Journal Paper Digests

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Journal Paper Digests 2017 #12

State-and-transition models in geomorphology

Authors: Phillips, JD; Van Dyke, C

Source: CATENA, 153 168-181; JUN 2017

Abstract: State-and-transition models (STM) are used to describe, model, interpret, and predict when landscapes will undergo a qualitative state change. Although rangeland ecologists pioneered STMs, geomorphological STM-type models were developed prior to and independently of ecological STMs. This study categorized 47 geomorphological STMs according to whether they were: based on single or multiple study areas; primarily for description and interpretation or predictive and prescriptive use; explicitly concerned with complex system dynamics; and the role of biogeomorphic interactions in the model. Each STM was represented as a graph and the structure identified. Spectral radii were calculated to measure the complexity of each STM. Although STMs are associated with conceptual frameworks that recognize the possibility of nonequilibrium, alternative states, and path dependency, results show that an explicit concern with complexity does not necessarily lead to the identification of more states and transitions, or a more complex transition pattern. The purpose for which a STM was created, as well as the number of study sites it can be applied to, also had little bearing on the models’ complexity. This review suggests that geomorphic STMs, rather than being used to fit explanations about landscape evolution into predefined theoretical categories, are veridical representations of empirical observations. Although STMs are particularly useful for grasping the biogeomorphological dynamics of landscapes, this review indicates their utility is not limited to biogeomorphology or to systems with a strong ecological imprint. Time scales involved in geomorphic change can make it difficult to observe a large number of states and transitions, which may constrain what types of STM structure can be identified, as the number of observed states and transitions required to develop particular graph structures varies widely.

A reference library of thermal infrared mineral reflectance spectra for the HyLogger-3 drill core logging system

Authors: Schodlok, MC; Green, A; Huntington, J

Source: AUSTRALIAN JOURNAL OF EARTH SCIENCES, 63 (8):941-949; 2016

Abstract: A new reference library of thermal infrared spectral reflectance measurements of the major rock-forming and alteration minerals has been compiled to support and enhance analysis of data acquired using the CSIRO HyLogger-3 drill-core logging system. The HyLogger-3 is a robotic system that acquires large volumes of bidirectional reflectance spectra from diamond drill core within the wavelength range of visible light, the near infrared and shortwave infrared (400-2500 nm) as well as the thermal infrared from 6000 to 14 000 nm. The library samples were selected as single pure solid mineral crystals or monomineralic hand samples judged to have a similar bidirectional spectral response to that of typical diamond drill cores. Furthermore, a large number of individual mineral samples were chosen to cover the various natural spectral variations within single mineral groups such as, for example, a range of solid solutions of plagioclase. Owing to the bidirectional measurement geometry of the HyLogger-3, spectral variations caused by crystal orientation effects are also expected. Accordingly, reflectance measurements were made for multiple surfaces/facets of each sample, and also for orthogonal orientations of the plane of incidence illumination for each facet measured. All measured spectra were compared with existing library spectra or with spectra measured from validated samples to judge whether the mineral samples could be regarded as pure and, where possible, their chemical composition and mineralogy were validated by X-ray fluorescence and X-ray diffraction. For quality control, all such relevant metadata, including macroscopic descriptions of each sample, were collated in an associated database. In total, the spectral library contains more than 2000 spectra, from 562 specimens, representing 130 mineral groups. This library focuses on the most common rock-forming minerals of relevance to metalliferous exploration and mining, with a few limitations resulting from availability of suitable samples, which will be addressed as new samples become available. Comparisons with emission spectra from existing spectral libraries show good agreement, indicating that this spectral library will also be useful in the remote sensing domain.

Statistical distributions for monthly aggregations of precipitation and streamflow in drought indicator applications

Authors: Svensson, C; Hannaford, J; Prosdocimi, I

Source: WATER RESOURCES RESEARCH, 53 (2):999-1018; FEB 2017

Abstract: Drought indicators are used as triggers for action and so are the foundation of drought monitoring and early warning. The computation of drought indicators like the standardized precipitation index (SPI) and standardized streamflow index (SSI) require a statistical probability distribution to be fitted to the observed data. Both precipitation and streamflow have a lower bound at zero, and their empirical distributions tend to have positive skewness. For deriving the SPI, the Gamma distribution has therefore often been a natural choice. The concept of the SSI is newer and there is no consensus regarding distribution. In the present study, twelve different probability distributions are fitted to streamflow and catchment average precipitation for four durations (1, 3, 6, and 12 months), for 121 catchments throughout the UK. The more flexible three- and four-parameter distributions generally do not have a lower bound at zero, and hence may attach some probability to values below zero. As a result, there is a censoring of the possible values of the calculated SPIs and SSIs. This can be avoided by using one of the bounded distributions, such as the reasonably flexible three-parameter Tweedie distribution, which has a lower bound (and potentially mass) at zero. The Tweedie distribution has only recently been applied to precipitation data, and only for a few sites. We find it fits both precipitation and streamflow data nearly as well as the best of the traditionally used three-parameter distributions, and should improve the accuracy of drought indices used for monitoring and early warning.

Soil carbon sequestration potential in semi-arid grasslands in the Conservation Reserve Program

Authors: Li, C; Fultz, LM; Moore-Kucera, J; Acosta-Martinez, V; Horita, J; Strauss, R; Zak, J; Calderon, F; Weindorf, D

Source: GEODERMA, 294 80-90; MAY 15 2017

Abstract: The Conservation Reserve Program (CRP) in the USA plays a major role in carbon (C) sequestration to help mitigate rising CO2 levels and climate change. The Southern High Plains (SHP) region contains >900.000 ha enrolled in CRP, but a regionally specific C sequestration rate has not been studied, and identification of the C pools and processes important in controlling C sequestration rates remain unresolved. We aimed to address these gaps by utilizing a CRP chronosequence with historical rangeland as a reference ecosystem. Soil samples (0-10 and 10-30 cm) were collected in 2012 and 2014 from a total of 26 fields across seven counties within the SHP and included seven croplands (0 y in CRP), 16 CRP fields that ranged from 6 to 26 y (as of 2012), plus three rangelands. Multiple regression analysis was conducted to gauge the rate of C sequestration under CRP within C pools: soil organic C (SOC), particulate organic matter C (POM-C), and microbial biomass C (MBC), with two additional predictors (soil clay + silt content and precipitation). Despite attempts to control for soil texture by targeting a dominant soil series (Amarillo fine sandy loam), the percent of clay + silt (15.2-48.7%) significantly influenced C accrual. The C sources (C-3 from previous cropping systems or C-4 from CRP grasses) in SOC and POMC were assessed using stable C isotope signatures. Additionally, the role of soil microbes in C sequestration was evaluated by investigating the relationship between MBC and CO2 flux and C sequestration. SOC increased at a rate of 69.82 and 132.87 kg C ha(-1) y(-1) and would take approximately 74 and 77 y to reach the rangeland C stocks at 0-10 and 0-30 cm, respectively. The C-4-C primarily from the introduced grasses was the main source of C sequestration. SOC gains were essentially due to increases in POM-C and MBC, accounting for 50.04 and 15.64% of SOC sequestration at 0-30 cm, respectively. The highest semi-partial correlation coefficients between the increasing years under CRP restoration and MBC indicated CRP had the strongest effect on MBC compared to other C pools. In addition, increasing soil CO2 flux and MBC:SOC ratio with years of CRP restoration indicated MBC played a critical role in the C sequestration process. Conservation of CRP lands and efforts to sustain perennial systems in this highly erodible landscape should be a high priority of conservation programs. In doing so, significant offsets to increasing atmospheric CO2 levels may be achieved in addition to erosion control and improved wildlife habitat.

Evaluation of two methods to eliminate the effect of water from soil vis-NIR spectra for predictions of organic carbon

Authors: Roudier, P; Hedley, CB; Lobsey, CR; Rossel, RAV; Leroux, C

Source: GEODERMA, 296 98-107; JUN 15 2017

Abstract: Visible near infrared reflectance spectroscopy (vis-NIR) is an increasingly popular measurement method that can provide cheaper and faster predictions of soil properties, including soil organic carbon content (SOC). The spectroscopic prediction method relies significantly on the development of regressions of data in spectral databases or libraries. While the vis-NIR estimation of SOC was developed in controlled laboratory conditions, its natural development in recent years has been to perform the vis-NIR measurements in situ, where soil spectra are recorded under field conditions. However, environmental factors, such as soil moisture content, have been shown to affect soil spectra, making the use of regressions derived using soil spectral libraries difficult. Direct standardization (DS) and external parameter orthogonalisation (EPO) are two methods that were proposed for the correction of variable moisture conditions and other environmental factors. In this study, we compared DS and EPO on a set of 150 soil samples (3 depths from each of 50 soil cores) from a farm in New Zealand. The samples were re-wetted under controlled conditions, and spectra were recorded at nine different moisture levels. Our results show that DS and EPO are two effective strategies to mitigate the effects of soil water content on vis-NIR spectra. While DS and EPO results were similar when a large number of soil cores were reserved for calibrating the moisture correction methods, SOC predictions using the EPO correction significantly outperformed those using the DS correction for a lower number of cores (5 cores, 15 samples).

Soil color sensor data collection using a GPS-enabled smartphone application

Authors: Stiglitz, R; Mikhailova, E; Post, C; Schlautman, M; Sharp, J; Pargas, R; Glover, B; Mooney, J

Source: GEODERMA, 296 108-114; JUN 15 2017

Abstract: Application of accurate and low-cost sensor technology to collect soil color data provides an opportunity to increase the density, quality and quantity of soil data to monitor our changing soil resources. The objective of this study was to develop a mobile application that would enable users to create their own soils database consisting of GPS location and soil color data gathered using the application and a mobile sensor. A mobile application was created utilizing the Nix(Tm) Pro color sensor that produces multiple color results, including Munsell color notation. The application also allows users to toggle between “in-field” sampling as well as dry or moist soil samples. Users can choose to record GPS location and a photo of the soil sample to upload into an online database for storage. The application was tested for functionality in the field and for its ability to match Munsell notation values determined using a Munsell Soil Color Chart (MSCC). Field data were synchronized to a cloud database and subsequently retrieved and used to produce a Geographic Information Systems (GIS) layout showing sample point locations and soil color attributes. The Soil Scanner application allows for rapid analysis and collection of soils data that can be stored for further study and reference using various color systems and location data.

Relationship between soil clay mineralogy and carbon protection capacity as influenced by temperature and moisture

Authors: Singh, M; Sarkar, B; Biswas, B; Bolan, NS; Churchman, GJ

Source: SOIL BIOLOGY & BIOCHEMISTRY, 109 95-106; JUN 2017

Abstract: Environmental conditions like temperature and moisture could affect the carbon protection capacity of various clay types in soils. Using dominantly kaolinitic-illitic, smectitic and allophanic soils, we conducted systematic incubation experiments over 42 days at different temperatures (4, 22 and 37 degrees C) and moisture contents (30, 60 and 90% of water holding capacity (available water)). The basal respiration was monitored to study the relative effect of moisture contents and temperature on the carbon protection capacities and mechanisms of the three clay types. The results indicated that carbon decomposition increased with increasing moisture and temperature. A two-component quadratic equation could explain the carbon mineralisation process. The highest C respiration was observed at 37 degrees C with a 60% moisture level in each of the soil types. Under these conditions, the smectitic soil recorded the highest carbon decomposition followed by the kaolinitic-illitic and allophanic soils. The study of the priming effect using C-14 lab-died malic acid confirmed the trend of the bulk respiration results. The allophanic soil showed the lowest amount of carbon mineralisation under all experimental conditions. A strong inverse correlation (R-2 = 0.90 at p < 0.05) was observed between CO2 emission rate and total sesquioxides (Fe and Al oxides) content. As evidenced by the pore size distribution, micromorphologies and thermogravimetric analyses, the microporous structure and micrbaggregate formation in the allophanic soil enhanced carbon sequestration. This study indicated that soil carbon stabilisation was related more to the sesquioxides content than to the clay types or their relative specific surface areas.

Measuring functional pedodiversity using spectroscopic information

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Authors: Fajardo, MP; McBratney, AB; Minasny, B

Source: CATENA, 152 103-114; MAY 2017

Abstract: Pedodiversity studies greatly depend on the discretization of the soil continuum via various soil classification standards. Soil taxonomic systems are constructed considering soil properties and their organization in the soil profile. Therefore, it seems logical that the pedodiversity of an area could be calculated by considering the simultaneous variation of multiple soil properties within that area. With the aim of creating a bridge between these two lines of thinking, this study presents the development of two new indices of pedodiversity (HULLdiv and EIGENdiv) which consider continuous variables as input. The soil input information tested was a) Visible and Near Infrared (Vis-NIR) reflectance values and b) values of five soil properties predicted from Vis-NIR spectra. Both indices were employed to measure the pedodiversity at different extents in two perpendicular transects containing 27 (North to South) and 22 (East to West) locations respectively in New South Wales (NSW), Australia. Each location considered natural and intervened land Use. The indices successfully represented the pedodiversity of the area of study, however they were different depending on the input soil information i.e., raw Vis-NIR and predicted properties. HULLdiv was affected by extreme soil observations and as a result its discrimination power between areas with different soil diversity was inferior. On the other hand, EIGENdiv represented well the pedodiversity of an area, despite the extreme observations. The results showed good agreement with conventional methods for assessing pedodiversity i.e., Shannon’s and Simpson’s indices. However, the new indices were more discriminating by being able to better represent the landuse effect. This study represents the first attempt to measure pedodiversity in a continuous way using Vis-NIR information.

A comparison of soil quality evaluation methods for Fluvisol along the lower Yellow River

Authors: Guo, LL; Sun, ZG; Ouyang, Z; Han, DR; Li, FD

Source: CATENA, 152 135-143; MAY 2017

Abstract: Soil quality evaluation as a decision-making tool to improve understanding of soil quality is essential for grading croplands and adopting proper agricultural practices. Various methods of soil quality evaluation have been developed, which have Occasionally generated inconsistent evaluation results between differing soil types. The applicability of these techniques is seldom tested before implementing an evaluation method on a specific soil region. Fluvisol is an important soil resource for agriculture in China, especially for irrigation districts along the lower Yellow River. In the present study, the soil quality of two typical agricultural counties (Yucheng and Kenli) along the lower Yellow River was evaluated using four commonly utilized methods. In the two counties, the overall spatial patterns of soil quality derived from the four methods were similar, with differences in details existing among these methods. The soil quality in Yucheng, ranging from moderate to high, is superior to that observed in Kenli, where salinity is the primary limiting factor. In addition, the applicability of soil quality evaluation methods on the Fluvisol was investigated. It was found that the integrated quality indexing-linear scoring (IQI-LS) and the Nemoro indexing-Linear scoring (NQI-LS) methods were the most accurate and practical of the four methods studied. These methods, which are based on the total data set of indicators, show better performance for soil quality evaluation on a Fluvisol. Further, different evaluation methods based on the Minimum data set of indicators were compared, considering both the accuracy of the evaluation and the economic cost of obtaining the soil data. The results from the present study indicate that the IQI-LS method based on the minimum data set of indictors is recommended for large-scale soil quality evaluations.

Soil microbes and their response to experimental warming over time: A meta-analysis of field studies

Authors: Romero-Olivares, AL; Allison, SD; Treseder, KK

Source: SOIL BIOLOGY & BIOCHEMISTRY, 107 32-40; APR 2017

Abstract: Numerous field studies have found changes in soil respiration and microbial abundance under experimental warming. Yet, it is uncertain whether the magnitude of these responses remains consistent over the long-term. We performed a meta-analysis on 25 field experiments to examine how warming effects on soil respiration, microbial biomass, and soil microbial C respond to the duration of warming. For each parameter, we hypothesized that effect sizes of warming would diminish as the duration of warming increased. In support of our hypothesis, warming initially increased soil respiration, but the magnitude of this effect declined significantly as warming progressed as evidenced by the two longest studies in our meta-analysis. In fact, after 10 years of warming, soil respiration in warmed treatments was similar to controls. In contrast, warming effect sizes for fungal biomass, bacterial biomass, and soil microbial C did not respond significantly to the duration of warming. Microbial acclimation, community shifts, adaptation, or reductions in labile C may have ameliorated warming effects on soil respiration in the longterm. Accordingly, long-term soil C losses might be smaller than those suggested by short-term warming studies

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