Effects of sewage sludge stabilization on fertilizer value and greenhouse gas emissions after soil application

Application of sewage sludge on agricultural land becomes more and more common in many parts of the world in order to recycle the nutrients from the sludge. A range of sewage sludge stabilization techniques are available to make the sludge more stable prior to storage, transportation, and application. These stabilization techniques include dewatering, drying, anaerobic digestion, composting, and reed bed sludge treatment. However, very few studies have investigated the effect of these techniques after the sludge has been applied to agricultural land. The objective of the current study was therefore to investigate the effect of sewage sludge stabilization techniques on the C and N mineralization and gaseous emissions from soil. A soil incubation was conducted to determine the rate of C and N mineralization and N₂O and CH₄ emissions of sewage sludge stabilized using different techniques. Unstabilized sludge released up to 90% of their C content as CO₂, part of which could be caused by release of CO₂ from carbonates. Compared with this, sludge stabilization including anaerobic digestion and drying resulted in a reduction of the C mineralization rate of about 40%. Liming reduced C mineralization with around 29%, while treatment in a reed bed system reduced it by 74%. The current study thus clearly demonstrated that stabilization techniques resulted in sludge that was more stable once they were applied to agricultural land. Stabilization also reduced the N immobilization phase, potentially improving the value of the sludge as a fertilizer. Emissions of CH₄ were also reduced through sludge stabilization and mainly occurred after application of easily degradable sludge types, which is likely to have enhanced the creation of anaerobic microsites. The stabilization processes also decreased emissions of N₂O. The results for both CH₄ and N₂O indicate that the stabilization tends to reduce the chance of developing conditions where these gases could be produced.     

Determining the bioavailability of contaminants and assessing the quality of sediments

Background, Aims and Scope  Our study determined the role of light, aeration, grain size, amount of sediments and of water, density of animals and presence of additional food on the movement of Ilyanassa obsoleta. Spiked relative to reference sediments were also tested for avoidance or preference by the mud snails. Our goal was to develop exposure conditions to be used in future assessment studies of the environmental quality of sediments inhabited by mud snails. The behavioural response of the snails towards different concentrations of contaminated Halifax Harbour sediments placed in one half of a tank relative to reference sediments in the other half is examined in Part 2 and a chemical link investigated. Methods  Animals were exposed in 7 L aquaria at 12°C to their native sediments placed in one or two halves of a tank and the effect due to the presence of a light source, air bubbles, sediment grain size, added algae examined relative to the snails’ behaviour. Preference or avoidance of one half of a tank relative to the second half, the immersed or dry glass surface represented the various media to be chosen by snails. After choosing the optimum set up, exposures were performed in triplicate, under slightly differing initial placement of the snails to compare means and variability in the results. Three specific biogenic chemicals, cholesterol, coprostanol and a fatty acid methyl ester (FAME) were spiked at 0.002, 0.01, 0.05, 0.25 and 1.2 mg/g, dry weight of sediment. A hexane, dichloromethane and methanol extract of harbour sediment were also spiked in reference sediments. In all cases, the location of the snails was recorded over a period extending up to 96 hrs. Results  Twenty snails exposed during a 72 hrs period in commercial 7 L tanks containing 50 g of sediments (wet weight) in the bottom half of a tank filled half way with seawater represented the chosen conditions to test the avoidance/preference behaviour of snails for part of a tank. The presence of additional food on sediments attracted snails within 24 hrs of exposure. Discussion  A general lack of preference was indicated in exposures to three biologically derived compounds spiked in reference sediments, i.e. a C-18 FAME, cholesterol and coprostanol. The repelling properties of a harbour sediment extract pointed to a role for non polar chemicals. Conclusions  It is proposed that behaviour reflects a balance between the repelling effects of contaminants and the attractive value of food. The present study provides a robust green assessment tool that is easy to set up to assess the quality of sediments. Recommendations and Perspectives  The interpretation of field observations regarding the abundance of animals during environmental assessments must consider both nutritional and toxicological causes. Additional laboratory exposures are needed to determine which chemicals play a role in the field.     

Characterisation of Escherichia coli O157 isolates from Danish cattle and human patients by genotyping and presence and variants of virulence genes

An important objective in vaccination strategies is to activate lymphocytes with particular effector functions. Cellular immunity and the type I cytokine IFN-gamma have been implicated in protective immunity to heartwater. Furthermore, low molecular weight proteins of Cowdria ruminantium have been shown to induce peripheral blood mononuclear cells to proliferate. To determine which lymphocyte subset responds when stimulated with fractionated C. ruminantium proteins, specific short-term lymphocyte cultures were established from cattle immunized with the Welgevonden isolate. Four cattle were immunized, two by infection and treatment and two with inactivated organisms. Cell surface phenotypic analysis of the cultures indicated that CD4+ lymphocytes were enriched over time. This coincided with increased antigen-specific proliferation and IFN-gamma production. Proteins of molecular weights 13-18kDa induced the CD4+-enriched T-cell cultures, derived from each of the animals, to proliferate and produce IFN-gamma. Although the two groups of cattle were immunized differently, their lymphocytes responded similarly. These results extend previous findings by identifying the responder cells as being predominantly IFN-gamma producing CD4+ lymphocytes. This cytokine has been implicated in immunity to the parasite. The low molecular weight proteins that induced CD4+ lymphocytes to proliferate and produce IFN-gamma are therefore likely to be important in protection against heartwater and may have a role in vaccine development.     

The effect of three different pesticides on soil protozoan activity

Three pesticides, dimethoate, pirimicarb and fenpropimorph, had a negative impact on the colonization of a sterilized soil by a natural population of soil protozoa. Fenpropimorph has an effect at the lowest concentration applied; 25 mg litre^?1. Dimethoate reduced the soil respiration significantly for about 10 days after application. In single species cultures of soil protozoa in liquid media, a flagellate Cercomonas sp., was a better test organism than a ciliate, Colpoda sp., or an amoeba, Acanthamoeba sp., with respect to interpretation of dose-response curves and ease of observation.     

Tissue-specific and substrate-specific mitochondrial bioenergetics in feline cardiac and skeletal muscles

No studies have investigated the mitochondrial function in permeabilized muscle fiber from cats. The aim of this study was to investigate tissue-specific and substrate-specific characteristics of mitochondrial oxidative phosphorylation (OXPHOS) capacity in feline permeabilized oxidative muscle fibers. Biopsies of left ventricular cardiac muscle and soleus muscle, a type I-rich oxidative skeletal muscle, were obtained from 15 healthy domestic cats. Enzymatic activity of citrate synthase (CS), a biomarker of mitochondrial content, was measured. Mitochondrial OXPHOS capacity with various kinds of non-fatty-acid substrates and fatty-acid substrate in permeabilized muscle fiber was measured by using high-resolution respirometry. CS activity in the heart was 3 times higher than in the soleus muscle. Mitochondrial state 3 respiration, ADP-stimulated respiration, with complex I-linked and complex I+II-linked substrates, respectively, was significantly higher in the heart than in the soleus muscle when normalized for muscle mass, but not for CS activity, indicating that greater capacity for mitochondrial OXPHOS with these non-fatty-acid substrates in the heart may depend on higher mitochondrial content. In contrast, the soleus muscle had higher mitochondrial state 3 respiration with fatty acids than the heart when normalized for CS activity, indicating greater capacity for fatty-acid oxidation per mitochondrion in the soleus. Our findings suggest that there are tissue- specific and substrate-specific quantitative and qualitative differences in mitochondrial OXPHOS capacity between the different types of oxidative muscles from cats.     

Bulk Carbohydrate Grain Filling of Barley β‐Glucan Mutants Studied by 1H HR MAS NMR

Temporal and genotypic differences in bulk carbohydrate accumulation in three barley genotypes differing in the content of mixed linkage β‐(1→3),(1→4)‐D‐glucan (β‐glucan) and starch were investigated using proton high‐resolution, magic angle spinning, nuclear magnetic resonance (¹H HR MAS NMR) during grain filling. For the first time, ¹H HR MAS NMR spectra of flour from immature barley seeds are analyzed. Spectral assignments are made using two‐dimensional (2D) NMR methods. Both α‐ and β‐glucan biosynthesis were characterized by inspection of the spectra as well as by calibration to the reference methods for starch and β‐glucan content. Starch was quantified with very good calibrations to the α‐(1→4) peak (5.29–5.40 ppm) and the region 3.67–3.83 ppm covering starch glycopyranosidic protons from H5 and H6. In contrast, the spectral inspection of the β‐anomeric region 4.45–4.85 ppm showed unexpected lack of intensity in the high β‐glucan mutant lys5f at seed maturity, resulting in poor calibration to reference β‐glucan content. We hypothesize that the lack of β‐glucan signal in lys5f indicates partial immobilization of the β‐glucan that appears to be either genotypic dependent or water/β‐glucan ratio dependent.     

To what extent does Tobler's 1st law of geography apply to macroecology? A case study using American palms (Arecaceae)

Background

Competitive displacement of a weakly virulent pathogen strain by a more virulent strain is one route to disease emergence. However the mechanisms by which pathogens compete for access to hosts are poorly understood. Among vector-borne pathogens, variation in the ability to infect vectors may effect displacement. The current study focused on competitive displacement in dengue virus serotype 3 (DENV3), a mosquito-borne pathogen of humans. In Sri Lanka in the 1980's, a native DENV3 strain associated with relatively mild dengue disease was displaced by an invasive DENV3 strain associated with the most severe disease manifestations, dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS), resulting in an outbreak of DHF/DSS. Here we tested the hypothesis that differences between the invasive and native strain in their infectivity for Aedes aegypti mosquitoes, the primary vector of DENV, contributed to the competitive success of the invasive strain

Results

To be transmitted by a mosquito, DENV must infect and replicate in the midgut, disseminate into the hemocoel, infect the salivary glands, and be released into the saliva. The ability of the native and invasive DENV3 strains to complete the first three steps of this process in Aedes aegypti mosquitoes was measured in vivo. The invasive strain infected a similar proportion of mosquitoes as the native strain but replicated to significantly higher titers in the midgut and disseminated with significantly greater efficiency than the native strain. In contrast, the native and invasive strain showed no significant difference in replication in cultured mosquito, monkey or human cells.

Conclusion

The invasive DENV3 strain infects and disseminates in Ae. aegypti more efficiently than the displaced native DENV3 strain, suggesting that the invasive strain is transmitted more efficiently. Replication in cultured cells did not adequately characterize the known phenotypic differences between native and invasive DENV3 strains. Infection dynamics within the vector may have a significant impact on the spread and replacement of dengue virus lineages.