlled setting of these simulation experiments can overcome logistical issues associated with in situ studies, as well as provide insight into regionally-specific drivers by allowing for more precise attribution of responses to controls. However, this type of analysis also presents new limitations including dissimilarities to natural settings and difficulties in upscaling results to the catchment scale 24,29 .…”