Quantifying and relating land-surface and subsurface variability in permafrost environments using LiDAR and surface geophysical datasets

The value of remote sensing and surface geophysical data for characterizing the spatial variability and relationships between land-surface and subsurface properties was explored in an Alaska (USA) coastal plain ecosystem. At this site, a nested suite of measurements was collected within a region where the land surface was dominated by polygons, including: LiDAR data; ground-penetrating radar, electromagnetic, and electrical-resistance tomography data; active-layer depth, soil temperature, soil-moisture content, soil texture, soil carbon and nitrogen content; and pore-fluid cations. LiDAR data were used to extract geomorphic metrics, which potentially indicate drainage potential. Geophysical data were used to characterize active-layer depth, soil-moisture content, and permafrost variability. Cluster analysis of the LiDAR and geophysical attributes revealed the presence of three spatial zones, which had unique distributions of geomorphic, hydrological, thermal, and geochemical properties. The correspondence between the LiDAR-based geomorphic zonation and the geophysics-based active-layer and permafrost zonation highlights the significant linkage between these ecosystem compartments. This study suggests the potential of combining LiDAR and surface geophysical measurements for providing high-resolution information about land-surface and subsurface properties as well as their spatial variations and linkages, all of which are important for quantifying terrestrial-ecosystem evolution and feedbacks to climate.     

A cluster-optimizing regression-based approach for precipitation spatial downscaling in mountainous terrain

Precipitation temporal and spatial variability often controls terrestrial hydrological processes and states. Common remote-sensing and modeling precipitation products have a spatial resolution that is often too coarse to reveal hydrologically important spatial variability. A statistical algorithm was developed for downscaling low-resolution spatial precipitation fields. This algorithm auto-searches precipitation spatial structures (rain-pixel clusters), and orographic effects on precipitation distribution without prior knowledge of atmospheric setting. It is composed of three components: rain-pixel clustering, multivariate regression, and random cascade. The only required input data for the downscaling algorithm are coarse-pixel precipitation map and a topographic map. The algorithm was demonstrated with 4 km × 4 km Next Generation Radar (NEXRAD) precipitation fields, and tested by downscaling NEXRAD-aggregated 16 km × 16 km precipitation fields to 4 km × 4 km pixel precipitation, which was then compared to the original NEXRAD data. The demonstration and testing were performed at both daily and hourly temporal resolutions for the northern New Mexico mountainous terrain and the central Texas Hill Country. The algorithm downscaled daily precipitation fields are in good agreement with the original 4 km × 4 km NEXRAD precipitation, as measured by precipitation spatial structures and the statistics between the downscaling and the original NEXRAD precipitation maps. For three daily precipitation events, downscaled precipitation map reproduces precipitation variance of the disaggregation field, and with Pearson correlation coefficients between the downscaled map and the NEXRAD map of 0.65, 0.71, and 0.80. The algorithm does not perform as well on downscaling hourly precipitation fields at the examined scale range (from 16 km to 4 km), which underestimates precipitation variance of the disaggregation field. For a scale range from 4 km to 1 km, the algorithm has potential to perform well at both daily and hourly precipitation fields, indicated from good regression performance.     

A transport‐distance approach to scaling erosion rates: 1. Background and model development

The process basis of existing soil‐erosion models is shown to be ill‐founded. The existing literature builds directly or indirectly on Bennett's (1974) paper, which provided a blueprint for integrated catchment‐scale erosion modelling. Whereas Bennett recognized the inherent assumptions of the approach suggested, subsequent readings of the paper have led to a less critical approach. Most notably, the assumption that sediment movement could be approximated by a continuity equation that related to transport in suspension has produced a series of submodels that assume that all movement occurs in suspension. For commonly occurring conditions on hillslopes, this case is demonstrably untrue both on theoretical grounds and from empirical observations. Elsewhere in the catchment system, it is only partially true, and the extent to which the assumption is reasonable varies both spatially and temporally. A second ground‐breaking paper – that of Foster and Meyer (1972) – was responsible for subsequent uncritical application of a first‐order approximation to deposition based on steady‐state analysis and again a weak empirical basis. We describe in this paper an alternative model (Mahleran – Model for Assessing Hillslope‐Landscape Erosion, Runoff And Nutrients) based upon particle‐travel distance that overcomes existing limitations by incorporating parameterizations of the different detachment and transport mechanisms that occur in water erosion in hillslopes and small catchments. In the second paper in the series, we consider the sensitivity and general behaviour of Mahleran , and test it in relation to data from a large rainfall‐simulation experiment. The third paper of the sequence evaluates the model using data from plots of different sizes in monitored rainfall events. From this evaluation, we consider the scaling characteristics of the current form of Mahleran and suggest that integrated modelling, laboratory and field approaches are required in order to advance the state of the art in soil‐erosion modelling. Copyright © 2008 John Wiley & Sons, Ltd.     

Vegetation patterns and diversity along an altitudinal and a grazing gradient in the Jabal al Akhdar mountain range of northern Oman

Little is known about the effects of grazing on vegetation composition on the Arabian Peninsula. The aim of this study therefore was to analyse the vegetation response to environmental conditions of open woodlands along an altitudinal and a grazing gradient in the Jabal al Akhdar mountain range of Oman. The species composition, vegetation structure, grazing damage and several environmental variables were investigated for 62 samples using a nested plot design. Classification analysis and a Canonical Variate Analysis (CVA) were used to define vegetation types and to identify underlying environmental gradients. The relationship between environmental variables and diversity was analysed using correlation coefficients and a main-effects ANOVA. The plant species richness followed a unimodal distribution along the altitudinal gradient with the highest number of species at the intermediate altitudinal belt. The cluster analysis led to five vegetation groups: The Sideroxylon mascatense–Dodonaea viscosa group on grazed and the Olea europaea–Fingerhuthia africana group on ungrazed plateau sites at 2000 m a.s.l., the Ziziphus spina-christi–Nerium oleander group at wadi sites and the Moringa peregrina–Pteropyrum scoparium group at 1200 m a.s.l, and the Acacia gerrardii–Leucas inflata group at 1700 m a.s.l. The CVA indicated a clear distinction of the groups obtained by the agglomerative cluster analysis. The landform, altitude and grazing intensity were found to be the most important variables distinguishing between clusters. Overgrazing of the studied rangeland is an increasing environmental problem, whereas the plant composition at ungrazed sites pointed to a relatively fast and high regeneration potential of the local vegetation.     

Evaluation of spatially clustered ordnance when using compliance sampling surveys after clean-up at military training sites

After site clean-up teams have removed all of what they believe to be UXO within a specific impact area, statistical compliance sampling is a possible method for verifying with a specified probability that this area has been cleaned to specifications. Schilling [J Qual Technol 10(2):47–51, 1978, Acceptance sampling in quality control. Marcel Dekker, Inc., New York, 1982] developed a compliance sampling methodology based on the hypergeometric distribution. Bowen and Bennett (1987) also use compliance sampling where they provide an approximation for estimating the number of samples (n) required to state with desired probability that the entire population of sample units (N, where n < N) are in compliance with cleanup goals. This article describes two methods (anomaly and transect) for applying the Schilling [J Qual Technol 10(2):47–51, 1978, Acceptance sampling in quality control. Marcel Dekker, Inc., New York, 1982] compliance sampling method to military training sites. After describing these methods, a simulation study is presented which demonstrates the performance of transect compliance sampling calculations based on varied degrees of clustered UXO within a specific impact area and different types of sampling routines.     

Functioning of intertidal flats inferred from temporal and spatial dynamics of O<Subscript>2</Subscript>, H<Subscript>2</Subscript>S and pH in their surface sediment

In this article, we describe the dynamics of pH, O₂ and H₂S in the top 5–10 cm of an intertidal flat consisting of permeable sand. These dynamics were measured at the low water line and higher up the flat and during several seasons. Together with pore water nutrient data, the dynamics confirm that two types of transport act as driving forces for the cycling of elements (Billerbeck et al. 2006b): Fast surface dynamics of pore water chemistry occur only during inundation. Thus, they must be driven by hydraulics (tidal and wave action) and are highly dependent on weather conditions. This was demonstrated clearly by quick variation in oxygen penetration depth: Seeps are active at low tide only, indicating that the pore water flow in them is driven by a pressure head developing at low tide. The seeps are fed by slow transport of pore water over long distances in the deeper sediment. In the seeps, high concentrations of degradation products such as nutrients and sulphide were found, showing them to be the outlets of deep-seated degradation processes. The degradation products appear toxic for bioturbating/bioirrigating organisms, as a consequence of which, these were absent in the wider seep areas. These two mechanisms driving advection determine oxygen dynamics in these flats, whereas bioirrigation plays a minor role. The deep circulation causes a characteristic distribution of strongly reduced pore water near the low water line and rather more oxidised sediments in the centre of the flats. The two combined transport phenomena determine the fluxes of solutes and gases from the sediment to the surface water and in this way create specific niches for various types of microorganisms.     

Analysis of burnt schist outcrops in the alps: Relation to historical archaeology and Hannibal's crossing in 218 B.C.

Identification of the exact route followed by Hannibal during his invasion of Italia in the Second Punic War is one of the major questions of antiquity and one that historians/archaeologists have long studied. One of the many clues in the ancient literature that can help answer this question is the mention of fired rock, the result of a conflagration Hannibal is reputed to have employed to reduce the size of boulders in a blocking rockslide some distance down from the high col on the Italian side. The only route with evidence of fired rock along the roadway leading into Italia follows the Col du Clapier, one of the possible northern routes discussed by historians. Radiocarbon dating of calcined rocks is not possible, but whereas Time‐of‐Flight Secondary Ion Mass Spectrometry (ToF‐SIMS), Field Emission Scanning Electron Microscope (FESEM‐EDS), backscatter electron scanning microscopy (BSE), High Resolution Transmission Electron Microscope (HRTEM), and Raman Spectroscopic data do not provide an age for the burnt rock, compositional evidence of the conflagration derived from these analyses may shed light on Hannibal's actual route. © 2007 Wiley Periodicals, Inc.     

Octahedral cation ordering in olivine at high temperature. I: in situ neutron single-crystal diffraction studies on natural mantle olivines (Fa12 and Fa10)

Crystallographic determinations on natural olivine single crystals of mantle composition and origin, carried out by in situ neutron diffraction at high temperature, show that the octahedrally co-ordinated Fe²⁺ and Mg cations undergo two successive trends of cation ordering with increasing temperature. An initial slight preference of Fe²⁺ for site M1, up to a temperature of about 850?°C, is followed by a reverse-ordering reaction with a site preference exchange between the two cations. The cross-over between the two regimes of ordering, corresponding to a situation of complete disorder, occurs at about 900?°C. Above this temperature Fe²⁺ progressively and strongly segregates into site M2 up to 1300?°C, the practical limit of the experimental setup utilized in the experiments. Care was taken to ensure that no chemical changes occurred in the crystals (i.e. oxidation), as testified by Mössbauer spectroscopy determinations carried out before and after the heat treatment. The cation-ordering behaviour is reflected in temperature-dependent changes of geometrical and atomic displacement parameters occurring in the octahedral sites M1 and M2. A thermodynamical explanation of this behaviour is proposed in terms of a prevailing vibrational contribution to entropy.