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Item Adsorption-desorption characteristics of phenoxyacetic acids and chlorophenols in a volcanic soil : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Process and Environmental Technology Department at Massey University, Palmerston North, New Zealand(Massey University, 1994) Susarla, SridharA study on the adsorption and desorption behaviour of 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), 2-methyl-4-chlorophenoxyacetic acid (MCPA), 2,4-dichlorophenol (2,4-DCP), 2,4,5-trichlorophenol (2,4,5-TCP) and para-chloro-ortho-cresol (PGOC), found in high concentrations in a New Zealand landfill. Volcanic soil with an organic matter content of 8.7% was used as adsorbent. Results of studies to determine the equilibrium sorption behaviour for each chemical showed the adsorption data for both phenoxyacetic acids and chlorophenols could be described by a Freundlich-type isotherm equation, the adsorption capacity followed the order: 2,4,5-T > MCPA > 2,4-D > 2,4,5-TCP > PCOC > 2,4-DCP at all pH and temperature values. Sorption capacity decreased with increasing pH and temperature; the heat of adsorption values indicating chemicals were adsorbed either by physical or hydrogen bonding to the soil surface. Results show only 2-4% of the total surface was occupied indicating chemical adsorption to specific sites present in the soil organic matter. The desorption results indicate isotherm parameters were dependent on the amount of each chemical adsorbed onto the soil. A linear relationship was developed to obtain the desorption parameters from the adsorption isotherm parameters. Desorption experimental results reveal that all the solutes adsorbed could not be desorbed, indicating a fraction of the chemical was resistant to desorption. A modified Freundlich-type equation described the competitive equilibrium adsorption and desorption of 2,4-D-MCPA, 2,4-D-PCOC and MCPA-PCOC mixtures. The model incorporated competition coefficients and was found to fit measured data, satisfactorily. The competition coefficients were linearly related to the initial concentration of the solutes in case of adsorption, and on the amount of chemical adsorbed for desorption. The results showed that the adsorption capacity of each solute decreased by about 8-12% in presence of the other competing solutes. However, in case of MCPA, the capacity decreased by 31% in the presence of 2,4-D. The desorption results reveal that 2,4-D and MCPA desorbed to a lesser extent in the bicomponent system compared to the corresponding single solute system. Similarly, the desorption of PCOC was less in the presence of 2,4-D than of MCPA compared to single solute system. A spinning basket reactor determined the kinetics of sorption for phenoxyacetic acids and chlorophenols. The film-mass transfer coefficients determined from the initial uptake rate data for the first 45 seconds, while the surface diffusion coefficients were obtained by fitting the experimental results with a homogeneous surface diffusion model solution. The desorption diffusion coefficients were found to be of the same order of magnitude as those of adsorption diffusion coefficients. The bicomponent surface diffusion coefficients were found to be slightly smaller (less than 10%) than single solute surface diffusion coefficients and this was due to competition between the solutes. A surface diffusion model based on equilibrium sorption, film-mass transfer and surface diffusion coefficient along with dispersion was used to predict the soil column data. All the parameters in the model were determined from independent experiments or calculated from literature correlations. The results from the column studies indicate that an increase in the concentration and flow rate resulted in the solutes moving faster in the column. A significant tailing of the chemical was observed at low concentrations for all the solutes. The results indicate that sorption played a dominant role in the transport of chemicals in columns. The breakthrough and elution for phenoxyacetic acids was in the order 2,4-D > MCPA > 2,4,5-T. For chlorophenols the order was: 2,4-DCP > PCOC > 2,4,5-TCP. The HSDM also used to predict the adsorption and desorption of bicomponent mixtures and the results indicated that the breakthrough and elution occurred earlier than in single solute systems. The order of breakthrough and elution was PCOC > 2,4-D > MCPA. To conclude, this thesis presents a detailed investigation of the adsorption and desorption characteristics of phenoxyacetic acids and chlorophenols for single and dual component systems in a volcanic soil. This study has identified the mechanisms and processes responsible for the leaching of the chemicals and can be used in remediation of a contaminated soil.Item An assessment of the revegetation potential of base-metal tailings from the Tui Mine, Te Aroha, New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University(Massey University, 1997) Morrell, William John; Morrell, William JohnThe overall objective of this study was to investigate the revegetation potential of abandoned base-metal (Cu-Pb-Zn) tailings at the Tui mine site near Te Aroha, New Zealand. An estimated 100,000 m3 of sulphide-rich tailings are the legacy of a once prosperous mining venture conducted at the site between 1967 and 1974 by the now defunct Norpac Mining Ltd. The oxidation of remnant sulphides, which constitute as much as 15% of the tailings by weight, has prevented plants from colonising the tailings for more than 20 years and resulted in the formation of Acid Mine Drainage (AMD) which continues to degrade ground and stream waters in the vicinity of the dam. This study focused on characterising the physical and chemical properties of the tailings in terms of their plant growth potential using a variety of techniques including; Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectrometry (EDS), Flame Atomic Absorption Spectrometry (FAAS), X-ray diffraction (XRD) as well as field based observations and standard laboratory analyses. A long term incubation experiment (carried out over a 1 1/2 year period) and two plant growth trials were also conducted to investigate the ability of liming materials and/or organic waste to ameliorate the tailings in order to provide a suitable growing medium for plants. The research indicated that, whilst the tailings do not exhibit any major physical limitations to plant growth, chemically the tailings are an extremely hostile plant growth medium. The surface tailings exhibited variable but generally very low pH (2.76 - 3.85) and high concentrations of potentially phytotoxic elements including As (254 mg/kg), Cu (26-991 mg/kg), Pb (1503-27416 mg/kg) and Zn (123-2333 mg/kg). The high availability of these and other metals, including Al and Fe. under the acidic conditions prevailing in the tailings, were identified as the primary factors currently inhibiting plant growth. The distribution of heavy metals, sulphate and total sulphur with depth indicated that the surface tailings (0-200 mm) have been extensively weathered since their deposition and contain relatively low concentrations of most heavy metals compared to subsurface tailings. An assessment of the Acid Generating Potential (AGP) of the tailings, using both static and kinetic tests, similarly indicated that the surface tailings have a comparatively low ability to generate acidity by sulphide oxidation. The application of lime at a rate of about 50 Mg CaCO3/ha is calculated to theoretically prevent the surface tailings from reacidifying. Below 200 mm depth, however, the AGP is appreciably higher (>140 Mg CaCO3/ha) and concentrations of both total and labile (0.1M HCl extractable) Cu, Fe and Zn were found to increase substantially, reflecting an increase in the abundance of chalcopyrite (CuFeS2), pyrite (FeS2) and sphalerite (ZnS) and sulphates with depth. The presence of high concentrations of acid-generating sulphide minerals (primarily pyrite) at shallow depths has important implications in that revegetation of the tailings should be based on techniques that minimise the exposure of the largely unweathered, sulphide-rich, subsurface tailings. The results obtained from the plant growth trials indicated that, on tailings treatments sown with metal-tolerant varieties of Festuca rubra or Agrostis capillaris, satisfactory cover was achieved upon the addition of lime at a rate of 16.5 Mg/ha or composted sewage sludge at rates >220 Mg/ha. These metal-tolerant plants were found to out yield their non-metal-tolerant counterparts on the limed treatments by as much as 4 and 10 times, respectively. Although vegetation was successfully established on Tui tailings treated with lime, dry matter yields were relatively low compared to treatments receiving high rates of sludge. The growth of all plant taxa was found to significantly decrease where very high rates of lime (112 Mg/ha) were added due to pH-induced nutrient deficiencies. Results obtained from both the plant growth trials and the lime incubation experiment indicated that the application of low rates of lime and/or sludge (8.25 and 110 Mg/ha respectively) were ineffective at creating a suitable plant growth medium and, in fact, exacerbated growing conditions within a few weeks of application by increasing the availability of labile (0.1M HCl extractable) metals. The findings of this study indicated that the use of amendments may provide a relatively inexpensive way of facilitating the establishment of plants on the tailings at the Tui mine site. It is envisaged that, at the very least, a vegetative cover will improve the aesthetic appearance of the site and at best reduce AMD by creating an oxygen-depleting, organic-rich cover which may ultimately facilitate the establishment of native species from the adjacent forest.Item The phytoextraction of heavy metals from metalliferous soils : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University(Massey University, 1997) Robinson, Brett Harvey; Robinson, Brett HarveyThis study concerns the investigation of the potential use of plants to remove heavy metals, in particular nickel, zinc and cadmium, from soils. The study is divided into three sections, bioavailability, phytomining, and phytoremediation. The effect of various extractants on the solubility of heavy metals in some soils was tested. It was found that the solubility of the metal invariably increased as the pH of the extractant decreased, and as the concentration of the extractant increased. These relationships could be predicted mathematically. It concluded that a more concentrated, neutral, non-chelating extractant such as 1M ammonium acetate, is the most suitable for estimating bioavailability. An investigation into the addition of some compounds to soils to increase metal solubility showed that EDTA and citric acid should maximise solubility while keeping soil parameters (pH, osmotic potential, nutrient availability) within the growth range of the plant. These compounds are also relatively inexpensive. The effect of bioavailable elements on a New Zealand serpentine flora was investigated with regard to the soil's potential for phytoextraction. It was found that nickel was the only element that would be suitable for phytoextraction from these soils. The relative infertility of the serpentines was attributed primarily to the toxic effects of magnesium and/or nickel. Removing nickel from the soil by phytoextraction may enable the soil to be used as a magnesium-rich fertiliser. The potential of the hyperaccumulator plants Alyssum bertolonii and Berkheya coddii for nickel phytoextraction was studied. With the addition of fertilisers, the plants could remove respectively in excess of 72 kg and 100 kg of nickel per hectare per annum. Were the metal to be sold, and energy from the plant's incineration utilised, the net profit per hectare would be greater than that of a crop of wheat. Both of these plants re-grew after harvesting without the need to re-sow. In the case of B. coddii, the nickel concentration in the regrowth was more than twice that of the original crop. Phytomining for nickel is a viable proposition provided the operation is carried out over a large area. The nickel concentration in the plants was logarithmically related to the nickel extracted by a 1M ammonium acetate extract. Theoretical nickel yields from various soils could be predicted by performing a 1M ammonium acetate extraction on the soils. About half of the soils tested from various locations around the world contained enough soluble nickel to be economically phytomined. Alyssum bertolonii and B. coddii also have the potential to remove nickel from polluted soils. The addition of EDTA and citric acid to the soil in which the plants grew actually decreased the nickel concentration in the plants despite increasing the nickel solubility in the soil. The economics of phytomining are closely linked to the value of the metal. Cobalt and possibly even the noble metals could be economically phytomined at low concentrations in plants: a fertile area for future research. Sequential extractions were used to model the effect of successive hyperaccumulator crops on the bioavailability of nickel in ultramafic soils from around the world. The nickel concentration in all of the soils tested, decreased in a regular manner and could be predicted mathematically. Assuming an initial nickel crop of 100 kg/ha, the number of nickel crops above 70 kg/ha that could be obtained was calculated for each soil. The number of economic nickel crops varied between 3 and 18 before the soil would have to have been modified to increase nickel bioavailability. The possibility of removing zinc and cadmium using Thlaspi caerulescens showed that the plant has a potential use for removing cadmium from weakly polluted soils. The low bioaccumulation factor for zinc accumulation means that this element will never be removed in a reasonable time span. The concentration of both zinc and cadmium in the plant could be predicted by the extractable fraction in the soil as estimated by using 1M ammonium acetate as extractant. It was concluded that phytomining and phytoremediation are feasible possibilities under certain conditions. (1) Metals necessarily have to be slightly soluble in the soil before they can be phytoextractcd. Metal solubility may be improved by the addition of chemicals such as chelating agents. (2) Due to relatively low yields, phytomining will only be viable for more valuable elements where the concentrations in soils are too low for conventional mining. (3) Phytoremediation will be most effective on weakly polluted soils. (4) The economics of phytoextraction favour its use over large areas. The amount of metal able to be extracted from an area can be predicted by performing an extraction with 1M ammonium acetate.Item The late Quaternary vegetational and climatic history of far northern New Zealand : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University(Massey University, 1997) Elliot, Michael Borlase; Elliot, Michael BorlaseSediments from 3 peat mires and two lakes from the Aupouri Peninsula, Karikari Peninsula and the Bay of Islands district of Northland, New Zealand, are analysed for their pollen and charcoal records to reconstruct a 100,000-year late Quaternary history of vegetational and climatic change. Northland has a complex geological history which includes Upper Pleistocene to Holocene volcanism. The region has a warm, moist climate, which promotes deep weathering of rocks, clay-rich soils and mass movement, particularly in the period following human settlement with clearance of most of the natural rainforest. Throughout the Pleistocene the climate of Northland remained relatively mild in comparison to the more southern regions of New Zealand. This thesis determines how the far northern vegetational cover and its composition have changed in response to late Quaternary climate changes through detailed pollen analysis of sediment cores. Studies of recent pollen deposits were undertaken to provide analogues for interpretation of the relationship between pollen rain and plant communities. Because New Zealand is one of the few land masses in the southern hemisphere south of 35° S, and lies just poleward of the subtropical convergence, it is uniquely placed to record climatic changes in the vast expanse of the Southern Ocean. These records of climatic fluctuations have global importance because of 1) New Zealand's small size and remoteness from other land masses, 2) the lack of large ice sheets at the Last Glacial Maximum which ensured rapid vegetational response to ameliorating climate, and 3) the potential for correlating high-resolution, well-dated terrestrial and marine records. At the height of the Last Glacial (Otiran) most of New Zealand south of 37° S was unforested. Landscapes not directly affected by glaciation were largely dominated by grass and shrublands. Forest patches survived in microclimatically favoured locations where they were protected from heavy frosts, cold maritime polar airmasses and strong winds. During the ca 100,000 years investigated, the pollen profiles demonstrate that the Northland region retained permanent forest cover, although composition of far northern forests changed significantly in response to fluctuating weather patterns. These vegetational and climatic changes are summarised below: 1) Kaihinu Interglacial, 18O Sub-stage 5c-a, ca 100-74 ka The regional vegetation of far northern New Zealand was dominated by kauri-podocarp-hardwood forest. The most important tall trees were Agathis australis, Dacrydium cupressinum and Phyllocladus. Ascarina lucida, a small, frost- and drought-sensitive understorey tree, was common. Angiosperm trees dominated coastal forest. The commonest species were Beilschmiedia, Quintinia, Metrosideros, Nestegis, Elaeocarpus and Ixerba brexioides. The climate is interpreted as having been mild and moist. Temperatures may have been 1-2° C cooler than present. 2) Last Glacial (Otiran), 18O Stages 4-2, ca 74-14 ka Regional vegetation changed significantly during the Otiran Glaciation. Whilst the far northern forests remained predominantly diverse conifer-hardwood assemblages, warmth-loving species became increasingly restricted in their distribution, particularly Ascarina lucida. From ca 74 ka, Agathis australis became scarce in the Kaitaia area, but remained a significant element of regional forest further east. Dacrydium cupressinum was a common emergent tree. Between 74-59 ka, climates were generally cool and moist with increased incidence of winter frost in exposed areas. Lowland forests moved seaward to occupy newly exposed continental margins as sea level retreated consequent upon expansion of global ice caps. The following period from 59-43 ka was characterised by increased abundance of Dacrycarpus dacrydioides, Metrosideros species, Quintinia and Syzygium maire. These species are associated with wetter conditions. Ascarina lucida was also more common at this time. Regional forests were predominantly podocarp-hardwood assemblages. Agathis australis was present in these forests, but not dominant. The climate between 59-43 ka (18O Sub-stage 3b) is considered to have been relatively warmer and wetter than the preceding Stage 4. From 43-24 ka (18O Sub-stage 3a) kauri-dominated mixed conifer-hardwood forest expanded. Significant increases of hardy podocarps Podocarpus and Prumnopitys taxifolia occurred. Agathis australis reached its greatest abundance since the Last Interglacial, and Ascarina lucida was scarce. Climate was characterised by drier summers and cooler winters. As glaciation in more southern latitudes intensified, northern climates became increasingly colder, drier and windier, particularly from ca 30 ka. Natural fires were more common. The replacement of kauri-podocarp-hardwood forest with beech-podocarp-hardwood forest followed rapidly, and by the Last Glacial Maximum (LGM) Northland forests as far north as Kaitaia were dominated by Fuscospora. From Kaitaia south all typically warm northern elements were restricted in their distribution. In the far northern region temperatures may have been depressed by as much as 3-3.5°C, and rainfall was probably reduced to about 2/3 it s present level. 3) The Lateglacial, 14-10 ka Dacrydium cupressinum, Dacrycarpus dacrydioides, Ascarina lucida and Dodonaea viscosa became more abundant from ca 14 ka. Fuscospora, Podocarpus and Prumnopitys taxifolia, which had expanded during the harsher climates of the LGM, became more restricted in their distribution. Climate became increasingly more equable as conditions ameliorated. 4) The Holocene, 10 ka to present Changes in composition of northern forests progressed even more rapidly from the onset of the Postglacial. Across the far northern region beech-dominated podocarp-hardwood forest was rapidly replaced by kauri-podocarp-hardwood forest. Fuscospora declined sharply and became very much restricted in its distribution. Dacrydium cupressinum dominated the regional forests. Hardy podocarps, Manoao colensoi, Podocarpus, Prumnopitys ferruginea and P. taxifolia became less common than previously. Ascarina lucida reached its greatest abundance between ca 10 - 7.6 ka. The early Postglacial climate was probably the warmest and most equable for the past 80 ka. Temperatures in the Kaitaia region may have been 1-2°C warmer than present. The mid- to late Postglacial, from ca 7-3 ka, is characterised by the decline in Ascarina lucida. Metrosideros and Libocedrus also became less common, whilst hardy podocarps such as Manoao colensoi, Podocarpus and Prumnopitys taxifolia increased in abundance. Far northern climates were probably slightly drier and cooler in this period as a more seasonal, dry summer/wet, cool winter regime became established. Increased cyclone activity is also suggested during this time. These weather patterns are in line with those suggested for other parts of New Zealand. Climatic variability continued into the late Holocene, and the pollen records indicate vegetation disturbance up to the time of first human settlement. The appearance of high frequencies of Pteridium esculentum and microscopic charcoal in pollen records, coincident with forest decline, is recognised as evidence for Polynesian deforestation. The clearance of indigenous forests occurred as a nation-wide event from 800-600 yr B. P. In Northland, where climates and soils were probably more favourable, deforestation events may have occurred a little earlier. At Lake Tauanui first human impact may have occurred as early as ca 1000 yr B. P., and at Lake Taumatawhana by ca 900 yr B. P. Forest clearance at the Wharau Road Swamp locality was somewhat later at ca 600 yr B. P. Subsequently, European settlement, commencing in the early 1800s, is identified by the advent of exotic pollen types such as Cupressus, Pinus, Ulex europaeus and Plantago lanceolata.Item A description of the soil potassium fertility of steepland pastures in the southern North Island of New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University(Massey University, 1999) Officer, Sally Jane; Officer, Sally JaneThe pattern of soil K fertility was investigated in two typical steepland pastures, located in the southern North Island of New Zealand. The parent materials of soils in this area are predominantly derived from sedimentary rocks. The soils have medium to high K reserves, and K fertilisers are not normally applied to the areas of steepland pasture. The study sites are part of well-established mixed stock grazing farms and have received regular aerial topdressing with superphosphate for at least 30 years. Grazing animals in steepland tend to favour the flatter areas, which are mainly on the crests of the ridges, and to spend relatively short periods of time grazing the steep slopes. Concerns have arisen as to the development of K deficiencies on the steep slopes, as stock are expected to graze these areas, and then to excrete most of the K ingested in the herbage onto the flatter areas. Two surveys were made of the K fertility patterns in two steepland paddocks. The first study was made over one paddock, by collecting soil samples along vectors of random direction, from points that were between 0.25 m and 25 m apart. The second survey targeted the main trends, sampling at regular intervals along the ridge crests and down the transects of the main slopes, at two paddocks The tests on the soil samples included exchangeable K (Quick test K), acid extractable K and the difference between the two factors, which was thought to provide a measure of plant available nonexchangeable K (Step K). The Quick test K values in one pasture alone ranged from 0.07 to 1.34 mg K/g soil, which was a range between very low and extremely high values for New Zealand soils. There was a similar wide range of values for other parameters. The frequency distributions of the soil test values were skewed, so that the arithmetic mean of the results was higher than 60-70% of the values. Spatial variability was at a maximum at a sampling distance of 0.25 m. The results indicated that the bulking of soil samples was a poor practise when sampling for exchangeable and plant available nonexchangeable K at these sites. Some relationships could be discerned between the soil K fertility patterns and the position of the topsoil in a steepland landscape, despite the high spatial variability. On the steep slopes, the Step K value of a soil was related to the soil moisture pattern, as determined by aspect and water seeps, and also to the pattern of the soil parent materials. Quick test K had no similar relationship to position in the landscape on the steep slopes. The spatial variability of both tests increased as the ground slope decreased. The mean and variability of Quick test K increased sharply on both well drained shoulder slopes and ridge-tops that were animal campsites. In contrast, the mean and variability of Step K increased markedly only on the well drained ridge-top campsites The different behaviour of cattle and sheep, the relatively large amounts of K deposited in excreta compared to P, and the slower rate of breakdown and dispersal of excreta in drier conditions, were all thought to contribute to these effects. The mineralogy of the topsoils at the two sites was also investigated. The clay mineralogy was dominated by a complex of 2:1 layer silicates, accompanied by lesser quantities of quartz, feldspars and kandites. The topsoils formed a sequence, which ranged from a 2:1 layer silicate clay complex that was dominated by mica and interlayered mica smectite (MS), to a 2:1 layer silicate clay complex that was dominated by vermiculite and hydroxy interlayered vermiculite (HIV). There was a very strong relationship between the Step K value and the mica content of a soil on the steep slopes. The relationship indicated that the dominance of either mica and MS, or vermiculite and HIV, in the clay fraction of a soil on the steep slopes depended on the original composition of the soil parent materials, the age of the soil profile, and the soil moisture conditions. On the shoulder slope and ridge-tops, there was a similar range of clay mineralogy, but Step K value now had a poor relationship to the mica content. This effect was mainly associated with soils under the well drained animal campsites, which had a distinctive mica and irregularly interstratified MS dominated clay mineralogy. The results were consistent with a reversal of the 2:1 layer silicate weathering processes under well drained animal campsites. Concentrations of total K and P were investigated in the topsoils of the two steepland pastures. The average difference between the total P of slope and ridge-top samples was about 200 kg P/ha, indicating a relatively small accumulation of P on the ridge-tops after many years of aerial topdressing and grazing. The expected accompanying increase in total K was not found. The marked effect of animal transfer processes on the plant available chemistry and mineralogy of the well drained ridge-top soils was thought to be a disproportionate indicator of the relatively small extent of total nutrient accumulation that appeared to have occurred on the ridge-top campsites. The plant response to K fertiliser was measured at the two steepland pastures sites. No K uptake response or growth response was identified at either site, despite low exchangeable K values in some areas and a low K content in some of the pasture samples, even after fertiliser was applied. In contrast, an exhaustive pot trial, using a selection of soils from the two sites, revealed a considerable range in the ability of the soils to supply K. Cation and anion concentrations were measured in the leachates of "stove pipe" soil cores collected from the ridge-tops and steep slopes. K concentration in the leachates of soil from the steep slopes were relatively low and reasonably consistent over time, compared to the Ca and Mg concentrations that were more sensitive to changes in the ionic strength. K concentration in the leachate of soils from different ridge-top locations varied markedly between the different locations. The increased leaching of K under animal campsites was identified as a significant loss mechanism for the K that is transferred to these areas. However, it was thought that an exact quantification of this process would be difficult, because the spatial variability of the concentration of K leaching from the topsoil into the subsoil under campsites was expected to be even higher than the spatial variability of exchangeable K in these soils. In conclusion, animal transfer losses of K from the steep slopes to the flatter areas at these sites appeared to be in the low range for New Zealand steepland pastures. No significant depletion of the K fertility appeared to have developed on the steep slopes, although the measurements were confounded by the very high degree of spatial variability found in all aspects of the K fertility patterns. The current conventional practice of not applying K fertiliser to these and similar sites was thought to be sustainable.Item Studies on the origin, distribution and mobility of cadmium in pastoral soils : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University(Massey University, 1998) Zanders, Julie Maria; Zanders, Julie MariaCadmium (Cd) is a toxic heavy metal with no known biological function. Exposure of the human population to Cd is predominantly through cigarette smoke and Cd-containing foodstuffs. Many phosphatic fertilizers contain Cd and their application to land used for food production results in increased concentrations of Cd in the soil. The fate of this Cd in soils is poorly understood. In this study, factors influencing the concentration and residence time of Cd in pastoral soils were investigated. Total Cd concentrations in topsoil samples (0 - 7.5 cm) from a regularly fertilized farm were found to range between 0.07 and 0.91 mg Cd kg-1 (arithmetic mean of 0.36 mg Cd kg-1). The top soil Cd concentration was unrelated to soil type or parent material but correlated well with total phosphorus and total carbon. In a study of the distribution of total Cd throughout the profiles of 17 soil types on the farm, Cd concentrations generally decreased with depth and soil parent material contributed little to topsoil Cd loads. A comparison of pedologically matched fertilized and unfertilized soils on the same farm confirmed that phosphatic fertilizer was the dominant source of Cd. Fertilized sites showed a 3- to 20-fold increase in soil Cd loading. Increased Cd concentrations were detectable to 15 cm. These increased Cd loads were easily accounted for by an estimated phosphatic fertilizer input of 6 g Cd ha-1 yr-1 over 7 decades. Soil Cd concentrations were also influenced by stock camping behaviour, although the magnitude of this effect was much less than that due to fertilizer. To investigate conditions under which Cd may move deeper in the soil profile, laboratory-based leaching studies on repacked soil columns using various electrolyte leaching solutions were conducted. Columns leached with 2.5 mM CaCl2, CaSO4 and Ca(NO3)2 showed some limited movement of Cd, but columns leached with 2.5 to 7.5 mM KCl showed no significant redistribution of the added Cd. Under the soil conditions studied (pHH2O 5.45), cation exchange appeared the predominant driving force behind Cd mobility, not anion complexation. On the same soil, Cd mobility increased linearly as leachate CaCl2 concentration increased. By 50 mM CaCl2 most Cd was leached from the column. In view of the dominance of Cl in coastal soil solutions, this mobility under the influence of CaCl2 may be important. In a further experiment, four soils differing in physical and chemical properties were leached with 2.5 mM CaCl2. The wide range of Cd mobility seen, could be explained by differences in soil pH (pHH2O 4.95 - 6.02). The movement observed in these columns was adequately modelled using a simple convection-dispersion equation and adsorption isotherms. The movement of Cd observed and modelled in these laboratory studies suggests that leaching is likely to be a much more important mechanism of Cd loss from the soil profile than removal of animal products. This work was supported by findings from a field-based mass balance study of Cd inputs and accumulation in soil developed under pasture on a Wharekohe podzol. Despite clear accumulation of fertilizer-derived Cd in the surface of these pastoral soils, up to 44% of the applied Cd remained unaccounted for. The most likely reason for this was leaching. Accurate modelling of the residence time and plant availability of Cd in soils will rely on a quantitative understanding of the factors influencing Cd mobility in soils. This is an area requiring further research.