Global Change Abstracts The Swiss Contribution - SCNAT

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144 Global Change Abstracts – The Swiss Contribution | Oceans and Fresh Water Systems 08.1-280 Iron-mediated microbial oxidation and abiotic reduction of organic contaminants under anoxic conditions Tobler N B, Hofstetter T B, Straub K L, Fontana D, Schwarzenbach R P Switzerland, Austria Microbiology , Geochemistry & Geophysics , Marine & Freshwater Biology In anoxic environments, the oxidation of organic compounds, such as BTEX fuel components, by dissimilatory Fe(III) reduction can generate reactive mineral-bound Fe(II) species, which in turn are able to reduce other classes of organic and inorganic groundwater contaminants. In this study, we designed and evaluated an anaerobic batch reactor that mimicks iron-reducing conditions to investigate the factors that favor the coupling of microbial toluene oxidation and abiotic reduction of nitroaromatic contaminants . We investigated the influence of different Fe(III)-bearing minerals and combinations thereof on the coupling of these two processes. Results from laboratory model systems show that complete oxidation of toluene to CO 2 by Geobacter metallireducens in the presence of Fe(III)-bearing minerals leads to the formation of mineral-bound Fe(II) species capable of the reduction of 4-nitroacetophenone. Whereas significant microbial toluene oxidation was only observed in the presence of amorphous Fe(III) phases, reduction of nitroaromatic compounds only proceeded with Fe(II) species bound to crystalline Fe(III) oxides. Our results suggest that in anoxic soils and sediments containing amorphous and crystalline iron phases simultaneously, coupling of microbial oxidation and abiotic reduction of organic compounds may allow for concurrent natural attenuation of different contaminant classes. Environmental Science Technology, 2007, V41, N22, NOV 15, pp 7765-7772. 08.1-281 Probabilistic flood forecasting with a limitedarea ensemble prediction system: Selected case studies Verbunt M, Walser A, Gurtz J, Montani A, Schär C Switzerland, Italy Modelling , Hydrology , Meteorology & Atmospheric Sciences A high-resolution atmospheric ensemble forecasting system is coupled to a hydrologic model to investigate probabilistic runoff forecasts for the alpine tributaries of the Rhine River basin (34 550 km(2)). Five-day ensemble forecasts consisting of 51 members, generated with the global ensemble prediction system (EPS) of the European Centre for Medium-Range Weather Forecasts (ECMWF), are downscaled with the limited-area model Lokal Modell (LM). The resulting limited-area ensemble prediction system (LEPS) uses a horizontal grid spacing of 10 km and provides one-hourly output for driving the distributed hydrologic model Precipitation-Runoff-Evapotranspiration-Hydrotope (PREVAH) hydrologic response unit (HRU) with a resolution of 500 x 500 m(2) and a time step of 1 h. The hydrologic model component is calibrated for the river catchments considered, which are characterized by highly complex topography, for the period 1997-98 using surface observations, and validated for 1999-2002. This study explores the feasibility of atmospheric ensemble predictions for runoff forecasting, in comparison with deterministic atmospheric forcing. Detailed analysis is presented for two case studies: the spring 1999 flood event affecting central Europe due to a combination of snowmelt and heavy precipitation, and the November 2002 flood in the Alpine Rhine catchment. For both cases, the deterministic simulations yield forecast failures, while the coupled atmospheric-hydrologic EPS provides appropriate probabilistic forecast guidance with early indications for extreme floods. It is further shown that probabilistic runoff forecasts using a subsample of EPS members, selected by a cluster analysis, properly represent the forecasts using all 51 EPS members, while forecasts from randomly chosen subsamples reveal a reduced spread compared to the representative members. Additional analyses show that the representation of horizontal advection of precipitation in the atmospheric model may be crucial for flood forecasts in alpine catchments. Journal of Hydrometeorology, 2007, V8, N4, AUG, pp 897-909. 08.1-282 Where a springhead becomes a springbrook - a regional zonation of springs von Fumetti S, Nagel P, Baltes B Switzerland Ecology , Marine & Freshwater Biology , Biodiversity Hydrology , Zoology Springs are important freshwater habitats that provide specific abiotic conditions for many species. These conditions may change very rapidly downstream. Limnologists tend to treat spring sources and their adjacent springbrooks as a unity because of the lack of clear criteria to separate these sections. In this study, we investigated the longitudinal distribution of macroinvertebrate assemblages in ten undisturbed springs in northwestern Switzerland at three different distances
Global Change Abstracts – The Swiss Contribution | Oceans and Fresh Water Systems from the source. Using non-metric multidimensional scaling and analysis of similarities, we detected significant differences between the macroinvertebrate assemblages of the investigated sections in all spring ecosystems, even over short distances. These results stress the importance of distinguishing between the sequential habitats in this upper region of headwaters. Although a complex of abiotic factors is responsible for the distribution of macroinvertebrates, we consider temperature to be of special importance. Based on our faunistic data, we propose that the rheocrene-like springs in the Jura Mountains consist of two sections: the springhead and the springbrook, with the springhead consisting of the source and the upper part of the adjacent downstream section. In accordance with literature and our faunistic and temperature data, we place the beginning of the springbrook at approximately 5 m from the springhead. With this distinction, we justify that springheads and springbrooks are unique, discrete ecosystems, and as such must be considered in conservation legislation. Fundamental and Applied Limnology, 2007, V169, N1, pp 37-48. 08.1-283 Nitrate-depleted conditions on the increase in shallow northern European lakes Weyhenmeyer G A, Jeppesen E, Adrian R, Arvola L, Blenckner T, Jankowski T, Jennings E, Noges P, Noges T, Straile D Sweden, Denmark, Germany, Finland, Switzerland, Ireland, Italy, Estonia Limnology , Geochemistry & Geophysics , Marine & Freshwater Biology We determined relative nitrate-nitrogen (NO 3- N) loss rates in 100 north-mid-European lakes from late spring to summer by using the exponential function N-2 5 N-1e(-k)((t)(2) - (t)(2)), where N-1 and N-2 are NO 3- N concentrations at the beginning (t(1)) and the end (t (2)) of the time interval, respectively, and k is the specific NO 3- N loss rate. We found that k decreased with increasing lake depth. Adjusting k to the lake depth (k(adj)), we observed that k(adj) was positively related to spring NO 3-N concentrations, but this relationship became insignificant at mean lake depths exceeding 12.5 m. A relationship between k(adj) and spring NO 3-N concentrations in lakes shallower than 12.5 m implies that changes in spring NO 3-N concentrations influence the NO 3- N loss rate and thereby summer NO 3- N concentrations. Time series from one Estonian, one German, and 14 Swedish lakes shallower than 12.5 m since 1988 revealed that May to August NO 3- N concentrations have decreased 145 over time everywhere, and the number of time periods exhibiting a NO 3- N depleted condition, i.e., NO3-N levels below 10 µ g L-1, in these lakes has tripled since 1988. We explained the decreasing NO 3- N concentrations by a reduction in external nitrogen loading including atmospheric deposition, and by changes in climate. The observed prolongation of NO 3- N depleted conditions might be one possible explanation for the increasing occurrence of nitrogen- fixing cyanobacteria in a variety of lake ecosystems. Limnology and Oceanography, 2007, V52, N4, JUL, pp 1346-1353. 08.1-284 Differential decline and recovery of haplochromine trophic groups in the Mwanza Gulf of Lake Victoria Witte F, Wanink J H, Kishe Machumu M, Mkumbo O C, Goudswaard P C, Seehausen O Netherlands, Tanzania, Switzerland Marine & Freshwater Biology , Biodiversity , Ecology Zoology Lake Victoria had a fish fauna dominated by 500+ species of haplochromine cichlids that made up more than 80% of the fish mass. The five main trophic groups caught with bottom trawlers in the sub- littoral areas of the Mwanza Gulf were: detritivores, zooplanktivores, insectivores, molluscivores and piscivores. The detritivores (13+ species) formed the most important guild, making up 60-80% of the number of individuals, followed by the zooplanktivores (12+ species), which comprised 10-30%. In the 1980s the haplochromines from the sub-littoral and offshore areas (estimated at some 200 species) vanished almost completely. Commercial trawl fishery, the upsurge of the introduced Nile perch, and an increase of eutrophication were potential causes of this decline. In the 1990s, when Nile perch was heavily fished, a recovery of some haplochromine species was observed. We studied the decline and partial recovery of the different haplochromine trophic groups in the northern part of the Mwanza Gulf. The rate at which the trophic groups declined differed; the relatively large piscivores, insectivores and molluscivores were the first to disappear from the catches. The small detritivores and zooplanktivores declined at lower rates, especially the latter group. From the beginning of the 1990s a resurgence of both groups was observed. By 2001, the zooplanktivores had reached their previous level of abundance, but their diversity declined from more than 12 species to only three. Though four detritivorous species began being regularly caught again, they constituted only about 15% of
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