Practical identifiability analysis of large environmental simulation models
Large environmental simulation models are usually overparameterized with respect to given sets of observations. This results in poorly identifiable or nonidentifiable model parameters. For small models, plots of sensitivity functions have proven to be useful for the analysis of parameter identifiability. For models with many parameters, however, near-linear dependence of sensitivity functions can no longer be assessed graphically. In this paper a systematic approach for tackling the parameter identifiability problem of large models based on local sensitivity analysis is presented. The calculation of two identifiability measures that are easy to handle and interpret is suggested. The first accounts for the sensitivity of model results to single parameters, and the second accounts for the degree of near-linear dependence of sensitivity functions of parameter subsets. It is shown how these measures provide identifiability diagnosis for parameter subsets, how they are able to guide the selection of identifiable parameter subsets for parameter estimation, and how they facilitate the interpretation of the correlation matrix of the parameter estimate with respect to parameter identifiability. In addition, we show how potential bias of the parameter estimates, due to a priori fixing of some of the parameters, can be analyzed. Finally, two case studies are presented in order to illustrate the suggested approach.
Limitations of using δ<SUP>18</SUP>O for the source identification of nitrate in agricultural soils
The stable isotopic composition (δ<SUP>15</SUP>N and δ<SUP>18</SUP>O) of nitrate was analyzed in two lysimeter field experiments in order to identify the conditions under which the dual isotope approach can be applied to identify the main source of nitrate in agricultural soils. The first field experiment involved six lysimeters beneath fields that had been fertilized for 10 yr with the same type of fertilizer (NH<SUB>4</SUB>NO<SUB>3</SUB>; δ<SUP>15</SUP>N = +1.2‰, δ<SUP>18</SUP>O = +18.6‰). The isotope ratios of NO<SUB>3</SUB><SUP>-</SUP> in the leachate (δ<SUP>15</SUP>N ≈ 0‰; δ<SUP>18</SUP>O ≈ +2‰) could not be interpreted in a conventional way with either fertilizer or soil organic nitrogen as main sources. These results provided clear evidence for the microbial immobilization and subsequent mineralization and nitrification to NO<SUB>3</SUB><SUP>-</SUP> (mineralization-immobilization turnover concept). This process masked the original oxygen isotope ratio of the fertilizer source during the summer when microbial activity was high. A second experiment involving the application of Ca(NO<SUB>3</SUB>)<SUB>2</SUB> to three lysimeters during the winter confirmed that the dual isotope approach remains valid for the source identification of nitrate under conditions of low microbial activity. The study reveals the limitation of the dual isotope approach to characterize nitrate sources under biologically active conditions and the ability to quantify microbial processes when the main sources can be controlled.
Morphological organ alterations and infectious diseases in brown trout <I>Salmo trutta </I>and rainbow trout <I>Oncorhynchus mykiss</I> exposed to polluted river water
Poor water quality is discussed as a major factor causing a decline of brown trout populations in Swiss rivers. For our study we have chosen a river in the Swiss midlands, where the brown trout population has decreased dramatically during the last 10 yr and where feral fish have shown distinctive pathological alterations. The objective of our study was to investigate whether river water may be responsible for impaired fish health leading to an increased mortality in the river. In an active monitoring program, groups of brown and rainbow trout were exposed to polluted river water for 24 mo. Fish held in tap water served as a reference. Mortality, macroscopic and histopathologic changes, and infectious agents were investigated. Compared with the reference group, high mortality rates and severe pathological alterations of the inner organs were observed in fish held in river water. Especially gills, liver and kidney of these fish showed significantly higher changes than fish from tap water. These changes were dominated by degenerative and inflammatory reactions. Additionally, several infectious agents were diagnosed in fish exposed to river water. The most important findings were furunculosis and proliferative kidney disease. Brown trout seemed to be more sensitive than rainbow trout to environmental stress and infectious agents.
By-products formation during drinking water disinfection: a tool to assess disinfection efficiency?
In drinking water treatment, the inactivation of microorganisms increases with increasing disinfectant exposure (product of concentration and contact time, <I>CT</I>). Also, the formation of undesired (toxic) disinfection by-products increases with <I>CT</I>. The present study proposes a new concept that uses this undesired side effect of chemical water disinfection fur a fast and reliable test of treatment efficiency. In laboratory systems, bromate formation during ozonation and the formation of trihalomethanes during chlorination were used to calculate the disinfectant exposure, which is a measure for the achieved degree of disinfection.
Oxidation of metal-diethylenetriamine-pentaacetate (DTPA)-complexes during drinking water ozonation
This study investigates the oxidative transformation of diethylenetriaminepentaacetate (DTPA), a synthetic ligand, during drinking water ozonation. The rate coefficients for the reactions of CaDTPA<sup>3-</sup> and ZnDTPA<sup>3-</sup> with ozone were determined to be 6200 and 3500 ± 150 M<sup>-1</sup>s<sup>-1</sup>, respectively. The reactivity of Fe(III)DTPA<sup>2-</sup> towards ozone was found to be much lower (<10 M<sup>-1</sup>s<sup>-1</sup>), but near neutral pH the reactivity of the Fe(III)-complexes is dominated by [Fe(III)(OH)]DTPA<sup>3-</sup>. For the reaction of Fe[(III)(OH)]DTPA<sup>3-</sup> with ozone a rate coefficient of 2.4 ± 0.2 × 10<sup>5</sup>M<sup>-1</sup>s<sup>-1</sup> was measured. The rate coefficients of the reactions of the ZnDTPA-and Fe(III)DTPA with OH radicals have been determined by a competitive method as 2.4 ± 0.4 × 10<sup>9</sup> and 1.5 ± 0.1 × 10<sup>9</sup>M<sup>-1</sup>s<sup>-1</sup>, respectively at pH=7. The degradation of low concentrations of DTPA complexes during ozonation was investigated in natural waters under drinking water relevant conditions. Based on our findings CaDTPA<sup>3-</sup> and ZnDTPA<sup>3-</sup> are judged as easily degradable. Fe(III)DTPA complexes showed a somewhat lower reactivity, but were still typically degraded by one order of magnitude at ozone dosages of ∼20 μM (1 mg L<sup>-1</sup>) in the three natural waters tested. Molecular ozone was found to be the major oxidant for the metal-DTPA complexes during ozonation.
A note on abiotic factors that constrain periphyton growth in alpine glacier streams
Periphyton growth limitation experiments were conducted in five glacier streams during the main ice melt period in late summer using nutrient diffusing substrata (NDS) that contained nitrate and/or phosphate. Periphyton net growth was determined as chlorophyll <I>a</I> accrual after an exposure time of 4 weeks. In addition, primary water chemistry and physical parameters of the study streams were measured. These chemical and physical parameters characterised the sites as kryal (glacial) systems. Neither nutrient limitation nor a significant correlation between water chemistry and physical data and chlorophyll <I>a</I> values were apparent. A comparison between current velocity and ln-transformed chlorophyll a values revealed a typical optimum curve with highest periphyton accrual at 0.5 m s<sup>–1</sup> on NDS. During the summer ablation period, the net growth of periphyton in these glacial streams appeared to be controlled primarily by current velocity.
Cytochrome P450 induction by nitrated polycyclic aromatic hydrocarbons, azaarenes, and binary mixtures in fish hepatoma cell line PLHC-1
Nitrated polycyclic aromatic hydrocarbons (NP AH) and N-heterocyclic aromatic hydrocarbons (azaarenes) are as ubiquitous in the environment as their parent PAH compounds, although occurring at lower concentrations. The toxicological importance of NPAHs and azaarenes is based on their mutagenic and carcinogenic potential. Azaarenes possess a higher solubility and mobility in the environment than PAHs. However, very little is known about the toxicity and cytochrome P450 (CYP)1A induction potencies of NPAHs and azaarenes in fish. Here we report on the cytotoxicities and relative CYP1A induction potencies of 12 NPAHs, 12 azaarenes, and 11 PAHs, determined as neutral red uptake and ethoxyresorufin-<em>O</em>-deethylase (EROD) activity, respectively, in fish hepatoma PLHC-1 cells. Additionally, CYP1A enzyme protein was determined by ELISA for two NPAHs, azaarenes, PAHs, and binary mixtures. Compared with the structurally analogous PAHs, 2-nitronaphthalene, 3-nitrofluoranthene, 2-aza- and 7-azafluor-anthene, 1,6-dinitropyrene, benzo[<em>a</em>]acridine and benzo[<em>h</em>]quinoline revealed higher induction potencies, whereas the other compounds showed similar or less activity. The induction potency was highly dependent on the compounds structural properties, reflected by significant correlations between the half-maximal EROD induction (-log EC50) and the molecular descriptors lipophilicity (log <em>K</em><sub>ow</sub>) and maximal molecular length (L<sub>max</sub>). Binary mixtures of 6-nitrochrysene + benzo[a]anthracene, 6-nitrochrysene + ben-zo[<em>a</em>]acridine, and benzo[<em>a</em>]acridine + benzo[<em>a</em>]anthracene showed an additive interaction. The CYP1A induction potencies of NPAHs and azaarenes, demonstrated here for the first time in fish hepatoma cells, suggest that their contribution to the overall CYP1A induction potencies in PAH-contaminated environmental samples have to be taken into account.
Electron-rich phenols for probing the photochemical reactivity of freshwaters
Different Swiss freshwater samples spiked with 3,4-dimethoxyphenol (DMOP) or 2,4,6-trimethylphenol (TMP) were irradiated using UV-A and visible light from a medium-pressure mercury lamp. The kinetics of depletion of both phenols at pH 8 revealed that in almost all samples the probe phenols disappeared more rapidly at 0.1 μM than 5 μM initial concentration. Pseudo-first-order rate coefficients were on average 2-3 times greater at the lower initial phenol concentration. A comparable effect was observed using buffered solutions of Suwannee River fulvic acid, which was also used as a model photosensitizer to study the influence of various parameters on such rate coefficients. Sensitizer concentration and photon fluence rate were found to be directly proportional to the rate coefficients for DMOP transformation at both initial concentrations. For both phenols, the rate coefficients increased with increasing pH in the range 4-10, but such an increase was much more pronounced at 0.1 μM than at 5 μM initial phenol concentration. The observed kinetic behavior is compatible with the assumption that electron-rich phenols are transformed by photooxidants of different lifetimes generated by photosensitization from the dissolved organic matter (DOM).
Development of macroinvertebrate-based index for bioassessment of Idaho Rivers
Theoretical constructs, such as the river continuum concept, predict that the composition of benthic fauna in rivers will be different from that of headwater streams. There exists a need to modify, for use on larger rivers, the bioassessment techniques commonly used on small streams. Using aquatic macroinvertebrates and the "reference condition" approach, we developed and tested a multimetric index for use on the rivers of Idaho. Reference sites were selected to represent the best current conditions (i.e., least impacted) among Idaho rivers. The index performed well in distinguishing reference sites from sites displaying some form of anthropogenic impairment. Individual metrics used in the index included: number of EPT taxa, total number of taxa, percent dominant taxon, percent Elmidae, and percent predators. The index we developed for Idaho rivers was essentially a modification of a framework designed for small streams, suggesting that techniques, including data analysis, currently used for streams can be adapted for use on larger rivers. Adapting these methods for use in rivers is primarily a matter of (1) selecting metrics relevant to the rivers of interest; (2) expanding the field sampling to encompass the greater habitat area and, potentially, heterogeneity of rivers; and (3) selecting an appropriate form of data analysis. The approach we describe here should be applicable to geographic regions other than Idaho.
Enrichment and characterization of an anammox bacterium from a rotating biological contactor treating ammonium-rich leachate
Anaerobic ammonium oxidation with nitrite to N<sub>2</sub> (anammox) is a recently discovered microbial reaction with interesting potential for nitrogen removal from wastewater. We enriched an anammox culture from a rotating disk contactor (near Kolliken, Switzerland) that was used to treat ammonium-rich leachate with low organic carbon content. This enrichment led to a relative population size of 88% anammox bacteria. The microorganism carrying out the anammox reaction was identified by analysis of the 16S rDNA sequence and by fluorescence in situ hybridization (FISH) with 16S-rRNA-targeting probes. The percentage sequence identity between the 16S rDNA sequences of the Kolliken anammox organism and the archetype anammox strain Candidatus <I>Brocadia anammoxidans</I> was 90.9%, but between 98.5 and 98.9% with Candidatus <I>Kuenenia stuttgartiensis</I>, an organism identified in biofilms by molecular methods. The Kolliken culture catalyzed the anaerobic oxidation of ammonium with nitrite In a manner seemingly identical to that of Candidatus <I>B. anammoxidans</I>, but exhibited higher tolerance to phosphate (up to 20 mM) and to nitrite (up to 13 mM) and was active at lower cell densities. Anammox activity was observed only between pH 6.5 and 9, with an optimum at pH 8 and a temperature optimum at 37 °C. Hydroxylamine and hydrazine, which are intermediates of the anammox reaction of Candidatus <I>B. anammoxidans</I>, were utilized by the Kolliken organisms, and approximately 15% of the nitrite utilized during autotrophic growth was converted to nitrate. Electron microscopy showed a protein-rich region in the center of the cells surrounded by a doughnut-shaped region containing ribosomes and DNA. This doughnut-shape region was observed with FISH as having a higher fluorescence intensity. Similar to Candidatus <I>B. anammoxidans</I>, the Kolliken anammox organism typically formed homogenous clusters containing up to several hundred cells within an extracellular matrix.
Chemical properties of catechols and their molecular modes of toxic action in cells, from microorganisms to mammals
Catechols can undergo a variety of chemical reactions. In this review, we particularly focus on complex formations and the redox chemistry of catechols, which play an inportant role in the toxicity of catechols. In the presence of heavy metals, such as iron or copper, stable complexes can be formed. In the presence of oxidizing agents, catechols can be oxidized to semiquinone radicals and in a next step to o-benzoquinones. Heavy metals may catalyse redox reactions in which catechols are involved. Further chemical properties like the acidity constant and the lipophilicity of different catechols are shortly described as well. As a consequence of the chemical properties and the chemical reactions of catechols, many different reactions can occur with biomolecules such as DNA, proteins and membranes, ultimately leading to non-repairable damage. Reactions with nucleic acids such as adduct formation and strand breaks are discussed among others. Interactions with proteins causing protein and enzyme inactivation are described. The membrane–catechol interactions discussed here are lipid peroxidation and uncoupling. The deleterious effect of the interactions between catechols and the different biomolecules is discussed in the context of the observed toxicities, caused by catechols.
The pattern of particle flux variability in Swedish and Swiss lakes
Particle settling flux in the upper and lower water column, measured with cylindrical sediment traps in 11 Swedish and nine Swiss lakes showed high temporal and spatial variability within and among lakes, ranging from 0.1 to 385 g m<sup>-2</sup> day<sup>-1</sup>. Such high variability reflects the large differences in lake morphology and trophic state. However, despite these differences, the particle flux variability followed a consistent pattern resulting in a significant relationship between minimum, mean and maximum particle flux. The mean particle flux is significantly related to the dynamic ratio (square root of area divided by mean depth) of the lake, provided that the lake is shallow (mean lake depth ≤9 m), its dynamic ratio is ≥0.15 and allochthonous particulate matter input is ≤10%. In such lakes, typically found in Sweden, the described relationships may be used to predict the variability of particle settling flux without developing complicated models.
Simultaneous quantification of neutral and acidic pharmaceuticals and pesticides at the low-ng/l level in surface and waste water
A new analytical method is presented that allows simultaneous determination of neutral and acidic pharmaceuticals and pesticides in natural waters. The compounds investigated include frequently used pharmaceuticals, i.e., the anti- epileptic carbamazepine, four analgesic/anti-flammatory drugs (ibuprofen, diclofenac, ketoprofen and naproxen) and the lipid regulator clofibric acid and important pesticides including triazines, acetamides and phenoxy acids. Sample enrichment was achieved in one step with a newly developed solid-phase extraction procedure using the Waters Oasis HLB sorbent. The neutral compounds were analyzed by GC-MS in a first step, and then the acidic compounds after derivatization with diazomethane. Relative recoveries using isotope labeled internal standards were between 71 and 118% and the detection limits were in the range of 1 to 10 ng/l in drinking water, surface water and waste water treatment plant effluents (precision: 1-15%). The developed analytical method proved to be very durable during a 3-month field study and the target analytes were detected in concentrations of 5-3500 ng/l in waste water treatment plant effluents, river water and lake water.
Determination of methane and other small hydrocarbons with a platinum-Nafion electrode by stripping voltammetry
Methane in the gas phase is determined via pre-adsorption on a dispersed platinum electrode backed by a solid polymer electrolyte (SPE) membrane (Nafion) which is in contact with 10 M sulfuric acid. The adsorption process is strongly temperature dependent with an activation energy of 8.7 kcal mol<sup>-1</sup>. Prior to the anodic stripping step the platinum electrode is flushed with nitrogen resulting in an acceptable selectivity against electroactive species which could otherwise interfere. During the anodic sweep the adsorbed methane is oxidized at the potential of the onset of the formation of the platinum oxide monolayer. Using a sensing electrode thermostatted at 348 K, a linear calibration curve was obtained from 0.1 up to 5% CH4 in nitrogen, with a detection limit of 130 ppm (<I>S/N</I> = 3), The determination of ethane, propane and butane was also found possible by this scheme and the cross-sensitivity to carbon monoxide and hydrogen could be significantly reduced by means of suitable chemical adsorption filters.
River water quality model no. 1 (RWQM1): II. Biochemical process equations
In this paper, biochemical process equations are presented as a basis for water quality modelling in rivers under aerobic and anoxic conditions. These equations are not new, but they summarise parts of the development over the past 75 years. The primary goals of the presentation are to stimulate communication among modellers and field-oriented researchers of river water quality and of wastewater treatment, to facilitate practical application of river water quality modelling, and to encourage the use of elemental mass balances for the derivation of stoichiometric coefficients of biochemical transformation processes. This paper is part of a series of three papers. In the first paper, the general modelling approach is described; in the present paper, the biochemical process equations of a complex model are presented; and in the third paper, recommendations are given for the selection of a reasonable submodel for a specific application.
Dynamics of mixed substrate growth of <I>Escherichia coli</I> in batch culture: the transition between simultaneous and sequential utilisation of carbon substrates
When offered mixtures of carbon sources, microorganisms exhibit fundamentally different
substrate utilisation patterns at high and at low substrate concentrations. For example, <I>Escherichia coli</I>
growing with mixtures of sugars at high concentrations in batch culture initially grows on glucose while the
utilisation of other sugars starts only after depletion of glucose in the medium. This phenomenon is referred to
as diauxic growth and its regulatory basis is thought to be catabolite repression and induced exclusion. In
contrast, in chemostat culture where steady-state substrate concentrations arc very low <I>E. coli</I> utilises
mixtures of sugars simultaneously. To determine what concentration levels of glucose arc necessary to exert
catabolite repression we carried out systematic batch experiments with mixtures of glucose and galactose or
glucose and fructose at low substrate concentrations. Chemostat grown cells of <I>E. coli</I> ML30 were used as
inocula to ensure that experiments could be carried out reproducibly. Glucose-galactose mixtures were utilised
simultaneously up to a glucose concentration of approximately 2-3 mg·L<SUP>-1</SUP> independent of whether the inocula
were grown in glucose- or galactose-limited chemostat culture. The utilisation pattern of glucose-fructose
mixtures depended strongly on the carbon source used to grow the inoculum in chemostat cultures. When
glucose-grown chemostat cells were used as inocula glucose was utilised first in batch cuiture and fructose
utilisation started only after glucose had depleted down to approximately 3 mg·L<SUP>-1</SUP>. In contrast, glucose and
fructose were always utilised simultaneously when inocula grown with a glucose-fructose mixture were used .
These results demonstrate first, that also in batch culture <I>E. coli</I> utilises mixtures of sugars simultaneously at
low substrate concentrations, and second, that the growth history of the inoculum can determine the utilisation
pattern of mixed substrates in batch culture.
Moderne biologische Analyse. Potential, Entwicklung und Anwendung
Due to political requirements in Switzerland and Europe, numerous biological effect analysis have to be performed in aquatic ecosystems. Biological tests should be fast, cheap, sensitive, specific, informative, easy handable. In this article, the various levels on which biological effect analysis could be performed, are analysed and discussed in the screening context. It is concluded that the further development and use of mechanism-based, (sub)cellular systems in effect analysis should be strongly stimulated. These systems fulfill the requirements, have a wide applicability and can be used complementary to already existing screening and risk assessment strategies.
Microbial biomass, growth, and respiration associated with submerged litter of <I>Phragmites australis</I> decomposing in a littoral reed stand of a large lake
This study examined the microbial dynamics associated with decomposing litter of the widespread emergent macrophyte <i>Phragmites australis</i> in a littoral reed stand of a large lake. Standing dead leaf and stem litter were collected, placed into fine and coarse mesh litter bags, and submerged in the reed stand. Litter bags were retrieved periodically and analyzed for fungal and bacterial 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<sup>-1</sup> detrital C) was predominantly fungal (always ≥90% of the total biomass), even thoug bacterial biomass (0.13 to 5.6 mg C g<sup>-1</sup> detrital C) increased and fungal biomass decreased or remained constant as litter decay proceeded. Although rates of fungal growth (0.02 to 0.08% h<sup>-1</sup>) and production (leaves only; 3 to 51 μg C g<sup>-1</sup> detrital C h<sup>-1</sup>), and rates of microbial respiration (11 to 257 μg C g<sup>-1</sup> detrital C h<sup>-1</sup>) decreased following litter submergence, fungi continued to be metabolically active in both leaf and stem litter. Significant 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 <i>P. australis</i> 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 <i>P. australis</i> litter in the aquatic environment.
A comparison of methods for detection of phosphate limitation in microalgae
This paper presents the results of studies into the use of the emerging techniques of nutrient induced fluorescence transients (NIFTs) and Fourier Transform InfraRed (FTIR) spectroscopy to determine the nutrient status of microalgae. Four species of microalgae were grown under conditions where growth rate was P-limited or P-replete, and NIFT responses and FTIR spectra in response to the re-supply of P (as PO<sub>4</sub><sup>3-</sup>) measured. These responses were compared to more conventional measures of algal nutrient status such as P-uptake rates, P quotas and transient effects of PO<sub>4</sub><sup>3-</sup> on oxygen exchange. The NIFT technique and FTIR spectroscopy gave results that were consistent with those obtained by the other techniques. Furthermore, we were able to demonstrate NIFT responses in phytoplankton samples taken from Lake Lucerne (total ambient P ≤ 0.13 μM) but not from Lake Zürich (total P 0.55 μM). The potential and limitations of the various techniques are discussed.
Some results relevant to the discussion of a possible link between cosmic rays and the Earth's climate
Based on a 16-year observation period (1980-1995), it was claimed recently that Earth's climate was linked to variations in the flux of cosmic rays penetrating into the atmosphere via their postulated effect on global cloud cover. Data from three independent studies yield information relevant to the ongoing discussion of the likelihood of the existence of such a link. (1) Model calculations show that the relative change in the ion production rate from a solar maximum to a solar minimum is of the same order as, or even greater than,the corresponding change in global cloud cover. (2) However, the smoothed combined flux of <SUP>10</SUP>Be and <SUP>36</SUP>Cl at Summit, Greenland, from 20-60 kyr B.P. (proportional to the geomagnetically modulated cosmic ray flux) is unrelated to the corresponding δ<SUP>18</SUP>O and CH<SUB>4</SUB> data (interpreted as supraregional climate proxies). (3) Furthermore, although a comparison of the incoming neutron flux with cloud cover in Switzerland over the last 5 decades shows a significant correlation at times during the 1980s and 1990s, this does not occur during the rest of the period.
Complex dynamics of adaptation in a nonaxenic <I>Microcystis</I> culture. 2. Computer simulation of dinitrophenol effects
A hypothesis was modeled to account for complex 20-day dynamics in a culture of blue-green algae <I>Microcystis</I> and heterotrophic bacteria exposed to 2,4-dinitrophenol (DNP), In trials with little or no added DNP, a limiting factor (light or CO<sub>2</sub>) may cause algal density to fluctuate after 14 days of increase. Such factors may be unimportant at levels of DNP that restrict photosynthesis, Bacterial growth may be limited by organic substrate, and bacteria may be more resistant to DNP than blue-green algae, Hence, at intermediate levels of DNP, substrate provided by increased algal death stimulates bacterial growth more than DNP retards it, causing a bacterial peak. Sorption of DNP to cells may cause the DNP decline. Greater growth and slower DNP decline in experiments with preexposed organisms indicate lower DNP sorption affinity in preexposed cells. Bacterial assimilation of DNP-containing substrate may cause the reappearance of DNP, The model reproduced the fluctuation in algal density after growth was limited and better growth and lower DNP decline with preexposed organisms, Reappearance of DNP occurred, but was not obvious. Bacterial dynamics were least well reproduced. Changes in bacterial constants most affected output. Despite model inadequacies, probable aspects of toxicant action in nature have been revealed. Ecological relationships among populations of different species and genetic differences among individuals may have led to lower than expected toxicity, adaptation, and even growth stimulation, Responses of single species tested in isolation may be inadequate to predict toxicant impact.
Complex dynamics of adaptation in a nonaxenic <I>Microcystis</I> culture. 1. Effects of dinitrophenol on population growth
Chronic exposure to toxicants is a selective pressure affecting populations and also the interactions between populations. Nonaxenic cultures of the blue-green alga <I>Microcystis aeruginosa</I> were used to investigate the ecological dynamics and the effect of preexposure to 2,4-dinitrophenol (DNP) on the tolerance toward subsequent DNP inputs. It was predicted that preexposure would induce an increased tolerance to further inputs. This should cause a higher population growth rate under a given DNP exposure, a broader tolerance range (the range of concentrations over which population growth can be sustained), a higher EC<sub>50</sub> and a lesser variability in growth rates, over the range of experimental exposure concentrations. DNP reduced <I>Microcystis</I> growth proportionally to exposure concentration, Light, inorganic carbon, and DNP were likely limiting factors for algal growth. Heterotrophic bacteria presumably used the dead cells and the exudate of living algae as substrates, Some unexpected effects occurred, such as an apparent increase in dissolved DNP in the medium following its initial decline and fluctuations of the bacterial population. The hypotheses were verified as concerns the effect of preexposure on tolerance. Changes were apparent in the EC<sub>50</sub> and in the breadth of the tolerance range, Moreover, the variability of preexposed populations, in terms of algal growth rate, over the range of exposure concentrations, was smaller than that of non- preexposed populations. Such a decrease in variability may reduce the potential of a population to resist further stresses.
Riparian vegetation and island formation along the gravel-bed Fiume Tagliamento, Italy
After more than 300 years of river management, scientific knowledge of European river systems has evolved with limited empirical knowledge of truly natural systems. In particular, little is known of the mechanisms supporting the evolution and maintenance of islands and secondary channels. The dynamic, gravel-bed Flume Tagliamento, Italy, provides an opportunity to acquire baseline data from a river where the level of direct engineering intervention along the main stem is remarkably small. Against a background of a strong alpine to mediterranean climatic and hydrological gradient, this paper explores relationships between topography, sediment and vegetation at eight sites along the active zone of the Tagliamento. A conceptual model of island development is proposed which integrates the interactions between large woody debris and vegetation, geomorphic features, sediment calibre and hydrological regime. Islands may develop on bare gravel sites or be dissected from the floodplain by channel avulsion. Depositional and erosional processes result in different island types and developmental stages. Differences in the apparent trajectories of island development are identified for each of the eight study sites along the river. The management implications of the model and associated observations of the role of riparian vegetation in island development are considered. In particular, the potential impacts of woody debris removal, riparian tree management, regulation of river flow and sediment regimes, and changes in riparian tree species' distribution are discussed.
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 how 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.
Model comparison of flow through a municipal solid waste incinerator ash landfill
The drainage discharge of a municipal solid waste incinerator (MSWI) bottom ash landfill was simulated using various modelling approaches. Two functional models including a neural networks approach and a hydrological linear storage model, and two mechanistic models requiring physical/hydrodynamic properties of the waste material, HYDRUS5 and MACRO (Version 4.0) were used. The models were calibrated using an 8-month data set from 1996 and validated on a 3-month data set from winter 1994/1995. The data sets comprised hourly values of rainfall, evaporation (estimated from the Penman–Monteith relationship), drainage discharge and electrical conductivity. Predicted and measured discharges were compared.<br/>
The discharge predicted by the functional models more exactly followed the discharge patterns of the measured data but, particularly the linear storage model, could not cope with the non-linearity of the system that was caused by seasonal changes in water content of the MSWI bottom ash. The fit of the neural networks model to the data improved with increasing prior information but was less smooth than the measured data. The mechanistic model that included preferential discharge, MACRO, better modelled the discharge characteristics when inversely applied, indicating that preferential flow does occur in this system. However, even the inverse application of HYDRUS5 could not describe the system discharge as well as the linear storage model. All model approaches would have benefited from a more exact knowledge of initial water content.
Exploring an aquifer system by integrating hydraulic, hydrogeologic and environmental tracer data in a three-dimensional hydrodynamic transport model
This article presents a numerical model of a part of an aquifer that is recharged by infiltration from the Swiss pre-Alpine river Töss in the Linsental (north-eastern Switzerland). The nearby city of Winterthur makes use of this aquifer as a resource of drinking water. The presented model is part of a larger interdisciplinary research program undertaken with the goal to evaluate the possible impacts of a planned revitalization of the severely canalized river Töss. Above all it should show the extent of decrease of the groundwater residence time if the river bed is allowed to move towards the drinking water wells.<br/>
The flow model was constrained and calibrated by transport modelling of tritiogenic <sup>3</sup>He. This tracer reflects both the aging of the water (by accumulation of <sup>3</sup>He resulting from tritium-decay) as well as the two different components of the mixture (river water free of tritiogenic <sup>3</sup>He due to degassing, and groundwater enriched in <sup>3</sup>He due to accumulation). By simulating a Dirac-pulse-shaped input of a conservative tracer at different sources (river cells or upstream flux boundary cells) it is possible to determine the age distributions as well as the mixing ratios of the two types of water at the two pumping stations within the model area. The same calculations for a hypothetical river course passing directly beside the pumping stations indicate a decrease of the mean residence time of the pumped water together with an increase of the amount of the younger river water component.
Climatically relevant periodicities in the thicknesses of biogenic carbonate varves in Soppensee, Switzerland (9740-6870 calendar yr BP)
Accurate determination of the thicknesses of 2717 biogenic carbonate varves from a Swiss lake (Soppensee), spanning the period from about 9740 to 6870 calendar yr BP, allowed the computation of a power spectrum using classical FFT methods. The presence of pronounced peaks at 40-50 and 20-25 yr agrees with the results of other studies on varve thickness and Δ<sup>14</sup>C which have been interpreted as indicating an association between solar forcing and varve thickness. The presence in the Soppensee varve series of an additional peak at 10.9 yr, corresponding to the Schwabe sunspot cycle, lends further support to this hypothesis, Because the Soppensee varves are of biogenic rather than elastic origin, any influence fluctuations in solar irradiance may have had on sedimentation rates is likely to have been exerted via primary production.
Growth and survival of Lake Hallwil whitefisch (<I>Coregonus</I> sp.) larvae reared on dry and live food
Two commercial dry diets and live zooplankton were tested as initial food for larvae of Lake Hallwil whitefish (<I>Coregonus</I> sp.) in comparison with a reference food type (<I>Artemia</I> nauplii). The ability of the larvae to switch from dry diet to live zooplankton was also investigated. After three weeks of feeding, the diets in all experimental tanks were changed to live zooplankton caught in Lake Hallwil and larvae were fed for another three weeks. Mean total length and dry weight of the <I>Artemia</I>-prefed larvae at the end of the experiment were 18 mm and 3 mg at 5°C, and 30 mm and 23 mg at 13°C. Dry-diet prefed larvae were 15 mm and 1.5 mg at 5°C, and 25 mm and 12.5 mg at 13°C. Zooplankton-prefed larvae reached 17 mm and 2.5 mg at 5°C, and 27 mm and 19 mg at 13°C. Overall mortality varied between 5 and 45 %. Larvae fed live zooplankton suffered less mortality than those fed dry diets. Feeding conditions during the first three weeks after hatching affected larval growth: After the switch to zooplankton diet at the end of the third week, slower growth of <I>Artemia</I> and dry-diet prefed larvae was recorded. We conclude that the dry diets tested give satisfactory rearing results, but zooplankton is still the best diet for mass rearing of whitefish.
Struktur der Wirbellosenfauna an der Flusssohle eines voralpinen Fliessgewässers (Necker SG)
Der Necker ist ein voralpines Fliessgewässer nördlich des Säntisgebietes in der Ostschweiz. Typisch für das Abflussregime sind die kaum vorhersagbaren Abflussspitzenwerte, deren Auftreten relativ unabhängig von der Jahreszeit ist. Die durch den Menschen verursachten chemischen, morphologischen und hydraulischen Beeinträchtigungen sind als gering einzustufen, weshalb der Necker als weitgehend naturnah bezeichnet werden kann.<br />
Das Ziel der vorliegenden Arbeit war es, die strukturellen und funktionellen Veränderungen in der Wirbellosenfauna entlang der Flusssohle des Neckers zu untersuchen und in Bezug zu den geomorphologischen Gradienten im Längsverlauf zu setzen. Dazu wurde im Juni 1994 an drei repräsentativen Stellen im Ober-, Mittel- und Unterlauf die Wirbellosenfauna an der Flusssohle beprobt. Zusätzlich wurden auch ausgewählte Umweltparameter erfasst, um Unterschiede zwischen den einzelnen Probestellen in der Morphologie und Hydrologie, im Temperaturregime, dem Chemismus sowie dem Nahrungsangebot für die Wirbellosen zu quantifizieren. Schliesslich wurde auch die Anwendbarkeit des 'River Continuum Concept' auf ein voralpines Fliessgewässer getestet.<br />
Die drei Probestellen konnten anhand der jeweiligen Umweltbedingungen klar voneinander getrennt werden. Auch die Wirbellosenfauna zeigte ausgeprägte Unterschiede hinsichtlich der Besiedlungsdichten, der Taxa-Zusammensetzung und der Anteile verschiedener Ernährungstypen zwischen den Probestellen. Dies weist auf die Anpassungen der Lebensgemeinschaften an die sich ändernden Umweltbedingungen im Längsverlauf des Flusses hin. Die Vorhersagen des bezüglich longitudinaler Veränderungen in der Zusammensetzung des partikulären organischen Materials und der Anteile der verschiedenen Emährungstypen an der Wirbellosenfauna konnten jedoch nur teilweise bestätigt werden.
The main features of seasonal variability in the external forcing and dynamics of a deep mountain lake (Redó, Pyrenees)
Lake Redó, a dimictic oligotrophic mountain lake, was monitored for two complete years from July 1996 to July 1998. The main seasonal variations in the physical, chemical and biological parameters are described, with special emphasis on the comparison of external forcing (weather and atmospheric deposition) with internal lake dynamics. Annual mean air temperature was estimated to be 3.6 °C. The duration of ice cover on the lake was 4.5 months in 1996/97 and 5.8 months in 1997/98. The lake water was very ion-poor (mean annual conductivity 12 μS cm<sup>-1</sup>); however, ion concentrations in the lake were higher than in the precipitation, the differences being due mainly to Ca<sup>2+</sup> and bicarbonates originating in the catchment. NH<sub>4</sub><sup>+</sup> was the main ion in the precipitation, with an average concentration of 17 μM, while in the lake it was always below 3 μM. However, the concentration of dissolved inorganic nitrogen always exceeded that of soluble reactive phosphorus by two or three orders of magnitude, so the latter is likely to be the limiting nutrient for phytoplankton growth. Four main production episodes were identified, occurring during spring and autumn overturn, in the upper hypolimnion during summer stratification, and under the ice at the beginning of the ice-covered period. The highest chlorophyll-<I>a</I> concentrations (1.2-2.2 μg l<sup>-1</sup>) were attained during spring overturn; concentrations of chlorophyll-<I>c</I> were high during both spring and autumn overturn, while chlorophyll-<I>b</I> was comparatively important in the upper hypolimnion during the stratification period. <I>Daphnia pulicaria</I> was the most abundant macrozooplankton species; its abundance was highest during the ice-covered period, when its biomass was comparable to the measured sestonic particulate carbon concentration. The <I>Daphnia</I> maximum was associated with higher concentrations of NH<sub>4</sub><sup>+</sup> and dissolved organic carbon, suggesting that it may play an important role in the pelagic biogeochemical compartment of the lake under ice. Winter respiration rates for the lake were estimated to be 339 mg O<sub>2</sub> m<sup>-2</sup> d<sup>-1</sup> for 1996/97 and 281 mg O<sub>2</sub> m<sup>-2</sup> d<sup>-1</sup> for 1997/98.
Causes and effects of long periods of ice cover on a remote high Alpine lake
The response of the physical and chemical limnology of Hagelseewli (2339 m a.s.l.) to local meteorological forcing was investigated from 1996 to 1998 using an automatic weather station, thermistor chains, water samples and sediment traps. On-site meteorological measurements revealed the paramount importance of local topographic shading for the limnology of the lake. A high cliff to the south diminishes incident radiation by 15% to 90%, resulting in a long period of ice cover. Hence, the spring and summer seasons are extremely condensed, allowing only about 2 months per year for mixing, oxygen uptake, nutrient inflow, water exchange and phytoplankton growth. Regular measurements of water temperature, chemistry and diatom composition show that Hagelseewli responds very rapidly to changes in nutrient concentrations and light conditions. This response is restricted mainly to an extremely short productivity pulse, which takes place as soon as the lake is completely free of ice. Ice-free conditions are indicated by the occurrence of planktonic diatoms. In contrast to most low-altitude lakes, maximum productivity occurs in the middle of the water column (6-9 m), where first light, and then soluble reactive phosphorus (SRP), are the limiting factors. During the period of thawing, large amounts of ammonium enter the lake. Nevertheless, allochthonous nutrient input is not important because SRP, the limiting nutrient for algal growth, originates from the sediments. Water chemistry data and data from sediment traps show that, although autochthonous calcite precipitation does occur, the calcite crystals are redissolved completely in the bottom waters during the extended period of ice cover. Thus, the most important factor for changes in the nutrient budget, primary production and preservation of calcite is the bottom water oxygen status, which is governed by the occurrence of an ice-free period. We hypothesise that the duration of the ice-free period is of minor importance for the generation of particles that might be archived in the sedimentary record as proxy climate indicators. Such particles are produced mainly during times of peak primary production, which last only for a few days before production decreases again to very low levels. Therefore, with respect to the type of climatic signal that might be recorded in Hagelseewli, we presume that what is most likely to be archived in the sedimentary record is the mere occurrence, rather than the duration of the ice-free period.
Sedimentological and biostratigraphical analyses of short sediment cores from Hagelseewli (2339 m a.s.l.) in the Swiss Alps
Several short sediment cores of between 35 and 40 cm from Hagelseewli, a small, remote lake in the Swiss Alps at an elevation of 2339 m a.s.l. were correlated according to their organic matter content. The sediments are characterized by organic silts and show in their uppermost part a surprisingly high amount of organic matter (30-35%). Synchronous changes, occurring in pollen from snow-bed vegetation, the alga Pediastrum, chironomids, and grain-size composition, point to a climatic change interpreted as cooler or shorter summers that led to prolonged ice-cover on the lake. According to palynological results the sediments date back to at least the early 15<sup>th</sup> century A.D., with the cooling phase encompassing the period between late 16<sup>th</sup> and the mid-19<sup>th</sup> century thus coinciding with the Little Ice Age. Low concentrations of both chironomid head capsules and cladoceran remains in combination with results from fossil pigment analyses point to longer periods of bottom-water anoxia as a result of long-lasting ice-cover that prevented mixing of the water column. According to our results aquatic biota in Hagelseewli are mainly indirectly influenced by climate change. The duration of ice-cover on the lake controls the mixing of the water column as well as light-availability for phytoplankton blooms.
Changes in the trophic level of an alpine lake, Jezero v. Ledvici (NW Slovenia), induced by earthquakes and climate change
Despite relatively high nutrient levels, the Slovenian Alpine lake Jezero v Ledvici (1824 m a.s.l.; max. depth 15 m) is oligotrophic, with high transparency and low chlorophyll concentrations (<1 μg l<sup>-1</sup>). Daily mean air temperatures at the lake are estimated to vary between –15.4 °C and +18.8 °C. Low air temperatures combined with the blocking of incident solar radiation by the local topography result in the lake being ice-covered for over six months of the year, suggesting that the effects of climate on the ecology of the lake may be mediated by the timing of the ice cover. Sediment cores taken in 1996 were dated by <sup>210</sup>Pb and <sup>137</sup>Cs and analysed for DW, LOI, cladoceran and diatom remains, pigments, C, N and S. A total of 50 diatom taxa and 4 cladoceran taxa were found. The base of the unsupported <sup>210</sup>Pb record at 17.4 cm was dated to 1825 AD ± 25 y. An abrupt change in DW and LOI was observed at a depth of 17 cm, coinciding with a change in the cladoceran community and in C and N concentrations. From a depth of 12 cm (83 ± 4 y BP) upward, a sharp change in S and plant pigment concentrations were recorded, followed by an increase in diatom abundance at a depth of about 10 cm (63 ± 4 y BP). The timing of quantitative changes in the physical and chemical properties of the sediment, and in the community structure of diatoms and Cladocera, coincides with the occurrence of three earthquakes in the 19th century. Changes in the diatom and cladoceran record were compared with a tree-ring width index based on <I>Larix decidua</I> from the shore of the lake over the last 136 years, and with reconstructed air temperatures from 1781 – 1996. With a 4-y lag, a weak positive correlation exists between the tree-ring width index and the air temperatures. Although diatom abundance generally shows no correlation with the tree-ring width index, a negative correlation was found in the case of Fragilaria pinnata and Amphora lybica, interrupted only between 1942 and 1955. A similar pattern to this latter was also observed in the case of the Cladocera. During the last 250 y, anthropogenic influence on the lake catchment area has been confined mainly to limited sheep grazing. The main cause of changes occurring in the lake itself is likely to be eutrophication resulting from the input of allochthonous material from landslides triggered by earthquakes. During the last three decades, however, the main factor influencing biotic change appears to have been the increase in mean air temperature, possibly acting via ice cover.
Zuströmbereiche für Grundwasserfassungen. Konzeptionelle Überlegungen zu Zweck und Abgrenzung
Present discussions concerning the new concept of catchment areas Z<sub>u</sub> of groundwater wells as a means to protect drinking water are dominated by the nitrate problem and its solution. However, measures to be taken to reduce water pollution from agriculture should not be restricted to single wells but be directed towards the protection of the total usable groundwater resource area. On the other hand, the determination of the aquifer area from which substantial amounts of water flow into a single well may be of utmost importance for predictive quality and risk assessments with respect to other pollutants originating from housing, traffic and industrial activities. Special attention should be given to the numerous water wells along rivers with appreciable amounts of infiltrated river water in which the substances to be considered are multifarious and where the transport pathways of water and substances are of complex nature.
The effect of microorganisms and seasonal factors on the isotopic composition of particulate organic carbon from the Black Sea
The isotopic composition of particulate organic carbon (POC) from the Black Sea deep-water zone was studied during a Russian-Swiss expedition in May 1998. POC from the upper part of the hydrogen sulfide zone (the C-layer) was found to be considerably enriched with the <sup>12</sup>C isotope, as compared to the POC of the oxycline and anaerobic zone. In the C-layer waters, the concurrent presence of dissolved oxygen and hydrogen sulfide and an increased rate of dark CO<sub>2</sub> fixation were recorded, suggesting that the change in the POC isotopic composition occurs at the expense of newly formed isotopically light organic matter of the biomass of autotrophic bacteria involved in the sulfur cycle. In the anaerobic waters below the C-layer, the organic matter of the biomass of autotrophs is consumed by the community of heterotrophic microorganisms; this results in weighting of the POC isotopic composition. Analysis of the data obtained and data available in the literature allows an inference to be made about the considerable seasonable variability of the POC δ<sup>13</sup>C value, which depends on the ratio of terrigenic and planktonogenic components in the particulate organic matter.
Microbial processes at the aerobic-anaerobic interface in the deep-water zone of the Black Sea
Chemical and key microbiological processes (assimilation of carbon dioxide, oxidation and formation of methane, and sulfate reduction) occurring at the aerobic-anaerobic interface in the deep-water zone of the Black Sea were investigated. Measurements were taken at depths from 90 to 300 m at intervals of 5-10 m. The integral rate of the dark assimilation of carbon dioxide varied from 120 to 207 mg C/(m<SUP>2</SUP> day) with a maximum at the boundary of cyclonic currents. The organic matter (OM) formed from methane comprised less than 5% of the OM formed from carbon dioxide. A comparison between the rates of methane oxidation and methane production suggests that methane that is oxidized at depths from 100 to 300 m was formed in deeper water horizons. The maximum rate of sulfate reduction (1230 mg S/(m<SUP>2</SUP> day)) was observed in the western halistatic region, and the minimum rate (490 mg S/(m<SUP>2</SUP> day)), in the eastern halistatic region. The average rate of hydrogen sulfide production measured at three deep-sea stations amounted to 755 mg S/(m<SUP>2</SUP> day), or 276 g S/(m<SUP>2</SUP> year).
Hormonaktive Stoffe im Abwasser. Sind Fische und andere wasserlebende Tiere betroffen?
This article presents the Swiss network declining fish fields project. In coming years, this project will analyse the causes and develop options for action to contend with the problem of declining fish catches and the observed deterioration of fish health. One possible cause are endocrine disrupting chemicals (EDC's), which are released to rivers by sewage treatment plants. Sources and known effects of EDC's on aquatic life are summarised in the second part of this paper.
Nickel speciation and complexation kinetics in freshwater by ligand exchange and DPCSV
A technique of ligand exchange with DMG (dimethylglyoxime) and DPCSV was applied to determine Ni speciation in lake, river, and groundwater samples. The working conditions related to ligand-exchange equilibrium were optimized, and the ligand-exchange kinetics were examined. The observed pseudo-first-order rate, <I>k</I><sub>obsd</sub>, was about 3 × 10<sup>-5</sup> (s<sup>-1</sup>) for Ni(DMG)<sub>2</sub> complex formation with an excess of DMG (μM) over Ni (nM) at pH 7.1-7.7. The second-order exchange kinetic constants, <I>k</I><sub>exch</sub>, were between 1.2 × 10<sup>2</sup> and 5.7 × 10<sup>3</sup> s<sup>-1</sup> M<sup>-1</sup> for ligand exchange of NiEDTA with DMG and between 5 × 10<sup>2</sup> and 7 × 10<sup>3</sup> s<sup>-1</sup> M<sup>-1</sup> for exchange of natural ligands with DMG in the freshwater samples under similar conditions. Ni ligand exchange between natural ligands and DMG occurred over days with half-lifes of 5-95 h. Total dissolved Ni concentrations in samples from various freshwater systems in Switzerland ranged from 4 nM in an oligotrophic lake to 30 nM in a small river affected by inputs from sewage effluents and agriculture. Free ionic Ni<sup>2+</sup> concentrations were determined in the range of 10<sup>-13</sup>-10<sup>-15</sup> M (pNi = 12.2-14.7), indicating that more than 99.9% of dissolved Ni was bound by organic ligands with strong affinity (log <I>K</I> 12.1-14.9) and low concentrations (13-100 nM) at pH 7.2-8.2. Because of slow ligand-exchange kinetics, Ni speciation in natural waters may in many cases not reach equilibrium.
Accumulation of poly[(R)-3-hydroxyalkanoates] in <I>Pseudomonas oleovorans</I> during growth in batch and chemostat culture with different carbon sources
<em>Pseudomonas oleovorans </em>(ATCC 29347) was grown in batch and chemostat cultures with citrate, hexanoate, heptanoate, octanoate, and nonanoate as single carbon substrates. The growth medium for batch cultures was adjusted such that nitrogen (NH<sub>4</sub><sup>+</sup>) limitation terminated the exponential-growth phase. During batch cultivation with octanoate or nonanoate the biomass continued to increase after depletion of ammonium due to the accumulation of medium-chain-length poly[(R)-3-hydroxyalkanoates] (mcl-PHAs). Additionally, a significant rate of mcl-PHA accumulation was also observed in the exponential-growth phase of batch cultures. It is well known that the accumulation of reserve materials is strongly dependent on the ratio of nutrients (here of carbon, C, and of nitrogen, N) and that in a batch culture the ratio of C:N is continuously changing. Therefore, we have also investigated the effect of defined ratios of C:N under constant cultivation conditions, namely at a fixed dilution rate (D) in a chemostat fed with different medium C:N ratios. These experiments were performed at a constant D of 0.2 h<sup>−1</sup>. The concentration of the nitrogen source in the inflowing medium (N) was kept constant, while its carbon concentration (C) was increased stepwise, resulting in an increase of the medium carbon to nitrogen ratio (C/N ratio). The culture parameters and the cell composition of steady-state cultures were determined as a function of the C/N ratio in the feed medium. Mcl-PHA accumulation was detected during growth with the fatty acids, and three distinct regimes of growth limitation were discovered: In addition to carbon limitation at low, and nitrogen limitation at high C/N ratios, an intermediate growth regime of simultaneous limitation by carbon and nitrogen was detected where both substrates were used to completion. The width of this dual-nutrient-limited growth regime was dependent on the change in the yield factors for carbon and nitrogen (Y<sub>X/C</sub>, Y<sub>X/N</sub>) measured during single-nutrient-limited growth.
Effluent from a sewage treatment works causes changes in serum chemistry of brown trout (<I>Salmo trutta</I> L.)
To evaluate the impact of effluent from a sewage treatment works on fish health, serum chemistry variables were investigated in brown trout (<I>Salmo trutta</I> L.) held in cages (active monitoring) and wild brown trout (passive monitoring). Means of the measured serum parameters of the different treatment groups were close or within normal ranges. However, the results of the active monitoring demonstrated that the serum variables of reference trout held in tap water were clearly different from those of the river treatment groups. In the active monitoring, fish exposed to effluent from the sewage treatment works had significantly different blood urea nitrogen and bilirubin values than fish kept in river water. In the passive monitoring, total protein, blood urea nitrogen, and alkaline phosphatase were significantly different between the two groups. Of the numerous correlations between serum chemistry parameters and histological lesions, blood urea nitrogen and alkaline phosphatase were found to most strongly indicate gill and liver lesions, respectively. In the passive monitoring correlations between serum chemistry variables and histopathological lesions were restricted to bilirubin and liver lesions. This indicates that the application of serum chemistry variables as indicators of histological lesions in case of chronic exposure is questionable. A multivariate discriminant analysis was used to consider relationships between the single serum variables concurrently.
Changes in deep-water formation during the Younger Dryas event inferred from <SUP>10</SUP>Be and <SUP>14</SUP>C records
Variations in atmospheric radiocarbon (<SUP>14</SUP>C) concentrations can be attributed either to changes in the carbon cycle<sup>1</sup>—through the rate of radiocarbon removal from the atmosphere—or to variations in the production rate of <SUP>14</SUP>C due to changes in solar activity or the Earth's magnetic field<sup>2</sup>. The production rates of <SUP>10</SUP>Be and <SUP>14</SUP>C vary in the same way, but whereas atmospheric radiocarbon concentrations are additionally affected by the carbon cycle, <SUP>10</SUP>Be concentrations reflect production rates more directly. A record of the <SUP>10</SUP>Be 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 <SUP>14</SUP>C concentrations, of unclear origin<sup>3</sup>, that occurred during the Younger Dryas cold period<sup>6</sup>. We use the <SUP>10</SUP>Be record from the GISP2 ice core<sup>5</sup> to model past production rates of radionuclides, and rnd that the largest part of the fluctuations in atmospheric radiocarbon concentrations can be attributed to variations in production rate. The residual difference between measured <SUP>14</SUP>C concentrations and those modelled using the <SUP>10</SUP>Be record can be explained with an additional change in the carbon cycle, most probably in the amount of deep-water formation.
Light-induced redox cycling of iron in circumneutral lakes
The light-induced redox cycling of Fe<sup>II</sup>/Fe<sup>III</sup> was studied both in laboratory experiments and in the field in two circumneutral Swiss lakes: Greifensee, a eutrophic, natural water body, and Melchsee, an oligotrophic, artificial mountain lake. To determine Fe<sup>II</sup> at the nanomolar level, an automated flow-injection analysis system was used. Irradiation by simulated sunlight leads to pH dependent (pH 6.9-9.1) steady-state Fe<sup>II</sup> concentrations which are similar in samples from both lakes. However, the kinetics of Fe<sup>III</sup> reduction and of apparent Fe<sup>II</sup> oxidation are considerably faster in Melchsee. On the basis of experimental results and on modeling that uses literature values of known chemical transformation processes, we suggest that superoxide may be a key parameter for light-induced iron redox cycling in these lakes. Field measurements of [Fe<sup>II</sup>] in Greifensee and Melchsee show a pronounced day/ night cycle, with Fe<sup>II</sup> concentrations of ∼0.1-0.2 nM at night and up to 0.9 nM near the surface during the day (pH 8.0-8.5). Depth profiles of [Fe<sup>II</sup>] have two maxima: one at the surface and the second one at a depth of 5-10 m. Empirical rates and measured physical parameters were included in a model to simulate [Fe<sup>II</sup>] as a function of time and depth. The model results indicate that Fe<sup>II</sup> at the surface of both lakes is produced by light-induced processes, whereas the deeper Fe<sup>II</sup> maxima at depths with maximal chlorophyll <em>a</em> concentrations are probably due to a combination of biologically and photochemically induced processes.
Environmental fate and microbial degradation of aminopolycarboxylic acids
Aminopolycarboxylic acids (APCAs) have the ability to form stable, water-soluble complexes with di- and trivalent metal ions. For that reason, synthetic APCAs are used in a broad range of domestic products and industrial applications to control solubility and precipitation of metal ions. Because most of these applications are water-based, APCAs are disposed of in wastewater and reach thus sewage treatment plants and the environment, where they undergo abiotic and/or biotic degradation processes. Recently, also natural APCAs have been described which are produced by plants or micro-organisms and are involved in the metal uptake by these organisms. For the two most widely used APCAs, nitrilotriacetate (NTA) and ethylenediaminetetraacetate (EDTA), transformation and mineralisation processes have been studied rather well, while for other xenobiotic APCAs and for the naturally occurring APCAs little is known on their fate in the environment. Whereas NTA is mainly degraded by bacteria under both oxic and anoxic conditions, biodegradation is apparently of minor importance for the environmental fate of EDTA. Photodegradation of iron(III)-complexed EDTA is supposed to be mostly responsible for its elimination. Isolation of a number of NTA- and EDTA-utilising bacterial strains has been reported and the spectrum of APCAs utilised by the different isolates indicates that some of them are able to utilise a range of different APCAs whereas others seem to be restricted to one compound. The two best characterised obligately aerobic NTA-utilising genera (<em>Chelatobacter</em> and <em>Chelatococcus</em>) are members of the α-subgroup of <em>Proteobacteria</em>. There is good evidence that they are present in fairly high numbers in surface waters, soils and sewage treatment plants. The key enzymes involved in NTA degradation in <em>Chelatobacter</em> and <em>Chelatococcus</em> have been isolated and characterised. The two first catabolic steps are catalysed by a monooxygenase (NTA MO) and a membrane-bound iminodiacetate dehydrogenase. NTA MO has been cloned and sequenced and its regulation as a function of growth conditions has been studied. Under denitrifying conditions, NTA catabolism is catalysed by a NTA dehydrogenase. EDTA breakdown was found to be initiated by a MO also which shares many characteristics with NTA MO from strictly aerobic NTA-degrading bacteria. In contrast, degradation of [<em>S,S</em>]-ethylenediaminedisuccinate ([<em>S,S</em>]-EDDS), a structural isomer of EDTA, was shown to be catalysed by an EDDS lyase in both an EDTA degrader and in a NTA-utilising <em>Chelatococcus</em> strain. So far, transport of APCAs into cells has only been studied for EDTA and the results obtained give strong evidence for an energy-dependent carrier system and Ca<sup>2+</sup> seems to be co-transported with EDTA. Due to their metal-complexing capacities, APCAs occur in the environment mostly in the metal-complexed form. Hence, the influence of metal speciation on various degradation processes is of utmost importance to understand the environmental behaviour of these compounds. In case of biodegradation, the effect of metal speciation is rather difficult to assess at the whole cell level and therefore only limited good data are available. In contrast, the influence of metal speciation on the intracellular enzymatic breakdown of APCAs is rather well documented but no generalising pattern applicable to all enzymes was found.