Does Tephrosia candida as fallow species, hedgerow or mulch improve nutrient cycling and prevent nutrient losses by erosion on slopes in northern Viet Nam?

Agroforestry is considered to be a promising alternative to short-fallow shifting cultivation or other monocropping systems. An on-farm experiment was established in 1996 in northern Viet Nam to examine the contribution of the leguminous bush Tephrosia candida (Roxb.) D.C. as a fallow or hedgerow species and as a mulch producer to improve nutrient cycling and prevent nutrient losses by erosion. The systems tested were upland rice monocropping (Mono), natural fallow (NaFa), fallow of Tephrosia (TepFa), hedgerow intercropping with upland rice (Oryza sativa L.) and internal mulching using pruned Tephrosia biomass (TepAl), and upland rice with external mulching using Tephrosia biomass (TepMu). Over two cropping seasons, from April 1996 to April 1998, nutrients recycled and inputs and exports were recorded, as well as changes in C-, N- and P-pools, and in pH in the 0–5 cm topsoil layer.The Tephrosia systems (TepFa, TepAl, TepMu) prevented nutrient losses by erosion effectively. Compared to the NaFa system, the TepFa system accumulated 34% more N in the above-ground plant parts and increased topsoil N by 20%, probably due to N-fixation. There was a trend that the less labile P-pools (NaOH-P) were reallocated into the more labile P-pools (Bicarb-P) in the soil of the TepFa system. Burning released significant amounts of the inorganic P-pools in both the NaFa and TepFa systems and this effect seemed to be more pronounced in the TepFa than in the NaFa. Organic input to crop export ratios for N and P were >1 in the TepAl and TepMu treatments. This was due to a sufficient quantity and quality of the Tephrosia mulching material. However, moderately labile NaOH-extractable organic P seemed to be depleted in the topsoil due to high P uptake in the TepMu treatment. Thus, nutrient cycling and nutrient balances were improved under the Tephrosia systems. But for long-term P sustainability, there is a belief that a combined use of mulching and mineral P fertiliser is needed.     

Dioxin reservoirs in southern Viet Nam--a legacy of Agent Orange

In the isolated Aluoi Valley of central Viet Nam, very high levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) were measured in soil, fish fat, duck fat, pooled human blood and breast milk samples collected from A So village between 1996 and 1999. The village was situated on a former military base occupied by US Special Forces between 1963 and 1966. TCDD was a contaminant of the herbicide "Agent Orange", aerially sprayed in the valley between 1965 and 1970, and stored at the A So base. Measured levels were lower near the sites of two other former US bases in the valley which had been occupied for shorter periods of time. In areas where Agent Orange had been applied by low-flying aircraft, levels of TCDD in soil, food and human samples were elevated, but lower than those near the three former US bases. We confirm the apparent food chain transfer of TCDD from contaminated soil to cultured fish pond sediments to fish and duck tissues, then to humans as measured in whole blood and breast milk. We theorize that the Aluoi Valley is a microcosm of southern Viet Nam, where numerous reservoirs of TCDD exist in the soil of former military installations south of the former demilitarized zone. Large quantities of Agent Orange were stored at many sites, used in ground and aerial applications, and spilled. TCDD, through various forms of soil disturbance, can be mobilized from these reservoirs after decades below the surface, and subsequently, introduced into the human food chain.     

Analysis of polychlorodibenzo-p-dioxins and dibenzofurans (PCDDs/PCDFs) in baked-salt food additives in Korea

Thirty-one samples of baked-salt products used in commercial food additives were analyzed for the presence of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs). Dioxins were highly detected in 12 samples of baked salts. The amount of dioxins found in the samples ranged from 12.47 pg/g to 406.56 pg/g (0.71 pg TEQ/g to 23.51 pg TEQ/g, respectively). The most abundant congeners, as TEQ values, were 2,3,4,7,8-PeCDF; 1,2,3,7,8-PeCDF; and 1,2,3,4,7,8-HxCDF in PCDF congeners and 1,2,3,7,8-PeCDD; 1,2,3,6,7,8-HxCDD; and 1,2,3,7,8,9-HxCDD in PCDD congeners. Meanwhile, PCDDs/PCDFs were analyzed in high-temperature-treated samples of natural sea salt alone and natural sea salt to which di-(2-ethylhexyl)phthalate (DEHP) had been added. In the former case, PCDD/PCDF formation was most evident at temperatures near 450 degrees C, the total amount of dioxins was 90.07 pg/g (6.07 pg TEQ/g), and PCDD congeners comprised less than 50% of the total PCDDs/PCDFs. However, when the latter samples were heated, the total PCDD/PCDF concentration was 512.30 pg/g (21.53 pg TEQ/g), with PCDD congeners comprising over 87% of the total PCDDs/PCDFs.     

Towards eco-agro industrial clusters in aquatic production: the case of shrimp processing industry in Vietnam

The concept of industrial ecology has been applied in this research to study possibilities to develop an eco-industrial cluster model for fishery production industry in Vietnam. By learning from experiments of other developed countries, we apply the principles of Industrial Ecology and of Ecological Modernization in the context of Vietnam. We design a physical-technological conceptual model for minimizing waste in agro-industries, with a case study of frozen shrimp production. The results indicate that it is possible and feasible to develop an eco-industrial cluster including aquaculture, fishery processing companies, by-product plants, and wastewater treatment units. By doing so, aquaculture and industry can cooperate for environmentally sound development. Actors and institutions that may govern the proposed eco-industrial cluster of shrimp processing industry are also analysed in this paper. The economic feasibility of the designed eco-agro industrial cluster for fish production in Vietnam depends on the energy savings and effective revenues gained from selling the produced valuable materials, such as Chitosan and animal feed.     

Incorporating differences between genetic diversity of trees and herbaceous plants in conservation strategies

Reviews that summarize the genetic diversity of plant species in relation to their life history and ecological traits show that forest trees have more genetic diversity at population and species levels than annuals or herbaceous perennials. In addition, among-population genetic differentiation is significantly lower in trees than in most herbaceous perennials and annuals. Possible reasons for these differences between trees and herbaceous perennials and annuals have not been discussed critically. Several traits, such as high rates of outcrossing, long-distance pollen and seed dispersal, large effective population sizes (N_e), arborescent stature, low population density, longevity, overlapping generations, and occurrence in late successional communities, may make trees less sensitive to genetic bottlenecks and more resistant to habitat fragmentation or climate change. We recommend that guidelines for genetic conservation strategies be designed differently for tree species versus other types of plant species. Because most tree species fit an LH scenario (low [L] genetic differentiation and high [H] genetic diversity), tree seeds could be sourced from a few populations distributed across the species’ range. For the in situ conservation of trees, translocation is a viable option to increase N_e. In contrast, rare herbaceous understory species are frequently HL (high differentiation and low diversity) species. Under the HL scenario, seeds should be taken from many populations with high genetic diversity. In situ conservation efforts for herbaceous plants should focus on protecting habitats because the typically small populations of these species are vulnerable to the loss of genetic diversity. The robust allozyme genetic diversity databases could be used to develop conservation strategies for species lacking genetic information. As a case study of reforestation with several tree species in denuded areas on the Korean Peninsula, we recommend the selection of local genotypes as suitable sources to prevent adverse effects and to insure the successful restoration in the long term.     

Drivers of Forest Cover Dynamics in Smallholder Farming Systems: The Case of Northwestern Vietnam

The national-scale forest recovery of Vietnam started in the early 1990s and is associated with a shift from net deforestation to net reforestation. Large disparities in forest cover dynamics are, however, observed at the local scale. This study aims to unravel the mechanisms driving forest cover change for a mountainous region located in northwest Vietnam. Statistical analyses were used to explore the association between forest cover change and household characteristics. In Sa Pa district, deforestation rates are decreasing, but forest degradation continues at similar rates. Deforestation is not necessarily associated with impoverished ethnic communities or high levels of subsistence farming, and the largest forest cover dynamics are found in villages with the best socio-economic conditions. Our empirical study does not provide strong evidence of a dominant role of agriculture in forest cover dynamics. It shows that empirical studies on local-scale forest dynamics remain important to unravel the complexity of human–environment interactions.     

Effects of chelates (EDTA,EDDS, NTA) on phytoavailability of heavy metals (As,Cd, Cu,Pb, Zn) using ryegrass (Lolium multiflorum Lam.)

Environmental Science and Pollution Research - This paper summarises a study of the application of the synthetic chelate ethylenediaminetetraacetic acid (EDTA), and the natural chelates...     

Steel slag quality control for road construction aggregates and its environmental impact: case study of Vietnamese steel industry—leaching of heavy metals from steel-making slag

Environmental Science and Pollution Research - Steel slag is an industrial by product of steel manufacturing processes and has been widely utilized within civil and construction materials for road...     

Prediction of groundwater nitrate concentration in a semiarid region using hybrid Bayesian artificial intelligence approaches

Environmental Science and Pollution Research - Nitrate is a major pollutant in groundwater whose main source is municipal wastewater and agricultural activities. In the present study, Bayesian...     

Evaluation of zeolite for control of odorants emissions from simulated poultry manure storage

Poultry operations are associated with emissions of aerial ammonia (NH3), volatile organic compounds (VOCs), and odor, and the magnitude of emissions is influenced by manure management practices. As a manure treatment additive, zeolites have been shown to have the potential to control NH3. Because of their properties it is also expected that zeolites could effectively adsorb VOCs and odor. The effectiveness of zeolite in controlling odor and VOCs was qualitatively evaluated in this controlled laboratory study involving simulated poultry manure storage. In the first two trials, zeolite was topically applied on nearly fresh laying hen manure at the rates of 0, 2.5, 5, and 10% (by weight). In the third trial, zeolite was topically applied at 5% with each addition of fresh manure into the storage vessel. Headspace samples from the emission vessels were collected with solid phase microextraction (SPME) and analyzed on a multidimensional-gas chromatograph-mass spectrometry-olfactometry (MDGC-MS-O) system for identification and prioritization of poultry manure odorants. Acetic acid, butanoic acid, isovaleric acid, indole, and skatole were consistently controlled in the headspace, with the reduction rate being proportional to the zeolite application rate. Dimethyl trisulfide and phenol were consistently generated, and with a few exceptions, the rate of generation was proportional to the application rate. Average reduction of the odor caused by all odorants evaluated with SPME-GC-O was 67% (+/-12%) and 51% (+/-26%) for the two topical applications, respectively, while no significant reduction of VOCs and odor was detected for the layered application.