Visible near-infrared reflectance spectroscopy as a predictive indicator of soil properties

It is becoming increasingly important to improve spatial resolutions of soil maps as a fundamental information layer for studying ecological processes and to tackle land degradation. There is growing interest in the use of remote sensing technologies to assist the identification and delineation of spatial variation in soils. This paper investigates whether selected properties of extensively weathered, low fertility soils can be predicted using high-resolution reflectance spectra over the range 400–2500 nm. Clay content, carbonate concentration, organic carbon content and iron oxide content were analysed for 300 soil samples collected from the Jamestown, Belalie district, South Australia. The paper also examines the efficacy of this soil analysis methodology to supplement or replace traditional soil sampling in soil survey to increase sampling density and improve the spatial resolution of soil maps.Reflectance spectra were obtained from air-dried samples under controlled laboratory conditions using an ASD FieldSpec Pro spectroradiometer. Partial least squares regression was used to examine relationships between soil mineralogy, clay content and organic carbon and the reflectance spectra and identify the wavelengths contributing to prediction of these soil properties. Results show that it is possible to predict clay content, soil organic carbon, iron oxide content and carbonate content. Cross-validation R² values for all analyses were above 0.5 and the residual prediction difference (RPD) was acceptable for all soil properties. Carbonate and clay content were more accurately predicted than iron oxide and organic carbon. All samples were collected from the same geographical area such that they represented physical properties over a naturally occurring range and provide a prediction that could be related to subsequent image analysis or be used to carry out local scale soil survey. A rapid and reliable form of soil mapping could be developed from this methodology.     

湛江高桥红树林表层沉积物的粒度空间分布特征

红树林湿地是滨海湿地的一个重要类型,也是重要的沉积库.沉积物是红树林定居与生长的基质,记载着红树林湿地的环境历史,可用于物源分析和沉积过程反演,对于红树林湿地的生态恢复和保护具有重要意义.2011年7月,以湛江国家级红树林自然保护区高桥片区红树林湿地为研究区,沿着水动力梯度进行取样,并基于沉积物粒度分析其表层沉积特征,通过地统计学方法生成预测表面,并结合有机质含量和群落结构进行相关性分析.结果表明:研究区沉积物是以粘、粉粒为主的混合沉积类型,砂粒、粘粒和粉粒平均含量分别为(27.8±15.4)%、(40.3±15.4)%和(32.1±11.4)%;表层沉积特征呈现明显的空间梯度,随着与陆地距离增加,从高潮位到低潮位方向上,沉积物砂粒含量增加,粘粒含量降低.表层沉积的有机质与粉粒含量呈正相关,而与砂粒呈负相关,且在水动力条件弱的高潮位区域,有机质含量高.表层沉积特征在不同群落生境间存在差异,沉积特征与不同红树林群落结构存在一定程度的相关性,反映了水动力条件与红树林之间的复杂关系.     

Prediction of Soil Organic Carbon at the European Scale by Visible and Near InfraRed Reflectance Spectroscopy

Soil organic carbon is a key soil property related to soil fertility, aggregate stability and the exchange of CO₂ with the atmosphere. Existing soil maps and inventories can rarely be used to monitor the state and evolution in soil organic carbon content due to their poor spatial resolution, lack of consistency and high updating costs. Visible and Near Infrared diffuse reflectance spectroscopy is an alternative method to provide cheap and high-density soil data. However, there are still some uncertainties on its capacity to produce reliable predictions for areas characterized by large soil diversity. Using a large-scale EU soil survey of about 20,000 samples and covering 23 countries, we assessed the performance of reflectance spectroscopy for the prediction of soil organic carbon content. The best calibrations achieved a root mean square error ranging from 4 to 15 g C kg⁻¹ for mineral soils and a root mean square error of 50 g C kg⁻¹ for organic soil materials. Model errors are shown to be related to the levels of soil organic carbon and variations in other soil properties such as sand and clay content. Although errors are ∼5 times larger than the reproducibility error of the laboratory method, reflectance spectroscopy provides unbiased predictions of the soil organic carbon content. Such estimates could be used for assessing the mean soil organic carbon content of large geographical entities or countries. This study is a first step towards providing uniform continental-scale spectroscopic estimations of soil organic carbon, meeting an increasing demand for information on the state of the soil that can be used in biogeochemical models and the monitoring of soil degradation.     

Towards Quantitative Spatial Models of Seabed Sediment Composition

There is a need for fit-for-purpose maps for accurately depicting the types of seabed substrate and habitat and the properties of the seabed for the benefits of research, resource management, conservation and spatial planning. The aim of this study is to determine whether it is possible to predict substrate composition across a large area of seabed using legacy grain-size data and environmental predictors. The study area includes the North Sea up to approximately 58.44°N and the United Kingdom’s parts of the English Channel and the Celtic Seas. The analysis combines outputs from hydrodynamic models as well as optical remote sensing data from satellite platforms and bathymetric variables, which are mainly derived from acoustic remote sensing. We build a statistical regression model to make quantitative predictions of sediment composition (fractions of mud, sand and gravel) using the random forest algorithm. The compositional data is analysed on the additive log-ratio scale. An independent test set indicates that approximately 66% and 71% of the variability of the two log-ratio variables are explained by the predictive models. A EUNIS substrate model, derived from the predicted sediment composition, achieved an overall accuracy of 83% and a kappa coefficient of 0.60. We demonstrate that it is feasible to spatially predict the seabed sediment composition across a large area of continental shelf in a repeatable and validated way. We also highlight the potential for further improvements to the method.     

Diel patterns in the habitat utilisation of sandeels revealed using integrated acoustic surveys

Tracking the movements of sandeels in relation to their habitat will provide an improved understanding of sandeel ecology, including their interrelationships with predators and fishing activity. We examined spatial and temporal changes in the behaviour and distribution of the lesser sandeel Ammodytes marinus by integrating the acoustic ground discrimination system QTC VIEW with a Simrad EK500 fisheries scientific echosounder. QTC VIEW was used to identify acoustic changes in the properties of the seabed in the presence of buried sandeels, whilst the EK500 simultaneously recorded temporal changes in their distribution throughout the water column. Our results suggest that high densities of sandeels buried in sediment give a different acoustic signal to that of its surroundings. This integrated approach showed that sandeels had a diurnal activity pattern that was strongly, although not exclusively, associated with day length. Using this integrated survey method will enable large-scale cost-effective surveys of sandeel behaviour, distribution and abundance to be conducted.     

Resource quality affects carbon cycling in deep-sea sediments

Deep-sea sediments cover ∼70% of Earth''s surface and represent the largest interface between the biological and geological cycles of carbon. Diatoms and zooplankton faecal pellets naturally transport organic material from the upper ocean down to the deep seabed, but how these qualitatively different substrates affect the fate of carbon in this permanently cold environment remains unknown. We added equal quantities of ¹³C-labelled diatoms and faecal pellets to a cold water (−0.7 °C) sediment community retrieved from 1080 m in the Faroe-Shetland Channel, Northeast Atlantic, and quantified carbon mineralization and uptake by the resident bacteria and macrofauna over a 6-day period. High-quality, diatom-derived carbon was mineralized >300% faster than that from low-quality faecal pellets, demonstrating that qualitative differences in organic matter drive major changes in the residence time of carbon at the deep seabed. Benthic bacteria dominated biological carbon processing in our experiments, yet showed no evidence of resource quality-limited growth; they displayed lower growth efficiencies when respiring diatoms. These effects were consistent in contrasting months. We contend that respiration and growth in the resident sediment microbial communities were substrate and temperature limited, respectively. Our study has important implications for how future changes in the biochemical makeup of exported organic matter will affect the balance between mineralization and sequestration of organic carbon in the largest ecosystem on Earth.     

Utility of amino acids as biomarkers in polar marine sediments: a study on the continental shelf of Larsen region, Eastern Antarctic Peninsula

Ongoing global warming is affecting the polar regions at a faster pace than in many other lower latitude environments. Based on the idea that the changes at the sea surface leave a signal in the sedimentary record, we analysed the total hydrolysable amino acid (THAA) and enzymatically hydrolysable amino acid (EHAA) contents in sediments off the coast of the eastern Antarctic Peninsula during the decade following the collapse of sections A and B of the Larsen ice shelf to check their utility as biomarkers of this event. Two organic matter lability indexes (the EHAA-to-THAA ratio and the Dauwe degradation index) were also calculated to assess the quality of the organic matter in the sediment column. The THAA and EHAA concentrations in the upper 5 mm varied between ~1 and ~10 nmol mg^?1 DW^?1, corresponding to an oligotrophic environment, whereas the quality of the organic matter as indicated by the lability indexes was relatively high in the upper sediment column (<2 cm deep). The amino acid profiles and indexes in the sediment column were compared to the pigment profiles and indexes published in previous studies for the same stations. The results suggest that in the sediment column, pigments track more accurately than amino acids the pelagic organic matter supply to the seabed after the collapse of the Larsen ice shelf.     

The Benthic Impacts of the Loch Linnhe Artificial Reef

Artificial reefs are man-made structures that are placed on the seabed to mimic natural reefs. The Loch Linnhe Artificial Reef will consist of up to 40 reef modules, when completed, each constructed using concrete blocks. As part of this complex, reef modules of approximately 200 tonnes were deployed in June 2001 and January 2002 and form the basis of this study. Sediment samples were taken adjacent to- and 5 m from the reef perimeters and characterised in terms of sediment oxygenation (redox), particle size, organic carbon (loss on ignition) and coarseness (material >1 mm and <5 mm). Changes in molluscs and ophiuroids (>1 mm) present in the sediment were linked to chemico-physical changes occurring as a consequence of the reef. Both reefs trapped macroalgal phytodetritus at the perimeters, which subsequently decomposed. This accumulated material isolated the seabed from the overlying water column and was associated with a decrease in sediment oxygenation that was linked to changes in community structure. LOI was significantly higher around one reef compared with 5 m from that reef. The reefs did not cause significant changes in the sediment texture (median particle size or coarseness) and neither LOI nor sedimentary texture changes were associated with community change.     

Microenvironments and microbial community structure in sediments

The aim of this study was to explore the potential of a combined chemical and microbiological approach as part of a study of organic carbon oxidation processes in sediments. An assessment of microbiological diversity using molecular techniques was carried out in combination with high resolution chemical measurements at the sediment-water interface of a coastal lagoon affected by eutrophication in autumn 2000. There was a 0.2 mm overlap between the O2 and H2S profiles. pH showed a maximum just above the sediment-water interface coinciding with an oxygen maximum, suggesting photosynthetic activity, and a minimum coinciding with the O2-H2S interface. The redox potential was high in bottom water and surface sediment, reflecting the presence of oxygen and oxides, and reached low values after a step-wise decrease at -18 mm. Reduction of Fe occurred within the biofilm at the O2-H2S interface and was mostly due to reduction by H2S. The elevated concentrations of dissolved Mn in the oxic water may have been caused either by in situ production within organic aggregates or lateral water flow from sites nearby at which Mn2+ diffuses out of the sediment. Sequences related to sulphur chemolitotrophs were retrieved from the biofilm samples, which is consistent with the small overlap between O2 and H2S observed in this biofilm. Although the resolution of techniques used was different, sequencing results were consistent with chemical data in delineating the same horizons according to redox, pH or ecological properties.     

Recent variations in sediment organic carbon content in Lake Soyang (Korea)

Four gravity cores were taken from Lake Soyang, which was created by the construction of an artificial dam in 1973. The variation of organic carbon content of the bottom sediments since the construction was interpreted using a variety of sedimentological and geochemical measurements. Based on the textural properties of sediments and the total organic carbon (TOC) content, it is clear that sediment organic carbon has been deposited very consistently throughout the postconstruction period, except for local sudden inputs caused by summer flooding events near fish farms or farmland areas. The autochthonous input resulting from the enhanced primary production led by phytoplanktons each year is likely to become a major problem at downstream sites within Lake Soyang. The vertical variation of δ¹³C values of sediment organic matter also reflects the fact that the level of autochthonous supply of organic carbon becomes high downstream.An erratum to this article can be found at .     

Measurements of Seasonal Rates and Annual Budgets of Organic Carbon Fluxes in an Antarctic Coastal Environment at Signy Island, South Orkney Islands, Suggest a Broad Balance between Production and Decomposition

We report here the first comprehensive seasonal study of benthic microbial activity in an Antarctic coastal environment. Measurements were made from December 1990 to February 1992 of oxygen uptake and sulfate reduction by inshore coastal sediments at Signy Island, South Orkney Islands, Antarctica. From these measurements the rate of benthic mineralization of organic matter was calculated. In addition, both the deposition rate of organic matter to the bottom sediment and the organic carbon content of the bottom sediment were measured during the same period. Organic matter input to the sediment was small under winter ice cover, and the benthic respiratory activity and the organic content of the surface sediment declined during this period as available organic matter was depleted. On an annual basis, about 32% of benthic organic matter mineralization was anoxic, but the proportion of anoxic compared with oxic mineralization increased during the winter as organic matter was increasingly buried by the amphipod infauna. Fresh organic input occurred as the sea ice melted and ice algae biomass sedimented onto the bottom, and input was sustained during the spring after ice breakup by continued primary production in the water column. The benthic respiratory rate and benthic organic matter content correspondingly increased towards the end of winter with the input of this fresh organic matter. The rates of oxygen uptake during the southern summer (80 to 90 mmol of O₂ m^-2 day^-1) were as high as those reported for other sediments at much higher environmental temperatures, and the annual mineralization of organic matter was equally high (12 mol of C m^-2 year^-1). Seasonal variations of benthic activity in this antarctic coastal sediment were regulated by the input and availability of organic matter and not by seasonal water temperature, which was relatively constant at between -1.8 and 0.5°C. We conclude that despite the low environmental temperature, organic matter degradation broadly balanced organic matter production, although there may be significant interrannual variations in the sources of the organic matter inputs.     

Total PCB-organic matter correlation in sediments from three estuarine areas of Portugal

Levels of tPCB and organic matter content were determined in surface sediments from Sado and Tagus estuaries and Ria Formosa lagoon, and in particles collected in sediment traps in Ria Formosa. Significant relationships (p<0.001) between concentrations of tPCB and organic matter content were obtained when the most contaminated samples and the less contaminated organic-rich sediments were excluded. The excluded samples originated from nearby PCB and organic matter sources. Organic matter appears, thus, the most important indicator of a sediment's sorptive capacity in these estuarine systems, except near the sources where the organic seeking effect is masked. On the basis of the relationship slopes one may conclude that Tagus and Sado estuaries are more contaminated than Alcacer channel (upper Sado estuary) and Ria Formosa.     

The Sedimentary Milieu and its Consequences for Resident Organisms

While benthic ecologists have often studied the inter-relationshipsof benthic animals and sediment, only recently has the sedimentbeen examined at a scale appropriate to the animals of interest.In studying sediment as food for benthic animals, it is commonplacefor the nutritional value of the sediment to be characterizedin terms of the size distribution of mineral grains and somemeasure of the organic matter content such as percent by weightof organic C and N. These measures have been shown to be nearlymeaningless and have been replaced by measures of proteins andamino acids, bacterial and eucaryote biomass, and by a visualexamination of the sediment using thin section techniques.Thelatter method also shows that marine muds are not very homogeneousover distances of hundreds of micrometers and that the relationshipbetween mineral grains and organic matter in sediment is verycomplex. The interstitial pore waters of marine sediment havealso come under increasing scrutiny, chiefly through the developmentand use of microelectrodes. Oxygen concentration is not wellcorrelated with sediment color but is controlled by the rateof consumption within the sediment and diffusion, which is afunction of distance and time from an oxygenated source, forexample, the overlying water at the sediment-water interfaceor an actively ventilated burrow. The delivery of oxygen, thedistribution of metabolizable organic matter, and the packingof sediment grains are all properties of sediment that varyon the scale of millimeters and may strongly affect the abilityof resident organisms to live and reproduce.     

Origin, biochemical composition and vertical flux of particulate organic matter under the pack ice in Terra Nova Bay (Ross Sea, Antarctica) during late summer 1995

Water samples and particulate materials settling under the pack ice were collected in an ice-covered area near the Terra Nova Bay Italian Station during late summer 1995, in order to study short-term changes in the biochemical composition of particulate organic matter. At the end of the study period the phytoplankton biomass increase (up to >3.0 μg chlorophyll-a l⁻¹) was probably related to the intrusion under the pack ice of chlorophylls-enriched surface waters coming from the near ice-free area. Such increase was associated also with a notable increase in particulate organic matter concentrations, as well as in particulate organic matter vertical fluxes (up to >100 mg C m⁻² day⁻¹). Proteins were the most abundant biochemical class of particulate organic matter (on average about 49%), followed by lipids (29%) and carbohydrates (22%). By contrast, organic matter collected in the sediment trap was characterized by the dominance of lipids (about 55% of the total biopolymeric carbon flux) over carbohydrates (28%) and proteins (17%). The hydrolizable particulate biopolymeric carbon accounted for about 23% of total biopolymeric carbon. This value was about one-half of that found in ice-free waters, suggesting that the suspended particulate organic material under the pack ice was less digestible than in ice-free waters or was already partially digested. Despite this, and the decay of labile organic compounds in the sediment trap during the deployment, material settling towards the sea bottom under the pack ice in Terra Nova Bay, owing to its high lipid content, might represent an important high-quality food source for benthic consumers. Finally, assuming as possible the intrusion under sea ice of primary organic matter-enriched waters, we hypothesize the occurrence of a “fertilization” effect deriving from ice-melting areas towards under-ice waters, supplying the latter with an additional rate of primary organic matter. Accepted: 18 February 1999     

The impact of the kelp (Laminaria hyperborea) forest on the organic matter content in sediment of the west coast of Norway

Sediment cores were collected from an area off the west coast of Norway, where a well-established kelp community made up mainly of Laminaria hyperborea is found. Chemical analyses of the sectioned sediment cores were made, which included organic carbon, carbohydrates and phenols. These were used to collate the sediments in order to establish whether the different sites had a common origin and if this was kelp-related. The organic matter content in the surface sediments appears to be related to the water depth, which determines the degree of perturbation at the sediment-water boundary and hence the sedimentation of the organic matter. The relation between carbohydrates and phenols in the sediment appears to indicate a common origin. However, the carbohydrate and phenol content in the sediment organic fraction appears to closely resemble (to be analogous) to that of the kelp Laminaria hyperborea. Although there are some diagenetic and decomposition changes in the subsurface (historical) organic matter (that may alter its findings), this study provides good evidence that the deposits were supplied by the kelp forest in the region. The sedimentation and export of kelp-derived material is of particular significance in terms of benthic ecology and production and may also play a significant role in the global carbon budget.     

基于小波变换的土壤有机质含量高光谱估测

利用统计分析方法选取了土壤N、P、K元素含量近似而有机质含量差异较大的样本60个,通过高光谱探测分析获得样本反射率对数的一阶导数光谱,采用Bior 1.3函数进行多层离散小波分解,剔除低频近似信号和高频噪声信号,得到反映土壤理化参数的特征光谱曲线;采用相关分析筛选土壤有机质含量的显著相关波段,基于显著相关波段和特征光谱曲线分别构建土壤有机质含量高光谱多元回归估测模型;通过比较分析,确定了提取土壤有机质特征光谱的最佳小波分解尺度并构建了最佳预测模型.结果表明： 提取土壤有机质特征光谱的最佳小波分解层数是9层,其次是8层和10层;基于小波9层分解特征光谱曲线的有机质含量估测模型最佳,其决定系数（R²）为0.89,比基于显著相关波段构建模型的R²增加了0.31,比基于原始光谱所构建模型的R²增加了0.10.     

Evidence for the influence of seagrasses on the benthic nitrogen cycle in a coastal plain estuary near Beaufort,North Carolina (USA)

A study was undertaken to evaluate the interrelationship between the presence of seagrasses, Zostera marina and Halodule wrightii, and the physical and chemical properties of sediments in a coastal plain estuary near Beaufort, North Carolina. In sediments underlying a cover of seagrass, silt-clay, organic matter, exchangeable ammonium, ammonium dissolved in pore waters and total nitrogen were larger than in unvegetated profiles. The magnitude of the physical and chemical properties of sediments varied according to the location of the station in relation to the vegetation, as well as the continuity in the distribution of the seagrass. The largest pools of nitrogen, the finest sediment texture, and the greatest organic matter content were in sediments associated with the mid bed regions of seagrass meadows, intermediate at the edges of the bed and small isolated patches of grass, and least in unvegetated substrate.General conclusions from this study are: 1) once established, seagrasses appear capable of modifying the sediment texture as well as the organic matter and nitrogen content; 2) nitrogen accumulates beneath the vegetation suggesting that vegetated sediments are sinks; however, functional recycling mechanisms seem to be operating as suggested by the larger magnitude of remineralized nitrogen in the vegetated profiles; and 3) the establishment of seagrasses in this geographical region are not necessarily restricted by the sediment properties measured in this study. These data and conclusions are discussed in regard to an application of contemporary theories of ecosystem development to seagrass systems.Contribution Number 82-22-B     

Massive uprooting of Littorella uniflora (L.) Asch. during a storm event and its relation to sediment and plant characteristics

During spring storms massive uprooting of Littorella uniflora occurred in a shallow Dutch softwater lake. The aim of this study was to test whether changes in plant morphology and sediment characteristics could explain the observed phenomenon. Uprooting was expected to occur in plants having a high shoot biomass and low root to shoot ratio (R:S), growing on sediments with a high organic matter content. Normally, uprooting of the relative buoyant L. uniflora is prevented by an extensive root system, expressed as a high R:S. This was studied by sampling floating and still rooted L. uniflora plants, as well as sediment and sediment pore water, along a gradient of increasing sediment organic matter content. Increasing organic matter content was related to increasing L. uniflora shoot biomass and consequently decreasing R:S. Furthermore, the results indicated that uprooting indeed occurred in plants growing on very organic sediments and was related to a low R:S. The increased shoot biomass on more organic sediments could be related to increased sediment pore water total inorganic carbon (TIC; mainly CO₂) availability. Additionally, increased phosphorus availability could also have played a role. The disappearance of L. uniflora might lead to higher nutrient availability in the sediments. It is suggested that this could eventually promote the expansion of faster‐growing macrophytes.     

Accuracy and precision in sediment chronology

Several complications are encountered in radiocarbon dating of limnological samples. The contamination problem is obvious. Since lake sediments are usually composed of both allochthonous and autochthonous material the origin must be considered. The organic content may give some guidance. Graphite in the catchment area and a low organic content indicate a potential risk of major errors in the dates. Organic material from the surroundings may be displaced into a lake by creeks, snowslides and wind. Such material may be older than, or contemporaneous with the sediment deposited at the same time. Water-level changes and wave action may cause erosion and thus admixture of old material. Such contamination can sometimes be traced via different fractions extracted mechanically or chemically. The accelerator technique has made it possible to date small samples and thus macrofossils can be selected as the material to be used for dating far more frequently than is possible with the conventional technique for activity measurement.Another problem is the reservoir effect — thus the lower ¹⁴C activity of the dissolved bicarbonate and carbon dioxide than of the atmosphere. There may be several reasons besides dissolved carbonates in hard-water lakes. Some plants even use carbon dioxide in the sediment. It is thus to be expected that submerged plants will be dated too old. Selection of plant remains for dating is thus no guarantee of an accurate date. The material to be preferred is terrestrial, such as tree leaves or remains of emergent plants.Bioturbation must not be forgotten since this means that old material may be found too high in a sediment, and young material can be brought downwards in the sediment. A single date may be very misleading. Under rather stable conditions the sediment accumulation rate can be roughly estimated and acceptable dates obtained despite the complications.It may be worth sieving gyttja samples to remove roots and rootlets. Roots in peat should also be removed. Diagrams are available of the errors due to certain degrees of contamination by younger or older material.The ¹³C content must be measured to allow a normalisation. The present knowledge of the secular variations of the ¹⁴C activity allows calibration of dates made on wood etc. The same curves cannot be used for submerged material because of the lower ¹⁴C activity. Sudden changes of the atmospheric ¹⁴C activity are smoothed. Certain age ranges give better resolution than others. Recent curves indicate that strange results are to be expected for Holecene samples with a real age of 7000 years or older. Finally bacterial influence during storage may influence the isotopic composition.