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Understanding the sources of primary production supporting marine food webs is important for conserving critical habitats. However, the importance of allochthonous versus autochthonous production is often unclear. We identify the sources of primary production supporting three species of predatory fish (Lutjanus carponotatus, Lutjanus fulviflamma, and Lethrinus punctulatus) in the Dampier Archipelago, Western Australia. The proportions of mangrove, seagrass, macroalgae, and suspended particulate organic matter (SPOM) assimilated by fish of different life-history stages and from different habitats were determined using stable isotopes and Bayesian mixing models. While contributions of sources varied among species and habitats, we found that SPOM was an important energetic resource for both adults and juveniles of all three fish species. Juvenile L. carponotatus and L. punctulatus inhabiting macroalgal habitats assimilated more seagrass- and macroalgae-derived material than fish from coral or mangrove habitats, while reliance on mangrove carbon was generally limited overall. Assimilation of macrophyte-derived material decreased throughout ontogeny for L. carponotatus, while L. fulviflamma relied on a combination of SPOM and seagrass into adulthood. The contribution of macroalgae and SPOM to the diets of juvenile L. punctulatus and L. carponotatus from macroalgal habitats varied spatially but was unrelated to seascape configuration, habitat quality, or hydrodynamic conditions. While mixing models suggested a modest degree of trophic connectivity, cross-habitat trophic subsidies provided by macrophytes play a minor role in supporting the studied fish of either life-history stage. Instead, microalgal production predominantly fuels the productivity of predatory fish in this turbid, macrotidal system. [ABSTRACT FROM AUTHOR]

In the sediments of seagrass meadows, allochthonous carbon sources can account for 50–90% of sediment organic carbon (SOC), in which non-seagrass carbon is derived from external organic matter advected into the meadow's sediments or trapped by the seagrass canopy. Identifying the SOC origin is essential to accurately estimate the climate change mitigation potential of seagrass ecosystems, yet the ratio of allochthonous to autochthonous SOC in South African seagrass populations has not been investigated. In this study, we measured the SOC and carbon isotope ratio (δ13C) in Zostera capensis seagrass meadows in the Berg River and Breede River estuaries and applied Bayesian mixing models to disentangle the SOC contributory sources. Sediment organic carbon differed not only between estuaries, but also showed variability within each estuary, with autochthonous carbon accounting for between ∼35% (SD 0.23) and ∼42.3% (SD 0.18) of total meadow SOC. Other sources of SOC included macroalgae, salt marsh and seagrass species. Our work highlights the importance of accounting for allochthonous carbon in disentangling the drivers of high variability of carbon stocks in estuarine environments and contributes to improving the accuracy of South African seagrass carbon stock estimates. [ABSTRACT FROM AUTHOR]

Introduction Makran geological province of SE Iran is an east-west trending mountain range related to the Cretaceous-to-recent subduction of the Indian oceanic lithosphere beneath the southeastern edge of the Eurasian plate (McCall, 1997; Saccani et al., 2022). Makran subduction zone from north to south is composed of remnants of Neo-Tethys oceanic crust, and the Late Cretaceous-Miocene sediments called Makran accretionary wedge (Figure 1). Volcanic fields of Shahsavaran, Bazman, West of Khash and Taftan are located north of Makran and have been considered as a subduction related volcanic arc (Dupuy and Dostal, 1978; Moinevaziri, 1985; Biabangard and Moradian, 2008; Saadat and Stern, 2011; Pang et al., 2014). More than 3 kilometers of mainly clastic sedimentary rocks have been subducted beneath the southeastern edge of the Eurasian plate (Kukowsky et al., 2001). Geochemical characteristics of the more primary basalts from the Makran arc indicate that sediments may have caused mantle source enrichment in the Makran subduction zone (Saadat and Stern, 2011). Quantitative approach to the contribution of subducting sediments to the enrichment of the source of basalts in such a voluminous accretionary prism is hard to attain. However, it is assumed here that subduction of sediments is at least one of the enrichment agents of mantle wedge beneath the Makran subduction zone. In this study, chemical composition of Late Cretaceous-Miocene claystones of turbidite suquences from the Fanouj-Bent area are compared with the chemical composition of sediments from other active subduction trenches. They are also deployed to construct binary melt-sediment mixing models in order to evaluate the postulated sediment contribution to the petrogenesis of the Makran basalts. Sedimentary rocks from the Fanouj–Bent area are the oldest among the Makran turbidites, and are thought to be representative of the most viably-recycled sediments in the mantle source of the Makran volcanic arc. Composition of near primary basalts from Makran volcanic arc (MVA) are then compared with the composition of various binary mixtures between a model basaltic melt and sediment-derived melts and fluids. Regional Geology The Late Cretaceous-Eocene (Mohammadi et al, 2016) deep marine turbidite sediments in this area are exposed together with the ophiolitic rocks of the oceanic crust of the Neotethys remnants (Figures 2A and 2B) and limestone (McCall, 1997). The younger Oligocene and Miocene turbidites include thick sequences of sandstone-claystone that were deposited in deep marine, continental slope, and delta environment in the course of evolution of the Makran accretionary wedge (Figures 2C, 2D). Volcanic rocks of MVA are mainly of andesitic and dacitic composition. The Bazman and Taftan stratovolcanoes are composed mainly of dacitic and andesitic pyroclastic rocks and lava flows. Basalts of MVA are: 1) volcanic centers of Shahsavaran which are shields volcanoes composed mainly of thin basaltic lavas (Figures 2E and 2F), 2) numerous monogenic satellite cinder cones scattered around the main Bazman volcano, and 3) cinder cones of west of Kash. Takhte Rostam is a basaltic center located on the southern flank of Taftan volcano. Analytical methods Major and trace element analyses for 2 claystone samples and 6 basaltic samples were performed using X-ray Fluorescence (XRF) spectrometry, and ICP-MS, respectively, at Acme Lab™, Canada. The 6 other claystone samples were analyzed for major and trace elements using XRF and ICP-OES methods in Central Lab of Isfahan University. Three samples of BCR-1 geostandard and three samples of an in-house standard were analyzed simultaneously in both labs, as unknown, to calculate accuracy and precision of the analyses. Table 1 shows geochemical data for the claystone and basaltic samples. Discussion In spidrgrams normalized to continental crust (Figure 7), the claystone samples are enriched in Cs, Rb, Th, U, Ta, Nb, K, Pb, Zr, and Hf and depleted in Ba, and Sr relative to the GLOSS II. These samples seem to be the most enriched sediments among all oceanic trenches of active subduction zones. The quantity of mobile elements in the claystones is comparable to those of the basaltic samples, but the Sr, Ba and Rb amounts are not consonant. Claystone samples are characterized by depletion in Sr (Ave: 171 ppm) and Ba (Ave: 213 ppm), and remarkable enrichment in Rb (Ave: 185 ppm). Compared to claystone samples, the contents of Sr, Ba and Rb in coastal Makran sample (CM) are more comparable to those of the basaltic samples. These similarities suggest that the coastal sediments may have accompanied the Late Cretaceous-Miocene clastic sediments in the mantle enrichment process. The geochemical evidence provided so far for island arc magmas are indicative of the presence and the influence of slab-fluids within and/or from the subducting slabs (Johnson and Plank, 1999; Nakamura and Iwamori, 2009; Schmidt and Poli, 2014; Turner and Langmuir, 2022). Below the solidus temperatures Rb, Sr, Ba, and Pb show more mobility, while at the solidus temperature Th and Be are notably partitioned into the melt rather than fluids (Johnson and Plank, 1999). To evaluate the rate of sediment contribution as a melt (Figure 8) or fluid (Figure 9) in magma generation, two models have been provided in this study. The three end member compositions for calculation of the none-modal batch melting models (Shaw, 1970) are: (1) a near-primary basaltic composition calculated from 15% partial melting of a spinel-lherzolie (MM), (2) average composition of 15% melting of claystone samples (Av.C), and (3) 15% melting of the coastal Makran sample of Jarrard and Lyle (1991). Finally, the binary mixing models between the basaltic MM and the other two end members are compared with the composition of Makran basalts. Th/Yb, Th/Ce, La/Sm, and Sr/Nd ratios are used to show the sediment contribution to the composition of the basaltic samples. Variations of Th/Ce versus Th/Yb ratios and Sm/Yb versus log Th/Yb ratios in basaltic samples show relative consistency with MM-Av.C binary mixing trend (Figure 8). Using these ratios, the sediment melt contribution rate is determined to be up to 10 %. To evaluate the effects of fluids rising from the sediments, in addition to MM, 3 other end members are deployed as: (1) the average composition of 15% fluid released from the claystone samples at 650oC (2) the average composition of 55% fluid released from the claystone samples at 700oC, and (3) 15% fluid released from the coastal Makran sample at 650oC. Binary mixing between MM and about 10% to more than 50% fluid derived from the coastal Makran sample at 650oC (Figure 9), is fairly comparable to the variations of Rb/Nd versus Ba/La and Rb/La versus Sr/Nd ratios. In addition, Elevated Sr/Nd, Ba/La and somehow Ce/Pb ratios are indicative of the contribution of slab derived fluids to the petrogenesis of the basalts. In all calculations, partition coefficients, D values, are taken from Johnson and Plank (1999).

Graviera Naxos, a renowned cheese with Protected Designation of Origin status, is crafted from a blend of cow, goat, and sheep milk. This study focused on assessing the Sr isotopic and multi-elemental composition of both the processed cheese and its ingredients, as well as the environmental context of Naxos Island, including samples of milk, water, soil, and feed. The objective was to delineate the geochemical signature of Graviera Naxos cheese and to explore the utility of Sr isotopes as indicators of geographic origin. The 87Sr/86Sr values for Graviera Naxos samples ranged from 0.70891 to 0.70952, indicating a relatively narrow range. However, the Sr isotopic signature of milk, heavily influenced by the feed, which originates from geologically distinct areas, does not always accurately reflect the local breeding environment. Multi-elemental analysis revealed variations in milk composition based on type and season; yet, no notable differences were found between raw and pasteurized milk. A mixing model evaluating the contributions of milk, sea salt, and rennet to the cheese's Sr isotopic signature suggested a significant average contribution of 73.1% from sea salt. This study highlights the complexities of linking dairy products with their geographical origins and emphasizes the need for sophisticated geochemical authentication methods. [ABSTRACT FROM AUTHOR]

Introduction Makran geological province of SE Iran is an east-west trending mountain range related to the Cretaceous-to-recent subduction of the Indian oceanic lithosphere beneath the southeastern edge of the Eurasian plate (McCall, 1997; Saccani et al., 2022). Makran subduction zone from north to south is composed of remnants of Neo-Tethys oceanic crust, and the Late Cretaceous-Miocene sediments called Makran accretionary wedge (Figure 1). Volcanic fields of Shahsavaran, Bazman, West of Khash and Taftan are located north of Makran and have been considered as a subduction related volcanic arc (Dupuy and Dostal, 1978; Moinevaziri, 1985; Biabangard and Moradian, 2008; Saadat and Stern, 2011; Pang et al., 2014). More than 3 kilometers of mainly clastic sedimentary rocks have been subducted beneath the southeastern edge of the Eurasian plate (Kukowsky et al., 2001). Geochemical characteristics of the more primary basalts from the Makran arc indicate that sediments may have caused mantle source enrichment in the Makran subduction zone (Saadat and Stern, 2011). Quantitative approach to the contribution of subducting sediments to the enrichment of the source of basalts in such a voluminous accretionary prism is hard to attain. However, it is assumed here that subduction of sediments is at least one of the enrichment agents of mantle wedge beneath the Makran subduction zone. In this study, chemical composition of Late Cretaceous-Miocene claystones of turbidite suquences from the Fanouj-Bent area are compared with the chemical composition of sediments from other active subduction trenches. They are also deployed to construct binary melt-sediment mixing models in order to evaluate the postulated sediment contribution to the petrogenesis of the Makran basalts. Sedimentary rocks from the Fanouj–Bent area are the oldest among the Makran turbidites, and are thought to be representative of the most viably-recycled sediments in the mantle source of the Makran volcanic arc. Composition of near primary basalts from Makran volcanic arc (MVA) are then compared with the composition of various binary mixtures between a model basaltic melt and sediment-derived melts and fluids. Regional Geology The Late Cretaceous-Eocene (Mohammadi et al, 2016) deep marine turbidite sediments in this area are exposed together with the ophiolitic rocks of the oceanic crust of the Neotethys remnants (Figures 2A and 2B) and limestone (McCall, 1997). The younger Oligocene and Miocene turbidites include thick sequences of sandstone-claystone that were deposited in deep marine, continental slope, and delta environment in the course of evolution of the Makran accretionary wedge (Figures 2C, 2D). Volcanic rocks of MVA are mainly of andesitic and dacitic composition. The Bazman and Taftan stratovolcanoes are composed mainly of dacitic and andesitic pyroclastic rocks and lava flows. Basalts of MVA are: 1) volcanic centers of Shahsavaran which are shields volcanoes composed mainly of thin basaltic lavas (Figures 2E and 2F), 2) numerous monogenic satellite cinder cones scattered around the main Bazman volcano, and 3) cinder cones of west of Kash. Takhte Rostam is a basaltic center located on the southern flank of Taftan volcano. Analytical methods Major and trace element analyses for 2 claystone samples and 6 basaltic samples were performed using X-ray Fluorescence (XRF) spectrometry, and ICP-MS, respectively, at Acme Lab™, Canada. The 6 other claystone samples were analyzed for major and trace elements using XRF and ICP-OES methods in Central Lab of Isfahan University. Three samples of BCR-1 geostandard and three samples of an in-house standard were analyzed simultaneously in both labs, as unknown, to calculate accuracy and precision of the analyses. Table 1 shows geochemical data for the claystone and basaltic samples. Discussion In spidrgrams normalized to continental crust (Figure 7), the claystone samples are enriched in Cs, Rb, Th, U, Ta, Nb, K, Pb, Zr, and Hf and depleted in Ba, and Sr relative to the GLOSS II. These samples seem to be the most enriched sediments among all oceanic trenches of active subduction zones. The quantity of mobile elements in the claystones is comparable to those of the basaltic samples, but the Sr, Ba and Rb amounts are not consonant. Claystone samples are characterized by depletion in Sr (Ave: 171 ppm) and Ba (Ave: 213 ppm), and remarkable enrichment in Rb (Ave: 185 ppm). Compared to claystone samples, the contents of Sr, Ba and Rb in coastal Makran sample (CM) are more comparable to those of the basaltic samples. These similarities suggest that the coastal sediments may have accompanied the Late Cretaceous-Miocene clastic sediments in the mantle enrichment process. The geochemical evidence provided so far for island arc magmas are indicative of the presence and the influence of slab-fluids within and/or from the subducting slabs (Johnson and Plank, 1999; Nakamura and Iwamori, 2009; Schmidt and Poli, 2014; Turner and Langmuir, 2022). Below the solidus temperatures Rb, Sr, Ba, and Pb show more mobility, while at the solidus temperature Th and Be are notably partitioned into the melt rather than fluids (Johnson and Plank, 1999). To evaluate the rate of sediment contribution as a melt (Figure 8) or fluid (Figure 9) in magma generation, two models have been provided in this study. The three end member compositions for calculation of the none-modal batch melting models (Shaw, 1970) are: (1) a near-primary basaltic composition calculated from 15% partial melting of a spinel-lherzolie (MM), (2) average composition of 15% melting of claystone samples (Av.C), and (3) 15% melting of the coastal Makran sample of Jarrard and Lyle (1991). Finally, the binary mixing models between the basaltic MM and the other two end members are compared with the composition of Makran basalts. Th/Yb, Th/Ce, La/Sm, and Sr/Nd ratios are used to show the sediment contribution to the composition of the basaltic samples. Variations of Th/Ce versus Th/Yb ratios and Sm/Yb versus log Th/Yb ratios in basaltic samples show relative consistency with MM-Av.C binary mixing trend (Figure 8). Using these ratios, the sediment melt contribution rate is determined to be up to 10 %. To evaluate the effects of fluids rising from the sediments, in addition to MM, 3 other end members are deployed as: (1) the average composition of 15% fluid released from the claystone samples at 650oC (2) the average composition of 55% fluid released from the claystone samples at 700oC, and (3) 15% fluid released from the coastal Makran sample at 650oC. Binary mixing between MM and about 10% to more than 50% fluid derived from the coastal Makran sample at 650oC (Figure 9), is fairly comparable to the variations of Rb/Nd versus Ba/La and Rb/La versus Sr/Nd ratios. In addition, Elevated Sr/Nd, Ba/La and somehow Ce/Pb ratios are indicative of the contribution of slab derived fluids to the petrogenesis of the basalts. In all calculations, partition coefficients, D values, are taken from Johnson and Plank (1999). [ABSTRACT FROM AUTHOR]

The Swedish Nuclear Fuel and Waste Management Co. (SKB) has been searching for a site to construct a deep geological repository for spent nuclear fuel in Sweden. In 2012, Forsmark was selected as the location for the nuclear fuel repository and construction will start in 2027. An understanding of the chemical composition and evolution of the groundwaters at the site is an integral part of the long-term safety case. SKB's traditional approach to describe a site has been to use M3 mixing of end-members as the main process controlling the groundwater composition. We propose a new approach using a Bayesian mixing model. Similarly to the traditional mixing approach, the fraction of each end-member for all samples in the dataset is calculated, with the exception of the deep saline end-member. Given the slow movement of the deep groundwaters, it is likely that they have reached equilibrium with the host rock and fracture minerals. Therefore, we introduce an additional step, consisting of a Phreeqc model to construct the theoretical composition of groundwater with an increasing Cl concentration in equilibrium with the mineralogy of the host rock. This is a way of introducing a geochemical explanation to deep saline waters found in the geosphere of the Forsmark site. The results indicated a higher fraction of glacial meltwater in deep groundwaters in Forsmark compared to previous models. This approach could be directly applied to other groundwater systems, with different mineralogy of the host rock, assuming slow moving groundwater in equilibrium. [ABSTRACT FROM AUTHOR]

Ali-HexA Deep eutectic solvent (DES) was synthesized using hexanoic acid as a hydrogen bond donor and Aliquat 336 as a hydrogen bond acceptor was confirmed by FTIR and proton NMR spectral studies. Density, molar volume, dielectric constant, refractive index, and ultrasonic velocity of binary mixtures of DES and kerosene have been determined at various mole fractions of DES. The excess properties were calculated using different model equations. The solvent extraction of Li, Co, and Ni from simulated lithium-ion battery waste solution using DES in kerosene under varying experimental conditions has been undertaken to know the suitableness of the novel DES extractant-diluent pair.

A conceptual model has been proposed based on water samples collected from geothermal springs in the Shyok suture zone of North-West Himalayas, Ladakh geothermal province, India by nurturing hydrogeochemistry, mineralogical insights, and stable isotopic (δD, δ18O) systematics. The reservoir rock is comprised of granitic segment with intrusion of volcano-plutonics and a variety of meta-sedimentaries which becomes more exposed towards western side of the valley in the form of Shyok Ophiolitic melange. Thermal waters, located above 3100 m above msl, with variable genetic classification (Changlung: Na–HCO3; Panamik: both Na–HCO3 and mixed type; Pulthang: purely mixed type), have TDS and temperature lying between 587 and 2278 mg/L and 28−78 °C, respectively. High concentration of trace elements (Li, B, As, Cs, Rb, W) in geothermal fluids points to the magmatic origin regarding their enrichment mechanism. Surface manifestation of hydrothermal/evaporitic minerals like thenardite, trona, sylvite, halite, nahcolite, thermonatrite, etc. establishes a signature of high-temperature at shallow level of reservoir and their dissolution kinetics decipher origin of solutes apart from weathering of alkali/alkaline aluminosilicates. Utilizing empirical chemical geothermometry and Si-Enthalpy mixing modelling, the estimated reservoir temperatures exhibit significant variability ranging from 100 to 210 °C and reservoir silica concentration 382 mg/L with average circulation depth of geothermal waters around 1.8 Km and fluid residence time of 2640 years. The Shyok-Nubra springs liberate substantial amount of CO2-enriched water, with degassing flux of 6.26 × 105 mol of CO2/year. δD and δ18O systematics reveal that geothermal springs are recharged by meteoric water, snow-melt and magmatic fluid with cold-water component of 27.1–62.4% mixed with hot fluids. Thermal springs are recharged from a single reservoir source located a shallow level towards North-West of Changlung having large lateral flow of about 25 Km generating Panamik and Pulthang fluids with subsequent dilution. This study highlights the extent and consequences of water–rock interaction across diverse lithologies (granite and mafic volcanics) in the Himalayas, emphasizing its implications over fluid circulation time and subsurface temperature considerations which rationalizes the evolution of geothermal fluids.

In this work, we propose a supervised framework for spectral unmixing of binary intimate mixtures. The core idea is based on geodesic distance measurements and regression to estimate the fractional abundances. The main assumption is that spectral reflectances of binary mixtures form a curve between the two endmembers, and the mixture's relative position on this curve serves as an indicator of its fractional abundances. We propose four novel approaches to approximate this relative position. From this, the fractional abundances are obtained using Gaussian process regression. The proposed framework simultaneously copes with the spectral variability by hypersphere and high-dimensional simplex projections. The approach is extensively validated on real datasets, including binary mineral mixtures and industrial clay powder mixtures produced in a laboratory setting, comprising 60 binary mixtures derived from five types of clay powders: kaolin, roof clay, red clay, mixed clay, and calcium hydroxide, measured by a variety of hyperspectral sensors in the VNIR–SWIR and mid-and longwave infrared regions. A comparison with the linear mixing model and several nonlinear mixing models demonstrates the superiority of the proposed approach.

The structure of food webs is a fundamental attribute of ecosystems, and their characterization provides an intrinsic knowledge of the trophic interactions among organisms and of nutrient and energy transfer within ecosystems. Over the last few decades, several chemical and biogeochemical approaches have been proposed to explore different aspects of food webs. In this sense, this study reviews the application of stable isotopes and mercury as main auxiliary tools to the characterization and modeling of aquatic food webs, including analytical and modeling advances, strengths and limitations. The metanalysis performed showed that the most used tools for trophic ecology studies are stable isotopes, and that they can provide better results when combined with mercury and specific chemical molecules such as amino and fatty acids. In addition, the statistical methods applied in the interpretation of results, such as isotope mixing models, have witnessed significant advances in the last two decades. All approaches have premises and limitations when applied to aquatic ecosystems, which must be well understood prior to results interpretation. The use of multiple tracers in trophic studies provides complementary information and in many cases is an appropriate alternative to overcome some limitations, allowing to expand the knowledge of the food webs.

Despite supporting a disproportionately large fraction of the global biodiversity, freshwater ecosystems are ranked as the most highly threatened habitats ahead of both terrestrial and marine ecosystems. Furthermore, many regions are still characterized by limited knowledge on taxonomy and ecology of freshwater fishes. The need for ecological information in understudied regions is important particularly where there are recent discoveries of new species and unique lineages and for threatened and endangered taxa that require conservation management.This study evaluated the trophic ecology of two freshwater fish species Sandelia bainsii and Amatolacypris trevelyani that are both classified as endangered in the International Union for Conservation of Nature (IUCN) Red List. These two species, which are narrow‐range endemics in the Eastern Cape, South Africa, comprise allopatric lineages whose ecology is poorly known. This study used stable isotope analysis to evaluate the food web patterns, explore the trophic niche dynamics and estimate the prey source contributions for the two species in different headwater habitats.The fishes isotopic niche sizes were spatially variable, suggesting the likely importance of stochastic variation in resource availability and probable interspecific interactions. The three lineages within S. bainsii exhibited low isotopic niche overlap onto those of sympatric fishes in most habitats. Isotopic mixing model revealed that these lineages' diets were mostly dominated by gatherers/collectors. In comparison, the two lineages within A. trevelyani exhibited high niche overlap with other species and generally had variable diets.Despite the low and high niche overlap patterns of S. bainsii and A. trevelyani, respectively, the isotopic niche overlap patterns of co‐occurring species onto those of the former suggest the likely lack of competitive hierarchies. The trophic niche patterns of these two endangered species helped to shed some light on the potential invasion risks by non‐piscivorous fishes with opportunistic feeding habits, which could exert competitive interspecific interactions. [ABSTRACT FROM AUTHOR]

The contribution of two basal energy sources - detrital organic matter and primary producers - as part of aquatic food webs varies typically along river continua. A host of barriers to river flow increase the water residence time and sediment and nutrient retention in reservoirs worldwide, and potentially alter the balance between detritus-based and algae-based energy pathways in the downstream food webs. We explored this issue on the Sélune River (Normandy, France), a small coastal stream that drains an agricultural catchment with high sediment runoff. Seasonal measurements of the following parameters were compared upstream and downstream of the reservoirs of two large dams (16 m and 36 m high): sediment fluxes, nutrient and chlorophyll a concentrations, algal communities in the epilithic biofilm (taxonomic composition, biomass and growth), and benthic invertebrate communities (abundance and trophic guild structure). As anticipated, annual sediment fluxes were much lower downstream of the reservoirs, where significant decreases in water turbidity, phosphate and silicate concentrations were recorded. A higher chlorophyll a concentration in water and a higher contribution of pelagic algae taxa to the photosynthetic biofilm suggested drifting and deposition of reservoir-borne phytoplankton downriver. Photosynthetic biofilm growth was higher downstream of the reservoirs in spring and fall, and so was the abundance of herbivores in the invertebrate community, notably scrapers and algae eaters. Energy pathways within riverine food webs were traced using stable isotope analyses of carbon (C) and nitrogen in the tissues of aquatic consumers (invertebrates and fish). Mixing models revealed a discontinuity in the origin of the C entering the food webs along the river continuum, confirming a greater contribution of algal C to aquatic consumers downstream of the reservoirs. These results illustrate mechanisms whereby large reservoirs can modulate C flow in food webs along a small coastal river with high sediment loads, and make it possible to anticipate the effects of dam removal on the future river ecosystem. [ABSTRACT FROM AUTHOR]

Graviera Naxos, a renowned cheese with Protected Designation of Origin status, is crafted from a blend of cow, goat, and sheep milk. This study focused on assessing the Sr isotopic and multi-elemental composition of both the processed cheese and its ingredients, as well as the environmental context of Naxos Island, including samples of milk, water, soil, and feed. The objective was to delineate the geochemical signature of Graviera Naxos cheese and to explore the utility of Sr isotopes as indicators of geographic origin. The 87Sr/86Sr values for Graviera Naxos samples ranged from 0.70891 to 0.70952, indicating a relatively narrow range. However, the Sr isotopic signature of milk, heavily influenced by the feed, which originates from geologically distinct areas, does not always accurately reflect the local breeding environment. Multi-elemental analysis revealed variations in milk composition based on type and season; yet, no notable differences were found between raw and pasteurized milk. A mixing model evaluating the contributions of milk, sea salt, and rennet to the cheese’s Sr isotopic signature suggested a significant average contribution of 73.1% from sea salt. This study highlights the complexities of linking dairy products with their geographical origins and emphasizes the need for sophisticated geochemical authentication methods.

• Standard reflectance hyperspace vs -log reflectance hyperspace. • Deep learning-based vs linear-based unmixing algorithms. • Unmixing performed in the SWIR range. • Combined metric for pigment identification. • Application to a painting with inscription "Boceto di Pablo Veronese" on the back. Hyperspectral imaging has recently consolidated as a useful technique for pigment mapping and identification, although it is commonly supported by additional non-invasive analytical methods. Since it is relatively rare to find pure pigments in aged paintings, spectral unmixing can be helpful in facilitating pigment identification if suitable mixing models and endmember extraction procedures are chosen. In this study, a subtractive mixing model is assumed, and two approaches are compared for endmember extraction: one based on a linear mixture model, and the other, nonlinear and Deep-Learning based. Two spectral hyperspaces are used: the spectral reflectance (R hyperspace) and the -log(R) hyperspace, for which the subtractive model becomes additive. The performance of unmixing is evaluated by the similarity of the estimated reflectance to the measured data, and pigment identification accuracy. Two spectral ranges (400 to 1000 nm and 900 to 1700 nm) and two objects (a laboratory sample and an aged painting, both on copper) are tested. The main conclusion is that unmixing in the -log(R) hyperspace with a linear mixing model is better than for the non-linear model in R hyperspace, and that pigment identification is generally better in R hyperspace, improving by merging the results in both spectral ranges. [ABSTRACT FROM AUTHOR]

Although stable isotope analysis (SIA) is widely used to address ecological research questions, its application in an ecotoxicological context has been limited. Recent studies have proposed an effect of chemical stressors on an organism's isotope signature, questioning the use of SIA in food webs impacted by toxicants. Against this background, the present study investigates 1) whether trophic enrichment factors (TEFs; i.e., the offset in stable isotope signatures of a consumer to its diet) are altered by the neonicotinoid thiacloprid, and 2) whether tracking toxicant effects on an organism's diet composition (i.e., indirect effect) with SIA fits direct observations of consumption. To address the former, the amphipod Gammarus fossarum (Koch) was exposed to three levels (0, 0.75, and 5 µg L–1) of thiacloprid and fed with either black alder leaves or Baetis rhodani (Pictet) larvae over 6 weeks (n = 35). The thiacloprid‐induced changes in TEFs that we found were statistically significant but small compared with other factors (e.g., resource quality, consumer, and physiological condition) and thus likely of minor importance. To address the latter issue, gammarids were exposed to two levels of thiacloprid (0 and 0.75 µg L–1) and fed with either black alder leaves, live B. rhodani larvae, or both over 2 weeks (n = 10). Dietary proportions as suggested by SIA were indeed in agreement with those derived from direct observation of consumption. The present study consequently suggests that SIA is as a robust tool to detect indirect toxicant effects especially if TEFs are assessed in parallel. Environ Toxicol Chem 2023;42:1937–1945. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. [ABSTRACT FROM AUTHOR]

In nature-based treatment systems, such as constructed wetlands, plant uptake of nutrients can be a significant removal pathway. Current methods for quantifying plant uptake of nitrogen in constructed wetlands, which often involve harvesting biomass and assuming that all nitrogen stored in plants was derived from wastewater, are inappropriate in pilot- and full-scale systems where other sources of nitrogen are available. To improve our understanding of nitrogen cycling in constructed wetlands, we developed a new method to quantify plant uptake of nitrogen by using stable isotopes and a mixing model to distinguish between nitrogen sources. We applied this new method to a pilot-scale horizontal levee system (i.e., a subsurface constructed wetland) over a two-year monitoring period, during which 14% of nitrogen in plants was wastewater-derived on average and the remaining plant nitrogen was obtained from the soil. Analysis of nitrogen isotopes indicated substantial spatial variability in the wetland: 82% of nitrogen in plants within the first 2 m of the slope came from wastewater while less than 12% of plant nitrogen in the remainder of the wetland originated from wastewater. By combining these source contributions with remote-sensing derived total biomass measurements, we calculated that 150 kg N (95% CI = 50 kg N, 330 kg N) was taken up and retained by plants during the two-year monitoring period, which corresponded to approximately 8% of nitrogen removed in the wetland. Nitrogen uptake followed seasonal trends, increased as plants matured, and varied based on design parameters (e.g., plant types), suggesting that design decisions can impact this removal pathway. This new method can help inform efforts to understand nitrogen cycling and optimize the design of nature-based nutrient control systems.

This study conducted stable isotope analysis (δ13C, δ15N, and δ34S) on the epidermis and two skeletal elements (rib and squamosal bones) of Hawaiian green turtles (Chelonia mydas) and putative diet items obtained from two neritic sites: the Kona/Kohala coast and Oahu. Turtle tissues were collected in 2018–2020 and diet samples in 2018, 2019, and 2021. The effect of body size and sampling locality on individual bulk tissue isotope values was evaluated, and stable isotope mixing models based on δ13C, δ15N, and δ34S values from those tissues and four groups of food sources were used to reconstruct diet histories of the turtles. Mixing models indicated that green turtles along the Kona/Kohala coast consumed an omnivorous diet, whereas those from Oahu had an herbivorous diet. These diet make-ups are consistent with published gut content analyses. However, mixing models using the stable isotope ratios in rib and squamosal bone failed to yield reasonable diet histories, probably due to inadequacies of the applied trophic discrimination factor (TDF), a key model parameter. These results further establish that stable isotope ratios in the epidermis can be used effectively to study green turtle diet, but also reveal that more validation—and establishment of appropriate TDFs—is needed before bone can be used reliably to assess green turtle diet. [ABSTRACT FROM AUTHOR]

Mixing models are used throughout earth and environmental science to quantify the relative contributions of sources to mixtures, based on chemical or isotopic tracers. Often, however, some end‐members are missing or their tracer distributions overlap, precluding the use of conventional mixing models. Here I show how these constraints can be overcome by exploiting the information contained in tracer time‐series fluctuations. This approach, ensemble end‐member mixing analysis (EEMMA), can potentially quantify many sources using a single tracer, even if their mean concentrations are indistinguishable. EEMMA can also quantify source contributions when some sources are unknown, and even infer the tracer time series of a missing source. Benchmark tests with synthetic data verify the reliability of this approach, thus expanding the range of mixing models that can be quantified using tracer time series. An R script is provided for the necessary calculations, including error propagation. Plain Language Summary: Chemical and isotopic tracers are widely used to partition mixtures (such as air masses, stream flows, xylem water, or biogeochemical fluxes) among potential contributing sources. These "mixing models" are widely used to improve process understanding throughout Earth and environmental science. However, because conventional mixing models are based on comparing the mean tracer concentrations in the sources and mixture, they typically require that all sources have been identified and sampled, their average tracer concentrations are distinctly different, and the number of sources does not exceed the number of independent tracers, plus one. Temporal fluctuations in tracer concentrations can provide additional information that loosens these constraints, thus expanding the range of feasible mixing models. Here I outline this approach and test its reliability using synthetic benchmark data. With this approach, in contrast to conventional mixing models, a single tracer can be used to quantify contributions from many different sources, even if their means overlap. Even when some sources are unmeasured or even unknown, this approach can estimate the remaining sources' mixing fractions, and even, given sufficiently accurate data, can estimate the mixing fraction and tracer signature of an unknown source. Thus, this approach expands the range of applications for mixing models. Key Points: Tracer fluctuations contain information that can help constrain mixing models, including those with overlapping end‐member signaturesThis approach can also constrain mixing models with many sources but only one tracer, or those in which some sources may be missingThe concepts and math behind this approach are outlined, and validated using benchmark tests; a script for the method is provided [ABSTRACT FROM AUTHOR]

Mangroves are coastal wetlands with high biodiversity and productivity, with great interaction with coastal environments. In the face of worldwide mangrove loss, restoration projects attempt to recover ecosystem composition and functioning over time. Our objective was to examine and compare the food webs in mangrove areas with different restoration times and in a reference mangrove in Términos Lagoon, Mexico. We estimated the trophic structure, identified the carbon resources that maintain aquatic consumers through the analysis of stable isotopes, and compared the trophic niche of the restored mangroves with the reference mangrove. We analyzed environmental variables, trophic structure, and contributions of resources during three seasons: rainy, dry, and "nortes". Environmental changes and food structure changed in response to regional seasons. Bayesian mixing models indicated that food webs varied seasonally as a response to the primary productivity developed at Términos Lagoon. As expected, the assimilation of C3 plants in the reference mangrove was highest, as a primary ("nortes" season) and secondary resource (dry and rainy seasons). The restored mangroves depended mainly on allochthonous resources (seagrass, epiphytes, and phytoplankton). The assimilation of these resources highlighted the importance of connectivity and the input of sources of carbon from nearby coastal environments. Trophic niche analysis showed that the area with longer restoration time was more similar to the reference mangrove, which is evidence of the importance and efficacy of the restoration process, as well as the restoration of the ecosystem function over time. [ABSTRACT FROM AUTHOR]

Mangroves are coastal wetlands with high biodiversity and productivity, with great interaction with coastal environments. In the face of worldwide mangrove loss, restoration projects attempt to recover ecosystem composition and functioning over time. Our objective was to examine and compare the food webs in mangrove areas with different restoration times and in a reference mangrove in Términos Lagoon, Mexico. We estimated the trophic structure, identified the carbon resources that maintain aquatic consumers through the analysis of stable isotopes, and compared the trophic niche of the restored mangroves with the reference mangrove. We analyzed environmental variables, trophic structure, and contributions of resources during three seasons: rainy, dry, and “nortes”. Environmental changes and food structure changed in response to regional seasons. Bayesian mixing models indicated that food webs varied seasonally as a response to the primary productivity developed at Términos Lagoon. As expected, the assimilation of C3 plants in the reference mangrove was highest, as a primary (“nortes” season) and secondary resource (dry and rainy seasons). The restored mangroves depended mainly on allochthonous resources (seagrass, epiphytes, and phytoplankton). The assimilation of these resources highlighted the importance of connectivity and the input of sources of carbon from nearby coastal environments. Trophic niche analysis showed that the area with longer restoration time was more similar to the reference mangrove, which is evidence of the importance and efficacy of the restoration process, as well as the restoration of the ecosystem function over time.

Stable carbon and nitrogen isotopic ratios (δ13C, δ15N) in bone collagen of archaeological skeletal finds are indicators of the protein sources in individuals’ basic diet. Isotopic sourcing allows us to quantify the biomass contribution of major dietary components and to differentiate between the source contribution of various animal species (domesticates, game). We re-evaluated previously published isotopic signatures in skeletons from three burial sites in Bavaria, dated from Late Antiquity to Early Mediaeval times (Erding-Klettham, Erding-Altenerding, Straubing-Bajuwarenstraße) by use of a mixing model. The result is a more detailed reconstruction, supported by contextual evidence, of both early subsistence economies and individual dietary preferences. We were able to confirm relationships between non-local dietary behaviour and foreign cultural influences (grave goods and artificial cranial modification) that have previously been suggested by the burial context and DNA analyses and that are plausibly explained by migration events. Moreover, we differentiated early and late immigrants from each other, requiring a re-evaluation of the earlier interpretation of exogamy. In addition, individual dietary preferences indicate even more migration events and social stratifications that could not previously be identified by the archaeological evidence alone. [ABSTRACT FROM AUTHOR]

In this work, chloride ions were used as conservative tracers and supplemented with conservative amounts of chloroethenes (PCE, TCE, Cis-DCE, 1,1-DCE), chloroethanes (1,1,1-TCA, 1,1-DCA), and the carbon isotope ratios of certain compounds, the most representative on the sites studied, which is a novelty compared to the optimization methods developed in the scientific literature so far. A location of the potential missing sources is then proposed in view of the balances of the calculated mixing fractions. A test of the influence of measurement errors on the results shows that the uncertainties in the calculation of the mixture fractions are less than 11%, indicating that the source identification method developed is a robust tool for identifying sources of chlorinated solvents in groundwater. [ABSTRACT FROM AUTHOR]

The hydrogeochemistry of hot springs located along the vast stretch of Munger–Saharsa Ridge Fault (MSR) zone in the Rajgir–Munger metasedimentary belt of eastern peninsular India is investigated. The temperature of springs lies between 25° and 65°C, with the highest surface manifestation in Bhimband. The thermal springs are issued from joints and fractures along MSR, East/West Patna faults of Precambrian quartzites and phyllites. The major ion composition elucidates that majority of waters are Ca–Mg–HCO3 type. The mechanisms controlling rock dominance origin of cations and both precipitation and rock dominance origin of anions in thermal waters are silicate rock weathering and ion-exchange processes between aquifer-rock and water. The mixing models illustrate that cold water causes intense dilution of geothermal fluids before discharge, with highest contribution in Bhaduria Bhar (76.6%) and lowest in Bhimband (55.4%) springs. The reservoir temperature as estimated based on quartz geothermometry ranges ~100°C grading springs as low enthalpic geothermal resources. Near-surface dilution disturbs Na/K-geochemical equilibrium and thus multi-component geothermometry furnish inaccurate results. Mineral phase saturation studies depict near equilibration of quartz and chalcedony with thermal waters. With all evidences of hydrogeochemical modelling, a conceptual model of recharge-mixing-discharge of thermal springs is proposed in the study. [ABSTRACT FROM AUTHOR]

A small imbalance in plant productivity and decomposition accounts for the carbon (C) accumulation capacity of peatlands. As climate changes, the continuity of peatland net C storage relies on rising primary production to offset increasing ecosystem respiration (ER) along with the persistence of older C in waterlogged peat. A lowering in the water table position in peatlands often increases decomposition rates, but concurrent plant community shifts can interactively alter ER and plant productivity responses. The combined effects of water table variation and plant communities on older peat C loss are unknown. We used a full‐factorial 1‐m3 mesocosm array with vascular plant functional group manipulations (Unmanipulated Control, Sedge only, and Ericaceous only) and water table depth (natural and lowered) treatments to test the effects of plants and water depth on CO2 fluxes, decomposition, and older C loss. We used Δ14C and δ13C of ecosystem CO2 respiration, bulk peat, plants, and porewater dissolved inorganic C to construct mixing models partitioning ER among potential sources. We found that the lowered water table treatments were respiring C fixed before the bomb spike (1955) from deep waterlogged peat. Lowered water table Sedge treatments had the oldest dissolved inorganic 14C signature and the highest proportional peat contribution to ER. Decomposition assays corroborated sustained high rates of decomposition with lowered water tables down to 40 cm below the peat surface. Heterotrophic respiration exceeded plant respiration at the height of the growing season in lowered water table treatments. Rates of gross primary production were only impacted by vegetation, whereas ER was affected by vegetation and water table depth treatments. The decoupling of respiration and primary production with lowered water tables combined with older C losses suggests that climate and land‐use‐induced changes in peatland hydrology can increase the vulnerability of peatland C stores. [ABSTRACT FROM AUTHOR]

In large lake ecosystems, fish movement between coastal littoral habitats such as wetlands and the adjacent open‐water nearshore represents an understudied but potentially important linkage supporting energy flow and fisheries production. We hypothesized that yellow perch (Perca flavescens), an ecologically and economically important sport fish in the Laurentian Great Lakes, transport energy from highly productive wetlands to nearshore food webs, but that their role changes with ontogenetic shifts in diet and habitat use. We also predicted that the relative strength of such fish‐mediated habitat linkages would vary depending on physical connectivity across habitats. We collected perch and potential prey resources from seven paired coastal wetland–nearshore sites across three regions of Lake Michigan and quantified resource and habitat use with Bayesian stable isotope mixing models and otolith microchemistry. We found that juvenile perch collected in nearshore habitats showed high use of wetland resources, and that diets of wetland‐collected juveniles typically contained a smaller proportion of nearshore resources than did more mobile adults from the same wetland. The least hydrologically connected sites had lower cross‐habitat resource use (e.g., wetland‐collected perch consumed fewer nearshore resources and vice versa) compared with sites with greater levels of hydrological connectivity. Otolith microchemistry confirmed the linkages revealed by stable isotopes, suggesting that a dual approach can increase understanding of habitat linkages in large lakes. Quantifying the importance of multiple lentic habitats (i.e., "lakescape connectivity") for fisheries production is critical for developing comprehensive large lake food web models and providing managers with information to prioritize locations for conservation and restoration. [ABSTRACT FROM AUTHOR]

This review provides an overview of concepts and approaches for the quantification of passive, non-reactive solute mixing in steady uniform porous media flows across scales. Mixing in porous media is the result of the interaction of spatial velocity fluctuations and diffusion or local-scale dispersion, which may lead to the homogenization of an initially segregated system. Velocity fluctuations are induced by spatial medium heterogeneities at the pore, Darcy or regional scales. Thus, mixing in porous media is a multiscale process, which depends on the medium structure and flow conditions. In the first part of the review, we discuss the interrelated processes of stirring, dispersion and mixing, and review approaches to quantify them that apply across scales. This implies concepts of hydrodynamic dispersion, approaches to quantify mixing state and mixing dynamics in terms of concentration statistics, and approaches to quantify the mechanisms of mixing. We review the characterization of stirring in terms of fluid deformation and folding and its relation with hydrodynamic dispersion. The integration of these dynamics to quantify the mechanisms of mixing is discussed in terms of lamellar mixing models. In the second part of this review, we discuss these concepts and approaches for the characterization of mixing in Poiseuille flow, and in porous media flows at the pore, Darcy and regional scales. Due to the fundamental nature of the mechanisms and processes of mixing, the concepts and approaches discussed in this review underpin the quantitative analysis of mixing phenomena in porous media flow systems in general. [ABSTRACT FROM AUTHOR]

Sediment source fingerprinting provides an effective and reliable way for targeted control of soil erosion. However, the accuracy of source contribution predictions of different fingerprinting methods has not been well verified, which affects the further application of these methods. Here, compared with the real sediment sources measured by indoor simulated scouring experiments, we verified the accuracy of two tracers (geochemical elements and n‐alkanes) and three mixing models (Walling model, MixSIAR, and Landwehr model). The results showed that geochemical properties have high accuracy in identifying sediment sources, with the mean absolute error (MAE) ranging from 3.5%–5.9%, while poor results were shown for n‐alkanes (MAE values 7.5%–45.7%). The Walling model and MixSIAR showed higher accuracy of contribution prediction, and the MAE was 3.5%–5.9% and 0.7%–3.5%, respectively. Although Landwehr also presented high accuracy of model output, it was relatively less robust compared with the former two mixing models (the MAE range was 3.8%–9.7%). Furthermore, the mixing model with three correction factors (particle size, organic matter (OM), and particle size with OM) showed poor output results for scouring experiments. This study provides a reference for the selection and determination of tracers, mixing models, and correction factors in field experiments. [ABSTRACT FROM AUTHOR]

Abstract In large lake ecosystems, fish movement between coastal littoral habitats such as wetlands and the adjacent open‐water nearshore represents an understudied but potentially important linkage supporting energy flow and fisheries production. We hypothesized that yellow perch (Perca flavescens), an ecologically and economically important sport fish in the Laurentian Great Lakes, transport energy from highly productive wetlands to nearshore food webs, but that their role changes with ontogenetic shifts in diet and habitat use. We also predicted that the relative strength of such fish‐mediated habitat linkages would vary depending on physical connectivity across habitats. We collected perch and potential prey resources from seven paired coastal wetland–nearshore sites across three regions of Lake Michigan and quantified resource and habitat use with Bayesian stable isotope mixing models and otolith microchemistry. We found that juvenile perch collected in nearshore habitats showed high use of wetland resources, and that diets of wetland‐collected juveniles typically contained a smaller proportion of nearshore resources than did more mobile adults from the same wetland. The least hydrologically connected sites had lower cross‐habitat resource use (e.g., wetland‐collected perch consumed fewer nearshore resources and vice versa) compared with sites with greater levels of hydrological connectivity. Otolith microchemistry confirmed the linkages revealed by stable isotopes, suggesting that a dual approach can increase understanding of habitat linkages in large lakes. Quantifying the importance of multiple lentic habitats (i.e., “lakescape connectivity”) for fisheries production is critical for developing comprehensive large lake food web models and providing managers with information to prioritize locations for conservation and restoration.

While an increasing number of studies are adopting molecular and chemical methods for dietary characterization, these studies often employ only one of these laboratory‐based techniques; this approach may yield an incomplete, or even biased, understanding of diet due to each method's inherent limitations. To explore the utility of coupling molecular and chemical techniques for dietary characterizations, we applied DNA metabarcoding alongside stable isotope analysis to characterize the dietary niche of breeding Louisiana waterthrush (Parkesia motacilla), a migratory songbird hypothesized to preferentially provision its offspring with pollution‐intolerant, aquatic arthropod prey. While DNA metabarcoding was unable to determine if waterthrush provision aquatic and terrestrial prey in different abundances, we found that specific aquatic taxa were more likely to be detected in successive seasons than their terrestrial counterparts, thus supporting the aquatic specialization hypothesis. Our isotopic analysis added greater context to this hypothesis by concluding that breeding waterthrush provisioned Ephemeroptera and Plecoptera, two pollution‐intolerant, aquatic orders, in higher quantities than other prey groups, and expanded their functional trophic niche when such prey were not abundantly provisioned. Finally, we found that the dietary characterizations from each approach were often uncorrelated, indicating that the results gleaned from a diet study can be particularly sensitive to the applied methodologies. Our findings contribute to a growing body of work indicating the importance of high‐quality, aquatic habitats for both consumers and their pollution‐intolerant prey, while also demonstrating how the application of multiple, laboratory‐based techniques can provide insights not offered by either technique alone. [ABSTRACT FROM AUTHOR]

Kelp forests dominated by Macrocystis pyrifera are widely distributed in coastal waters from boreal, temperate and subantarctic regions. This widespread distribution may result in regional differences in food web structure and functioning. In temperate northern regions, where most studies on kelp forest benthic food webs have been conducted, kelp grazing is a well-documented phenomenon and can lead to the overgrazing of M. pyrifera by sea urchins when their predators (e.g., sea otters) are absent. In contrast, little is known about their counterparts in subantarctic areas. The present study aimed to reconstruct the benthic food web of a kelp forest dominated by M. pyrifera in a subantarctic environment using stable isotope analysis. Stable carbon (δ13C), nitrogen (δ15N) and sulfur (δ34S) isotope ratios were measured from food sources (macrophytobenthos, suspended particulate organic matter SPOM, and sediment) and consumers (sponges, bivalves, gastropods, sedentary and mobile polychaetes, arthropods and echinoderms) which were sampled in a kelp forest of the Kerguelen archipelago. Mixing models highlighted two interconnected trophic pathways which were either supported by SPOM and resuspended macrophytobenthos detritus (bentho-pelagic), or by live micro/macrophytobenthos (phytobenthos-based). No major prey were highlighted for several consumers, indicating the existence of potential supplementary trophic pathways. No consumer relying primarily on living M. pyrifera was highlighted by the mixing models. The investigated kelp forest is hence a complex ecosystem supporting multiple trophic pathways, and direct consumption of M. pyrifera is limited. Nonetheless, M. pyrifera and other macrophytobenthos species may constitute a pool of detritus supporting several trophic pathways. [ABSTRACT FROM AUTHOR]

The time domain reflectometry (TDR) technique is a geophysical method that allows, in a time-varying electric field, the determination of dielectric permittivity and electrical conductivity of a wide class of porous materials. Measurements of the volumetric water content (θw) in soils is the most frequent application of TDR in Soil Science and Soil Hydrology. In last four decades several studies have sought to explore potential applications of TDR. Such studies (except those conducted on θw estimation) mainly focused on monitoring soil solute transport. In more recent times, innovative TDR approaches have also been implemented to extend current TDR fields of application to the problem of monitoring non-aqueous phase liquids (NAPLs) in variable saturated soils. NAPLs are organic compounds with low solubility in water and are characterised by a high mobility in the vadose zone. Due to their high toxicity, NAPLs constitute a severe geo-environmental problem, thus making detection and observation of such substances in soils an increasingly important issue. The present paper deals with these studies and aims to provide an up-to-date review of the main NAPL-TDR studies. To date, the literature has focused on TDR applications in three main fields: (i) NAPL monitoring in homogeneous, variable saturated soils, (ii) NAPL monitoring in layered variable saturated soils, and (iii) NAPL monitoring during soil decontamination processes. For an exhaustive and complete overview of TDR research in this field, we also recall the basic principles of TDR signal propagation, the functioning of a typical TDR device, and the dielectric mixing models that are widely used to interpret the dielectric response of NAPL-contaminated soils.

Sinkholes play a critical role in groundwater systems by facilitating both recharge and discharge of groundwater, serving as indicators of underlying geologic processes, shaping subsurface hydrology, and influencing water quality. Therefore, studying karst groundwater systems is essential for effective groundwater management, especially in areas with limestone sequences. Spatial variations of water isotopes (δ2H, δ18O), dissolved inorganic and organic carbon (DIC and DOC), including their isotopes alone with pH, EC, alkalinity and chloride were determined in surface- and groundwater of the Mulankavil karst aquifer basin in the northwest of Sri Lanka. Twenty-seven groundwater wells, one offshore spring and two sinkholes were selected for sampling. The contribution of sinkhole water and seawater to karst aquifers was calculated using δ18O and chloride as tracers. In addition, deuterium excess (d-excess) values were used to determine groundwater evaporative loss before infiltration. Near the Mulankavil sinkhole area, the mixing of surface water and infiltrating rainwater was found to vary between 26 and 60%, with an average of 56%. In contrast, surface water mixing in the Nagapadduvan and Vellankulam sinkholes was about 41–59% and 33–70%, respectively. In near coastal wells, these values fell to 20% due to the influence of seawater intrusion. During the dry season, groundwater d-excess varied between −5.0 and + 10.8‰, while surface water in sinkholes showed values between +1.8 and −9.4‰. Groundwater wells near the Mulankavil sinkhole showed lower DIC (<5.5 mmol/L) with enriched δ13C DIC (>-14‰). The karst aquifer systems in northern Sri Lanka exhibit two main recharge mechanisms: (a) selective recharge by surface water at sinkholes and (b) diffuse recharge by direct rainfall over the study area. Seawater intrusion near the coast can be prevented by artificially recharging rainwater during the monsoon season. [Display omitted] • The Mulankavil Karst groundwater basin is a vital freshwater reserve in Sri Lanka. • A geochemical proxy approach was used to quantify water fluxes from different sources. • The mixing of evaporated sinkholes and seawater determines the geochemistry of groundwater. • Conversion of DOC to DIC was evident in the studies of karst aquifer systems. [ABSTRACT FROM AUTHOR]

Premise: Invasive plants in wetlands are often ecosystem engineers, mediating changes in ecosystem functions like trophic support. We documented the impacts of Lepidium latifolium, an invasive plant, on the food web of omnivorous birds (Suisun song sparrows, Melospiza melodia maxillaris) in a tidal wetland of northern California, USA. Methods: We used analysis of natural abundance stable isotopes of 13C and 15N in song sparrow blood, invertebrate food sources, L. latifolium seeds, and other marsh plant seeds to inform Bayesian, concentration‐dependent mixing models that predicted average song sparrow diets. Results: Season and plant phenology influenced food source incorporation and isotopic signatures. Song sparrows showed higher isotopic variability in the summer. The observed changes in song sparrow diets were driven by altered invertebrate communities related to seasonal L. latifolium presence and by shifts from seeds to consumption of invertebrate food sources during the breeding season in the spring and summer. Discussion: This study used stable isotope tools and modeling to demonstrate two mechanisms of isotopic influence by L. latifolium on omnivorous song sparrows. This study can inform site‐ and species‐specific management strategies by demonstrating how changes to the plant community can impact entire trophic systems. [ABSTRACT FROM AUTHOR]

Species introductions are a major concern for ecosystem functioning, socio-economic wealth, and human well-being. Preventing introductions proved to be the most effective management strategy, and various tools such as species distribution models and risk assessment protocols have been developed or applied to this purpose. These approaches use information on a species to predict its potential invasiveness and impact in the case of its introduction into a new area. At the same time, much biodiversity has been lost due to multiple drivers. Ways to determine the potential for successful reintroductions of once native but now extinct species as well as assisted migrations are yet missing. Stable isotope analyses are commonly used to reconstruct a species' feeding ecology and trophic interactions within communities. Recently, this method has been used to predict potentially arising trophic interactions in the absence of the target species. Here we propose the implementation of stable isotope analysis as an approach for assessment schemes to increase the accuracy in predicting invader impacts as well as the success of reintroductions and assisted migrations. We review and discuss possibilities and limitations of this methods usage, suggesting promising and useful applications for scientists and managers. [ABSTRACT FROM AUTHOR]

Non-indigenous freshwater bivalves negatively affect invaded ecosystems through different mechanisms, including inter-specific competition for trophic resources. Here, we investigated in Lake Trasimeno (Central Italy) the diet of the invasive Dreissena polymorpha and the native Anodonta anatina. δ15N and δ13C stable isotopes were measured in winter and summer in bivalves, phytoplankton, and sedimentary organic matter (SOM); the relative dietary contributions of the two resources were determined using Bayesian mixing models. To elucidate the different carbon and nitrogen pools characterizing the study site, isotopic analyses were extended to zooplankton and to representatives of the benthic flora and macroinvertebrate fauna. Independently from the season, the two bivalves showed a limited trophic overlap, as mixing models indicated for D. polymorpha a diet based primarily on phytoplankton, while A. anatina relied mainly on SOM. Dietary differences were less marked in summer, when comparable isotopic values characterized phytoplankton and SOM. In winter, conversely, the trophic differentiation between the two species was more evident, and corresponded with a significant enrichment in SOM δ13C values, likely due to a substantial contribution of carbon deriving from decaying macrophytes. Whether differences in ecological and behavioral traits alone can explain the observed trophic segregation between the two species, or if they have actively shifted their diet to reduce competition for food is discussed. We conclude emphasizing the need of an advanced resolution of the influence of non-indigenous species on the flux of energy and matter in invaded lentic systems, including Lake Trasimeno. [ABSTRACT FROM AUTHOR]

The blue crab Callinectes sapidus was first observed in the Ebro Delta in 2012 and since then captures have increased exponentially up to over 2 t per day, while its presence remains low in other Catalonian estuarine areas. Here, we use a stable isotope approach (δ15N and δ13C) to explore the dietary habits of adult blue crab in four different invaded habitats—bays, coastal lagoons, rice field drainage channels, and the Ebro River—in order to assess the strength of bottom-up forces and identify risks for native and aquaculture species, as well as patterns of site fidelity (male individuals). Mixing models showed average contributions of 35.89% from organic matter in sediments, 34.25% from animal resources (fish, crustaceans, gastropods, and bivalves), and 23.84% from vegetal resources (aquatic plants and algae), although there were important differences across habitat sites. In sites where bivalves were available, they can represent up to ca. 75% of the diet, thus threatening natural banks and local oyster and mussel farms. The average estimated trophic position of blue crabs in those sites was only 2.8, which confirms an omnivorous behavior but also can be attributed to the fact that mollusks were rare in the majority of the areas sampled in the Ebro Delta. Crabs from the same habitat site exhibited very little isotopic variability, suggesting that they remain in those environments long enough to reflect local salinity conditions. Overall, our results suggest that blue crabs are likely using all locally available resources and remain in certain sites, even when preferred animal preys are scarce and low-quality items are the main dietary option. [ABSTRACT FROM AUTHOR]

Fungus‐growing termites and their symbiotic Termitomyces fungi are critically important carbon and nutrient recyclers in arid and semiarid environments of sub‐Saharan Africa. A major proportion of plant litter produced in these ecosystems is decomposed within nest chambers of termite mounds, where temperature and humidity are kept optimal for the fungal symbionts. While fungus‐growing termites are generally believed to exploit a wide range of different plant substrates, the actual diets of most species remain elusive. We studied dietary niches of two Macrotermes species across the semiarid savanna landscape in the Tsavo Ecosystem, southern Kenya, based on carbon (C) and nitrogen (N) stable isotopes in Termitomyces fungus combs. We applied Bayesian mixing models to determine the proportion of grass and woody plant matter in the combs, these being the two major food sources available for Macrotermes species in the region. Our results showed that both termite species, and colonies cultivating different Termitomyces fungi, occupied broad and largely overlapping isotopic niches, indicating no dietary specialization. Including laser scanning derived vegetation cover estimates to the dietary mixing model revealed that the proportion of woody plant matter in fungus combs increased with increasing woody plant cover in the nest surroundings. Nitrogen content of fungus combs was positively correlated with woody plant cover around the mounds and negatively correlated with the proportion of grass matter in the comb. Considering the high N demand of large Macrotermes colonies, woody plant matter seems to thus represent a more profitable food source than grass. As grass is also utilized by grazing mammals, and the availability of grass matter typically fluctuates over the year, mixed woodland‐grasslands and bushlands seem to represent more favorable habitats for large Macrotermes colonies than open grasslands. [ABSTRACT FROM AUTHOR]

Soil erosion and associated sediment redistribution are key environmental problems in Central Argentina. Specific land uses and management practices, such as intensive grazing and crop cultivation, are considered to be significantly driving and accelerating these processes. This research focuses on the identification of suitable soil tracers from hot spots of land degradation and sediment fate in an agricultural catchment of central Argentina with erodible loess soils. Using Energy Dispersive X-Ray Fluorescence (EDXRF), elemental concentrations were determined and later used as soil tracers for geochemical characterization. The best set of tracers were identified using two artificial mixtures composed of known proportions of soil sources collected from different lands having contrasting soil uses. Barium, calcium, iron, phosphorus, and titanium were identified for obtaining the best suitable reconstruction of source proportions in the laboratory-prepared artificial mixtures. Then, these elements, as well as the total organic carbon, were applied for pinpointing critical hot spots of erosion within the studied catchment. Feedlots were identified to be the main source of sediments, river banks and dirt roads together are the second most important source. This investigation provides key information for optimizing soil conservation strategies and selecting land management practices and land uses which do not generate great contribution of sediment, preventing pollution of the waterways of the region.

Abstract Habitat fragmentation of submerged aquatic vegetation (SAV) transforms the spatial pattern of seascapes by changing both the total area and spatial configuration of the habitat patches. The ecological effects of SAV seascapes are most often assessed using metrics of biological community composition (e.g., species and assemblage changes). We know considerably less about the effects of seascape structure on ecological processes such as food web function and energy flow. Here, we assess the difference in the trophic niche of Pinfish (Lagodon rhomboides, a generalist omnivore) across a spatial gradient of SAV from continuous to highly fragmented seascapes in Biscayne Bay (Miami, Florida, USA). The Bay seascapes are influenced by freshwater management practices that alter the distribution of SAV habitat and fish species abundance, diversity, and community assemblage. We combined SAV seascape maps with stable isotope and hypervolume analyses to determine how trophic niche size and overlap varied with changes in the seascape. We observed similar resource use across the seascape, but trophic niche size increased in more fragmented SAV seascapes, suggesting diversification of trophic roles and energy flow pathways. Pinfish collected from more continuous SAV habitats had smaller trophic niche size and higher trophic levels. Both trophic response metrics manifested a threshold response that depended on distinct SAV spatial characteristics (amount vs. spatial configuration) and environmental conditions. Our results suggest that habitat fragmentation of SAV seascape structure has ecological implications that could affect energy flow with cascading consequences for food web stability and ecosystem functioning.

Habitat fragmentation of submerged aquatic vegetation (SAV) transforms the spatial pattern of seascapes by changing both the total area and spatial configuration of the habitat patches. The ecological effects of SAV seascapes are most often assessed using metrics of biological community composition (e.g., species and assemblage changes). We know considerably less about the effects of seascape structure on ecological processes such as food web function and energy flow. Here, we assess the difference in the trophic niche of Pinfish (Lagodon rhomboides, a generalist omnivore) across a spatial gradient of SAV from continuous to highly fragmented seascapes in Biscayne Bay (Miami, Florida, USA). The Bay seascapes are influenced by freshwater management practices that alter the distribution of SAV habitat and fish species abundance, diversity, and community assemblage. We combined SAV seascape maps with stable isotope and hypervolume analyses to determine how trophic niche size and overlap varied with changes in the seascape. We observed similar resource use across the seascape, but trophic niche size increased in more fragmented SAV seascapes, suggesting diversification of trophic roles and energy flow pathways. Pinfish collected from more continuous SAV habitats had smaller trophic niche size and higher trophic levels. Both trophic response metrics manifested a threshold response that depended on distinct SAV spatial characteristics (amount vs. spatial configuration) and environmental conditions. Our results suggest that habitat fragmentation of SAV seascape structure has ecological implications that could affect energy flow with cascading consequences for food web stability and ecosystem functioning. [ABSTRACT FROM AUTHOR]

We assessed the applicability of end-member mixing analysis (EMMA) in a high mountain catchment (Central Pyrenees) to quantify the contributions of snowpack, rainwater, lake water, and shallow and deep groundwater to surface flow. The sampling was conducted from March to November 2010, using an automated system that allowed stream water sampling with high temporal resolution (from 10 minutes in the rising limb to eight hours in the receding limb) to capture all discharge events in detail. We measured conductivity, alkalinity, pH, dissolved inorganic carbon and dissolved organic carbon (DOC), Na+, K+, Ca2+, Mg2+, Cl−, SO42−, NO3−, NH4+, NO2−, and dissolved reactive silica (DRSi). Using a hydrological diagnostic tool set prior to the EMMA, we determined that only Na+, Ca+, DRSi, and DOC could be used as tracers. Three end members were defined (atmospheric water, shallow groundwater, and deep groundwater), and the EMMA results showed that groundwater (deep plus shallow) was an important (~50%) year-round contributor to the surface flow, with peaks reaching > 70% during rainfall episodes. [ABSTRACT FROM AUTHOR]

Palaeodietary reconstruction using stable isotope analysis is becoming increasingly common, as is the practice of using mixing models to quantify ancient dietary compositions. However, many archaeologists may be unaware of the complexities and pitfalls of stable isotope mixing models (SIMMs). This study serves to provide an overview of the basic principles of SIMMs, evaluates the performances of several of the most commonly used SIMM software packages, and offers some field-specific guidelines for the application of SIMMs in archaeological contexts. We present a series of simulated and published archaeological data to demonstrate and evaluate the different types of SIMMs. We compared the outputs of linear mixing models, simple probabilistic models (IsoSource), and conditional probabilistic models (FRUITS and MixSIAR). Our results show that each mixing model has its pros and cons, and archaeologists should select the best model based on a number of factors, including familiarity with coding languages, sample characteristics (i.e. sample size and normality) of the consumer groups, and research questions. [ABSTRACT FROM AUTHOR]

Abstract Ecosystems are experiencing elevated levels of disturbance, and species with narrower niches are often more vulnerable to disturbances. Niche breadth is often measured in terms of either diet or habitat use but diet and spatial use are infrequently considered in tandem. These different aspects of niche breadth potentially expose species to different types of disturbances; species with narrow dietary niches may be more affected by disturbances that alter trophic relationships, while species with narrow habitat niches may be more vulnerable to habitat loss and point‐source pollutants. We examined dietary and habitat niche breadth of common bottlenose dolphins, Tursiops truncatus truncatus, from three different nearshore sites in the Gulf of Mexico (GoM). Using stable isotopes, we determined proportional contributions of different prey groups to dolphin diets at each site and through time at one site. We used satellite‐linked telemetry at two sites to determine habitat use and site fidelity. Additionally, we examined the literature on cetacean diet, habitat use, movement, and IUCN status to determine relationships between niche breadth and population status for different species. Dolphin diets varied among sites as available prey varied, but Perciformes fish were the most frequently consumed prey. At the site for which we had temporal data, dolphins consumed more cephalopods in 2015 and 2018 but otherwise consumed primarily Perciformes fish. Dolphins had small utilization distributions and exhibited high site fidelity. Data from 31 cetacean species revealed that most species with vulnerable, threatened, or endangered IUCN statuses not only have specialized diets but also exhibit high site fidelity. Dolphins had diet characteristic of flexible generalists but were habitat specialists with high site fidelity. Dolphin populations in the GoM may have altered their diets in response to environmental changes that have altered community composition and trophic dynamics. On the other hand, their high site fidelity has exposed them to point‐source pollutants, such as oil spills, persistent organic pollutants, and freshwater. Our broader analysis of cetaceans confirmed that species with specialized diets and high site fidelity were the most vulnerable to disturbances, providing a framework to predict which nearshore dolphin populations, and cetaceans in general, are most vulnerable to environmental changes.

Ecosystems are experiencing elevated levels of disturbance, and species with narrower niches are often more vulnerable to disturbances. Niche breadth is often measured in terms of either diet or habitat use but diet and spatial use are infrequently considered in tandem. These different aspects of niche breadth potentially expose species to different types of disturbances; species with narrow dietary niches may be more affected by disturbances that alter trophic relationships, while species with narrow habitat niches may be more vulnerable to habitat loss and point‐source pollutants. We examined dietary and habitat niche breadth of common bottlenose dolphins, Tursiops truncatus truncatus, from three different nearshore sites in the Gulf of Mexico (GoM). Using stable isotopes, we determined proportional contributions of different prey groups to dolphin diets at each site and through time at one site. We used satellite‐linked telemetry at two sites to determine habitat use and site fidelity. Additionally, we examined the literature on cetacean diet, habitat use, movement, and IUCN status to determine relationships between niche breadth and population status for different species. Dolphin diets varied among sites as available prey varied, but Perciformes fish were the most frequently consumed prey. At the site for which we had temporal data, dolphins consumed more cephalopods in 2015 and 2018 but otherwise consumed primarily Perciformes fish. Dolphins had small utilization distributions and exhibited high site fidelity. Data from 31 cetacean species revealed that most species with vulnerable, threatened, or endangered IUCN statuses not only have specialized diets but also exhibit high site fidelity. Dolphins had diet characteristic of flexible generalists but were habitat specialists with high site fidelity. Dolphin populations in the GoM may have altered their diets in response to environmental changes that have altered community composition and trophic dynamics. On the other hand, their high site fidelity has exposed them to point‐source pollutants, such as oil spills, persistent organic pollutants, and freshwater. Our broader analysis of cetaceans confirmed that species with specialized diets and high site fidelity were the most vulnerable to disturbances, providing a framework to predict which nearshore dolphin populations, and cetaceans in general, are most vulnerable to environmental changes. [ABSTRACT FROM AUTHOR]