Sediment Variables Research Articles

Response of marine amphipods to sediment variables (Chabahar Bay- Iran): A step toward localizing amphipod-based bioindices

Chabahar Bay will undergo industrial and coastal pressures according to the government plan to develop the Makran coasts. Therefore, knowing its biological community as well as their possible interactions with environmental variables, before and after coastal development, is important. The amphipod community structure and their response to the structural and contaminant parameters of the sediment include: granulometry, total organic matter (TOM) overloading, heavy metal contamination based on the Pollution Load Index (PLI) and polycyclic aromatic hydrocarbons (PAHs) during post monsoon season of 2017 were investigated from 19 stations. Traditional diversity and taxonomic distinctness indices were calculated. Multivariate analysis revealed the main role of sediment grain size and depth in shaping amphipod community structure. Consequently, two specific ecological niches were determined: species that prefer non-muddy substrates; and those dwelling in muddy or muddy sandy biotopes. No correlation was found between the Shannon diversity (H’), the average taxonomic distinctness indices (Δ+) together and both with contamination parameters. The Δ+ funnel plot well separated under-stressed stations from the healthy ones. The presence of only Ampelisca congeners in under-stressed stations revealed the tolerant nature as well as species-specific response of the genus to anthropogenic impacts. Considerable tolerant response (P > 0.05, r2 = 0.4) of A. zamboangae to PAHs; A. persicus to TOM were observed. High concentration of nickel (Ni) in the studied area already stated due to erosion of ophiolite units from Makran Mountains. The significant correlation of the recently described Iranian species A. lowryi with Ni assumes that it is a native species that is well adapted to the geological conditions of the seabed. Instead Urothoe platydactyla can be considered as early warning signal for PAHs, TOM, Ni and cadmium (Cd) contamination particularly for non-muddy substrates. Our findings help to localize common biotic indices (e.g. AMBI, BENTIX, and BOPA) for studied area through correctly assignment of amphipods to the sensitive/tolerant ecological groups. Finally, we state that in the current situation of Chabahar Bay, in which no special industrial complexes have been established, any sediment-disrupting activity (i.e. sedimentation, dredging, trawling) affects its amphipod communities more than chemical pollutants.

Sedimentation as a Support Ecosystem Service in Different Ecological Types of Mangroves

Mangrove vegetation is strongly dependent on the climate, the physicochemical variables of the sediment, and the hydrological dynamics. These drivers regulate the distribution of different mangrove ecotypes and their ecosystem services, so the net sediment accumulation rates in different mangrove ecotypes in Celestun Lagoon, a karstic zone in the NW Yucatan Peninsula, SE Mexico, were estimated. The measurements considering mangrove ecotypes and their spatial variability concerning the lagoon's salinity gradient (inner, middle, and outer lagoon zones) in three climate seasons (dry, rain, and “nortes”) were realized. We registered the structural variables of the forest, interstitial water physicochemical characteristics, and sediment variables that could influence the net sediment deposition. Fringe mangroves are exposed to low hydrodynamism and show the highest sedimentation rate (3.37 ± 0.49 kg m−2 year−1) compared to basin (1.68 ± 0.22 kg m−2 year−1), dwarf (1.27 ± 0.27 kg m−2 year−1), and “peten” (0.52 ± 0.12 kg m−2 year−1) mangroves. The highest sedimentation rate was recorded in the rainy season (0.24 ± 0.08 kg m−2 month−1), while spatially, the highest value was registered in the outer zone (0.44 ± 0.09 kg m−2 month−1). If the extension of each mangrove ecotype is considered, dwarf mangroves have the highest annual sediment accumulation (1,465 t year−1 in 14,706 ha). The structural, physicochemical, and sediment variables of the sites by mangrove ecotype show that dwarf mangroves represent a distinct group from those formed by fringe, basin, and peten mangroves. However, the sedimentation is high in fringe mangroves at the front of the lagoon and diminishes inland where peten mangroves exist. The differences are given by tree density, but salinity, as a proxy variable of the freshwater influence, significantly influences the sedimentation rate. These results indicate that mangroves in karstic environments can have critical roles in confronting climate change, considering water and sediment flows are the basis of sediment accumulation. According to their hydrogeomorphological drivers, conserving, managing, and restoring the mosaic of mangrove ecotypes improves ecosystem services, including mitigation and adaptation to climate change.

Insights into Bacterial Community Structure and Metabolic Diversity of Mercury-Contaminated Sediments from Hyeongsan River, Pohang, South Korea.

This study investigated the bacterial community structure and metabolic diversity and their relationship with Hg and other environmental variables in sediments collected from different locations (HSR-1-HSR-6) in the Hyeongsan River estuary in South Korea. The results showed that the highest total mercury (THg) and methylmercury (MeHg) concentrations were in HSR-2, with values of 4585.3µg/kg and 13.4µg/kg, respectively. The lowest THg (31.9µg/kg) and MeHg (0.1µg/kg) concentrations were found in HSR-1. Sulfate and organic matter (OM) were more influential environmental variables, revealing a positive association with THg and MeHg and negatively affecting bacterial and metabolic diversities. Bacterial and metabolic diversities were also negatively impacted by the THg and MeHg concentrations. Proteobacteria and Bacteroidetes were abundantly distributed in all the sediments. The dominance of Proteobacteria was upscaled in all the heavily Hg-contaminated sites (HSR-2-HSR-6), and it was the only phylum that showed a significant positive correlation with THg, MeHg, and OM. The genera Sulfurovum and Sulfurimonas were abundantly observed in sites with high Hg contamination, whereas Congregibacter, Gaetbulibacter, Ilumatobacter, Methylotenera, Nevskia, and Sediminibacter were only detected in low Hg-contaminated sites (HSR-1). The community-level physiological profile data showed the highest (1.0) average well color development (AWCD) value in HSR-1 and the lowest (0.45) AWCD value in HSR-2. Overall, these results demonstrated the inhibitory effects of THg, MeHg, and other environmental variables on microbial communities and metabolic diversity. These findings broaden the current knowledge on the dynamics of bacterial and metabolic diversities in Hg-contaminated sediments and might be useful in the management of Hg pollution.

How many grains are needed for quantifying catchment erosion from tracer thermochronology?

Abstract. Detrital tracer thermochronology utilizes the relationship between bedrock thermochronometric age–elevation profiles and a distribution of detrital grain ages collected from riverine, glacial, or other sediment to study spatial variations in the distribution of catchment erosion. If bedrock ages increase linearly with elevation, spatially uniform erosion is expected to yield a detrital age distribution that mimics the shape of a catchment's hypsometric curve. Alternatively, a mismatch between detrital and hypsometric distributions may indicate spatial variability of sediment production within the source area. For studies seeking to identify the pattern of sediment production, detrital samples rarely exceed 100 grains due to the time and costs related to individual measurements. With sample sizes of this order, detecting the dissimilarity between two detrital age distributions produced by different catchment erosion scenarios can be difficult at a high statistical confidence level. However, there are no established software tools to quantify the uncertainty inherent to detrital tracer thermochronology as a function of sample size and spatial pattern of sediment production. As a result, practitioners are often left wondering “how many grains is enough to detect a certain signal?”. Here, we investigate how sample size affects the uncertainty of detrital age distributions and how such uncertainty affects the ability to infer a pattern of sediment production of the upstream area. We do this using the Kolmogorov–Smirnov statistic as a metric of dissimilarity among distributions. From this, we perform statistical hypothesis testing by means of Monte Carlo sampling. These techniques are implemented in a new tool (ESD_thermotrace) to (i) consistently report the confidence level allowed by the sample size as a function of application-specific variables and given a set of user-defined hypothetical erosion scenarios, (ii) analyze the statistical power to discern each scenario from the uniform erosion hypothesis, and (iii) identify the erosion scenario that is least dissimilar to the observed detrital sample (if available). ESD_thermotrace is made available as a new open-source Python-based script alongside the test data. Testing between different hypothesized erosion scenarios with this tool provides thermochronologists with the minimum sample size (i.e., number of bedrock and detrital grain ages) required to answer their specific scientific question at their desired level of statistical confidence.

Stratigraphic variability of Upper Holocene marginal marine sediments along the Al Qahmah Coast of Red Sea, Saudi Arabia

The stratigraphic architecture of Upper Holocene sediments along the coast of Al Qahmah in southern Red Sea, Saudi Arabia, provides a high-resolution analog of marginal marine carbonate and siliciclastic sedimentation under variable climatic, tectonic, and sea-level conditions. The sediments include a basal shallow marine limestone and overlying beach, deltaic, fluvial, eolian, and sabkha siliciclastic deposits, comprising four stratigraphic units ranging from 10s to 100 s cm thick. A lithostratigraphy is established using subsurface stratigraphic and petrographic data from 64 trenches and three shallow refraction seismic sections. A chronostratigraphy is established using four age points and sedimentation rates. The entire interval has been deposited in the last ~4000 years. Significant stratigraphic variability is reflected by vertical and lateral changes in the thickness, type, and stratal geometry of the four units. Five major geological events are interpreted: Initial shallow marine carbonate deposition during a relative sea-level highstand was terminated by seaward progradation of deltaic-beach sediments during a slow shoreline regression. This is followed by a major stream channel incision during the maximum regression and a relative sea-level fall. The ensuing fluvial channel filling, transgressive ravinement, and deposition of beach sediments signify a relative sea-level rise. Finally, eolian, sabkha, and beach sediments have been deposited in a stabilized and diversified environmental setting under an arid climate. The lacuna associated with stream erosion and transgressive ravinement is up to ~400 years long, resulting in a stratigraphic completeness of ~88%. The sedimentation rate of the siliciclastic sediments is ~0.1 cm/year estimated at a scale of 1000s of years. Episodic syn-depositional faulting in the source area and depositional site, relative seal-level change, autogenic environmental shift, and/or climatic changes between humid and arid conditions have collectively played variable roles in the formation of the stratigraphic variability. The interpreted tectonic, relative sea-level, and climatic trends offer an important data point for future studies in the Red Sea region and beyond for the Late Holocene.

Association between Lake Sediment Nutrients and Climate Change, Human Activities: A Time-Series Analysis.

Climate change and human activities are closely linked with the nutrient accumulation in sediments, but the role of influence factors and the driving mechanisms are unclear. Here, by using the generalized additive model (GAM), we investigated the contributions and driving mechanisms of climate change and human activities on TON, TN, and TP accumulation in sediments of typical lakes in the Huai River basin (Nansi Lake and Hongze Lake) from 1988 to 2018. The impacts of factors, such as air temperature (AT), real GDP per capita (GDP), population density (PD), crop sown area (CSA), artificial impervious area (AIA), and domestic sewage discharge (DSD) were considered in this study. The results of the multivariate GAM showed that the sediment variables were significantly affected by climate change in Nansi Lake, but not in Hongze Lake. AT and DSD contributed the most to the variation of sediment TOC in Nansi Lake, while the most critical factors affecting TN and TP were AT, PD and DSD. PD and CSA showed strong ability to explain the change of TOC in Hongze Lake, while CSA and DSD showed strong ability to explain the variations of TN and TP. The results show that the selected optimal multivariate GAM can well quantify the effects of climate change and human activities on nutrient enrichment in lake sediments. Effective recommendations are provided for decision-makers in developing water quality management plans to prevent eutrophication outbreaks in lake waters by targeting and controlling key factors.

The Features of Distribution of Chemical Elements, including Heavy Metals and Cs-137, in Surface Sediments of the Barents, Kara, Laptev and East Siberian Seas

Over the recent few decades, due to climate warming and the continuing exploration of Arctic seas’ mineral resources, the scientific interest in contamination problems has deepened significantly. In this study, for the first time, we characterize the distribution features of 47 elements (major and trace elements, including heavy metals, metalloid As, and Cs-137 technogenic radionuclide) in surface bottom sediments from some areas of the Barents, Kara, Laptev, and East-Siberian Seas. The lithogenic material was the main factor that controlled variability in many elements (Be, Al, Ti, Cr, Ga, Rb, Sr, Y, Zr, Nb, Ba, REE, Pb, Th, U, W, and Cs). Among the hydrogenic processes, the formation of Fe and Mn oxyhydroxides has the greatest impact on the Mn, Fe, Co, Ni, Cu, Ge, and Mo, and insignificantly V and Sb, variability in sediments. These, along with minor to moderate values of enrichment factor (EF) for most elements, allowed us to conclude that the observed element distribution is related to predominantly natural processes of thermal abrasion, river-run, and atmospheric input. The exception is As, which exhibited the elevated EF (up to 20) in the western and central Kara Sea, as well as in the Vilkitsky Strait. Since no significant relationship between As and Fe andMn oxyhydroxides distribution was found, we may assume primarily an anthropogenic source of As, related to the peat and/or coal combustion. According to the criteria of Ecological Risks assessment, all the examined areas have a low degree of risk. Data on the specific activity of Cs-137 correspond to the background average values characteristic for these regions. The highest levels of Cs-137 concentration (Bq/kg) were detected in the sediments of the Ob and Yenisei Rivers’ estuaries.

Concurrent effects of flooding regimes and floodwater quality on sediment properties in a Yangtze River-connected floodplain wetland: Insights from field investigations during 2011–2020

Changes in flood regimes, floodwater quality, and macrophyte types may affect sediment characteristics post-flooding. However, few studies have attempted to unravel their complex influences in floodplain wetlands. From 2011 to 2020, the physical and chemical properties of surface layer sediment pre- and post-flooding was investigated through field surveys in the Dongting Lake wetland. Results indicated that the pre-flooding soil total phosphorus (TP) and total nitrogen (TN) exhibited an increasing trend during 2011–2020. Soil TP increased post-flooding relative to that pre-flooding. The changes in TN, sediment organic matter (SOM), sediment moisture content (SMC), and sediment bulk density (SBD) fluctuated over the years. The best-fitting multi-regression model demonstrated that the changes in sediment variables post-flooding showed a parabolic trajectory along the inundation duration (ID), except for SMC. Changes in soil properties post-flooding were negatively correlated with ID for sediment with a low IDs (<148 days). Meanwhile, changes in soil properties post flooding were positively correlated with ID for sediment with a high IDs (>193 days). Changes in SBD and SOM post-flooding were positively influenced by the TP content in the floodwater. These findings indicate that changes in the flooding regime, and water quality generated by anthropogenic disturbances such as the Three Gorges Dam significantly affect sediment properties, and subsequently influence the ecological functions of the Dongting Lake wetland.

Benthic diatoms and macroinvertebrates status with relevant to sediment quality of islands shores in the Nile River, Egypt

Sediments are utilized as a marker for events that endure long enough to manifest their environmental impacts and determine the contamination levels. The purpose of the present study was to highlight the current sediment quality of four Nile islands shores by utilizing a variety of physical, chemical, and biological aspects and indices. In addition, the status of benthic diatoms and macroinvertebrates, as well as their responses to sediment variables were investigated. The metals followed a decreasing concentration order: Al > Fe > Mn > Zn > Ni ≈ Cr > Cu > Co > Pb > Cd. The outcomes of metal pollution indices revealed some localized contaminated sites, by mostly Ni and Cd. In addition, a moderate toxic risk from metals was observed for El-Keratten shores, while the sediments of El-Warraq, El-Zamalek, and El-Manial islands shores were at low toxic risk. A total of 112 diatom species belonging to 24 genera were identified in the total sample set, where most of the diatoms encountered were cosmopolitan. Metals had a remarkable impact on the composition, distribution, and dominance of diatom assemblages, but had little effect on diatom diversity, while there was a noticeable effect of grain size on diatom distribution and diversity. Thirty-four species of benthic invertebrates were identified in the collected samples from the islands shores. The dominant taxa and groups of benthic invertebrates at different islands were affected by various sediment parameters, where the levels and types of such variables differed from one species to another.Graphical abstract

Coarsening of sediments from the Huanghe (Yellow River) delta-coast and its environmental implications

We studied temporal-spatial variations in the grain size of sediments from the Huanghe (Yellow River) delta-coast. Four sediment push-cores and more than 200 surface sediment samples were collected. Key factors that control the sediment variability were revealed, as well as their environmental significance. Analytical results indicated that sediments of the Huanghe delta-coast have coarsened over the past decades, and that this coarsening has intensified in recent years. The average mean grain size (Mz) of two cores in the offshore area from the abandoned delta lobe increased by approximately 18%–32% in the 2010s compared to the 1990s. Surface sediments in the nearshore area were coarsened by about 25% on average from 28.6 μm in 1992 to 35.7 μm in 2000. The sediment coarsening of the abandoned delta lobe began in the 1990s due to the extensive erosion caused by the absence of riverine-sediment supply. Coarse-grained sediments that were resuspended and transported offshore also made the sediment of the abandoned delta lobe coarser. In contrast, sediments of two cores in the offshore area of the active delta lobe were coarsened by more than 30% in the 2010s compared to the 1990s. The average Mz of surface sediments in the nearshore area increased by more than 22% from 23.5 μm in 1992 to 28.7 μm in 2000. The sediment coarsening of the active delta lobe began in the 1990s and became more significant in the 2000s. This trend was due to the rapid decrease of the sediment load from the Huanghe, as well as the coarsening of river-delivered sediments (from 17.7 μm to 22.9 μm) caused by the Water-Sediment Regulation Scheme that has been in place since 2002. Increasing coastal hydrodynamics and the loss of riverine sediment also account for the coarsening of sediments of the delta lobe. Our data clearly indicate that the critical bed-shear stress of the Huanghe delta-coast increased significantly. As a result, it was more difficult to initiate motion of the seabed sediments, leading to the decline of resuspension and erosion. Moreover, since the content of sedimentary organic carbon is negatively correlated with sediment grain size, the coarsening sediment of the study area will have inevitably degraded the carbon-related biogeochemical processes of the Huanghe delta-coast. Our findings have significant implications for the evolution of large river deltas, which are now threatened by sediment starvation and erosion.

Background Contribution to Assess the Trophic Water Conditions and Organic Components in Sediments at Santos and Cananeia Estuarine Systems-Brazil

The dissolved inorganic compounds are normally used to identify the water quality of the coastal ecosystems. In the last decades, the dissolved organic compounds acquired a new dimension, in the water and in the sediments, due to its important role in the biogeochemical cycle of the organic matter. Concerning it, proteins, carbohydrates and lipids present on the sediments could be used in order to access the environmental trophic state. In this study, water properties and organic matter compounds in sediments were used in order to verify the trophic condition once it is a rare data from these regions. Although the PCA groupings are based on specific variables, such as water and sediment parameters, two specific groups were observed in both cases (a and b). Group a suggests stations with eutrophication tendency or, based on sediment variables, in hypertrophic condition, while Group b suggests areas in healthier conditions as meso-oligotrophic environments. Similarities on grouping based on water and sediment parameters were observed. The study of coupling water and sediment properties (pelagic and benthic coupling) and organic compounds constitute an important focus for improving the access to the trophic state avoiding the evaluation based only on sediment parameters that could cause more incertitude.

К 90-ЛЕТИЮ И.О. МУРДМАА

On August 6, 2021, the chief researcher of the IO RAS, Doctor of Geological and Mineralogical Sciences, Professor Ivar Oskarovich Murdmaa turned 90 years old. The main focus of I.O. Murdmaa is the study of bottom sediments of seas and oceans, their lithology, mineralogy, deposition processes, facies and formations, the theory of oceanic sedimentogenesis. He first distinguished marine volcanoterrigenous sediments and described the facies variability of modern sediments of island arcs. Ivar Murdmaa is known for his studies in mineralogy of oceanic sediments, processes of pelagic sedimentogenesis and associated iron-manganese nodules formation. Studying sediment formation in rift zones of mid-ocean ridges, he identified a new genetic type of sediments named edaphogeonus sediments, elaborated mineralogical criteria for their recognition and formation processes. In recent years I.O. Murdmaa is actively developing the theoretical concept of "sedimentosphere", paying special attention to a new direction – the study of the erosion-accumulative activity of bottom currents and the formation of contourites.

Measurement of suspended sediment concentration in open channel flows based on hyperspectral imagery from UAVs

Since conventional in situ measurements of suspended sediments in the river system are labor-intensive and time-consuming, remote sensing approaches using multi- or hyper-spectral cameras have widely been applied to obtain high-resolution suspended sediment concentration (SSC) distributions in rivers and streams. However, in nature, the properties of heterogeneous sediment, such as the mineral content and particle size distribution, induce a strong variability in the optical images of the suspended sediments. For this reason, the robust estimation of the suspended sediment using the remote sensing technique is challenging due to the optical variability of the suspended sediment. Thus, it is necessary to deal with this variability of the optical images to improve the accuracy of remote sensing-based SSC measurements and extend them to the global estimator. In this study, a robust Machine Learning (ML) model for SSC estimation based on hyperspectral images was developed by considering the optical variability of the suspended sediment in water bodies. A series of field-scale tracer experiments were conducted in open channels with three different sediment types in order to obtain both the SSC using laser diffraction sensors and hyperspectral images using a UAV camera. The experimental results showed that the optical characteristics of SSC were critically heterogeneous due to the properties of the sediment. Using these experimental dataset, four explicit regression models and two implicit ML regression models were developed and compared to select an optimal estimator. Consequently, a Support Vector Regression (SVR) model using relevant spectral bands in a wide wavelength range yielded the most accurate results, with an R2 of 0.90 for the whole dataset. However, linear regression models, which could not consider various spectral bands and the nonlinear effect of the optical variability of SSC, were limited in their ability to retrieve SSC from hyperspectral images. Furthermore, the SVR model accurately reproduced the spatio-temporal SSC distributions in all study cases, including low-visibility suspended sediments, thus successfully resolved the optical variability of SSC with widely selected spectral bands from recursive feature elimination (RFE). The SVR model also successfully retrieved the SSC distribution in uncalibrated rivers. The results of this study demonstrated that the proposed ML regression models based on the hyperspectral imagery achieved a significant improvement in SSC estimation in terms of accuracy and global applicability.

Effects of Waves and Sediment Disturbance on Seed Bank Persistence at Tidal Flats

Coastal wetlands such as salt marshes have been increasingly valued for their capacity to buffer global climate change effects, yet their long-term persistence is threatened by environmental changes. Whereas, previous studies largely focused on lateral erosion risk induced by stressors like sea level rise, it remains poorly understood of the response of lateral expansion to changing environments. Seedling establishment is a key process governing lateral marsh expansion as seen in many coastal regions such as Europe and East Asia. Here, we evaluate mechanistically the response of seed bank dynamics to changing physical disturbance at tidal flats, using the globally common coastal foundation plant, cordgrass as a model. We conducted a large-scale field study in an estuary in Northwest Europe, where seed bank dynamics of cordgrass in the tidal flats was determined and linked to in situ hydrodynamics and sediment dynamics. The results revealed that wave disturbance reduced the persistence of seeds on the surface, whereas amplified sediment disturbance lowered the persistence of both surface and buried seeds. Overall, this indicates that increasing storminess and associated sediment variability under climate change threatens seed bank persistence in tidal flats, and hence need urgently be incorporated into models for long-term bio-geomorphological development of vegetated coastal ecosystems. The knowledge gained here provides a basis for more accurate predictions on how climatically driven environmental changes may alter the fitness, resilience and persistence of coastal foundation plants, with significant implications for nature-based solutions with coastal vegetation to mitigate climate change effects.

Seasonal climate signals preserved in biochemical varves: insights from novel high-resolution sediment scanning techniques

Abstract. Varved lake sediments are exceptional archives of paleoclimatic information due to their precise chronological control and annual resolution. However, quantitative paleoclimate reconstructions based on the biogeochemical composition of biochemical varves are extremely rare, mainly because the climate–proxy relationships are complex and obtaining biogeochemical proxy data at very high (annual) resolution is difficult. Recent developments in high-resolution hyperspectral imaging (HSI) of sedimentary pigment biomarkers combined with micro X-ray fluorescence (µXRF) elemental mapping make it possible to measure the structure and composition of varves at unprecedented resolution. This provides opportunities to explore seasonal climate signals preserved in biochemical varves and, thus, assess the potential for annual-resolution climate reconstruction from biochemical varves. Here, we present a geochemical dataset including HSI-inferred sedimentary pigments and µXRF-inferred elements at very high spatial resolution (60 µm, i.e. &gt; 100 data points per varve year) in varved sediments of Lake Żabińskie, Poland, over the period 1966–2019 CE. We compare these data with local meteorological observations to explore and quantify how changing seasonal meteorological conditions influenced sediment composition and varve formation processes. Based on the dissimilarity of within-varve multivariate geochemical time series, we classified varves into four types. Multivariate analysis of variance shows that these four varve types were formed in years with significantly different seasonal meteorological conditions. Generalized additive models (GAMs) were used to infer seasonal climate conditions based on sedimentary variables. Spring and summer (MAMJJA) temperatures were predicted using Ti and total C (Radj2=0.55; cross-validated root mean square error (CV-RMSE) = 0.7 ∘C, 14.4 %). Windy days from March to December (mean daily wind speed &gt; 7 m s−1) were predicted using mass accumulation rate (MAR) and Si (Radj2=0.48; CV-RMSE = 19.0 %). This study demonstrates that high-resolution scanning techniques are promising tools to improve our understanding of varve formation processes and climate–proxy relationships in biochemical varves. This knowledge is the basis for quantitative high-resolution paleoclimate reconstructions, and here we provide examples of calibration and validation of annual-resolution seasonal weather inference from varve biogeochemical data.

Fluvial suspended sediment transfer and lacustrine sedimentation of recent flood turbidites in proglacial Eklutna Lake, western Chugach Mountains, Alaska

AbstractSuspended sediment delivery and deposition in proglacial lakes is generally sensitive to a wide range of hydrometeorologic and geomorphic controls. High discharge conditions are of particular importance in many glaciolacustrine records, with individual floods potentially recorded as distinctive turbidites. We used an extensive network of surface sediment cores and hydroclimatic monitoring data to analyse recent flood turbidites and associated sediment transfer controls over instrumental periods at Eklutna Lake, western Chugach Mountains, Alaska. Close to a decade of fluvial data from primary catchment tributaries show a dominating influence of discharge on sediment delivery, with various interconnections with other related hydroclimatic controls. Multivariate fluvial models highlight and help quantify some complexities in sediment transfer, including intra‐annual variations, meteorological controls, and the influence of subcatchment glacierization. Sediments deposited in Eklutna Lake during the last half century are discontinuously varved and contain multiple distinctive turbidites. Over a 30‐year period of stratigraphic calibration, we correlate the four thickest flood turbidites (1989, 1995, 2006, and 2012) to specific regional storms. The studied turbidites correlate with late‐summer and early‐autumn rainstorms with a magnitude of relatively instantaneous sedimentation 3–15 times greater than annual background accumulation. Our network of sediment core data captured the broad extent and sediment variability among the study turbidites and background sediment yield. Within‐lake spatial modelling of deposition quantifies variable rates of downlake thinning and sediment focusing effects, and highlights especially large differences between the thickest flood turbidites and background sedimentation. This we primarily relate to strongly contrasting dispersion processes controlled by inflow current strength and turbidity. Sediment delivery is of interest for this catchment because of reservoir and water supply operations. Furthermore, although smaller floods may not be consistently represented, the lake likely contains a valuable proxy record of regional flooding proximal to major population centers of south‐central Alaska including Anchorage.

Benthic community responses to organic enrichment during an ENSO event (2009–2010), in the north coast of Rio de la Plata estuary

The 2009–2010 “El Niño”-Southern Oscillation (ENSO) event was characterized by a warm-phase leading to a five-fold increase in the Río de la Plata river flow and an associated change in trophic state because of organic enrichment. We analyzed the biotic response of benthic communities to such an increased trophic state during this ENSO event using community and biotic indices (diversity indices and AMBI). Polychaeta exhibited the highest richness and second the most abundant values while the small gastropod Heleobia australis was the most abundant and frequent species. An increase in richness and diversity of Polychaeta was associated to a concomitant increase of RdlP flow and the organic enrichment of the macrobenthic species. Community indices (richness and diversity) showed variability at both temporal and spatial scale but only AMBI exhibited spatial variability without significant differences between contrasting environmental conditions (ENOS phases). • An ENSO event promoted changes in chemical and biotic sediment variables. • Variability in salinity and protein sediment content were reflected in macrobenthic community indices. • AMBI was useful to infer spatial differences between zones with different environmental quality. • Richness, diversity and AMBI are recommended for the Montevideo Coastal zone environmental monitoring programs.

Petrophysics and sediment variability in a mixed alluvial to lacustrine carbonate system (Miocene, Madrid Basin, Central Spain)

AbstractThis study evaluates variations in petrophysical properties within a mixed alluvial to lacustrine carbonate system (Miocene, Madrid Basin, Central Spain). The transition from alluvial environments to lake margins settings displays a shift from alluvial, siliciclastic red sandstones and mudstones to palustrine–lacustrine mudstones to packstones. Fluctuations in lake‐water level enabled land plants to occupy the lake margins during periods of low lake levels. The palustrine carbonates include features like pseudo‐microkarst, nodular and mottled limestones; the lacustrine deposits include enlarged root cavities, desiccation cracks and channel bodies. Scarce fresh water biota comprises charophytes, gastropods and ostracods. The sediments possess high natural, irregular varying, gamma‐ray values at the alluvial–lacustrine transition, and low, but constant values at full lacustrine sites. Acoustic properties agree with lithological variations within individual facies. Porosity is the most important parameter influencing P‐wave and S‐wave velocities. The scatter in the velocity–porosity relationship links to the porosity type; macro‐porosity or microporosity. The wide range of pore types and pore sizes results in a weak porosity to permeability relationship for the carbonate‐dominated rocks with low permeability for microporous and high permeability for macro‐porous carbonates. The sandstones (probably only inhibiting interparticle porosity), and to a lesser extent the sandy wackestones to packstones, show quite a strong relationship between porosity and permeability. Elastic properties of mixed alluvial–lacustrine deposits (this study) and marine deposits (literature data) overlap as variations in pore structures and porosity values are similar. Only 16% of the marine and lacustrine carbonate sediments display Equivalent Pore Aspect Ratio values above 0.2. In travertine deposits, 83% of the samples exceed Equivalent Pore Aspect Ratio values above 0.2, which highlights that travertine deposits are dominated by larger Equivalent Pore Aspect Ratios compared to lacustrine and marine carbonate deposits. Travertines display other rock frameworks with different pore types, pore distribution and amount of porosity.

Sediment provenance, routing and tectonic linkages in the Nankai forearc region, Japan

AbstractUnderstanding sedimentary routing systems at continental margins can be challenging in tectonically active regions such as forearc basins. Here, we combine sand modal composition and detrital zircon U‐Pb data from the Kumano Basin and surrounding Nankai Trough region of Japan to explore sedimentation in an active forearc and its linkages to the regional tectonic history. Our analyses are on Miocene‐to‐Pleistocene samples collected by the Integrated Ocean Drilling Program (IODP) at inner and outer forearc basin sites C0009 and C0002, river samples from onshore Honshu, and published results from other Nankai IODP sites. Results show the sediments of many IODP samples are similar to that of the modern rivers. Data from C0009 demonstrate that the early accretionary prism already contained slope basins fed by sediments similar to those in the modern Kumano River by 7.1 Ma. The more distal C0002 section was predominantly fed by a system similar to the modern Yodo River, located to the west‐southwest. We conclude that the section was therefore tectonically transported, in agreement with the ‘mobile model’ of oblique tectonic convergence across SW Japan during late Miocene time. Deposition resumed after a ca. 5.6–3.8 Ma hiatus, with sediments primarily fed from the paleo‐Kumano River, with some input from the paleo‐Tenryu and Kiso/Nagara rivers located to the northeast. Input from the paleo‐Tenryu and Kiso/Nagara rivers was likely re‐routed towards the trench by ca. 1.3 Ma. Sediments similar to those of the distal Yodo River also make up part of the Kumano basin fill and are best explained by erosion of uplifted older accretionary prism sediments along the Megasplay Fault that bounds the forearc basin. Despite the temporal variability in sedimentation routed to the basin, basin‐fill dynamics appear to have been governed primarily by the critical‐wedge style dynamics driven by variations in frontal accretion and in‐ or out‐of‐sequence thrusting response.

Mercury distribution around the Siele Hg mine (Mt. Amiata district, Italy) twenty years after reclamation: Spatial and temporal variability in soil, stream sediments, and air

The Siele mine and its smelting plant are part of the world class Monte Amiata Hg district (southern Tuscany, Italy). After closure in 1981, the area was subjected to the first reclamation in the district, completed in 2001. However, stream sediments in the Siele creek downstream of the mine still present highly anomalous Hg values (up to 5400 mg/kg). Gaseous elemental mercury (GEM) concentrations in air near the former metallurgical buildings, and immediately downstream of the mining area, are also high (up to 16,233 ng/m3), although lower than before reclamation, when values up to 237,000 ng/m3 had been measured. On the other hand, Hg mobility, determined by leaching tests, is mostly below the limits defined by pending regulations (1 μg/L), and methyl-Hg concentrations are mostly below 1 ng/kg (with a single value of 6 ng/kg). Therefore, the actual risk to environment and health is deemed low. In summary, reclamation reduced, but did not stop, the release of Hg from the Siele mining area. Results show that the Siele system has a low resilience and natural recovery will take many years (probably decades), during which the area will remain an important source of Hg for the Paglia and Tiber River systems, and eventually for the Mediterranean Sea.