Effect of soil water-repellent layer depth on post-wildfire hydrological processes     

Jingjing Chen  Kevin J. McGuire  Ryan D. Stewart 《水文研究》2020,34(2):270-283

Soil water repellency induced by wildfires can alter hydraulic properties and hydrologic processes; however, the persistence and vertical position (i.e., depth) of water-repellent layers can vary between systems and fires, with limited understanding of how those variations affect infiltration processes. This study occurred in two forested locations in the south-central Appalachian Mountains that experienced wildfires in late 2016: Mount Pleasant Wildfire Refuge, Virginia, and Chimney Rock State Park, North Carolina. In each location, sites were selected to represent unburned conditions and low to moderate burn intensities. At each site, we measured the soil water repellency at the surface (ash layer or O horizon) and ~2 cm below the surface (A horizon) using the water drop penetration time method (n = 10–14). Soil water content was also measured over the upper 10 cm of the soil (n = 10), and infiltration tests were conducted using a tension infiltrometer (n = 6–8). The results showed that soil repellency was highest in the surface layer at the Mount Pleasant location and was highest in the subsurface layer at the Chimney Rock location. Soil water content was lower in unburned soil than in burned soil, especially for measurements taken immediately postfire, with soil water content negatively correlated with water repellency. Water repellency in the surface layer significantly reduced relative infiltration rates (estimated as differences between initial and steady-state rates), whereas subsurface water repellency did not affect relative infiltration. As a result, water repellency persisted longer in sites with surface as opposed to subsurface water repellency. Finally, differences between burned and unburned sites showed that although the wildfires increased the occurrence of water repellency, they did not alter the underlying relationship between relative infiltration and water repellency of the surface soil.  相似文献   

Dissolved organic matter dynamics during the spring snowmelt at a boreal river valley mire complex in Northwest Russia          下载免费PDF全文

Armine Avagyan  Benjamin R. K. Runkle  Nina Hennings  Hannes Haupt  Tarmo Virtanen  Lars Kutzbach 《水文研究》2016,30(11):1727-1741

Boreal mire landscapes are rich in soil carbon and significantly contribute to the carbon input of aquatic ecosystems. They are composed of different mesoscale ecohydrological subunits, whose individual contributions to the water and carbon export of mire catchments are not well understood. The spring snowmelt period is the major hydrological event in the annual water cycle of the boreal regions and strongly influences the carbon flux between the terrestrial and aquatic systems. The aim of this study was (1) to provide a conceptual understanding of the spatial and temporal dynamics of the surface water chemistry along a swamp forest‐fen‐bog gradient during the snowmelt period, (2) to quantify the exported dissolved organic carbon (DOC) content in the runoff and (3) to identify the ecohydrological landscape unit that contributes most to DOC export during the snowmelt period in a heterogeneous mire complex in Northwest Russia. The highest DOC concentrations were detected in the swamp forest, and the lowest concentrations were observed at the treeless bog by the end of the snowmelt period (swamp forest: 37–43 mg l^?1, bog: 13–17 mg l^?1). During the spring snowmelt period, a significant amount (~1.7 g C m^?2) of DOC was transferred by the ~74 mm of runoff from the catchment into the river. Variability in the thawing periods led to differences in the relative contributions of each ecohydrological zone to the carbon export measured at a stream channel draining the studied part of the mire complex. An increased understanding of the variation in DOC concentrations and contributions from the mesoscale ecohydrological subunits to carbon export can help to predict the potential regional loss of DOC based on land cover type under climate change. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Securing the climate benefits of stable forests     

Jason M. Funk  William Baldwin-Cantello  Jonah Busch  Evgeny Chuvasov  Tom Evans 《Climate Policy》2019,19(7):845-860

Stable forests – those not already significantly disturbed nor facing predictable near-future risks of anthropogenic disturbance – may play a large role in the climate solution, due to their carbon sequestration and storage capabilities. Their importance is recognized by the Paris Agreement, but stable forests have received comparatively little attention through existing forest protection mechanisms and finance. Instead, emphasis has been placed on targeting locations where deforestation and forest degradation are happening actively. Yet stopping deforestation and forest degradation does not guarantee durable success, especially outside the geographic scope of targeted efforts. As a result, today’s stable forests may be at risk without additional efforts to secure their long-term conservation.

We synthesize the gaps in existing policy efforts that could address the climate-related benefits derived from stable forests, noting several barriers to action, such as uncertainty around the level of climate services that stable forests provide and difficulties describing the real level of threat posed. We argue that resource and finance allocation for stable forests should be incorporated into countries’ and donors’ comprehensive portfolios aimed at tackling deforestation and forest degradation as well as resulting emissions. A holistic and forward-looking approach will be particularly important, given that success in tackling deforestation and forest degradation where it is currently happening will need to be sustained in the long term.

Key policy insights

• Climate policies, finance, and implementation have tended to focus on areas of recent forest loss and near-term threats of anthropogenic disturbance, resulting in an imbalance of effort that fails to adequately address stable forests.

• In some contexts, policy measuresintended to secure the climate-related benefits of stable forests have competed poorly against more urgent threats. Policymakers and finance mechanisms should view stable forests as a complementary element within a holistic, long-term approach to resource management.

• International mechanisms and national frameworks should be adjusted and resourced to promote the long-term sustainability and permanence of stable forests.

• Beyond additional resources, the climate benefits of stable forests may be best secured by pro-actively designing implementing policies that recognize the rights and interests of stakeholders who are affected by land management decisions.

  相似文献   

Relevance of airborne lidar and multispectral image data for urban scene classification using Random Forests   总被引：3，自引：0，他引：3  

Li GuoNesrine Chehata  Clément MalletSamia Boukir 《ISPRS Journal of Photogrammetry and Remote Sensing》2011,66(1):56-66

Airborne lidar systems have become a source for the acquisition of elevation data. They provide georeferenced, irregularly distributed 3D point clouds of high altimetric accuracy. Moreover, these systems can provide for a single laser pulse, multiple returns or echoes, which correspond to different illuminated objects. In addition to multi-echo laser scanners, full-waveform systems are able to record 1D signals representing a train of echoes caused by reflections at different targets. These systems provide more information about the structure and the physical characteristics of the targets. Many approaches have been developed, for urban mapping, based on aerial lidar solely or combined with multispectral image data. However, they have not assessed the importance of input features. In this paper, we focus on a multi-source framework using aerial lidar (multi-echo and full waveform) and aerial multispectral image data. We aim to study the feature relevance for dense urban scenes. The Random Forests algorithm is chosen as a classifier: it runs efficiently on large datasets, and provides measures of feature importance for each class. The margin theory is used as a confidence measure of the classifier, and to confirm the relevance of input features for urban classification. The quantitative results confirm the importance of the joint use of optical multispectral and lidar data. Moreover, the relevance of full-waveform lidar features is demonstrated for building and vegetation area discrimination.  相似文献   

万木林青年和老龄常绿阔叶林乔木层碳贮量分配特征     

黄蓉  王超  杨智杰  陈光水 《福建地理》2011,(2):29-35

了解森林生物量碳分配特征,对于森林碳贮量和碳汇估算、森林碳汇经营和生物多样性保护有重要意义.本课题选择福建省万木林自然保护区青年(约47 a生)和老龄(约120 a生)常绿阔叶林为研究对象,根据生物多样性调查结果和生物量异速方程,计算乔木层生物量碳贮量,并分析其高度级、径级和树种间的分配特征.结果表明:1)青年林碳贮量为115.03 t.hm-2,老龄林碳贮量为224.43 t.hm-2;2)青年林最大碳贮量出现在高度级Ⅶ级(15～17 m),为23.17 t.hm-2,而老年林最大碳贮量出现在高度级Ⅷ级(17～19 m),为62.96 t.hm-2;3)青年林中Ⅵ级(15 cm≤DBH<17 cm)的碳贮量最高,为34.25 t.hm-2,占总碳贮量的29.77%;在老龄林中最高碳贮量集中在XIX级(DBH≥41 cm),为60.03t.hm-2,占总碳贮量的26.78%;4)2个林分绝大部分碳贮量都集中在少数树种,大多数物种对碳贮量的贡献很微小.  相似文献   

Devonian formations,vertebrate faunas and age control on the far south coast of New South Wales and adjacent Victoria     

G. C. Young 《Australian Journal of Earth Sciences》2013,60(7):991-1008

A diverse fossil vertebrate record in the Devonian of coastal southeastern Australia includes at least 30 genera and species representing all three major groups of extant jawed vertebrates (bony and cartilaginous fishes, and tetrapods), and both extinct groups (placoderm and acanthodian fishes). A bone recorded by W. B. Clarke in 1860 from Twofold Bay is the first published record of a Devonian vertebrate from the Southern Hemisphere. Abundant plant remains at some localities include large impressions of arborescent lycopsids, indicating one of the earliest forest environments for the Gondwana supercontinent. An early terrestrial invertebrate fauna is evidenced by fossil millipede remains. A review of the evidence for age control using paleontology and isotopic dating suggests that the lower part of the Devonian sequence (Bunga beds, Boyd Volcanic Complex) may be somewhat older (Emsian – Eifelian) than recently proposed; the tetrapod trackways at Genoa River in Victoria (lower part of the Combyingbar Formation) may correlate with the lowermost Twofold Bay Formation of the Merrimbula Group, which is overlain by the marine Bellbird Creek Formation, a manifestation of the global late Frasnian marine transgression and extinction event. Abundant placoderm remains at all higher fossil fish horizons in the overlying Worange Point Formation indicate a latest Devonian rather than Carboniferous age for the upper Merrimbula Group.  相似文献   

Evaluation of storage–discharge relationships and recession analysis-based distributed hourly runoff simulation in large-scale,mountainous and snow-influenced catchment     

Teklu T. Hailegeorgis  Knut Alfredsen  Yisak S. Abdella  Sjur Kolberg 《水文科学杂志》2013,58(16):2872-2886

ABSTRACT

Evaluation of a recession-based “top-down” model for distributed hourly runoff simulation in macroscale mountainous catchments is rare in the literature. We evaluated such a model for a 3090 km² boreal catchment and its internal sub-catchments. The main research question is how the model performs when parameters are either estimated from streamflow recession or obtained by calibration. The model reproduced observed streamflow hydrographs (Nash-Sutcliffe efficiency up to 0.83) and flow duration curves. Transferability of parameters to the sub-catchments validates the performance of the model, and indicates an opportunity for prediction in ungauged sites. However, the cases of parameter estimation and calibration excluding the effects of runoff routing underestimate peak flows. The lower end of the recession and the minimum length of recession segments included are the main sources of uncertainty for parameter estimation. Despite the small number of calibrated parameters, the model is susceptible to parameter uncertainty and identifiability problems.