The apparent quantum yield matrix (AQY-M) of CDOM photobleaching in estuarine, coastal, and oceanic surface waters.

The photochemical degradation of chromophoric dissolved organic matter (CDOM) upon solar exposure, known as photobleaching, can significantly alter the optical properties of the surface ocean. By leading to the breakdown of UV- and visible-radiation-absorbing moieties within dissolved organic matter, photobleaching regulates solar heating, the vertical distribution of photochemical processes, and UV exposure and light availability to the biota in surface waters. Despite its biogeochemical and ecological relevance, this sink of CDOM remains poorly quantified. Efforts to quantify photobleaching globally have long been hampered by the inherent challenge of determining representative apparent quantum yields (AQYs) for this process, and by the resulting lack of understanding of their variability in natural waters. Measuring photobleaching AQY is made challenging by the need to determine AQY matrices (AQY-M) that capture the dual spectral dependency of this process (i.e., magnitude varies with both excitation wavelength and response wavelength). A new experimental approach now greatly facilitates the quantification of AQY-M for natural waters, and can help address this problem. Here, we conducted controlled photochemical experiments and applied this new approach to determine the AQY-M of 27 contrasting water samples collected globally along the land-ocean aquatic continuum (i.e., rivers, estuaries, coastal ocean, and open ocean). The experiments and analyses revealed considerable variability in the magnitude and spectral characteristics of the AQY-M among samples, with strong dependencies on CDOM composition/origin (as indicated by the CDOM 275-295-nm spectral slope coefficient, S275-295), solar exposure duration, and water temperature. The experimental data facilitated the development and validation of a statistical model capable of accurately predicting the AQY-M from three simple predictor variables: 1) S275-295, 2) water temperature, and 3) a standardized measure of solar exposure. The model will help constrain the variability of the AQY-M when modeling photobleaching rates on regional and global scales.

Evaluation of fatty acids and carnitine as biomarkers of PFOS exposure in biota (fish and dolphin) from Galveston Bay and the northwestern Gulf of Mexico.

Perfluorooctane sulfonate (PFOS) is a ubiquitous pollutant that elicits a wide range of toxic effects in exposed biota. Coastal zones in highly urbanized or industrial areas are particularly vulnerable to PFOS pollution. At present, information is lacking on biomarkers to assess PFOS effects on aquatic wildlife. This study investigated the efficacy of l-carnitine (or carnitine) and fatty acids as biomarkers of PFOS exposure in aquatic biota. The levels of PFOS, total and free carnitine, and 24 fatty acids (measured as fatty acid methyl esters or FAMEs) were measured in the liver, and muscle or blubber, of fish and dolphins sampled from Galveston Bay and the northern Gulf of Mexico (nGoM). Overall, bottlenose dolphins (Tursiops truncatus) had the highest hepatic PFOS levels. Galveston Bay fish, gafftopsail catfish (Bagre marinus), red drum (Sciaenops ocellatus), and spotted seatrout (Cynoscion nebulosus), had hepatic PFOS levels ∼8-13× higher than nGoM pelagic fish species, red snapper (Lutjanus campechanus) and yellowfin tuna (Thunnus albacares). The multivariate analysis of PFOS liver body-burdens and biomarkers found carnitine to be a more modal biomarker of PFOS exposure than FAMEs. Significant positive correlation of hepatic PFOS levels with total carnitine was evident for biota from Galveston Bay (fish only), and a significant correlation between PFOS and total and free carnitine was evident for biota from the nGoM (fish and dolphins). Given the essential role of carnitine in mediating fatty acid ß-oxidation, our results suggest carnitine to be a likely candidate biomarker of environmental PFOS exposure and indicative of potential dyslipidemia effects.

How does buoyancy behavior impact microplastic transport in an estuarine environment?

Much is still unknown about the transport behavior of microplastic pollutants within the marine environment, particularly smaller scale coastal systems such as estuaries. Through the use of a Lagrangian particle-tracking model coupled with a validated 3D hydrodynamic model, we examined the transport, pathway and ultimate fate of microplastic particles, both in an idealized estuary and Galveston Bay, Texas, USA. Emphasis was placed on differences based on settling behavior (neutrally versus negatively buoyant), use of random walk for diffusion processes, and release location. For Galveston Bay, settling behavior had a noteworthy impact on both the transport pathway of microplastic particles, as well as overall time spent within the bay. Particles with negative buoyancy were retained approximately seven times longer than those with neutral buoyancy. Negatively buoyant particles also showed a tendency to be dispersed eastward to Trinity Bay through the bottom baroclinic flow, while neutrally buoyant particles took a more direct route along the ship channel to the mouth of the bay. Idealized model simulations suggest impact of settling depends on the vertical mixing strength. For a system with stronger tidal mixing, negatively buoyant particles with small settling velocities may still behave similarly to neutrally buoyant particles, and differences only become apparent for particles that sink rather quickly (> 10 m d-1). Future sea-level rise or channel deepening tends to flush out neutrally buoyant particles more quickly, while increasing the retention time for negatively buoyant particles. Our results suggest that plastics within estuaries could show substantially different behavior depending on their buoyancy characteristics, highlighting a need to quantify specific settling velocities of plastic pollutants entering the coastal estuarine system.

Functionally diverse microbial communities show resilience in response to a record-breaking rain event.

Estuaries provide many ecosystem services and host a majority of the world's population. Here, the response of microbial communities after a record-breaking flood event in a highly urbanized estuary was followed. Hurricane Harvey (hereafter Harvey) was a category 4 hurricane that made landfall on the Texas coast in 2017 and lashed the Houston area with 1.4-1.7 × 1010 m3 of rainfall, disrupting the natural gradients of nutrients and salinity. Here, we utilized metagenomics to analyze how Harvey altered the microbial community of Galveston Bay over five weeks following the storm. We hypothesized that the community would shift from a marine dominated community to that of a terrestrial and freshwater origin. We found that following the storm there were changes in the distribution of species with specific metabolic capacities, such as Cyanobacteria, enriched in oxygenic photosynthesis and nitrogen fixation genes, as well as Verrucomicrobia and Betaproteobacteria, with high prevalence of the SOX complex and anoxygenic photosynthesis genes. On the other hand, dominant members of the community with more diverse metabolic capabilities showed less fluctuations in their distribution. Our results highlight how massive precipitation disturbances can alter microbial communities and how the coalescence of diverse microorganisms creates a resilient community able to maintain ecosystem services even when the system is in an altered state.

PFASs pollution in Galveston Bay surface waters and biota (shellfish and fish) following AFFFs use during the ITC fire at Deer Park (March 17th-20th 2019), Houston, TX.

The use of aqueous film forming foams (AFFFs) as fire retardants is an critical point-source for per- and polyfluoroalkyl substances (PFASs) pollution into the aquatic environment. This study investigated PFASs pollution in the surface waters and biota (shellfish and fish) of Galveston Bay, following AFFFs use to extinguish a petrochemical fire (March 17th to 20th, 2019) of oil storage tanks at the International Terminals Company (ITC) in Deer Park (Houston, TX). The levels of up to twelve EPA priority PFASs were measured in surface waters and biota from March-November 2019. PFASs levels in surface waters showed mean total levels in March and April 2019 to be from 4× to ~300× higher than those measured in the following months. PFOS (perfluorooctanesulfonic acid) was the most abundant homolog measured at ≥66% of total PFASs. Maximal PFOS levels exceeded the State of Texas' water regulatory limit of 0.6 µg L-1 in 3% of the samples analyzed in March and April 2019. PFOS was also the most prominent homolog (≥66% of total PFASs) measured in eastern oysters (Crassostrea virginica), red drum (Sciaenops ocellatus), gafftopsail catfish (Bagre marinus), and spotted seatrout (Cynoscion nebulosus). A statistically significant elevation of PFOS body-burdens was measured in oysters and spotted seatrout in April and May 2019, respectively. A Hazard Ratio calculation for seafood safety suggests an advisory of 1-2 meals per week for gafftopsail catfish and red drum, and 2 meals per week for spotted seatrout to be protective for human exposure to PFOS. The levels in oysters indicated no immediate concerns for the dietary exposure of humans. Our results highlight a need for continual monitoring to assess the long-term fate and seafood advisories for PFASs.

Polycyclic aromatic hydrocarbons (PAHs) and putative PAH-degrading bacteria in Galveston Bay, TX (USA), following Hurricane Harvey (2017).

Hurricane Harvey was the wettest hurricane in US history bringing record rainfall and widespread flooding in Houston, TX. The resulting storm- and floodwaters largely emptied into the Galveston Bay. Surface water was collected from 10 stations during five cruises to investigate the concentrations and sources of 16 priority polycyclic aromatic hydrocarbons (PAHs), and relative abundances of PAH-degrading bacteria. Highest PAH levels (102-167 ng/L) were detected during the first sampling event, decreasing to 36-69 ng/L within a week. Four sites had elevated concentrations of carcinogenic benzo[a]pyrene that exceeded the Texas Standard for Surface Water threshold. The highest relative abundances of known PAH-degrading bacteria Burkholderiaceae, Comamonadaceae, and Sphingomonadales were detected during the first and second sampling events. PAH origins were about 60% pyrogenic, 2% petrogenic, and the remainder of mixed sources. This study improves our understanding on the fate, source, and distributions of PAHs in Galveston Bay after an extreme flooding event.

Ultralow Sample Volume Cupric Sulfate Oxidation Method for the Analysis of Dissolved Lignin.

A novel cupric sulfate (CuSO4) oxidation method was developed to enable the analysis of dissolved lignin phenols in small volumes of open ocean seawater (<200 mL for deep ocean) or river water (<17 mL) samples. Dissolved lignin phenols were isolated by automated reversed-phase (octadecyl) extraction from seawater before oxidation, whereas for freshwater samples, oxidation was performed without prior extraction. Optimized reaction conditions using alkaline CuSO4 at 150 °C effectively limited losses of lignin phenols and suppressed side reactions at 5-100 µg of sample organic carbon. The method yielded up to ∼33% higher lignin phenol concentrations and 24-36% lower acid/aldehyde ratios of lignin phenols than existing CuO oxidation methods. The microscale design (200 µL reaction volume) resulted in extremely low blanks allowing accurate and precise quantification of lignin phenols. A comparison of silica-based octadecyl-bonded sorbents (C18) with copolymer-type sorbents (PPL) indicated that sorbent type affected concentrations and diagnostic ratios of dissolved lignin phenols. For robust intercomparability of measured lignin phenol concentrations and in consideration of method detection limits for quantification, a constant sample organic carbon content of ∼30 µg C and the addition of 150 µg ascorbic acid-C are recommended. Small sample volumes avoid time-consuming extraction steps in the field, and the simplified oxidation and sample processing procedures make the new method ideal for high-throughput analysis of dissolved lignin phenols in marine and freshwater environments.

A rapid and sensitive method for the analysis of lignin phenols in environmental samples using ultra-high performance liquid chromatography-electrospray ionization-tandem mass spectrometry with multiple reaction monitoring.

A novel ultra-high performance liquid chromatography-electrospray ionization-tandem mass spectrometry method was developed to enable the analysis of ultra-low levels of lignin phenols (<100 fmol) in environmental samples. The method included a sample clean-up with a polymer sorbent based solid-phase extraction and reversed-phase chromatography that allowed separation of all lignin phenols with minimal interference from co-eluting matrix components. The application of 13C-labeled surrogate standards effectively compensated for variability associated with sample preparation and ion suppression. The method was fully validated and compared to gas chromatography-electron impact ionization-tandem mass spectrometry for Suwannee River humic acid standard reference material and extracted riverine dissolved organic matter. The comparison demonstrated the robustness and suitability of the method for ultra-low lignin phenol concentrations and high matrix interference. The simple and fast sample preparation coupled to analysis without derivatization makes it feasible for routine and high-volume analyses.

Centennial record of anthropogenic impacts in Galveston Bay: Evidence from trace metals (Hg, Pb, Ni, Zn) and lignin oxidation products.

During the 20th century the impacts of industrialization and urbanization in Galveston Bay resulted in significant shifts in trace metals (Hg, Pb, Ni, Zn) and vascular plant biomarkers (lignin phenols) recorded within the surface sediments and sediment cores profile. A total of 22 sediment cores were collected in Galveston Bay in order to reconstruct the historical input of Hg, Pb, Ni, Zn and terrestrial organic matter. Total Hg (T-Hg) concentration ranged between 6 and 162 ng g-1 in surface sediments, and showed decreasing concentrations southward from the Houston Ship Channel (HSC) toward the open estuary. Core profiles of T-Hg and trace metals (Ni, Zn) showed substantial inputs starting in 1905, with peak concentrations between 1960 and 1970's, and decreasing thereafter with exception to Pb, which peaked around 1930-1940s. Stable carbon isotopes and lignin phenols showed an increasing input of terrestrial organic matter driven by urban development within the watershed in the early 1940s. Both the enrichment factor and the geoaccumulation index (Igeo) for T-Hg as a measure of the effectiveness of environmental management practices showed substantial improvements since the 1970s. The natural recovery rate in Galveston Bay since the peak input of T-Hg was non-linear and displayed a slow recovery during the twenty-first century.

Origins and transformations of dissolved organic matter in large Arctic rivers.

Arctic river watersheds are important components of the global climate system and show an amplified response to climate change. Here, we characterize origins and transformations of dissolved organic matter (DOM) in five major Arctic rivers (Kolyma, Lena, Yenisei, Ob, Mackenzie) over 3 years with seasonal sampling periods using measurements of carbohydrates, amino acids, bacterial biomarkers (D-amino acids), and plant protein biomarkers (hydroxyproline). A strong seasonal cycle of bioavailable DOM export was observed that correlated with discharge, vegetation, river morphology and water residence time. The chemical composition of bioavailable DOM was different among rivers reflecting unique characteristics of Arctic river watersheds. Trends in specific bacterial biomarkers were synchronous to changes in bacterial community compositions demonstrating that bacterial communities responded to the seasonal shifts in organic matter quality and chemical composition. Extensive heterotrophic processing of plant and soil-derived DOM resulted in major inputs of bacterial detritus, and bacterial organic matter accounted for 21-42% of DOC in all watersheds. Dissolved organic nitrogen sources were dominated by bacterially-derived nitrogen and important contributions of soluble plant protein during the Spring freshet. Overall, our results demonstrated the importance of watershed characteristics and bacterial metabolism in regulating DOM composition, reactivity and carbon fluxes in Arctic river watersheds.

Peatland Ecosystem Processes in the Maritime Antarctic During Warm Climates.

We discovered a 50-cm-thick peat deposit near Cape Rasmussen (65.2°S), in the maritime Antarctic. To our knowledge, while aerobic 'moss banks' have often been examined, waterlogged 'peatlands' have never been described in this region before. The waterlogged system is approximately 100 m2, with a shallow water table. Surface vegetation is dominated by Warnstorfia fontinaliopsis, a wet-adapted moss commonly found in the Antarctic Peninsula. Peat inception was dated at 2750 cal. BP and was followed by relatively rapid peat accumulation (~0.1 cm/year) until 2150 cal. BP. Our multi-proxy analysis then shows a 2000-year-long stratigraphic hiatus as well as the recent resurgence of peat accumulation, sometime after 1950 AD. The existence of a thriving peatland at 2700-2150 cal. BP implies regionally warm summer conditions extending beyond the mid-Holocene; this finding is corroborated by many regional records showing moss bank initiation and decreased sea ice extent during this time period. Recent peatland recovery at the study site (<50 years ago) might have been triggered by ongoing rapid warming, as the area is experiencing climatic conditions approaching those found on milder, peatland-rich sub-Antarctic islands (50-60°S). Assuming that colonization opportunities and stabilization mechanisms would allow peat to persist in Antarctica, our results suggest that longer and warmer growing seasons in the maritime Antarctic region may promote a more peatland-rich landscape in the future.

Pan-Arctic distributions of continental runoff in the Arctic Ocean.

Continental runoff is a major source of freshwater, nutrients and terrigenous material to the Arctic Ocean. As such, it influences water column stratification, light attenuation, surface heating, gas exchange, biological productivity and carbon sequestration. Increasing river discharge and thawing permafrost suggest that the impacts of continental runoff on these processes are changing. Here, a new optical proxy was developed and implemented with remote sensing to determine the first pan-Arctic distribution of terrigenous dissolved organic matter (tDOM) and continental runoff in the surface Arctic Ocean. Retrospective analyses revealed connections between the routing of North American runoff and the recent freshening of the Canada Basin, and indicated a correspondence between climate-driven changes in river discharge and tDOM inventories in the Kara Sea. By facilitating the real-time, synoptic monitoring of tDOM and freshwater runoff in surface polar waters, this novel approach will help understand the manifestations of climate change in this remote region.

Dissolved oxygen as an indicator of bioavailable dissolved organic carbon in groundwater.

Concentrations of dissolved oxygen (DO) plotted vs. dissolved organic carbon (DOC) in groundwater samples taken from a coastal plain aquifer of South Carolina (SC) showed a statistically significant hyperbolic relationship. In contrast, DO-DOC plots of groundwater samples taken from the eastern San Joaquin Valley of California (CA) showed a random scatter. It was hypothesized that differences in the bioavailability of naturally occurring DOC might contribute to these observations. This hypothesis was examined by comparing nine different biochemical indicators of DOC bioavailability in groundwater sampled from these two systems. Concentrations of DOC, total hydrolysable neutral sugars (THNS), total hydrolysable amino acids (THAA), mole% glycine of THAA, initial bacterial cell counts, bacterial growth rates, and carbon dioxide production/consumption were greater in SC samples relative to CA samples. In contrast, the mole% glucose of THNS and the aromaticity (SUVA(254)) of DOC was greater in CA samples. Each of these indicator parameters were observed to change with depth in the SC system in a manner consistent with active biodegradation. These results are uniformly consistent with the hypothesis that the bioavailability of DOC is greater in SC relative to CA groundwater samples. This, in turn, suggests that the presence/absence of a hyperbolic DO-DOC relationship may be a qualitative indicator of relative DOC bioavailability in groundwater systems.

Characterization of lignin by gas chromatography and mass spectrometry using a simplified CuO oxidation method.

An efficient and high-throughput method to characterize lignin in environmental samples using alkaline CuO oxidation and capillary gas chromatography with mass detection is presented. Monomeric lignin phenols released during oxidation were selectively extracted using a polymer-based solid phase sorbent rather than liquid phase extraction. Sample size and matrix were found to influence lignin phenol yields. Increasing the sample size to an organic carbon content ≥1.5 mg of C minimizes phenol oxidation losses, and the addition of glucose as a sacrificial carbon source helped minimize oxidation losses in samples with <5 mg of organic carbon.

Biochemical indicators for the bioavailability of organic carbon in ground water.

The bioavailability of total organic carbon (TOC) was examined in ground water from two hydrologically distinct aquifers using biochemical indicators widely employed in chemical oceanography. Concentrations of total hydrolyzable neutral sugars (THNS), total hydrolyzable amino acids (THAA), and carbon-normalized percentages of TOC present as THNS and THAA (referred to as "yields") were assessed as indicators of bioavailability. A shallow coastal plain aquifer in Kings Bay, Georgia, was characterized by relatively high concentrations (425 to 1492 microM; 5.1 to 17.9 mg/L) of TOC but relatively low THNS and THAA yields (approximately 0.2%-1.0%). These low yields are consistent with the highly biodegraded nature of TOC mobilized from relatively ancient (Pleistocene) sediments overlying the aquifer. In contrast, a shallow fractured rock aquifer in West Trenton, New Jersey, exhibited lower TOC concentrations (47 to 325 microM; 0.6 to 3.9 mg/L) but higher THNS and THAA yields (approximately 1% to 4%). These higher yields were consistent with the younger, and thus more bioavailable, TOC being mobilized from modern soils overlying the aquifer. Consistent with these apparent differences in TOC bioavailability, no significant correlation between TOC and dissolved inorganic carbon (DIC), a product of organic carbon mineralization, was observed at Kings Bay, whereas a strong correlation was observed at West Trenton. In contrast to TOC, THNS and THAA concentrations were observed to correlate with DIC at the Kings Bay site. These observations suggest that biochemical indicators such as THNS and THAA may provide information concerning the bioavailability of organic carbon present in ground water that is not available from TOC measurements alone.

Application of biotin-4-fluorescein in homogeneous fluorescence assays for avidin, streptavidin, and biotin or biotin derivatives.

Biotin-4-fluorescein (B4F) is a convenient molecular probe for (strept)avidin and for unlabeled biotin in homogeneous fluorescence assays. The primary standard is a 16 microM working solution of d-biotin which is used to titrate an aliquot of a (strept)avidin stock solution while monitoring the tryptophane fluorescence of (strept)avidin. This serves to standardize the (strept)avidin stock solution, an aliquot of which is then titrated with a roughly 16 microM working solution of B4F while monitoring the fluorescence of B4F. Specific binding is accompanied by quenching, but after saturation of all binding sites, the appearance of free ligand causes a sharp rise of intense fluorescence, the beginning of which allows to calculate the effective concentration of B4F in the working solution. Measurement of avidin in a crude sample is exemplified by mixing 8 pmol of B4F with various amounts of diluted egg white in a volume of 1 mL. Hereby, the extent of fluorescence quenching linearly correlates with the concentration of functional avidin. Moreover, a sharp minimum of fluorescence is observed when exactly 2 pmol of avidin is present in the sample. The latter assay has been adapted to measure between 0.5 and 5 pmol of d-biotin in 1 mL of sample by adding 1.9 pmol of avidin and 8 pmol of B4F. This competitive assay correctly measures the small dose of d-biotin in multivitamin tablets (e.g., 150 microg in 5 g of solid) after subtracting the background fluorescence of the colored aqueous solution.