Distinct Modes Of Aged Soil Carbon Export In A Large Tropical Lake Basin Identified Using Bulk And Compound-Specific Radiocarbon Analyses Of Fluvial And Lacustrine Sediment

The 14C content of sedimentary organic matter (OM) and specific organic molecules provide valuable information on the source and age of OM stored in sediments, but these data are limited for tropical fluvial and lake sediments. We analyzed 14C in bulk OM, palmitic acid (C16), and long-chain n-alkanoic acids (C24, C26, and C28), within fluvial and lake sediments in the catchment of Lake Izabal, a large tectonic lake basin in Guatemala. We combined these measurements with bulk and compound-specific δ13C measurements, as well as sediment organic carbon to nitrogen (OC:N) ratios, to understand the source and age of sedimentary OM in different regions of the lake catchment. Most fatty acid and bulk OM samples were characterized by pre-modern carbon, indicating important input of aged carbon with residence times of hundreds to thousands of years into sediments. We identified two mechanisms leading to aged carbon export to sediments. In the high-relief and deforested Polochic catchment, older OM and fatty acids are associated with low % total organic carbon (TOC) and low OC:N, indicating aged OM associated with eroded mineral soil. In the smaller, low-relief, and largely forested Oscuro catchment, old OM and fatty acids are associated with high %TOC and high OC:N ratios, indicating export of undegraded aged plant biomass from swamp peat. The age of bulk OM and fatty acids in Lake Izabal sediments is similar to the ages observed in fluvial sediments, implying that fluvial input of aged soil carbon makes an important contribution to lake sediment carbon reservoirs in this large tropical lake

Modern sediment records of hydroclimatic extremes and associated potential contaminant mobilization in semi-arid environments : lessons learnt from recent flood-drought cycles in southern Botswana

Open access via the Springer Compact Agreement This research was funded by the UK Natural Environment Research Council NERC Urgency grant NE/R002568/1 (PULA Project). Acknowledgments The authors would like to thank the Editor and two anonymous reviewers for their comments and suggestions which have contributed to improve the quality of this paper. The authors would like to thank all the BIUST students that took part in one or more field campaigns in the Notwane river catchment; their work and interests were remarkable. Thanks are due to Trust Manyiwa (BIUST) for the assistance with grain size and OM analyses and to Serwalo M. Mokgosi (BIUST) for assistance with the MP-AES measurements of sediment materials. We would like to thank the staff at the University of Aberdeen laboratory (Michael McGibbon) for assistance with the water quality analyses.Peer reviewedPublisher PD

Advances in Distinguishing Groundwater Influenced by Oil Sands Process-Affected Water (OSPW) from Natural Bitumen-Influenced Groundwater

The objective of this study was to advance analytical methods for detecting oil sands process-affected water (OSPW) seepage from mining containments and discriminating any such seepage from the natural bitumen background in groundwaters influenced by the Alberta McMurray formation. Improved sampling methods and quantitative analyses of two groups of monoaromatic acids were employed to analyze OSPW and bitumen-affected natural background groundwaters for source discrimination. Both groups of monoaromatic acids showed significant enrichment in OSPW, while ratios of O /O containing heteroatomic ion classes of acid extractable organics (AEOs) did not exhibit diagnostic differences. Evaluating the monoaromatic acids to track a known plume of OSPW-affected groundwater confirmed their diagnostic abilities. A secondary objective was to assess anthropogenically derived artificial sweeteners and per- and polyfluoroalkyl substances (PFAS) as potential tracers for OSPW. Despite the discovery of acesulfame and PFAS in most OSPW samples, trace levels in groundwaters influenced by general anthropogenic activities preclude them as individual robust tracers. However, their inclusion with the other metrics employed in this study served to augment the tiered, weight of evidence methodology developed. This methodology was then used to confirm earlier findings of OSPW migrations into groundwater reaching the Athabasca River system adjacent to the reclaimed pond at Tar Island Dyke

Using tree cores to evaluate historic atmospheric concentrations and trends of polycyclic aromatic compounds in the Oil Sands region of Alberta, Canada

Tree cores and bark were sampled from jack pine trees at 18 sites in the Athabasca Oil Sands Region (AOSR) of Alberta, Canada, to investigate spatial and temporal trends of polycyclic aromatic compounds (PACs). Spatial trends were investigated in the bark samples, where ΣPAC concentrations ranged from 75 to 3615 ng/g. Highest concentrations were observed from trees within 40 km of the nearest mining or upgrading facility perimeter fence, in line with previous deposition studies in the AOSR. The sampled tree cores were separated into segments representing 5 years of growth/atmospheric collection by counting tree rings. A significant increase in PAC concentrations over the lifetime of the tree was observed at sites with the highest PAC concentrations, and the average % increase in concentration from 1970 to 2015 was in line with average % growth in bitumen extraction in the AOSR. Finally, the concentrations in the tree core segments representing collection from 2010 to 2015 were converted into an atmospheric PAC concentration using previously published wood-air partition coefficients. The calculated atmospheric concentrations were within the same range as concentrations reported from the passive atmospheric sampling network in this region. The importance of site location is highlighted, with forest edge sites providing an improved comparison for atmospheric exposure and deposition. This is the first study to use tree cores to calculate an atmospheric concentration of PACs, demonstrating the applicability of this methodology for providing historic atmospheric data

Characterization of the boron, lithium, and strontium isotopic variations of oil sands process-affected water in Alberta, Canada

International audienc

Sources of n-alkanes in an urbanized estuary: insights from molecular distributions and compound-specific stable and radiocarbon isotopes

Diagnostic molecular ratios and compound-specific <sup>13</sup>C and <sup>14</sup>C analyses were used to identify n-alkane sources in surface sediments collected along a transect from an urbanized estuary draining a peat-rich catchment (Tyne, UK). The most abundant homologues were generally C<sub>29</sub> or C<sub>31</sub>, and the carbon preference index (CPI; 1.8 to 6.4) and average chain length (ACL; 28.5 to 29.5) of C<sub>25</sub>–C<sub>33</sub>n-alkanes became progressively lower in samples closer to the mouth of estuary. δ<sup>13</sup>C signatures of C<sub>19</sub>–C<sub>31</sub>n-alkanes ranged from − 37.1 to − 29.3‰ and in general became more depleted with increasing carbon number. Δ<sup>14</sup>C values for C<sub>21</sub> (− 945 to − 738‰) were significantly more depleted compared to C<sub>29</sub> (− 591 to − 65‰) and C<sub>31</sub> (− 382 to − 96‰), pointing to a much higher component of fossil (i.e., <sup>14</sup>C-free) carbon in the shorter homologue. The radiocarbon contents for these three n-alkanes decreased toward the North Sea, which in conjunction with an up to 4‰ seaward <sup>13</sup>C-enrichment in C<sub>29</sub> and C<sub>31</sub> and seaward decreases in CPI and ACL pointed to petrogenic hydrocarbon contamination in lower estuarine sediments. Independent <sup>13</sup>C and <sup>14</sup>C mass balances used to calculate the relative proportions of modern (i.e., plant wax) and fossil (i.e., petrogenic) <i>n</i>-alkanes yielded similar results and demonstrated that mixing with marine-derived organic matter (OM) or microbial degradation during estuarine transport led to a seaward decline in modern, longer-chain homologues, resulting in an increasingly larger fossil carbon contribution toward the mouth of estuary. The ability to clearly distinguish anthropogenic from natural inputs suggests that compound-specific radiocarbon analysis can successfully delineate the age of terrigenous OM delivered to the coastal zone even near historically polluted systems such as the Tyne