Deep Sea Research Part II: Topical Studies in Oceanography
Distribution and optical properties of CDOM in the Arabian Sea during the 1995 Southwest Monsoon
Abstract
Spatial and temporal variability in concentration and optical properties of colored dissolved organic matter (CDOM) were examined in the Arabian Sea during the 1995 Southwest (Summer) Monsoon on NRL/Seasoar Cruise, 21 June–12 July 1995. Classical upwelling patterns were observed near the coast, with strong fronts characterized by cold water, high chlorophyll a, and high nutrients. CDOM concentration showed a negative correlation with temperature in the surface waters throughout the study region, reflecting upwelling as the major source of CDOM to surface waters. Three water mass types were identified and found to have distinctive excitation–emission matrix (EEM) fingerprints. Persian Gulf Water had two fluorescence maxima due to UV and visible humic substance fluorescence. Maximum CDOM concentrations were found in the core of this water mass. Upwelling water had five or six fluorescence peaks, due to new and old CDOM. Elevated CDOM concentrations at the depth of the chlorophyll a maximum indicated production of new CDOM associated with the phytoplankton bloom. Oligotrophic water had extremely low CDOM concentrations, and only UV-absorbing and fluorescing compounds were found. This is consistent with CDOM which has been subjected to extensive exposure to solar irradiation at the sea surface. A new fluorophore with an Ex/Em maximum at 280/340 nm is described from highly productive waters. Two new EEM fingerprints are presented, one for oligotrophic blue waters showing photoresistant DOM, and one for upwelling water that may be of biological origin.
References (0)
Cited by (601)
Temporal variability and sources of PFAS in the Rio Grande, New Mexico through an arid urban area using multiple tracers and high-frequency sampling
2024, Emerging ContaminantsPer- and polyfluoroalkyl substances (PFAS) are ubiquitous in the environment but sources are not well defined for temporal and spatial aspects within an urban environment, and especially for an arid urban environment subject to seasonal short term high-intensity precipitation events. A focused diel sampling was conducted in the summer of 2021 to assess the temporal and spatial variability of PFAS in the Rio Grande near Albuquerque, New Mexico and showed an order of magnitude increase of PFAS as it flows through the Albuquerque urban area. Discrete samples were collected at two different locations on the Rio Grande in addition to wastewater treatment plant (WWTP) effluent that discharges directly to the Rio Grande between the sampling locations. Short-term high-intensity precipitation events occurred during the study period and mobilized PFAS from urban runoff. Dissolved organic matter composed of tryptophan-like organic substances and refined fuel and fuel byproducts, characteristic of an urban signature, were also related to the precipitation events. The PFAS in discharge from the WWTP was consistent over a 24-h period with slight differences in some compounds. Wastewater presence on the Rio Grande downstream of the WWTP was evidenced by a gadolinium anomaly as well as increases in several other trace elements, total dissolved nitrogen, and fluorescence indicators, in addition to PFAS. PFAS varied depending on source contribution, where urban runoff was associated with PFOA, PFOS, and PFBA, whereas PFHxA and PFPeA were associated with wastewater effluent. In addition, passive polar organic chemical integrative samplers (POCIS) using hydrophilic-lipid balance (HLB) sorption media were deployed for a month at two locations on the Rio Grande to assess longer term PFAS concentrations. The POCIS results show some compounds (PFPeA and PFHpA) were greater than the average concentration from discrete samples, whereas other compounds (PFHxA, PFOA, PFDA, and PFNA) were lower in the POCIS, and PFOS was very similar between the two. The POCIS did not detect PFBA, which may be related to the HLB media not performing well for short chain PFAS compounds. The results show promise for integrative samplers utilizing sorbent media. More detailed investigation of the spatial and temporal variability of water chemistry on the Rio Grande as it flows through Albuquerque could provide information applicable to urban areas worldwide.
Non-additive effect: Variation in the effects of the interaction between primitive components in anaerobic digestion
2024, Resources, Conservation and RecyclingInherent characteristics of complex organic components and their interactive coupling with environmental factors limit the comprehensive understanding of biotransformation in anaerobic digestion. In this study, we elucidated the mechanism underlying an interesting phenomenon, where a non-additive effect for methane production was recorded when primitive components, i.e., alpha-cellulose (α-CE), xylan (XY), and alkali lignin (AL), were used. The interaction of α-CE and XY produced a supra-additive effect due to the reduction of the energy barrier of carbonyl compound degradation. The degradation of non-conjugated C
O, with lower kinetic stability, was preferred to the degradation of conjugated CO. The introduction of AL produced a sub-additive effect, and AL exerted a stronger inhibitory effect on the methanogenesis of XY than α-CE. The preferential change in the relevant structural units occurred due to the deposition of AL on the surface of XY or the wrapping of XY by AL. In this study, we described a multiphase integrated influence mechanism, which can be used to more effectively design anaerobic co-digestion strategies and achieve the controlled enhancement of methane yield of perishable organic solid waste.Adsorption of humic acid from different organic solid waste compost to phenanthrene, is fluorescence excitation or quenching?
2024, Environmental PollutionHumic acid (HA) from different organic solid waste (OSW) compost has been shown good adsorption properties for phenanthrene. However, the raw material of HA can affect its structure, resulting in differences in adsorption capacity. Therefore, this study focused on the adsorption characteristics of phenanthrene by HA from different OSW compost. In this work, chicken manure (CM), rice straw (RS) and lawn waste (LW) were selected as sources of composted HA. The adsorption mechanism of HA from different OSW compost were revealed through analytical techniques including three-dimensional fluorescence spectroscopy (EEM), two-dimensional correlation spectroscopy (2DCOS), and Fourier-transform infrared spectroscopy (FTIR). The results suggested that HA from LW compost had a better adsorption affinity for phenanthrene because of its more complex fluorescent component, where C1 as a simple component determined the adsorption process specifically. Furthermore, after HA from LW compost adsorbed phenanthrene, the increase in aromatic –COOH and –NH was the main reason for fluorescence quenching. These results indicated that HA from LW compost had better adsorption effect for phenanthrene. The results of this study were expected to provide a selection scheme for the control of phenanthrene pollution and environmental remediation.
Rainfall-induced changes in aquatic microbial communities and stability of dissolved organic matter: Insight from a Fen river analysis
2024, Environmental ResearchMicrobial communities are pivotal in aquatic ecosystems, as they affect water quality, energy dynamics, nutrient cycling, and hydrological stability. This study explored the effects of rainfall on hydrological and photosynthetic parameters, microbial composition, and functional gene profiles in the Fen River. Our results demonstrated that rainfall-induced decreases in stream temperature, dissolved oxygen, pH, total phosphorus, chemical oxygen demand, and dissolved organic carbon concentrations. In contrast, rainfall increased total dissolved solids, salinity, and ammonia-nitrogen concentrations. A detailed microbial community structure analysis revealed that Cyanobacteria was the dominant microbial taxon in the Fen River, accounting for approximately 75% and 25% of the microalgal and bacterial communities, respectively. The abundance of Chlorophyta and Bacillariophyta increased by 47.66% and 29.92%, respectively, whereas the relative abundance of Bacteroidetes decreased by 37.55% under rainfall conditions. Stochastic processes predominantly affected the assembly of the bacterial community on rainy days. Functional gene analysis revealed variations in bacterial functions between sunny (Sun) and rainy (Rain) conditions, particularly in genes associated with the carbon cycle. The 3-oxoacyl-[acyl-carrier-protein] reductase gene was more abundant in the Fen River bacterial community. Particular genes involved in metabolism and environmental information processing, including the acetyl-CoA C-acetyltransferase (atoB), enoyl-CoA hydratase (paaF), and branched-chain amino acid transport system gene (livK), which are integral to environmental information processing, were more abundant in Sun than the Rain conditions. In contrast, the phosphate transport system gene, the galactose metabolic gene, and the pyruvate metabolic gene were more abundant in Rain. The excitation-emission matrix analysis with parallel factor analysis identified four fluorescence components (C1–C4) in the river, which were predominantly protein- (C1) and humic-like (C2–C4) substances. Rainfall affected organic matter production and transport, leading to changes in the degradation and stability of dissolved organic matter. Overall, this study offers insight into how rainfall affects aquatic ecosystems.
Composition characteristics and metal binding behavior of macrophyte-derived DOM (MDOM) under microbial combined photodegradation: A state closer to actual macrophytic lakes
2024, Journal of Hazardous MaterialsIn actual lakes, the “unstable components” of macrophyte-derived DOM (MDOM) are always degraded and cannot exist abidingly, but the environmental impact brought by it is ignored. In this study, MDOM from Potamogeton crispus was extracted to carry out microbial combined photodegradation (M-Photodegradation) and fluorescence titration experiments. Then the traits and metal binding reaction of MDOM under M-Photodegradation were analysed and compared with the features of lake-derived DOM (LDOM) from point monitoring of Dongping Lake through EEM-PARAFAC, 2D-SF-COS, and 2D-FTIR-COS. The results showed that the features of MDOM after M-Photodegradation were closer to those of LDOM. The degradation amplitudes were 93.53% ± 0.53% for C4 in microbial degradation and 78.31% ± 0.74% for C3 in photodegradation. Correspondingly, both were hardly detected in LDOM. Protein-like substances and aliphatic C–OH were preferentially selected by Cu2+, while humic-like matter and phenolic hydroxyl O–H responded faster to Pb2+. Although the binding sequences remained unchanged after M-Photodegradation, the LogKCu and LogKPb of components decreased overall, indicating increased environmental risks. This study proves that the refractory MDOM retained after degradation was more consistent with the actual state of macrophytic lakes and provides more information for the treatment of heavy metal pollution in lakes.
Stratification of dissolved organic matter in the upper 5000 m water column in the western Pacific Ocean
2024, Marine Environmental ResearchMarine dissolved organic matter (DOM) is a principal reservoir involved in biogeochemical cycles and exerts a pivotal influence on global carbon flux dynamics. In this study, excitation-emission matrix fluorescence spectroscopy combined with parallel factor analysis (EEM-PARAFAC) was conducted on 230 DOM samples collected from 21 sites between February and April 2022 in the Western Pacific Ocean (WPO). We identified five distinct fluorescence peaks (peaks B, T, A, C, and M), predominantly protein-like and humic-like components. These findings, marked by significant differences (p < 0.01) in fluorescence intensities and spectral indices, characterized the transformation of DOM with ocean depth, illustrating a transition from active to recalcitrant forms. Additionally, random forest analysis (RFA) identified depth as a key factor influencing marine dissolved organic carbon (DOC), with a 32.59% importance value. Correlations between hydrological and fluorescent parameters underscored the complexity of DOM sources and influencing processes. Overall, this work broadens our understanding of DOM variability in the upper 5000 m of the WPO, enhancing our knowledge of the marine environment's role in the global carbon cycle.