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We studied the features of PAHs extraction by QuEChERS in the sample preparation of soils and bottom sediments of various compositions followed their determination by gas chromatography-mass-spectrometry. The test samples were soils of sandy, loamy sand, loamy, and clayey types and bottom sediments of loamy sand type. The mineralogical composition and organic matter content of the samples were used to predict how PAHs were retained by the soils and sediments. The impact of ultrasonic treatment on analyte extraction with subsequent identification by chromatography was assessed. No ultrasonic treatment was required to extract and determine all PAHs (up to 100%) in sandy and loamy sand soils and low-molecular-weight PAHs in all test samples. The QuEChERS extraction and determination of high-molecular-weight PAHs in clay type soil samples and loamy sand bottom sediments required a 10-min ultrasonic treatment, while the recoveries of analytes were higher than 87 and 90%, respectively. The analysis of a loamy soil sample with a high organic matter content was the most challenging. To extract over 70% of high-molecular-weight PAHs from a sample of this type using the QuEChERS technique, the binary acetonitrile-acetone (1 : 1) extractant rather than conventional acetonitrile was used with the simultaneous 15-min ultrasonic treatment., Author(s): Z. A. Temerdashev [sup.1] , S. K. Ovsepyan [sup.1] , T. N. Musorina [sup.1] , L. V. Vasileva [sup.1] , A. M. Vasilev [sup.1] , I. G. Korpakova [sup.1] [...]

Monte Verde II in southern Chile is one of the most important, and debated, sites for understanding of the early peopling of the Americas. The authors present 43 radiocarbon measurements based on cores of sediments that overlie the archaeological deposits adjacent to the site. Statistical analysis of these dates narrows the deposition of the earliest sediments sealing the occupational layer to c. 14 550 cal BP. The consistency between the dates of the site's archaeological strata and its adjacent deposits allows not only consolidation of the site's chronology, but also illustration of how a multi-pronged approach can inform debates surrounding the peopling of new lands--in the Americas or elsewhere. Keywords: Patagonia, Monte Verde, Late Pleistocene, human migration, AMS radiocarbon dating, sedimentology, Introduction The initial peopling of the Americas has been one of the most intriguing questions debated by archaeologists, palaeoanthropologists, geneticists and geologists in recent years (e.g. Waters & Stafford 2014; [...]

Confirming ephemeral human occupation is a crucial issue in cave archaeology. The project 'Tracing human presence in caves of Polish Jura' focuses on the application of molecular methods to decode the history of past human activities in cave sediments in the Krakow-Czestochowa Upland. The results will be compared with archaeological and palaeoecological proxies. Keywords: Poland, molecular analyses, sedimentary sequence, cave occupation, Introduction Caves have attracted people since the dawn of time and have accumulated a record of repeated human entries through many millennia. Detailed archaeological fieldwork allows us to understand many [...]

Partially exposed bedrock beneath Pleistocene glacial till in Erie County (north-central Ohio) displays unusual structural deformation in the Devonian Berea Sandstone, Bedford Shale, and Ohio Shale. These folded and faulted units are exposed in creeks as anticlines and synclines. Past studies of this area proposed Pleistocene ice movement and soft-sediment deformation during the Late Paleozoic as the deformation mechanisms, but these hypotheses cannot explain the extent of layer displacement or the contradiction between the southwest travel direction of the ice sheet and the structural sense of motion on the folded units. A new interpretation using field data and constructing geologic profiles explains the development of these structures. This study investigated 17 anticlines that trend in different directions. Four of these anticlines are tightly folded with steep or overturned flanks and thrust-faulted Ohio Shale in their cores. Structural analysis of these folds shows that the incompetent shaly units of the Plum Brook-Ohio-Bedford and competent Berea Sandstone were folded above the Delaware-Niagara carbonates as a result of the compressional stress during the Late Paleozoic. Development of these tight or overturned folds, and change in trend of the anticlines, is caused by unusual stratigraphic thickness variations in the Berea and Bedford units. Preserved and undeformed fine sedimentary structures, and sharply faulted beds, in the Berea and Bedford indicate that soft-sediment deformation was not the cause of the regional structural deformation. Finally, the absence of physical features of glacially deformed bedrock demonstrates that Pleistocene glacial ice shove was not the cause of deformed bedrock units in the study area., INTRODUCTION Unusual geologic structures near Chappel Creek in north-central Ohio have drawn the attention of geologists for many decades (Fig. 1). Unlike the horizontal to sub-horizontal sedimentary layers of most [...]

The authors discuss new sediment coring at the Early Neolithic submerged site of Atlit-Yam, Israel, that reveals stratified archaeological deposits 0.7-0.9m below the seabed. They demonstrate the potential of microgeoarchaeological analysis to generate new chrono-stratigraphic data for the onset of Early Neolithic coastal occupation in the Eastern Mediterranean. Keywords: Southern Levant, Neolithic, underwater archaeology, submerged settlements, geoarchaeology, Introduction and background Coastal societies are vital to our understanding of Mediterranean history; however, the archaeological record for the earliest of such societies tends to be obscured. Post-glacial sea-level rise [...]

Whiteschists from the Dora-Maira massif (Western Alps, Italy) are Mg and K-rich metasomatised granites which experienced ultra-high-pressure metamorphism and fluid-rock interaction during Alpine continental subduction. The sources and timing of fluid infiltration are a source of significant debate. In this study, we present boron (B) isotopes and other fluid-mobile trace-element (FME) concentrations in various generations of phengite from whiteschists and their country rock protoliths to investigate the sources and timing of metasomatic fluid influx. Reconstructed bulk rock concentrations based on modal data and mineral compositions indicate that significant amounts B and other FME were added to the rock during prograde metamorphism, but that this fluid influx postdates the main Mg metasomatic event. High B concentrations (150-350 [Formula omitted]g/g) and light [Formula omitted] values (- 16 to -4 â°) recorded in phengite point to a B-rich sediment-derived fluid as the main source of B in the whiteschists. Further redistribution of FME during metamorphism was associated with breakdown of hydrous minerals, such as talc, phlogopite, and ellenbergerite. The source of the Mg-rich fluids cannot be constrained based on the B data in phengite, since its signature was overprinted by the later main B metasomatic event. Rare tourmaline-bearing whiteschists record additional information about B processes. Tourmaline [Formula omitted] values (- 6 to +1 â°) are in isotopic equilibrium with similar fluids to those recorded in most phengite, but phengites in tourmaline-bearing samples record anomalous B isotope compositions that reflect later redistribution of B. This study demonstrates the utility of in situ analyses in unravelling complex fluid-rock interaction histories, where whole-rock analyses make it difficult to distinguish between different stages of fluid-rock interaction. Polymetasomatism may result in decoupling of different isotopic systems, thus complicating their interpretation. The Dora-Maira whiteschists interacted with multiple generations of fluids during subduction and therefore may represent a long-lived fluid pathway., Author(s): Benedict J. R. Harris [sup.1], Jan C. M. De Hoog [sup.1], Ralf Halama [sup.2], Hans-Peter Schertl [sup.3], Yi-Xiang Chen [sup.4] Author Affiliations: (1) https://ror.org/01nrxwf90, grid.4305.2, 0000 0004 1936 7988, [...]

Artificial reefs are now commonly used as a tool to restore degraded coral reefs and have a proven potential to enhance biodiversity. Despite this, there is currently a limited understanding of ecosystem functioning on artificial reefs, and how this compares to natural reefs. We used water sampling (bottom water sampling and pore water sampling), as well as surface sediment sampling and sediment traps, to examine the storage of total organic matter (as a measure of total organic carbon) and dynamics of dissolved inorganic nitrate, nitrite, phosphate and ammonium. These biogeochemical parameters were used as measures of ecosystem functioning, which were compared between an artificial reef and natural coral reef, as well as a degraded sand flat (as a control habitat), in Bali, Indonesia. We also linked the differences in these parameters to observable changes in the community structure of mobile, cryptobenthic and benthic organisms between habitat types. Our key findings showed: (1) there were no significant differences in inorganic nutrients between habitat types for bottom water samples, (2) pore water phosphate concentrations were significantly higher on the artificial reef than on both other habitats, (3) total organic matter content in sediments was significantly higher on the coral reef than both other habitat types, and (4) total organic matter in sediment traps in sampling periods May and September were higher on coral reefs than other habitats, but no differences were found in November. Overall, in terms of ecosystem functioning (specifically nutrient storage and dynamics), the artificial reef showed differences from the nearby degraded sand flat, and appeared to have some similarities with the coral reef. However, it was shown to not yet be fully functioning as the coral reef, which we hypothesise is due its relatively less complex benthic community and different fish community. We highlight the need for longer term studies on artificial reef functioning, to assess if these habitats can replace the ecological function of coral reefs at a local level., Author(s): Zach Boakes [sup.1] , I. Gusti Ngurah A. Suryaputra [sup.2] , Alice E. Hall [sup.3] , Daniel J. Franklin [sup.1] , Richard Stafford [sup.1] Author Affiliations: (1) grid.17236.31, 0000 [...]

Microlitter is a widespread contaminant with implications for aquatic health; however, knowledge of its distribution in fresh waters is limited. We examined microlitter in surface water, sediment, and mussels within the Saint John River and four major tributaries. Microlitter was present at all 89 sites, with concentrations in water equivalent to other Canadian watersheds. Microlitter concentrations likely reflected differences in land use and development. Comparisons between rivers generally revealed distinct water microlitter particle compositions, suggesting that input sources were specific to each river, while microlitter in sediments and mussels was largely homogeneous among rivers. There was little similarity in concentration and composition of microlitter among the three matrices sampled. Microlitter in sediments and mussels may not reliably track concentration and composition in aquatic environments. Microlitter concentration was not significantly greater downstream of wastewater treatment plants. Airborne microlitter transportation was evident, as remote sites in two tributary rivers demonstrated the highest concentrations of microlitter. Our data highlights the prevalence of microlitter in rural rivers, underscoring the ubiquity of this emerging contaminant and its integration into food webs. Si les microdechets constituent un contaminant repandu qui a des repercussions sur la sante des milieux aquatiques, les connaissances sur sa repartition dans les plans d'eau douce sont limitees. Nous avons examine les microdechets dans l'eau de surface, les sediments et les moules dans le fleuve Saint-Jean et quatre principaux affluents. Des microdechets etaient presents dans les 89 sites etudies a des concentrations comparables a celles observees dans d'autres bassins hydrographiques canadiens. Les concentrations de microdechets refletent probablement differentes utilisations et occupations du sol. Des comparaisons des differents cours d'eau etudies revelent generalement differentes compositions de particules de microdechets dans l'eau, ce qui indiquerait des sources distinctes pour chaque riviere, alors que les microdechets dans les sediments et les moules sont generalement homogenes d'une riviere a l'autre. Les trois matrices echantillonnees presentent peu de similitudes entre elles en ce qui concerne les concentrations et la composition de microdechets. Les microdechets dans les sediments et les moules pourraient ne pas donner un portrait fidele de la concentration et de la composition des microdechets dans les milieux aquatiques. La concentration de microdechets n'est pas significativement plus elevee en aval d'usines de traitement des eaux usees. Les plus grandes concentrations de microdechets sont observees dans des sites eloignes dans deux affluents, ce qui temoigne du transport aerien de microdechets. Nos donnees font ressortir la prevalence des microdechets dans les rivieres rurales, soulignant l'ubiquite de ce nouveau contaminant et son incorporation dans les reseaux trophiques. [Traduit par la Redaction], 1. Introduction Microlitter has gained global attention as a nearly ubiquitous environmental contaminant; however, at present, the fate, transport, and extent of microlitter in fresh waters--especially within rural regions--remains poorly [...]

The Cenozoic Himalayan leucogranites are generally regarded as the representative S-type granites, derived from partial melting of (meta-)sedimentary rocks in the Higher Himalayan Sequences. This interpretation is challenged by the increasing finding of abundant relict zircons with Cambrian-Ordovician ages in the granites. These ages are lacking in the assumed (meta-)sedimentary sources but are close to the formation timing of early Paleozoic granites (presently as orthogneisses) in the Himalaya. Therefore, it is unclear how the early Paleozoic relict zircons were incorporated into the granites and what the real sources of the Cenozoic Himalayan leucogranites are. This study presents U-Pb ages, trace-element, and Lu-Hf isotope compositions of zircon from both the Cenozoic granites and their country rocks (Paleozoic orthogneisses) from Kuday in the Sakya dome, central Himalaya. Our results indicate that the autocryst zircons from the gneiss samples formed at 494-499 Ma and display obvious negative correlations in the Hf-Ti, Hf-Th/U, and Hf-Eu/Eu* binary plots. Their [epsilon].sub.Hf(420 Ma) values have relatively restricted variations of -7.2 to -0.5. In contrast, the early Paleozoic relict zircons from granites form scattered and contrasting fields in these binary plots with largely varied U-Pb ages (ca. 410-520 Ma) and [epsilon].sub.Hf(420 Ma) values of -35.4 to + 6.7. These observations suggest that the autocryst zircons from gneisses are a cogenetic population and their compositional variations are controlled by crystallization differentiation, whereas the relict zircons from granites were probably originated from sedimentary rocks in which detrital grains were weathered from a variety of protoliths. We argue that the early Paleozoic relict zircon population was not incorporated into the Cenozoic granites by assimilation of the orthogneissic country rocks. This is supported by whole-rock Nd-Hf isotope analyses, which yield [epsilon].sub.Nd(t) and [epsilon].sub.Hf(t) values of -12.6 ~ -12.5 and of -10.4, respectively, for granites and of -8.8 ~ -8.1 and of -5.9, respectively, for orthogneisses (all calculated at 20 Ma). Furthermore, our compiled whole-rock Sr-Nd isotope data indicate that the Cenozoic Himalayan granites differ from the Paleozoic orthogneisses but overlap with the Himalayan (meta-)sedimentary rocks. Phase equilibrium modeling demonstrates that the Paleozoic orthogneisses are relatively infertile due to their low fractions of hydrous minerals and thus low bulk water contents as compared with the metapelites assuming no free fluid is present. Therefore, although the contribution of the Paleozoic orthogneisses cannot be totally precluded, the observed evidence suggests that they are not the main source components of the Cenozoic Himalayan granites. It is speculated that Ordovician and later sediments which can receive the weathered clasts of the early Paleozoic granites can act as the unrecognized sources of the Cenozoic granites. However, more work is required to characterize these sediments before drawing firm conclusions on the sources of these granites., Author(s): Peng Gao [sup.1], Yan Wang [sup.1], Guo-Chao Sun [sup.2], Matthew Jason Mayne [sup.3], Jian Zhang [sup.4], Changqing Yin [sup.1], Jiahui Qian [sup.1] Author Affiliations: (1) grid.12981.33, 0000 0001 2360 [...]

The Imlay Channel in Lapeer County, Michigan, was one of two outlets for the glacial Lake Maumee phase of ancestral Lake Erie. Fifteen new radiocarbon and optical ages from within and adjacent to the Imlay Channel constrain sedimentation rates within the channel and the timing of regional deglaciation. For nearly 50 years, the deglaciation of this region of Michigan has been based on a single age from the Weaver Drain site located near the Imlay Channel, and a new radiocarbon age of 16.7-17.0 cal ka BP from 3 km east of the Imlay Channel supports this long-standing deglacial age. On average, there is a 14 m thick sediment fill within the channel. Radiocarbon and optically stimulated luminescence ages reveal that much of the alluvial fill was deposited by 14.9 ka, and alluvial fans building into the channel stabilized in the early Holocene. Cross-sections along and perpendicular to the Imlay Channel, built from geotechnical borings and water-well records, reveal a current-day bedrock sill elevation at 235 m a.s.l. that would have permitted drainage of all stages of glacial Lake Maumee in the past. Key words: Lake Maumee, Imlay Channel, ancestral Lake Erie, Great Lakes, Fort Wayne outlet. Le chenal Imlay, dans le comté de Lapeer (Michigan), était une des deux décharges pour la phase du lac Maumee du proto-lac Érié. Quinze nouveaux âges optiques et au radiocarbone d'échantillons provenant du chenal Imlay et des environs permettent de mieux délimiter les taux de sédimentation dans le chenal et la chronologie de la déglaciation régionale. Pendant près de 50 ans, la compréhension de la déglaciation de cette région du Michigan reposait sur un seul âge du site de Weaver Drain à proximité du chenal Imley, et un nouvel âge au radiocarbone de 16, 7-17, 0 cal ka BP pour un site à 3 km à l'est du chenal Imlay appuie cet âge de déglaciation établi de longue date. Le remplissage sédimentaire dans le chenal fait en moyenne 14 m d'épaisseur. Les âges au radiocarbone et par luminescence stimulée optiquement révèlent qu'une bonne partie du remplissage alluvial a été déposée avant 14,9 ka et que des cônes alluviaux s'accumulant dans le chenal se sont stabilisés au début de l'Holocène. Des coupes longitudinales et perpendiculaires au chenal Imlay, constituées à partir de sondages géotechniques et de journaux de puits d'eau, révèlent que la hauteur de seuil actuelle du substrat rocheux est de 235 m a.s.l., ce qui aurait permis la vidange de toutes les phases du lac glaciaire Maumee dans le passé. [Traduit par la Rédaction] Mots-clés : lac Maumee, chenal Imlay, proto-lac Érié, Grands Lacs, décharge de Fort Wayne., Introduction The chronology and history of the Imlay Channel and its role in draining glacial Lake Maumee in the Lake Erie and Lake Huron basins remains poorly understood. Leverett and [...]

Boat Harbour, Nova Scotia, Canada, has served as a polishing pond for treated pulp and paper effluent since 1967. In 2020, the effluent flow ceased, and the site will be remediated. The focus of the remediation is the removal of a layer of contaminated sediment, shown to contain high levels of metals and dioxins and furans. Our primary objective was to test whether the underlying pre-industrial sediment could support growth and survival of estuarine plants. A large-diameter (15 cm) corer was used to extract cores from underneath the contaminated layer. These cores were inserted into a reference estuary, along with cores of reference estuarine sediment. Four 3 x 3 subtidal plots were used to test transplants of the estuarine plant Zostera marina, and five 1 x 9 marsh edge plots were used to test Spartina alterniflora. No significant differences in plant growth or survival were observed between Boat Harbour and reference sediment after 2 months. Postexperiment analysis of contaminants (metals and polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans (PCDD/Fs)) in both types of sediment and plant tissues showed similarly low levels of contaminants. Findings indicate that pre-industrial sediment in the harbor should be able to support plant growth after removal of overlying contaminated sediment. Boat Harbour (Nouvelle-Ecosse, Canada) a servi de lagune de finition pour des effluents traites d'usine de pates et papiers depuis 1867. Le deversement d'effluents a cesse en 2020, et le site sera remis en etat. Les efforts de remise en etat se concentrent sur le retrait d'une couche de sediments contamines presentant des teneurs elevees en metaux et en dioxines et furannes. Notre objectif principal consistait a verifier si les sediments preindustriels sous cette couche peuvent soutenir la croissance et la survie de plantes estuariennes. Un carottier de grand diametre (15 cm) a ete utilise pour extraire des carottes de sous la couche contaminee. Ces carottes ont ete inserees dans un estuaire temoin, en plus de carottes de sediments estuariens temoins. Quatre parcelles de 3 x 3 specimens en zone infratidale ont ete utilisees pour verifier la performance de plants repiques de la plante estuarienne Zostera marina et cinq parcelles lineaires de 1 x 9 specimens en bordure du marais ont ete utilisees pour des plants de Spartina alterniflora. Aucune difference significative de la croissance ou de la survie des plants n'a ete observee entre les sediments de Boat Harbour et les sediments temoins apres deux mois. L'analyse postexperimentale des contaminants (metaux, dibenzo-p-dioxines polychlorees et dibenzofurannes polychlores (PCDD et PCDF)) dans les deux types de sediments et les tissus des plants releve des concentrations faibles et semblables de contaminants. Les resultats indiquent que les sediments preindustriels de Boat Harbour devraient pouvoir soutenir la croissance de plantes une fois les sediments contamines sus-jacents retires. [Traduit par la Redaction], 367-1-3 Introduction Prior to 1967, Boat Harbour (hereinafter BH), Nova Scotia (Fig. 1A) was a small tidal estuary adjacent to the Pictou Landing First Nation (PLFN) reserve. The inhabitants of [...]

A method has been developed for the separation of lanthanides, Ce, Nd, Gd, La, Pr, Sm, Dy, Eu, Er, Ho, Yb, Tm, Tb and Lu, using oxalate form of Dowex-1, a reactive ion-exchanger. Lanthanides present in such samples as monazite sand, coal fly ash and sediment were separated from matrix at pH 2.5 in a column containing oxalate form of Dowex-1 resin. The samples have been decomposed in H.sub.2SO.sub.4 and taken in 0.36 M H.sub.2SO.sub.4 prior to separation. The lanthanides in the column were eluted with 2 M HNO.sub.3. Lanthanides present in the eluent were determined by inductively coupled plasma optical emission spectrometry (ICP-OES) and the recovery of analytes ranged from 92 to 105%. Matrix free solutions were analyzed for lanthanides by ICP-OES. The relative standard deviation was in the range of 4-7% and limits of detection were between 0.015-0.16 mg/kg. The developed procedure was applied to the separation and determination of lanthanides in a standard reference material NIST Coal Fly Ash 1633b, a lake sediment and monazite sand. The results obtained by the present method are in close agreement with certified values in case of certified reference material and microwave digestion method for other samples. Accuracy of other samples is ensured based on standard addition recoveries., Author(s): Gumma Venkateswarlu [sup.1], Puttam Reddy Mamatha [sup.2], Shanmugam Thangavel [sup.1], Athyala Christian Sahayam [sup.1] Author Affiliations: (1) grid.418304.a, 0000 0001 0674 4228, National Centre for Compositional Characterisation of Matertials [...]

Oyster habitat restoration seeks to recover lost ecosystem services including increased provisioning of refuge and foraging habitat for fish and invertebrate communities. The goal of this study was to quantify the ecosystem service benefit of habitat provisioning in Ninigret Pond, RI, following oyster restoration. Four metrics were measured, abundance, biomass, species richness, and diversity, as well as isotopic composition in fish and invertebrates collected seasonally from restored oyster, aquaculture, and bare sediment sites, to examine whether the oyster habitat outperformed the bare sediment habitat. Sampling locations were chosen in Foster's Cove north and south. Grassy Point, South Sanctuary, and an Aquaculture lease; each had two restored oyster sites and one bare sediment site. Each site was sampled using a box trap, seine net, shrimp trap, and minnow trap. Oyster habitats had significantly greater metrics than did bare sediment habitats in some comparisons from the box trap and seine net samples. Restored oyster sites at South Sanctuary had lower metric values than the other oyster sites. Metrics from the Aquaculture sites were comparable to the Foster's Cove and Grassy Point restored oyster sites and often outperformed South Sanctuaryrestored oyster sites. Seasonally, spring and autumn samples tended to have higher abundance and biomass values than summer samples. Isotopic composition of five species occurring at both restored oyster and bare sediment sites demonstrated some differences in the trophic levels between species but not between habitat types. In Ninigret Pond, fish and invertebrate abundance, biomass, species richness, and diversity benefit from the use of oyster and bare sediment habitats. Coastal zone managers interested in restoring the ecological function of oyster reefs to support fish and invertebrate communities should consider strategically locating restoration projects within the mosaic of structured habitats and monitoring them for selected ecosystem services. KEY WORDS: nekton, habitat preference, oyster reef, aquaculture, restoration, INTRODUCTION During the past century, degradation of habitats and the ecosystem services they provide in coastal and marine environments has resulted from multiple stressors including nutrient pollution, overexploitation of resources, [...]

Both seagrasses and bivalves molluscs act as ecosystem engineers in marine systems by forming habitat or modifying environmental conditions. They also have the potential for reciprocal interactions when colocated, through a wide variety of potential mechanisms involving different directions in effect. Pathways mediated by biogenic structure could be facilitative through protection from predation or bioturbators, or by harboring beneficial interactors, or alternatively could result in competition for space or reduced food supply. Other pathways mediated by biological activity could positively link autotrophic roles of seagrass and heterotrophic roles of bivalves, but excessive organic matter production or nutrient release could be damaging. Published studies were compiled for a meta-analysis of field experiments testing bivalve response to seagrass (25 studies) and vice versa (11 studies), as well as for surveys of bivalves in and out of seagrass (39 studies). In experiments, seagrass improved bivalve survival, and bivalves at high cover reduced seagrass density, but seven other response metrics showed no consistent change. In surveys of particular bivalve species, densities were 1.6 times higher in seagrass than out of seagrass. This augmentation did not differ by body size but was especially pronounced in some functional groups, especially lucinid and solemyid bivalves harboring sulfide-oxidizing bacteria. Weak overall directional effects of colocation of seagrass and bivalves reflect weak effects in some individual studies, for instance because of low densities in soft-sediment systems, as well as strong but inconsistent effects because different pathways of interaction dominate. Therefore, generalizations about the outcome of interactions between these two ecosystem engineers when they are colocated cannot be made, although coexistence is typically enabled by weak or positive interactions. Further work is needed, especially outside of some well-studied regions, to explore the specific mechanisms and spatiotemporal scales enabling seagrasses and bivalves to coexist because there are many pathways at work. KEY WORDS: bivalves, molluscs, seagrass, INTRODUCTION Seagrasses and bivalves are ecosystem engineers in shallow marine waters, creating habitat structure and modifying abiotic conditions and resource availability (Gutierrez et al. 2011). Yet their environmental effects are [...]

Mantle heterogeneity is caused by recycling of crustal materials into the mantle, and mafic arc magmatism provides important imformation on the nature of crust-mantle interaction. Here we undertake an integrated study of whole rock major-trace elements and Sr-Nd-Hf isotopes, in-situ zircon U-Pb ages and Hf-O isotopes as well as mineral major-trace elements and clinopyroxene Sr isotopes for mafic intrusives in the Qilian orogen. The studied Jinyuan and Jishishan mafic igneous rocks show consistent zircon U-Pb ages of ca. 448-450 Ma. They all display arc-like trace element distribution patterns, relatively depleted Sr-Nd isotope compositions, and variably high zircon O isotopes. In comparison, the Jinyuan mafic igneous rocks have less depleted Sr-Nd-Hf and higher O isotope compositions than the Jishishan mafic rocks. These geochemicial features indicate they originated from a heterogeneous orogenic lithospheric mantle source, which resulted from the incorporation of variable crustal materials into the mantle. Model calculations confirm that the heterogeneous mantle source would be generated by reaction of the mantle wedge peridotite with different proportions of the subducting Proto-Tethyan oceanic crust-derived aqueous solutions and sediment-derived hydrous melts. Partial melting of the heterogeneous mantle source would generate different batches of mafic melts, which led to magma mixing and recharge processes prior to emplacement as evidenced by mineral compositional zonings. Therefore, in addition to heterogeneous crust-mantle interaction during oceanic subduction, magmatic processes such as magma recharge and mixing may also contribute to the petrogenesis of arc igneous rocks above the oceanic subduction zone., Author(s): Qi Chen [sup.1], Li-Qun Dai [sup.1] [sup.2] [sup.3], Zi-Fu Zhao [sup.1] [sup.2] [sup.3], Yong-Fei Zheng [sup.1] [sup.2], Yao Zhou [sup.1] Author Affiliations: (1) grid.59053.3a, 0000000121679639, CAS Key Laboratory of [...]