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CURATOR
A pinboard by
Mengran Yu

Ph.D. Student, The University of Sydney

PINBOARD SUMMARY

Use SWAT model test fire effect on water quality.

Wild fire can effect the hydrological cycle of forested water catchments, both in terms of quantity and quality of the stream water. Two major reasons for this are the effect that wildfire has on surface vegetation and soil organic carbon content. A reduction in surface vegetation effects catchment evapotranspiration, increase erosion and runoff. Another important but less studied fire effect is the reduction of soil organic carbon content. The soil surface and organic layer are important sources of nutrients and help maintain soil structure, and any reduction can make soil more easily eroded and able to hold less water.. In this study we use the SWAT (soil and water assessment tool) hydrological model to assess the individual and combined effects of each on stream water quantity and quality. The case study is the 2002/2003 wildfires around Sydney, New South Wales. Five catchments were used to calibrate the SWAT model with 10 years’ pre-fire water quantity and quality data and simulations were then performed for 10 years’ post-fire period. The fire severity, and impact on surface vegetation, of these burnt catchments were estimated based on the difference between pre-fire and post-fire Landsat images. This was used to modify the land use layer to predict the land use change effect. To investigate the effect of soil carbon change, we first tested the fire effect on soil carbon from 80 prescribed burnt sites in NSW, where pre-fire and post fire soil organic carbon content was measured. In addition at each site the burn severity was calculated based on Landsat images. The soil carbon change was modelled based on particle size fraction and fire severity were calculated; which then enable mapping of soil carbon change for each of the study catchments. Then 3 model variants were run (i) modified land use layer (ii) modified soil carbon layer (iii) both (i) and (ii). The flow and TSS output from these modified models were extracted and compared with the original calibrated models’ water quality output and then, the results were compared with the observed post-fire water quality data. The results will enable quantification of the sensitivity of SWAT to changes in vegetation cover and soil carbon due to fire, both of which were quantified based on empirical data.

5 ITEMS PINNED

Medium-term dynamics of soil respiration in a Mediterranean mountain ecosystem: The effects of burn severity, post-fire burnt-wood management, and slope-aspect

Abstract: The interaction between burn severity and subsequent post-fire logging practices may exert a direct effect on soil respiration (SR) in recently burnt stands. This effect is associated with the modification of microclimatic conditions, soil carbon inputs, and the decay rates of woody detritus. In addition, slope aspect may determine SR rates by modifying the microclimatic conditions in post-fire environments. In this study, we assessed the changes in SR rates during the early (1.5–4 years) post-fire stages in a burnt and logged Spanish Black pine forest along a burn-severity gradient: (1) an unburnt site (UB), (2) a low burn-severity site (LS), (3) a south-facing high burn-severity site (HSS), and (4) a north-facing high burn-severity site (HSN). Monthly or fortnightly manual SR measurements (SRM) were taken at midday between 2011 and 2013. In addition, we also quantified the litter layer and fine-root biomass at each site. Multiple regression models combining abiotic (both soil temperature and water content, Ts and SWC, respectively) and biotic (tree diameter at breast height, 1.30 m) were used for midday SRM modelling. For temporal and spatial scaling of SR at the stand-level, we performed 8 seasonal campaigns of automated SR measurements (SRA) along 4 linear gradients from trees or stumps to inter-tree/stump gaps with the aim of: (1) determining the main soil-surface areas (soil close to trees or stumps and/or soil away from them; SC and SA soil, respectively) and (2) correcting the modelled daily daytime and night-time SRM rates.

Pub.: 03 Dec '16, Pinned: 30 Aug '17

Effect of fire disturbance on active organic carbon of Larix gmelinii forest soil in Northeastern China

Abstract: Abstract Active organic carbon in soil has high biological activity and plays an important role in forest soil ecosystem structure and function. Fire is an important disturbance factor in many forest ecosystems and occurs frequently over forested soils. However, little is known about its impact on soil active organic carbon (SAOC), which is important to the global carbon cycle. To investigate this issue, we studied the active organic carbon in soils in the Larix gmelinii forests of the Da Xing’an Mountains (Greater Xing’an Mountains) in Northeastern China, which had been burned by high-intensity wildfire in two different years (2002 and 2008). Soil samples were collected monthly during the 2011 growing season from over 12 sample plots in burned and unburned soils and then analyzed to examine the dynamics of SAOC. Our results showed that active organic carbon content changed greatly after fire disturbance in relation to the amount of time elapsed since the fire. There were significant differences in microbial biomass carbon, dissolved organic carbon, light fraction organic carbon, particulate organic carbon between burned and unburned sample plots in 2002 and 2008 (p < 0.05). The correlations between active organic carbon and environmental factors such as water content, pH value and temperature of soils, and correlations between each carbon component changed after fire disturbance, also in relation to time since the fire. The seasonal dynamics of SAOC in all of the sample plots changed after fire disturbance; peak values appeared during the growing season. In plots burned in 2002 and 2008, the magnitude and occurrence time of peak values differed. Our findings provide basic data regarding the impact of fire disturbance on boreal forest soil-carbon cycling, carbon-balance mechanisms, and carbon contributions of forest ecosystem after wildfire disturbance.AbstractActive organic carbon in soil has high biological activity and plays an important role in forest soil ecosystem structure and function. Fire is an important disturbance factor in many forest ecosystems and occurs frequently over forested soils. However, little is known about its impact on soil active organic carbon (SAOC), which is important to the global carbon cycle. To investigate this issue, we studied the active organic carbon in soils in the Larix gmelinii forests of the Da Xing’an Mountains (Greater Xing’an Mountains) in Northeastern China, which had been burned by high-intensity wildfire in two different years (2002 and 2008). Soil samples were collected monthly during the 2011 growing season from over 12 sample plots in burned and unburned soils and then analyzed to examine the dynamics of SAOC. Our results showed that active organic carbon content changed greatly after fire disturbance in relation to the amount of time elapsed since the fire. There were significant differences in microbial biomass carbon, dissolved organic carbon, light fraction organic carbon, particulate organic carbon between burned and unburned sample plots in 2002 and 2008 (p < 0.05). The correlations between active organic carbon and environmental factors such as water content, pH value and temperature of soils, and correlations between each carbon component changed after fire disturbance, also in relation to time since the fire. The seasonal dynamics of SAOC in all of the sample plots changed after fire disturbance; peak values appeared during the growing season. In plots burned in 2002 and 2008, the magnitude and occurrence time of peak values differed. Our findings provide basic data regarding the impact of fire disturbance on boreal forest soil-carbon cycling, carbon-balance mechanisms, and carbon contributions of forest ecosystem after wildfire disturbance.Larix gmeliniip

Pub.: 07 Jan '17, Pinned: 30 Aug '17

Regional patterns of postwildfire streamflow response in the Western United States: The importance of scale-specific connectivity

Abstract: Wildfires can impact streamflow by modifying net precipitation, infiltration, evapotranspiration, snowmelt, and hillslope run-off pathways. Regional differences in fire trends and postwildfire streamflow responses across the conterminous United States have spurred concerns about the impact on streamflow in forests that serve as water resource areas. This is notably the case for the Western United States, where fire activity and burn severity have increased in conjunction with climate change and increased forest density due to human fire suppression. In this review, we discuss the effects of wildfire on hydrological processes with a special focus on regional differences in postwildfire streamflow responses in forests. Postwildfire peak flows and annual water yields are generally higher in regions with a Mediterranean or semi-arid climate (Southern California and the Southwest) compared to the highlands (Rocky Mountains and the Pacific Northwest), where fire-induced changes in hydraulic connectivity along the hillslope results in the delivery of more water, more rapidly to streams. No clear streamflow response patterns have been identified in the humid subtropical Southeastern United States, where most fires are prescribed fires with a low burn severity, and more research is needed in that region. Improved assessment of postwildfire streamflow relies on quantitative spatial knowledge of landscape variables such as prestorm soil moisture, burn severity and correlations with soil surface sealing, water repellency, and ash deposition. The latest studies furthermore emphasize that understanding the effects of hydrological processes on postwildfire dynamic hydraulic connectivity, notably at the hillslope and watershed scales, and the relationship between overlapping disturbances including those other than wildfire is necessary for the development of risk assessment tools.

Pub.: 01 Jun '17, Pinned: 30 Aug '17

Groundwater connectivity controls peat burn severity in the boreal plains

Abstract: Wildfire is the largest disturbance affecting peatland ecosystems and can typically result in the combustion of 2–3 kg C m−2 of near‐surface peat. We hypothesized that organic soil burn severity, as well as the associated carbon emissions, varies significantly as a function of hydrogeological setting due to groundwater impacts on peat bulk density and moisture content. We measured depth of burn (DOB) in three peatlands located along a hydrogeological and topographic gradient in Alberta's Boreal Plains. Peatland margins across all hydrogeological settings burned significantly deeper (0.245 ± 0.018 m) than peatland middles (0.057 ± 0.002 m). Further, hydrogeological setting strongly impacted DOB. A bog with an ephemeral groundwater connection in a coarse‐textured glaciofluvial outwash experienced the greatest DOB at its margins (0.514 ± 0.018 m) due to large water table fluctuations, while a low‐lying oligotrophic groundwater flow‐through bog in a coarse‐textured glaciofluvial outwash experienced limited water table fluctuations and had the lowest margin burn severity (0.072 ± 0.002 m). In an expansive peatland in a lacustrine clay plain, DOB at the margins bordering an isolated domed bog portion (0.186 ± 0.003 m, range: 0.0–0.748 m) was considerably greater than the DOB observed at fen margins with a longer groundwater flow path (<0.05 m). Our research indicates that groundwater connectivity can have a dominant control on soil carbon combustion across and within hydrogeological settings. We suggest that hydrogeological setting be used to identify potential deep burning ‘hotspots’ on the landscape to increase the efficacy of wildfire management and mitigation strategies. Copyright © 2015 John Wiley & Sons, Ltd.

Pub.: 30 Jul '15, Pinned: 30 Aug '17

Wildfire effects on carbon and nitrogen in inland coniferous forests

Abstract: A ponderosa pine/Douglas-fir forest (Pinus ponderosa Dougl., Pseudotsuga menziesii (Mirb.) Franco; PP/DF) and a lodgepole pine/Engelmann spruce forest (Pinus contorta Loud., Picea engelmannii Parry ex Engelm.; LP/ES) located on the eastern slopes of the Cascade Mountains in Washington state, USA, were examined following severe wildfire to compare total soil carbon and nitrogen capitals with unburned (control) forests. One year after fire, the average C content (60 cm depth) of PP/DF and LP/ES soil was 30% (25 Mg ha-1) and 10% (7 Mg ha-1) lower than control soil. Average N content on the burned PP/DF and LP/ES plots was 46% (3.0 Mg ha-1) and 13% (0.4 Mg ha-1) lower than control soil. The reduction in C and N in the PP/DF soil was largely the result of lower nutrient capitals in the burned Bw horizons (12–60 cm depth) relative to control plots. It is unlikely that the 1994 fire substantially affected nutrient capitals in the Bw horizons; however, natural variability or past fire history could be responsible for the varied nutrient capitals observed in the subsurface soils. Surface erosion (sheet plus rill) removed between 15 and 18 Mg ha-1 of soil from the burned plots. Nutrient losses through surface erosion were 280 kg C ha-1 and 14 kg N ha-1 in the PP/DF, whereas LP/ES losses were 640 and 22 kg ha-1 for C and N, respectively. In both forests, surface erosion of C and N was ∼1% to 2% of the A-horizon capital of these elements in unburned soil. A bioassay (with lettuce as an indicator plant) was used to compare soils from low-, moderate- and high-severity burn areas relative to control soil. In both forests, low-severity fire increased lettuce yield by 70–100% of controls. With more severe fire, yield decreased in the LP/ES relative to the low-intensity burn soil; however, only in the high-severity treatment was yield reduced (14%) from the control. Moderate- and high-severity burn areas in the PP/DF were fertilized with ∼56 kg ha-1 of N four months prior to soil sampling. In these soils, yield was 70–80% greater than the control. These results suggest that short-term site productivity can be stimulated by low-severity fire, but unaffected or reduced by more severe fire in the types of forests studied. Post-fire fertilization with N could increase soil productivity where other environmental factors do not limit growth.

Pub.: 01 Feb '99, Pinned: 30 Aug '17