Abstract. Global projections for ocean conditions in 2100 predict that the North Pacific will experience some of the largest changes. Coastal processes that drive variability in the region can alter these projected changes but are poorly resolved by global coarse-resolution models. We quantify the degree to which local processes modify biogeochemical changes in the eastern boundary California Current System (CCS) using multi-model regionally downscaled climate projections of multiple climate-associated stressors (temperature, O2, pH, saturation state (Ω), and CO2). The downscaled projections predict changes consistent with the directional change from the global projections for the same emissions scenario. However, the magnitude and spatial variability of projected changes are modified in the downscaled projections for carbon variables. Future changes in pCO2 and surface Ω are amplified, while changes in pH and upper 200 m Ω are dampened relative to the projected change in global models. Surface carbon variable changes are highly correlated to changes in dissolved inorganic carbon (DIC), pCO2 changes over the upper 200 m are correlated to total alkalinity (TA), and changes at the bottom are correlated to DIC and nutrient changes. The correlations in these latter two regions suggest that future changes in carbon variables are influenced by nutrient cycling, changes in benthic–pelagic coupling, and TA resolved by the downscaled projections. Within the CCS, differences in global and downscaled climate stressors are spatially variable, and the northern CCS experiences the most intense modification. These projected changes are consistent with the continued reduction in source water oxygen; increase in source water nutrients; and, combined with solubility-driven changes, altered future upwelled source waters in the CCS. The results presented here suggest that projections that resolve coastal processes are necessary for adequate representation of the magnitude of projected change in carbon stressors in the CCS.
more »
« less
The Reactivity of Polyethylene Microplastics in Water under Low Oxygen Conditions Using Radiation Chemistry
Polyethylene (PE) is an intensely utilized polymer, which has consequently led to it becoming a common environmental contaminant. PE and other plastic waste are known to be highly persistent in surface waters; however, chemical and physical changes do take place over time, dependent mostly on highly variable natural conditions, such as oxygen (O2) availability. Gamma radiation was used to generate reactive oxygen species, namely hydroxyl radicals, in initially aerated aqueous solutions to simulate the natural weathering of microplastics in waters where there are fluctuations and often depletions in dissolved O2. The headspace of the irradiated PE-containing solutions was probed for the formation of degradation products using solid-phase microextraction (SPME) fibers in combination with gas chromatography mass spectrometry (GCMS). The major species detected were n-dodecane, with trace levels of tridecane, 2-dodecanone, and hexadecane, which were believed to be predominately adsorbed in the PE microplastics in excess of their aqueous solubility limits. Surface characterization by Raman spectroscopy and light and dark field microscopy indicated no change in the chemical composition of the irradiated PE microplastics under low O2 to anaerobic conditions. However, morphological changes were observed, indicating radical combination reactions.
more »
« less
- Award ID(s):
- 2035499
- NSF-PAR ID:
- 10351489
- Date Published:
- Journal Name:
- Water
- Volume:
- 13
- Issue:
- 21
- ISSN:
- 2073-4441
- Page Range / eLocation ID:
- 3120
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Microplastics in the aquatic system are among the many inevitable consequences of plastic pollution, which has cascading environmental and public health impacts. Our study aimed at analyzing surface interactions and leachate production of six microplastics under ultraviolet (UV) irradiation. Leachate production was analyzed for the dissolved organic content (DOC), UV 254 , and fluorescence through excitation emission (EEM) to determine the kinetics and mechanisms involved in the release of organic matter by UV irradiation. The results suggested there was a clear trend of organic matter being released from the surface of the six microplastics caused by UV irradiation based on DOC, UV 254 absorbance, and EEM intensity increasing with time. Polystyrene had the greatest and fastest increase in DOC concentrations, followed by the resin coated polystyrene. Experiments conducted at different temperatures indicated the endothermic nature of these leaching mechanisms. The differences in leachate formation for different polymers were attributed to their chemical makeup and their potency to interact with UV. The aged microplastic samples were analyzed by Fourier-transform infrared spectroscopy (FT-IR), Raman, and X-ray photoelectron spectroscopy (XPS), to determine the surface changes with respect to leachate formation. Results indicated that all microplastics had increasing carbonyl indices when aged by UV with polystyrene being the greatest. These findings affirm that the leachate formation is an interfacial interaction and could be a significant source of organic compound influx to natural waters due to the extremely abundant occurrence of microplastics and their large surface areas.more » « less
-
Iron (Fe) is ubiquitous in nature and found as Fe II or Fe III in minerals or as dissolved ions Fe 2+ or Fe 3+ in aqueous systems. The interactions of soluble Fe have important implications for fresh water and marine biogeochemical cycles, which have impacts on global terrestrial and atmospheric environments. Upon dissolution of Fe III into natural aquatic systems, organic carboxylic acids efficiently chelate Fe III to form [Fe III –carboxylate] 2+ complexes that undergo a wide range of photochemistry-induced radical reactions. The chemical composition and photochemical transformations of these mixtures are largely unknown, making it challenging to estimate their environmental impact. To investigate the photochemical process of Fe III –carboxylates at the molecular level, we conduct a comprehensive experimental study employing UV-visible spectroscopy, liquid chromatography coupled to photodiode array and high-resolution mass spectrometry detection, and oil immersion flow microscopy. In this study, aqueous solutions of Fe III –citrate were photolyzed under 365 nm light in an experimental setup with an apparent quantum yield of ( φ ) ∼0.02, followed by chemical analyses of reacted mixtures withdrawn at increment time intervals of the experiment. The apparent photochemical reaction kinetics of Fe 3+ –citrates (aq) were expressed as two generalized consecutive reactions of with the experimental rate constants of j 1 ∼ 0.12 min −1 and j 2 ∼ 0.05 min −1 , respectively. Molecular characterization results indicate that R and I consist of both water-soluble organic and Fe–organic species, while P compounds are a mixture of water-soluble and colloidal materials. The latter were identified as Fe–carbonaceous colloids formed at long photolysis times. The carbonaceous content of these colloids was identified as unsaturated organic species with low oxygen content and carbon with a reduced oxidation state, indicative of their plausible radical recombination mechanism under oxygen-deprived conditions typical for the extensively photolyzed mixtures. Based on the molecular characterization results, we discuss the comprehensive reaction mechanism of Fe III –citrate photochemistry and report on the formation of previously unexplored colloidal reaction products, which may contribute to atmospheric and terrestrial light-absorbing materials in aquatic environments.more » « less
-
none. (Ed.)Foraminifera are single celled organisms that have tests that are composed of calcium carbonate or detrital materials. The assemblages of foraminifera have been influenced by their immediate environment which depict the influence and results of man’s activities and other natural processes that occur in the environment. These environmental changes include salinity, pH, hydrocarbon pollution and organic matter. With these factors, paleoenvironmental interpretations are made by identifying the different patterns in the foraminifera communities. Variations in oxygen concentrations at the sediment-water interface have a significant impact on benthic foraminiferal assemblages and morphologic properties. This is seen in the vertical distribution of foraminifera in response to factors such as food, pore water, and oxygen. This study documents foraminiferal ecology and abundances across an oxygen transect off the coast of San Diego. Available oxygen ranges from >1.0ml/l are considered oxic; O2 values from 0.1 - 1.0ml/l will be considered dysoxic and O2 values <0.10ml/l will be considered anoxic. Previous work in this region has suggested that sediment grain size, rather than oxygen availability, may have as much of an impact on foraminiferal assemblages. These observations were made based on the fact that Cibicidoides wuellerstorfi, an epibenthic foraminifera preferring elevated substrates in well-oxygenated environments, were found in greater abundances at areas with coarser grained materials despite low available oxygen. C. wuellerstorfi has also been found to have I/Ca and test porosity (size and abundance of pores on the surface of the test) which correlate to the available oxygen in bottom waters at the time of test formation. Not only will this study document foraminiferal assemblages and abundances across an oxygen transect, but C. wuellerstorfi from key oxygen environments will be examined under SEM and used in porosity and I/Ca analyses which will contribute to the development of a quantitative oxygen proxy. The development of this quantitative oxygen proxy is essential because despite oxygen being one of the primary variables influencing major geochemical and faunal responses within the world’s ocean, no clear proxy currently exists in paleoceanographic reconstructions.more » « less
-
null (Ed.)Abstract. In the aqueous phase, fine particulate matter can form reactive species (RS)that influence the aging, properties, and health effects of atmosphericaerosols. In this study, we explore the RS yields of aerosol samples froma remote forest (Hyytiälä, Finland) and polluted urban locations(Mainz, Germany; Beijing, China), and we relate the RS yields to differentchemical constituents and reaction mechanisms. Ultra-high-resolution massspectrometry was used to characterize organic aerosol composition, electronparamagnetic resonance (EPR) spectroscopy with a spin-trapping technique wasapplied to determine the concentrations of ⚫OH,O2⚫-, and carbon- or oxygen-centered organic radicals, anda fluorometric assay was used to quantify H2O2. The aqueousH2O2-forming potential per mass unit of ambient PM2.5(particle diameter < 2.5 µm) was roughly the same for allinvestigated samples, whereas the mass-specific yields of radicals werelower for sampling sites with higher concentrations of PM2.5. Theabundances of water-soluble transition metals and aromatics in ambientPM2.5 were positively correlated with the relative fraction of⚫OH and negatively correlated with the relative fraction ofcarbon-centered radicals. In contrast, highly oxygenated organic molecules(HOM) were positively correlated with the relative fraction ofcarbon-centered radicals and negatively correlated with the relativefraction of ⚫OH. Moreover, we found that the relative fractionsof different types of radicals formed by ambient PM2.5 were comparableto surrogate mixtures comprising transition metal ions, organichydroperoxide, H2O2, and humic or fulvic acids. The interplay oftransition metal ions (e.g., iron and copper ions), highly oxidized organicmolecules (e.g., hydroperoxides), and complexing or scavenging agents (e.g.,humic or fulvic acids) leads to nonlinear concentration dependencies inaqueous-phase RS production. A strong dependence on chemical compositionwas also observed for the aqueous-phase radical yields oflaboratory-generated secondary organic aerosols (SOA) from precursormixtures of naphthalene and β-pinene. Our findings show how thecomposition of PM2.5 can influence the amount and nature ofaqueous-phase RS, which may explain differences in the chemical reactivityand health effects of particulate matter in clean and polluted air.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/w13213120
