Parent and alkyl PAHs (51 compounds and alkyl homologues) have been quantified in suspended particulates and sediments (345 samples) from the Fraser River system, British Columbia, Canada. The best ...potential to distinguish natural and anthropogenic sources is exhibited by ratios of the principal mass 178, 202, 228 and 276 parent PAHs, 1,7/2,6+1,7-DMP (dimethylphenanthrene), the phenanthrene/anthracene and fluoranthene/pyrene alkyl PAH series and several less commonly applied PAHs (e.g. acephenanthrylene and pentaphene). Using these ratios we infer sources of PAH to the Fraser basin and evaluate the consistency of these source assignments and the suitability of various commonly applied PAH ratios as indicators. PAH ratios and total concentration data reveal a basin lightly impacted by a variety of sources in its remote regions, especially near roads, but heavily impacted in urban areas, particularly near Vancouver. Contamination sources shift from biomass (e.g. wood and grass) burning to vehicle emissions between remote and urban locations. Stormwater and wastewater discharges appear to collect PAH from urban areas and release them as point sources. In contaminated areas ratios are specific for combustion vs. petroleum sources, and some ratios (202 and 276) distinguish biomass or coal from liquid fossil fuel combustion. At lower concentrations multiple sources at times make interpretations based on a single ratio misleading and the higher mass ratios (228 and 276) may be most applicable to urban areas. In all cases the examination of a variety of PAH indicator ratios that encompass a range of masses is necessary for a robust interpretation.
► Terrigenous organic flux to basin sediment responds to glacial–interglacial sea level. ► Lena River basin coals main source for petrogenic hydrocarbons in central Arctic Ocean. ► Anthropogenic PAHs ...absent from basins due to weak particle transport and degradation. ► High MW PAHs provide best tracers of combustion and petroleum in basin sediments. ► PCA and PLS provide robust source apportionment for Arctic Ocean sediments.
We present the first sedimentary biomarker study encompassing the entire Arctic Ocean. A large data set of organic markers for terrigenous, petroleum and combustion inputs alkanes, hopanes and steranes, parent and alkyl polycyclic aromatic hydrocarbons (PAHs) is examined for patterns in space and time using principal components analysis (PCA) and partial least squares (PLS). Biomarker patterns reveal the central Arctic Ocean basin sediments to be compositionally distinct from those of the Mackenzie River/Beaufort Sea and Barents Sea, but similar to those of the Laptev Sea. PAH distributions reflected in PAH ratios and PCA projections demonstrate that Arctic Ocean sediment is dominated by natural inputs to the extent that anthropogenic combustion PAHs are not significant. We find only modest changes between the glacial and post-glacial sediments for atmospherically transported hydrocarbon biomarkers, while particle associated biomarkers were captured strongly at basin edges during the glacial period, and much more evenly transported across basins during the post-glacial period. The orders of magnitude decreases in particle associated petrogenic alkanes and PAHs in central basins during glacial times, coupled with the uniformity of most petrogenic biomarker parameters for most basin and shelf locations, reflect a massive reduction in ice transport that makes the margins the most likely source of petrogenic material for the Pleistocene/Holocene central Arctic basins. The proximity of large coal deposits of various maturity levels along the Lena River, the overlap in PAH and biomarker composition of the Laptev Sea and surficial sediments from the central Arctic Ocean and the location of the Laptev Sea at the origin of the main Transpolar Drift all point to eroded coals from the Lena River/Laptev Sea as the likely source of petrogenic hydrocarbons to the central Arctic Ocean. The ubiquitous presence of allochthonous coal in Arctic Ocean surface sediments provides a major constraint on the use of petrogenic biomarkers to infer the presence of subsurface petroleum reserves.
► Coal from the collier could account for most alkyl PAHs in sediments. ► Waste from a former coal gas plant is a likely source for elevated parent PAHs in sediments. ► Wastewater PAHs from oils and ...liquid fossil fuel combustion soot are dispersed and degraded. ► PAHs in wood char particles predominate in sediments near the outfalls.
Previous studies have suggested that coal from the 1891 shipwreck of a collier off Victoria, BC, Canada is responsible for elevated parent (unsubstituted) PAH concentrations in sediments near deep marine outfalls from Esquimalt and Victoria in the Strait of Juan de Fuca. To resolve this question, we analysed a comprehensive suite of resolved and unresolved complex mixture (UCM) alkanes, tricyclic terpane, hopane and sterane biomarkers, and parent and alkyl polycyclic aromatic hydrocarbons (PAHs) in samples of coal, wastewater and sediments. Composition patterns, principal components analysis (PCA) models and PAH and biomarker ratios all indicate that coal from the collier does not make a dominant contribution to any sediment sample. Mass balance calculations based on the n-C24 content and 24/4 tetracyclic terpane to 26/3R tricyclic terpane ratio in coal provide a particularly good match between predicted and observed alkyl PAH concentrations for sediments with high alkyl naphthalenes and phenanthrene/anthracenes and low UCM, but the predicted coal contribution substantially underestimates the measured parent PAHs for all sediment samples. Methylbenzaanthracene/chrysene profiles for sediments with a dominance of parent PAHs are very close to coal tar, with a marked predominance of methylbenzaanthracenes and the possible 10-methylbenzaanthracene as a major constituent, while the methylchrysenes predominate in coal. Hence, coal from the collier could account for most alkyl PAHs in the sediments, but dredged sediment containing pyrolised coal waste from a former coal gas plant in Victoria Harbour is a more likely source for the samples with elevated parent PAHs. PAH ratios indicate that these sources are superimposed on combustion PAHs introduced by a combination of atmospheric deposition and delivery via stormwater and the outfalls. Parent PAH distributions also suggest that PAHs in wastewater that originate from oils and soot in liquid fossil fuel combustion are dispersed and degraded, while the larger wood char particles (containing PAHs more protected from degradation) settle closer to the outfalls. Overall, results suggest that PAHs have predominant sources in wood combustion, coal and possibly coke, with a likelihood of much lower bioavailability than would be expected from wastewater dominated by oils and soot from vehicle combustion.
Hydrocarbon data for dated sediment cores from Fraser Basin lakes and the Strait of Georgia in Canada reveal a pristine pre-industrial background that remains unaltered in modern sediments far from ...human activities. These pristine sediments contain polycyclic aromatic hydrocarbons (PAHs) from combustion (natural forest and prairie fires), and alkanes and PAHs from weathering of soils containing vascular plant remains and natural petroleum hydrocarbons, and algal production. At other locations examined, however, these natural loadings have been augmented over the past century by hydrocarbons from petroleum, the combustion of liquid (oil, gasoline) and solid (coal, wood) fuels and from processing of wood either directly from disturbed land and slash burning or indirectly through pulp mill effluent. Although contamination is clearest where there are nearby human activities, alkane profiles, PAH distributions and alkane unresolved complex mixtures suggest a widespread contamination from petroleum. Combustion products from human activities can also be identified, although with less source specificity than with the petroleum products. Regional emissions from anthropogenic combustion processes appear to support modern PAH increases within the Fraser River Basin and there is little evidence of inputs from global emissions. Principal components analysis using the new centred log ratio normalisation procedure to normalise data discriminates well between PAHs entering lakes from runoff or the atmosphere and PAH formed diagenetically within lake sediments, as well as between combustion and petroleum PAHs.
On the morning of April 9, 2015, citizens in Vancouver (British Columbia, Canada) awoke to the sight and smell of oil on the shores of popular downtown beaches. Because the oil also had spread over ...the shallow seawater intakes for the Vancouver Aquarium, a preliminary screening of samples was performed as a prompt, first response to assess the risks to the Aquarium collection and guide the emergency operational response. A subsequent, more detailed examination for the presence of spilled oil in sediment, biota and water samples from the Vancouver Harbour region was then conducted based on the analysis of a large suite of alkanes, petroleum biomarkers, parent polycyclic aromatic hydrocarbons (PAHs) and alkyl PAH isomers. Most of the commonly applied biomarker ratios exhibit similar values for the spilled oil, Alberta oil (the main petroleum source for British Columbia), and pre-spill and un-oiled sediment samples. In contrast, alkyl PAH isomer ratios showed a clear distinction between the spilled oil and pre-spill samples, with the largest differences shown by isomers of the methyl fluoranthene/pyrene alkyl PAH series. This novel use of alkyl PAH isomers for fingerprinting petroleum helped to confirm the grain carrier
MV Marathassa
as the source of the oil that affected beach and mussel samples to document definitively the spread of the oil and to establish which samples contained a mix of the oil and hydrocarbons linked to historical activities. Finally, an initial evaluation of the biological risks of the
MV Marathassa
oil spill in Vancouver Harbour showed that oiled beach sediments had priority parent PAH concentrations that are likely to harm marine life.
Sediment-associated hydrocarbons can pose a risk to wildlife that rely on benthic marine food webs. We measured hydrocarbons in sediments from the habitat of protected sea otters in coastal British ...Columbia, Canada. Alkane concentrations were dominated by higher odd-chain n-alkanes at all sites, indicating terrestrial plant inputs. While remote sites were dominated by petrogenic polycyclic aromatic hydrocarbons (PAHs), small harbour sites within sea otter habitat and sites from an urban reference area reflected weathered petroleum and biomass and fossil fuel combustion. The partitioning of hydrocarbons between sediments and adjacent food webs provides an important exposure route for sea otters, as they consume ∼25% of their body weight per day in benthic invertebrates. Thus, exceedences of PAH sediment quality guidelines designed to protect aquatic biota at 20% of the sites in sea otter habitat suggest that sea otters are vulnerable to hydrocarbon contamination even in the absence of catastrophic oil spills.
► Sediment hydrocarbon signatures differed between remote and impacted coastal sites. ► A natural background comprised terrestrial plant alkanes and petrogenic PAHs. ► Impacted sites reflected a history of petrogenic and pyrogenic hydrocarbon inputs. ► Hydrocarbons at some sites exceeded guidelines for the protection of aquatic life. ► Protected sea otters may thus be at risk as they rely primarily on benthic prey.
Anthropogenically-derived hydrocarbons in coastal sediments in British Columbia may pose a risk to protected sea otters.
Suspended sediments from the Mackenzie River Delta and surface sediments from the Beaufort Shelf were analyzed by alkaline CuO oxidation. In addition, elemental (percentage total organic carbon, ...inorganic carbon and silica) and stable carbon isotope compositions were determined for all samples. The carbon-normalized yields of over 60 different compounds derived from the oxidative hydrolysis of several biochemicals, including lignin, cutin, proteins, polysaccharides and lipids were quantified and subjected to principal component analyses (PCA). The results of these investigations indicate that most lignin and cutin products originate from non-woody angiosperm vascular vegetation such as that present in the tundra. For example, lignin-derived product compositions are characterized by relatively high syringyl:vanillyl and cinnamyl:vanillyl phenol ratios (exceeding 0.4 and 0.15, respectively). The compositions of these biomarkers, especially the elevated (0.5 to 1.5) acid:aldehyde ratios for vanillyl and syringyl phenols, also suggest that the land-derived organic matter (OM) exported by the Mackenzie River is highly degraded. Non-lignin CuO reaction products derived from proteins, polysaccharides and lipids display distributions that are consistent with a predominant marine (autochthonous) source. The composition of lipid-derived fatty acid products, which is in shelf sediments are dominated by hexanedecenoic acid, suggests a planktonic origin, likely from diatoms. The distribution of these biomarkers across the shelf indicates the presence of relatively fresh algal remains in at least one sample. The relationships between terrigenous biomarker concentrations and bulk
13C/
12C ratios in surface sediments indicate that terrestrial organic carbon dominates in abundance (80% to 50% of total organic carbon) over much of the shelf. Marine/algal-derived carbon represents 20% to 50% of the total carbon in shelf sediments, with the largest fraction being present in the outer mid-shelf. The large variability in the yields of CuO biomarkers from the river suspended sediment samples highlights the heterogeneous nature of the particle load exported by the Mackenzie River. Such variability must be taken into account during the development of quantitative carbon budgets for the Beaufort Shelf.
•Sediments have low petrogenic and pyrogenic inputs, with no anthropogenic input.•Most sediments have similar alkane, and parent and alkyl PAH composition.•Immature coals constitute the most likely ...petrogenic source to sediments.•There is little evidence of an oil contribution to sediments.
Significant reserves of oil and gas have been predicted for Hecate Strait, a pristine, semi-enclosed sea on the continental shelf adjacent to British Columbia, on the west coast of Canada. To establish a baseline for the natural background of hydrocarbons in sediment prior to any further offshore oil and gas development or increase in oil tanker traffic in the Hecate Strait region, three sediment box cores were collected along a west to east transect across southern Hecate Strait in September 2003. 210Pb measurements established that the bottom sections date to ∼1920, pre-1800 and ∼1870, respectively, which predate any significant industrial development on the coast. Alkane and polycyclic aromatic hydrocarbon (PAH) concentrations are low in most sediment samples and both the concentrations and fluxes differ little between surface and bottom core sections. PAH profiles exhibit a dominance of alkyl PAHs for each alkyl PAH homologous series with varying amounts of parent (unsubstituted) PAHs, while alkane chromatograms show no unresolved complex mixture (UCM), and there is little change in composition between present day and pre-1800 sediments for most parameters. Principal components analysis (PCA) models, and PAH and biomarker ratios indicate that composition patterns are consistent with low and varying natural petrogenic and pyrogenic inputs, with little or no anthropogenic input. The most likely primary source of petrogenic PAHs to the sediments is Cenozoic lignites from the Skonun Formation, which outcrops on Haida Gwai and underlies most of Hecate Strait. Two subsurface sections (deposited in ∼1990 and ∼1930) in the core from Milbanke Sound, on the east side of the transect, have elevated concentrations for the alkyl phenanthrene/anthracenes and dibenzothiophenes with no UCM, and most likely also have a source in immature coal. This study suggests that the Hecate Strait environment has low hydrocarbon concentrations, with an apparent minor role for oil seeps and a likelihood that most of the petrogenic PAH sources are shales or immature coals with limited PAH bioavailability. If these characteristics are representative of Hecate Strait sediments overlying the Queen Charlotte Basin, it may mean that biota are likely unadapted to the presence of oil and thus would be more sensitive to exposure to oil from an oil spill than those in a more impacted environment.
The provenance of organic matter in sediments from the Mackenzie River and Beaufort Shelf was investigated using the stable carbon and radiocarbon isotopic compositions of bulk organic matter and the ...stable carbon isotopic compositions of individual organic compounds, including lignin-derived phenols and lipid-derived fatty acids. Most river suspended sediments and shelf surface sediments contained organic carbon characterized by highly depleted
Δ
14C values that were consistent with average radiocarbon ages exceeding 7000 years. The stable carbon isotopic signatures of lignin phenols were uniformly depleted (−25≥
δ
13C≥−32‰), indicating the predominant contributions of C
3 vascular plant sources. The isotopic compositions of C
14 and C
16 fatty acids exhibited important contrasts between the river (−36‰ to −40‰) and shelf (−25‰ to −29‰) sediments that were consistent with contributions from freshwater algae and/or vascular plants in the former and marine phytoplankton in the latter. Using
14C isotopic mass balance, the abundances of modern and ancient organic matter were quantitatively constrained. The fate of organic matter in the Beaufort Shelf was explored by normalizing these abundances to the specific surface area of sediments. Ancient organic carbon, which may include old pre-aged soil material as well as fossil bitumen or kerogen, accounted for the majority (∼70%) of the particulate organic matter exported by the Mackenzie River and deposited in surface sediments of the Beaufort Shelf. Modern organic carbon accounted for ∼30% in both river and shelf sediments, with significant contributions from vascular plant-derived materials in both river and shelf samples and from marine algae in the shelf sediments. Respiration (and/or leaching) of particle-bound marine organic matter dominates the carbon metabolism in the Mackenzie Delta/Beaufort Shelf region. However, land-derived pools, including modern carbon derived from vascular plants as well as ancient carbon also appeared to undergo a degree of post-depositional degradation prior to burial in the shelf. These novel source apportionments are reflected in an updated carbon budget for the study area.
Distinguishing the sources, ages, and fate of various terrestrial organic carbon (OC) pools mobilized from heterogeneous Arctic landscapes is key to assessing climatic impacts on the fluvial release ...of carbon from permafrost. Through molecular 14C measurements, including novel analyses of suberin‐ and/or cutin‐derived diacids (DAs) and hydroxy fatty acids (FAs), we compared the radiocarbon characteristics of a comprehensive suite of terrestrial markers (including plant wax lipids, cutin, suberin, lignin, and hydroxy phenols) in the sedimentary particles from nine major arctic and subarctic rivers in order to establish a benchmark assessment of the mobilization patterns of terrestrial OC pools across the pan‐Arctic. Terrestrial lipids, including suberin‐derived longer‐chain DAs (C24,26,28), plant wax FAs (C24,26,28), and n‐alkanes (C27,29,31), incorporated significant inputs of aged carbon, presumably from deeper soil horizons. Mobilization and translocation of these “old” terrestrial carbon components was dependent on nonlinear processes associated with permafrost distributions. By contrast, shorter‐chain (C16,18) DAs and lignin phenols (as well as hydroxy phenols in rivers outside eastern Eurasian Arctic) were much more enriched in 14C, suggesting incorporation of relatively young carbon supplied by runoff processes from recent vegetation debris and surface layers. Furthermore, the radiocarbon content of terrestrial markers is heavily influenced by specific OC sources and degradation status. Overall, multitracer molecular 14C analysis sheds new light on the mobilization of terrestrial OC from arctic watersheds. Our findings of distinct ages for various terrestrial carbon components may aid in elucidating fate of different terrestrial OC pools in the face of increasing arctic permafrost thaw.
Key Points
Molecular 14C content of multiple terrestrial markers is compared in pan‐arctic sediments
Suberin‐ and cutin‐derived diacids trace old and young terrestrial carbon separately
New light is shed on terrestrial carbon sources and mobilization pathways in arctic basins
PDF