Carbon isotopic characterisation of dissolved organic mater during water treatment

Water treatment is a series of physio-chemical processes to aid organic matter (OM) removal, which helps to minimise the formation of potentially carcinogenic disinfection by-products and microbial regrowth. Changes in OM character through the treatment processes can provide insight into the treatment efficiency, but radiogenic isotopic characterisation techniques have yet to be applied. Here, we show for the first time that analysis of 13C and 14C of dissolved organic carbon (DOC) effectively characterises dissolved OM through a water treatment works. At the sites investigated: post-clarification, DOC becomes isotopically lighter, due to an increased proportion of relatively hydrophilic DOC. Filtration adds ‘old’ 14C-DOC from abrasion of the filter media, whilst the use of activated carbon adds ‘young’ 14C-DOC, most likely from the presence of biofilms. Overall, carbon isotopes provide clear evidence for the first time that new sources of organic carbon are added within the treatment processes, and that treated water is isotopically lighter and typically younger in 14C-DOC age than untreated water. We anticipate our findings will precipitate real-time monitoring of treatment performance using stable carbon isotopes, with associated improvements in energy and carbon footprint (e.g. isotopic analysis used as triggers for filter washing and activated carbon regeneration) and public health benefits resulting from improved carbon removal

Geochemistry and budgetary considerations of 14C in the Irish Sea

Sellafield nuclear fuel reprocessing plant has been discharging 14C as a component of the low level liquid radioactive waste into the Irish Sea since 1952. This 14C is of radiological importance due to its long half-life, mobility in the environment and propensity for entering the food chain. Unlike the overall tend towards lower discharge activities since the peak in discharge activity during the 1970s (for example 137Cs and 241Am), the discharge activities for 14C have increased since 1994/95 due to a change in discharge policy from mainly atmospheric discharges to mainly marine discharges. In contrast with other Sellafield derived radionuclides (for example 137Cs and 241Am), the behaviour of 14C in the Irish Sea is, however, poorly understood despite an increase in research effort in recent years. This study was therefore undertaken to improve our understanding of temporal variations in specific activities in the biogeochemical fractions of the water column and biota in the Irish Sea and North Channel in relation to the Sellafield discharges. The project also determined a budget of Sellafield derived 14C in the sediments of the NE Irish Sea and measured the flux of this 14C from the Irish Sea. Before the contribution of Sellafield derived 14C to any carbon fraction can be made the activity of the marine background must first be estimated. The dissolved inorganic carbon (DIC) fraction of the water column, mussel, seaweed, crab, flatfish and roundfish samples were collected annually from the west coast of Co. Donegal, Ireland, and from these, the average current marine background activity was estimated to be approximately 253 Bq kg-1 C. There were clear signs of incorporation of Sellafield derived 14C to the biogeochemical fractions (dissolved inorganic carbon or DIC, dissolved organic carbon or DOC, particulate inorganic carbon or PIC and particulate organic carbon or POC) of the water column in seawater from the NE Irish Sea (Nethertown and St. Bees Head site) and North Channel (Portpatrick), although 14C specific activities of the biogeochemical fractions of the water column in the North Channel were lower than those found close to the point of discharge. Temporal trends in DIG specific activities at Nethertown bore no relationship to temporal trends in the discharge activities. In contrast with the Nethertown site temporal trends in the biogeochemical fractions (DIG, PIG and POG) at the St. Bees Head site rapidly responded to temporal trends in the discharge activity, with the most rapid changes in specific activity being exhibited by the DIG, followed by the POG. In the North Ghannel trends in the DIG specific activities were similar to those for the discharge activities, although a 1-2 month lag time was apparent before peaks in the discharge activity were seen in the DIG specific activities at the North Ghannel. Temporal trends of 14C specific activities for the other biogeochemical fractions (DOG, POG and PIG) at Portpatrick did not bear any relationship to the temporal trends in the discharge. Using the monthly discharge data and monthly specific activities in the DIG at Portpatrick the data can be modelled to give a flow rate of 4.6 km3 d-1 through the North Channel (David Prandle Pers. Comm.). This is in good agreement with the flow rate of 5 km3 d-1 used in previous studies to estimate the removal of Sellafield derived radionuclides from the Irish Sea through the North Channel. Using the flow rate of 5 km3 d-1 an estimated removal from the Irish Sea during the 2 year study period of 11.4 +/- 0.7 TBq in the DIG fraction, 0.9 TBq in the DOG fraction, <0.01 TBq in the PIG fraction and 0.07 TBq in the POG fraction was calculated. This gave a total of 12.4 TBq of 14C removed from the Irish Sea through the North Channel, approximately 100% of the total Sellafield discharges during the study period

A rapid method to collect methane from peatland streams for radiocarbon analysis

Peatland streams typically contain high methane concentrations and act as conduits for the release of this greenhouse gas to the atmosphere. Radiocarbon analysis provides a unique tracer that can be used to identify the methane source, and quantify the time elapsed between carbon fixation and return to the atmosphere as CH4. Few studies &ndash; those that have focus largely on sites with bubble (ebullition) emissions &ndash; have investigated the14C age of methane in surface waters because of the difficulty in collecting sufficient CH4for analysis. Here, we describe new sampling methods for the collection of CH4samples from CH4-oversaturated peatland streams for radiocarbon analysis. We report the results of a suite of tests, including using methane14C standards and replicated field measurements, to verify the methods. The methods are not restricted to ebullition sites, and can be applied to peatland streams with lower methane concentrations. We report the14C age of methane extracted from surface water samples (~4&ndash;13 l) at two contrasting locations in a temperate raised peat bog. Results indicate substantial spatial variation with ages ranging from ~400 (ditch in afforested peatland) to ~3000 years BP (bog perimeter stream). These contrasting ages suggest that methane in stream water can be derived from a wide range of peat depths. This new method provides a rapid (10&ndash;15 min per sample) and convenient approach, which should make14CH4dating of surface water more accessible and lead to an increased understanding of carbon cycling within the soil&ndash;water&ndash;atmosphere system

Transitions in coral reef accretion rates linked to intrinsic ecological shifts on turbid-zone nearshore reefs

Nearshore coral communities within turbid settings are typically perceived to have limited reef-building capacity. However, several recent studies have reported reef growth over millennial time scales within such environments and have hypothesized that depth-variable community assemblages may act as equally important controls on reef growth as they do in clear-water settings. Here, we explicitly test this idea using a newly compiled chronostratigraphic record (31 cores, 142 radiometric dates) from seven proximal (but discrete) nearshore coral reefs located along the central Great Barrier Reef (Australia). Uniquely, these reefs span distinct stages of geomorphological maturity, as reflected in their elevations below sea level. Integrated age-depth and ecological data sets indicate that contemporary coral assemblage shifts, associated with changing light availability and wave exposure as reefs shallowed, coincided with transitions in accretion rates at equivalent core depths. Reef initiation followed a regional ∼1 m drop in sea level (1200–800 calibrated yr B.P.) which would have lowered the photic floor and exposed new substrate for coral recruitment by winnowing away fine seafloor sediments. We propose that a two-way feedback mechanism exists where past growth history influences current reef morphology and ecology, ultimately driving future reef accumulation and morphological change. These findings provide the first empirical evidence that nearshore reef growth trajectories are intrinsically driven by changes in coral community structure as reefs move toward sea level, a finding of direct significance for predicting the impacts of extrinsically driven ecological change (e.g., coral-algal phase shifts) on reef growth potential within the wider coastal zone on the Great Barrier Reef

Performance of the rebuilt SUERC single-stage accelerator mass spectrometer

The SUERC bipolar single-stage accelerator mass spectrometer (SSAMS) has been dismantled and rebuilt to accommodate an additional rotatable pre-accelerator electrostatic spherical analyser (ESA) and a second ion source injector. This is for the attachment of an experimental positive-ion electron cyclotron resonance (ECR) ion source in addition to a Cs-sputter source. The ESA significantly suppresses oxygen interference to radiocarbon detection, and remaining measurement interference is now thought to be from 13C injected as 13CH molecule scattering off the plates of a second original pre-detector ESA

Assessing the Effect of Sterilization on the Radiocarbon Signature of Freshwater Dissolved Organic Carbon

Radiocarbon analysis of freshwater dissolved organic carbon (DOC) involves substantial sample pretreatment, including an initial rotary evaporation stage necessary to concentrate large volumes of freshwater sample. This may lead to a health risk from the exposure to pathogens, and there is the additional concern that the warm conditions during the rotary evaporation stage may provide ideal growing conditions for some pathogens. To remove any pathogen risk in water samples, boiling or autoclaving can be undertaken. However, to date, no studies have been undertaken to investigate whether boiling will alter the 14C signature of dissolved organic carbon. Here, we analyze the effect of sterilization on 9 contrasting river water samples. Comparing filtered, filtered and boiled, and filtered and sterilized dissolved organic matter, we observe that both boiling and autoclaving increases the uncertainty associated with the 14C and 13C of DOC, that the 14C and 13C changes are not unidirectional, and that they are not related to original DOC composition. Neither sterilization method is recommended unless essential, in which instance we recommend a 3 uncertainty on 14C and that the 13C is not considered representative of the original sample.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Using environmental tracers to evaluate the preservation of palaeoclimate signals in aquifers of the London Basin, UK

The concept of aquifer basins as palaeoclimate archives has existed for some decades, yet few detailed studies comparing aquifer types have been carried out. To assess the potential of a particular aquifer as an archive, its hydrogeochemical characteristics must be thoroughly investigated, ideally in comparison to an adjacent aquifer which can be shown to substantially preserve its ice-age endowment at depth. The London Basin (UK) presents such an opportunity, containing two main aquifers of contrasting type: the Chalk, a fractured microporous limestone, and the Lower Greensand, a porous sandstone. Despite intensive exploitation of both, evidence for Devensian (late-glacial) water remains at depth, though this differs between aquifer type. To understand the reasons for this, a suite of environmental tracers has been applied. In addition to hydrochemistry, stable isotopes (δ18O, δ2H), carbon isotopes (δ13C-DIC, 14C-DIC) and noble gases (He, Ne, Ar, Kr and Xe), two tracers new to the basin (CFCs and 14C-DOC) have been used. In effect the Lower Greensand appears to be the ‘reference aquifer’, preserving recharge from prior to the Last Glacial Maximum (LGM), while the Chalk contains mixed water, with no remaining trace of the undiluted pre-LGM end member even at depth in remote parts of the confined basin. Whereas both aquifers had in the past given maximum 14C-DIC model ages ≥ 30 kyr (the effective limit of that method), in the present study the use of 14C-DOC has reduced this to 23.4 kyr (Lower Greensand) and 17.2 kyr (Chalk). Similar contrasts in maximum stable isotope depletions (−8.2 ‰ and −7.8 ‰ δ18O) and noble-gas-derived recharge temperature minima (2.6° and 4.1 °C) were also observed. CFCs were found at all Chalk sites, with traces detectable even at 40 km from outcrop, so some climate signal degradation appears inevitable throughout the Chalk aquifer of the basin. A correlation between 14C activity and excess 4He suggests that deep saline water in the Lower Greensand could be ≥ 50 kyr old. The use of 14C-DOC in particular appears to be key to understanding how reliable these individual aquifers are as palaeoarchives

Another 6 years of radiocarbon secondary-standard AMS with two spectrometers

The Scottish Universities Environmental Research Centre (SUERC) has analysed &gt;100,000 individual graphite preparations with two accelerator mass spectrometers. Analysis quality is maintained by a programme of secondary-standards measurement, and annual assessment of the resulting large dataset can provide insight into subtle effects. The same analyses that are used to derive external errors within individual batches of samples, or to monitor inter-batch variance, are also employed in aggregate to determine overall instrument and process performance. The recent 2021 findings are consistent with prior years’, including the apparent contradiction that secondary standard analysis can be both consistent and slightly discordant between the two instruments. However, individual sample radiocarbon measurement on both machines remains accurate and typically 3 ‰ precise

Aquatic community response to volcanic eruptions on the Ecuadorian Andean flank: evidence from the palaeoecological record

Aquatic ecosystems in the tropical Andes are under increasing pressure from human modification of the landscape (deforestation and dams) and climatic change (increase of extreme events and 1.5 °C on average temperatures are projected for AD 2100). However, the resilience of these ecosystems to perturbations is poorly understood. Here we use a multi-proxy palaeoecological approach to assess the response of aquatic ecosystems to a major mechanism for natural disturbance, volcanic ash deposition. Specifically, we present data from two Neotropical lakes located on the eastern Andean flank of Ecuador. Laguna Pindo (1°27.132′S–78°04.847′W) is a tectonically formed closed basin surrounded by a dense mid-elevation forest, whereas Laguna Baños (0°19.328′S–78°09.175′W) is a glacially formed lake with an inflow and outflow in high Andean Páramo grasslands. In each lake we examined the dynamics of chironomids and other aquatic and semi-aquatic organisms to explore the effect of thick (> 5 cm) volcanic deposits on the aquatic communities in these two systems with different catchment features. In both lakes past volcanic ash deposition was evident from four large tephras dated to c.850 cal year BP (Pindo), and 4600, 3600 and 1500 cal year BP (Baños). Examination of the chironomid and aquatic assemblages before and after the ash depositions revealed no shift in composition at Pindo, but a major change at Baños occurred after the last event around 1500 cal year BP. Chironomids at Baños changed from an assemblage dominated by Pseudochironomus and Polypedilum nubifer-type to Cricotopus/Paratrichocladius type-II, and such a dominance lasted for approximately 380 years. We suggest that, despite potential changes in the water chemistry, the major effect on the chironomid community resulted from the thickness of the tephra being deposited, which acted to shallow the water body beyond a depth threshold. Changes in the aquatic flora and fauna at the base of the trophic chain can promote cascade effects that may deteriorate the ecosystem, especially when already influenced by human activities, such as deforestation and dams, which is frequent in the high Andes

Landscape-scale drivers of glacial ecosystem change in the montane forests of the eastern Andean flank, Ecuador

Understanding the impact of landscape-scale disturbance events during the last glacial period is vital in accu- rately reconstructing the ecosystem dynamics of montane environments. Here, a sedimentary succession from the tropical montane cloud forest of the eastern Andean flank of Ecuador provides evidence of the role of non- climate drivers of vegetation change (volcanic events, fire regime and herbivory) during the late-Pleistocene. Multiproxy analysis (pollen, non-pollen palynomorphs, charcoal, geochemistry and carbon content) of the se- diments, radiocarbon dated to ca. 45–42 ka, provide a snap shot of the depositional environment, vegetation community and non-climate drivers of ecosystem dynamics. The geomorphology of the Vinillos study area, along with the organic‐carbon content, and aquatic remains suggest deposition took place near a valley floor in a swamp or shallow water environment. The pollen assemblage initially composed primarily of herbaceous types (Poaceae-Asteraceae-Solanaceae) is replaced by assemblages characterised by Andean forest taxa, (first Melastomataceae-Weinmannia-Ilex, and later, Alnus-Hedyosmum-Myrica). The pollen assemblages have no modern analogues in the tropical montane cloud forest of Ecuador. High micro-charcoal and rare macro-charcoal abundances co-occur with volcanic tephra deposits suggesting transportation from extra-local regions and that volcanic eruptions were an important source of ignition in the wider glacial landscape. The presence of the coprophilous fungi Sporormiella reveals the occurrence of herbivores in the glacial montane forest landscape. Pollen analysis indicates a stable regional vegetation community, with changes in vegetation population co- varying with large volcanic tephra deposits suggesting that the structure of glacial vegetation at Vinillos was driven by volcanic activity