Biochar incorporation increased nitrogen and carbon retention in a waste-derived soil

The synthesis of manufactured soils converts waste materials to value-added products, alleviating pressures on both waste disposal infrastructure and topsoils. For manufactured soils to be effective media for plant growth, they must retain and store plant-available nutrients, including nitrogen. In this study, biochar applications were tested for their ability to retain nitrogen in a soil manufactured from waste materials. A biochar, produced from horticultural green waste, was added to a manufactured soil at 2, 5 and 10 % (by weight), then maintained at 15 °C and irrigated with water (0.84 mL m–2 d–1 ) over 6 weeks. Total dissolved nitrogen concentrations in soil leachate decreased by 25.2, 30.6 and 44.0 % at biochar concentrations of 2, 5 and 10 %, respectively. Biochar also changed the proportions of each nitrogen-fraction in collected samples. Three mechanisms for biochar-induced nitrogen retention were possible: i) increased cation and anion exchange capacity of the substrate; ii) retention of molecules within the biochar pore spaces; iii) immobilisation of nitrogen through microbial utilisation of labile carbon further supported by increased soil moisture content, surface area, and pH. Dissolved organic carbon concentrations in leachate were reduced (−34.7 %, −28.9 %, and −16.7 %) in the substrate with 2, 5 and 10 % biochar additions, respectively. Fluorescein diacetate hydrolysis data showed increased microbial metabolic activity with biochar application (14.7 ± 0.5, 25.4 ± 5.3, 27.0 ± 0.1, 46.1 ± 6.1 µg FL g–1 h–1 for applications at 0, 2, 5, and 10 %, respectively), linking biochar addition to enhanced microbial activity. These data highlight the potential for biochar to suppress the long-term turnover of SOM and promote carbon sequestration, and a long-term sustainable growth substrate provided by the reuse of waste materials diverted from landfill

Variation in microbial communities colonizing horticultural slow sand filter beds : implications for filter function

The effect of microbial colonization on the function and rejuvenation of slow sand filters was investigated using culture-independent profiling. Colonization resulted in significant reduction in filter pore size, which may be important in order to fully remove pathogens, but was not associated with a specific microbial component. Communities were highly variable, and no common microbial groups were found in effective filters. Bacterial community composition was affected by sand particle size, although high levels of microbial turnover during filter maturation suggested that this was unlikely to have a major influence on community composition. The composition of microbial inoculum from a previous filter could not be maintained through a cycle of culture, storage and re-culture. Furthermore, no significant proportion of the inoculum persisted in filter maturity, and no advantages in terms of time to filter maturation or final filter efficiency were evident. These results may explain why filtration is such an effective and robust water treatment and emphasize the need for further research on the mechanisms involved in pathogen elimination

Recent changes in extreme rainfall events in Peninsular Malaysia : 1971-2005

This paper assesses recent changes in extremes of annual rainfall in Peninsular Malaysia based on daily rainfall data for ten rain-gauged stations over the period 1971-2005. Eight indices that represent the extreme events are defined and analyzed. Maps of trends for these indices, which are extreme dry spell (XDS), extreme rain sum (XRS), extreme wet day intensities at 95% and 99% percentiles (I95 and I99), proportion of extreme wet day to the total wet day (R95 and R99), and frequency of extreme wet day at 95% and 99% percentiles (N95 and N99), were analyzed based on annual data and seasons. When the indices are evaluated annually, the Mann-Kendall and linear regression trend tests showed increasing trends in the extreme intensity indices (I95 and I99) at two stations. A significant decrease in N99, associated with the frequency of extremely wet days, was observed at 60% of the stations. The change points for these indices are found to occur in the period of the 1980s. There is no significant trend detected for XDS, XRS, and proportion of extreme rainfall over total rainfall amount indices during the period considered in this study. Descriptive analysis of indices during the monsoon period showed that the annual spatial pattern for the peninsula is very much influenced by the northeast monsoon where the highest mean values for majority of the indices occur during this time period