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Characterisation and potential optimisation of seepage wetlands for nitrate mitigation in New Zealand hill country : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science, Massey University, School of Agriculture and Environment, Palmerston North, New Zealand
(Massey University, 2023) Sanwar, Suha
Diffuse nitrate (NO₃⁻) loss to pastoral waterways in hill country headwater catchments is a water quality concern in many countries with pasture-dependent economies, including New Zealand (NZ). Sheep and beef farming is the dominant land use in NZ hill country which are often located in headwater catchments. As these primary industries strive toward production growth to meet global demand for meat exports, this agricultural intensification will introduce more NO₃⁻ to its waterways. This contrasts with the recently enacted National Policy Statement for Freshwater Management 2020 (NPS-FM) which recognises the significance and calls for the protection of small wetlands in recognition of their ecosystem services including nutrient regulation, water quality improvement as well as associated social well-being. Nitrate mitigation in low-order streams in pastoral headwater catchments are important due to their proportionally large catchment coverage and major contribution to the national NO₃⁻ load to NZ rivers. Seepage wetlands in hill country landscapes can be a N-sink and, therefore, is a potentially cost-effective and natural NO₃⁻-mitigation tool for improved water quality from the pastoral headwater catchments. Seepage wetlands are features that occur along low-order streams in the low gradient of hill country landscapes. Their organic matter-rich sediment, saturated conditions and locations at the convergence of surface and subsurface NO₃⁻ rich flow pathways make seepage wetlands a unique landscape feature in terms of NO₃⁻ reduction via denitrification processes. However, denitrification is spatially and temporally variable as the process is influenced by the wetland sediment and hydrological properties. Several studies have demonstrated that seepage wetlands can be a potential NO₃⁻ sink and have quantified high sediment denitrification capacities in individual wetlands. However, variations in sediment and denitrification properties across a range of wetlands and a comprehensive study of seepage wetland hydrological characteristics that influence NO₃⁻ attenuation have not been undertaken, particularly in pastoral hill country landscapes in NZ. This thesis has examined the spatial variabilities of seepage wetland denitrification and the denitrification-influencing sediment properties across four hill country seepage wetlands within the Horizons Regional Council administrative boundary in NZ. The spatial gradients of sediment properties were examined vertically (at 15 cm depth intervals) and horizontally (within- and between- wetlands) in seepage wetland sites. Sediment physicochemical (water content (WC), pH, Eh) and chemical properties (dissolved organic carbon (DOC), NO₃⁻, NH⁴⁺, %total carbon or %TC, %total nitrogen or %TN, C:N, dissolved Fe²⁺ and dissolved Mn²⁺) and sediment denitrification enzyme activity (DEA), that represents sediment denitrification capacity, were quantified. The DEA values were highest at the surface depths across all wetland sites. Based on the wide range (560-5371 µg N₂O-N kg⁻¹ DS h⁻¹) and distinctive surface DEA values, the seepage wetland study sites were categorised into high-performing H-DEA (>3000 µg N₂O-N kg⁻¹ DS h⁻¹) and comparatively low-performing L-DEA (<1000 µg N₂O-N kg⁻¹ DS h⁻¹) sites. The H-DEA sites measured 7 to 10 times higher surface DEA values compared to the L-DEA sites. Spatial variability of denitrification in seepage wetlands was mainly driven by sediment WC, NO₃⁻, %TC, %TN, C:N, dissolved Fe²⁺ and dissolved Mn²⁺ (p≤0.05). The H-DEA site measured high WC (78%) which was above the threshold for denitrification and high sediment NO₃⁻ (15.9-18.5 mg NO₃⁻N/kg DS), in contrast to the L-DEA sites (WC 39.8-37.4%, 2.5-3.97 mg NO₃⁻N/kg DS). The heterogeneity of WC explained the heterogeneous distribution of DEA within the individual L-DEA sites. The sediment properties accounted for only 58-73% of the overall spatial variability in DEA, suggesting that additional wetland characteristics such as wetland hydrology, could have an important influence on denitrification in seepage wetlands. The seepage wetland hydrology and associated NO₃⁻ removal were characterised in detail at one of the L-DEA sites located on Tuapaka farm. During the hydrological characterisation, streamflow discharge and water quality were monitored at inflow and outflow for a 2-year period (June 2019-May 2021). Shallow groundwater quality was monitored at the 0.5, 1 and 1.5 m depths at the inflow, midflow and outflow positions in the wetland for a 1.5-year period (November 2019-May 2021). The seepage wetlands site demonstrated a stream inflow-dominated hydrology (83-87%) with small seepage contributions (8-14%) to the seepage wetland hydrology. Precipitation was found to be the major hydrological and associated NO₃⁻ removal (means attenuation) driver in the seepage wetland site. The seepage wetland was found an overall NO₃⁻ sink that on an average removed 23% of the annual NO₃⁻ inflow. Compared to the stream inflow (<0.03 mg NO₃⁻N/L), higher shallow groundwater NO₃⁻ concentrations (<0.11 mg NO₃⁻N/L) suggests that seepage is potentially an important NO₃⁻ source in these wetlands. High flow conditions, high winter precipitation and direct grazing during low flow periods are potentially major NO₃⁻ loss hot moments. In contrast, initial rapid infiltration at the onset of high precipitation events in early winter and spring and dissipated flow conditions highlighted opportunities for NO₃⁻ attenuation in the wetland and were identified as major NO₃⁻ removal hot moments. An overall dissipated flow condition driven by seasonally equivalent precipitation (22% of annual precipitation in winter) facilitated considerably higher annual NO₃⁻ removal of 40.8% (2.78 kg NO₃⁻N) in the wetland in year 2, in contrast to very low NO₃⁻ removal (0.3%, ~0.02 kg NO₃⁻N) under an erratic annual precipitation distribution (38% of annual precipitation in winter) in year 1. These findings suggest there is scope to improve NO₃⁻ removal by optimising flow conditions to slow flow in seepage wetlands to minimise NO₃⁻ loss during NO₃⁻ loss hot moments. In a follow-up laboratory-scale seepage wetland intact sediment column experiment, the effectiveness of diffuse flow, via subsurface outflow, was investigated for the optimisation of the wetland NO₃⁻ removal. During the experiment, the flow intervention altered the NO₃⁻ reduction-constraints observed in the preceding hydrological study and facilitated anaerobic conditions conducive to denitrification to capitalise on the sediment denitrification capacity, which was quantified during the preceding seepage wetland sediment characterisation study. The flow intervention involved vertical downwelling of NO₃⁻ rich (5 mg NO₃⁻N/L) pastoral surface runoff and subsequent horizontal discharge through a subsurface sediment column depth of 15 cm depth, collected from the Tuapaka seepage wetland site. The effectiveness of the subsurface drainage intervention for NO₃⁻ removal was assessed by monitoring the subsurface outflow water quality. The study showed that flow intervention achieved 50-96% NO₃⁻ removal from NO₃⁻ rich surface runoff. Based on the observations from the column study, two separate optimal operational HRTs of 2 and 13 hr are recommended to achieve large NO₃⁻ removal (50% from NO₃⁻ input of 5 mg NO₃⁻N/L) in a short period of time and large reduction in NO₃⁻ concentration at the outflow (<0.15 mg NO₃⁻N/L), respectively. The reasonably short period of HRT for such high NO₃⁻ removal efficiency (50-96%) supports the potential for the application of subsurface outflow intervention as a practical in-situ NO₃⁻ mitigation strategy, which warrants further research. This study also acknowledges the associated technical limitations of translating the laboratory-based findings to the field scale and recommends future studies to overcome these research limitations including high sediment compressions during intact sediment column samplings from the field, for example. The thesis not only demonstrates a flow intervention strategy to improve NO₃⁻ mitigation via flow regulation in seepage wetlands, but also guides future management by identifying the potential seepage wetland hot spots in the landscape (chapter 3) and the NO₃⁻ removal hot moments in the wetlands (chapter 4) and also by recommending necessary HRTs for flow intervention (chapter 5). In summary, this thesis has generated a robust dataset that improves our understanding of seepage wetland characteristics and their influences on NO₃⁻ removal at spatial and temporal scales. From an application perspective, this research provides new knowledge as to ‘where’, ‘when’ and ‘how’ seepage wetlands can be targeted to enhance their role in NO₃⁻ mitigations in hill country landscapes. This information has the potential to accelerate the integration of seepage wetlands into the toolbox of NO₃⁻ management strategies that could be used at a farm scale to improve water quality leaving NZ pastoral headwater catchments.
Purpose built standoff on dairy farms for environmental protection and efficient production : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Agricultural Science, Massey University, Palmerston North, New Zealand
(Massey University, 2018) Villacres Tapia, Santiago Raul
Farmers are increasingly concerned about pasture and soil protection and nutrient loss from their farms to receiving surface and ground waters. The practise of standoff using purpose built facilities is one potential solution to these twin problems. However, the adoption of standoff is expensive as it incurs numerous costs such as those associated with the construction of the feed and loafing areas and the handling of the extra volumes of effluent that are produced. This study investigates the implementation of standoff on four case study farms in the Manawatu region. One of the farmers is contemplating adopting standoff for soil and pasture protection, one of the farmers is considering the use of standoff to lower leaching from his farm while two of the case study farms are wondering about the use of standoff for both purposes i.e. soil/pasture and environmental protection. A range of tools was used to simulate the role and impact of standoff in the four cases study farms including; the soil water balance, the Farm Dairy Effluent Storage Calculator, Overseer and the DairyNZ investment tool. The soil water balance was used to identify the timing and extent of standoff, which are in turn important inputs into other the other models. The two major benefits of standoff in winter and spring for farm profitability are a potential increase in milk production and improved utilisation of supplements. Where standoff was practised for soil and pasture protection it was assumed that milk yield would increase by a relatively modest amount (10%) over the months August to October inclusive. The conservative nature of the analysis performed here recognises that the cases study farms are currently well managed. The simulations suggest that standoff for soil/pasture and environmental protection would be effective in helping the farmers meet these objectives. The case study farms with poorly drained soil would stand cows off for significant periods in order to protect soils and pastures. The cost of standoff is dependent on a number of factors. In this study, the impact of standoff on the costs associated with managing increased volumes of effluent were investigated in more detail. Standoff obviously results in the generation of more effluent. The costs associated with handling this effluent varied across the case study farms. Farms where large periods of standoff occurred in winter and where the effluent was irrigated to high risk soils required large increases is storage volume. Farms where standoff was only practised in summer and autumn to reduce leaching from free draining soils required very little increase in storage volume. The required expansion of the effluent block varied across the cases study farms but was typically 500 to 710 m2 per cow. Overseer suggests that standoff would decrease N leaching from the farms by 4 to 26%. The DairyNZ tool suggests that there is the risk that standoff will not be a good financial investment on the case study farms. Only one of the scenarios explored here had acceptable values for the financial parameters such as NPV. For all other scenarios, standoff was not a financially viable proposition. This would be expected for the farm where standoff was only practised over the summer and autumn periods as standoff at this time of the year has few other financial benefits. In this case, standoff should be compared with the cost of other mitigation options. Given the complexity of identifying the advantages and costs of standoff, any farmer contemplating adopting standoff needs to perform their own comprehensive and detailed analysis. If milk production is greater than the value assumed here or the standoff facility can be constructed and operated more cheaply than assumed here then standoff may well be a sound financial investment.
The incidence and variation of bacteria in a stock dam : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Plant Science at Massey University
(Massey University, 1974) Pyle, Barry Hubert
The effects of agricultural activities, including grazing and fertilizer application, and environmental factors, on the incidence and variation of bacteria in a stock dean were investigated. A survey of water quality at sites around the edge of a dam was carried out over a period of 15 months. Samples were analysed for water temperature, pH, turbidity, dissolved oxygen, 5-day biochemical oxygen demand (BOD5), total and soluble phosphorus, total nitrogen, ammonia, nitrite, nitrate, total plate count (TPC), total coliform (TC), faecal coliform (FC) and faecal streptococcal (FS) counts. The bacterial content of faecal samples from animals around the dam and of littoral sediments were determined. Experiments with incubation of fresh and sterilized pond water samples were carried out to examine the effects of trophic status and nitrate and phosphate addition on bacterial growth and survival. The presence of grazing animals and wildlife around the dam resulted in significant increases in BOD5 , turbidity, FS and FC counts. Turbidity, ammonia, nitrate, log10 TPC, log10 TC and log10 FC were positively correlated with the amount of rainfall in the 5 days prior to sampling. While dissolved oxygen saturation was positively correlated with water temperature, ammonia, nitrate, log10 TPC and log10 TC exhibited a negative correlation. Ammonia, nitrate and log10 TPC were correlated with turbidity, and log10 TPC was correlated positively with ammonia and nitrate concentrations. Fertilizer application resulted in slightly increased phosphate concentrations. The bacterial content of cattle and goose faeces was similar to those reported in the literature, with FC/FS ratios less than 0.01. FC and FS bacteria were observed to grow in sterilized pondwater samples in pure cultures and in a community of indigenous bacteria harvested from the water. Addition of phosphate and nitrate, and increasing trophic status caused growth stimulation in both pure culture and in the mixed community. In fresh samples, while indigenous bacterial populations increased, indicator bacteria survived longer in less eutrophic water. It was concluded that BOD5 , turbidity, FC and FS counts were good indicators of animal pollution in this situation. Land drainage and mixing of dam sediments resulted in increased indigenous bacterial counts and chemical enrichment. While the physico-chemical nature and trophic status of the water may have influenced bacterial growth and survival, direct pollution, land drainage and mixing of sediments were overriding factors. The concentrations of faecal indicator bacteria encountered suggested that pathogenic organisms such as Salmonella could be present in littoral water and bottom sediments.
The effects of tillage practices and cropping pattern on nonpoint source pollution and soil quality : a thesis presented in partial fulfilment of the requirements for the degree of Master of Applied Science in Agricultural Engineering at Massey University
(Massey University, 1997) Guo, Peng
Soil erosion is one of the most serious environmental problems facing world agriculture. In New Zealand, with the current low financial returns from pastoral-based farming, land which was previously unaffected by soil erosion is being intensively farmed and therefore becoming more susceptible to soil erosion and nonpoint source pollution. Adoption of soil resource management and agricultural practices that seek to conserve soil and water resources and minimise environmental degradation is attracting overwhelming interest among scientists and general public. Therefore, the main objective of this study was to assess the effects of selected tillage practices on soil physical properties, soil and water runoff, and water quality under selected cropping pattern. Experiments were conducted on a Ohakea silt loam comparing crop production (barley and oats double crop rotation) using conventional tillage (MP), no-tillage (NT), and pasture (P) (as a control treatment) and assess their impact on erosion and selected soil properties. It was expected that this relatively heavy soil type would be sensitive to cultivation management systems and was therefore suitable for a comparison of tillage methods. The treatments were arranged in a randomised complete block (RCB) design with four blocks of three treatments. In the field experiment, soil bulk density, water content, infiltrability, penetration resistance and earthworm populations were measured during two cropping seasons after barley and oats crops harvest in March and August 1996 respectively. Generally, these soil properties were significantly (P≤ 0.05) affected by tillage practices. Soil water content, infiltrability, and earthworm populations were similar in the NT and P treatments, but significantly higher than those found in the MP treatment. Conversely, soil bulk density at 0 - 50 mm depth was in the order of MP > NT > P. In the laboratory experiment, soil and water runoff, leachate volume, pH and nutrient losses from soil erosion were measured under a rainfall simulator. "Rainfall" intensity used was at an average application rate of 50 mm/hr for one hour, simulating a rainstorm. Mean data from the two experiments suggested that the surface water runoff and soil sediment in runoff were higher in the MP treatment than in the NT and P treatments, and were in the order of MP > NT = P and in a ratio of 4:1:1 and 30:1:1 respectively. Conversely, the volumes of water leachate were higher for the NT and P treatments than for the MP treatment, and in a ratio of 4:1:1 respectively. Soil pH from both water runoff and leachate was at an average of 7.4 and 7.2 respectively, but not different among the three treatments. Nutrient losses in surface water runoff were found to be significantly higher (P≤ 0.05) in the MP treatment (N=1.45 mg/m2, P=1.02 mg/m2, and K=8.3 mg/m2) than those with the NT (N=0.76 mg/m2, P=0.65 mg/m2, and K=6.8 mg/m2). Nutrient losses from NT and pasture treatments were similar. One year's data including two cropping seasons indicate that conventional tillage practices can result in high surface runoff and sediment loss and adversely affect runoff water quality. Such tillage practices are likely to lead to unsustainable land resource management and decreasing crop yields. On the other hand, conservation tillage practices such as no-tillage and continuous pasture cover reduced soil and water erosion, improved soil physical properties and runoff water quality, and conserved land resources leading to enhanced land productivity and agricultural sustainability.
Left in the dark : the effect of agriculture on cave streams = Mahue i roto i te pō : ko te ariā o te ahuwhenua i ngā hikuawa o ngā ana : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Science in Ecology at Massey University, Palmerston North, New Zealand
(Massey University, 2015) McNie, Pierce Malcolm
The ecology of cave stream environments has received far less attention than surface streams in New Zealand. As a result, the impacts of human stressors on the communities of caves are uncertain. The impacts of agricultural practices on surface stream communities are wide spread and well-studied. In the surface environment, agricultural use of the surrounding catchment has been associated with lower QMCI and EPT scores and influences the structuring of communities and trophic base. Given the knowledge that the effects found on the surface are so far reaching, the aim of this thesis was to establish the effect of agricultural land use on cave stream communities in comparison to surface stream communities, find principal stressors to the cave communities and to examine how land use practices alter the trophic bases of underground communities. The relationships between land use and cave stream communities were examined for four cave streams and their surface stream origins in the Manawatu region of New Zealand. The communities were sampled and in stream environmental measurements were taken. Catchment and riparian zones were mapped using GIS software to establish the extent of agricultural use of land. Stable isotope ratios of carbon and nitrogen were analysed for the communities at each site and for a few potential food sources to determine the source of energy for the communities. Cave stream communities were found to be influenced by surface land management practices. For both the cave and the surface environments, a negative relationship was found for QMCI and EPT against agricultural development. When cave and surface streams are considered apart, the relationship between QMCI and EPT with agriculture was not as steep. This was attributed to the attenuation of sediment transport through caves and the lack of photosynthetic ability limiting the negative impacts of nutrient sequestration. Although sediment attenuated through the cave, it was the primary stressor on stream communities both on the surface and within the caves. Between cave and surface environments within the same dominant catchment cover type, resource use was similar. Between catchment types, however, the use of resources was different with an increased reliance on biofilm derived energy in agricultural catchments for both cave and surface sites. Considered along with the change in functional feeding groups that was detected, it is likely that the changes in resource use by communities as a response to the different inputs from agriculture are reflected in a different community structure. Overall agriculture was found to have a definite impact on cave stream communities. It is likely that through sedimentation and changing resource uses, the communities are altered in a way similar to what is found on the surface but to a lesser degree, reflecting the lower range of potential stressors on the cave from agriculture.
Investigating the transport and fate of nitrogen from farms to river in the Lower Rangitikei catchment : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Earth Science at Massey University, Manawatu, New Zealand
(Massey University, 2015) Collins, Stephen Brian
A sound understanding of the transport and fate of leached nitrate-nitrogen (NO3--N) in shallow groundwater is key to understanding the impacts of land use intensification on the quality of groundwater and surface water bodies. However, these are not well understood in the Lower Rangitikei catchment. This study was undertaken to assess the groundwater flow pattern and its interactions with the Rangitikei River; the redox conditions of the groundwater; and the extent of NO3--N attenuation in shallow groundwater in the Lower Rangitikei catchment. Groundwater depths were collected from more than 100 wells to map the piezometric surface to inform the groundwater flow pattern within the study area. Groundwater interactions with the Rangitikei River were estimated qualitatively from two longitudinal river flow and water quality surveys (on 6th and 20th January 2015) under low-flow conditions. Fifteen wells were sampled and analysed in the study area during December 2014 to characterise the groundwater redox condition. A total of nine piezometers were installed at a range of depths (3 m and 6 m) on two dairy farms (sand country and river terrace) and one cropping farm (sand country). In these piezometers, NO3--N, dissolved oxygen (DO) and other parameters were monitored over March, April and May 2015. Single-well push-pull tests were used to measure NO3--N attenuation in shallow groundwater during May 2015. Groundwater flow was largely influenced by the regional topography, particularly shallow groundwater (<30 m), where it flows from elevated areas such as Marton in a southerly direction towards the Rangitikei River. The longitudinal river flow and water quality surveys revealed a dynamic relationship between the river and the underlying aquifer. The surveys suggested groundwater discharges into the river both upstream and downstream of Bulls. The groundwater redox characterisation showed generally anoxic/reduced groundwater across the lower Rangitikei catchment area. Groundwater typically has a low DO concentration (<1 mg/L) with elevated levels of available electron donors, particularly dissolved organic carbon and Fe2+. These groundwater characteristics provide for generally favourable conditions for NO3--N reduction. Monitoring at the installed piezometers showed a generally low NO3--N concentration at these sites. The push-pull tests revealed NO3--N reduction occurring at all three sites, with the rate of reduction varying between 0.04 mg N L-1 hr-1 to 1.57 mg N L-1 hr-1. These results suggest that groundwater is likely to be connected with the Lower Rangitikei River. However, NO3--N concentrations in the river and groundwater were generally low, especially for the river at low flows. This suggests NO3--N may be undergoing reduction within shallow groundwater before it has a chance to seep into the river. Further evidence for appreciable levels of NO3--N reduction in the shallow groundwater is provided by the redox characterisation of reduced groundwater and the push-pull tests. However, more spatial and temporal surveys and in-situ measurements of denitrification occurrence in the shallow groundwater of the study area are required.
Remediation of New Zealand sheep dip sites using biochar and phytoextraction technologies : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science, Institute of Agriculture and Environment, College of Sciences, Massey University, Palmerston North, New Zealand
(Massey University, 2013) Gregory, Samuel
The practice of sheep dipping, which subjected livestock to inorganic and organic agricultural pesticides to eradicate pests such as lice and keds, is a historic practice; sheep dipping is no longer practiced in New Zealand today. Animals would be submerged in solid structures known as dips containing chemicals such as arsenicals and organochlorines with the leftover solution pumped onto surrounding soil. The use of pesticides such as these is now banned by law due to their persistence in the environment. Today an estimated 50,000 contaminated sheep dip sites exist in New Zealand representing perhaps the countries’ most significant, but understated, environmental challenge. To determine whether this historic agricultural practice had led to contamination of the environment, an investigation into the extent of contamination resulting from sheep dipping at a known historic dip site in Te Mahia, New Zealand was carried out. Characterisation of the site by arsenic soil concentration mapping revealed that 500 m2 of agricultural land has been contaminated with this metalloid and that arsenic exists at varying high concentrations through the soil profile. Environmental risk from these historic pesticides was established by analysing plant and water samples below the dip site. Staple Maori food varieties such as watercress were significantly contaminated with arsenic while water samples taken from the stream below the dip returned spiked arsenic concentrations. Based on this, it was justified that arsenic/organochlorine contamination would need to be managed to reduce their effect on these food sources. The design of a coupled remediation strategy using phytoextraction and biochar was utilized to reduce remediation times and is the basis of this thesis. Contaminated soil from the site was removed and amended with two types of biochar produced from willow feedstock. These biochars, known as 350°C and 550°C biochar were added into the soil at application rates of 30 t ha-1 and 60 t ha-1. During a series of 180 d glasshouse trials, the phytoextraction of arsenic into Lolium perenne (ryegrass) shoot tissue was analysed along with growth parameters of shoot and root biomass and corresponding response to arsenic at the molecular level. In soil; microbial activity, soil bacterial community, organochlorine concentration, and element dynamics were analysed as a function of biochar amendment. Soil microbial activity, analysed using the dehydrogenase assay (DHA), was significantly increased (P<0.01) under all biochar treatments compared to the control after 180 d during two glasshouse trials. Metagenomic analysis of the soil bacterial community revealed that biochar amended soils were selecting for bacterial species such as Chryseobacterium, Flavobacterium and Dyadobacter and the family Pseudomonadaceae which are known bioremediators of hydrocarbons. This resulted in isomers of the organochlorine hexachlorocyclohexane (HCH), particularly alpha-HCH and gamma-HCH (lindane), undergoing 10-fold and 4-fold reductions in soil concentrations respectively (2.2 mg kg-1 and 0.4mg kg-1) compared to the control (25 mg kg-1 and 1.6 mg kg-1 respectively). Amendment of soil with both biochars also caused a significant reduction (P<0.01) in soil DDT levels. Biochar promoted a 2-fold increase in shoot dry weight (DW) and a 3-fold increase in root DW after 180 d during one glasshouse trial while during the second trial only ryegrass root biomass was significantly increased as a function of biochar amendment. This increase was attributed, at least in part, to the fertility value of biochar. No negative effect of biochar amendments on ryegrass germination was observed. All biochar amendments resulted in significant increases in arsenic concentrations within ryegrass shoot material. Through extrapolation, 350°C biochar amended soils was estimated to have the potential to increase ryegrass sward DW growth by 0.68 t ha-1 compared to ryegrass grown on unamended soils and would correspond to an increase in the extraction of total arsenic by 14,000 mg ha-1 compared to unamended soils and in doing so decrease soil remediation times by over 50 %. Increased arsenic uptake as a function of biochar amendment resulted in increased enzymic activity of components of the antioxidant pathway including SOD and APX in most biochar treatments but across all treatments a reduction in GPX activity was observed. Analysis of specific metabolites utilizing metabolomics also suggest a definitive metabolite profile under biochar amendment compared to contaminated control ryegrass samples. However, there was no significant difference (P<0.05) in chlorophyll content in response to the total arsenic concentration in ryegrass shoot tissue grown on contaminated soil. The observed increases in activity of SOD, APX and steady CAT activity is suggested to be efficiently catalysing the production of harmful ROS in this soil. A 6-month field investigation into the effect of biochar amendment on the extraction of arsenic into a high biomass crop (Salix sp) resulted in significant increases of arsenic in stem biomass as a function of biochar amendment. When data was extrapolated to predict results of a long-term field trial and scale under willow treatment (stem) it was calculated that over 67.7 g of arsenic could be extracted in soils amended with 350°C biochar compared to 5.9 g extracted under control treatment. This could result - assuming a similar rate of extraction with time - in levels of arsenic concentration in soils reaching background concentrations in as little as 6 years, a reduction in remediation times of 92%.
An investigation of the spatial distribution of N2O emissions from sheep grazed hill country pastures in New Zealand :|ba thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy (PhD) in Environmental Science at Massey University, Palmerston North, New Zealand
(Massey University, 2012) Letica, Selai Ahovelo
New Zealand’s (NZ) greenhouse gas (GHG) profile is unique amongst developed countries as almost 50% of GHG emissions are derived from agriculture. In contrast, agricultural sectors of other developed countries typically contribute <10% to the national total GHG profile. In NZ, agricultural GHG emissions are dominated by methane (CH4) from enteric fermentation and nitrous oxide (N2O) from excreta deposition and nitrogen (N) fertiliser application. Nitrous oxide emissions from agricultural soils are largely affected by N inputs and soil moisture conditions, and contribute 33% of agricultural GHG emissions. In pastoral hill country these factors are inherently more variable than in flat land pastures due to topographydriven differences in excretal N returns and in soil moisture. This limits the application of N2O emission data collected from trials conducted on flat land to hill country situations. The objective of this thesis was to determine the influence of topography and fertiliser N inputs to soil on N2O emissions in hill country. Small scale trials were conducted to measure these aspects of N cycling. Three trials were conducted to measure the effect of slope and fertiliser N input on nitrification potential (NP) and N2O emissions. The results of these short term trials suggested that slope class and fertiliser N rates significantly affected nitrification rates and N2O emissions in hill country due to differences in N inputs and moisture status, as affected by slope. Both NP and N2O emissions were highly spatially variable during the measurement periods and the results presented in this thesis suggest that the majority of N2O emissions in sheep grazed hill country are produced from low slope/stock camping areas. Based on our findings it is recommended that mitigation options to reduce the risk of N loss from sheep grazed hill country should be targeted at low slope/stock campsite areas. Due to the significant relationship between slope class and N2O emissions, slope class may be a suitable parameter for up-scaling estimates of N2O emissions from sheep grazed hill country.

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