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tephras, erupted before ca 18,000 cal. yr BP, were dated by calibrating limited numbers of 14 C ages using IntCal04 (Okareka) or comparison curves of the expanded Cariaco Basin sequence (Te Rere, Kawakawa/Oruanui, Poihipi, Okaia). Kawakawa/Oruanui tephra, the most widely distributed marker tephra, was erupted probably ca 27,097 ± 957 cal. yr BP. Potential dating approaches for the older tephras include their identification in Antarctic ice cores (if present) or annually laminated sediments for which robust calendar-age models have been constructed, high-precision AMS 14 C dating on appropriate material from environmentally stable sites, systematic luminescence dating, or new radiometric techniques (e.g. U-Th/He) if suitable minerals are available and errors markedly reduced. Further application of Bayesian age-modelling to stratigraphic sequences of 14 C ages, possibly augmented with luminescence ages, may help refine age models for pre-Holocene tephras with the largest errors. Finally, we discuss the critical role these marker tephras play in the ongoing construction of an event stratigraphy for the New Zealand region, which is a key objective of Australasian and Southern Hemisphere INTIMATE projects. Source: Quaternary Science Reviews (2008) 27: 95-126. _______________________ Selected abstracts from the New Zealand Trace elements Group Conference 2008, WEL Energy Trust Academy of Performing Arts, University of Waikato, Hamilton, New Zealand; 13-15 February 2008. Copper and zinc in soils: Too little or too much? Brian J. Alloway Dept of Soil Science, School of Human and Environmental Sciences, University of Reading, UK Copper and zinc are essential for the normal healthy growth of plants (and animals/humans). When the available concentration of either element in the soil is too low, plants suffer from deficiency and when it is too high, toxicity will occur, at least in the more sensitive organisms. Ideally, the available concentrations should be in the window of essentiality between the two extremes. Background concentrations of copper and zinc in selected countries and the critical concentrations used in the interpretation of soil test extractions will be considered. Brief mention will be made of the essential functions of copper and zinc in plants, the soil and plant factors affecting bioavailability and examples of the effects of deficiencies of on crop yield and quality. The main sources of copper and zinc contamination will also be covered, together with typical soil concentrations encountered at different types of contaminated sites. The upper critical concentrations (PNEC, NOAEL etc) adopted in different countries to protect soil organisms and processes will be compared and the risks to soil fertility discussed. The key themes emerging from these considerations of copper and zinc in soils are: Low available concentrations can reduce crop yields and quality without the appearance of obvious symptoms (hidden deficiencies). Existing upper limit values are helpful for protecting soils from toxic accumulations, but need to be tailored to local soils, environmental conditions and land management. Intensive livestock production and fungicidal formulations are the main sources, except where sewage sludge is applied to land or zinc fertilisers are used on a regular basis. 77
Soil properties affecting the bioavailability of copper and zinc, respectively, can alter over time as a result of climate change and/or changes in farming practice. These, together with any new crops and/or cultivars grown, have to be considered in relation to both potential deficiencies and toxicities. The zinc content of grains is becoming increasingly important because < 50% of the world’s population have insufficient zinc in their diet. Metal chemistry and bioavailability in a biosolids-amended forest soil following conversion of the land for agricultural usage R G McLaren and L M Clucas Centre for Soil and Environmental Quality, Agriculture and Life Sciences Division, PO Box 84 Lincoln University, Lincoln 7647, Canterbury Application of biosolids to forests as a method of disposal is currently being used by authorities around the world, including New Zealand. This practice can lead to a build up of metals (from the biosolids) within the forest litter layer. However, as long as the land remains under forest, the chance of these metals entering the human food chain is low. This may cease to be the case if the forest is cleared for conversion of the land back for agriculture. This study, using incubation and plant growth techniques, examines the fate of metals in a Pinus radiata plantation forest treated with metal-spiked biosolids, following simulated conversion of the land back for agricultural use. Mixing of the biosolids-treated forest litter into the underlying mineral soil resulted in high concentrations of metals (Cu, Ni and Zn) in easily extractable forms, and there was also very little change in these concentrations during a subsequent 2-year incubation of the samples. Soil solution concentrations of the metals were also enhanced substantially by the various original biosolids treatments. Chemical speciation of the soil solutions using WHAM 6 showed that whereas solution Cu was dominated by organic complexes, most Ni and Zn was present at Ni 2+ and Zn 2+ , with generally less than 5% of these elements present as organic complexes. Addition of lime to the soils substantially decreased both readily extractable and soil solution metal concentrations, however, even in their unlimed state there were no adverse effects due to the metals on plant growth as determined in a wheat germination and seedling growth test. Nevertheless, metal concentrations in the wheat seedlings were increased by the various original biosolids treatments. Plant metal concentrations showed strong correlations with either soil solution metal ion activities, or effective soil solution concentrations as determined by diffusive gradients in thin films (DGT). The results from this study are discussed in relation to the possible consequences of growing agricultural crops on land converted from forest soils that have previously received applications of biosolids. Accumulation, dynamics and risks of fertiliser-derived fluorine in grazed pasture systems: a review P Loganathan 1 , MJ Hedley 1 and ND Grace 2 1 Fertilizer and Lime Research Centre, Institute of Natural Resources, Massey University, Private Bag 11222, Palmerston North, New Zealand. 2 AgResearch Limited, Grasslands Research Centre, Private Bag 11008, Palmerston North, New Zealand. Fluorine (F) continues to accumulate in biologically active topsoils under pasture mainly as a result of phosphorus (P) fertiliser input. Excessive levels of soil F have the potential to cause adverse effects on 78
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