Composition regulates dissolved organic matter adsorption onto iron (oxy)hydroxides and its competition with phosphate: Implications for organic carbon and phosphorus immobilization in lakes.

Dissolved organic matter (DOM) is a heterogeneous pool of compounds and exhibits diverse adsorption characteristics with or without phosphorous (P) competition. The impacts of these factors on the burial and mobilization of organic carbon and P in aquatic ecosystems remain uncertain. In this study, an algae-derived DOM (ADOM) and a commercially available humic acid (HA) with distinct compositions were assessed for their adsorption behaviors onto iron (oxy)hydroxides (FeOx), both in the absence and presence of phosphate. ADOM contained less aromatics but more protein-like and highly unsaturated structures with oxygen compounds (HUSO) than HA. The adsorption capacity of FeOx was significantly greater for ADOM than for HA. Protein-like and HUSO compounds in ADOM and humic-like compounds and macromolecular aromatics in HA were preferentially adsorbed by FeOx. Moreover, ADOM demonstrated a stronger inhibitory effect on phosphate adsorption than HA. This observation suggests that the substantial release of autochthonous ADOM by algae could elevate internal P loading and pose challenges for the restoration of restore eutrophic lakes. The presence of phosphate suppressed the adsorption of protein-like compounds in ADOM onto FeOx, resulting in an increase in the relative abundance of protein-like compounds and a decrease in the relative abundance of humic-like compounds in post-adsorption ADOM. In contrast, phosphate exhibited no discernible impact on the compositional fractionation of HA. Collectively, our results show the source-composition characters of DOM influence the immobilization of both DOM and P in aquatic ecosystems through adsorption processes. The preferential adsorption of proteinaceous compounds within ADOM and aromatics within HA highlights the potential for the attachment with FeOx to diminish the original source-specific signatures of DOM, thereby contributing to the shared DOM characteristics observed across diverse aquatic environments.

CD147 mediates the CD44s-dependent differentiation of myofibroblasts driven by transforming growth factor-ß1.

Progressive fibrosis leads to loss of organ function and affects many organs as a result of excessive extracellular matrix production. The ubiquitous matrix polysaccharide hyaluronan (HA) is central to this through association with its primary receptor, CD44, which exists as standard CD44 (CD44s) or multiple splice variants. Mediators such as profibrotic transforming growth factor (TGF)-ß1 and proinflammatory interleukin (IL)-1ß are widely associated with fibrotic progression. TGF-ß1 induces myofibroblast differentiation, while IL-1ß induces a proinflammatory fibroblast phenotype that promotes fibroblast binding to monocyte/macrophages. CD44 expression is essential for both responses. Potential CD44 splice variants involved, however, are unidentified. The TGF-ß1-activated CD44/epidermal growth factor receptor complex induces differentiation of metastatic cells through interactions with the matrix metalloproteinase inducer, CD147. This study aimed to determine the CD44 variants involved in TGF-ß1- and IL-1ß-mediated responses and to investigate the potential profibrotic role of CD147. Using immunocytochemistry and quantitative PCR, standard CD44s were shown to be essential for both TGF-ß1-induced fibroblast/myofibroblast differentiation and IL-1ß-induced monocyte binding. Co-immunoprecipitation identified that CD147 associated with CD44s. Using CD147-siRNA and confocal microscopy, we also determined that incorporation of the myofibroblast marker, αSMA, into F-actin stress fibers was prevented in the absence of CD147 and myofibroblast-dependent collagen gel contraction was inhibited. CD147 did not associate with HA, but removal of HA prevented the association of CD44s with CD147 at points of cell-cell contact. Taken together, our data suggest that CD44s/CD147 colocalization is essential in regulating the mechanical tension required for the αSMA incorporation into F-actin stress fibers that regulates myofibroblast phenotype.

Single-Nucleus RNA Sequencing Identifies New Classes of Proximal Tubular Epithelial Cells in Kidney Fibrosis.

BACKGROUND: Proximal tubular cells (PTCs) are the most abundant cell type in the kidney. PTCs are central to normal kidney function and to regeneration versus organ fibrosis following injury. This study used single-nucleus RNA sequencing (snRNAseq) to describe the phenotype of PTCs in renal fibrosis. METHODS: Kidneys were harvested from naïve mice and from mice with renal fibrosis induced by chronic aristolochic acid administration. Nuclei were isolated using Nuclei EZ Lysis buffer. Libraries were prepared on the 10× platform, and snRNAseq was completed using the Illumina NextSeq 550 System. Genome mapping was carried out with high-performance computing. RESULTS: A total of 23,885 nuclei were analyzed. PTCs were found in five abundant clusters, mapping to S1, S1-S2, S2, S2-cortical S3, and medullary S3 segments. Additional cell clusters ("new PTC clusters") were at low abundance in normal kidney and in increased number in kidneys undergoing regeneration/fibrosis following injury. These clusters exhibited clear molecular phenotypes, permitting labeling as proliferating, New-PT1, New-PT2, and (present only following injury) New-PT3. Each cluster exhibited a unique gene expression signature, including multiple genes previously associated with renal injury response and fibrosis progression. Comprehensive pathway analyses revealed metabolic reprogramming, enrichment of cellular communication and cell motility, and various immune activations in new PTC clusters. In ligand-receptor analysis, new PTC clusters promoted fibrotic signaling to fibroblasts and inflammatory activation to macrophages. CONCLUSIONS: These data identify unrecognized PTC phenotype heterogeneity and reveal novel PTCs associated with kidney fibrosis.

Seasonal changes of trace elements, nutrients, dissolved organic matter, and coastal acidification over the largest oyster reef in the Western Mississippi Sound, USA.

Seasonal changes of trace elements, nutrients, dissolved organic matter (DOM), and carbonate system parameters were evaluated over the largest deteriorating oyster reef in the Western Mississippi Sound using data collected during spring, summer, and winter of 2018, and summer of 2019. Higher concentrations of Pb (224%), Cu (211%), Zn (2400%), and Ca (240%) were observed during winter of 2018 compared to summer 2019. Phosphate and ammonia concentrations were higher (> 800%) during both summers of 2018 and 2019 than winter of 2018. Among the three distinct DOM components identified, two terrestrial humic-like components were more abundant during both spring (12% and 36%) and summer (11% and 33%) of 2018 than winter of 2018, implying a relatively lesser supply of humic-like components from terrestrial sources during winter. On the other hand, the protein-like component was more abundant during summer of 2019 compared to rest of the study period, suggesting a higher rate of autochthonous production during summer 2019. In addition, to their significant depth-wise variation, ocean acidification parameters including pH, pCO2, CO32-, and carbonate saturation states were all higher during both summers of 2018 and 2019. The measured variables such as trace elements, organic carbon, suspended particulates, and acidification parameters exhibited conservative mixing behavior against salinity. These observations have strong implications for the health of the oyster reefs, which provides ecologically important habitats and supports the economy of the Gulf Coast.

Intravenous iron supplementation does not increase infectious disease risk in hemodialysis patients: a nationwide cohort-based case-crossover study.

BACKGROUND: Studies have reported conflicting findings on the infection risk posed by intravenous iron supplementation among hemodialysis (HD) patients. We used a novel study design to assess associations between intravenous iron and infectious diseases. METHODS: Patients initiating HD between 1998 and 2008 were extracted from Taiwan's National Health Insurance Research Database. Their first infectious disease in the period between 1.5 years after dialysis initiation and 2010 was identified and defined as the index date. Through the case-crossover design, the odds of exposure to intravenous iron within the 1-month period immediately preceding the index date (i.e., the case period) were compared with iron exposure in three different matched control periods for the same enrollee, thus possibly reducing some unmeasured confounders. RESULTS: A total of 1410 patients who met our enrollment criteria were extracted from incident HD patients. The odds of intravenous iron exposure during the case period versus total control periods exhibited no significant difference (odds ratio: 1.000, 95% confidence interval: 0.75-1.33). In subgroup analyses, this association remained nonsignificant across patients with diabetes mellitus, heart failure, chronic lung disease, venous catheter for HD, and higher iron load. CONCLUSIONS: We found that intravenous iron supplementation did not increase short-term infection risk among HD patients.

Identifying risk groups of infectious spondylitis in patients with end-stage renal disease under hemodialysis: a propensity score-matched case-control study.

BACKGROUND: Patients with end-stage renal disease (ESRD) under hemodialysis (HD) are at greater risks of infectious spondylitis (IS), but there is no reliable predictor that facilitate early detection of this relatively rare and insidious disease. METHODS: A retrospective review of the medical records from patients with ESRD under HD over a 12-year period was performed at a tertiary teaching hospital, and those with a first-time diagnosis of IS were identified. A 1:4 propensity score-matched case-control study was carried out, and baseline characteristics, underlying diseases, and laboratory data were compared between the study group and the control group, one month before the date of diagnosis or the index date respectively. RESULTS: A total of 16 patients with IS were compared with 64 controls. After adjustment, recent access operation (odds ratio [OR], 13.27; 95% confidence interval [CI], 3.53 to 49.91; p <  0.001), degenerative spinal disease (OR, 12.87; 95% CI, 1.89 to 87.41; p = 0.009), HD through a tunneled cuffed catheter (OR, 6.75; 95% CI, 1.74 to 26.14; p = 0.006), low serum levels of hemoglobin, albumin, as well as high levels of red blood cell volume distribution width (RDW), alkaline phosphatase (ALP), and high sensitivity C-reactive protein were significant predictors for a IS diagnosis one month later. Receiver operating characteristic curves for hemoglobin, RDW, ALP, and albumin all showed good discrimination. The further multivariate models identified both high serum ALP levels and low serum RDW levels following a recent access intervention in patients with relatively short HD vintages may be indicative of the development of IS. CONCLUSION: Patients under HD with relatively short HD vintages showing either elevated ALP levels or low RDW levels following a recent access intervention should prompt clinical awareness about IS for timely diagnosis.

Serum indoxyl sulfate predicts adverse cardiovascular events in patients with chronic kidney disease.

BACKGROUND/PURPOSE: Indoxyl sulfate (IS) is a protein-binding molecule that exhibits cardiovascular (CV) toxicity. This study determined whether the serum IS level can be used to predict the risk of major adverse CV events (MACEs) in patients with chronic kidney disease (CKD). METHODS: We studied 147 patients with CKD stage 1-5 over a 3-year follow-up period. IS was measured through mass spectrometry. Patients' demographics were collected and analyzed to predict outcomes by using multivariable Cox regression. RESULTS: Forty-seven (32.0%) patients had MACEs. IS remained significantly associated with MACEs after multivariable regression analysis. The area under the receiver operating characteristic curve for IS levels was 0.708 (95% confidence interval: 0.618-0.798). CONCLUSION: IS may have a critical role in the prediction of CV disease in patients with CKD. Further large-scale investigations are warranted and suggested.

Assessing pollution and risk of polycyclic aromatic hydrocarbons in sewage sludge from wastewater treatment plants in China's top coal-producing region.

Managing and disposing of sewage sludge have been a severe environmental challenge around the world. China produces hundreds of million tons of sewage sludge annually, and a better understanding of the extent and risk of the associated pollution is of critical importance for implementing environmentally safe regulations and practices. The present study examined the quantity, composition, source, and risk of polycyclic aromatic hydrocarbons (PAHs) in sewage sludge from 18 wastewater treatment plants (WWTPs) in Shaanxi, one of China's top coal-producing provinces. The total concentrations of 16 PAHs varied from 778 to 3264 ng/g dry weight, which is below the upper safety limit (5000 ng/g dry weight) set for the disposal of sludge from municipal wastewater treatment plants for agricultural use in China. However, the concentration of individual PAH compound exceeded the acceptable level prescribed by the Netherland Soil Standard. Three-ring PAHs were the most abundant constituent (50% of total PAHs on average), followed by four-ring PAHs averaging 25%. Relative to sludge PAHs in the same region a decade ago, the total concentrations decreased by more than 27% and the composition shifted to a more pronounced dominance by low molecular weight compounds. This compositional shift suggests higher contributions of petrogenic sources, which may reflect China's increasing consumption of petroleum products over the past decade. The flux of sludge PAHs from each WWTP was positively correlated with the corresponding city's GDP and population, and the total flux amounted to over 100 kg each year for WWTPs in the Xi'an city. The mean toxicity equivalent quantity (TEQ) value was more than twice higher than the value recommended by the Netherlands Soil Standard, and seven carcinogenic PAHs were the primary contributor (i.e., 89-99%) of the TEQ. Collectively, our findings demonstrate that sewage sludge PAHs in Shaanxi constitute a significant source of environmental pollution and toxicity, which cautions against the direct discharge and reuse of sewage sludge and further highlights challenges in managing and disposing of the vast quantities of sewage sludge in China.

Effect of photo-biodegradation and biodegradation on the biogeochemical cycling of dissolved organic matter across diverse surface water bodies.

The objective of this research was to quantify the temporal variation of dissolved organic matter (DOM) in five distinct waterbodies in watersheds with diverse types of land use and land cover in the presence and absence of sunlight. The water bodies were an agricultural pond, a lake in a forested watershed, a man-made reservoir, an estuary, and a bay. Two sets of samples were prepared by dispensing unfiltered samples into filtered samples in 1:10 ratio (V/V). The first set was exposed to sunlight (10 hr per day for 30 days) for examining the combined effect of photo-biodegradation, while the second set was stored in dark for examining biodegradation alone. Spectroscopic measurements in tandem with multivariate statistics were used to interpret DOM lability and composition. The results suggest that the agricultural pond behaved differently compared to other study locations during degradation experiments due to the presence of higher amount of microbial humic-like and protein-like components derived from microbial/anthropogenic sources. For all samples, a larger decrease in dissolved organic carbon (DOC) concentration (10.12% ±â€¯9.81% for photo-biodegradation and 6.65% ±â€¯2.83% for biodegradation) and rapid transformation of DOM components (i.e., terrestrial humic-like components into microbial humic and protein-like components) were observed during photo-biodegradation experiments. Results suggest that sunlight facilitated DOM biodegradation, resulting in simpler recalcitrant molecules regardless of original composition. Overall, it was found that combined effects of light and bacteria are more efficient than bacterial effects alone in remineralizing and altering DOM, which highlights the crucial importance of sunlight in transforming aquatic DOM.

Epidemiology and outcomes of Endophthalmitis in chronic dialysis patients: a 13-year experience in a tertiary referral center in Taiwan.

BACKGROUND: Endophthalmitis is a severe eye infection leading to disabling outcome. Because there were only a few case report illustrating endophthalmitis in chronic dialysis patient, we would like to investigate the epidemiology and clinical features of endophthalmitis in chronic dialysis patient in a tertiary referral center. METHODS: We searched the health information system in the study hospital with ICD9 encoding endophthalmitis during Jan. 2002 to Dec. 2015. A total of 32 episodes of endophthalmitis occurred in chronic dialysis patients. We performed an 1:2 case-control match on propensity score. The demographic features, clinical manifestation, infection focus and visual outcome were recorded. RESULTS: Of the total of 32 patients, 25 were classified as endogenous endophthalmitis and another seven were exogenous. Most patients presented with ophthalmalgia (n = 32, 100%) and periocular swelling (n = 31, 96.8%), whereas half of the patients suffered blurred vision (n = 16, 50%). Staphylococcus aureus, Klebsiella pneumoniae, and Pseudomonas aeruginosa were the most frequent causative pathogens. Dialysis vascular infection was also a possible unique focus for bacteremia. The visual acuity of the endogenous groups were less likely to improve in the chronic dialysis patients compared with control group. CONCLUSION: This is the first and the largest case series focusing on endophthalmitis in chronic dialysis patients. Our study showed different pathogen spectrum, an unique bacterial origin and worse visual outcome in these group of patients. Prompt referral to ophthalmologists when the patients present with suspicious symptoms (blurred vision, ophthalmalgia and periocular swelling) is crucial.

Red cell distribution width associated with adverse cardiovascular outcomes in patients with chronic kidney disease.

BACKGROUND: Recent studies have demonstrated that red cell distribution width (RDW) is associated with cardiovascular (CV) events and mortality. Patients with chronic kidney disease (CKD) are often anemic and have high RDW levels. In this study, we investigated the effect of RDW on major composite CV outcomes among patients with CKD. METHODS: We retrospectively analyzed patients with CKD who were admitted to the department of cardiology of a tertiary hospital in 2011. The patients were divided into 2 groups: normal RDW (RDW < 14.5%) and elevated RDW (RDW ≥ 14.5%). Demographic characteristics, comorbidities, blood investigation results, prescriptions, and outcomes were analyzed after a 3-year follow-up period. Six adjustment levels were performed to evaluate the effect of RDW on outcomes. RESULTS: This study involved 282 patients with CKD: 213 in the elevated RDW group and 69 in the normal RDW group. The elevated RDW group had older patients, a lower proportion of male patients, lower left ventricular ejection fraction (LVEF) values, lower hemoglobin levels, lower serum albumin levels, and higher creatinine levels, compared with the normal RDW group. A linear trend was observed toward higher RDW in patients with deteriorating renal function. In the final adjusted model, RDW ≥ 14.5%, older age, and lower LVEF were associated with an increased risk of major composite CV outcomes. CONCLUSION: RDW is a potentially useful cost-effective indicator of major composite CV outcomes in patients with CKD.

Infective spondylodiscitis in patients on maintenance hemodialysis: a case series.

Infective spondylodiscitis is a rare disease. This case review describes the clinical course, risk factors, and outcomes of adult patients on maintenance hemodialysis who presented with infective spondylodiscitis at a single medical center in Taiwan. There were 18 cases (mean age: 64.9 ± 10.8 years) over more than 10 years. Analysis of underlying diseases indicated that 50% of patients had diabetes, 55.6% had hypertension, 55.6% had coronary artery disease, 22.2% had congestive heart failure, 22.2% had a cerebral vascular accident, 16.7% had liver cirrhosis, and 11.1% had malignancies. Sixty-one percent of patients had a degenerative spinal disease and the most common symptom was back pain (83.3%). A total of 38.9% of patients had leukocytosis, 99.4% had elevated levels of C-reactive protein, 78.6% had elevated erythrocyte sedimentation rates, and 55.6% had elevated levels of alkaline phosphatase. The average hemodialysis duration was 72.8 ± 87.5 months, and 8 patients (44.4%) started hemodialysis within 1 year prior to infective spondylodiscitis. Four patients (22.2%) had vascular access infection-associated spondylodiscitis. The lumbar region was the most common location of infection (77.8%), 44.4% of patients developed abscesses, and Staphylococci were the most common pathogen (38.9%). The mortality rate was 16.7%, all due to sepsis. Thirty-three percent of the survivors had recurrent infective spondylodiscitis within 1 year. Infective spondylodiscitis should be considered in hemodialysis patients who present with prolonged back pain with or without fever. Non-contrast MRI is an appropriate diagnostic tool for this condition. Vascular access infection increases the risk for infective spondylodiscitis in hemodialysis patients.

Temporal-Spatial Evolution of Groundwater Nitrogen Pollution Over Seven Years in a Highly Urbanized City in the Southern China.

Understanding the temporospatial variation in nitrogen pollution in groundwater and the associated controlling factors is important to establish management practices that ensure sustainable use of groundwater. In this study, we analyzed inorganic nitrogen content (nitrate, nitrite, and ammonium) in 1164 groundwater samples from shallow, middle-deep, and deep aquifers in Zhanjiang, a highly urbanized city in the southern China. Our data span a range of 7 years from 2005 to 2011. Results show that shallow aquifers had been heavily contaminated by nitrate and ammonium. Temporal patterns show that N contamination levels remained high and relatively stable over time in urban areas. This stability and high concentration is hypothesized as a result of uncontrolled, illicit sewer discharges from nearby business facilities. Groundwater in urban land and farmland displays systematic differences in geochemical characteristics. Collectively, our findings demonstrate the importance of continuously monitoring groundwater quality and strictly regulating sewage discharges in Zhanjiang.

Enameloid-bound δ15 N reveals large trophic separation among Late Cretaceous sharks in the northern Gulf of Mexico.

The nitrogen isotopic composition (15 N/14 N ratio, or δ15 N) of enameloid-bound organic matter (δ15 NEB ) in shark teeth was recently developed to investigate the biogeochemistry and trophic structures (i.e., food webs) of the ancient ocean. Using δ15 NEB , we present the first nitrogen isotopic evidence for trophic differences between shark taxa from a single fossil locality. We analyze the teeth of four taxa (Meristodonoides, Ptychodus, Scapanorhynchus, and Squalicorax) from the Late Cretaceous (83-84 Ma) Trussells Creek site in Alabama, USA, and compare the N isotopic findings with predictions from tooth morphology, the traditional method for inferring shark paleo-diets. Our δ15 NEB data indicate two distinct trophic groups, with averages separated by 6.1 ± 2.1‰. The lower group consists of Meristodonoides and Ptychodus, and the higher group consists of Scapanorhynchus and Squalicorax (i.e., lamniforms). This δ15 NEB difference indicates a 1.5 ± 0.5 trophic-level separation between the two groups, a finding that is in line with paleontological predictions of a higher trophic level for these lamniforms over Meristodonoides and Ptychodus. However, the δ15 NEB of Meristodonoides is lower than suggested by tooth morphology, although consistent with mechanical tests suggesting that higher trophic-level bony fishes were not a major component of their diet. Further, δ15 NEB indicates that the two sampled lamniform taxa fed at similar trophic levels despite their different inferred tooth functions. These two findings suggest that tooth morphology alone may not always be a sufficient indicator of dietary niche. The large trophic separation revealed by the δ15 NEB offset leaves open the possibility that higher trophic-level lamniforms, such as those measured here, preyed upon smaller, lower trophic-level sharks like Meristodonoides.

Invasive Listeriosis in End-Stage Kidney Disease (ESKD) Patients Receiving Long-Term Dialysis: A 21-Year Case Series.

Background: Listeriosis is caused by the facultative anaerobic bacterium Listeria monocytogenes. Infection from Listeria-contaminated food or water is the main etiology. If Listeria travels outside the intestines, it can cause invasive listeriosis, such as sepsis, meningitis, and meningoencephalitis. Invasive illness is especially dangerous for pregnant women and their newborns, elderly people, and people with compromised immune systems or medical conditions such as end-stage kidney disease (ESKD) patients receiving long-term dialysis. Purpose: Describe the manifestations and hospital outcomes of invasive listeriosis and identify the risk factors for in-hospital and one-year mortality in ESKD patients receiving long-term dialysis. Patients and Methods: This retrospective observational study examined hospitalized patient records at a Taiwanese tertiary medical center from August 1, 2000, to August 31, 2021. ESKD patients on chronic dialysis were identified with invasive listeriosis by blood culture and discharge diagnosis. Over 21 years, we accurately recorded 26 cases. Results: ESKD patients on chronic dialysis with invasive listeriosis have a poor prognosis. Only 53.8% of chronic dialysis patients with invasive listeriosis survived their first hospital episode. 42.3% of hospitalized ESKD patients with invasive listeriosis survived one year later. In univariate analysis, shock, tachypnea (RR ≥ 22), respiratory failure, qSOFA score ≥ 2, and lower initial platelet count were linked to greater in-hospital mortality rates. Conclusion: ESKD patients with invasive listeriosis have a grave prognosis. Our research reveals that an early blood sample for a bacterial culture may identify invasive listeriosis in chronic dialysis patients with fever, nausea or vomiting, confusion, and respiratory distress. This study is the first to identify a lower platelet count and qSOFA score ≥ 2 as markers of high-risk invasive listeriosis in ESKD patients.

Lipid biomarkers recording marine microbial community structure changes through the Frasnian-Famennian mass extinction event.

Studying the response and recovery of marine microbial communities during mass extinction events provides an evolutionary window through which to understand the adaptation and resilience of the marine ecosystem in the face of significant environmental disturbances. The goal of this study is to reconstruct changes in the marine microbial community structure through the Late Devonian Frasnian-Famennian (F-F) transition. We performed a multiproxy investigation on a drill core of the Upper Devonian New Albany Shale from the Illinois Basin (western Kentucky, USA). Aryl isoprenoids show green sulfur bacteria expansion and associated photic zone euxinia (PZE) enhancement during the F-F interval. These changes can be attributed to augmented terrigenous influxes, as recorded collectively by the long-chain/short-chain normal alkane ratio, carbon preference index, C30 moretane/C30 hopane, and diahopane index. Hopane/sterane ratios reveal a more pronounced dominance of eukaryotic over prokaryotic production during the mass extinction interval. Sterane distributions indicate that the microalgal community was primarily composed of green algae clades, and their dominance became more pronounced during the F-F interval and continued to rise in the subsequent periods. The 2α-methylhopane index values do not show an evident shift during the mass extinction interval, whereas the 3ß-methylhopane index values record a greater abundance of methanotrophic bacteria during the extinction interval, suggesting enhanced methane cycling due to intensified oxygen depletion. Overall, the Illinois Basin during the F-F extinction experienced heightened algal productivity due to intensified terrigenous influxes, exhibiting similarities to contemporary coastal oceans that are currently undergoing globalized cultural eutrophication. The observed microbial community shifts associated with the F-F environmental disturbances were largely restricted to the extinction interval, which suggests a relatively stable, resilient marine microbial ecosystem during the Late Devonian.

Stability of organic matter-iron-phosphate associations during abiotic reduction of iron.

The stability of organic matter-iron-phosphate (OM-Fe-P) association has an important impact on the migration and sequestration of organic carbon (OC) and P in the environment. Here, we examined the release characteristics of Fe, P and OM due to the abiotic reduction of OM-Fe-P associations by Na-dithionite. The associations were synthesized with algae-derived OM (AOM) and terrestrial humic acid (HA) through either adsorption onto iron (hydr)oxide or coprecipitation with Fe(III). Results indicated that OM and P adsorbed onto the associations were rapidly released, whereas coprecipitation yielded much lower release rates of Fe, P, and OM. The stronger inhibitory effect on reduction from coprecipitation can be explained by larger particles formed by coprecipitation and coprecipitation taking up more OC that had a passivation effect on the associations. The release rates of OM and P were lower in coprecipitates formed with HA than formed with AOM for a given OC/Fe ratio. This observation can be attributed to a patchy distribution of OC in AOM associated coprecipitates, which showed a weaker aggregation of OC with Fe and P. In contrast, the distribution of OC in HA-associated coprecipitates was more homogenous, enabling a stronger aggregation of OM with P and a greater passivation effect on P release. Our results revealed that OM sources, association formation pathways, and elemental stoichiometry collectively controlled the stability of OM-Fe-P associations.

Assessment of phthalic acid esters plasticizers in sediments of coastal Alabama, USA: Occurrence, source, and ecological risk.

Considering the ubiquitous occurrences and ecotoxicity of phthalates (PAEs), it is essential to understand their sources, distribution, and associated ecological risks of PAEs in sediments to assess the environmental health of estuaries and support effective management practices. This study provides the first comprehensive dataset on the occurrence, spatial variation, inventory, and potential ecological risk assessment of PAEs in surface sediments of commercially and ecologically significant estuaries in the southeastern United States, Mobile Bay and adjoining eastern Mississippi Sound. Fifteen PAEs were widely detected in the sediments of the study region, with total concentrations varying between 0.02 and 3.37 µg/g. The dominance of low-molecular-weight (LMW) PAEs (DEP, DBP and DiBP) relative to high-molecular-weight (HMW) PAEs (DEHP, DOP, DNP) indicates that residential activities have stronger impacts than industrial activities on PAE distributions. The total PAE concentrations displayed an overall decreasing trend with increasing bottom water salinity, with the maximum concentrations occurring near river mouths. These observations suggest that river inputs were an important pathway by which PAEs were transported to the estuary. Linear regression models identified sediment adsorption (measured by total organic carbon and median grain size) and riverine inputs (measured by bottom water salinity) as significant predictors for the concentrations of LMW and HMW PAEs. Estimated 5-year total inventories of sedimentary PAEs in Mobile Bay and the eastern Mississippi Sound were 13.82 tons and 1.16 tons, respectively. Risk assessment calculations suggest that LMW PAEs posed a medium-to-high risk to sensitive aquatic organisms, and DEHP posed a low or negligible risk to the aquatic organisms. The results of this study provide important information needed for establishing and implementing effective practices for monitoring and regulating plasticizer pollutants in estuaries.

Adsorption of humic acids to lake sediments: Compositional fractionation, inhibitory effect of phosphate, and implications for lake eutrophication.

Humic acid (HA) and phosphate interactions play a vital role in the biogeochemical cycle of carbon and nutrients and thus the trophic state of a lake. The adsorption behavior of HAs to sediments in the absence and presence of phosphate was investigated in this study. Three types of HAs were used, AHA from algae-dominated lake sediments, MHA from macrophyte-dominated lake sediments, and a reference HA (RHA) with terrestrial sources. The adsorption capacity of lake sediments was highest for AHA, which can be explained by that AHA contained more carboxyl-containing molecules, proteinaceous compounds and polysaccharides that were preferentially adsorbed by minerals. Phosphate showed a stronger inhibitory effect on MHA adsorption than on AHA adsorption, suggesting that AHA can more effectively replace phosphate adsorbed to sediments. Our findings show that the functional groups of organic compounds control not only their fractionation and burial but also their ability to replace phosphate in sediments. We propose a novel mechanism to explain the legacy effect of lake eutrophication. That is, as lakes shift from a macrophyte-dominated state to more eutrophic, algae-dominated state, increasing algae-derived organic compounds can promote the release of phosphate from sediments, forming a positive feedback loop that sustains internal phosphorus loading and hence lake eutrophication.

Sources and composition of natural and anthropogenic hydrocarbons in sediments from an impacted estuary.

Hydrocarbons in estuarine sediments provide information on sources of sedimentary organic matter (OM), and they are thus useful for tracing natural and anthropogenic OM inputs to the estuary. Here, we assessed the amounts, compositions and sources of natural and anthropogenic hydrocarbons from the sediments of a large, ecologically important estuary, Mobile Bay in Southeast USA. TOC/TN ratios and δ13C of organic carbon suggest that the bulk natural OM was sourced from marine phytoplankton and bacteria mixed with marsh and terrigenous C3 plants. Normal alkanes show high proportions of long-chain compounds with a high Carbon Preference Index, indicating the importance of C3 plants-derived OM in Mobile Bay. High concentrations of biogenic hopanes and perylene indicate microbial sources and degradation played an important role in shaping OM compositions. Anthropogenic hydrocarbons, αß-hopanes and polycyclic aromatic hydrocarbons (PAHs), were widely detected in Mobile Bay sediments. The source diagnostic ratios of hopanes and steranes suggest they were sourced from coal and diesel combustions. The source diagnostic ratios of PAHs, together with a positive correlation between PAHs and total mercury, suggests that PAHs originated primarily from coal combustion. We proposed two ratios, αß-hopanes/(ßß-hopanes+hopenes) and 16 PAHs/perylene, to evaluate anthropogenic versus natural contributions of hydrocarbons. These ratios were higher in the western estuary than in the eastern estuary, suggesting elevated anthropogenic hydrocarbon inputs to the western estuary. Correspondingly, the toxic equivalent quantity (TEQBaQ) of PAHs showed a higher ecological risk for the western estuary. This spatially uneven distribution of hydrocarbon pollutants can be attributed to more concentrated urban and industrial areas on the western shore, suggesting the importance of adjacent pollution sources. Collectively, our results provide new insights into the origins and dynamics of natural and anthropogenic OM and highlight the significance of coal combustion in contributing hydrocarbon pollutants in Mobile Bay sediments.