A Microcosm Treatability Study for Evaluating Wood Mulch-Based Amendments as Electron Donors for Trichloroethene (TCE) Reductive Dechlorination

In this study, wood mulch-based amendments were tested in a bench-scale microcosm experiment in order to assess the treatability of saturated soils and groundwater from an industrial site contaminated by chlorinated ethenes. Wood mulch was tested alone as the only electron donor in order to assess its potential for stimulating the biological reductive dechlorination. It was also tested in combination with millimetric iron filings in order to assess the ability of the additive to accelerate/improve the bioremediation process. The efficacy of the selected amendments was compared with that of unamended control microcosms. The results demonstrated that wood mulch is an effective natural and low-cost electron donor to stimulate the complete reductive dechlorination of chlorinated solvents to ethene. Being a side-product of the wood industry, mulch can be used in environmental remediation, an approach which perfectly fits the principles of circular economy and addresses the compelling needs of a sustainable and low environmental impact remediation. The efficacy of mulch was further improved by the co-presence of iron filings, which accelerated the conversion of vinyl chloride into the ethene by increasing the H2 availability rather than by catalyzing the direct abiotic dechlorination of contaminants. Chemical analyses were corroborated by biomolecular assays, which confirmed the stimulatory effect of the selected amendments on the abundance of Dehalococcoides mccartyi and related reductive dehalogenase genes. Overall, this paper further highlights the application potential and environmental sustainability of wood mulch-based amendments as low-cost electron donors for the biological treatment of chlorinated ethenes.

Innovative process and technology for the production of wood mulch

Plant nurseries usually control weed growth with N-(phosphonomethyl) glycine treatment. Some studies have suggested potential impacts of this treatment on both the environment and users. A possible ecological alternative is the use of ground wood particles for mulching. However, the production of the required wood particles for use in potted plants is challenging. In this article, the classical chipping and sieving process is compared with a new proposed process involving chipping and refining phases. The two processes were applied to wood logs (spruce) from the forests of the Tosco-Emiliano Apennine. The tests were performed over a week using the machinery available at the Mo.To.R.E. (Montagna Toscana Ricerca Energie) consortium. Although the results achieved were based on preliminary evaluations, they indicated the potential superiority of the new process in terms of both economic and ecological efficiency. These findings can pave the way to the development of optimized processes aimed at a significant reduction in the use of chemical herbicides for weed control.

The Effect of Irrigation Frequency, Phosphorus Fertigation, and Cultivar on Levels of Phenolic Compounds in Sweet Cherries

This work examined the effect of irrigation frequency and phosphorus (P) fertigation on the levels of phenolic compounds present in two sweet cherry cultivars, ‘Skeena’ and ‘Cristalina’, over three growing seasons (2012–14). Two irrigation treatments were tested: a high irrigation frequency (I1) and a low irrigation frequency (I2). Both irrigation treatments applied the same quantities of water [100% evapotranspiration (ET)], but the high irrigation frequency applied water four times daily (0300, 0900, 1500, and 2100 hr) whereas the low irrigation frequency was applied at one time (0900 hr) every second day. Three soil management treatments were investigated, including 1) an unmulched control receiving no P, 2) a 10-cm waste wood mulch receiving no P, and 3) a treatment involving annual fertigation of 20 g P/tree at full bloom as ammonium polyphosphate. It was determined that cultivar was the most important factor affecting levels of phenolic compounds in sweet cherries, with generally greater levels associated with ‘Skeena’. The effect of different irrigation and fertilization strategies showed less promising results in terms of influencing levels of phenolic compounds. Both severe and mild water stress did not show an appreciable influence on increasing levels of phenolic compounds in cherries. Furthermore, severe water stress, which occurred during 2012, was associated with the lowest annual concentration of phenolic compounds and an economically unacceptable reduction in fruit size. Phosphorus fertigation influenced cherry phosphorus status positively by increasing leaf and fruit P concentrations consistently, yet these fruit exhibited lower levels of phenolic compounds.

Examining the Potential of Forest Residue-Based Amendments for Post-Wildfire Rehabilitation in Colorado, USA

Wildfire is a natural disturbance, though elemental losses and changes that occur during combustion and post-fire erosion can have long-term impacts on soil properties, ecosystem productivity, and watershed condition. Here we evaluate the potential of forest residue-based materials to rehabilitate burned soils. We compare soil nutrient and water availability, and plant recovery after application of 37 t ha−1of wood mulch, 20 t ha−1of biochar, and the combination of the two amendments with untreated, burned soils. We also conducted a greenhouse trial to examine how biochar influenced soil nutrient and water content under two wetting regimes. The effects of wood mulch on plant-available soil N and water content were significant and seasonally consistent during the three-year field study. Biochar applied alone had few effects under field conditions, but significantly increased soil pH, Ca, P, and water in the greenhouse. The mulched biochar treatment had the greatest effects on soil N and water availability and increased cover of the most abundant native plant. We found that rehabilitation treatments consisting of forest residue-based products have potential to enhance soil N and water dynamics and plant recovery following severe wildfire and may be justified where erosion risk or water supply protection are crucial.

Tree-Based Mulches and their Leachate Suppress Weed Seed Emergence

The objectives of this research were to compare the effects of eastern redcedar (bark and wood), hardwood (bark and wood), pine bark nugget (bark), pine (bark and wood), eucalyptus (bark and wood), cypress (bark and wood), and red-dyed (bark and wood) mulches on emergence of large crabgrass, johnsongrass, common lambsquarter, and redroot pigweed and to determine the possible chemical effects of these mulches by treating seeds with mulch leachate before and after planting. In the first experiment, seeds were planted in pots and one of each mulch type was applied directly above seeds. In the second study the seeds were pre-soaked and watered with mulch leachate. Although interactions between mulch type and weed species occurred, mulch reduced weed emergence by an average of 79% compared to non-mulched pots with eucalyptus having the least effect of the mulches (average 50% reduction). Leachate treatments had less of an effect than mulch, but reduced weed emergence by 16% averaged across all treatments. Red-dyed mulch leachate lowered weed emergence by 41%, more than all other mulch leachate, while eastern redcedar leachate reduced emergence by 23%. Overall, the wood mulch treatments had beneficial effects of reduced weed emergence compared to not using mulch and the response was dominated by physical rather than chemical influences.