We have examined populations of brown trout in low-conductivity mountain lakes (5.0–13.7 μS/cm and 0.14–0.41 mg/l Ca) in southwestern Norway during the period 2000–2010. Inlets to the lakes were occasionally even more dilute (2007; conductivity = 2.9–4.8 μS/cm and Ca = 0.06–0.17 mg/l). The combination of pH and conductivity was the best predictor to fish status (CPUE), indicating that availability of essential ions was the primary restricting factor to fish populations in these extremely diluted water qualities. We suggest that conductivity <5 μS/cm is detrimental to early life stages of brown trout, and subsequently that there are lakes in these mountains having too low conductivity to support self-reproducing trout populations. Limited significance of alkalinity, Ca, Al, and color suggests that effects of ion deficit apparently overruled the effects of other parameters.

Mature landfill leachate contains some macromolecular organic substances that are resistant to biodegradation. The photocatalytic process helps to enhance biodegradability of landfill leachate. Batch experiments were employed to determine the optimum conditions for removal of organic matter by UV-TiO2 photocatalysis. Under optimum conditions, the removal of chemical oxygen demand (COD), dissolved organic carbon (DOC), biological oxygen demand (BOD), and color was determined. Moreover, gas chromatography coupled with mass spectrometry (GC/MS) was used to analyze the organic matter in the treated leachate before and after treatment by the photocatalysis. The experimental results indicated that the removal of COD, DOC, and color by UV-TiO2 photocatalysis could reach above 60%, 70% and 97%, respectively. Under optimal conditions, the ratio of biological oxygen demand (BOD)/chemical oxygen demand (COD) was elevated from 0.09 to 0.39, representing substantial improvement in biodegradability. GC/MS analysis revealed that 37 out of 72 kinds of organic pollutants in the leachate remained after 72 h treatment. Esters were produced during photocatalytic process and ketones, hydrocarbons, aromatic hydrocarbons, hydroxybenzenes, and acids were easier to be degraded during photocatalytic oxidation processes. The UV-TiO2 photocatalysis systems proposed may be a cost-effective approach for pre-treatment of landfill leachate.

Cyanide is found as free cyanide and metal–cyanide complexes in metal finishing rinse wastewaters. Experiments were performed to seek removal of cyanide in Ni(II)–cyanide and Ni(II)–cyanide–ethylenediaminetetraacetate (EDTA) solutions by the environmentally friendly oxidant, ferrate(VI) (FeO4 2−, Fe(VI)) as a function of pH (8.0–11.0). Incomplete removal of cyanide in Ni(II)–cyanide solutions (≤60%) was observed at the studied pH range. However, cyanide removal efficiency approached to 100% in Ni(II)–cyanide–EDTA solutions. Formation of Ni(II)–cyanide and Ni(II)–EDTA complexes and relative rates of the reactions of Fe(VI) with various species (water, cyanide, Ni(II)–cyanide, and EDTA) present in solutions were responsible for the variation in removal efficiencies in mixtures at various pH. The oxidation of cyanide by Fe(VI) produced cyanate. Tests using electroplating rinse wastewaters demonstrated that Fe(VI) was highly effective in removing cyanide.

The Nyabugogo natural wetland (Kigali City, Rwanda) receives all kinds of untreated wastewaters, including those from industrial areas. This study monitored heavy metal concentrations (Cd, Cr, Cu, Pb, and Zn) in all environmental compartments of the swamp: water and sediment, the dominant plant species Cyperus papyrus, and fish (Clarias sp. and Oreochromis sp.) and Oligochaetes. Cr, Cu, and Zn concentrations in the water were generally below the WHO (2008) drinking water standards, whereas Cd and Pb were consistently above these limits. Except Cd, all metal concentrations were below the threshold levels for irrigation. The highest metal accumulation occurred in the sediment with up to 4.2 mg/kg for Cd, 68 mg/kg for Cu, 58.3 mg/kg for Pb, and 188.0 mg/kg for Zn, followed by accumulation in the roots of C. papyrus with up to 4.2 mg/kg for Cd, 45.8 mg/kg for Cr, 29.7 mg/kg for Cu, and 56.1 mg/kg for Pb. Except Cu and Zn, other heavy metal (Cd, Cr, and Pb) concentrations were high in Clarias sp., Oreochromis sp., and Oligochaetes. Therefore, there is a human health concern for people using water and products from the swamp.

The spread of antibiotic-resistant bacteria in the environment is raising serious public health concerns, and manure is being increasingly recognized as a major source of antibiotic-resistant bacteria. In this research, we isolated Escherichia coli and enterococci from manure produced in a Wisconsin, USA family dairy farm to determine their resistance to six representative antibiotics. The average densities for E. coli and enterococci were 6.37(±4.38) × 107 colony formation units (CFU) g−1 and 1.60(±1.57) × 104 CFU g−1, respectively. The E. coli isolates were found to be resistant to cephalothin, ampicillin, tetracycline, and erythromycin. In addition to these four antibiotics, the Enterococcus isolates were also resistant to gentamicin and ciprofloxacin. Additionally, we examined the survival and growth of E. coli and enterococci in dairy manure over a period of ~3 days. While the densities of enterococci remained stable over the study period, the concentrations of E. coli on average increased by 1.5 log10 units. Further tests of the bacterial antibiotic resistance over time showed no significant changes in the prevalence of antibiotic resistance. This result indicated that slightly aged manure could represent a larger source of antibiotic-resistant E. coli than fresh manure and the accumulation of antibiotic-resistant E. coli and enterococci in the agricultural fields must be accounted for in the modeling of the spread of antibiotic-resistant bacteria in the environment.

This paper presents an efficient and effective modeling approach to estimation of nitrogen retention in streams and rivers. The approach involves an extension of a newly developed longitudinal solute transport model, variable residence time (VART), by incorporating a first-order nitrogen reaction term. Parameters involved in the VART model are estimated using monthly mean flow and water quality data obtained through both field measurements and watershed modeling using the Hydrologic Simulation Program Fortran model. It is found that there is a strong correlation between nitrate-nitrogen removal rate and water temperature. In addition, low nitrate-nitrogen concentrations commonly occur when total organic carbon (TOC) and dissolved oxygen (DO) are also low, and high nitrogen concentrations correspond to high DO and TOC, indicating that denitrification is the primary biogeochemical process controlling nitrogen removal in natural rivers. The new approach is demonstrated through the computation of nitrogen removal in the Amite River, LA, USA. Functional relationships between the nitrate-nitrogen removal rate and water temperature are established for the Amite River. Monthly mean nitrate-nitrogen concentrations along the river are computed using the extended VART model, and computed nitrogen concentrations fit observed ones very well. The estimated annual nitrate-nitrogen removal in the Amite River is 27.4 tons or 15.5% of total nitrate-nitrogen transported annually through the Amite River.

This study assessed effects of a mixture of two pesticides, diazinon and permethrin, on 48-h sediment toxicity to Hyalella azteca in a constructed wetland mesocosm containing non-vegetated and vegetated sections. Sediment samples were collected at inflow, middle, and back points within each section 5, 24, 72 h, 7, 14, and 21 days post-amendment. Pesticides were detected in sediments throughout non-vegetated and vegetated wetland sections. H. azteca 48-h survival varied across sampling period, wetland location, and vegetation type with lowest survival occurring within the first 72 h of the inflow and middle locations of the non-vegetated section. Sediment toxicity was ameliorated by 14 and 7 days within the non-vegetated and vegetated sections, respectively. Relationships between pesticide concentrations and animal survival indicated toxicity was from both diazinon and cis-permethrin in the non-vegetated section and primarily cis-permethrin in the vegetated section. Results show that vegetation ameliorated pesticide mixture 48-h sediment toxicity to H. azteca earlier and to a greater extent than non-vegetated constructed wetlands. A 21-day retention time is necessary to improve 48-h H. azteca sediment survival to ≥90% in wetlands of this size.

Forebays, small settling basins placed at the inlet of Stormwater Best Management Practices, encourage sedimentation with the intention of pollutant consolidation and capture. Regularly, accumulated sediments are excavated to restore forebay storage volume and to further prevent contamination of downstream waterbodies during large storm events. Disposal measures vary according to the toxicity of sediments. To test for the potential toxicity of forebay spoils, 30 stormwater wetland and wetpond forebays of varying age, size, and upstream landuse were sampled across North Carolina and analyzed for seven metals: cadmium, chromium, copper, iron, lead, nickel, and zinc. Ten of 30 sites were also sampled near the outlet structures for spatial comparison of settled sediment and pollutant presence. The relative toxicity of all sampled sediment metal concentrations was evaluated using existing aquatic health sediment guidelines and US Environmental Protection Agency standards for the land application of biosolids (40 CFR503). Of 30 sites, 17 exceeded sediment guidelines for aquatic health, emphasizing the need for routine forebay sediment removal. However, all samples were less than 40 CFR 503 limits with factors of safety ranging from 2.3 to 28, indicating that land application of forebay sediment is unlikely to pose an environmental threat. Additionally, forebay sediment tended to have lower metal toxicity than sediment collected at the pond or wetland outlet.

As a new approach, urban air pollution was characterised by the variation of columnar content of the pollutants. Columnar content (CC) was estimated as the product of the pollutant’s mixing ratio and the mixing height. Mixing ratio data of the Metropolitan Air Quality Monitoring Network of Budapest were used, whilst mixing height was calculated by the meteorological AERMET model code. Time variation of CC refers to the real pollution exchange in the atmosphere that allows direct investigation of the emissions as well as post-emission modifications of the pollutants (such as chemical degradation or production). The diurnal urban CO cycle was found to be determined by two or three main influx peaks according to the traffic pattern of the site. The diurnal variation of NOx level was found to be driven by traffic emission as well. Variant ratios of NOx to CO influxes obtained for the different locations of the city range from 0.12 to 0.23, probably according to the vehicle composition of the traffic. The daily balance of photochemical production, chemical degradation and deposition of ozone yielded negative or positive depending on the location. Negative balances imply that the polluted urban atmosphere is a net ozone neutraliser source. Entrainment from the free troposphere yielded the major contributor to the diurnal ozone level at each site. The diurnal urban PM10 cycle was found to be determined by traffic emission during the morning and evening rush hours whilst secondary aerosol formation around noon. In the evening, high PM10 level rise was observed due to direct traffic emission as well as rapid conversion of the fine aerosol fraction to the coarse fraction.

Diatoms are good indicators of water quality in lotic systems. Unlike in the temperate region, the effect of substrate on diatom-based water quality assessment in tropical streams is not fully understood. The purpose of this study was to assess the effect of substrate on diatom-based multivariate water quality assessment. Epilithic, epiphytic, epipsammic and epipelic diatom community and water quality sampling was done four times at 10 sites during the dry season (2008 and 2009). Artificial substrates (brick and glasses) were also placed at the sampling sites during this period and sampled after 1 month. Cluster analysis was performed to show the main differences and similarities in community composition amongst substrates sampled and amongst sampling sites. The IndVal method was used to identify indicator species characterising different substrates. Canonical correspondence analyses (CCAs) were performed to relate the structure of diatom communities from different substrates to predictor variables. A gradient of increasing metal and organic pollution, eutrophication and ionic strength was observed from the agricultural/forested area to the urban area. Diatom community structure closely reflected this gradient, with communities from polluted sites (8, 9 and 10) being different from other communities. Polluted sites were associated with such species as Nitzschia palea, Plantago lanceolata, Achnanthes exigua, Caloneis hyaline, Cyclotella meneghiniana, Gomphonema parvulum, Fallacia monoculata, Luticola goeppertiana, Pinnularia microstauron, Pinnularia subcapitata and Sellaphora pupula. Indicator species analysis showed that common diatom species were not restricted to a single substrate, though preference was generally high for natural (especially macrophytes) compared to artificial substrates. Six CCAs corresponding to six substrates performed to relate diatom community structure to simultaneous effects of predictor variables explained ∼50% of the diatom species variance in all cases and roughly separated highly polluted sites from the rest of the sites. This indicates that the results of diatom-based multivariate water quality assessment based on different substrates may be interchangeable. Only one substrate has to be collected at each site for water quality assessment surveys, thus avoiding unnecessary expensive and time-consuming oversampling. Given the limitations of artificial substrates, sampling of natural substrates is highly recommended.