Economic and environmental impacts of increased nitrogen use in grazed pastures and role of inhibitors in mitigating nitrogen losses

Addition of nitrogen (N) to soils not only increases plant productivity but also results in increased nitrate (NO3 –) leaching and release of gaseous N such as ammonia (NH3) and nitrous oxide (N2O). Recent sharp increases in fertiliser N inputs to grazed pastures in New Zealand have rekindled the debate on its impact on atmospheric, terrestrial and aquatic environments. There has been increasing interest in the use of inhibitors to mitigate environmental impacts of N losses from animal excreta and effluent application through leaching and gaseous emissions. This article gives an overview of the environmental impacts of N losses, discusses the role of inhibitors in mitigating N losses, and identifies gaps and limitations from existing New Zealand information. It also suggests the main research needed for devising mitigation strategies with inhibitors

Heavy Metals in Indonesian Paddy Soils

Long-term cultivation of paddy soils has resulted in Pb and Cd accumulation that exceeds the WHO tolerance levels of 2 mg kg−1 and 0.24 mg kg−1 in food. In Musi Rawas, South Sumatra, Indonesia, the paddy soils with the greatest levels of Pb and Cd were those that had been intensively farmed for 80 years, reaching the concentrations of 20.56 mg kg−1 Pb and 0.72 mg kg−1 Cd for soil, and 3.11 mg kg−1 Pb and 0.29 mg kg−1 Cd for rice. The lowest concentrations were obtained with 20 years of cultivation at 17.82 mg kg−1 and 0.26 mg kg−1, for Pb and Cd in soils, respectively. The Pb content in the paddy fields in Pati, Central Java, ranged from 0.23 to 2.55 mg kg−1, while the Pb content in the lowland watershed of Solo Hilir ranged from 0.20 to 2.94 mg kg−1. The highest concentration of Pb and Cd in rice was found at 80 years old in paddy soils with the value of 3.11 mg kg−1 and 0.29 mg kg−1, respectively. The lowest concentrations were found at 20 years old of soils with a value of 2.35 mg kg−1 Pb and 0.15 mg kg−1 Cd, respectively

An assessment of the drainage quality and quantity associated with recycled wastewater irrigation in an urban park

8 p.International audienceQuantification of drainage to remove excess water from the soil profile and provide a suitable environment for vegetation has been developed over the years. Drainage estimation is fairly challenging particularly in the heterogeneous urban environs. This research studied the temporal variation of drainage rate and nutrient leaching in Veale Gardens of Adelaide Parklands, Australia. A zero tension pan lysimeter was installed in an urban mixed vegetation park to study the quantity and quality of leachate solute. EM38 soil mapping and spatial analysis allowed mapping of two EC zones. Temporal changes of volume and characteristics of drained water were studied in the low EC zone for two seasons of summer and winter. The outcomes showed that the volume of drained water in the summer time was considerably less than in the winter time. This is likely to be the cause of the winter dormancy in most plants and evapotranspiration reduction in winter time. Chemical analyses of leachate solute showed a significant drop in the values of EC, potassium, total N, total P, and ionic balance from summer to winter despite a large increase in SAR. In terms of nutrient loading during the study period, this work has shown that there would be very little impact from using recycled waste water compared to conventional water sources

Irrigating Horticultural Crops with Recycled Water: An Australian Perspective

Access to water has been identified as one of the most limiting factors in economic growth of Australia's horticultural sector. Water reclaimed from wastewater (sewage) is being increasingly recognized as an important resource and agricultural sector is currently the largest consumer of this resource. An overview of the Australian experience of using reclaimed wastewater to grow horticultural crops is presented in this paper: from regulations governing it and treatment processes, to management and risk-minimization practices that ensure this resource is used in a sustainable manner, not impacting adversely human health or environment. A case study covering socio-economic and environmental implications of recycled-water irrigation is also presented

The role of soils in the disposition, sequestration and decontamination of environmental contaminants

Soil serves as both a ‘source’ and ‘sink’ for contaminants. As a source, contaminants are derived from both ‘geogenic’ and ‘anthropogenic’ origins. Typically, while some of the inorganic contaminants including potentially toxic elements are derived from geogenic origin (e.g. arsenic and selenium) through weathering of parent materials, the majority of organic (e.g. pesticides and microplastics) as well as inorganic (e.g. lead, cadmium) contaminants are derived from anthropogenic origin. As a sink, soil plays a critical role in the transformation of these contaminants and their subsequent transfer to environmental compartments, including groundwater (e.g. pesticides), surface water (phosphate and nitrate), ocean (e.g. microplastics) and atmosphere (e.g. nitrous oxide emission). A complex transformation process of contaminants in soil involving adsorption, precipitation, redox reactions and biodegradation control the mobility, bioavailability and environmental toxicity of these contaminants. Soil also plays a major role in the decontamination of contaminants, and the ‘cleaning’ action of soil is controlled primarily by the physico-chemical interactions of contaminants with various soil components, and the biochemical transformations facilitated by soil microorganisms. In this article, we examine the geogenic and anthropogenic sources of contaminants reaching the soil, and discuss the role of soil in the sequestration and decontamination of contaminants in relation to various physico-chemical and microbial transformation reactions of contaminants with various soil components. Finally, we propose future actions that would help to maintain the role of soils in protecting the environment from contaminants and delivering sustainable development goals. This article is part of the theme issue ‘The role of soils in delivering Nature's Contributions to People’

Clay minerals as the key to the sequestration of carbon in soils

Results from earlier laboratory and field experiments were interrogated for the possibilities of sequestration, or longterm accumulation, of carbon from excess greenhouse gases in the atmosphere. In the laboratory study, samples of three (top) soils dominated by kaolinite and illite (together), smectite, and allophane were examined for the adsorption and desorption of dissolved organic carbon (DOC). Adsorption and desorption of DOC were carried out on clay fractions extracted physically and after first native organic matter and then iron oxides were removed chemically. Labeled organic material was added to the soils to assess the priming effect of organic carbon (OC). In the field, changes in OC were measured in sandy soils that had been amended by additions of clay for between 3 and 17 years, both through incorporation of exogenous clay and delving of in situ clay. The laboratory experiments demonstrated that a portion of DOC was held strongly in all soils. The amount of DOC adsorbed depended on clay mineral types, including Fe oxides. Much adsorbed DOC was lost by desorption in water and a substantial amount of native OC was lost on priming with new OC. Addition of clay to soils led to increased OC. Therefore, addition of clay to soil may enhance net sequestration of C. Organic carbon close to mineral surfaces or within microaggregates is held most strongly. Carbon sequestration may occur in subsoils with unsaturated mineral surfaces. However, incorporation of carbon into macroaggregates from enhanced plant growth might be most effective in removing excess carbon from the atmosphere, albeit over the short-term

A review of microplastics aggregation in aquatic environment: Influence factors, analytical methods, and environmental implications

A large amount of plastic waste released into natural waters and their demonstrated toxicity have made the transformation of microplastics (MPs; < 5 mm) and nanoplastics (NPs; < 100 nm) an emerging environmental concern. Aggregation is one of the most important environmental behaviors of MPs, especially in aquatic environments, which determines the mobility, distribution and bioavailability of MPs. In this paper, the sources and inputs of MPs in aquatic environments were first summarized followed by the analytical methods for investigating MP aggregation, including the sampling, visualization, and quantification procedures of MP’ particle sizes. We critically evaluated the sampling methods that still remains a methodological gap. Identification and quantification of MPs were mostly carried out by visual, spectroscopic and spectrometric techniques, and modeling analysis. Important factors affecting MP aggregation in natural waters and environmental implications of the aggregation process were also reviewed. Finally, recommendations for future research were discussed, including (1) conducting more field studies; (2) using MPs in laboratory works representing those in the environment; and (3) standardizing methods of identification and quantification. The review gives a comprehensive overview of current knowledge for MP aggregation in natural waters, identifies knowledge gaps, and provides suggestions for future research

The effects of light regime on carbon cycling, nutrient removal, biomass yield, and polyhydroxybutyrate (PHB) production by a constructed photosynthetic consortium

Microalgae can add value to biological wastewater treatment processes by capturing carbon and nutrients and producing valuable biomass. Harvesting small cells from liquid media is a challenge easily addressed with biofilm cultivation. Three experimental photobioreactors were constructed from inexpensive materials (e.g. plexiglass, silicone) for hybrid liquid/biofilm cultivation of a microalgal-bacterial consortia in aquaculture effluent. Three light regimes (full-spectrum, blue-white, and red) were implemented to test light spectra as a process control. High-intensity full-spectrum light caused photoinhibition and low biomass yield, but produced the most polyhydroxybutyrate (PHB) (0.14 mg g−1); a renewable bioplastic polymer. Medium-intensity blue-white light was less effective for carbon capture, but removed up to 82 % of phosphorus. Low-intensity red light was the only net carbon-negative regime, but increased phosphorus (+4.98 mg/L) in the culture medium. Light spectra and intensity have potential as easily-implemented process controls for targeted wastewater treatment, biomass production, and PHB synthesis using photosynthetic consortia