Regular Sampling Grid Research Articles

Spatial distribution of soil heavy metals in different land uses of an industrial area of Tehran (Iran)

Vegetation and different land uses may affect the spatial distribution of heavy metals in soils. The objective of the current article was to study the impact of industrial activities and land use type on the distribution of heavy metals in soils of Chitgar Forrest Park, located in industrial zone in the west of Tehran City. The soil samples were taken from 116 sites in a regular sampling grid (250 × 250 m) at a depth of 0–20 cm, including three different land uses, needle leaf forests, broadleaf forests and rangeland. Nitric acid-extractable form of seven metals, Cu, Cd, Fe, Mn, Ni, Pb and Zn, and DTPA-extractable form of Cu, Fe, Mn and Zn were measured. Soil texture, pH, organic carbon, carbon-to-nitrogen ratio, percentage of calcium carbonate and electrical conductivity (EC) were also determined. According to the maps and background amounts, heavy metals were affected by industrial activities and road traffic. Proximity to heavy traffic highway of Tehran–Karaj and large autoindustry plants can be considered for increasing metal concentrations. Results of statistical methods (coefficient variation and cluster analysis), besides geostatistical analysis (variogram and map), showed that total concentrations of heavy metals are controlled by intrinsic and extrinsic factors in the studied area. Although land use type did not affect the alteration in the distribution of total concentrations of heavy metals, it changed the distribution of DTPA form of heavy metals in the soils through affecting the soil organic matter.

Recent shifts in plant species suggest opposing land-use changes in alpine pastures

Land abandonment and intensification of management have been suggested as major drivers of biodiversity change in subalpine and alpine grasslands, but the relative importance of these concomitant trends has not been extensively studied. Here, we use plant indicator values to infer patterns of change in the management intensity of summer pastures. Occurrence data of vascular plants from 192 plots surveyed in the Swiss Biodiversity Monitoring BDM programme were used to analyse changes in five species-based indicator values that express the management intensity of sites. Each plot was surveyed twice between 2002 and 2011 with a time span of 5 years between surveys. We looked for an overall trend in management intensity and examined whether a supposed change of management intensity depends on site conditions. In addition, we tested whether a change in indicator values for management intensity accompanies a change in species richness. Over the whole study area, there was no overall change in mean indicator values. However, we found weak but significant relations between changes in mean indicator values and accessibility of the sites. According to plant indicator values, intensification of management takes place at well-accessible and lower-elevation sites, whereas remote sites and sites at higher elevation tend to show a decrease in management intensity. Sites where indicators suggested intensified management showed a decrease of both total species richness and richness of target species relevant for conservation. On the other hand, a supposed decrease in land-use intensity led to an increase in species richness within the surveyed time period. This study confirms that moderate management intensity of summer pastures will best maintain the plant diversity of alpine summer pastures. Because the surveyed plots stem from a rigorously standardized regular-grid sampling, we attribute high reliability and generality to our findings.

Detecting Cyclostationarity in Re-Captured LCD Screens

It is easy to display a video or picture on an LCD screen and recapture it by using a camera to hide traces of digital image manipulation or fool an access system based on face recognition technique. In this paper, we show that humans do not have a good performance in detecting recaptured data from LCD screens. Hence, it is important to have methods capable of distinguishing between natural videos and pictures and those recaptured ones. In this paper, we show that, typically, recaptured images and videos from LCD screens exhibit detectable periodic patterns that are caused by regular sampling grid of the LCD monitor and aliasing. We develop our method using the theory of cyclostationarity and experimentally validate it. The term cyclostationarity refers to a special class of signals which exhibit periodicity in their statistics. Our method will be based on the fact that a cyclostationary signal has a frequency spectrum correlated with a shifted version of itself.

Caracterização da variabilidade espacial do índice relativo de clorofila na cultura do trigo

A aplicação localizada de nitrogênio, baseada no índice relativo de clorofila das folhas, pode proporcionar inúmeros benefícios econômicos e ambientais, no entanto, o conhecimento sobre a metodologia de amostragem ainda é incipiente. Nesse sentido, este estudo objetivou avaliar o uso de diferentes malhas amostrais na caracterização da variabilidade espacial do índice relativo de clorofila das folhas da cultura do trigo e na confecção de mapas temáticos para a aplicação localizada de nitrogênio. Para determinação do índice relativo de clorofila, utilizou-se clorofilômetro CFL 1030, em uma malha amostral regular de 10 m x 10 m, com 472 pontos amostrais. A partir da malha amostral inicial, pela técnica de eliminação de pontos, realizou-se a simulação da utilização das seguintes malhas: 10 m x 20 m; 20 m x 20 m; 20 m x 30 m; 30 m x 30 m; 30 m x 40 m; e 40 m x 40 m. O aumento da malha amostral promoveu redução na acurácia do diagnóstico do índice relativo de clorofila, nas folhas de trigo. À medida que se aumentou a malha amostral, os mapas tornaram-se mais generalistas e informações da variabilidade espacial do índice relativo de clorofila foram perdidas. Malhas amostrais menores ou iguais a 20 m x 20 m mostraram-se eficazes para a detecção da variabilidade espacial do índice relativo de clorofila em folhas de trigo e para a confecção de mapas temáticos de aplicação localizada de nitrogênio.

Sampling grid density and lime recommendation in an Oxisol

The objective of this study was to evaluate the influence of different sampling grids density in the lime requirements in an Oxisol. The experiment was conducted at a rural property located in Sidrolândia city, Mato Grosso do Sul state, in the Brazilian ‘Cerrado’. In the soil attributes mapping, regular sampling grid was used consisting of 99 points, spread over an area of 90 ha. Other two grids (51 and 27 points) were derived by deleting lines or lines and points from the original one. Based on the results of soil analysis, the lime requirement at each sample point was calculated. Using geostatistical techniques the spatial variability of lime requirement was studied and grid configuration for each sample was tested. By kriging, maps were made. By reducing the number of sampling points, 11% of the experimental area showed an overestimation and 8% underestimation comparing with the lime requirement made using the highest sampling grid density.

Effectiveness of Chlorophyll Meter Measurement in Winter Wheat at Field Scale Level

Abstract This paper examines the relationship among chlorophyll meter Yara N-Tester readings, nutrition status and growth parameters (leaf area index (LAI), plant height) of the winter wheat plants. Data used in this study were collected in 2010 from two fields located in the Czech Republic (area 52 and 38 ha) from different farms, both with uniform and conventional crop management. The monitoring of crop stands was done at growth stage BBCH 30 in a regular sampling grid with 150 m distance between points (27 and 18 points). At each sampling point, the plant height, LAI (Delta-T SunScan) and the chlorophyll concentration (Yara N-Tester) were recorded. Plant samples were taken to analyse the content of main nutrients (N, P, K, Mg, Ca and S). The results of plant analysis showed that both fields were in different nutrition status: one in a correct status and another had a complex nutritional deficit (K, Ca and N). Linear regressions and ANOVA proved that under a multiple nutritional deficit, N-Tester readings responded to the growth of the crop, while in the adequate nutritional conditions the sensitivity of N-Tester to the variation in the nitrogen concentration is lower. The relationships between crop parameters and chlorophyll meter readings are not generalisable and thus the interpretation of N-Tester results has to be done separately for each field.

Spatial variability of general stand characteristics in central European beech-dominated natural stands – Effects of scale

Unlike many studies on the stand structure of European beech-dominated natural forests we explicitly examined the spatial variability of six general stand characteristics: density, basal area and volume of living trees, volume of deadwood, total volume and the proportion of deadwood in the total volume. We asked whether and how these stand characteristics are spatially organized and autocorrelated, and how their spatial autocorrelation varies among particular characteristics, study sites and observation scales.The study was conducted at three forest stands dominated by Fagus sylvatica L. and co-dominated by Picea abies (L.) Karsten and Abies alba Mill., which represent the few sizable remnants of beech-dominated natural forests in central Europe. Vector stem position maps of the three sites were examined by the computer-simulated placement of differently sized square sample plots (10×10; 20×20; 30×30; 50×50 and 70×70m). The six general stand characteristics were calculated for every simulated sample plot. Experimental semivariograms were calculated for all sampling plot (grain) sizes, model semivariograms were only fitted for 20×20m plots.The spatial variability of stand characteristics significantly changes with the scale of observation. At the finest grain the spatial autocorrelation is mostly quite low and usually very nearly approximate the nugget model. However, autocorrelation increases with increasing sampling plot size. A peak in the first lag of the semivariograms was observed only at the finest grains, documenting the competition of large trees, whereas a recurring pattern of patches with similar stand characteristics was identified at larger observation scales. Nested structures formed by the high nugget and relatively less distinct but still apparent sill/range and fluctuation signal were detected in most of the model semivariograms, indicating different sources of variability operating at multiple scales. Moreover, significant differences among particular stand variables were demonstrated. The relative nugget varied from 61% (stand density) to 96% (stand volume) at the 20×20m sampling plots; the autocorrelation ranges varied from more than 320m to 64m, respectively.The irregular periodic patchiness found (usually 400–1100m2 in size) may serve as a model for close-to-nature forestry, which emulates the spatial structures of natural forests. The level of positive spatial autocorrelation acknowledged for stand density should be reflected in an effective sampling design. For better estimates of the variance in this variable, sampling in a regular grid or stratified sampling is suggested.

Structure of tree vegetation may reduce costs of territory defence in Eurasian Nuthatch Sitta europaea

Capsule In pastured old oak woodland, breeding pairs of Eurasian Nuthatch selected territories with significantly higher densities of trees and cavities.Aims To define territorial borders that exist within a nuthatch population and to compare densities of trees and cavities between used and non-used parts of their available habitat in order to determine habitat preferences.Methods The number and location of territories was estimated by mapping the individual positions of colour-ringed birds. We measured habitat characteristics in regular sampling grid (number of trees and number of cavities per 50 × 50 m) during three successive seasons and modelled probability of occurrence of nuthatch territories in the area.Results Breeding pairs were observed to defend territories of median size between 1.46 and 2.93 ha. These sizes correspond well to high-quality habitat territories for this species. We found that pairs tended to occupy territories with higher densities of trees and cavities. Based on generalized linear mixed-effects model estimates, we found that in pastured oak woodland habitat with density of 60 trees per ha, the estimated probability of occurrence (with 95% confidence interval) of a nuthatch territory was about 96% (83−99). For cavity density, the probability of territory occurrence was about 74% (52−89) at the level of 60 cavities per ha.Conclusion We suggest that higher tree and cavity densities reduce territory defence costs in the species because birds may use less energy during foraging, predation avoidance and competition for a nest hole.

Target Detection and Tracking of moving objects for characterizing landslide displacements from time-lapse terrestrial optical images

Terrestrial Optical Photogrammetry (TOP) is a low-cost monitoring technique that is commonly used in change detection studies. For landslide monitoring, image correlation techniques are frequently used to generate Digital Surface Models (DSMs) from stereo-pairs or to measure the 2D surface displacement field from single-view time-lapse sequences. Image correlation allows for detecting spatially continuous displacement fields at a sub-pixel precision. The technique, however, has several limitations for assessing displacement because 1) of its sensitiveness to changes in texture, shape and radiometry in the image pile, 2) of the need of spatially regular sampling grids, and 3) of possible high computation time that can impede the processing of large image datasets.To address these limitations, an alternative and complementary approach based on a Target Detection and Tracking (TDT) algorithm is proposed for a rapid calculation of the displacement of targets in image time series. The TDT code, developed as a MATLAB-based tool, is able to track natural or man-made targets. The precision of the TDT code is assessed using several image time series acquired at the Super-Sauze landslide (Southern French Alps) and compared to ground based measurements. The computed relative accuracy is between 10−3 and 10−4 (5cm at a distance of 115m). Although the TDT approach does not provide spatially continuous information, it provides 1) a quantification of the object displacements at the same order of precision as image correlation (sub-pixel accuracy) and 2) information in regions where image correlation fails because of too large ground displacements. A sensitivity analysis reveals that the major sources of uncertainty are camera movement and/or lens distortion and not the TDT method itself.

Habitat vs. dispersal constraints on bryophyte diversity in the Mojave Desert, USA

Preserving desert plant diversity requires an understanding of the degree to which plant communities are constrained either by suitable habitat or by dispersal limitations. Using a spatially explicit approach, we surveyed diversity in an undisturbed xeric bryophyte community within a regular sampling grid of 1000 adjacent cells. Eigenvector mapping and variation partitioning revealed that spatially independent habitat processes accounted for little of the variation in community composition (2.0%); most variation was attributed either to habitats that were spatially structured (25.6%) or to dispersal independent of habitat (28.0%). At three nested scales, the most influential habitat factors were topography (broad-scale >5 m2), shrub “islands” (meso-scale 1−5 m2), and physical substrate characteristics (fine-scale < 1 m2). Dispersal limitation was less obviously scale-dependent at the community level, yet was important when considering individual species, which showed a wide range of spatial autocorrelation (Moran's I = −0.003–0.601). Our findings suggest that bryophyte diversity is the joint result of dispersal limitations and the distinctive spatially patterned environment of desert shrublands. Therefore, conservation efforts must not only account for dispersal limitations of individual species of concern, but should also seek to retain native shrubs and consequent landscape physiognomy that create bryophyte habitat.

Spatial interpretation of plant parameters in winter wheat

A methodology is described for the spatial interpretation of plant parameters (SIOPP), which was used to diagnose the nutritional status of winter wheat. The data used in this study were collected in 2010 throughout the monitoring of two fields (52 and 38 ha) with uniform and conventional agricultural management, located in the Czech Republic. The survey was carried out at BBCH 30 phenological stage in a regular sampling grid with 150 m of distance between grid points (27 and 18 samples). The plant height and the chlorophyll concentration (Yara N-Tester) were recorded. Plant and soil samples were taken to analyse the nutrient concentrations (N, P, K, Mg, Ca, and S). A crop development index (CDI) was developed combining plant height and N-Tester values to quantify the growth of the plant (biomass and vigour). The relationship between this index and the concentration of nutrients were studied and confirmed by cross-validation and spatial analysis; the aim was to determine the factors that limit plant growth. The method revealed the limiting factors in field #1 were potassium, calcium (pH problems) and nitrogen (in descending order of relevance). In field #2, CDI was only related to the soil moisture. In all cases, it was found that the spatial variability of the indices and the limiting factors followed a pattern result of the combination of the gradients in climate, topography and soils of each field. This allowed the interpolation of the maps for variable-rate application using only 0.5 samples per hectare arranged in regular mesh, which was insufficient for the use of geostatistics. All diagnoses were consistent with the crop yield, the soil sampling and the DRIS diagnoses. The results showed that if leaf analyses are complemented with a few additional measures, instantaneous and with a minimal cost, it is possible to deduce the diagnosis using statistical and spatial analysis.

Qualitative Land Suitability Evaluation for Main Irrigated Crops in the Shahrekord Plain, Iran: A Geostatistical Approach Compared with Conventional Method

The purity of soil map units and their quality for various uses like land suitability evaluation are always questioned. The main objective of this study was to compare the precision of qualitative land suitability classification based on geostatistical and conventional soil mapping methods for main irrigated crops in the Shahrekord Plain, Central Iran. A regular grid sampling method consisting 104 sample points was designed and soil samples were collected. Ordinary kriged maps were achieved for all studied soil attributes after physico-chemical analyses. Afterward, to combine kriged maps and ecological requirements of the studied crops, a script was designed in ILWIS 3.4 software and consequently, kriged qualitative land suitability maps were generated. Conventional qualitative land suitability was also mapped based on the representative pedon analysis in each soil map unit. Finally, comparison of the conventional and kriged maps was carried out using the statistical method, error matrix. The results showed that the overall accuracies of wheat, sugar beet, potato and alfalfa maps were 39.8%, 24.3%, 18.7% and 18.6% at subclass category, respectively, whereas these values increased to 80.9%, 82.3%, 23.7% and 82.3% at class level, respectively. Hence, it can be stated that thanks to the relative facility of conventional soil survey compared with geostatistical methods, this method can be expressed as a preferable way for handling a usual land suitability evaluation design; but using soil map units as land suitability delineations may lead to unsatisfactory results in estimation of quantity and type of existing limitations.

Spatial distribution of tuna larvae in the Gulf of Gabes (Eastern Mediterranean) in relation with environmental parameters

Spatial distribution and ecology of the larvae of three tuna species (Thunnus thynnus, Auxis rochei and Euthynnus alletteratus) were studied during an ichthyoplankton survey carried out in the Gulf of Gabes (Tunisia) in June and July 2009. A total of 80 stations, distributed on a regular sampling grid, were sampled. The main objectives of this survey were to provide information on tuna larvae distribution in the Gulf of Gabes in relation to the environmental parameters. Regarding small tunas, larvae of A. rochei (bullet tuna) showed the more widespread distribution, being found at both inshore and offshore stations. E. alletteratus (Atlantic black skipjack) larvae were mainly found at the inshore stations covering the wide continental shelf of this region. On the other hand, larvae of the large migratory tuna T. Thynnus (Atlantic bluefin tuna), were mainly recorded at offshore stations, suggesting that spawning possibly takes place mainly near the shelf break. Regarding the biological and physical parameters examined, our results indicate that tuna larvae were mainly collected in oligotrophic and mixed waters resulting from the confluence of surface water of recent Atlantic origin and resident surface Mediterranean waters, as shown by their preference for lower chlorophyll a concentrations (from 1.4 to 2.5 mg m-3) and moderate salinity values (between 37.35 and 37.75). Significantly, tuna larvae seemed to avoid the more eutrophic and saltier waters of the gulf situated very close to the coast and around Kerkennah and Djerba islands.

Espacialização da precipitação pluvial por meio de krigagem e cokrigagem

O objetivo deste trabalho foi avaliar a cokrigagem ordinária, com dados de altitude e distância do mar, em comparação à krigagem ordinária, na espacialização da precipitação pluvial dos períodos anual, seco e úmido, no Estado do Espírito Santo. Os dados de altitude e distância do mar foram obtidos de pontos de amostragem em grades regulares e irregulares. Foram utilizados dados de 108 postos pluviométricos. A avaliação dos métodos e das variáveis foi realizada com base na validação cruzada, tendo-se considerado os erros dos valores preditos e o ajuste dos modelos de regressão linear para valores observados e preditos. A grade regular para amostragem das covariáveis apresentou melhor acurácia de predição em comparação à grade irregular. A cokrigagem produziu resultados mais acurados do que a krigagem, verificados por pequenas diferenças nos erros médios absolutos, capazes de produzir mapas estatisticamente diferentes. A interpolação por cokrigagem e o uso de grades regulares para amostragem são preferíveis, principalmente se as covariáveis são de fácil obtenção e de baixo custo.

Fourier analysis of stochastic sampling strategies for assessing bias and variance in integration

Each pixel in a photorealistic, computer generated picture is calculated by approximately integrating all the light arriving at the pixel, from the virtual scene. A common strategy to calculate these high-dimensional integrals is to average the estimates at stochastically sampled locations. The strategy with which the sampled locations are chosen is of utmost importance in deciding the quality of the approximation, and hence rendered image. We derive connections between the spectral properties of stochastic sampling patterns and the first and second order statistics of estimates of integration using the samples. Our equations provide insight into the assessment of stochastic sampling strategies for integration. We show that the amplitude of the expected Fourier spectrum of sampling patterns is a useful indicator of the bias when used in numerical integration. We deduce that estimator variance is directly dependent on the variance of the sampling spectrum over multiple realizations of the sampling pattern. We then analyse Gaussian jittered sampling, a simple variant of jittered sampling, that allows a smooth trade-off of bias for variance in uniform (regular grid) sampling. We verify our predictions using spectral measurement, quantitative integration experiments and qualitative comparisons of rendered images.

Spatial variability of soil CO2 emission in a sugarcane area characterized by secondary information

Soil CO2 emission (FCO2) is governed by the inherent properties of the soil, such as bulk density (BD). Mapping of FCO2 allows the evaluation and identification of areas with different accumulation potential of carbon. However, FCO2 mapping over larger areas is not feasible due to the period required for evaluation. This study aimed to assess the quality of FCO2 spatial estimates using values of BD as secondary information. FCO2 and BD were evaluated on a regular sampling grid of 60 m × 60 m comprising 141 points, which was established on a sugarcane area. Four scenarios were defined according to the proportion of the number of sampling points of FCO2 to those of BD. For these scenarios, 67 (F67), 87 (F87), 107 (F107) and 127 (F127) FCO2 sampling points were used in addition to 127 BD sampling points used as supplementary information. The use of additional information from the BD provided an increase in the accuracy of the estimates only in the F107, F67 and F87 scenarios, respectively. The F87 scenario, with the approximate ratio between the FCO2 and BD of 1.00:1.50, presented the best relative improvement in the quality of estimates, thereby indicating that the BD should be sampled at a density 1.5 time greater than that applied for the FCO2. This procedure avoided problems related to the high temporal variability associated with FCO2, which enabled the mapping of this variable to be elaborated in large areas.

Lateral diffusivity from tracer release experiments in the tropical North Atlantic thermocline

Lateral diffusivity is computed from a tracer release experiment in the northeastern tropical Atlantic thermocline. The uncertainties of the estimates are inferred from a synthetic particle release using a high‐resolution ocean circulation model. The main method employed to compute zonal and meridional components of lateral diffusivity is the growth of the second moment of a cloud of tracer. The application of an areal comparison method for estimating tracer‐based diffusivity in the field experiments is also discussed. The best estimate of meridional eddy diffusivity in the Guinea Upwelling region at about 300 m depth is estimated to be m2 s−1. The zonal component of lateral diffusivity is estimated to be m2 s−1, while areal comparison method yields areal equivalent zonal diffusivity component of m2 s−1. In comparison to Ky, Kx is about twice larger, resulting from the tracer patch stretching by zonal jets. Employed conceptual jet model indicates that zonal jet velocities of about m s−1 are required to explain the enhancement of the zonal eddy diffusivity component. Finally, different sampling strategies are tested on synthetic tracer release experiments. They indicate that the best sampling strategy is a sparse regular sampling grid covering most of the tracer patch.

Spatial distribution of tuna larvae in the Gulf of Gabes (Eastern Mediterranean) in relation with environmental parameters

Spatial distribution and ecology of the larvae of three tuna species (Thunnus thynnus, Auxis rochei and Euthynnus alletteratus) were studied during an ichthyoplankton survey carried out in the Gulf of Gabes (Tunisia) in June and July 2009. A total of 80 stations, distributed on a regular sampling grid, were sampled. The main objectives of this survey were to provide information on tuna larvae distribution in the Gulf of Gabes in relation to the environmental parameters. Regarding small tunas, larvae of A. rochei (bullet tuna) showed the more widespread distribution, being found at both inshore and offshore stations. E. alletteratus (Atlantic black skipjack) larvae were mainly found at the inshore stations covering the wide continental shelf of this region. On the other hand, larvae of the large migratory tuna T. Thynnus (Atlantic bluefin tuna), were mainly recorded at offshore stations, suggesting that spawning possibly takes place mainly near the shelf break. Regarding the biological and physical parameters examined, our results indicate that tuna larvae were mainly collected in oligotrophic and mixed waters resulting from the confluence of surface water of recent Atlantic origin and resident surface Mediterranean waters, as shown by their preference for lower chlorophyll a concentrations (from 1.4 to 2.5 mg m-3) and moderate salinity values (between 37.35 and 37.75). Significantly, tuna larvae seemed to avoid the more eutrophic and saltier waters of the gulf situated very close to the coast and around Kerkennah and Djerba islands.

Influences of forest roads and their edge effects on the spatial pattern of burn severity

Previous research has shown that forest roads are an important feature in many landscapes and have significant effects on wildfire ignition and cessation. However, forest road effects on burn severity have not been studied at the landscape level. Therefore, the overarching goal of our study is to identify the influences of road edge effects on the spatial patterns of burn severity. We analyzed six fires within the Okanogan–Wenatchee National Forest on the eastern slope of the Cascades mountain range of central Washington.We generated two categories for assessing road variables: (1) Primary Road Effect Zone (area within 150m of the nearest road) and (2) Secondary Road Effect Zone (area from 150m to 300m to the nearest road). A regular sampling grid including one out of every 9cells was created for each fire.These grids were intersected with burn severity data in the form of the Relative Differenced Normalized Burn Ratio (RdNBR), road distance category, stream distance, elevation, slope, terrain shape index, heat load index, canopy cover, and fuel type. We fit spatial regression models with RdNBR as the dependent variable.We found that high burn severity is less likely to occur in the Primary Road Effect Zone for most fires, although one fire exhibited the opposite relationship. Forest road edge effects were hypothesized to be an important determinant of burn severity because fragmentation created by roads alters the roadside fuel profile and environment and because road corridors create barriers to fire spread. Recognizing roadside effects on burn severity patterns highlights the need for further study of the range of effects that roads have on fuels and the fire environment and the potential for incorporating road effects into landscape-level assessments of fire risk.

Uncertainties in the prediction of spatial variability of soil CO2 emissions and related properties

The soil CO2 emission has high spatial variability because it depends strongly on soil properties. The purpose of this study was to (i) characterize the spatial variability of soil respiration and related properties, (ii) evaluate the accuracy of results of the ordinary kriging method and sequential Gaussian simulation, and (iii) evaluate the uncertainty in predicting the spatial variability of soil CO2 emission and other properties using sequential Gaussian simulations. The study was conducted in a sugarcane area, using a regular sampling grid with 141 points, where soil CO2 emission, soil temperature, air-filled pore space, soil organic matter and soil bulk density were evaluated. All variables showed spatial dependence structure. The soil CO2 emission was positively correlated with organic matter (r = 0.25, p &lt; 0.05) and air-filled pore space (r = 0.27, p &lt; 0.01) and negatively with soil bulk density (r = -0.41, p &lt; 0.01). However, when the estimated spatial values were considered, the air-filled pore space was the variable mainly responsible for the spatial characteristics of soil respiration, with a correlation of 0.26 (p &lt; 0.01). For all variables, individual simulations represented the cumulative distribution functions and variograms better than ordinary kriging and E-type estimates. The greatest uncertainties in predicting soil CO2 emission were associated with areas with the highest estimated values, which produced estimates from 0.18 to 1.85 t CO2 ha-1, according to the different scenarios considered. The knowledge of the uncertainties generated by the different scenarios can be used in inventories of greenhouse gases, to provide conservative estimates of the potential emission of these gases.