Langenargen, Germany
Langenargen, Germany

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Fink G.,Eawag - Swiss Federal Institute of Aquatic Science and Technology | Schmid M.,Eawag - Swiss Federal Institute of Aquatic Science and Technology | Wahl B.,Institute for Lake Research | Wolf T.,Institute for Lake Research | And 2 more authors.
Water Resources Research | Year: 2014

Within the last decades, the water temperature of several European lakes has risen. It is assumed that these temperature increases are due to a reconfiguration of the heat-balance components. This study explores the dominant modifications of heat exchange with the atmosphere and their temporal evolutions. The objective is to identify the primary changes in heat fluxes and the sequence of events of the reconfiguration for the period 1984-2011. For this purpose, a model was applied to Lake Constance to estimate the contributions of the individual heat fluxes to the total heat balance. The results show that increasing absorption of solar radiation (+0.21 ± 0.13 W m-2 yr-1) and of longwave radiation (+0.25 ± 0.11 W m-2 yr-1) was responsible for the lake surface warming of 0.046 ± 0.011C yr-1. Heat losses to the atmosphere by longwave emission (-0.24 ± 0.06 W m-2 yr-1) and by latent heat flux (-0.27 ± 0.12 W m-2 yr-1) have intensified in parallel due to higher lake surface temperatures. The heat budget is in a quasi-steady state, whereas incoming solar radiation and the warmer atmosphere increased the lake surface temperature; the warmer surface emits more longwave radiation and more water is evaporated. At each level of the slowly increasing water temperature, the heat fluxes are balanced. The overall change of the total heat content, however, is relatively little. Although the cooling effect of inflowing rivers decreased, this contribution is also small. Key Points Estimation of trends in surface heat fluxes in Lake Constance over three decades Increased shortwave and longwave radiation cause higher water temperatures Increased heat loss by nonradiative fluxes maintain a constant heat content in the lake © 2014. American Geophysical Union. All Rights Reserved.


Matter M.,Eawag - Swiss Federal Institute of Aquatic Science and Technology | Anselmetti F.S.,Eawag - Swiss Federal Institute of Aquatic Science and Technology | Jordanoska B.,Hydrobiological Institute Ohrid | Wagner B.,University of Cologne | And 3 more authors.
Biogeosciences | Year: 2010

To date, little is known about the role of spring waters with respect to authigenic carbonate precipitation in a shallow lacustrine setting. Lake Ohrid, located in Southeastern Europe, is a large lake fed to over 50% by karstic springs of which half enter subaquatically and influence significantly its ecology and species distribution. In order to evaluate how sedimentological processes are influenced by such shallow-water springs, the Kališta subaquatic spring area in the north west of Lake Ohrid was investigated by a sidescan sonar survey and with sediment traps and three transects of gravity short cores. Results indicate that sedimentation in the spring area is dominated by authigenic carbonate precipitation. High sedimentation rates and evidences for bio-induced precipitation processes were observed in the water column and in the sediments. Two distinct stratigraphic units characterize the shallow subsurface, both composed of carbonate silts with high carbonate contents of up to 96%, but differing in color, carbonate content and diatom content. A chronological correlation of the cores by radiocarbon dates and 137Cs activities places the transition between the two stratigraphic units after ∼1955 AD. At that time, coastal sedimentation changed drastically to significantly darker sediments with higher contents of organic matter and more abundant diatoms. This change coincides with the recent human impact of littoral eutrophication. © 2010 Author(s).


Lindhorst K.,Leibniz Institute of Marine Science | Vogel H.,University of Cologne | Krastel S.,Leibniz Institute of Marine Science | Wagner B.,University of Cologne | And 5 more authors.
Biogeosciences | Year: 2010

Ancient Lake Ohrid is a steep-sided, oligotrophic, karst lake that was tectonically formed most likely within the Pliocene and often referred to as a hotspot of endemic biodiversity. This study aims on tracing significant lake level fluctuations at Lake Ohrid using high-resolution acoustic data in combination with lithological, geochemical, and chronological information from two sediment cores recovered from sub-aquatic terrace levels at ca. 32 and 60 m water depth. According to our data, significant lake level fluctuations with prominent lowstands of ca. 60 and 35 m below the present water level occurred during Marine Isotope Stage (MIS) 6 and MIS 5, respectively. The effect of these lowstands on biodiversity in most coastal parts of the lake is negligible, due to only small changes in lake surface area, coastline, and habitat. In contrast, biodiversity in shallower areas was more severely affected due to disconnection of today sub-lacustrine springs from the main water body. Multichannel seismic data from deeper parts of the lake clearly image several clinoform structures stacked on top of each other. These stacked clinoforms indicate significantly lower lake levels prior to MIS 6 and a stepwise rise of water level with intermittent stillstands since its existence as water-filled body, which might have caused enhanced expansion of endemic species within Lake Ohrid. © Author(s) 2010.


Luddeke F.,Institute for Lake Research | Hess S.,Karlsruhe Institute of Technology | Gallert C.,Emden Leer University of Applied Sciences | Winter J.,Karlsruhe Institute of Technology | And 2 more authors.
Water Research | Year: 2015

Elimination of bacteria by ozonation in combination with charcoal or slow sand filtration for advanced sewage treatment to improve the quality of treated sewage and to reduce the potential risk for human health of receiving surface waters was investigated in pilot scale at the sewage treatment plant Eriskirch, Baden-Wuerttemberg/Germany. To determine the elimination of sewage bacteria, inflowing and leaving wastewater of different treatment processes was analysed in a culture-based approach for its content of Escherichia coli, enterococci and staphylococci and their resistance against selected antibiotics over a period of 17 month. For enterococci, single species and their antibiotic resistances were identified. In comparison to the established flocculation filtration at Eriskirch, ozonation plus charcoal or sand filtration (pilot-scale) reduced the concentrations of total and antibiotic resistant E. coli, enterococci and staphylococci. However, antibiotic resistant E. coli and staphylococci apparently survived ozone treatment better than antibiotic sensitive strains. Neither vancomycin resistant enterococci nor methicillin resistant Staphylococcus aureus (MRSA) were detected. The decreased percentage of antibiotic resistant enterococci after ozonation may be explained by a different ozone sensitivity of species: Enterococcus faecium and Enterococcus faecalis, which determined the resistance-level, seemed to be more sensitive for ozone than other Enterococcus-species. Overall, ozonation followed by charcoal or sand filtration led to 0.8-1.1 log-units less total and antibiotic resistant E. coli, enterococci and staphylococci, as compared to the respective concentrations in treated sewage by only flocculation filtration. Thus, advanced wastewater treatment by ozonation plus charcoal or sand filtration after common sewage treatment is an effective tool for further elimination of microorganisms from sewage before discharge in surface waters. © 2014 Elsevier Ltd.


Traunspurger W.,Bielefeld University | Hoss S.,Ecossa | Witthoft-Muhlmann A.,Institute for Lake Research | Wessels M.,Institute for Lake Research | Gude H.,Bielefeld University
Fundamental and Applied Limnology | Year: 2012

Between February and April 2004, 48 sites in Lake Constance (Germany) were investigated to determine the distribution of the meiobenthic community, including 16 sites from the sub-littoral (13 - 30 m water depth), 16 sites from the profundal (31- 99 m) and 16 sites from the deep profundal (100 - 250 m). Lake-wide analysis showed no simple distribution pattern, but rather a heterogenic meiobenthic community composition, with nematodes representing the dominant group (48.7 %), followed by rotifers (27.7 %), harpacticoids (7.7 %), copepods (5.0 %), oligochaetes (3.7 %), ostracods (3.1 %), nauplii (1.9 %) and tardigrades (1.2 %). The relative abundances of all other investigated meiobenthic groups (cladocerans, chironomids, arachnids, gastrotrichs) were below 1 %. The densities of meiobenthic organisms varied greatly between sites, with nematodes reaching up to 3,336,676 and rotifers up to 6,357,008 individuals per m2. The abundances of most organisms varied significantly between the different water zones. Nematodes, copepods, nauplii and cladocerans, however, were equally distributed between sub-littoral and the profundal zones. Organisms showed their highest levels of abundance in the sub-littoral zone, with the exception of harpacticoids and ostracods, which were most abundant in the profundal and deep profundal respectively. A multivariate statistical analysis revealed that besides Chl-a explaining 47 % of the variance degenerated algae, water depth, mean grain size, organic carbon, C/N ratio and total phosphorus were significantly correlated with lake-wide community structure. In the sub-littoral, mean grain size was the most important parameter explaining 25.4 % of the variance, while in the profundal Chl-a (29.4 %) and in the deep profundal algae pigments (38.6 %) were the most important parameters for meiofaunal distribution and environmental variables. © 2012 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.


Wessels M.,Institute for Lake Research | Bussmann I.,Alfred Wegener Institute for Polar and Marine Research | Schloemer S.,Federal Institute for Geosciences and Natural Resources | Schluter M.,Alfred Wegener Institute for Polar and Marine Research | Boder V.,HafenCity University Hamburg
Limnology and Oceanography | Year: 2010

Pockmarks are well known in the marine environment but almost unreported from limnic systems. In Lake Constance we investigated pockmarks near the mouth of the main tributary, Alpine Rhine River, using sediment cores and hydroacoustics (sidescan sonar, subbottom profiler, horizontal scanning sonar, multibeam echo sounder). The maximum dimension of an individual pockmark is about 16 m in diameter and 3-4-m deep, often with a round shape. Most pockmarks are located on top of morphological high points such as sediment waves or shoulders of old channels in front of the Alpine Rhine River. They are collapse structures formed when a reservoir of biogenic methane rapidly empties into the water column. Ebullition of gas very often was observed, indicating that biogenic methane still migrates toward pockmarks. © 2010, by the American Society of Limnology and Oceanography, Inc.


Bussmann I.,Alfred Wegener Institute for Polar and Marine Research | Damm E.,Alfred Wegener Institute for Polar and Marine Research | Schluter M.,Alfred Wegener Institute for Polar and Marine Research | Wessels M.,Institute for Lake Research
Biogeochemistry | Year: 2013

In the eastern part of Lake Constance, the second largest pre-alpine lake in Europe, about five hundred pockmarks (morphological depressions on the lake floor) were recently discovered of which ~40 % release methane bubbles. The carbon isotopic composition of the escaping gas indicated that the methane is of biogenic origin. In our study, we investigated the fate of the released methane bubbles, i. e., the dissolution, oxidation or transport of the bubbles to the surface. At a littoral pockmark site (PM12, 12 m water depth) and a profundal pockmark (PM80, 80 m water depth), we analysed the dissolved methane concentrations and the methane isotopic carbon signature in the water column. At PM80, higher methane concentrations (up to 1,523 nM), compared to the control site and the surface waters (225 ± 72 nM), were recorded only on some occasions and only in the bottom water, despite the fact that the released bubbles were dissolving within the hypolimnion based on bubble modeling. The isotope data suggest that most of the dissolved methane is oxidized below 40 m water depth. The isotopic signature of the methane in the surface water at PM80, however, differed from that of the methane in the hypolimnion; therefore, the surface methane at this profundal site is most likely an export product from the littoral zone. Assuming an initial bubble diameter of 5 mm, we calculated that these small bubbles would reach the surface, but approximately 96 % of the methane would have dissolved from the bubble into the hypolimnion. At PM12, we observed higher concentrations of dissolved methane (312 ± 52 nM) with no significant differences between seasons or between control sites versus pockmark site. In the shallow water, divers estimated the bubble size to be 10-15 mm, which from a release depth of 12 m would barely dissolved into the water column. The isotopic signature also indicated that there had been almost no methane oxidation in the shallow water column. Thus, the water depth of bubble release as well as the initial bubble size determine whether the methane enters the atmosphere largely unhindered (shallow site) or if the released methane is incorporated into the profundal water column. © 2012 Springer Science+Business Media B.V.


Bussmann I.,Alfred Wegener Institute for Polar and Marine Research | Schlomer S.,Federal Institute for Geosciences and Natural Resources | Schluter M.,Alfred Wegener Institute for Polar and Marine Research | Wessels M.,Institute for Lake Research
Limnology and Oceanography | Year: 2011

In the eastern part of Lake Constance, the second largest prealpine lake in Europe, about 500 pockmarks (morphological depressions on the lake floor) were recently discovered. The diameters of these pockmarks are as large as 16 m, and about 24% of them continuously release methane in the form of visible bubbles. The isotopic composition of the escaping gas indicated that the methane was of biogenic origin and was predominantly produced by the CO2-reduction pathway. In shallow-water pockmarks (9 m and 12 m), pore-water analysis revealed increased methane concentrations of > 1100 μmol L-1 in the sediment. Diffusive methane fluxes and oxidation rates within these shallow pockmarks were much higher than in sediments outside pockmarks. An estimated methane ebullition into the water column of about 40 L h-1 per pockmark showed that methane ebullition is by far the dominant pathway of methane release from these shallow pockmarks. Meiofauna abundance and organic carbon contents of the sediment were also higher in the shallow pockmarks, but there were no differences in macrofauna. In a deep pockmark (80 m), even though bubble release was observed, the sediment inside the pockmark had almost the same methane concentrations and isotopic compositions as a site outside of the pockmark. At both sites, the shallow and deep pockmark act mainly as sedimentation traps, the emanating gas has only minor influence on the methane inventory of the sediments and, therefore, gas bubbles enter the water column essentially unaffected. © 2011, by the American Society of Limnology and Oceanography, Inc.


Vogel H.,University of Cologne | Wessels M.,Institute for Lake Research | Albrecht C.,Justus Liebig University | Stich H.-B.,Institute for Lake Research | Wagner B.,University of Cologne
Biogeosciences | Year: 2010

Lake Ohrid is likely of Pliocene age and thus commonly referred to as the oldest existing lake in Europe. In this study spatial variability of recent sediment composition is assessed using >50 basin wide distributed surface sediment samples. Analysis of biogeochemical bulk parameters, selected metals, pigment concentrations as well as grain size distributions revealed a significant spatial heterogeneity in surface sediment composition. It implies that sedimentation in Lake Ohrid is controlled by an interaction of multiple natural and anthropogenic factors and processes. Major factors controlling surface sediment composition are related to differences in geological catchment characteristics, anthropogenic land use, and a counterclockwise rotating surface water current. In some instances processes controlling sediment composition also seem to impact distribution patterns of biodiversity, which suggests a common interaction of processes responsible for both patterns.


Fuentes N.,Institute for Lake Research | Fuentes N.,University of Los Lagos | Gude H.,Institute for Lake Research | Straile D.,University of Konstanz
International Review of Hydrobiology | Year: 2013

This study evaluates the nutritional importance of allochthonous matter supply for profundal macrozoobenthic communities and determines abundances and carbon sources used by chironomids and oligochaetes at two sampling sites with different allochthonous contributions, in the deep oligotrophic waters of Lake Constance. Site AL, characterized by sedimenting organic matter (POMsed) with a more allochthonous origin was dominated by oligochaetes, whereas site AU characterized by POMsed of predominantly autochthonous origin, was dominated by chironomids. Total macroinvertebrate abundances were 10-20 times higher at site AL compared to site AU. At site AL microbial biomass per gram dry sediment (indicated by ATP content and bacterial abundances) was lower, whereas microbial activity (incorporation of leucine, respiration of glucose) was higher than at site AU. A higher metabolic activity at site AL was also indicated by steeper oxygen gradients in sediment microprofiles. Mean δ13C stable isotope signatures of oligochaetes (δ13C=-33.24±1.27‰) and, to an even greater extent, of the dominant chironomid Micropsectra sp. (δ13C=-40.08±1.65) at site AL were depleted compared to site AU for oligochaetes (δ13C=-30.19±0.60‰) and chironomids (δ13C=-30.40±0.75‰). At site AL, mean δ13C values of chironomids and oligochaetes were 11‰ and 4‰ lower, respectively, than mean POMsed δ13C. At site AU, benthic macroinvertebrates and POMsed were of comparable magnitude. The lower invertebrate δ13C values at site AL suggest an increased contribution of methane oxidizing bacteria (MOB) to the diet of the benthic organisms. A mixing model based on stable carbon isotopes suggests that at site AL 21 to 44% of chironomid diet and 9 to 19% of oligochaete diet stems from MOB consumption, whereas calculated MOB consumption was zero at site AU. Mean δ15N values of chironomids and oligochaetes were higher at both sites compared to POMsed, but at site AL (oligochaetes=7.07±0.61‰, "Micropsectra sp."=8.62±0.30‰) the difference was less pronounced than at site AU (oligochaetes=13.71±0.30‰, "Micropsectra sp."=14.00±0.95‰). These differences are considered to reflect mainly the degree of biotic processing of POMsed before consumption by invertebrates. Given that autochthonous POMsed, i.e. chlorophyll sedimentation, was comparable at both sites, but differences were observed with respect to total POMsed sedimentation rates, δ13C and δ15N isotope signatures of POMsed, and microbial activities in the sediments, we suggest that there is a strong contribution of allochthonous POMsed supply to the nutrition of macrobenthic communities at site AL. This suggests that allochthonous carbon supply is at least partly bioavailable and stimulates microbial growth and metabolic activities in lake sediments, which in turn provides additional nutritional sources for benthic organisms. Furthermore, the example of Lake Constance shows that, even in a well-oxygenated oligotrophic lake, at least part of the allochthonous POMsed is made available to higher trophic levels via methane production and MOB biomass. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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