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Abstract: The 14C and 13C content of the hydrophobic fraction (C18 extractable) of dissolved organic carbon (DOC) in Wilmington North Carolina USA rainwater was determined for six rain events to elucidate potential sources. A two end member mass-balance calculation indicated that 42–61% of the hydrophobic DOC was of fossil fuel origin compared to previously published values (4–24%) for bulk rain DOC indicating a strong anthropogenic contribution to the hydrophobic component. All fossil fuel derived organic carbon in the bulk DOC (∼15% fossil fuel derived) could be accounted for in the hydrophobic fraction (∼52% fossil fuel derived) which represents approximately 1/3 of the bulk DOC. The δ13C values of the hydrophobic DOC were consistent (−28.8 ± 0.9‰) similar to that for terrestrial and fossil fuel derived organic carbon. This is in contrast to previously published bulk rain DOC δ13C values that displayed a strong influence of air-mass back-trajectory with δ13C values ranging from −20.8‰ (typical of marine organic carbon) for marine air-mass back-trajectory rain to −28.2‰ (typical of terrestrial or fossil fuel derived organic carbon) for terrestrial air-mass back-trajectory rain. The combination of 14C and 13C isotopic data strongly suggests that a large fraction of hydrophobic organic material in rain comes from incompletely combusted fossil fuels. Changes in energy usage patterns and efforts to reduce fossil fuel emissions will alter the abundance of this hydrophobic material in the atmosphere which may impact the spectral distribution of sunlight reaching the earth''s surface as well as the degree of oceanic primary productivity. [Copyright &y& Elsevier]

Abstract: The purpose of this study was to determine the flux of dissolved organic carbon (DOC) from high-energy beach sand to the coastal ocean. The DOC concentration of seawater was measured before and after exposure to the beach sand in laboratory experiments. Increases were observed in all experiments (n=36) conducted on seawater and high-energy beach sand collected on a monthly basis for one year. Final dissolved organic carbon in seawater after exposure to surface sands were positively correlated with water column DOC concentrations measured in the surf zone at the same time of sand collection for laboratory experiments. Increases in DOC during laboratory experiments displayed marked seasonality with larger increases observed during summer with a corresponding low DOC carbon to nitrogen ratio (C:N) suggesting phytoplankton as the source of DOC during this time of year. Higher DOC C:N was observed during winter indicating a more aged organic material as the source of DOC during this time of low flux. Sandy beach sediments release over an order of magnitude more DOC per meter squared compared to coastal shelf sediments and rainwater suggesting that in locations where there are no direct river inputs these beach environments play a significant, previously unrecognized role as an external source of DOC to the immediate coastal ocean. It is likely that DOC released from these environments has a significant effect on surf zone biogeochemistry potentially affecting oxygen concentrations in coastal regions. [Copyright &y& Elsevier]

• Sediment irradiation enhanced dissolved organic carbon release by up to 43%. • Suspended sediment was a source of labile photo-released dissolved organic carbon. • Photoinduced lability was attributed to CHOS, CHON, and marine-like humic compounds. Photochemically-released dissolved organic matter (PR-DOM) from resuspended sediments is an understudied flux of dissolved organic carbon (DOC) and nutrients with the potential to influence estuarine microbial food webs. There is currently limited knowledge on the composition, lability and biological alterations of this material once released into the water column. This study addresses the composition and fate of PR-DOM from resuspended sediments of the Cape Fear River Estuary (CFRE) in southeastern North Carolina. Six-hour irradiation released 22–44% more DOC, and PR-DOM was of a different composition and enhanced lability, relative to dark controls. Irradiation led to release of humic-like DOM, indicated by increased chromophoric and fluorescent dissolved organic matter, substantial increases in the humification index, and production of oxidized higher molecular weight compounds with higher aromaticity, relative to dark controls. However, DOM of lower molecular weight and reduced aromaticity was produced as well. This was indicated by increased spectral slope (S 275–295) and decreased specific ultraviolet absorbance at 254 nm (SUVA 254), relative to dark controls. This latter pool of DOM may be linked to nitrogen-(N-) and sulfur-(S-)containing compounds that were photodegraded or biologically altered during irradiation experiments. In subsequent lability incubation experiments, degradation of PR-DOM was more rapid than DOM released from dark controls, especially for marine humic-like fluorophores. Incubation of PR-DOM led to an 8-fold increase in compounds with molecular formulas that were unique to light-exposed DOM relative to unexposed DOM, the majority of which were N- and S-containing compounds. Given that coastal sediments are typically enriched in these nutrients, N- and S-containing compounds appear to influence the lability of PR-DOM from estuarine resuspended sediments. Estimated lability of photoreleased DOC from resuspension events in the CFRE is comparable to previous bioavailable DOC estimates and suggests that episodic photochemical interactions with sediments may act as a previously unrecognized source of labile DOC to bacteria and plankton in these coastal waters. [ABSTRACT FROM AUTHOR]

Highlights: [•] Sucrose was the dominant carbohydrate detected in the spring and summer. [•] Glucose was the dominant carbohydrate detected in the autumn and winter. [•] Carbohydrates were highest in rain events with terrestrial air mass origins. [•] Carbohydrates usually made a small contribution (<1%) to dissolved organic carbon. [Copyright &y& Elsevier]

The H+ (aq) concentration in Wilmington, NC, precipitation has decreased by approximately 50% during the preceding two decades, similar to trends seen nationwide. The decrease in acidity is important because solution pH plays a key role in atmospheric reactions, and because the change is so large. This study presents the first long-range study of dissolved organic carbon (DOC) levels in precipitation which demonstrates that DOC concentrations have decreased by approximately half in Wilmington, NC, precipitation. The concentrations of H+ (aq) and DOC are highly correlated primarily because small organic acids contribute to both DOC and H+ (aq) in precipitation. Ammonium ion concentrations in precipitation have increased due to increased agricultural activities, and this also affects precipitation pH. The reduction of SO2 emissions in 1995 imposed by the Clean Air Act Amendment, better control of emissions of volatile organic compounds, and the increase in ammonia emissions all contribute to the decreasing H+ (aq) in precipitation nationwide. These compositional changes in precipitation have many environmental implications, such as decreased acid deposition to lakes, changing speciation for trace metals in precipitation, increased ammonium deposition to coastal waters, and decreased DOC transport to the open ocean. [ABSTRACT FROM AUTHOR]

Measurements of hydrogen peroxide (H2O2), pH, dissolved organic carbon (DOC), and inorganic anions (chloride, nitrate, and sulfate) in rainwater were conducted on an event basis at a single site in Wilmington, NC for the past decade in a study that included over 600 individual rain events. Annual volume weighted average (VWA) H2O2 concentrations were negatively correlated (p < 0.001) with annual VWA nonseasalt sulfate (NSS) concentrations in low pH (<5) rainwater. Under these conditions H2O2 is the primary aqueous-phase oxidant of SO2 in the atmosphere. We attribute the increase of H2O2 to decreasing SO2 emissions which has had the effect of reducing a major tropospheric sink for H2O2. Annual VWA H2O2 concentrations in low pH (<5) rains showed a significant increase over the time scale of this study, which represents the only long-term continuous data set of H2O2 concentrations in wet deposition at a single location. This compositional change has important implications because H2O2 is a source of highly reactive free radicals so its increase reflects a higher overall oxidation capacity of atmospheric waters. Also, because rainwater is an important mechanism by which H2O2 is transported from the atmosphere to surface waters, greater wet deposition of H2O2 could influence the redox chemistry of receiving watersheds which typically have concentrations 2-3 orders of magnitude lower than rainwater. [ABSTRACT FROM AUTHOR]

Abstract: Presently there is a paucity of knowledge regarding the influence of sedimentary organic matter (SOM) source and diagenetic state on photolytic fluxes of dissolved organic matter and nutrients from sediments likely to be resuspended during high energy events such as storms. Here we present data on the photochemical release of dissolved organic carbon (DOC), total dissolved nitrogen (TDN), dissolved organic nitrogen (DON), NH4 +, and PO4 3− from the fine fraction of sediments obtained along an estuarine gradient, coupled with analyses of biogeochemical and molecular indicators of SOM source. Photochemical release of DOC and PO4 3− was significantly higher than dark controls at all sites. DOC photorelease from fine (

Per- and polyfluoroalkyl substances (PFAS) have become ubiquitous environmental contaminants found in many parts of the globe and in all environmental compartments. The phase out of legacy C8 PFAS has led to an increase in functionality of the carbon backbone chain to include ether linkages and branching points. With the increased production of functionalized PFAS, there remains a paucity of information regarding the occurrence of constitutional isomers in the environment. In this study, a series of novel PFAS constitutional isomers were detected by high resolution mass spectrometry and characterized by MS/MS in river water collected weekly over 40 weeks. Constitutional isomers of C 4 H 2 F 8 O 4 S 1 (−1.8 ± 2.5 ppm) were detected for the first time in 83% of the samples analyzed and the MS/MS fragmentation patterns clearly indicated there were two coeluting isomers present. Two chromatographically resolved peaks with deprotonated molecular formula C 7 H 1 F 14 O 5 S 1 (1.9 ± 2.7 and 2.2 ± 3.1 ppm) were detected in 85% of the samples measured. MS/MS fragmentation patterns and a standard provided by a fluorochemical manufacturer confirmed the two isomers. A series of novel chlorinated PFAS were detected (M-1: C 11 H 1 Cl 1 F 20 O 5 0.9 ± 2.7 ppm and C 14 H 1 Cl 1 F 26 O 6 2.1 ± 2.6 ppm) in 34% of the water samples analyzed. The exact structure is not confirmed. River sediment collected below the water sample location contained several of the compounds detected in the water column illustrating the connectivity between the environmental compartments. Results highlight the need for further studies on the occurrence of isomers and authentic standards to confirm structures. • Constitutional Isomers of C 7 H 1 F 14 O 5 S 1 (M-1) detected in water and sediments. • Novel homologous series of monochlorinated perfluoroether carboxylic acids. • First reported differentiation of constitutional isomers of C 4 H 1 F 8 O 4 S 1 (M-1) by MS/MS. [ABSTRACT FROM AUTHOR]