Relationship between CH₄ and N₂O flux from soil and their ambient mixing ratio in a riparian rice-based agroecosystem of tropical region

Temporal variations of the ambient mixing ratio of greenhouse gas (CH(4) and N(2)O) in a riparian rice-based agro-ecosystem of tropical region were studied during 2005-2006 in coastal Odisha. The endeavour was made with the hypothesis that the ambient mixing ratio of CH(4) and N(2)O depends on the changes in the flux of CH(4) and N(2)O from the rice fields in the riparian rice ecosystems. A higher ambient mixing ratio of CH(4) was recorded during the tillering to grain filling stages of the rice crop, during both dry and wet seasons. The higher ambient mixing ratio of CH(4) during the wet season may attribute to the higher CH(4) emission from the rice field. The average mixing ratio of CH(4) was recorded as 1.84 ± 0.05 ppmv and 1.85 ± 0.06 ppmv during 2005 and 2006, respectively. The ambient CH(4) mixing ratio was recorded negatively correlated with the average ambient temperature. The N(2)O mixing ratio ranged from 261.57 to 399.44 ppbv with an average of 330.57 ppbv during 2005. However, the average mixing ratio of N(2)O was recorded as 318.83 ± 20.00 ppbv during 2006. The N(2)O mixing ratio was recorded to be negatively correlated with rainfall and average ambient temperature. Significant negative correlation (r = -0.209) of N(2)O with sunshine hours may attribute to the photochemical break down of N(2)O. The temporal variation of N(2)O flux from the rice field does not affect the ambient mixing ratio of N(2)O in the same way as in the case of the ambient mixing ratio of CH(4). However, the higher mixing ratio of N(2)O during the fallow period of the post monsoon period may attribute to the N(2)O flux from soil. Results indicate that intensively cultivated coastal ecosystems can be a major source of ambient greenhouse gas.     

A feeding inhibition based prediction of the toxic effect of dissolved metal mixtures upon Echinogammarus marinus (Crustacea: Amphipoda) at field relevant concentrations across a latitudinal gradient

Risk assessment of metals in the environment is performed mainly with toxicity evaluations on single metals, which is largely inadequate since these substances occur in mixtures. The development of models predicting combined toxic effects on the basis of the concentration-response relationships of individual compounds has emerged as an answer. In the present study, metal effects on post-exposure anorexia (the concept of FdC(50)--concentration causing 50% of feeding inhibition--is implemented) in Echinogammarus marinus, a widely distributed gammarid amphipod, were assessed and compared with modelled ones obtained through the application of the concentration addition (CA) model, which represents a reasonable worst-case scenario for the risk assessment of metal mixtures. Data were validated using in situ experiments performed along a latitudinal gradient (Iceland, Scotland and Portugal) aiming at establishing a geographic profile of autochthonous population susceptibilities to metals. For all of the metals studied concentrations in the water column at exposure sites were in good agreement with feeding inhibition levels. Models gave low to relatively high percentage agreement between predictions and experimental data. Boreal populations demonstrated higher susceptibility to single metals, but not to mixture exposures. Meridional populations denoted lower susceptibilities with higher FdC(50).     

Hg bioavailability and impact on bacterial communities in a long-term polluted soil

Different soil samples characterised by a long-term Hg-pollution were studied for Hg total content, fractionation, phytotoxicity and influence on the bacterial community. Hg pollution ranged from 1 to 50 mg kg(-1) and most of it was speciated in scarcely soluble forms. In agreement with this, the biochemical quality indexes were investigated (biomass, enzyme activities) and the bacterial community (viable heterotrophic (VH) bacteria, functional diversity) apparently was not influenced by the degree of Hg pollution. In particular, the investigated soils exhibited a low percentage of Hg-resistant (Hg(R)) bacteria ranging from less than 0.001% to 0.25% of the VH and the addition of available Hg in the form of HgCl(2) induced an enrichment of resistant Hg(R) populations. The general biodiversity of the bacterial community was evaluated by denaturing gradient gel electrophoresis of DNA of Hg spiked soil microcosms and of control soils. Hg(R) bacteria capable to grow in a minimal medium containing HgCl(2) were also isolated and identified. MerA and merB gene PCR fragments were obtained from different Hg(R) strains and the range of similarities at the DNA level and at the deduced amino acid level showed that they carried mercuric reductase and lyase. Differently from bacteria, some influence of soil Hg content on seeds' germination and root elongation was observed for Lepidium sativum L. and Solanum lycopersicum L. In conclusion, most of the Hg in these long-term polluted soils was scarcely mobile and available and did not significantly influence the soil bacterial community. The risk of potential Hg remobilization over time, that could be naturally favoured by the activity of plant roots or other inorganic processes occurring in soil, can be extenuated since bacterial community was resistant and resilient to subsequent Hg stress.     

Heavy metal pollution in water and sediments in the Kabini River, Karnataka, India

Critical to habitat management is the understanding of not only the location of animal food resources, but also the timing of their availability. Grizzly bear (Ursus arctos) diets, for example, shift seasonally as different vegetation species enter key phenological phases. In this paper, we describe the use of a network of seven ground-based digital camera systems to monitor understorey and overstorey vegetation within species-specific regions of interest. Established across an elevation gradient in western Alberta, Canada, the cameras collected true-colour (RGB) images daily from 13 April 2009 to 27 October 2009. Fourth-order polynomials were fit to an RGB-derived index, which was then compared to field-based observations of phenological phases. Using linear regression to statistically relate the camera and field data, results indicated that 61% (r (2)?= 0.61, df = 1, F?= 14.3, p?= 0.0043) of the variance observed in the field phenological phase data is captured by the cameras for the start of the growing season and 72% (r (2)?= 0.72, df = 1, F?= 23.09, p?= 0.0009) of the variance in length of growing season. Based on the linear regression models, the mean absolute differences in residuals between predicted and observed start of growing season and length of growing season were 4 and 6?days, respectively. This work extends upon previous research by demonstrating that specific understorey and overstorey species can be targeted for phenological monitoring in a forested environment, using readily available digital camera technology and RGB-based vegetation indices.     

Effectiveness of amendments on re-acidification and heavy metal immobilization in an extremely acidic mine soil

Previous studies have shown that the application of soil amendments is efficient in reducing acidity and heavy metal bioavailability in mine soils. However, it remains a challenge for environmentalists to predict accurately and control economically the re-acidification in re-vegetated mine soils. In this study, net acid generation (NAG) test and bioassay technique were employed to assess the effectiveness of the amendments [including lime, N-P-K (nitrogen, phosphorous and potassium) fertilizer, phosphate and river sediment] on re-acidification and heavy metal immobilization in an extremely acid (pH < 3) mine soil. Our results suggested that NAG test was a rapid and accurate approach to assess the effectiveness of the amendments on re-acidification potential of the mine soil. Interestingly, it was found that phosphate and river sediment played quite specific roles in preventing the re-acidification in the mine soil. In addition, the results also indicated that the addition of 25 t ha(-1) lime combined with river sediment (30%) might be an economical method to successfully control the acidification and re-acidification in the extremely acid mine soil, allowing the re-establishment of the plants. Collectively, our results implied that the combined use of NAG test and bioassay assessment was effective in evaluating a reclamation strategy for extremely acidic mine soils.     

Characterization of ambient black carbon and wood burning particles in two urban areas

Previously it has been suggested that certain organic aerosol components of wood smoke have enhanced ultraviolet absorption at 370 nm relative to 880 nm in two-wavelength aethalometer measurements. This enhanced absorption could serve as an indicator of wood burning particles. Two-wavelength (370 nm and 880 nm) aethalometer measurements were made at urban sites in Rochester, New York and Laredo, Texas from August 1 to December 31, 2009 and from December 23, 2007 to January 2, 2008, respectively. In Rochester, Delta-C (UVBC(370 nm)- BC(880 nm)) values were higher by a factor of 3 during the night than during the day in November and December when residential wood burning was common. In Laredo, particularly high Delta-C values were observed on Christmas Eve and New Year's Eve and were attributed to biomass burning and firework emissions. Exponential decay was found to be a good estimator for predicting BC concentrations at different wind speeds regardless of wind directions.     

Longitudinal variability in streamwater chemistry and carbon and nitrogen fluxes in restored and degraded urban stream networks

Stream restoration has increasingly been used as a best management practice for improving water quality in urbanizing watersheds, yet few data exist to assess restoration effectiveness. This study examined the longitudinal patterns in carbon and nitrogen concentrations and mass balance in two restored (Minebank Run and Spring Branch) and two unrestored (Powder Mill Run and Dead Run) stream networks in Baltimore, Maryland, USA. Longitudinal synoptic sampling showed that there was considerable reach-scale variability in biogeochemistry (e.g., total dissolved nitrogen (TDN), dissolved organic carbon (DOC), cations, pH, oxidation/reduction potential, dissolved oxygen, and temperature). TDN concentrations were typically higher than DOC in restored streams, but the opposite pattern was observed in unrestored streams. Mass balances in restored stream networks showed net uptake of TDN across subreaches (mean ± standard error net uptake rate of TDN across sampling dates for Minebank Run and Spring Branch was 420.3 ± 312.2 and 821.8 ± 570.3 mg m(-2) d(-1), respectively). There was net release of DOC in the restored streams (1344 ± 1063 and 1017 ± 944.5 mg m(-2) d(-1) for Minebank Run and Spring Branch, respectively). Conversely, degraded streams, Powder Mill Run and Dead Run showed mean net release of TDN across sampling dates (629.2 ± 167.5 and 327.1 ± 134.5 mg m(-2) d(-1), respectively) and net uptake of DOC (1642 ± 505.0 and 233.7 ± 125.1 mg m(-2) d(-1), respectively). There can be substantial C and N transformations in stream networks with hydrologically connected floodplain and pond features. Assessment of restoration effectiveness depends strongly on where monitoring is conducted along the stream network. Monitoring beyond the stream-reach scale is recommended for a complete perspective of evaluation of biogeochemical function in restored and degraded urban streams.     

Characterization of PM10-bound polycyclic aromatic hydrocarbons in the ambient air of Spanish urban and rural areas

Urban areas constitute major pollution sources due to anthropogenic activities located in these areas. Among the legislated air pollutants, the particulate matter with an aerodynamic diameter less than or equal to 10 microns (PM10) and polycyclic aromatic hydrocarbons (PAH) are controlled under Directive 2008/50/EC and Directive 2004/107/EC, respectively due to their adverse health effects. A study was carried out at four urban and rural Spanish areas during the warm and cold seasons in 2008-2009 to quantify 19 PAH associated with the atmospheric PM10 by gas chromatography-mass spectrometry-mass spectrometry detection (GC-MS-MS) with the internal standard method. The particle-bound composition of the analysed PAH was 5 and 10 times greater in industrial and urban areas, respectively when compared to those measured in rural areas. The highest PAH concentrations during the cold period were possibly due to the additional contribution of domestic heating sources and meteorological conditions such as low temperature and solar irradiation. The use of molecular diagnostic ratios indicated that the possible, major PAH pollution sources in the most polluted areas were pyrogenic sources, mainly attributed to petroleum combustion sources (motor vehicle emissions and crude oil combustion). Petrogenic sources related to evaporative emissions also seemed to contribute in the most polluted area during the warm period. Those dates with high carcinogenic character according to the benzo(a)pyrene equivalent (BaP-eq) were also possibly attributed to petroleum combustion sources.     

Optical fiber based methodology for assessment of thiocyanate in seawater

A new methodology for the assessment of thiocyanate (SCN(-)) is proposed based on optical fiber (OF) detection coupled to a liquid chromatography system (LC). The developed methodology showed an adequate performance for the analysis of SCN(-) comparable to a high performance liquid chromatography with UV detector (HPLC-UV) methodology: a detection limit of 3 μg L(-1), a linear range from 4 to 400 μg L(-1), and an analytical time of less than 6 min. The OF based methodology was of compact design and easy operation. This simple system has the potential to be used as a sensing approach for SCN(-) in seawater.     

Long-term changes of heavy metal and sulphur concentrations in ecosystems of the Taymyr Peninsula (Russian Federation) North of the Norilsk Industrial Complex

The Norilsk industrial ore smelting complex (Taymyr Peninsula, Russian Federation) has significantly impacted many components of local terrestrial and aquatic environments. Whether it has had a major impact on the wider Russian Arctic remains controversial as studies are scarce. From 1986 to 2004, data on heavy metal (Cu, Ni, Zn, Hg, Cd and Hg) concentrations in fish (burbot), moss, lichens, periphyton, hydric soils and snow in and around Norilsk and the most northern parts of the Taymyr Peninsula were analysed. Very high concentrations of Cu (203 μg L?1 ± 51 μg L?1) and Ni (113 μg L?1 ± 15 μg L?1) were found in the water of the Schuchya River close to Norilsk. Heavy metal concentrations in burbot liver were highest in Lake Pyasino near Norilsk compared to other study regions that were >100 km distant. From 1989-1996, Cu (121 μg L?1 ± 39 μg L?1 SD), Zn (150 μg L?1) ± 70 μg L?1) and Ni (149 μg L?1 ± 72 μg L?1) snow concentrations were greatest in Norilsk, but were low elsewhere. By 2004, these concentrations had dropped significantly, especially for Cu-74 μg L?1 (±18.7 μg L?1 SD), Zn-81.7 μg L?1 (± 31.3 μg L?1 SD) and Ni-80 μg L?1(±18.0 μg L?1 SD). Norilsk and its surroundings are subject to heavy pollution from the Norilsk metallurgical industry but these are absent from the greater Arctic region due to the prevailing winds and the Byrranga Mountains. Pollution abatement measures have been made so further investigations are necessary in order to assess their efficiency.