Search Results (171)

This study evaluates the potential health risks posed by geogenic arsenic in environments suitable for leisure activities, such as walking, bathing, and playing, for adults and children alike, as well as in neighbouring agricultural areas. The study includes an analysis of environmental characteristics and the main stream originating in the adjacent mining area, with water and sediment samples taken. The study area is representative of other areas in the vicinity of the Mar Menor Lagoon, which is one of the largest and most biodiverse coastal lagoons in the Mediterranean Sea. The general characteristics of the soil and water were determined for this study, as was the concentration of As in the soil and water samples. A granulometric separation was carried out into four different fractions (<2 mm, <250 µm, <100 µm, and <65 µm). The mineralogical composition, total As content, and bioaccessible As content are analysed in each of these fractions. This provides data with which to calculate the danger of arsenic (As) to human health by ingestion and to contribute to As bioaccessibility studies and the role played by the mineralogical composition and particle size of soil ingestion. The conclusions rule out residential use of this environment, although they allow for eventual tourist use and traditional agricultural use of the surrounding soils. Full article

The present study investigates the extent and spatial distribution of metal concentration in stream sediments that flow into Keban Dam Lake, Turkey. Sediment samples were analysed for trace and potentially toxic elements (PTEs), including V, Cr, Co, Ni, Cu, Zn, Pb, Tl, Th, and U. Enrichment Factor (EF), Contamination Factor (CF), Geo-accumulation Index (Igeo), and Pollution Load Index (PLI) were employed to assess contamination levels. Results reveal that Cr exhibited very high enrichment (EF = 15.95) in downstream urban samples, while Cu and Zn showed high enrichment in samples collected from the middle to lower reaches of the stream, probably indicating anthropogenic contributions. Most other elements, such as Pb, Tl, Th, and U, were within natural background levels. Sediment Quality Guidelines (SQGs) indicate that Cr, Ni, and Cu may pose potential ecological risks, especially in samples from urban-influenced and downstream areas where concentrations exceed the Probable Effect Levels (PEL; Cr: 160 mg/kg, Ni: 42.8 mg/kg, Cu: 108 mg/kg). Multivariate statistical analyses, including Pearson correlation and hierarchical clustering, reveal three distinct geochemical groupings. Among these, the most contaminated cluster—corresponding to midstream and downstream regions—is characterized by elevated Cu and Zn concentrations. Strong correlations among Cu–Zn, Ni–Cu, and Th–U suggest there is a combination of anthropogenic and lithogenic sources for most metals. While most sites showed low to moderate pollution, urban downstream locations exhibited significant metal accumulation, necessitating the region’s continued environmental monitoring and management strategies. Full article

Rare earth elements (REEs) are critical mineral resources that play a pivotal role in modern technology and industry. Currently, the global supply of light rare earth elements (LREEs) remains adequate. However, the supply of heavy rare earth elements (HREEs) is associated with substantial risks due to their limited availability. Ion-adsorption type rare earth deposits (IAREDs), which represent the predominant source of HREEs, have become a focal point for exploration activities, with a notable increase in global interest in recent years. This study systematically collected stream sediments and stream water samples from the Jiaping IARED in Guangxi, as well as from adjacent granitic and carbonate background areas, to investigate the exploration significance of geochemical surveys for IAREDs. Additionally, mineralized soil layers, non-mineralized soil layers, and bedrock samples from the weathering crust of the Jiaping deposit were analyzed. The results indicate that stream sediments originating from the Jiaping IARED and granite-hosted background regions display substantially elevated REE concentrations relative to those from carbonate-hosted background areas. Moreover, δEu values in stream sediments can serve as an effective indicator for differentiating weathering products derived from granitic and carbonate lithologies. Within the mining area, three coarse-grained fractions of stream sediments (i.e., +20 mesh, 20–60 mesh, and 60–150 mesh) exhibit REE concentrations comparable to those observed in both granite-hosted and carbonate-hosted background regions. However, the HREEs content in the finer -150-mesh stream sediments from Jiaping IARED is markedly higher than that in the two background regions. The (La/Sm)_N versus (La/Yb)_N ratios of -150-mesh stream sediments in the Jiaping IARED may reflect the mixing processes involving HREE-enriched ore layer, non-mineralized layer, and LREE-enriched ore layer. This observation implies that fine-grained (-150-mesh) stream sediments can partially inherit the REE characteristics of mineralized layers within IAREDs. Scanning electron microscopy (SEM) observations indicate that the enrichment of REEs in fine-grained stream sediments primarily originates from REE-rich accessory minerals derived from parent rocks and mineralized weathering crusts. A comparative analysis reveals that the concentrations of REEs in stream water collected during the rainy season are significantly higher than those collected during the dry season. Moreover, the levels of REEs, especially HREE, in stream water from the Jiaping IARED substantially exceed those in background areas. Collectively, these findings suggest that the geochemical signatures of REEs in rainy season stream water possess diagnostic potential for identifying IAREDs. In conclusion, the integrated application of geochemical surveys of stream water and -150-mesh stream sediments can effectively delineate exploration targets for IAREDs. Full article

The classification of shale is commonly based on lithofacies structure, mineral content, organic carbon content, physical and chemical parameters, and element contents. A geochemical classification method based on the compositional data of shale is proposed which divides shale, sedimentary rocks, sediments, and soils into six types, named siliceous, felsic, silicate, calcsilicate, dolomitic, and calcareous components, and numbered from type 1 to type 6, respectively. Sedimentary rocks in China, including mudstone (shale), sandstone, carbonate rocks, and siliceous rocks, are selected to test the method, and the results show that the method can accurately classify not only shale but also other sedimentary rocks. Shale samples from a drill well in southern Sichuan area are classified based on the proposed method as an illustration in a line graph. Furthermore, the stream sediments and soils from geochemical survey projects in the southern Sichuan area are also classified based on their compositional data. Based on the classification results, a geochemical map is drawn and compared with the strata lithology. These results indicate that the new classification method is suitable for shale, sedimentary rocks, sediments, and soils, and illustrates clear geochemical properties based on their classified types. Full article

This study focused on the aquatic insect orders that serve as biological indicators. Ephemeroptera, Plecoptera, Trichoptera, Coleoptera, and Odonata were studied with their relationships to physical, chemical, hydrological and morphological variables in 14 streams on three Croatian mountains: Papuk, Medvednica and Psunj. From 675 samples collected in three dominant sediment microhabitats (e.g., macrolithal and mesolithal) in each stream, we identified 130 macroinvertebrate taxa. The most abundant group was Ephemeroptera (36 taxa). Aquatic insect assemblages between Papuk and Psunj showed higher similarity due to the geographical proximity of these two mountains, which is expressed as spatial connectivity. In spring, greater variability and diversity of investigated aquatic insects were observed due to the phenology of studied insects. The combination of environmental and morphological properties (e.g., oxygen concentration and substrate type) had the most significant influence on shaping the assemblage of aquatic insects of Psunj, while morphological properties were the most important in shaping aquatic insect assemblages on Papuk (e.g., streambed width) and Medvednica (e.g., elevation). Baetis sp. was the dominant taxon in summer, Protonemura montana in spring, and Leuctra sp. in autumn. Seasonal shifts in environmental conditions lead to functionally unique communities that utilize the pool of available seasonal resources. The dominance of feeding groups varied by season, with scrapers and collector–gatherers being most prevalent in summer, while shredders were dominant in spring. The results on the relationships between environmental characteristics and species richness, functional structure, and distribution of aquatic insects in mountain streams provide important clues for future research and conservation strategies in these vulnerable ecosystems. Full article

Some of the largest Mexican uranium (U) deposits are located in Chihuahua. The most important is in Sierra Peña Blanca, northwest of the capital, which was explored and partially exploited in the 1980s. After the closure of activities, the mining projects were left exposed to weathering. To characterize the spread of U minerals towards the neighboring Laguna del Cuervo, sediment samples were collected in the main streams of the drainage pattern of the largest deposits. The U mineral fragments from the fine sand portion were extracted using fluorescence light at 365 nm. The morphology and elemental composition of these particles were analyzed by focused ion beam microscopy (FIB) and scanning transmission electron microscopy (STEM). The particle density in samples close to the U sources was quantified using gamma spectrometry. The highest density was 2500 part./g, and the lowest was 124 part./g. X-ray absorption spectroscopy (XAS) allowed us to establish via XANES the speciation of U in the U particles, confirming the U(VI) oxidation state, while the exploitation of the EXAFS spectrum put in evidence of the presence of uranophane. Finally, the Fe, Sr, and U distributions in the particle and its matrix were obtained via X-ray fluorescence microtomography (XRF-µCT). It was concluded that the particle is composed of uranophane, imbricated with quartz and other oxides. Full article

The contamination of the Lower Danube Basin with trace elements has been the subject of intense study in recent years, with several pollution indices being employed for the assessment of water, soil, and sediment quality. Most pollution indices are calculated by comparing the measured concentration to a reference value, with different values from various sources being used. In this study, the threshold values for trace elements (As, Cd, Cu, Hg, Ni, Pb, and Zn) in Romania were selected based on the median of their concentration in stream sediment from 167 locations, which were carefully selected to be far from contamination sources. The threshold values were established based on a calculation starting from the geochemical concentration presented in the Geochemical Atlas of Romania (scale: 1:3,000,000, developed in 2006 by a collaborative Romanian-German team). By using these thresholds, pollution indices were calculated for nine sampling locations, from which suspended sediment, bottom sediment, and active floodplain sediment samples were collected and analyzed in an accredited laboratory. Most of the selected thresholds were found to be below the limits for sediments established by Romanian legislation, except for Cr and Ni, the higher values of which are consistent with the specific geological background of the country and the broader Balkan region. Full article

In a broad project designed to examine uranium transport by surface water from Sierra Peña Blanca to Laguna del Cuervo in the Chihuahuan Desert, sediments from intermittent streams and the lagoon have been extracted and studied. Two samples were sediments from the high area of the Sierra, close to the uranium deposit “El Nopal.” Moreover, 23 core segments extracted for dating sediments were analyzed to consider changes in the fine component concentrations. The techniques of scanning electron microscopy–energy dispersive X-ray spectroscopy, XRD in a conventional diffractometer, and high-resolution synchrotron XRD analysis were applied. The crystallographic objective of the present work was to evaluate the functionality of various methodologies when applied to cases of a detailed analysis of many polyphase samples with cryptocrystals. The methods for processing the experimental data were the Rietveld method in the current multi-pattern variant of the Fullprof program and the degree of crystallinity method for the rapid estimation of the proportion of cryptocrystals in a mixture. This last technique was developed with an ad hoc software package deposited in the GitLab public repository. Full article

Catastrophic typhoons with heavy rainfall introduce massive flow and fine sediments into stream channels. In addition, the natural disturbances and engineering practices afterward may strongly alter the fish abundance and their environment. This study compared physical habitat parameters and fish abundance before and after two major typhoons using two sampling period datasets (November 2008–March 2009 and May 2011–March 2012). The study area was in the Cishan Stream, a tributary of the Gaoping River in southern Taiwan. This area experienced two strong typhoons (Morakot and Fanapi) between the two sampling periods, providing an opportunity to compare pre- and post-typhoon conditions. The collected species were Hemimyzon formosanus, Rhinogobius nantaiensis, Onychostoma alticorpus, Candidia barbata, Acrossocheilus paradoxus, and Spinibarbus hollandi. Our results show a decrease in substrate size, fish size, and fish weight after typhoons. The river channel transformed into an unstable condition after the heavy rains, as major habitat types in our sampling stations changed from riffles with coarse substrate to runs with fine substrate. The results of statistical tests indicate the different habitat requirements of three major fish species (H. formosanus, R. nantaiensis, and O. alticorpus) and can indicate whether species’ requirements change between the two sampling periods. Water depth and pebbles were critical habitat requirements for the adults of H. formosanus; water depth, pebbles, and sand were critical habitat requirements for the adults of R. nantaiensis; and flow velocity and standard deviation of flow velocity were critical requirements for the juveniles of O. alticorpus. Understanding habitat requirements can provide useful information for post-disaster restoration and contribute to eco-sensitive river engineering. Full article

Extraction activities can have a significant impact on the environment due to the mobilization of trace elements. These elements can pose a risk to soils, biota, water, and human health when incorporated into nearby ecosystems. To evaluate the transfer of As, Cd, Pb, and Zn from mine areas to the marine environment, a study was conducted in the Cartagena-La Union mining district (SE Spain). The study area included the mouth of a stream affected by waste materials from tailing ponds. In addition, a maritime area without mining influence was selected as a control site. Sediment samples were collected (three transects with nine sampling points and three depths) at the El Gorguel shoreline, and analyzed for pH, electrical conductivity, total metal(loid)s content, water-soluble anions, and metal(loid)s in chemical fraction distribution. Water and biota samples (Paracentrotus lividus, Patella vulgata, Hexaplex trunculus, Anemonia viridis, and Trachinotus ovatus) were also collected for metal(loid) content analysis. The results showed that the metal(loid)s concentration in the sediment increased compared to the control site, which was not influenced by mining activities. The chemical composition of metal(loid)s in the sediments revealed that Cd is the most hazardous element due to its high concentration in the labile fractions (20%), suggesting easy transfer to the marine environment. However, transfer mechanisms should be studied in various scenarios with different climatic, wave, and tidal conditions. Marine biota metal(loid)s concentrations showed an increase in specimens collected under the influence of mining activities but without exceeding limits that would affect incorporation into the trophic chain. Consequently, bioaccumulation and biomagnification processes must be considered in a future biomonitoring program. Full article

Critical shear stress and erosion rate are two key factors for the prediction of the incipient motion of sediment and the transport of sediment. Seabed seepage can significantly alter the pore pressure gradient within the soil and the hydrodynamics around the surface of the seabed, further affecting erosion processes. Previous studies attempted to theoretically clarify the effect of the seepage force on sediment incipient motion. In this study, a newly designed erosion–seepage system (ESS) that considers the effect of seepage under steady or oscillatory flow is used to simulate the erosion process. Through the designed ESS, the erosion height per unit time was measured directly on the Yellow River sand, and the upward seepage force was applied at the bottom of the soil sample in the process. Then, the relationship between the erosion rate and seepage was established.The experimental results show that upward seepage reduces the critical shear stress of the sand bed and increases the erosion rate of the soils under both steady flow and oscillatory flow conditions. The erosion coefficients in the erosion models decrease with increasing seepage gradient. The effect of seepage on erosion is more obvious when the flow velocity of the steady stream is large, while the effect of seepage on erosion is relatively small under the oscillatory state with a shorter period. However, when violent erosion of soil samples occurs, seepage under both flow conditions greatly increases the erosion rate. Full article

Prior to implementing watershed-wide projects to reduce the impacts of agriculture on regional streams and rivers, stream habitats and benthic aquatic macroinvertebrate communities were assessed at 15 sites on the South Branch Root River and its major tributaries in southeastern Minnesota, USA. Triplicate kick-net samples were collected from each site during three time periods (1998, 1999, 2006/2008) and stream habitats were inventoried within 150 m long sections at each site. In total, 26,760 invertebrates representing 84 taxa were collected and used to rate stream sites using a regional multi-metric benthic index of biotic integrity (BIBI). BIBI scores were significantly correlated with total invertebrate taxa richness. BIBI ratings improved from poor and very poor at headwater sites in channelized stream sections draining agricultural lands to fair to good to excellent in downstream sections flowing through natural channels in largely forested lands. Fifty percent of samples rated stream sites as poor or very poor. Over 85% of stream habitat assessments indicated the presence of fair to good habitats, although stream sites were relatively wide and shallow and dominated by fine sediments that also embedded coarser substrates. BIBI metrics and scores were strongly positively correlated with pool area, riffle spacing-to-stream width ratios, and silt-free substrate, and negatively correlated with width-to-depth ratios. Most stream sites had few Ephemeroptera, Plecoptera, Trichoptera, and Diptera taxa and too few intolerant taxa. It is expected that benthic invertebrate communities should improve as more riparian buffers are added along all streams. However, on-going channel maintenance activities in headwater stream sections, mandated to encourage drainage of adjacent agricultural fields, will continue to negatively impact headwater habitats and biotic communities. Full article

Acid mine drainage (AMD) generated during the exploitation and utilization of mineral resources poses a severe environmental problem globally within the mining industry. The Xiaomixi Stream in Ziyang County, Shaanxi Province, is a primary tributary of the Han River, which is surrounded by historically concentrated mining areas for stone coal and vanadium ores. Rainwater erosion of abandoned mine tunnels and waste rock piles has led to the leaching of acidic substances and heavy metals, which then enter the Haoping River and its tributaries through surface runoff. This results in acidic water, posing a significant threat to the water quality of the South-to-North Water Diversion Middle Route within the Han River basin. According to this study’s investigation, Xiaomixi’s acidic water exhibits yellow and white precipitates upstream and downstream of the river, respectively. These precipitates stem from the oxidation of iron-bearing minerals and aluminum-bearing minerals. The precipitation process is controlled by factors such as the pH and temperature, exhibiting seasonal variations. Taking the Xiaomixi Stream in Ziyang County, Shaanxi Province, as the study area, this paper conducts field investigations, systematic sampling of water bodies and river sediments, testing for iron and aluminum pollutants in water, and micro-area observations using field emission scanning electron microscopy (FESEM) on sediments, along with analyzing the iron and aluminum content. The deposition is analyzed using handheld X-ray fluorescence (XRF) analyzers, X-ray diffraction (XRD), and visible–near-infrared spectroscopy data, and a geochemical model is established using PHREEQC software. This paper summarizes the migration and transformation mechanisms of iron and aluminum pollutants in acidic water and proposes appropriate prevention and control measures. Full article

Yap diatoms—from freshwater streams through estuaries and mangroves to the marine coral reefs—had been sampled in 1988 and 2014 and a few species from the 1988 collections described in a 2009 report. The present paper documents 168 new records, including seven new species, mostly from coral reef habitats, but including some interesting new species from mangroves, and incorporates records published in taxonomic papers. In addition, 44 Mastogloia records were published separately, bringing the taxon total to 245. In the present paper, 32 records are new for Micronesia, while many others are species described from neighboring Guam in the past 15 years. The total represents probably less than one-quarter of the species present on the reef because many specimens of Navicula, Nitzschia, Amphora, etc., have so far been identified only to genus. Floristic studies of benthic diatoms are limited partly by the shortage of taxonomic studies, and we present the taxa for which we can make reasonable arguments for identification, supporting light microscopy with scanning electron micrographs whenever possible. New taxa include Ehrenbergiopsis gen. nov. for Ehrenbergiulva hauckii; Biddulphiella cuniculopsis sp. nov.; Campylodiscus tatreauae sp. nov.; Cymatoneis belauensis from Palau and Cymatoneis yapensis from Yap; Diploneis denticulata sp. nov.; Entomoneis yudinii sp. nov.; and Nitzschia pseudohybridopsis sp. nov. Interesting new records include: Achnanthes cf. brevipes; Actinocyclus decussatus; Caloneis ophiocephala; Licmophora cf. hastata; Lyrella cf. rudiformis; and an unidentified cymatosiroid. One sediment sample included the remains of a planktonic community with Chaetoceros peruvianus, Skeletonema grevillei, Thalassiothrix gibberula and two species of Lioloma, rarely seen in the oligotrophic waters of Micronesia. Full article

On the outskirts of the Pinios dam reservoir (Ilia Regional Unit, Greece), a water treatment plant serves the water supply needs of the surrounding municipalities, in which high concentrations of Fe and Mn, before treatment, have been observed. The main purpose of this research was to investigate the mechanism of increased iron (Fe) and manganese (Mn) levels in the reservoir of the Pinios dam, which impacts its water treatment plant operation. A wide range of hydrochemical and sedimentological analyses were conducted over a hydrological year, focusing on the spatial and temporal distribution of Fe and Mn in both water and sediment samples across the established research monitoring stations. Sediment samples from the reservoir’s bottom revealed predominantly fine-grained material, rich in total organic carbon, with elevated Mn and Fe oxide levels. Significant seasonal variations in Fe and Mn levels were also discovered, with higher Mn levels observed in the anoxic bottom waters of the reservoir during the dry season, attributed to the reduced conditions favoring Mn oxide dissolution over Fe. Conversely, during the wet season, a homogenization of metal concentrations throughout the water column was observed due to increased oxygenation and freshwater inflow. These outcomes were confirmed by the hydrochemical analysis, indicating that the redox conditions, pH, and temperature, as well as the presence of organic matter, significantly influence the mobility and bioavailability of these metals in the reservoir. The findings of this study clarify that the high concentration of Fe and Mn can be linked to the mineral composition of the upstream Neogene and flysch formations in the study area. As these formations are affected by geological weathering, they tend to enrich the streams, through soil erosion and runoff processes, with metals like Fe and Mn, which are eventually transported into the dam reservoir. This study highlights the critical influence of lithological, sedimentological, and hydrological factors on the redox conditions and seasonal stratification that govern the behavior of Fe and Mn concentrations and mobility in dam reservoirs. These findings are critical for informing water resource management practices and dam infrastructure operators and developing effective environmental conservation strategies in similar cases. Full article