Short-term Laboratory Experiments Research Articles

Integrated methodology to evaluate bioremediation potential of creosote-contaminated soils

Integrated methodology including chemical analyses as well as biological and ecotoxicological testing of soil was used to evaluate bioremediation potential of an aged, highly contaminated soil from a wood preservation plant. The soils contaminated with coal tar creosote originated from two sites (Site I: 8000 mg/kg and Site II: 133,800 mg/kg). A toxicity test-battery able to detect different effects using a variety of endpoints was developed and applied for the ecotoxicological assessment of creosote in soils: Azotobacter agile and Pseudomonas fluorescens dehydrogenase enzyme activity test, Vibrio fischeri bioluminescence test, Sinapis alba root and shoot elongation test and Folsomia candida mortality test. The biodegradation and its enhancement were investigated in small-scale bioreactors in short-term laboratory experiments. The joint evaluation of chemical, biological and ecotoxicological results made possible to compare different technologies, and investigate their applicability for remediation of soils contaminated with coal tar. The most sensitive direct contact tests that also correlated well with the creosote-reduction were Vibrio fischeri bioluminescence test, followed by Folsomia candida mortality test and Sinapis alba shoot elongation test.

Incorporating temporal variability of stressors into studies: An example using suspension-feeding bivalves and elevated suspended sediment concentrations

While spatial scale is increasingly incorporated into ecological experiments, the effect of temporal scale is explicitly investigated less frequently, despite the potential for temporal-scale dependent results. This study was designed to investigate the effect of variations in stress duration on responses, in a situation where stress duration is driven by natural storm events. Specifically, the utility of combining short-term laboratory and longer-term field transplant experiments in assessing the effect of increased suspended sediment concentrations on suspension-feeding bivalves ( Austrovenus stutchburyi and Paphies australis) was tested. Short-term (2 days) feeding responses did not reflect feeding or biomass responses over slightly longer time-scales (8–14 days). Also, stronger biomass responses to suspended sediment concentrations were observed after three months in the field, than after 14 days in the laboratory. For unimodal responses, increased stress duration decreased the peak and shifted its location to lower suspended sediment levels. Using continuous measures of field suspended sediment concentrations, the study was able to determine the temporal scale of variability most related to the response. With such information, field surveys and transplants together make a useful tool, preventing co-occurring factors and changes in the duration and intensity of the factors of interest from obscuring results.

Effects of nutrient availability and Ochromonas sp. predation on size and composition of a simplified aquatic bacterial community

Predation and competition are two main factors that determine the size and composition of aquatic bacterial populations. Using a simplified bacterial community, composed of three strains characterized by different responses to predation, a short-term laboratory experiment was performed to evaluate adaptations and relative success in communities with experimentally controlled levels of predation and nutrient availability. A strain with a short generation time (Pseudomonas putida), one with high plasticity in cell morphology (Flectobacillus sp. GC5), and one that develops microcolonies (Pseudomonas sp. CM10), were selected. The voracious flagellate Ochromonas sp. was chosen as a predator. To describe adaptations against grazing and starvation, abundance, biomass and relative heterogeneity of bacteria were measured. On the whole, the strains in the predation-free cultures exhibited unicellular growth, and P. putida represented the largest group. The presence of Ochromonas strongly reduced bacterial abundance, but not always the total biomass. The activity of grazers changed the morphological composition of the bacterial communities. Under grazing pressure the relative composition of the community depended on the substrate availability. In the presence of predators, P. putida abundance declined in both high and low nutrient treatments, and Pseudomonas CM10 developed colonies. Flectobacillus was only numerically codominant in the nutrient-rich environments.

NOVEL APPLICATION OF MTT REDUCTION: A VIABILITY ASSAY FOR TEMPERATE SHALLOW-WATER BENTHIC FORAMINIFERA

Research Article| July 01, 2006 NOVEL APPLICATION OF MTT REDUCTION: A VIABILITY ASSAY FOR TEMPERATE SHALLOW-WATER BENTHIC FORAMINIFERA L. J. de Nooijer; L. J. de Nooijer 1Department of Stratigraphy and Paleontology, Faculty of Geosciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, The Netherlands. Email: nooijer@geo.uu.nl Search for other works by this author on: GSW Google Scholar I. A. P. Duijnstee; I. A. P. Duijnstee 1Department of Stratigraphy and Paleontology, Faculty of Geosciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, The Netherlands. Email: nooijer@geo.uu.nl2Department of Biogeology, Faculty of Sciences, Radboud University, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands. Search for other works by this author on: GSW Google Scholar G. J. van der Zwaan G. J. van der Zwaan 1Department of Stratigraphy and Paleontology, Faculty of Geosciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, The Netherlands. Email: nooijer@geo.uu.nl2Department of Biogeology, Faculty of Sciences, Radboud University, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands. Search for other works by this author on: GSW Google Scholar Journal of Foraminiferal Research (2006) 36 (3): 195–200. https://doi.org/10.2113/gsjfr.36.3.195 Article history received: 18 Mar 2005 accepted: 19 Mar 2006 first online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation L. J. de Nooijer, I. A. P. Duijnstee, G. J. van der Zwaan; NOVEL APPLICATION OF MTT REDUCTION: A VIABILITY ASSAY FOR TEMPERATE SHALLOW-WATER BENTHIC FORAMINIFERA. Journal of Foraminiferal Research 2006;; 36 (3): 195–200. doi: https://doi.org/10.2113/gsjfr.36.3.195 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyJournal of Foraminiferal Research Search Advanced Search Abstract Studies on living benthic foraminifera commonly involve staining samples with rose Bengal (RB) to distinguish living from dead individuals. Since RB also stains individuals that have died recently (sometimes weeks earlier) and are not fully decayed, standing stocks of foraminiferal communities are usually overestimated. To overcome this bias, we discuss a new viability assay based on the reduction of a tetrazolium salt, MTT (3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide or thiazolyl blue) by living foraminifera. The tetrazolium salt MTT is actively ingested by cells and subsequently converted enzymatically from a yellow, soluble form to a reddish purple crystal. Experiments confirm that living individuals of Ammonia beccarii and Globobulimina turgida convert MTT and become stained within 24 hours. Some dead foraminifers may continue enzymatic activity for several days, but produce a different coloration than that of stained living foraminifers. With the reduced problem of false positives, this assay is an improvement over staining samples with RB whenever a higher accuracy is required (e.g., in short-term laboratory experiments). You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Suppression of negative self-referent thoughts: A field study

We examined the effects of suppressing negative self-referent thoughts on thought frequency, mood, and self-esteem over an 11-day period. Participants were randomly assigned to a suppression or control group and completed a nightly Web survey. Compared with controls, participants who suppressed a specific thought experienced it more frequently and had more anxious and depressed mood. Self-reported shamefulness of the thought moderated the effect of suppression on self-esteem. Suppression participants who rated their thoughts as shame-producing had lower self-esteem than did all other participants. These findings generally replicate results from a previous laboratory study (Borton, Markowitz, & Dieterich, 2005) and demonstrate that the deleterious effects of suppression are not confined to short-term laboratory experiments.

Influence of Light Intensity, Photoperiod, and Temperature on the Efficacy of Two Aphelinid Parasitoids of the Greenhouse Whitefly

In short-term laboratory experiments, we studied the influence of light intensity, photoperiod, and temperature on the feeding and oviposition activity of two aphelinid parasitoids, Encarsia formosa Gahan and Eretmocerus eremicus Rose and Zolnerowich, on the greenhouse whitefly, Trialeurodes vaporariorum (Westwood). E. eremicus parasitized significantly more whitefly hosts than E. formosa in all treatment combinations of light intensity and photoperiod at 24 and 20°C. At 24°C, both E. formosa and E. eremicus parasitized approximately twice as many whitefly hosts at the high light intensity (112–114 W/m2)–long daylength (L 16:D 8 h) treatment than at the low light intensity (12–14 W/m2)–short daylength (L 8:D 16 h) treatment. In most instances at 20 and 24°C, significantly more dead whitefly hosts were recorded in leaf cages introduced with parasitoids than leaf cages with no parasitoids, indicating that host feeding occurred. Both E. formosa and E. eremicus parasitized significantly more whitefly hosts under the simulated summer (i.e., high light intensity [82.0–83.6 W/m2]; long daylength [L 16:D 8 h], 24°C) treatment than the winter (i.e., low light intensity [10.8–11.1 W/m2]; short daylength [L 8:D 16 h], 20°C) treatment. In addition, significantly more dead whitefly hosts were observed in leaf cages introduced with E. eremicus than E. formosa under the winter treatment, suggesting that E. eremicus killed more whitefly hosts through host feeding than E. formosa. This was not the case for the other treatment combinations. E. eremicus contributes more to greenhouse whitefly mortality than E. formosa by a combination of greater parasitism and host feeding and therefore is recommended for use in winter months with day temperatures ≥ 20°C, in addition to later in the season, where it is currently being used.

A DIRECT, EXPERIMENTAL TEST OF RESOURCE VS. CONSUMER DEPENDENCE

The uptake of resources from the environment is a vital process for all organisms. Many experimental studies have revealed that the rate at which this process occurs depends critically on the resource concentration, a relationship called “functional response.” However, whether the concentration of the consumer normally affects the functional response has been the subject of a long-standing, predominantly theoretical, debate in ecology. Here we present an experimental test between the alternative hypotheses that food uptake depends either only on the resource concentration or on both the resource and the consumer concentrations. In short-term laboratory experiments, we measured the uptake of radioactively labeled, unicellular green algae (Monoraphidium minutum, resource) by the rotifer Brachionus calyciflorus (a consumer) for varying combinations of resource and consumer concentrations. We found that the food uptake by Brachionus depended on the algal concentration with the relationship best described by a Holling type 3 functional response. We detected significant consumer effects on the functional response only at an extraordinarily high Brachionus density (∼125 rotifers/mL), which by far exceeds concentrations normally encountered in the field. We conclude that consumer-dependent food uptake by planktonic rotifers is a phenomenon that can occur under extreme conditions, but probably plays a minor role in natural environments.

Widening the window of persistence in seasonal pathogen–host systems

Local instability of exploiter–victim systems is well-known in both theory and in nature. Victims can be too sparse to support exploiter reproduction (under-exploitation) or they can be too readily driven to extinction (over-exploitation). Exploiters of seasonal resources face the additional challenge of surviving periods when victims are rare or unavailable. We formulate a fully stochastic model of highly seasonal pathogen–host dynamics and explore the interactions between an entomopathogenic nematode and its lepidopteran host. Our model suggests that if nematode populations experience the high rates of mortality predicted by short-term laboratory experiments, the paired threats of under- and over-exploitation should preclude the long-term persistence of this exploiter–victim system. We measured nematode mortality rates in the field and found that long-term mortality is lower than that predicted by short-term experiments. Incorporation of this new data into our model produces long-term persistence of local nematode populations across a range of initial nematode densities.

Interactive effects of functionally different earthworm species on aggregation and incorporation and decomposition of newly added residue carbon

The interactive effects of two functionally different earthworm species ( Aporrectodea caliginosa (endogeic species) and Lumbricus rubellus (epigeic species)) on the incorporation of fresh residue into large macroaggregates and formation of microaggregates within these large macroaggregates were investigated during a short-term laboratory experiment using 13C-labelled sorghum ( Sorghum bicolor (L.) Moench) residues. Soil was collected from a long-term no-tillage agricultural field, crushed through a 250-μm sieve and incubated under laboratory conditions. The following earthworm treatments were applied: (i) soil+ 13C-labelled residue+ A. caliginosa; (ii) soil+ 13C-labelled residue+ L. rubellus; (iii) soil+ 13C-labelled residue+ A. caliginosa+ L. rubellus and; (iv) soil+ 13C-labelled residue. Two residue placement treatments (i.e. surface and incorporated) were superimposed on the earthworm treatments. Earthworms were added after 8 days of incubation. Aggregate size distribution and total C and 13C were measured after 22 days. Microaggregates, fine inter-microaggregate particulate organic matter (inter-POM) and intra-microaggregate POM (intra-POM) were isolated from macroaggregates. Earthworms had a greater stimulating effect on the formation of large macroaggregates (>2000 μm) and microaggregates within large macroaggregates when residue was incorporated in the soil, especially in the presence of A. caliginosa. When residue was placed on the surface, residue-derived intra-POM C was highest when L. rubellus was present and significantly lower in the presence of A. caliginosa. Residue-derived inter-POM C was highest when a mix of both species was present. These results indicate that earthworm species differentially affect incorporation of fresh organic matter into stable microaggregates within macroaggregates, and that interactive effects of earthworm species might have important consequences for the incorporation and protection of C inside of microaggregates within macroaggregates especially when residues are placed on the soil surface.

Growth Dilution of Metals in Microalgal Biofilms

Despite the key role microalgae play in introducing toxicants into aquatic food webs, little is known about the effects of environmental factors on metal accumulation by these primary producers. Environmental factors such as light and nutrients alter growth rates and may consequently influence metal concentrations in microalgae through growth dilution. Laboratory experiments suggested that metal uptake and elimination by microalgal biofilms were gradual enough to enable dilution of metals within the biofilms by photosynthetically accrued carbon, and a simple kinetic model of metal accumulation predicted significant variation in metal content due to growth dilution over the natural range of microalgal growth rates. The ratio of metal uptake to carbon uptake by microalgal biofilms decreased exponentially with increasing light in short-term laboratory experiments because photosynthesis was much more sensitive to a light gradient than was metal uptake. The effect of light on biofilm metal concentrations was confirmed in situ with a long-term experiment in which experimental shading of biofilms in a metal-contaminated stream decreased biofilm growth rates and caused a 3x increase in biofilm concentrations of twelve metals, including methylmercury. Slow growth at the primary producer level is a likely contributor to higher biotic metal concentrations in shaded, oligotrophic, or cold ecosystems.

Sorption Kinetics of Organic Contaminants by Sandy Aquifer and Its Kerogen Isolate

Long-term sorption behaviors of phenanthrene (Phen) on the Borden sand from 1 min to 365 days and of Phen and 1,2-dichlorobenzene (DCB) on the isolated kerogen from 1 to 120 days were characterized by examining the time dependence of solute phase distribution relationships (PDRs) and compared with the prior reported sorption of tetrachlorobenzene (TeCB) and tetrachloroethene (PCE) on the pulverized and/or acid-treated bulk sand and size fractions. The sorption kinetics for Phen on the bulk sand and its kerogen isolate can well be described by the fractional power kinetics equation (q(e) = kt(b)). The similar rate parameter b for q(e)(t) vs t at 5-7 levels of initial concentrations of Phen on the two sorbents, respectively, ranging from 0.077 to 0.099 and from 0.072 to 0.086, indicates the similar sorption kinetics rate. The modified-Freundlich parameters of TeCB on the pulverized or acid-treated 0.3-mm size fraction match those of Phen on the isolated kerogen, suggesting the same natural organic matter (NOM) property of the two sorbents. As the prior investigation underestimated the Koc value for the TeCB sorption on the acid-treated 0.3-mm size fraction by a factor of 1.76, the estimated time to reach 95% of sorption equilibrium is much longer than the prior estimation (over 10 years vs about 2.5 years). The estimated times to reach 95% of sorption equilibrium at three levels of relative solubility for Phen on the bulk sand and its isolated kerogen are, respectively, longer than one decade, demonstrating the similar diffusion length for Phen on the two sorbents. The observed slow sorption kinetics is related to nanometer-pore diffusion within kerogen matrix. The investigation supplies new clues for explaining the often observed much longer persistence of organic contaminants in soils and sediments than the prediction based on the short-term laboratory experiment.

The Effectiveness of Internet-Controlled Astronomical Research Instrumentation for Education

Over the last decade, remote instruments have become widely used in astronomy. Educational applications are more recent. This paper describes a program to bring radio astronomy into the undergraduate classroom through the use of a remote research-grade radio telescope, the MIT Haystack Observatory 37 m telescope. We examine the effectiveness of such remote access in the classroom. The remote use of the large telescope has opened up a research facility for undergraduate students. The experience has been largely successful with over 150 students from about 20 colleges using the telescope every year. The student experiments have included classroom demonstrations by faculty, and short-term laboratory experiments and long-term research experiments performed by students. Although a visit to the site provided students with a sense of the scale of the antenna, operating on a purely remote basis still gave the students a rewarding research and learning experience. The effectiveness of the remote instrument is judged mainly by the student presentations and papers that have been generated, by the enthusiasm of the faculty to continue using the facility as part of their curricula, and through a survey of students and faculty.

Short-term response of benthic bacteria and nanoflagellates to sediment resuspension: an experimental study

We investigated benthic bacterial abundance, biomass and activities and heterotrophic nanoflagellate (HNF) abundance and biomass during sediment resuspension and after a resilience period through short-term laboratory experiments. The strong sediment resuspension increased bacterial carbon production only slightly (Tukey's test, P < 0.05) but somehow interfered with microbial growth. During sediment resuspension, after an initial increase (at 48 and 72 h) bacterial abundance and biomass decreased until the end of resuspension. Sediment resuspension also altered the relationship between HNFs and bacteria (increase in the ratios of bacterium to HNF abundance and biomass after sediment resuspension; Tukey's test, P < 0.01). After sediment resuspension, the fraction of bacterial C production removed by flagellates decreased, whereas bacterial turnover did not change significantly, suggesting that HNF pressure on bacteria decreased. These results are consistent with the significant decrease in both HNF abundance and biomass (Tukey's test, P < 0.01) and suggest that this small benthic component is less resilient to sediment resuspension than bacteria. Sediment resuspension also determined significant changes in sediment organic matter pools (proteins and carbohydrates). Sediment resuspension determined a decrease in total protein concentrations, whereas total carbohydrate concentrations did not change significantly. Sediment resuspension had significant effects on extracellular enzymatic activities, as aminopeptidase increased and β-glucosidase activity decreased. Based on total protein and carbohydrate concentrations and enzymatic activities, we observed that sediment resuspension resulted in an increase in protein turnover and a decrease in carbohydrate turnover. These results indicate that sediment resuspension plays a major role in the early diagenesis of sediment organic matter.

Physiological responses of a bloom-forming green macroalga to short-term change in salinity, nutrients, and light help explain its ecological success

Enteromorpha intestinalis is a bloom-forming species of macroalgae associated with eutrophication. The objective of this study was to investigate how this alga performs osmoregulation and nutrient uptake in order to proliferate under environmental conditions that covary with eutrophication. We quantified the response ofE. intestinalis to salinity, light, and nutrients. We performed two short-term (48 h) laboratory experiments (salinity alone and salinity × nutrients × light) to examine the algal responses of tissue water, potassium (K+), and nutrient (NO 3 − and total N) content. Tissue water content decreased with increasing salinity, and although K+ concentration decreased from the initial concentration, it decreased less with increased salinity treatment demonstrating two mechanisms to withstand short-term salinity fluctuation. The salinity × nutrient × light experiment showed that, in the short term, light had an interaction with tissue K+. Total tissue N content was positively related to N treatment level, and light did not affect total nutrient concentration. The effect of light was present whether the nutrients were present in the tissue as inorganic or organic forms. With reduced light, we hypothe size that the assimilation of inorganic to organic N was energy limited. The ability of this alga to take up available nutrients rapidly for growth and short-term osmoregulation, even under low light and salinity levels, helps to explain the bloom potential ofE. intestinalis.

Fertile temperate grassland under elevated atmospheric CO 2—role of feed-back mechanisms and availability of growth resources

Human activities are responsible for the strong and very fast increase in the concentration of atmospheric CO 2 over the past 100 years; this trend will continue. An increase in CO 2 is expected to affect significantly grassland vegetation, which covers approximately 70% of agricultural land world-wide and undoubtedly plays an important role in the global C cycle. This review summarises the information about the response of temperate, intensively managed grassland to elevated atmospheric CO 2 under field conditions. 1. The yield response of grassland to elevated CO 2 under field conditions was weaker than expected from short-term laboratory experiments. 2. Different functional types of plant species responded differently to elevated CO 2, leading to changes in the proportion of plant species in grassland. 3. Adapted management of grassland was able to counteract—at least partly—CO 2-induced changes in species proportion. 4. The availability of growth resources other than CO 2 (e.g., N and P) strongly affected the plant’s response to elevated CO 2. 5. Symbiotic N 2 fixation and a strong sink for additionally fixed C (high growth rate, tillering, storage organs) were the functional traits that played a key role in the strong increase in yield under elevated CO 2. 6. An increased input of N through symbiotic N 2 fixation under elevated CO 2 played an important role in maintaining the C/N balance of the legume plant and of entire fertile grassland ecosystems. 7. The yield response to elevated CO 2 changed in the long-term indicating that processes in the soil that responded slowly (e.g., nutrient cycling and sequestration, activity and mass of micro-organisms) gradually adapted to the new environmental conditions. These results demonstrate that the response of ecosystems to elevated CO 2 cannot be deduced from measurements based on individual plants in controlled environments. Long-term experiments in the field where the availability of growth resources is varied, the plants interact with each other and the soil interacts with the plants (feed-back mechanisms) are necessary for predicting the effect of elevated CO 2.

Differential sensitivity of green algae to allelopathic substances from Chara

Three short-term laboratory experiments were conducted to investigate allelopathic effects of a mixture of Chara globularis var. globularis Thuillier and Chara contraria var. contraria A. Braun ex Kutzing on three different green algae. Single phytoplankton species were exposed to filtered water originating from charophyte cultures. Phytoplankton growth was monitored by determination of chlorophyll concentrations in batch cultures. The change in chlorophyll concentration during the experiments was analysed with a logistic growth model, resulting in an estimate of the exponential growth rate and the duration of the lag phase of the single green algae. The results indicate allelopathic effects of Chara on the growth of the green algae Selenastrum capricornutum Printz and Chlorella minutissima Fott et Novakova, whereas Scenedesmus obliquus (Turpin) Kutzing did not seem to be affected. The exponential growth rate of S. capricornutum decreased 7% in the presence of water from a charophyte culture, while the growth rate of C. minutissima decreased with 3%. The allelopathic effect of Chara did not increase when the green alga C. minutissima was P-limited. The effect of Chara was different when young sprouts were used. With young sprouts the duration of the lag phase of C. minutissima was extended (25%), whilst for old plants the growth rate of this green alga decreased. Although the inhibiting effect of charophytes on specific phytoplankton species is rather small, the differential sensitivity of the species to Chara might influence the composition and biomass of phytoplankton communities in the field.

Metal Remobilisation during Resuspension of Anoxic Contaminated Sediment: Short-Term Laboratory Study

The sediments of the Tagus estuary North Channel arecharacterised by high concentrations of trace metals andmonosulphides. During dredging operations Cd, Cu and Pb wereanalysed in water and suspended sediments collected 50 to 100 m around the dredging point. Concentrations in bothfractions fluctuated randomly: 2–3 fold for Cd and Cu and 10 for Pb. Since sampling in the dredging point reflectsintegration of rapid chemical reactions, a short-termlaboratory experiment was conducted to follow the geochemicalalterations occurring in the highest turbidity sites. Theexperiment was monitored as a function of time over a period of4 hr in short time intervals. Dissolved oxygen, pH, EH,AVS, SO42-, Cl- and metals were monitored in theslurry samples. Iron, Mn, Cd, Pb and Cu were determined in thedissolved fraction (<0.45 μm), in the reactive solid phaseand in the total fraction. Resuspension resulted in asignificant release of Fe, Mn, Cd, Cu and Pb from the solids.Following the release Pb and Cu were almost totally scavengedin the 4 hr by the newly precipitated Fe oxyhydroxides, while more than 50% of the mobilised Cd remained in the dissolved fraction. The less efficient removal of Cd from solution implies a prolonged availability of this metal in the environment.

In situ determination of long-term basaltic glass dissolution in the unsaturated zone

Maximum in situ weathering rates of basaltic glass measured at the El Malpais National Monument in New Mexico are on the order of 2–5×10 −19 mol/cm 2 s. Rates were calculated from backscattered electron (BSE) imaging of weathered porosity and are equivalent to 1.7–5% of the surface per 1000 years. Weathering is independent of glass composition but appears to increase with flow elevation at El Malpais. Measured rates represent weathering over 3000 years and are substantially lower than glass dissolution rates measured in the laboratory over much shorter time spans. Basaltic glass is a close chemical analogue to glass hosts proposed for encapsulation of high-level nuclear wastes. Radionuclide release rates predicted from the basis of in situ field rates are substantially less than those predicted from short-term laboratory experiments.

Enhanced erodibility of fine-grained marine sediments by Hydrobia ulvae

The common mud snail Hydrobia ulvae is a widespread and dominant deposit feeder on fine-grained substrata along the European Atlantic coastline. Previous studies have shown that mud snail activities such as grazing, faecal pellet production and mucous production may influence physical properties of the surface sediment layer and thus depositional and erosional processes. To quantify the influence of Hydrobia density on key parameters such as erosion threshold and erosion rate, a short-term laboratory experiment was conducted. Snails were placed on fine-grained sediment at densities of 10 000 and 50 000 ind m −2 and erosion experiments were carried out one, three and five days after establishment of the sediment beds. Controls without H. ulvae were treated the same way. The presence of H. ulvae significantly increased the erosion rate and decreased the erosion threshold compared to snail-free control plots. The erosion rate was increased by a factor of 2 to 4 when H. ulvae were present and showed stronger influence by the snail than the erosion threshold. Snail density did not affect the erosion threshold, but the erosion rate doubled with an increase in density from 10 000 to 50 000 ind m −2. The erosion rate was only marginally different after one day but the difference increased over time and the erosion rate was significantly different for all treatments after five days. No significant time dependence was observed for the erosion threshold. The results generally confirm results obtained in situ and differences can be related to different hydrodynamic conditions under field and laboratory conditions.

Monitoring and troubleshooting of non-filamentous settling and dewatering problems in an industrial activated sludge treatment plant

A large industrial activated sludge wastewater treatment plant had temporary problems with settling and dewatering of the sludge. Microscopical investigations revealed that the poor settling properties were not due to presence of filamentous bacteria, but poor floc properties. In order to characterise the changes in floc properties that led to settling and dewatering problems and to find reasons for this taking place, a comprehensive monitoring program was conducted during more than one year. The monitoring program included various measurements of floc settleability, floc strength and sludge dewaterability. The monitoring program revealed that a deterioration of the floc strength and the settling properties in the process tanks was closely connected to downstream dewatering problems and poor effluent quality. Particularly severe problems were observed a few weeks after the production at the factory had started after summer closedown. Possible reasons for the changes in floc properties in the process tanks were found by a) analysing change in wastewater composition by evaluating the different production lines in the industrial plant, b) evaluating the operation of the plant, and c) performing short-term laboratory experiments testing factors that could potentially affect floc properties (absence of oxygen, presence of sulphide, detergents, etc). Among several measured parameters, the use of floc strength measurements in particular proved useful to monitor the activated sludge floc properties at this industrial plant. The described strategy can be useful in general to find and solve many solid/liquid separation problems in activated sludge wastewater treatment plants.