This study examines the effects of erythromycin on activated sludge from two French urban wastewater treatment plants (WWTPs). Wastewater spiked with 10 mg/L erythromycin inhibited the specific evolution rate of chemical oxygen demand (COD) by 79% (standard deviation 34%) and the specific N–NH4+ evolution rate by 41% (standard deviation 25%). A temporary increase in COD and tryptophan-like fluorescence, as well as a decrease in suspended solids, were observed in reactors with wastewater containing erythromycin. The destruction of activated sludge flocs was monitored by automated image analysis. The effect of erythromycin on nitrification was variable depending on the sludge origin. Erythromycin inhibited the specific nitrification rate in sludge from one WWTP, but increased the nitrification rate at the other facility. Erythromycin toxicity on activated sludge is expected to reduce pollution removal.

Hydrogen (δ2H), carbon (δ13C), oxygen (δ18O) and nitrogen (δ15N) isotopes of tree rings growing in field conditions can be indicative of past pollution effects. The characteristic δ13C trend is a positive shift generally explained by invoking closure of stomata, but experimental studies suggest that increased rates of carboxylation could also generate such trends. In many cases the δ18O and δ2H values decrease in trees exposed to pollution and exhibit inverse coinciding long-term trends with δ13C values. However, some trees exposed to diffuse pollution and experimental conditions can show an increase or no δ18O change even if δ13C values increase. These diverse responses depend on how stress conditions modify physiological functions such as stomatal conductance, carboxylation, respiration, and perhaps water assimilation by the root system. Recent studies suggest that δ15N changes in trees can be caused by soil acidification and accumulation of anthropogenic emissions with isotopic signals deviating from natural N.

Here we synthesize key findings from a series of experiments to gain new insight on inter-plant competition between juvenile beech (Fagus sylvatica) and spruce (Picea abies) under the influence of increased O3 and CO2 concentrations. Competitiveness of plants was quantified and mechanistically interpreted as space-related resource investments and gains. Stable isotopes were addressed as temporal integrators of plant performance, such as photosynthesis and its relation to water use and nitrogen uptake. In the weaker competitor, beech, efficiency in space-related aboveground resource investment was decreased in competition with spruce and positively related to Δ13C, as well as stomatal conductance, but negatively related to δ18O. Likewise, our synthesis revealed that strong belowground competition for water in spruce was paralleled in this species by high N assimilation capacity. We suggest combining the time-integrative potential of stable isotopes with space-related investigations of competitiveness to accomplish mechanistic understanding of plant competition for resources. Combination of space-related concepts of competitiveness with stable isotopes has potential to clarify mechanisms of competition.

The research and interest towards the use of constructed floating wetlands for (waste)water treatment is emerging as more treatment opportunities are marked out, and the technique is applied more often. To evaluate the effect of a floating macrophyte mat and the influence of temperature and season on physico-chemical changes and removal, two constructed floating wetlands (CFWs), including a floating macrophyte mat, and a control, without emergent vegetation, were built. Raw domestic wastewater from a wastewater treatment plant was added on day 0. Removal of total nitrogen, NH₄-N, NO₃-N, P, chemical oxygen demand (COD), total organic carbon and heavy metals (Cu, Fe, Mn, Ni, Pb and Zn) was studied during 17 batch-fed testing periods with a retention time of 11 days (February-March 2007 and August 2007-September 2008). In general, the CFWs performed better than the control. Average removal efficiencies for NH₄-N, total nitrogen, P and COD were respectively 35%, 42%, 22% and 53% for the CFWs, and 3%, 15%, 6% and 33% for the control. The pH was significantly lower in the CFWs (7.08 ± 0.21) than in the control (7.48 ± 0.26) after 11 days. The removal efficiencies of NH₄-N, total nitrogen and COD were significantly higher in the CFWs as the presence of the floating macrophyte mat influenced positively their removal. Total nitrogen, NH₄-N and P removal was significantly influenced by temperature with the highest removal between 5°C and 15°C. At lower and higher temperatures, removal relapsed. In general, temperature seemed to be the steering factor rather than season. The presence of the floating macrophyte mat restrained the increase of the water temperature when air temperature was >15°C. Although the mat hampered oxygen diffusion from the air towards the water column, the redox potential measured in the rootmat was higher than the value obtained in the control at the same depth, indicating that the release of oxygen from the roots could stimulate oxygen consuming reactions within the root mat, and root oxygen release was higher than oxygen diffusion from the air.

In this report, the toxic effect of TCE (trichloroethylene), PCE (tetrachloroethylene), and potassium dichromate on P. subcapitata was investigated. The test was conducted at different concentrations of pollutants, starting from the European Community limit values defined for each analysed contaminant. Mixtures of pollutants were also tested to verify the combined effect of algae cells. Results suggest that both TCE and PCE were able to reduce P. subcapitata growth and metabolism starting from 0.05 and 0.02 mg L⁻¹ of contaminant, respectively. PCE seems to be substantially more toxic than TCE. Chromium produces a clear effect on algae growth and esterase activity only starting from 1 mg L⁻¹ of potassium dichromate; this result confirms the suitability of EU limit value. AFLP analysis showed that all tested pollutants produce DNA mutations probably due to oxygen radicals. Generally, chromium, at high concentrations, is more toxic and genotoxic that TCE or PCE. Test performed with a mixture of pollutants showed a synergic effect of chromium and organic compounds suggesting that the membrane damage induced from organic substances should increase the chromium cellular access.

The primary purpose of water aeration is to increase the oxygen saturation of the water. This can be achieved by using hydraulic structures because of substantial air bubble entrainment at these structures. This paper reviewed the literature on hydraulic structures used in water aeration processes. The hydraulic structures were divided into two groups as the high-head flow systems and the free-surface flow systems. The high-head flow systems were circular and venturi nozzles, pipe with venturi tube, and high-head conduit, and the free-surface flow systems were weir, stepped cascade, and free-surface conduit. Air/water flow ratio and aeration efficiency in circular nozzles with air holes and venturi nozzles were significantly high. Pipes with venturi tubes showed high aeration efficiency although they had low air/water flow ratio. In high-head and free-surface conduits, almost full oxygen transfer, up to the saturation value, occurred. Forty-five degrees triangular sharp-crested weir had significantly better air/water flow ratio and aeration efficiency than other sharp-crested weir shapes. Stepped cascades, in particular nappe flow regime, were very efficient means of aeration.

Side effects related to liming have been studied in four dimictic lakes (553-642 m a.s.l.; 59°57′N) in Finnemarka, a forested area in Southern Norway with poor catchment buffer capacity. Data series from lake profiles have been sampled two decades apart; 10 years prior to liming and after 10 years of liming. Water samples were collected during spring after ice breakup and during summer after the development of thermal stratification. Before liming, there were very low concentrations of bicarbonate (HCO ₃ ⁻ ; or alkalinity) in the lakes. After 10 years of liming, up to 90% of the ions in hypolimnion originate from lime products. Hence, liming strengthened the chemical stratification and increased the vertical stability. Differences in chemocline developments between lakes were explained by differences in physical properties, i.e. their depth/surface area ratio. The chemocline developments lead to increased concentrations of organic matter in the hypolimnion with a subsequent reduction in oxygen concentrations. Lime additions during late spring, as an alternative to early autumn, lead to pronounced anoxic conditions in the hypolimnion.

Background, aim, and scope Building up a comprehensive accurate monitoring program requires the knowledge on the contamination in principal, complemented by detailed information on individual contaminants. The selection of pollutants to be considered in monitoring actions is based dominantly on the information available about their environmental relevance (e.g., persistence, bioaccumulation potential, toxicological and ecotoxicological properties) and their occurrence within the affected environmental system. Therefore, this study focused on the identification of organic contaminants in selected German and European rivers to demonstrate the usefulness of a screening approach as complementary base for the compound selection process within monitoring activities. Materials and methods Gas chromatography-mass spectrometry-based screening analyses were performed on five and six samples from German and European rivers, respectively. Identification of individual contaminants was based on the investigation of mass spectral and gas chromatographic properties compared with databases and reference materials. Results This study summarized the results of non-target screening analyses applied to river water samples and focused dominantly on, so far, unnoticed organic contaminants. Numerous compounds have been identified belonging to the groups of pharmaceuticals, technical additives, pesticides, personal care products, and oxygen-, nitrogen-, and sulfur-containing compounds of obviously anthropogenic origin. They are discussed in terms of their structural properties, their possible application or usage, and the environmental information available so far. Discussion Generally, two different groups of compounds have been differentiated that might contribute to potential monitoring programs. Firstly, more specific contaminants characterizing the individual riverine systems have been depicted (e.g., 4-chloro-2-(trifluoromethyl)aniline, di-iso-propylurea). The consideration of these substances in monitoring analyses to be applied to the corresponding catchment areas is recommended in order to monitor the real state of pollution. Secondly, contaminants have been introduced that appeared with higher multiplicity throughout the different river systems (e.g., TMDD, TXIB). Since these compounds tend to obviously have an elevated environmental stability accompanied by a widespread distribution, it is recommended to consider them in international high-scale monitoring programs. Conclusions For monitoring purposes, a fundamental knowledge on the diversity of pollutants is an important precondition, which can be supported by screening analyses. Obviously, numerous organic contaminants have been neglected so far in environmental studies on river water, comprising also investigation on potential harmful effects and, therefore, their implementation in monitoring activities has been hindered. Recommendations and perspectives Therefore, based on the results of this study, screening analyses should be established as principle tools to improve and complement the substance spectra for monitoring purposes. Secondly, scientific efforts should be strengthened to expand our knowledge on actually appearing organic contaminants in riverine systems.

Background, aim, and scope Due to the active production and transport of crude oil in the Arabian Gulf region, the Arabian Gulf coasts are routinely polluted with oil. Therefore, such coasts have been subject of studies aiming at assessing the roles of indigenous microbial consortia in cleaning these environments. In the present study, epilithic microbial communities along Kuwait coasts were studied for their oil degradation potential. Materials and methods Gravel particles coated with deep green biofilms were collected from four coastal sites in autumn, winter, and spring. Phototrophs in these consortia were determined in terms of their chlorophyll a contents and identified by their morphological characteristics. Total bacteria were counted microscopically and cultivable bacteria by the dilution plating method on nutrient agar as well as on inorganic medium containing oil as a sole source of carbon and energy. The bacterial community structures were also characterized and compared by denaturing gradient gel electrophoresis (DGGE). Results Epilithic biomass samples from the four sites in the three seasons were rich in diatoms and picocyanobacteria as well as total bacteria. Direct counting gave bacterial numbers per square centimeter gravel surface of 2 to 6 × 10⁷ cells depending on the sampling site and season. Cultivable bacterial numbers on nutrient agar and crude oil as a sole source of carbon were 3 × 10³ to 8 × 10⁴ and 1 × 10³ to 7 × 10³ cells/cm² gravel surface, respectively. The DGGE profiles of epilithon biomass samples revealed major 16S rDNA bands that matched bands of pure oil-utilizing bacterial isolates. Discussion The microbial communities showed a degree of consistency in all sites and seasons. Conclusions The microbial consortia coating gravel particles are potentially suitable tools for self-cleaning of oily Gulf coasts. They are rich in oil-utilizing bacteria whose activities are probably enhanced by oxygen produced by the phototrophic partners in the consortia. Recommendations and perspectives The combination of conventional microbiological analysis with molecular approaches gives an enhanced idea about natural microbial communities especially those with environmental application potential.

Global warming has become a source of awareness regarding the potential deleterious effects of extreme abiotic factors (e.g., temperature, dissolved oxygen (DO) levels) and also their influence on chemicals toxicity. In this work, we studied the combined effects of nickel and temperature (low and high levels) and nickel and low levels of DO to Daphnia magna, and concentration addition and independent action concepts as well as their deviations for synergism/antagonism, dose ratio and dose level dependency, were applied to survival and feeding rate data. Nickel single exposure showed an LC₅₀ value for 48 h of 7.36 mg l⁻¹ and an EC₅₀ value for feeding impairment at 2.41 mg l⁻¹. In the acute exposures to high and low temperatures, 50% of mortality was observed, respectively, at 30.7°C and 4.2°C whereas 50% reduction on the feeding activity was recorded at 22.6°C and 16.0°C. Relatively to low DO levels, a LC₅₀ value for 48 h of 0.5 mg l⁻¹ was obtained; feeding activity EC₅₀ value was 2 mg l⁻¹. On acute combined experiments, antagonism was observed for the combination of nickel and extreme temperatures, whereas a synergistic behaviour was observed in the combined exposure of nickel and low DO levels. At sublethal levels, nickel showed to be the main inducer of toxicity at high and low temperatures but not at low levels of dissolved oxygen. Toxicokinetics and toxicodynamics modelling studies should be made in the future to understand the toxicological pathways involved on complex combinations of stressors and to validate any conclusions.