Chemical characterization of dissolved organic matter (DOM): A prerequisite for understanding UV-induced changes of DOM absorption properties and bioavailability

Abstract.: UV-induced transformations of colored dissolved organic matter (CDOM, which is part of dissolved organic matter, DOM) affect CDOM absorption properties resulting in the loss of color (referred to as photobleaching). CDOM photobleaching increases the penetration depths of the damaging UV-B radiation into water bodies and strongly depends on the wavelength of solar radiation and on the pH of aquatic systems. UV-induced transformations also affect DOM availability to bacterioplankton, often enhancing the bioavailability of terrigenous DOM and in turn microbial respiration. The combination of UV-induced enhancement of DOM bioavailability and increased export of terrigeneous DOM into estuaries and coastal waters due to climate-related changes in continental hydrology could result in a UV-mediated positive feedback of CO2 accumulation in the atmosphere. The extent and type of CDOM photobleaching and of UV-induced changes in DOM bioavailability depend on (C)DOM chemical composition, which in turn undergoes drastic changes upon UV-induced transformations. Therefore, the chemical characterization of (C)DOM is key for rationalizing UV-induced transformations. In the second section (after the "Introduction”), we review important methods for the elucidation of the chemical composition of (C)DOM. However, this article is not intended to be comprehensive regarding (C)DOM chemical characterization. An important purpose is to provide photochemical bases for the understanding of UV-induced changes of (C)DOM absorption properties and bioavailability (mainly discussed in the sections "Pathways of DOM phototransformations” and ”UV-induced changes of the absorption properties of CDOM”

Sources and emission of greenhouse gases in Danube Delta lakes

Production of methane and carbon dioxide as well as methane concentrations in surface waters and emissions to the atmosphere were investigated in two flow-through lake complexes (Uzlina-Isac and Puiu-Rosu-Rosulet) in the Danube Delta during post-flood conditions in May and low water level in September 2006. Retained nutrients fuelled primary production and remineralisation of bioavailable organic matter. This led to an observable net release of methane, particularly in the lakes Uzlina, Puiu and Rosu in May. Input from the Danube River, from redbuds and benthic release contributed to CH4 concentrations in surface waters. In addition to significant river input of CO2, this trace gas was released via aerobic remineralisation within the water column and in top sediments. Emission patterns of CO2 widely overlapped with those of CH4. Generally, greenhouse gas emissions peaked in the lake complex adjacent to the Danube River in May due to strong winds and decreased with increasing hydrological distance from the Danube River. Intense remineralisation of organic matter in the Danube Delta lakes results in a net source of atmospheric greenhouse gase

Evolution of chlorinated paraffin and olefin fingerprints in sewage sludge from 1993 to 2020 of a Swiss municipal wastewater treatment plant

Exposure of humans to chlorinated paraffins (CPs) and chlorinated olefins (COs) can occur via contact with CP-containing plastic materials. Such plastic materials can contain short-chain CPs (SCCPs), which are regulated as persistent organic pollutants (POPs) under the Stockholm Convention since 2017. Municipal wastewater treatment plants (WWTP) collect effluents of thousands of households and their sludge is a marker for CP exposure. We investigated digested sewage sludge collected in the years 1993, 2002, 2007, 2012, and 2020 from a Swiss WWTP serving between 20000 and 23000 inhabitants. A liquid chromatography mass spectrometry (R > 100000) method, in combination with an atmospheric pressure chemical ionization source (LC-APCI-MS), was used to detect mass spectra of CPs and olefinic side products. A R-based automated spectra evaluation routine (RASER) was applied to search for ∼23000 ions whereof ∼6000 ions could be assigned to CPs, chlorinated mono- (COs), di- (CdiOs) and tri-olefins (CtriOs). Up to 230 CP-, 120 CO-, 50 CdiO- and 20 CtriO-homologues could be identified in sludge. Characteristic fingerprints were deduced describing C- and Cl-homologue distributions, chlorine- (nCl) and carbon- (nC) numbers of CPs and COs. In addition, proportions of saturated and unsaturated material were determined together with proportions of different chain length classes including short- (SC), medium- (MC), long- (LC) and very long-chain (vLC) material. A substantial reduction of SCCPs of 84% was observed from 1993 to 2020. Respective levels of MCCPs, LCCPs and vLCCPs decreased by 61, 69 and 58%. These trends confirm that banned SCCPs and non-regulated CPs are present in WWTP sludge and higher-chlorinated SCCPs were replaced by lower chlorinated MCCPs. Combining high-resolution mass spectrometry with a selective and fast data evaluation method can produce characteristic fingerprints of sewage sludge describing the long-term trends in a WWTP catchment area

Methanotropic microbial communities associated with bubble plumes above gas seeps in the Black Sea

Bubbles evolving from active gas seeps can be traced by hydroacoustic imaging up to 1000 m high in the Black Sea water column. Although methane concentrations are not distinguishable between the water column above the deep seep and reference sites, atmospheric noble gas measurements clearly show the constant input of gases (mainly methane) via seepage into the Black Sea. Archaea (ANME-1, ANME-2) and methanotrophic bacteria detected with specific 16S rRNA-targeted oligonucleotide probes are related to active gas seeps in the oxic and anoxic water column. It is suggested that methane seeps have a much greater influence on the Black Sea methane budget than previously acknowledged and that ANME-1 and ANME-2 are injected via gas bubbles from the sediment into the anoxic water column mediating methane oxidation. Our results show further that only minor amounts of methane evolving from Black Sea gas seeps reach the atmosphere due to the very effective microbial barrier. Hence only major thermodynamically and/or tectonically triggered gas hydrate dissociation has the potential to induce rapid climate changes as suggested by the “clathrate gun hypothesis.

Chemical characterization of dissolved organic matter (DOM): A prerequisite for understanding UV-induced changes of DOM absorption properties and bioavailability

ISSN:1015-1621ISSN:1420-905

Evidence of Intense Archaeal and Bacterial Methanotrophic Activity in the Black Sea Water Column

In the northwestern Black Sea, methane oxidation rates reveal that above shallow and deep gas seeps methane is removed from the water column as efficiently as it is at sites located off seeps. Hence, seeps should not have a significant impact on the estimated annual flux of ∼4.1 × 10(9) mol methane to the atmosphere [W. S. Reeburgh, B. B. Ward, S. C. Wahlen, K. A. Sandbeck, K. A. Kilatrick, and L. J. Kerkhof, Deep-Sea Res. 38(Suppl. 2):S1189-S1210, 1991]. Both the stable carbon isotopic composition of dissolved methane and the microbial community structure analyzed by fluorescent in situ hybridization provide strong evidence that microbially mediated methane oxidation occurs. At the shelf, strong isotope fractionation was observed above high-intensity seeps. This effect was attributed to bacterial type I and II methanotrophs, which on average accounted for 2.5% of the DAPI (4′,6′-diamidino-2-phenylindole)-stained cells in the whole oxic water column. At deep sites, in the oxic-anoxic transition zone, strong isotopic fractionation of methane overlapped with an increased abundance of Archaea and Bacteria, indicating that these organisms are involved in the oxidation of methane. In underlying anoxic water, we successfully identified the archaeal methanotrophs ANME-1 and ANME-2, eachof which accounted for 3 to 4% of the total cell counts. ANME-1 and ANME-2 appear as single cells in anoxicwater, compared to the sediment, where they may form cell aggregates with sulfate-reducing bacteria (A. Boetius, K. Ravenschlag, C. J. Schubert, D. Rickert, F. Widdel, A. Giesecke, R. Amann, B. B. Jørgensen, U. Witte, and O. Pfannkuche, Nature 407:623-626, 2000; V. J. Orphan, C. H. House, K.-U. Hinrichs, K. D. McKeegan, and E. F. DeLong, Proc. Natl. Acad. Sci. USA 99:7663-7668, 2002)

Flood-controlled excess-air formation favors aerobic respiration and limits denitrification activity in riparian groundwater

The saturated riparian zones of rivers act as spatially and temporally variable biogeochemical reactors. This complicates the assessment of biogeochemical transport and transformation processes. During a flood event, excess-air formation, i.e., the inclusion and dissolution of air bubbles into groundwater, can introduce high amounts of dissolved O2 and thereby affect biogeochemical processes in groundwater. With the help of a field-installed membrane-inlet mass-spectrometer we resolved the effects of flood induced excess-air formation on organic carbon (OC) and nitrogen transformations in groundwater of different riparian zones of a restored section of the River Thur, Switzerland. The results show that the flood event triggered high aerobic respiration activity in the groundwater below a zone densely populated with willow plants. The flood introduced high concentrations of O2 (230 μmol L−1) to the groundwater through the formation of excess air and transported up to ~400 μmol L−1 OC from the soil/root layer into groundwater during the movement of the water table. A rapid respiration process, quantified via the measurements of O2, CO2, and noble-gas concentrations, led to fast depletion of the introduced O2 and OC and to high CO2 concentration (590 μmol L−1) in the groundwater shortly after the flood. The synchronous analysis of different nitrogen species allowed studying the importance of denitrification activity. The results indicate that in the willow zone excess-air formation inhibited denitrification through high O2 concentration input. Instead, the observed decrease in nitrate concentration (~50 μmol N L−1) may be related to fostered nitrate uptake by plants. In the other riparian zones closer to the river, no significant excess-air formation and corresponding respiration activity was observed. Overall, analyzing the dissolved gases in the groundwater significantly contributed to deciphering biogeochemical processes in the riparian aquifer characterized by pronounced changes in the flow regime and by spatial heterogeneity of the vegetation. Measuring excess-air formation helped identifying and explaining the low denitrification activity in a zone with high OC turnover and to quantify OC sources

Der Östrogenisierung der Umwelt auf der Spur : Wirkprofile östrogen-aktiver Substanzen in kommunalem Abwasser

In den letzten 50 Jahren hat sich die Wasserqualität der Schweizer Gewässer stark verbessert, dies nicht zuletzt wegen des hohen technischen Stands der Abwasserentsorgung und -reinigung. Heutzutage ist der Gewässerschutz u.a. mit der Problematik der Mikroverunreinigungen konfrontiert. Zu diesen Spurenstoffen zählen auch östrogen-aktive Substanzen, wie z.B. Östron (E1), 17β-Östradiol (E2) und 17-Ethinylöstradiol (EE2). Diese Substanzen sind bereits in sehr niedrigen Konzentrationen problematisch in Gewässern. Aus diesem Grund hat das Ökotoxzentrum der Schweiz einen akuten Ökotoxizitätswert von 0.4 ng/L für hormonaktive Subtanzen vorgeschlagenen. In dieser Studie wurden nun 20 verschiedene Abwasserreinigungsanlagen (ARA) des Kantons Zürich mittels dem planar-Yeast Estrogen Screen (planar-YES), welcher Dünnschichtchromatographie und Biotest koppelt, auf östrogenaktive Substanzen untersucht. Nur in vier Abwasserproben wurden keine östrogen-aktiven Substanzen gefunden, jedoch die Hälfte der 24 Proben wies eine Östrogenaktivität auf, die über dem vorgeschlagenen Schwellenwert von 0.4 ng/l lag. Die maximale Anzahl detektierter östrogen-aktiver Substanzen betrug 8 und wurde im Ablauf einer Vorklärung gefunden. Im Ablauf der Nachklärungen lag die maximale Anzahl östrogen-aktiver Substanzen bei 6, im Ablauf nach Filtration nurmehr bei 5. Die durchgeführte Studie zeigt klar, dass der planar-YES geeignet ist, in grosser Auflösung östrogene Aktivitätsprofile und deren zeitliche Änderung in ARA zu erstellen. Der planar-YES ist damit ein effizienter und kostengünstiger Biotest, der eine detaillierte Charakterisierung der östrogenen Aktivität von Abwasserproben erlaub

Sources and emission of greenhouse gases in Danube Delta lakes

ISSN:0944-1344ISSN:1614-749

Anaerobic ammonium oxidation in a tropical freshwater system (Lake Tanganyika)

Here we provide the first direct evidence for the anammox process (anaerobic ammonium oxidation) in a lacustrine system, Lake Tanganyika, the second largest lake in the world. Incubations with (15)N labelled nitrate showed that anammox occurred in the suboxic water layer at 100-110 m water depth. Anammox rates up to 10 nM N(2) h(-1) are comparable to those reported for the marine water column. Up to approximately 13% of produced N(2) could be attributed to the anammox process whereas the remainder was related to denitrification. Typical lipid biomarkers characteristic of anammox bacteria were found in filtered water from the depths where anammox occurred, thus supporting the presence of anammox bacteria. Further evidence is provided by fluorescence in situ hybridization (FISH), revealing up to 13 000 anammox bacteria cells per ml or 1.4% of all DAPI (4'-6-Diamidino-2-phenylindole)-stained cells. Phylogenetic analyses of partial 16S rRNA genes indicated the presence of sequences most closely related to the known anammox bacterium Candidatus "Scalindua brodae" (95.7% similarity). Using the incubation results, a total loss of 0.2 Tg N(2) per year linked to anammox was estimated for the Northern basin of Lake Tanganyika