Seasonal variability in carbon:234thorium ratios of suspended and sinking particles in coastal Antarctic waters: Field data and modeling synthesis

238U-234Th disequilibrium is a powerful tool for investigating particle cycling and carbon export associated with the ocean's biological carbon pump. However, the interpretation of this method is complicated by multiple processes that can modify carbon:thorium ratios over small spatial scales. We investigated seasonal variability in the thorium and carbon cycles at a coastal site in the Western Antarctic Peninsula. Throughout the ice-free summer season, we quantified carbon and 234Th vertical flux, total water column 234Th, particulate 234Th, and the C:234Th ratios of sinking material and bulk suspended material. Simultaneous identification and separation of fecal pellets from sinking material showed that fecal pellets (primarily from krill) contributed 56% of carbon flux and that as a result of lower C:234Th ratios than suspended particles, these fecal pellets were primary drivers of variability in the C:234Th ratios of sinking material. Bulk suspended particles had highly variable C:234Th ratios and were consistently elevated in the euphotic zone relative to deeper waters. The fraction of 234Th adsorbed onto particles was positively correlated with chlorophyll and particulate organic carbon (POC) concentrations. The C:234Th ratios of suspended particles were positively correlated with POC, although during the spring diatom bloom C:234Th ratios were lower than would have been predicted based on POC concentrations alone. We hypothesize that diatom production of transparent exopolymers may have led to enhanced rates of thorium adsorption during the bloom, thus decreasing the C:234Th ratios. We used a Bayesian model selection approach to develop and parameterize mechanistic models to simulate thorium sorption dynamics. The best model incorporated one slowly-sinking POC pool and rapidly-sinking fecal pellets, with second-order sorption kinetics. The model accurately simulated temporal patterns in the C:234Th ratios of sinking and suspended particles and the fraction of 234Th adsorbed to particles. However, it slightly over-estimated C:234Th ratios during the spring (diatom-dominated) bloom and underestimated C:234Th ratios during the fall (mixed-assemblage) bloom. Optimized model parameters for thorium sorption and desorption were 0.0047 +/- 0.0002 m3 mmol C-1 d-1 and 0.017 +/- 0.008 d-1, respectively. Our results highlight the important role that specific taxa can play in modifying the C:234Th ratio of sinking and suspended particles and provide guidance for future studies that use 234Th measurements to investigate the functional relationships driving the efficiency of the biological pump.

Justification of measures to protect against exposure nicotine-containing products in enclosed spaces

Introduction. The introduction of amendments and additions to the anti-smoking Federal Law No. 15-FZ of 23.02.2013 in 2020 contributed to the cardinal revision of the name of this law and the introduction of a ban on consumption of any nicotine-containing products in public places. There are no separate, specially allocated isolated premises provided for the consumption of tobacco products and other types of nicotine-containing products by law, even though specially conducted studies have shown significantly different levels of additional inhalation risk arising from air pollution when consuming tobacco products and electronic nicotine delivery systems or heating tobacco. The aim of the study: based on experimental data, to justify the multiplicity of air exchange in unique isolated rooms designed to protect against the effects of ambient tobacco smoke, the consequences of tobacco consumption or nicotine-containing products. Materials and methods. The study was subject to 3 types of nicotine-containing products: tobacco cigarettes (cigarettes), an electronic nicotine delivery system (ENDS) and an electronic tobacco heating system (ETHS). In the course of the study were carried out: a series of experiments on the consumption of nicotine-containing products in various ways in a specially equipped indoor room, air sampling and laboratory studies were performed, the gross and specific emissions of chemicals entering the air environment from one unit of production per hour were calculated, the selection of priority chemicals for calculating the air removed from the room when using nicotine-containing products of each type was carried out, the necessary level of air exchange of premises was calculated, intended for the consumption of tobacco or nicotine. Results. The indoor air quality assessment showed that the main components of the gross intake into the air environment are suspended particles and carbon monoxide when smoking cigarettes. However, taking into account the values of the maximum permissible concentrations, the most significant contribution to the integral indicator is made by acetaldehyde and suspended particles PM10 and PM2.5. Using ENDS, the most significant pollutants were acetaldehyde and carbon monoxide, using ETHS - acetaldehyde and suspended particles PM10 and PM2.5. For all the investigation types of products, the priority substance for calculating the removed air is acetaldehyde, its share in the structure of all detected pollutants was: for cigarettes - 56.27%, for ENDS - 62.7%, for ETHS - 82.51%, in connection with which its specific values can be used to calculate the consumption of the removed air when modelling a specially allocated room intended for the consumption of tobacco products and other types of nicotine-containing products. Conclusion. The obtained findings demonstrated an obvious, more than 10-fold difference in the requirements for air exchange of premises intended for cigarette smoking and premises intended for the consumption of ENDS or ETHS, at the same intensity of consumption. Therefore, when organizing specially designated places for smoking or the consumption of nicotine-containing products, it is advisable to separate them depending on the type of products consumed: tobacco smoking separately, ENDS and ETHS consumption separately.

Wind-Induced Resuspension and Transport of Contaminated Sediment from the Rove Canal into the Etang De Berre, France

The present study concerns the erosion and transport of severely contaminated sediments in a Canal. It begins in the context of an engineering project aimed to re-introduce a forced convection at the entrance of this Canal by pumping marine water. The local wind is often strong enough to overpass the resuspension threshold; thus, there is a serious risk of downstream contamination of a Mediterranean lagoon. So, the goal is to evaluate this risk as a function of the pumping rate; this contamination is transported by the fine suspended particles. Different scenarios are investigated to determine the downstream transport of suspensions in terms of runoff. These scenarios (of 24 h) contains a succession of 3 periods: constant wind speed, wind slowdown and calm, for two opposite wind directions. Special attention is devoted to the modeling of complex mechanisms of erosion and resuspension during wind periods, deposition during windless periods and sediment consolidation. The main results concern the total flux of the suspended particles through the exit of the Canal at the confluence with the lagoon. It is shown that even for moderate runoff (<6 m3/s) this total flux is large enough, not only during the wind period, but also after several hours of calm.

Features of the distribution of the suspended form of iron in the water column of the Caspian Sea

Статья посвящена изучению распределения железа в водной взвеси Среднего Каспия. Актуальность работыопределяется необходимостью оценки естественного состоя­ния морской среды и фиксации ее базового состояния (в том числе различных форм химических элементов) для дальнейшего использования с целью мониторинга экологической ситуации на шельфе Каспийского моря в условиях интенсификации геологоразве­дочных работ и разработки месторождений нефти. Цель работы. Установить характерные особенности поведения взвешенного железа в водах Среднего Каспия. Материалы и методы работы. Изучался материал, отобранный в 1989-1990 годах в ходе выполнения рейсов исследовательских судов. Принадлежащих Каспийскому НИИ рыбного хозяйства, до начала освоения нефтегазовых месторождений. Он представлен отфильтрованными частицами взвеси из 178 проб воды, взятых из различных слоев водной толщи на 63 станциях. Определение содержаний железа проводилось на спектрографе PGS-2 способом испарения. Результаты работы. Минимальные концентрации взвешенной формы железа в поверхностном слое водной толщи установлены на участке внутреннего шельфа и подводного склона котловины Среднего Каспия, что связано с выносом твердых частиц дрейфовыми течениями. Концентрации взвешенной формы железа в поверхностном слое возрастают к середине моря, что обусловлено стягиванием взвешенных частиц центростремительными силами циклонального течения. Придонный слой отличается повышенными концентрациями взвешенной формы железа. Возле дельт рек они связаны с оседанием выносимых с суши твердых частиц. Аномально высокие содержания взвешенной формы железа в придонном горизонте центральной части Среднекаспийской котловины, фиксируемые на отдельных станциях, обусловлены поступлением железа с эманациями донных грязевых вулканов и его коагуляцией в условиях щелочной среды. В целом, с увеличением глубины наблюдается последовательный рост концентраций взвешенной формы железа. Это связано с изменением солености и усилением вертикальной стратификации (уменьшением солености поверхностного горизонта и увеличением солености глубоких слоев). Это приводит к коагу­ляции и флокуляции органических и металлор­ганических коллоидов и переводу растворенного железа во взвесь The article is devoted to the study of the distribution of iron in the water suspension of the Middle Caspian Sea. The relevance of the work is determined by the need to assess the natural state of the marine environment and fix its basic state (including various forms of chemical elements) for further use in order to monitor the environmental situation on the shelf of the Caspian Sea in the conditions of intensification of exploration and development of oil fields. Aim. To establish the characteristic features of the behavior of suspended iron in the waters of the Middle Caspian. Materials and methods. The material selected in 1989-1990 during the voyages of research vessels was studied. owned by the Caspian Research Institute of Fisheries, before the development of oil and gas fields. It is represented by filtered suspended particles from 178 water samples taken from various layers of the water column at 63 stations. Determination of iron content was carried out on the PGS-2 spectrograph by evaporation. Results. The minimum concentrations of the suspended form of iron inthe surface layer of the water column were established on the section of the inner shelf and the underwater slope of the Middle Caspian basin, which is associated with the removal of solid particles by drift currents. The concentrations of the suspended form of iron in the surface layer increase towards the middle of the sea, which is caused by the contraction of suspended particles by the centripetal forces of the cyclonic current. The bottom layer is characterized by increased concentrations of the suspended form of iron. Near river deltas, they are associated with the subsidence of solid particles carried out from the land. Abnormally high concentrations of suspended iron in the bottom horizon of the central part of the Middle Caspian basin, recorded at individual stations, are due to the influx of iron with emanations of bottom mud volcanoes and its coagulation in an alkaline environment. In general, with increasing depth, there is a consistent increase in the concentrations of the suspended form of iron. This is due to a change in salinity and an increase in vertical stratification (a decrease in the salinity of the surface horizon and an increase in the salinity of the deep layers). This leads to coagulation and flocculation of organic and organometallic colloids and the transfer of dissolved iron into suspension.

On predicting particle capture rates in aquatic ecosystems

Recent advances in understanding the capture of moving suspended particles in aquatic ecosystems have opened up new possibilities for predicting rates of suspension feeding, larval settlement, seagrass pollination and sediment removal. Drawing on results from both highly-resolved computational fluid dynamics (CFD) simulations and existing experimental data, we quantify the controlling influence of flow velocity, particle size and collector size on rates of contact between suspended particles and biological collectors over the parameter space characterising a diverse range of aquatic ecosystems. As distinct from assumptions in previous modeling studies, the functional relationships describing capture are highly variable. Contact rates can vary in opposing directions in response to changes in collector size, an organism’s size, the size of particles being intercepted (related to diet in the case of suspension feeders), and the flow strength. Contact rates shift from decreasing to increasing with collector diameter when particles become relatively large and there is vortex shedding in the collector wake. And in some ranges of the ecologically relevant parameter space, contact rates do not increase strongly with velocity or particle size. The understanding of these complex dependencies allows us to reformulate some hypotheses of selection pressure on the physiology and ecology of aquatic organisms. We discuss the benefits and limitations of CFD tools in predicting rates of particle capture in aquatic ecosystems. Finally, across the complete parameter space relevant to real aquatic ecosystems, all quantitative estimates of particle capture from our model are provided here.