Extending the leaf economics spectrum to decomposition: evidence from a tropical forest

I investigated the relationship between leaf physiological traits and decomposition of leaf litter for 35 plant species of contrasting growth forms from a lowland tropical forest in Panama to determine whether leaf traits could be used to predict decomposition. Decomposition rate (k) was correlated with specific leaf area (SLA), leaf nitrogen (N), phosphorus (P), and potassium (K) across all species. Photosynthetic rate per unit mass (Amass) was not correlated with k, but structural equation modeling showed support for a causal model with significant indirect effects of Amass on k through SLA, N, and P, but not K. The results indicate that the decomposability of leaf tissue in this tropical forest is related to a global spectrum of leaf economics that varies from thin, easily decomposable leaves with high nutrient concentrations and high photosynthetic rates to thick, relatively recalcitrant leaves with greater physical toughness and defenses and low photosynthetic rates. If this pattern is robust across biomes, then selection for suites of traits that maximize photosynthetic carbon gain over the lifetime of the leaf may be used to predict the effects of plant species on leaf litter decomposition, thus placing the ecosystem process of decomposition in an evolutionary context.     

Valorization of sodium sulfate waste to potassium sulfate fertilizer: experimental studies,process modeling,and optimization

ABSTRACT

Sodium sulfate is a common low-value industrial by-product but can be managed using the Glaserite process to convert it into high-value potassium sulfate. The aim of the study is to investigate the potential for implementing this process in an industrial application. Experimental studies were completed to determine the yield and purity of both glaserite and potassium sulfate. Process simulation using SysCAD was utilized to optimize a two-stage glaserite process to produce potassium sulfate. Comparison of experimental and simulated data was made to validate the simulator’s results, finding the AAD in solid and liquid phase for glaserite production to be 6.9% and 5.7%, respectively, and for potassium sulfate to be 5.7% and 2.3%, respectively. For a process treating seven MT/hr of Na₂SO₄, a KCl feed strategy of 3.0 MT/hr to the glaserite reactor and 4.5 MT/hr to the K₂SO₄ reactor was found to maximize yield and minimize water demand. It was also found that ambient temperatures were preferred for the K₂SO₄ reactor and that K₂SO₄ yield suffered significantly under certain conditions when the glaserite reactor operated at 50°C or above.     

A Heuristic Method for Determining Changes of Source Loads to Comply with Water Quality Limits in Catchments

A common land and water management task is to determine where and by how much source loadings need to change to meet water quality limits in receiving environments. This paper addresses the problem of quantifying changes in loading when limits are specified in many locations in a large and spatially heterogeneous catchment, accounting for cumulative downstream impacts. Current approaches to this problem tend to use either scenario analysis or optimization, which suffer from difficulties of generating scenarios that meet the limits, or high complexity of optimization approaches. In contrast, we present a novel method in which simple catchment models, load limits, upstream/downstream spatial relationships and spatial allocation rules are combined to arrive at source load changes. The process iteratively establishes the critical location (river segment or lake) where the limits are most constraining, and then adjusts sources upstream of the critical location to meet the limit at that location. The method is demonstrated with application to New Zealand (268,000 km2) for nutrients and the microbial indicator E. coli, which was conducted to support policy development regarding water quality limits. The model provided useful insights, such as a source load excess (the need for source load reduction) even after mitigation measures are introduced in order to comply with E. coli limits. On the other hand, there was headroom (ability to increase source loading) for nutrients. The method enables assessment of the necessary source load reductions to achieve water quality limits over broad areas such as large catchments or whole regions.     

Woody plant encroachment following grazing abandonment in the subalpine belt: a case study in northern Spain

Regional Environmental Change - The montane and subalpine belts in European mountains were affected by intense land use/land cover changes during the twentieth century. In the case of the subalpine...     

Biomonitoring acidic drainage impact in a complex setting using periphyton

Acid mine drainage (AMD) often exerts various environmental pressures on nearby water courses: chemical stress from low pH and dissolved metals; physical stress from metal oxide deposits. Affected streams can thus display a spatially variable combination of stress agents that may complicate its biomonitoring using native communities such as periphyton. Here, we have measured water and periphyton variables in four streams that surround an abandoned copper mine to determine which periphyton attributes consistently detected AMD impact in a complex environmental setting. Seventeen years after the end of commercial exploitation, the abandoned mine still decreases water quality in nearby streams: moderate acidification, very high metal load (Al, Ni, Cu, Zn), and a conspicuous presence of metal oxide deposits with diverse composition. Even under the resultant complex pattern of polluted conditions, periphyton was a reliable bioindicator of AMD. Epilithic diatom taxa tolerant of acidic conditions increased in AMD sites and, at severely impacted locations, species richness decreased. Also, algal biomass may have been negatively affected in some stream reaches affected by metal oxide deposits. Other periphyton attributes (total biomass, diatom diversity) seemed mostly unrelated to AMD. Diatom assemblage composition was the most sensitive and consistent bioindicator of mine drainage; besides, it rendered a biological assessment of AMD impact that largely coincided with the physicochemical evaluation. Still, including other taxonomic (proportion of acid-tolerant diatom species, diatom richness) and non-taxonomic (algal biomass) attributes in the biomonitoring procedure rendered a more comprehensive assessment of the negative consequences generated by AMD.     

Higher intrinsic photocatalytic efficiency of 2,4,6-triphenylpyrylium-based photocatalysts compared to TiO2 P-25 for the degradation of 2,4-dichlorophenol using solar simulated light

The photocatalytic efficiency of two 2,4,6-triphenylpyrylium (TP(+)) based photocatalysts (supported on silica or incorporated inside zeolite Beta, 3wt%) for the degradation of 2,4-dichlorophenol (DCP) in aqueous media has been compared with TiO(2) (Degussa P-25). It was found that the efficiency of the degradation depends on the photocatalytic setup, recirculation through a tubular reactor being highly unfavorable for the TP(+)-based photocatalysts due to the deposition of the silica or zeolite particles. In contrast, high efficiency in DCP disappearance (up to 87%) and in the total organic content decrease (up to 62%) were obtained using a discontinuous batch reactor in which the TP(+) photocatalysts were uniformly suspended. Kinetic studies were also made and DCP degradation follows a first order kinetics. The obtained kinetic constants when corrected to account for the influence of the fraction of light absorbed and the amount of active sites shows that the intrinsic activity of TP(+) adsorbed on silica or incorporated inside zeolite Beta was over one order of magnitude higher than TiO(2) activity.     

A methodology to urban air quality assessment during large time periods of winter using computational fluid dynamic models

The representativeness of point measurements in urban areas is limited due to the strong heterogeneity of the atmospheric flows in cities. To get information on air quality in the gaps between measurement points, and have a 3D field of pollutant concentration, Computational Fluid Dynamic (CFD) models can be used. However, unsteady simulations during time periods of the order of months, often required for regulatory purposes, are not possible for computational reasons. The main objective of this study is to develop a methodology to evaluate the air quality in a real urban area during large time periods by means of steady CFD simulations. One steady simulation for each inlet wind direction was performed and factors like the number of cars inside each street, the length of streets and the wind speed and direction were taken into account to compute the pollutant concentration. This approach is only valid in winter time when the pollutant concentrations are less affected by atmospheric chemistry. A model based on the steady-state Reynolds-Averaged Navier–Stokes equations (RANS) and standard k-? turbulence model was used to simulate a set of 16 different inlet wind directions over a real urban area (downtown Pamplona, Spain). The temporal series of NO_x and PM₁₀ and the spatial differences in pollutant concentration of NO₂ and BTEX obtained were in agreement with experimental data. Inside urban canopy, an important influence of urban boundary layer dynamics on the pollutant concentration patterns was observed. Large concentration differences between different zones of the same square were found. This showed that concentration levels measured by an automatic monitoring station depend on its location in the street or square, and a modelling methodology like this is useful to complement the experimental information. On the other hand, this methodology can also be applied to evaluate abatement strategies by redistributing traffic emissions.     

Palladium nanoparticles supported on silica,alumina or titania: greener alternatives for Suzuki–Miyaura and other C–C coupling reactions

Environmental Chemistry Letters - Most of the catalytic systems for C–C coupling reactions are based on homogeneous catalysts which are normally used only once and do not have a sustainable...