International audienceUrban agriculture is receiving increasing attention throughout the developing world, but debate rages as to whether it is a blessing or a curse. Some see it as savior for the poor, providing food, and livelihoods, yet to others it is responsible for harboring and vectoring pathogenic diseases and is an archaic practice that has no place along the path toward development. Consequently, the activity receives a mixed reception, and despite much support in many instances, it certainly does not enjoy universal unimpeded progress. Here, we undertake a global tour of urban agriculture throughout the developing world in an attempt to elucidate the various benefits, costs, and hindrances associated with the practice. Through this analysis we identify the need for better understanding of the following six aspects if urban agriculture is to make a meaningful contribution to food security and sustenance of livelihoods in the future: (1) the global and regional extent of urban agriculture; (2) the contribution of urban agriculture to communicable diseases, especially malaria but also diarrheal disease; (3) the role that urban agriculture does and/or could play in abating both malnutrition and obesity; (4) the impacts of urban agriculture on women; (5) appropriate methods of achieving governance and institutional support; and (6) the risks posed by chemical pollutants, particularly as Africa becomes increasingly industrialized. Overlaying these, we suggest that the time is ripe to extend the debate about urban agriculture’s positive and negative environmental impacts—especially in relation to carbon emissions—from primarily a developed world concern to the developing world, particularly since it is the developing world where population growth and consequent resource use is increasing most rapidly
The sensitivity of early plant regeneration to environmental change makes regeneration a critical stage for understanding species response to climate change. We investigated the spatial and temporal response of eucalypt trees in the Central Highland region of south eastern Australia to high and low climate change scenarios. We developed a novel mechanistic model incorporating germination processes, TACA-GEM, to evaluate establishment probabilities of five key eucalypt species, Eucalyptus pauciflora, Eucalyptus delegatensis, Eucalyptus regnans, Eucalyptus nitens and Eucalyptus obliqua. Changes to regeneration potential at landscape and site levels were calculated to determine climate thresholds. Model results demonstrated that climate change is likely to impact plant regeneration. We observed increases and decreases in regeneration potential depending on the ecosystem, indicating that some species will increase in abundance in some forest types, whilst other forest types will become inhabitable. In general, the dry forest ecosystems were most impacted, whilst the wet forests were least impacted. We also observed that species with seed dormancy mechanisms, like E. pauciflora and E. delegatensis, are likely to be at higher risk than those without. Landscape-and site-level analysis revealed heterogeneity in species response at different scales. On a landscape scale, a 4.3°C mean temperature increase and 22% decline in precipitation (predicted for 2080) is predicted to be a threshold for large spatial shifts in species regeneration niches across the study region, while a 2.6°C increase and 15% decline in precipitation (predicted for 2050) will likely result in local site-level shifts. Site-level analysis showed that considerable declines in regeneration potential for E. delegatensis, E. pauciflora and E. nitens were modelled to occur in some ecosystems by 2050. While overall model performance and accuracy was good, better understanding of effects from extreme events and other underlying processes on regeneration will improve modelling and development of species conservation strategies.
Many farmers in water-scarce regions of developing countries use wastewater to irrigate vegetables and other agricultural crops, a practice that may expand with climate change. There is a number of health risks associated with wastewater irrigation for human food crops, particularly with surface irrigation techniques common in the developing world. The World Health Organization recommends using quantitative microbial risk assessment (QMRA) to determine if the irrigation scheme meets health standards. However, only a few vegetables have been studied for wastewater risk and little information is known about the disease burden of wastewater-irrigated vegetable consumption in China. To bridge this knowledge gap, an experiment was conducted to determine volume of water left on Asian vegetables and lettuce after irrigation. One hundred samples each of Chinese chard (Brassica rapa var. chinensis), Chinese broccoli (Brassica oleracea var. alboglabra), Chinese flowering cabbage (Brassica rapa var. parachinensis), and lettuce (Lactuca sativa) were harvested after overhead sprinkler irrigation. Chinese broccoli and flowering cabbage were found to capture the most water and lettuce the least. QMRAs were then constructed to estimate rotavirus disease burden from consumption of wastewater-irrigated Asian vegetables in Beijing. Results indicate that estimated risks from these reuse scenarios exceed WHO guideline thresholds for acceptable disease burden for wastewater use, signifying that reduction of pathogen concentration or stricter risk management is necessary for safe reuse. Considering the widespread practice of wastewater irrigation for food production, particularly in developing countries, incorporation of water retention factors in QMRAs can reduce uncertainty regarding health risks for consumers worldwide.
Selecting native plant species with characteristics suitable for extraction of heavy metals may have multiple advantages over non-native plants. Six Australian perennial woody plant species and one willow were grown in a pot trial in heavy metal-contaminated biosolids and a potting mix. The plants were harvested after fourteen months and above-ground parts were analysed for heavy metal concentrations and total metal contents. All native species were capable of growing in biosolids and extracted heavy metals to varying degrees. No single species was able to accumulate heavy metals at particularly high levels and metal extraction depended upon the bioavailability of the metal in the substrate. Metal extraction efficiency was driven by biomass accumulation, with the species extracting the most metals also having the greatest biomass yield. The study demonstrated that Grevillea robusta, Acacia mearnsii, Eucalyptus polybractea, and E. cladocalyx have the greatest potential as phytoextractor species in the remediation of heavy metal-contaminated biosolids. Species survival and growth were the main determinants of metal extraction efficiency and these traits will be important for future screening of native species.
In Australia, interest in wastewater reuse has grown. While wastewater can potentially offer a nutrient advantage over conventional irrigation, crop yield increases may be offset by effects of high salinity. Effects of wastewater irrigation on crop production and soil health were investigated in two ways: a field experiment addressing short-term effects and modeling longer-term impacts. The field experiment was established at the Shepparton Wastewater Treatment Plant in Shepparton, Victoria to compare effects of wastewater irrigation to conventional irrigation. Silage maize and sweet corn (Zea mays L.) were grown over the summer of 2012-2013 under the following flood irrigation treatments: wastewater and fresh water with and without fertilizer. Both harvests produced yields and qualities comparable to commercial farm standards and no significant differences were found between water types. Maize production with long-term wastewater irrigation at various salinities was modeled and no significant yield losses were observed after 50 years of simulated irrigation. Topsoil electroconductivity doubled after the field trial and simulation results predicted significant soil salt accumulation by factor of 2. Mean wastewater sodium absorption ratio of 4.52 and electroconductivity of 1.52 dS/m indicate potential for sodicity-related soil problems for long-term irrigation. Management of soil health may be necessary.
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