Showing papers by "Swiss Federal Institute of Aquatic Science and Technology published in 2000"

An extension of the flood pulse concept.

Abstract: The flood pulse concept of Junk, Bayley and Sparks is a major contribution to our understanding of river–floodplain interactions and has become an important paradigm in lotic ecology. The concept is based mainly on large tropical lowland rivers. Floodplains may, however, develop in all geographical areas and at different locations along a river corridor. We extend this concept to temperate areas by including information derived from near-natural proglacial, headwater and lowland floodplains. Specific attention is directed to the role of temperature as a major determinant of floodplain ecology. Further attention is directed to the importance of expansion–contraction cycles occurring well below bankfull (‘flow pulse’ versus ‘flood pulse’). Selected examples are presented that highlight the complexity of expansion–contraction events and their consequences on habitat heterogeneity and functional processes. Habitat heterogeneity is mainly a product of shifting water sources, different flow paths and the relative importance of autogenic processes. In different floodplain systems, expansion may enhance habitat heterogeneity (e.g. glacial floodplain) or create homogeneity (e.g. Danubian floodplain). Further, the ecological consequences of episodic flow and flood pulses are discussed. Finally, a landscape approach is suggested in order to document expansion and contraction processes and to elucidate how these processes influence landscape heterogeneity and biodiversity patterns. Such a landscape-based ecosystem model can be applied to rigorously assess the ecological integrity of river–floodplain systems. Copyright © 2000 John Wiley & Sons, Ltd.

Mobilization of Arsenite by Dissimilatory Reduction of Adsorbed Arsenate

Abstract: Sulfurospirillum barnesii is capable of anaerobic growth using ferric iron or arsenate as electron acceptors. Cell suspensions of S. barnesii were able to reduce arsenate to arsenite when the former oxyanion was dissolved in solution, or when it was adsorbed onto the surface of ferrihydrite, a common soil mineral, by a variety of mechanisms (e.g., coprecipitation, presorption). Reduction of Fe(III) in ferrihydrite to soluble Fe(II) also occurred, but dissolution of ferrihydrite was not required in order for adsorbed arsenate reduction to be achieved. This was illustrated by bacterial reduction of arsenate coprecipitated with aluminum hydroxide, a mineral that does not undergo reductive dissolution. The rate of arsenate reduction was influenced by the method in which arsenate became associated with the mineral phases and may have been strongly coupled with arsenate desorption rates. The extent of release of arsenite into solution was governed by adsorption of arsenite onto the ferrihydrite or alumina phase...

Degradation Kinetics of Atrazine and Its Degradation Products with Ozone and OH Radicals: A Predictive Tool for Drinking Water Treatment

Abstract: The present study investigates the degradation of atrazine (2-chloro-4-(ethylamino)-6-isopropylamino-s-triazine) by ozone and OH radicals during ozonation and advanced oxidation processes, with the identification of the main degradation products. Besides the dealkylated and amide degradation products(6-amino-2-chloro-4-isopropylamino-s-triazine, 6-amino-2-chloro-4-(ethylamino)-s-triazine, 4-acetamido-2-chloro-6-isopropylamino-s-triazine, 4-acetamido-6-amino-2-chloro-s-triazine, and chlorodiamino-striazine), two new degradation products with an imine group were identified (2-chloro-4-ethylimino-6-isopropylamino-s-triazine and 6-amino-2-chloro-4-ethylimino-s-triazine). The contribution of the different pathways (direct ozone and OH radical reaction) to the overall degradation process has been quantified, and the rate constants of the reactions of atrazine and its main degradation products with both oxidants have been measured. The ethyl group is more reactive than the isopropyl group (i.e. 19 times during ozonation and four times during OH radical attack). The ethyl group reacts in higher proportion through oxidation to acetamide or imine derivates than to dealkylation. In contrast, the isopropyl group reacts mainly through dealkylation to the free amino group. Acetamido and imino groups a re found to be resistant to chemical oxidation. These reactivities were corroborated by the measured values of the rate constants with both oxidants. A combination of product distribution and the kinetic parameters together with ozone and OH radical concentrations allowed us to calculate the evolution of the concentration of the degradation products for a given ozonation process.

Formation of Iodo-Trihalomethanes during Disinfection and Oxidation of Iodide-Containing Waters

Abstract: The formation of iodo-trihalomethanes (I-THMs) such as iodoform (CHI3) during oxidative treatment of iodide-containing drinking waters can be responsible for taste and odor problems. I-THMs are formed by reactions of hypoiodous acid (HOI) with natural organic matter. HOI is quickly formed from naturally occurring iodide (I-) by oxidation with ozone, chlorine, or chloramine. The kinetics of reactions of HOI with organic model compounds as well as the resulting CHI3 formation were measured. Substituted phenols, phenol, and, to a smaller extent, α-methyl carbonyl compounds were found to be reactive toward HOI and also to yield CHI3. Resorcinol (m-hydroxyphenol) had the highest yield of CHI3. The kinetics of I-THM formation were also measured in natural waters which were oxidatively treated with ozone, chlorine, or chloramine. When ozone was used, no I-THMs were detected and ≥90% of I- was transformed to IO3-. Chlorine led to the formation of both IO3- and I-THMs. With increasing chlorine doses, the CHI3 form...

Palaeotemperature reconstruction from noble gases in ground water taking into account equilibration with entrapped air

Abstract: Noble-gas concentrations in ground water have been used as a proxy for past air temperatures1,2,3,4,5,6,7, but the accuracy of this approach has been limited by the existence of a temperature-independent component of the noble gases in ground water, termed ‘excess air’, whose origin and composition is poorly understood7,8,9. In particular, the evidence from noble gases in a Brazilian aquifer for a cooling of more than 5 °C in tropical America during the Last Glacial Maximum4 has been called into question9. Here we propose a model for dissolved gases in ground water, which describes the formation of excess air by equilibration of ground water with entrapped air in quasi-saturated soils10,11,12. Our model predicts previously unexplained noble-gas data sets, including the concentration of atmospheric helium, and yields consistent results for the non-atmospheric helium isotopes that are used for dating ground water. Using this model of excess air, we re-evaluate the use of noble gases from ground water for reconstructing past temperatures. Our results corroborate the inferred cooling in Brazil during the Last Glacial Maximum4, and indicate that even larger cooling took place at mid-latitudes.

Factors Determining the Element Behavior in Municipal Solid Waste Incinerators. 1. Field Studies

Abstract: This paper investigates the factors determining element behavior in municipal solid waste incinerators. The method is based primarily on field measurements in full-scale incinerators. Material flow analyses are carried out in an incinerator. The main focus is placed on the processes in the furnace. The following master variables determine element transfer behavior to the raw gas in the furnace: (i) occurrence and distribution of the elements in the input waste; (ii) temperature, redox conditions, and content of chlorine and of reaction partners other than oxygen and chlorine in the furnace bed; and (iii) residence time and mixing conditions in the furnace bed. Twenty-nine elements are divided into two groups with respect to their transfer behavior to the raw gas and to the bottom ash in the furnace. The results indicate that the elements Si, Fe, Co, Cr, Mn, Ni, P, Al, Ca, Mg, Na, Ba, Li, Ti, and K are transferred mainly to the raw gas by entrainment. Occurrence and distribution of these elements in the i...

Response of climate to solar forcing recorded in a 6000-yearδ18O time-series of Chinese peat cellulose

Abstract: Previous studies have shown that the oxygen isotope ratio (d18O) of plant cellulose can serve as a sensitive proxy indicator of past climate, but its application has mainly been restricted to tree-rings. Here we present a 6000-year high-resolution d18O record of peat plant cellulose from northeastern China. The d18O variation is interpreted as reflecting changes in regional surface air temperature. The climate events inferred from the isotope data agree well with archaeological and historic evidence. The record shows a striking corre- spondence of climate events to nearly all of the apparent solar activity changes characterized by the atmospheric radiocarbon in tree-rings over the past 6000 years. Spectral analysis of the d 18 O record reveals the periodicities of around 86, 93, 101, 110, 127, 132, 140, 155, 207, 245, 311, 590, 820 and 1046 years, which are similar to those detected in the solar excursions. We consider these observations as further evidence for a close relation- ship between solar activity and climate variations on timescales of decades to centuries. Our results also have implications for distinguishing between natural and anthropogenic contributions to future climate change.

Long-term indirect indices of solar variability

Abstract: Continuous direct records of solar variability are limited to the telescopic era covering approximately the past four centuries. For longer records one has to rely on indirect indices such as cosmogenic radionuclides. Their production rate is modulated by magnetic properties of the solar wind. Using a parameterisation of the solar activity and a Monte Carlo simulation model describing the interaction of the cosmic rays with the atmosphere, the production rate for each cosmogenic nuclide of interest can be calculated as a function of solar activity. Analysis of appropriate well-dated natural archives such as ice cores or tree rings offers the possibility to reconstruct the solar activity over many millennia. However, the interpretation of the cosmogenic nuclide records from these archives is difficult. The measured concentrations contain not only information on solar activity but also on changes in the geomagnetic field intensity and the transport from the atmosphere into the archive where, under ideal conditions, no further processes take place. Comparison of different nuclides (e.g. 10Be and 14C) that are produced in a very similar way but exhibit a completely different geochemical behaviour, allows us to separate production effects from system effects. The presently available data show cyclic variability ranging from 11-year to millennial time scale periodicities with changing amplitudes, as well as irregularly distributed intervals of very low solar activity (so called minima, e.g. Maunder minimum) lasting typically 100 years.

Turbulent kinetic energy balance as a tool for estimating vertical diffusivity in wind‐forced stratified waters

Abstract: Based on microstructure measurements in a simply shaped lake basin, the sources of vertical mixing in the stratified part of the water body were identified and estimates of their relative importance obtained by balancing turbulent kinetic energy introduced by the wind. It was found that (1) similar to 1.9% of the vertical wind energy flux P-10 (similar to 39 mW m(-2)), estimated 10 m above the lake surface, was available for turbulent mixing in the entire lake water body; (2) similar to 1.5% of P-10 was dissipated by turbulence in the weakly stratified surface layer (epilimnion similar to 6 m deep), and similar to 0.42% of P-10 reached the stratified deep water (hypolimnion) as turbulent kinetic energy via internal seiching; (3) similar to 90% of the turbulent kinetic energy in the stratified water (i.e., 0.38% of P-10) was dissipated within the bottom boundary layer of a few meters thickness, whereas only similar to 10% was lost in the interior (away from the boundary; 0.04% of P-10); and (4) as a consequence mixing within the bottom boundary was found to be the main source of vertical mixing for the deep waters of the whole lake. The ratio of buoyancy flux to dissipation (i.e., the mixing efficiency) was found to be gamma(mix) approximate to 0.15, leading to agreement between the Osborn-Cox microstructure diffusivities and basin-wide tracer diffusivities. Comparison with turbulent kinetic energy balances, performed in five other lakes, demonstrates that this analysis is representative for many enclosed water bodies, as long as wind is the dominant source of turbulent energy (i.e., if other processes, such as convective mixing, double diffusion, or riverine intrusions can be neglected). Although the lakes under consideration were Very different in size and shape and although the currents in Lake Baikal were inertial rather than seiching related as in the other lakes, the turbulent kinetic energy balance was very similar and the mixing efficiency was identical. Typically, 0.3 +/- 0.1% of P-10 is transferred as turbulent kinetic energy into the stratified part of the water body, and 0.04 +/- 0.02% of P-10 is stored as potential energy in the stratification. This analysis provides a tool for estimating vertical diffusivity for wind-driven hypolimnetic mixing within a factor of two based on stratification and wind measurements alone.

Nutrient addition accelerates leaf breakdown in an alpine springbrook.

Abstract: This study assessed the effect of nutrient enrichment on organic matter breakdown in an alpine springbrook, using alder leaf packs to which phosphorus and nitrogen were added in the form of slow-release fertilizer briquettes. The breakdown of leaf packs with nutrients added (k=0.0284 day–1) was significantly faster than that of unfertilized packs (k=0.0137 day–1), resulting in a 30% higher mass loss after 42 days. Unfertilized leaves enclosed in fine-mesh bags broke down at an even slower rate (k=0.0062 day–1). Phosphorus and nitrogen concentrations were initially higher in leaf packs with nutrients added, but this difference disappeared within 3 weeks. Fungal biomass developing in decomposing leaves was substantial (c. 55 mg dry mass per 1 g leaf dry mass) although similar between fertilized and unfertilized packs, as was the sporulation activity of aquatic hyphomycetes. There was a significantly greater number and higher biomass of macroinvertebrates (shredding nemourid stoneflies in particular) on the fertilized packs, suggesting that the increased leaf mass loss was brought about by shredder feeding.

Microbial biomass, growth, and respiration associated with submerged litter of Phragmites australis decomposing in a littoral reed stand of a large lake

Abstract: This study examined the microbial dynamics associated with decomposing litter of the widespread emergent macrophyte Phragmites australis in a littoral reed stand of a large lake. Stand- ing dead leaf and stem litter were collected, placed into fine and coarse mesh litter bags, and sub- merged in the reed stand. Litter bags were retrieved periodically and analyzed for fungal and bacte- rial biomass, fungal growth rates and production, rates of microbial respiration, litter mass loss, nutrient concentrations (N and P), and rates of dissolved organic carbon (DOC) release. Microbial biomass associated with both leaf and stem litter (12 to 85 mg C g -1 detrital C) was predominantly fungal (always ♢90% of the total biomass), even though bacterial biomass (0.13 to 5.6 mg C g -1 detri- tal C) increased and fungal biomass decreased or remained constant as litter decay proceeded. Although rates of fungal growth (0.02 to 0.08% h -1 ) and production (leaves only; 3 to 51 µg C g -1 detrital C h -1 ), and rates of microbial respiration (11 to 257 µg C g -1 detrital C h -1 ) decreased follow- ing litter submergence, fungi continued to be metabolically active in both leaf and stem litter. Signif- icant differences in fungal and bacterial biomass, fungal production rates, and rates of respiration were observed between leaf and stem material, with leaves often having 5 times higher values than corresponding stems. Rates of mass loss differed significantly between leaf litter in fine and coarse mesh bags, with less than 10% of the initial mass remaining in coarse mesh bags after 86 d, versus nearly 60% remaining in fine mesh bags. Nitrogen and P concentrations of leaf litter enclosed in fine mesh bags increased during litter decay, whereas N concentrations of leaf litter in coarse mesh bags remained unchanged and P concentrations decreased. Both N and P concentrations of stem litter were similar among litter bags and varied little throughout the study period. Results obtained in this study indicate that significant changes in microbial colonization and activity associated with P. aus- tralis litter can occur following the collapse of standing dead plant matter to the water. Furthermore, these findings suggest that fungi are active on submerged litter and thus play a vital role in the decomposition of P. australis litter in the aquatic environment.

Cool glacial temperatures and changes in moisture source recorded in Oman groundwaters

Abstract: Concentrations of atmospheric noble gases (neon, argon, krypton, and xenon) dissolved in groundwaters from northern Oman indicate that the average ground temperature during the Late Pleistocene (15,000 to 24,000 years before present) was 65° ± 06°C lower than that of today Stable oxygen and hydrogen isotopic groundwater data show that the origin of atmospheric water vapor changed from a primarily southern, Indian Ocean source during the Late Pleistocene to a dominantly northern, Mediterranean source today The reduced northern water vapor source is consistent with a drier Last Glacial Maximum through much of northern Africa and Arabia

Resistance and resilience of ecosystem metabolism in a flood-prone river system

Abstract: 1. Gross primary production (GPP) and ecosystem respiration (ER) were analysed for 18 months in two reaches of the River Thur, a prealpine river in Switzerland. The upper reach at 655 m above sea level (a.s.l.) is bedrock constrained, has a high slope (0.60%) and a catchment area of 126 km 2 . The lower reach at 370 m a.s.l. has a more extensive hyporheic zone, a lower slope (0.17%) and a catchment of 1696 km 2 . 2. In both reaches, temporal patterns of stream metabolism reflected the occurrence of bed-moving spates. Average reductions of GPP and ER by spates were 53 and 24% in the upper reach, and 37 and 14% in the lower reach, respectively. The greater resistance of ER than GPP in both reaches shifted the ecosystem metabolism towards heterotrophy (decrease of the ratio of GPP to ER (P/R)) following spates. 3. Recovery of GPP was significantly faster in the lower reach and exhibited distinct seasonal variation (positive correlation with incident light). The differences in stability (both resistance and resilience) between reaches reflected differences in geomorphic settings and disturbance regime. 4. Stepwise regression analysis was used to explore the potential influence of season, disturbance and prevailing environmental conditions on stream metabolism in each reach. Time since spate plus temperature explained 73 and 86% of variation in ER and GPP, respectively, in the upper reach and 55% of variation in ER in the lower reach. Season plus prevailing environmental conditions explained 67% of variation in GPP in the lower reach. 5. To test how the perception of stability may change with increasing scale of observation, the disturbance regimes of 12 sites were compared with the disturbance regime of the entire Thur catchment. The analysis suggests that stream metabolism at the catchment scale is far more resistant to high flow events than at the reach scale.

Large wood retention in river channels: the case of the Fiume Tagliamento, Italy

Abstract: After more than 300 years of widespread and intensive river management, few examples of complex, unmanaged river systems remain within Europe. An exception is the Fiume Tagliamento, Italy, which retains a riparian woodland margin and unconfined river channel system throughout almost the entire 170 km length of its river corridor. A research programme is underway focusing on a range of related aspects of the hydrology, fluvial geomorphology and ecology of the Tagliamento. This paper contributes to that programme by focusing on large wood retention. The paper adopts a simple force:resistance approach at the scale of the entire river corridor in order to identify reaches of the river with a high wood retention potential. Information on the character of the river corridor is derived from 1:10 000 scale topographic maps. A range of indices measured at 330 transects across the river corridor supports a classification of the geomorphological style of the river which reflects the presence and abundance of properties previously identified in the literature as large wood retention sites. This classification provides a qualitative representation of the resistance of the corridor to wood movement and thus its overall wood-retention potential. The map-derived indices are also used to extrapolate estimates of the ten year return period flood to each of the 330 transects so that the downstream pattern of unit stream power can be quantified as an index representing force in the analysis. Although input of wood is an important factor in many river systems, it is assumed not to be a limiting factor along the Tagliamento, where riparian woodland is abundant. Field observations of large wood storage illustrate that wood retention at eight sites along the river reflects the presence and abundance of the features incorporated in the classification of geomorphological style, including the complexity of the channel network, the availability of exposed gravel areas, and the presence of islands. In general at the time of survey in August 1998, open gravel areas were estimated to store approximately 1 t ha-1 of wood in single-thread reaches and 6 t ha-1 in multiple-thread reaches. Established islands were estimated to store an average of 80 t ha-1 of wood. Nevertheless, there was considerable variability between sites, and pioneer islands, which are not represented on maps or readily identified from air photographs because of their small size, were estimated to store an order of magnitude more wood than established islands. Furthermore, the wood storage from this sample of eight sites did not reflect variability in estimated unit stream power. A series of areas for further research are identified, which can be explored using field data, and which will throw more light on the processes of wood retention in this extremely dynamic fluvial environment.

Reconstruction of the geomagnetic field between 20 and 60 kyr BP from cosmogenic radionuclides in the GRIP ice core

Abstract: A pure physical model for the simulation of cosmic ray particle interactions with the Earth’s atmosphere was used to investigate the effects of a changing geomagnetic field on the production rates of cosmogenic nuclides. Analytical dependencies of the production rates of 3H, 7Be, 10Be, 14C and 36Cl on geomagnetic field intensity were developed. Applying those relations to the 10Be and 36Cl fluxes measured in the GRIP ice core, the geomagnetic field intensity for the period between 20 and 60 kyr BP was reconstructed. Comparison with remnant magnetism records from marine sediment cores shows excellent agreement. This validates the use of cosmogenic nuclides in ice cores to reconstruct geomagnetic field variations.

Changes in deep-water formation during the Younger Dryas event inferred from 10Be and 14C records.

Abstract: Variations in atmospheric radiocarbon (14C) concentrations can be attributed either to changes in the carbon cycle1—through the rate of radiocarbon removal from the atmosphere—or to variations in the production rate of 14C due to changes in solar activity or the Earth's magnetic field2. The production rates of 10Be and 14C vary in the same way, but whereas atmospheric radiocarbon concentrations are additionally affected by the carbon cycle, 10Be concentrations reflect production rates more directly. A record of the 10Be production-rate variations can therefore be used to separate the two influences—production rates and the carbon cycle—on radiocarbon concentrations. Here we present such an analysis of the large fluctuations in atmospheric 14C concentrations, of unclear origin3, that occurred during the Younger Dryas cold period6. We use the 10Be record from the GISP2 ice core5 to model past production rates of radionuclides, and find that the largest part of the fluctuations in atmospheric radiocarbon concentrations can be attributed to variations in production rate. The residual difference between measured 14C concentrations and those modelled using the 10Be record can be explained with an additional change in the carbon cycle, most probably in the amount of deep-water formation.

Participatory integrated assessment of adaptation to climate change in Alpine tourism and mountain agriculture

Abstract: Winter tourism and mountain agriculture are the most important economic sectors in a major part of the Swiss Alps. Both are highly sensitive to changing climatic conditions. In the framework of the CLEAR project, results from climate impact research in the field of tourism and agricultural production were used to investigate the perception of climatic change by stakeholders and to assess possible adaptations. We used a participatory integrated assessment (PIA) to involve the knowledge, values and experiences of the various social actors in tourism and agriculture (e.g., skiers, tourism managers, farmers) in the research process. Whereas climate change may have various severe direct impacts on the tourism industry, depending on the region, agricultural production may generally benefit from changed climatic conditions. But because of the dependence of farmers on “off-farm” income, the loss due to declining winter tourism in specific areas may cause more important indirect effects. However, the two sectors may adapt actively by choosing from a variety of strategies, and the loss of income from the tourism industry may support the re-evaluation of the various functions agriculture plays in mountain regions, beyond the production of food. The study demonstrates the suitability of the PIA approach to elucidate the interactions between different stakeholders and their perception of the climate change phenomena. A similar participatory approach could be a useful tool to transfer research results and expert knowledge to the political process addressing adaptations to climate change.

Factors Determining the Element Behavior in Municipal Solid Waste Incinerators. 2. Laboratory Experiments

Abstract: Laboratory experiments with synthetic samples are conducted to obtain information on the evaporation behavior of metals in incinerators. In combining the results obtained through field measurements presented in a companion paper in this issue, hypotheses are postulated on the influence of physical and chemical conditions as well as of kinetics on the evaporation behavior of the chosen elements in the furnace bed. These are validated by thermal treatment of bottom ash samples in the laboratory. A temperature increase of from 500 °C to 900 °C causes higher transfers of most metals into the gaseous phase. Mo and Sb are the exceptions. Chlorine availability generally favors evaporation. Increasing oxidative conditions cause lower Sn transfers. Transfer of the elements Cd, Mo, Sb, Sn, and Zn is negatively affected by their reaction with reaction partners other than oxygen and chlorine occurring in municipal solid waste. Oxidation of organic carbon to CO and CO2 as well as HCl formation determine the distributi...

Variability of soil methane production on the micro-scale: spatial association with hot spots of organic material and Archaeal populations

Abstract: High temporal and spatial variability is a key problem when quantifying methane emissions from soils. Whereas the spatial variability on the landscape scale has been investigated in different studies, we investigated the spatial heterogeneity of CH4 production on 1 cm scale, as well as the role of organic material as a relevant factor. Undisturbed soil cores (dia. 6 cm) of two mineral and one peaty wetland soils (Typic Humaquept, Aeric Endoaquept and Limnic Haplohemist) from the cool-humid region in southwest Germany were anaerobically incubated for 3 months. The time course of the CH4 production rates was dependent on the water-table-level history of the incubated horizon and on the soil type. However, the absolute amounts of CH4 production differed largely between parallel cores from each soil type, although they were obtained within 1 m2. The native structures of the soil cores were determined by computed tomography. Fresh organic material was observed in all highly productive soil cores, whereas soil cores with low methanogenic activity included far less fresh organic material. The observed hot spots of fresh organic material were correlated to high amounts of Archaea, as analyzed by etherlipid analysis as well as by in situ hybridization using an Archaea-specific probe. The most dominant factor for the spatial variation in CH4 production on the micro-scale is the distribution of fresh organic material, which activates and possibly attracts methanogenic Archaea (methanogens).

Physico-chemical heterogeneity in a glacial riverscape

Abstract: Spatio-temporal heterogeneity in physico-chemical conditions associated with the annual expansion/contraction cycle in a complex glacial flood plain of the Swiss Alps was investigated employing a landscape approach. The diverse and dynamic aquatic habitats of the flood plain were visualized as an aquatic mosaic or riverscape. Based on samples collected at ca. monthly intervals for 1.5 yr along 17 floodplain transects, the 3 components of riverscape heterogeneity, extent, composition, and configuration, were quantified using categorical maps and indices of landscape patterns for turbidity and specific conductance. Changes in the spatial heterogeneity of 13 other physico-chemical parameters were further analyzed by means of a within-dates principal component analysis. Riverscape heterogeneity (RH), quantified by applying several indices of landscape pattern to turbidity and specific conductance data, was minimum during groundwater-dominated base flow in winter. Despite an increase in surface connectivity in the channel network with rising discharge, RH rose in spring and summer as additional chemically-distinct water sources (i.e., snowmelt runoff and glacial ablation) contributed to surface flow within the flood plain. Most other physico-chemical variables measured during this study exhibited the same spatio-temporal heterogeneity as turbidity and specific conductance. Overall, the glacial flood plain shifted from a monotonous physico-chemical riverscape in winter to a complex mosaic in summer, this seasonal pattern being clearly driven by hydrological factors operating at the catchment scale rather than by autogenic processes within individual water bodies. Although RH exhibited a predictable annual pattern in response to the seasonal flow regime, we expect the channel network to undergo future modifications from stochastic factors associated with flood events and long-term changes reflecting movements of the glaciers.

Accumulation of Poly[(R)-3-hydroxyalkanoates] in Pseudomonas oleovorans during growth with octanoate in continuous culture at different dilution rates.

Abstract: Pseudomonas oleovorans ATCC 29347 was grown in chemostat culture at different dilution rates with mineral media varying in their ratios of octanoate to ammonia (C0/N0 ratio). At all dilution rates tested, three distinct growth regimes were observed: (i) carbon limitation with NH4+ in excess at low C0/N0 ratios, (ii) purely nitrogen-limited growth conditions at high C0/N0 ratios with residual octanoate in the culture supernatant, and (iii) an intermediate zone of dual-nutrient-limited growth conditions where both the concentration of octanoate and that of ammonia were very low. The dual-nutrient-limited growth zone shifted to higher C0/N0 ratios with decreasing dilution rates, and the extension of the dual-nutrient-limited growth zone was inversely proportional to the growth rate. The cells accumulated the storage compound medium-chain-length poly[(R)-3-hydroxyalkanoate] (mcl-PHA) during dual (C and N)-nutrient-limited and N-limited growth conditions. Within the dual-nutrient-limited growth zone, the cellular mcl-PHA contents increased when the C0/N0 ratio in the feed was increased, whereas the cellular mcl-PHA level was independent from the feed C0/N0 ratio during N-limited growth. The monomeric composition of the accumulated mcl-PHA was independent of both the dilution rate and the feed C0/N0 ratio and consisted of 12 mol% 3-hydroxyhexanoic acid and 88 mol% 3-hydroxyoctanoic acid. Accumulation of mcl-PHA led to an increase in the cellular C/N ratio and to changes in elemental growth yields for nitrogen and carbon.