Occurrence and origins of biomarker aliphatic hydrocarbons and their indications in surface sediments of the East China Sea

Examining the source and composition of organic matter through saturated hydrocarbons, δ13C, and δ15N in a subtropical water reservoir

The sources of organic matter in the sediments of the Passaúna reservoir, an important water supply for the local population, were thoroughly investigated. The objective was to identify the origins of organic matter through the analysis of saturated hydrocarbons, elemental composition (total organic carbon and total nitrogen), and the content of δ13C and δ15N isotopes. This comprehensive approach allowed us to trace the sources of organic matter and discerns indicating heightened primary productivity within the reservoir. To achieve this, two sediment cores spanning a 140-year interval (1880-2020) were retrieved from the reservoir. Core 2 accumulates the majority of sediments, particularly near the dam area. In these parts, sediment deposits can reach up to 1 m above the pre-impoundment soil. Sediments near the area where core 1 was collected contain more sand, resulting in lower thickness compared to core 2. Sediment core 1 primarily reflects terrestrial sources of organic matter, as supported by stable isotope values of δ13C and δ15N. The δ13C values ranged from -23.0 ‰ to -25.7 ‰ in core 1 and from -28.4 ‰ to -29.2 ‰ in core 2. Meanwhile, the δ15N values ranged from 6.6 ‰ to 10.8 ‰ in core 1 and from 3.8 ‰ to 7.6 ‰ in core 2. The distribution of saturated hydrocarbons revealed that organic matter originates from both allochthonous and autochthonous sources. Periods of intense primary productivity were indicated by the presence of n-C16, n-C17, n-C18, and n-C19 alkanes. Additionally, we observed periods characterized by high primary productivity, indicative of elevated nutrient input likely resulting from increased urbanization and industrial activity in the area.

Unraveling seasonal shifts in microbial and geochemical mediated arsenic mobilization at the estuarine sediment-water interface under redox changes

The mobilization of arsenic (As) at the sediment-water interface (SWI) is crucial for determining the accumulation of dissolved As to potentially toxic levels. However, the specific impacts of redox processes involving iron (Fe) and sulfur (S), as well as microbial activities occurring in sediments, on As mobilization at the marine SWI remain poorly understood. In this study, we investigated As mobilization at the SWI in the Changjiang Estuary during three different seasons with different benthic redox conditions. The preferential reduction of arsenate (As(V)) to arsenite (As(III)) and subsequent re-adsorption onto newly formed crystalline Fe oxides restricted As release in the As(V) reduction layer. Enhanced Fe(III) reduction in the Fe(III) reduction layer contributed to As release, while the presence of low As-high Fe-high SO42- levels resulted in As removal through adsorption onto pyrite in the sulfate reduction layer. Analysis of functional genes indicated that As(V) in sediments was released into porewater through the reductive dissolution of As(V)-bearing Fe(III) oxides by Geobacter species, followed by microbial reduction of the liberated As(V) to As(III) by microbes carrying the arrA gene. The dominant pathway governing As mobilization at the SWI in the Changjiang Estuary shifted from microbial reduction control during the hypoxic summer to Fe redox control during the aerobic autumn and winter. These findings provide valuable insights into the complex mechanisms driving As mobilization and highlight the importance of considering seasonal variations in understanding As dynamics at the marine SWI.

Polycyclic aromatic hydrocarbons in estuarine sediments as a consequence of the mine tailings remobilization and transport in the Rio Doce basin

The Fundão dam failure in 2015 severely impaired the economy, the lives of riverine communities, and the aquatic ecosystems of the Rio Doce basin in southeast Brazil. Several contaminants, including polycyclic aromatic hydrocarbons (PAHs), were transported downstream, deposited in the estuary, and released into the Atlantic Ocean. The high concentration of PAHs in estuarine sediments may pose ecological risks and deleterious effects to benthic organisms, so here we aimed at determining the source and fate of these compounds before and after the tailings' arrival. The mean concentration of the analyzed Σ16PAHs increased from 34.05 µg kg-1 in the prefailure period to 751.77 µg kg-1 one year after the arrival of the tailing. The classification of the sediment quality changed from low to moderate contamination. Our results suggest that there was PAHs remobilization by mine tailings along the Rio Doce basin. The target analytes exhibited mostly a pyrolytic profile from fossil fuel and biomass burning. In addition to other contaminants deposited in the estuary after the arrival of the tailings, this study revealed that the profile change of PAHs in the estuary region is a consequence of the mud's erosive power. Integr Environ Assess Manag 2024;20:169-178. © 2023 SETAC.

A new spatial estimation model and source apportionment of aliphatic hydrocarbons in coastal surface sediments of the Nayband Bay, Persian Gulf

Hydrocarbons, originating from oil and gas industries, are considered a potential risk for Nayband Bay, a natural marine park with extended mangroves, located on the north coastlines of the Persian Gulf, Iran. This paper determines the potential sources and spatial distribution of hydrocarbons, especially aliphatic hydrocarbons (AHCs), in Nayband Bay through the simultaneous application of three indices in the coastline surface sediments. To this end, a field study was conducted in the inter-tidal coastal zones and wetlands. Sediment samples were taken from surface layers along four transects with four sampling points at different distances from the gulf. The hydrocarbon compounds of the samples including AHCs, total petroleum hydrocarbons, and heavy metals (Ni, V as crude oil indicators) were analyzed and classified to discover the pollution indicators. Pearson pairwise correlation and cluster analyses along with pollution indices were employed to describe the spatial distribution pattern of hydrocarbons, identify hot spots, and determine the potential origin of AHCs. Different interpolation scenarios based on topographic and oceanic features were proposed to detect the spatial dynamics of AHCs. The results revealed that hydrocarbons mainly originated from anthropogenic sources including oil and gas industries located far from the affected area. It was also concluded that the long-distance pollution transfer was based on oceanic currents and wind direction in the bay. The proposed scenarios showed that the mean concentration values of total organic carbon and total organic material vary in the range 0.19 ppm to 0.4 ppm and 2.88 ppm to 3.20 ppm, respectively.

Nitrogen loss from the coastal shelf of the East China Sea: Implications of the organic matter

Organic matter is a critical factor which regulates nitrogen loss pathways of denitrification and anammox for microbes in marine ecosystems. However, only a little attention has been paid to contrasting studies on denitrification and anammox in sandy and muddy sediments, especially in the coastal continental shelf dominated by sandy sediments. This study determined the bulk properties and associated microbial nitrogen transformation processes of surface sediments in the East China Sea coastal shelf, with the aim of gaining insight into the interaction of nitrogen loss with organic matter at the molecular level. The results illustrate that nitrogen loss dominates in organic-rich muddy sediments, and its denitrification rate (14.39 nmol N g-1 h-1) and anammox rate (2.73 nmol N g-1 h-1) are greater than those of sandy sediments (denitrification rate = 5.55 nmol N g-1 h-1, anammox rate = 1.57 nmol N g-1 h-1). Furthermore, determination of the mean summed ladderanes shows higher anammox generated in the muddy sediments with a value of 167.78 ng g-1dw. Quantitative analysis demonstrated that organic-rich muddy sediments enhanced the copy number of the denitrifying functional gene nosZ and anammox functional gene hzsB. We inferred that the greater rate of nitrogen loss in muddy sediments was due to the coupling relationship between anammox and denitrification. Overall, the community distribution and abundance of denitrifying bacteria and anammox bacteria changed intricately under the influence of organic matter. Moreover, this study further improves the understanding of nitrogen loss pathways and mechanistic factors from sediments.

Occurrence, sources and spatial distribution of n-alkanes in surface soils from the Amu Darya Delta, Uzbekistan, arid Central Asia

Central Asia (CA) has attracted global attention because of either water scarcity or ecosystem degradation. The Amu Darya Delta (ADD), one of the most important oases in CA, is endowed with valuable wetlands and biological resources that provide good ecosystem services to inhabitants. However, the region has experienced climate warming and large-scale anthropogenic changes since the last century. To assess the influences of anthropogenic interventions on the soil environment in this area, surface soil samples collected from the ADD were analysed for aliphatic hydrocarbon fractions and five heavy metals (HMs; including Cd, Zn, Cu, Ni and V). The results indicated that the n-alkanes extracted from surface soils were composed of homologous series from C14 to C35. Relatively high abundances of short-chain n-alkanes (<n-C21) were observed in cluster 1 samples (mainly from the lakeshore of the Aral Sea), while significantly high abundances of mid-chain (n-C21 to n-C25) and long-chain (n-C26 to n-C32) n-alkanes were found in cluster 3 samples, which were distributed in urban and agricultural drainage areas. In addition, very-long-chain n-alkanes (>n-C33) occurred in most surface soils, which might be a sign of a hot and arid climatic environment. Notably, almost all samples presented a clear even carbon dominance of short-chain n-alkanes, especially for cluster 1, which possibly represented the influence of hydrocarbon contamination and highly saline carbonate environments in addition to bacterial degradation. The biomarker indices and HM enrichment index indicated greater effects of crude oil pollution on cluster 1 (specifically samples 2, 4, 5, 6, 13, 16 and 34) and anthropogenic activities such as traffic emissions and agricultural drainage on cluster 3 samples. The results of this study provide evidence that the n-alkane composition and abundance in surface soils respond sensitively to anthropogenic interventions, arid climate and petroleum hydrocarbon pollution.

Detailing the organic matter in suspended sediments as a tool to assess the impact of land occupation in water bodies: a case of Barigui Watershed (Southern Brazil)

Suspended sediments were collected to examine the organic carbon content and n-alkanes in order to assess the impact on water bodies caused by soil and land occupation. For this, samples from distinct areas based on the level of land occupation of the Barigui Watershed and different areas under the influence of human activities were examined. The number of industries increasing along the river was also considered. Twenty-two sediment samples were collected using a time-integrated sediment sampler. Samples were extracted with dichloromethane:methanol (DCM:methanol) (2:1) in an ultrasound bath, treated and injected using gas chromatography coupled with mass spectrometry (GC-MS) for separation and quantification. Twenty-one n-alkanes were identified and were used to track both biogenic and anthropogenic inputs. The concentration of total n-alkanes varied from 38.72 to 222.76 µg g^-1, due to the impact of urbanization. Diagnostic indexes indicated high numbers of plants, bacteria and petroleum as n-alkanes sources. The following results were obtained using: carbon preference index (CPI), 1.96-2.22 (rainy season) and 2.12-5.80 (summer season); average chain length (ACL), 30.37-31.17 (rainy season) and 30.05-30.50 (summer season) and terrigenous aquatic ratio (TAR), 0.39-5.47 (rainy season) and 2.98-5.06 (summer season); n-alkanes had two main sources: terrestrial plant and petroleum. It is clear that the source of n-alkanes is different in each season (rainy and dry) demonstrated by n-alkanes occurrence. During the rainy season, there was an increase in organic matter of oil origin which was mainly associated with the increased runoff and rain drainage. Finally, the input of organic matter associated with land occupation and erosion can be distinguished by higher concentration in the most urbanized site (PB).

The influence of nutrients on the composition and quantity of buried organic carbon in a eutrophic plateau lake, Southwest China

The regulation of lacustrine organic carbon (OC) burial by nutrient is an outstanding knowledge gap in the current understanding of lake carbon cycles. In this study, we determined how nutrients quantitatively correspond with OC burial using the parallel factor analysis (PARAFAC) method in Dianchi Lake, southwest China. Factors were classified into three types according to their historical sedimentation characteristics: the background factor (BF), response factor (RF), and contingency factor (CF). The BF represented the original OC input combination in the lake and was insensitive to nutrient changes. The RF represented the OC input combination that was induced or promoted by nutrient changes in the lake. The CF represented short-term discontinuous factors in sedimentary history, which may be related to unique historical events. The results indicate that changes in the total nitrogen (TN) to total phosphorus (TP) ratio correlated with changes in the BF contribution; whereas the quantity of OC was mainly correlated with TN. The >90% of OC buried in sediment was quantitatively simulated by BF and RF; the driving effect of RF on OC burial was approximately 13 times higher than that of BF. It was observed that a 1 mg kg^-1 increase in TN led to approximately 2.2 units increase in RF contribution in Dianchi Lake, while the BF was insensitive to changes in TN. Thus, changes in lake nutrients may effectively change the composition and quantity of OC buried in lake sediment.

Historical reconstructions of sedimentary organic matter sources and phytoplankton evolution in the Jiaozhou Bay based on sterols and carbon isotope

Bulk organic matter proxies including total organic carbon (TOC), total nitrogen (TN), C/N ratio and carbon stable isotopic composition (δ¹³C) combined with sterols in a sediment core were studied to reconstruct both organic matter (OM) sources and phytoplankton evolutions of the Jiaozhou Bay (JZB) during the past ~ 80 years. The OM source allocations were calculated based on δ¹³C and sterol. The results showed that the marine OM (MOM) input was the dominant OM sources, with the marine organic carbon (OC_M) proportion of 54.2-78.4% and marine sterol proportion of 63.9-72.7%. The Terrestrial OM (TOM) contribution increased especially since the 1960s, mainly attributed to the increased sewage discharge and usage of fertilizer. Elevated marine primary productivity since the 1980s was mainly attributed to the increased nutrient inputs. Evolution of diatom compared with dinoflagellate in the JZB was closely related to the anthropogenic forcing and climate change.

Characterization and ecological function of bacterial communities in seabed sediments of the southwestern Yellow Sea and northwestern East China Sea, Western Pacific

The marine ecosystems of the marginal seas of the Western Pacific region are frequently disturbed by terrigenous materials. It is of great significance to investigate the ecological functioning of these marine areas, which can be well understood by exploring the microbial communities of sediments. However, the geographical distribution, composition, and genetic functions of sedimentary bacterial communities of the Yellow Sea and East China Sea (YEC Seas) are poorly understood. In this work, sediment samples were collected from YEC Sea areas to investigate bacterial communities by high-throughput sequencing. A total of 1960 genera were determined, with Proteobacteria being the dominant phylum (45.03%), followed by Planctomycetes, Bacteroidetes, Acidobacteria, and Chloroflexi. Correlation analysis indicates that the bacterial composition is influenced by environmental factors, including pressure, depth, seawater density, salinity, organic matter content, nutrient, and heavy metal. Approximately 178 metabolism pathways annotated in the Kyoto Encyclopedia of Genes and Genomes (KEGG) database were detected in the bacterial communities, including ones for nutrient metabolism (C, 3.04%; S, 0.70%; N, 0.52%; and P, 0.22%) and exogenous pollutant metabolism (e.g., polycyclic aromatic hydrocarbons (PAHs), chlorobenzene, and benzoate; up to 4.97%). The results demonstrate that the abundant bacterial communities in the sediments of the YEC Seas are important for maintaining marine ecological functioning, especially for elemental biogeochemical cycling and exogenous pollutant transformation.

Pharmaceutically active compounds (PhACs) in surface sediments of the Jiaozhou Bay, north China

Pharmaceutically active compounds (PhACs) have attracted increasing attention due to their large consumption volumes, high bioactivity and potential ecotoxicity. In this study, a total of 150 commonly used drugs were investigated in sediments of Jiaozhou Bay (JZB). Twenty-five target compounds were detected, of which ten were discovered for the first time in marine sediments. The range of total PhAC content was 3.62-21.4 ng/g dry weight. Ketoprofen (2.49 ng/g), oxytetracycline (1.00 ng/g) and roxithromycin (0.97 ng/g) were the preponderant PhACs. PhACs gradually decreased from east to west, and the distribution of PhACs in the sediment was controlled by the source channel, seawater dynamic process and sediment composition. The diatom, organic matter, and clay proportions in the sediments and the nutrients in the overlying water were the most important environmental factors affecting the distribution of PhACs. PhAC pollution in the sediments of the JZB exhibited an increasing trend. Coprostanol could be used as a chemical indicator of the PhAC concentration in JZB sediments. PhACs were mainly derived from direct pollution due to human fecal excretion in the eastern region. Ofloxacin, tetracycline and oxytetracycline were found to pose high or medium risks to aquatic organisms. It is necessary and urgent to improve the treatment technology of drug residues in sewage treatment plants to decrease the pollution of PhAC residues. With the continuous aging of the global population, the use of PhACs will increase rapidly, which may cause more unpredictable threats to the marine ecosystem. Therefore, the monitoring of PhACs in the marine environment needs to be strengthened, and studies on PhAC occurrence and effects must be considered a priority in global environmental research.