14 research outputs found
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 "Introductionâ), 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 phototransformationsâ and âUV-induced changes of the absorption properties of CDOMâ
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
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 âclathrate 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 âŒ4.1 Ă 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 (4âČ,6âČ-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. JĂžrgensen, 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 ÎŒmol Lâ1) to the groundwater through the formation of excess air and transported up to ~400 ÎŒmol Lâ1 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 ÎŒmol Lâ1) 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 ÎŒmol N Lâ1) 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 Ăstrogenisierung der Umwelt auf der Spur : Wirkprofile östrogen-aktiver Substanzen in kommunalem Abwasser
In den letzten 50 Jahren hat sich die WasserqualitĂ€t der Schweizer GewĂ€sser stark verbessert, dies nicht zuletzt wegen des hohen technischen Stands der Abwasserentsorgung und -reinigung. Heutzutage ist der GewĂ€sserschutz u.a. mit der Problematik der Mikroverunreinigungen konfrontiert. Zu diesen Spurenstoffen zĂ€hlen auch östrogen-aktive Substanzen, wie z.B. Ăstron (E1), 17ÎČ-Ăstradiol (E2) und 17-Ethinylöstradiol (EE2). Diese Substanzen sind bereits in sehr niedrigen Konzentrationen problematisch in GewĂ€ssern. Aus diesem Grund hat das Ăkotoxzentrum der Schweiz einen akuten ĂkotoxizitĂ€tswert von 0.4 ng/L fĂŒr hormonaktive Subtanzen vorgeschlagenen. In dieser Studie wurden nun 20 verschiedene Abwasserreinigungsanlagen (ARA) des Kantons ZĂŒrich mittels dem planar-Yeast Estrogen Screen (planar-YES), welcher DĂŒnnschichtchromatographie und Biotest koppelt, auf östrogenaktive Substanzen untersucht. Nur in vier Abwasserproben wurden keine östrogen-aktiven Substanzen gefunden, jedoch die HĂ€lfte der 24 Proben wies eine ĂstrogenaktivitĂ€t auf, die ĂŒber dem vorgeschlagenen Schwellenwert von 0.4 ng/l lag. Die maximale Anzahl detektierter östrogen-aktiver Substanzen betrug 8 und wurde im Ablauf einer VorklĂ€rung gefunden. Im Ablauf der NachklĂ€rungen lag die maximale Anzahl östrogen-aktiver Substanzen bei 6, im Ablauf nach Filtration nurmehr bei 5. Die durchgefĂŒhrte Studie zeigt klar, dass der planar-YES geeignet ist, in grosser Auflösung östrogene AktivitĂ€tsprofile und deren zeitliche Ănderung in ARA zu erstellen. Der planar-YES ist damit ein effizienter und kostengĂŒnstiger Biotest, der eine detaillierte Charakterisierung der östrogenen AktivitĂ€t 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