End-member Analysis Research Articles

Metal-fluxes characterization at a catchment scale: Study of mixing processes and end-member analysis in the Meca River watershed (SW Spain)

Fluxes of acidity and contaminants from acid mine drainage (AMD) sources to the receiving surface water bodies were studied in a mining-impacted watershed (Meca River, SW Spain) using a novel methodology based on the joint application of EMMA and MIX codes. The application of EMMA and elemental ratios allowed delimiting the end-members responsible for water quality variations at a catchment scale. The further application of MIX quantified the significant impact of AMD on the river quality; less than 10% of AMD relative contribution is enough to maintain acidic conditions during most of the year. The mixing model also provided information about the element mobility, distinguishing those elements with a quasi-conservative behavior (e.g., Cu, Zn, Al, Co or Ni) from those affected by mineral precipitation/dissolution (e.g., K, Si, Na, Sr, Ca, Fe, Pb, or As). Floods are the main driver of dissolved and, mainly particulate, contaminants in the catchment. Thus, the first rainfall events in November only accounted for 19% of the annual Meca flow but yielded between 26 and 43% of the net acidity and dissolved metal loads (mainly, Fe, As and Pb). Concerning particulate transport, around 332tons of particulate Fe, 49tons of Al, 0.79tons of As and 0.37tons of Pb were recorded during these first floods. The particulate As concentration can be up to 34 times higher than the dissolved one during floods and between 2 and 4 times higher for Fe, Pb and Cr. This integrated modeling approach could be a promising and useful tool to face future restoration plans in derelict mines worldwide. This approach would allow prioritizing remedial measures, achieving an environmental and cost-effective restoration of degraded areas.

New methods for unmixing sediment grain size data

AbstractGrain size distribution (GSD) data are widely used in Earth sciences and although large data sets are regularly generated, detailed numerical analyses are not routine. Unmixing GSDs into components can help understand sediment provenance and depositional regimes/processes. End‐member analysis (EMA), which fits one set of end‐members to a given data set, is a powerful way to unmix GSDs into geologically meaningful parts. EMA estimates end‐members based on covariability within a data set and can be considered as a nonparametric approach. Available EMA algorithms, however, either produce suboptimal solutions or are time consuming. We introduce unmixing algorithms inspired by hyperspectral image analysis that can be applied to GSD data and which provide an improvement over current techniques. Nonparametric EMA is often unable to identify unimodal grain size subpopulations that correspond to single sediment sources. An alternative approach is single‐specimen unmixing (SSU), which unmixes individual GSDs into unimodal parametric distributions (e.g., lognormal). We demonstrate that the inherent nonuniqueness of SSU solutions renders this approach unviable for estimating underlying mixing processes. To overcome this, we develop a new algorithm to perform parametric EMA, whereby an entire data set can be unmixed into unimodal parametric end‐members (e.g., Weibull distributions). This makes it easier to identify individual grain size subpopulations in highly mixed data sets. To aid investigators in applying these methods, all of the new algorithms are available in AnalySize, which is GUI software for processing and unmixing grain size data.

Abnormal trace element concentrations in a shallow aquifer belonging to saline reclaimed environments, Codigoro (Italy)

Geogenic trace element (TE) contamination is an upcoming concern. The present study reports the temporal and spatial variation of major ions and TEs in a shallow unconfined aquifer belonging to a complex marsh saline environment reclaimed in modern age and intensively cultivated. The use of intensive depth profiles in five different locations gave insights into groundwater and sediment matrix interactions. Data indicate that the dominant factor involved in determining the spatial variability of TE is the sediment–water interaction, while the temporal variation of TE is due to the organic matter content and to the water table oscillation, which in turn drive the groundwater redox status and the mobilization of some inorganic microconstituents, such as Fe and Mn. Despite that the anthropogenic input of TEs in groundwater from fertilizer sources cannot be undoubtedly ruled out, given the elevated TE background concentrations, the combined use of high-resolution sediment profiles, seasonal groundwater sampling and end-member analyses is a promising procedure to distinguish between anthropogenic metal contamination and geogenic contribution in reclaimed deltaic environments. Finally, this study underlines the need of having a dense piezometer network and to perform several monitoring campaigns to ensure that the temporal and spatial variability could be correctly represented and background values of TE confidently determined.

The Jiulong River plume as cross-strait exporter and along-strait barrier for suspended sediment: Evidence from the endmember analysis of in-situ particle size

The influences of the Jiulong River on Taiwan Strait sediment resuspension and transport systems was conducted to reveal the extent to which longshore gradients in fine sediments could be related to the existence of a fresh water plume from the Jiulong River. An endmember model was used in the analysis of in-situ suspended particle size data obtained by a LISST Particle Analyzer Device, in order to understand the effect of Jiulong River plume on Taiwan Strait waters during the summer period of 2010. Three in-situ suspended particle endmembers, associated with particular sediment dynamic processes, are identified: Endmember 1, associated with estuarine waters; Endmember 2, associated with a fine sediment zone over longshore clinothem; and Endmember 3, associated with a coarse sediment zone over outer shelf and main channel of the strait. The spatial distribution of the Endmember 1 shows the adjustment of estuarine-related suspended particles from the upper water layer to the halocline layer when they were transported along the plume. The spatial distribution of Endmember 1 can also indicate how the Jiulong River estuarine-related suspended particles transport across the Taiwan Strait, although such a relatively small amount of river-derived suspended particle transport provides limited fine sediment source to the inner-shelf of the west Taiwan Strait. The distribution of the reworking fine sediment dominating Endmember 2 illustrates that the Jiulong River plume acts as a barrier to alter the along-strait transport of fine particles and the strengthened cross-strait transport traps them into the distal depocenter in west part of Taiwan Strait.

An appraisal of an iterative construction of the endmembers controlling the composition of deep-sea manganese nodules from the Central Indian Ocean Basin

This paper describes an estimation of endmember compositions followed by the assessment of those results by log-ratio variance analysis. As an appraisal, it deals only with the first objective of an endmember analysis namely, to identify endmembers if they exist by estimating their compositions. Following the creation of the endmember estimates, the computation of an array of log-ratio variances was a key innovation in this type of study. Log-ratio variances revealed intrinsic linear associations between the dominant elements on each of the estimated endmember compositions, largely confirming the endmember analysis. The dataset under study contained the concentrations of 16 elements in 93 samples of deep-sea manganese nodules from the Central Indian Ocean Basin. Many previous analyses of these nodules were undertaken to assess the economic potential of the deposits. This study by contrast, quantified the inter-element associations that account for the nodule compositions. Four endmembers were identified. The elements loaded on each were: (1) Mn, Zn, Ni, Cu, Mn-rich, (2) Fe, Ti, P, Co, Fe-rich, (3) Si, Al, Na, K, clay minerals, (3) Mg, ultramafic material, possibly including Mn, Cr, V, Ca, Na. These latter elements were also detected by their log-ratio variances to be associated with Mg on the 4th endmember.

Old carbon contributes to aquatic emissions of carbon dioxide in the Amazon

Abstract. Knowing the rate at which carbon is cycled is crucial to understanding the dynamics of carbon transfer pathways. Recent technical developments now support measurement of the 14C age of evaded CO2 from fluvial systems, which provides an important "fingerprint" of the source of C. Here we report the first direct measurements of the 14C age of effluxed CO2 from two small streams and two rivers within the western Amazonian Basin. The rate of degassing and hydrochemical controls on degassing are also considered. We observe that CO2 efflux from all systems except for the seasonal small stream was 14C-depleted relative to the contemporary atmosphere, indicating a contribution from "old" carbon fixed before ~ 1955 AD. Further, "old" CO2 was effluxed from the perennial stream in the rainforest; this was unexpected as here connectivity with the contemporary C cycle is likely greatest. The effluxed gas represents all sources of CO2 in the aquatic system and thus we used end-member analysis to identify the relative inputs of fossil, modern and intermediately aged C. The most likely solutions indicated a contribution from fossil carbon sources of between 3 and 9% which we interpret as being derived from carbonate weathering. This is significant as the currently observed intensification of weather has the potential to increase the future release of old carbon, which can be subsequently degassed to the atmosphere, and so renders older, slower C cycles faster. Thus 14C fingerprinting of evaded CO2 provides understanding which is essential to more accurately model the carbon cycle in the Amazon Basin.

A multi-tracer study of groundwater origin and transit-time in the aquifers of the Venice region (Italy)

Located in the northeastern region of Italy, the Venetian Plain (VP) is a sedimentary basin containing an extensively exploited groundwater system. The northern part is characterised by a large undifferentiated phreatic aquifer constituted by coarse grain alluvial deposits and recharged by local rainfalls and discharges from the rivers Brenta and Piave. The southern plain is characterised by a series of aquitards and sandy aquifers forming a well-defined artesian multi-aquifer system. In order to determine origins, transit times and mixing proportions of different components in groundwater (GW), a multi tracer study (3H, 3He/4He, 14C, CFC, SF6, 85Kr, 39Ar, 87Sr/86Sr, 18O, 2H, cations, and anions) has been carried out in VP between the rivers Brenta and Piave. The geochemical pattern of GW allows a distinction of the different water origins in the system, in particular based on HCO3-,SO42-,Ca/Mg,NO3-, 18O, 2H. A radiogenic 87Sr signature clearly marks GW originated from the Brenta and Tertiary catchments. End-member analysis and geochemical modelling highlight the existence of a mixing process involving waters recharged from the Brenta and Piave rivers, from the phreatic aquifer and from another GW reservoirs characterised by very low mineralization.Noble gas excesses in respect to atmospheric equilibrium occur in all samples, particularly in the deeper aquifers of the Piave river, but also in phreatic water of the undifferentiated aquifers. 3He–3H ages in the phreatic aquifer and in the shallower level of the multi-aquifer system indicate recharge times in the years 1970–2008. The progression of 3H–3He ages with the distance from the recharge areas together with initial tritium concentration (3H+3Hetrit) imply an infiltration rate of about 1km/y and the absence of older components in these GW. SF6 and 85Kr data corroborate these conclusions. 3H−3He ages in the deeper artesian aquifers suggest a dilution process with older, tritium free waters. 14C Fontes–Garnier model ages of the old GW components range from 1 to 12ka, yielding an apparent GW velocity of about 1–10m/y. Increase of radiogenic 4He follows the progression of 14C ages. 39Ar, radiogenic 4He and 14C tracers yield model-dependent age-ranges in overall good agreement once diffusion of 14C from aquitards, GW dispersion, lithogenic 39Ar production, and 4He production-rate heterogeneities are taken into account. The rate of radiogenic 4He increase with time, deduced by comparison with 14C model ages, is however very low compared to other studies. Comparison with 14C and 13C data obtained 40years ago on the same aquifer system shows that exploitation of GW caused a significant loss of the old groundwater reservoir during this time.

DETERMINING REFLECTANCE SPECTRA OF SURFACES AND CLOUDS ON EXOPLANETS

Planned missions will spatially resolve temperate terrestrial planets from their host star. Although reflected light from such a planet encodes information about its surface, it has not been shown how to establish surface characteristics of a planet without assuming known surfaces to begin with. We present a re-analysis of disk-integrated, time-resolved, multiband photometry of Earth obtained by the Deep Impact spacecraft as part of the EPOXI Mission of Opportunity. We extract reflectance spectra of clouds, ocean and land without a priori knowledge of the numbers or colors of these surfaces. We show that the inverse problem of extracting surface spectra from such data is a novel and extreme instance of spectral unmixing, a well-studied problem in remote sensing. Principal component analysis is used to determine an appropriate number of model surfaces with which to interpret the data. Shrink-wrapping a simplex to the color excursions of the planet yields a conservative estimate of the planet's endmember spectra. The resulting surface maps are unphysical, however, requiring negative or larger-than-unity surface coverage at certain locations. Our "rotational unmixing" supersedes the endmember analysis by simultaneously solving for the surface spectra and their geographical distributions on the planet, under the assumption of diffuse reflection and known viewing geometry. We use a Markov Chain Monte Carlo to determine best-fit parameters and their uncertainties. The resulting albedo spectra are similar to clouds, ocean and land seen through a Rayleigh-scattering atmosphere. This study suggests that future direct-imaging efforts could identify and map unknown surfaces and clouds on exoplanets.

Absorption-Based Hyperspectral Imaging and Analysis of Single Erythrocytes

We report an absorption-based hyperspectral imaging and analysis technique to resolve unique physicochemical characteristics of subcellular substances in single erythrocytes. We constructed a microscope system installed with a spectral light engine capable of controlling the spectral shape of the illumination light by a digital micromirror device. The hyperspectral imaging system and the sequential maximum angle convex cone algorithm allow us to extract unique spectral signatures (i.e., endmembers) for different types of hemoglobin, such as oxyhemoglobin, methemoglobin, and hemozoin, and scatter from cell membrane in single erythrocytes. Further statistical endmember analysis, conducted on the hyperspectral image data, provides the abundances of specific endmembers, which can be used to build intracellular maps of the distribution of substances of interest. In addition, we perform modeling based on Mie theory to explain the scattering signatures as a function of scattering angle. The developed imaging and analysis technique enables label-free molecular imaging of endogenous biomarkers in single erythrocytes in order to build oxymetric standards on a cellular level and ultimately for in vivo as well.

Spatial Distribution of Δ14C Values of Organic Matter in Surface Sediments Off Saru River in Northern Japan, One Year After a Flood Event in 2006

Dispersion and deposition of terrestrial organic matter by flooding on the inner shelf were studied using C/N ratios, δ13C, and Δ14C values of sedimentary organic matter. Surface sediment samples (top 2 cm) were collected from coastal areas near the Saru River in southwestern Hokkaido, northern Japan, 1 yr after a flood event in 2006. Riverine suspended solids were also collected at a fixed station downstream during 2006–2008. Sandy sediments were located at the front of the river mouth and the western part of the sampling area, with the δ13C of organic matter ranging from −23.8‰ to −22.0‰, Δ14C of –655‰ to –388‰, and an organic carbon/total nitrogen (C/N) ratio of 5.9–7.7. On the other hand, silt and clay sediments were distributed in a restricted area 11–16 km from the river mouth, with lighter δ13C (–26.7‰ to −24.1‰) and higher Δ14C (–240‰ to –77‰) of organic matter and C/N ratio (7.8–13.3). From end-member analysis, the apparently younger and less degraded organic matter in the silt and clay sediments consists mainly of terrestrial organic matter released by flood events. They remain in the depression, although most flood deposits were moved to deep-sea environments.

A Bayesian Statistical Model for End Member Analysis of Sediment Geochemistry, Incorporating Spatial Dependences

Summary An important problem in the management of water supplies is identifying the sources of sediment. The paper develops a Bayesian approach, utilizing an end member model, to estimate the proportion of various sources of sediments in samples taken from a dam. This approach not only allows for the incorporation of prior knowledge about the geochemical compositions of the sources (or end members) but also allows for correlation between spatially contiguous samples and the prediction of the sediment's composition at unsampled locations. Sediments that were sampled from the North Pine Dam in south-east Queensland, Australia, are analysed to illustrate the approach.

End Member Analysis of Spaceborne Thermal Infrared Data of Meteor Crater, Arizona and Application to Future Mars Data Sets

End Member Analysis of Spaceborne Thermal Infrared Data of Meteor Crater, Arizona and Application to Future Mars Data Sets

A three‐component end‐member analysis of streamwater hydrochemistry in a small Japanese forested headwater catchment

AbstractIntensive water sampling in conjunction with hydrological observations was conducted during three different rainstorms in order to understand the effects of rainfall events on the temporal variation of streamwater chemistry in a small headwater forest catchment. Concentrations of Na+ and SO42− decreased as the discharge rate increased. Hydrograph separation of the components was made using the three‐component model based on the end‐members mixing analysis (EMMA). The three end‐members were: the groundwater in the saturated zone that prescribes the chemistry of the baseflow; the throughfall that dilutes the streamwater; the groundwater in the transient saturated zone prescribed, which was dependent on the groundwater level. When the groundwater level was lower, only the two components, groundwater in the saturated zone and throughfall, affected the streamwater chemistry. When the groundwater level rose and the saturated zone spread, the groundwater in the transient saturated zone became the third component. When the groundwater in the transient saturated zone contributed to the discharge, this component became the dominant source and the streamwater chemistry was affected by the groundwater chemistry in the transient saturated zone. When this component was discharged as the saturation overland flow, the streamwater chemistry was greatly affected by this component. Copyright © 2001 John Wiley & Sons, Ltd.

A least squares algorithm for a mixture model for compositional data

The estimation of a model for compositional data is studied where the data are approximated by a mixture of latent compositions. This model is variously known as “endmember analysis” or “latent budget analysis”. Two estimation procedures are available. The first uses a procedure which is incorrect in the sense that, although it claims to be a least squares procedure, it does not always minimize a least squares criterion. The second uses a maximum likelihood procedure starting from assumptions that are often violated for compositional data. In this paper we propose a constrained (weighted) least squares procedure for the estimation of the model.

Nearshore Regions of Lake Superior: Multi-element Signatures of Mining Discharges and a Test of Pb-210 Deposition under Conditions of Variable Sediment Mass Flux

Around the turn-of-the century, mining activities greatly increased sediment accumulation and metal fluxes in nearshore regions of Lake Superior. In the low-energy environment of Portage Lake, within the Keweenaw Waterway estuary, sediment accumulation increased 33X, whereas elemental Cu flux increased 312X. One difficulty in establishing the dispersion of mining discharges is that stamp sands were derived from local ore deposits, hence few elements are “unique” to the source materials. One approach is to search for multi-elemental “signatures” in concentration and flux profiles. For example, several rare earth elements of the lanthanide series are characteristic of source materials and have the potential to identify stamp sand material across Lake Superior. Although conditions of variable mass loading from multiple sources can produce complicating dilution effects in concentration profiles, multivariate techniques are capable of deciphering original source signals. Here non-destructive neutron activation analysis was utilized to construct elemental flux and concentration profiles, then multivariate techniques (Factor Analysis, End-member Analysis) were used to illustrate how partial mass flux signatures can be assigned to two different types of ore lodes (conglomerate, amygdaloid) and to background (erosional) sedimentation. Temporal patterns were verified through archived company discharge records. Also exploited were the varve-like deposition of slime clays to independently check 210Pb determinations under conditions of variable sediment mass flux and to demonstrate constant excess 210Pb delivery to sediments in the presence of massive slime clay loading. The results suggest assumptions of 210Pb dating may apply under conditions where sediment accumulation is highly variable.

Endmember analysis of heavy-metal pollution in surficial sediments from the Gulf of Gdansk and the southern Baltic Sea off Poland

Thirty one bulk (<2 mm) samples of surficial sediments from the Gulf of Gdansk and the Southern Baltic Sea off Poland were analyzed for 20 elements and the resulting compositional dataset was subjected to endmember analysis. The compositions of 4 endmember estimates were constructed and the abundances of these endmembers were calculated for each sample. Copper, Zn and Ag appear on one endmember and Cd and Pb on another. This suggests that Cu, Zn and Ag are introduced into the Gulf of Gdansk principally from the Vistula River whereas Cd and Pb are introduced as a result of atmospheric and riverine transport of these elements. The dual source of Cd and Pb into the Gulf of Gdansk may explain the complex interelement relationships displayoed by these elements in the sediments from this region.

Endmember analysis of metalliferous sediments from the Galapagos Rift and East Pacific Rise between 2°N and 42°S

594 sediment samples from the Galapagos Rift System (GRS) and the crest of the East Pacific Rise (EPR) were chemically analyzed for 12 elements. Carbonate-free compositional datasets associated with each of 3 regions, the GRS, the EPR 2°N–4°S and the EPR 10°S–42°S, were separately subjected to endmember analysis. The compositions of endmember estimates were constructed for each dataset. These composition largely confirmed theidentities of endmembers that had previously been inferred from the varimax rotated loadings of a conventional factor analysis (of the correlation matrices) of the same 3 datasets. In view of the widely-reported unreliability of the correlation structure of compositional data, the confirmation by endmember analysis of the results of a factor analysis is itself quite remarkable. However, the particular advantage of endmember analysis is that the chemical compositions of extreme sources are estimated, and may readily be interpreted. The samples in the dataset can then be expressed as mixtures of these extreme sources. By contrast, the varimax rotated loadings of a factor analysis indicate only those elements that are associated together on a single factor which may or may not be an endmember, the composition of which nevertheless remains unknown.

End-member Analysis and Latent Budget Analysis

End-member Analysis and Latent Budget Analysis

Analyses of Forest Foliage II: Measurement of Carbon Fraction and Nitrogen Content by End-Member Analysis

Chemical constituents of forest canopies are accepted as key indicators of ecosystem state and function. Remote sensing of these parameters offers the potential for rapid and accurate assessment of rates of key biogeochemical processes over large regions. NASA's Accelerated Canopy Chemistry Program was established to test the accuracy and generality of high-spectral resolution remote sensing in the measurement of lignin, cellulose and nitrogen concentrations in forest canopies. One of the most straightforward methods for extracting constituent concentration information from spectra is through simple linear mixing models of pre-determined end-member or pure compound spectra. While there are ample reasons to expect that linear mixing models will not work in foliar and whole-canopy samples, end-member analysis might still provide important information in support of standard and emerging statistical techniques, such as linear regression and partial least squares regression on first and second difference spectra, by indicating which parts of the spectrum should contain information on the concentrations of important constituents. The purpose of this paper is to present the results of two approaches to determining the value of end-member spectra for estimating constituent concentrations in foliage of temperate zone forest species. The first examines the spectral changes accompanying each step in the chemical proximate analysis method used to determine concentrations in the laboratory, and from them to infer the spectra of the fractions removed at each step. The second is the combination of known materials which approximate these same fractions in foliage into well-mixed samples to determine whether a simple linear mixing model can be used to predict the spectrum of the resulting mixture. Results confirm that the combination of linear mixing models and end-member analysis is not an appropriate technique for obtaining quantitative estimates of constituent concentrations for the major components of foliage of native woody plants, nor do we expect that more detailed analyses of plant ultrastructure or foliar spectra will correct the deficiencies identified. However, these results do suggest that the wet chemical procedures used to extract different carbon fractions produce consistent results with regard to the location of spectral features associated with the compounds removed at each step, and that the spectra of the cellulose and lignin isolated by this technique are very similar to those from pure materials. This in turn suggests that statistical techniques such as linear regression on first and second difference spectra and partial least squares methods which allow or correct for non-linear mixing, should be successful.

Comparative mineralogy and geochemistry of hydrothermal iron‐rich crusts from the Pitcairn, Teahitia‐mehetia, and Macdonald hot spot areas of the S. W. pacific

Abstract Hydrothermal iron‐rich crusts have been recovered from a number of hot spot volcanos including Crough Seamount, Pitcairn Volcanos 2 and 1, Cyana Seamount, Teahitia, Moua Pihaa, and Macdonald Seamount in the S. W. Pacific. Mineralogically, the crusts consists of ferrihydrite with traces of the weathering products of volcanic ash (feldspar, nontronite, pyroxene, and serpentinite). The iron oxyhydroxide phase has a mean particle size of 3–4 nm indicating rapid deposition. Electron microprobe studies have revealed the presence of filamentous iron‐silica deposits within the crusts reflecting the possible bacterial oxidation of iron from the hydrothermal fluids. The crusts display wide variability in composition both between individual sampling stations and between seamounts. Endmember analysis shows that the compositional data can be resolved into three endmembers: a Fe‐rich endmember, a light and heavy rare earth element endmember, and a Ba (barite)‐rich endmember. The Fe‐rich endmember appears to contain very low concentrations of most trace elements. For bulk samples, the composition of the iron‐rich crusts reflects dilution of the iron oxyhydroxide phase by volcanic ash and, to a lesser extent, a hydrogenous component. This is illustrated by the wide variability in SiO2 (11.1–71.3%) and Mn (0.01–1.21%) contents of the crusts. For iron‐rich crusts containing greater than 40% Fe, the Pitcairn crusts display lower contents of Pb, Ba, Mo, U, Th, As, and rare earth elements (REE) and lower cerium anomalies than those from Teahitia. REE profiles of crusts from each of the hot spot volcanoes are characterized by small negative cerium anomalies but pronounced positive europium anomalies. The low average La/Fe ratios of the crusts from the various seamounts (47–572 X 10‐6) and positive Eu anomalies of the crusts suggest rapid deposition of the iron oxyhydroxide near the hydrothermal vent. The high Fe/Mn ratio of vent fluids at hot spot volcanoes (8.5–5.6) may account for the formation of these iron‐rich crusts. The present data indicate that there may be differences in the nature of the iron‐rich crusts based on the depth of occurrence. This influences the temperature of the venting hydrothermal fluids and the possibility of occurrence of submarine phreatomagmatic eruptions.