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Item 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, SuhaDiffuse 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.Item Prioritisation of wetlands of the Rangitikei catchment : a thesis presented in partial fulfilment of the requirements for the degree of Master of Applied Science in Natural Resource Management at Massey University(Massey University, 2003) Amaranathan, UsharaniThis study aimed to prioritise wetlands of the Rangitikei Catchment. The prioritisation will enable the Manawatu-Wanganui Regional Council to apply its limited resources in an effective way to preserve the biodiversity of the wetlands of the catchment. A process was designed to achieve the project aim. The first step in the process was the establishment of two conservation goals: 1)Maintain species diversity, 2)Eliminate threats within wetlands. Secondly, the wetlands of the Rangitikei Catchment were surveyed to collect state and pressure information. 25 wetland sites were surveyed using the REWA survey method. Data collected was then analysed, first using the complementarity programme Sites V1.0. However, complementarity analysis did not achieve a clarified prioritisation of wetland sites because extreme variability was found among sites. In particular, complementarity analysis did not respond well to having two very different conservation goals of pressure and state. Therefore, 13 prioritisation criteria were employed based on elements of pressure and state. A method was devised to overcome problems of weighting criteria. True scores were converted to adjusted scores of 1 to 4 using the box and whisker division method. This method also allowed for easier replication and manipulation of data as well as clear visual representation, unlike other methods. A unique prioritisation framework was then devised which allowed multiple criteria (in this study pressure and state) to be assessed simultaneously. The framework also allowed the large amounts of data involved in the prioritisation process to be presented as a single priority ranking. The prioritisation framework is a relatively simple, repeatable and highly adaptable method. The framework does not compromise the contribution of each criterion to the overall value of the wetland. This resulted in prioritisation of the surveyed wetland sites of the Rangitikei Catchment and allowed achievement of the study's conservation goals. The box and whisker division method and prioritisation framework presented in the study are two unique methods that may be applied in future prioritisation programmes. Both methods provide simple and visual representations of the complex processes involved in the prioritisation of wetland sites and respond to multiple and opposing conservation goals. The nature of the prioritisation framework allows information to be added as it becomes available as well as accommodating the addition and expansion of conservation goals.Item The impact of urban development and habitat fragmentation on aquatic invertebrate communities in remnant wetlands : a Christchurch case study : a thesis presented in partial fulfillment of the requirements for the degree of Master of Applied Science in Natural Resource Management at Massey University(Massey University, 2004) Knight, JohnThe coastal plains that are now occupied by Christchurch City, in the South Island of New Zealand, were once dominated by palustrine and estuarine wetland systems. These wetlands were almost completely drained over a 100-year period in order to allow the construction of the city and to provide arable land for farming. However, remnants of the original wetlands have been preserved and are scattered throughout the present metropolitan area. Most of these are small riparian wetlands associated with Christchurch's many streams and three major river systems. In addition, there are also several large remnant wetland reserves that each cover many hectares. These remnant wetlands experience a range of environmental pressures from adjacent urban development, including stormwater discharge, landscaping, flood control, the presence of dense housing, pressure from introduced plants and insects, and more recently, wetland enhancement programmes. This study investigated the impact of urban development and habitat fragmentation on remnant urban riparian wetlands primarily by comparing the aquatic invertebrate communities that they support, with the same communities in three unmodified 'natural' wetlands associated with lowland streams flowing through native tussock and scrubland. A range of physical parameters (water clarity, conductivity, pH, temperature) were also measured. Three wetlands of a similar type and size located in pastoral grazing areas, and three artificially constructed urban wetlands, were also assessed to provide additional points of reference. The unmodified wetlands exhibited slightly higher species richness and abundance when compared to the remnant urban wetlands. However, this difference was not statistically significant (p>0.05). The unmodified wetlands showed significantly higher species richness than both the constructed and pastoral wetlands (p<0.01). Both of these highly modified wetland types contained large numbers of dipterans and molluscs, whereas the unmodified and remnant wetlands contained higher proportions of coleoptera and hemiptera. Significant differences were also detected between some of the pH, water clarity and temperature levels measured in the various wetland types. The effect of wetland size was also measured by comparing the invertebrate faunas in small, medium and large remnant fragments. Although lower macroinvertebrate abundance and species richness was observed in the small fragments, no statistically significant difference was detected between the three fragment sizes (p>0.05). There was also no significant difference between the unmodified wetlands and the remnant fragments. It was concluded that fragment size did not have a significant effect on the aquatic invertebrate communities in remnant urban wetlands, and adjacent urban development did not have a significant adverse impact on remnant urban wetlands when compared to natural wetland systems. Intensive pastoral grazing had a significant and quite severe effect on wetland systems, probably due to eutrophication and sediment wash-off. Artificially constructed wetlands contained significantly lower species richness than natural wetland systems. Remnant urban fragments appear to be resistant to the effects of urbanisation, and are considered to be suitable habitats for preserving native aquatic biodiversity in urban areas.Item The status of wetlands in the Manawatu : a thesis presented in partial fulfilment of the requirements for the Master of Applied Science in Natural Resource Management at Massey University(Massey University, 2000) Kerr, Peter ThomasWetlands have been severely degraded throughout history, particularly by agricultural activities. In addition, legislation has played a role in the sustainability of this resource. The purpose of this study was to determine the status of wetlands within the Manawatu, requiring an assessment of the physical attributes of the wetland, as well as reviewing the legislation, policies and plans governing how these areas arc managed. The objectives were to determine whether wetlands should be protected, and if so are they adequately preserved within a sample group. The sample group was determined by a number of factors including site access, landowner permission, and time restrictions If it is shown that these wetlands are not in acceptable environmental condition, then details of what should be done to improve their status are included. To achieve these objectives a wetland field assessment sheet that could be used by someone not familiar with the various plant and animal species found around wetlands, was designed. This field assessment sheet assessed the surrounding land use, threats, functions (of the wetland), and assessment of other attributes such as bank stability, water quality, and the effects of humans in the area. This field assessment sheet was necessary in order to determine whether the wetlands in the selected group were adequately preserved. Relevant wetland legislation and planning documents were also assessed. These were used to determine whether wetlands are given adequate protection under current laws such as the Resource Management Act (1991). Aerial photographs at a scale of 1:27 500 were used to identify the changes in numbers of wetlands between the 1940s and 1990s, and to measure the change in size of the sampled wetlands between the same time period. A main result showed that wetlands are generally increasing in number within four random aerial photo transects. The wetlands that were selected for field assessment proved to be in reasonable environmental condition. Zones within the wetlands that need improvement lie within the amount and composition of bank vegetation surrounding the wetland. In almost all cases, the average width of the surrounding riparian margin was less than five metres. Analysis of the legislation and planning documents showed that great emphasis is placed on those wetlands that are identified as being of national or regional significance. Those wetlands that are not classified as such are left to the maintenance of the landowner. Ultimately the status of these wetlands, not identified as being of regional or national significance, lies in the good will of the landowners. In most case studies, landowners were aware and mindful of the wetlands on their property. It is this attitude that must not change if the desired outcome is a continuation of wetlands throughout the region. It is concluded that a regional wetland plan or strategy should be designed in order to give greater importance to those wetlands not identified in the Regional Policy Statement (1998), so their status is more likely to be preserved. This plan should contain encouragement for landowners to provide a more suitable buffer zone around their wetlands - not only for the provision of suitable habitat for wildlife, but also to act as a filter for nutrients entering the wetland system.Item Preserving the Whangamarino Wetland : an application of the contingent valuation method : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science at Massey University(Massey University, 1988) Kirkland, William ThomsonThis thesis essentially describes the principal competing uses of the Whangamarino Wetland and derives estimates of the national economic benefit provided by each use. The wetland is a large swamp area in the upper North Island of New Zealand and provides an important wildlife habitat for many varied plants and animals. The wetland also has significant potential for agricultural and horticultural development as well as providing benefits in the form of fishing revenues and flood control. This study describes the major uses of the wetland in detail and goes on to apply economic evaluation techniques to each of them. Particular emphasis is placed on applying the Contingent Valuation Method (CVM) to evaluate the non-market benefits from preserving and improving the wetland as an environmental amenity. The CVM is discussed in detail with its theory, strengths, and weaknesses highlighted. A commentary on the methodology used in applying the CVM proceeds to outline the derivation of the national sampling frame, the design and implementation of the postal survey questionnaire and the results obtained. Information collected in the postal survey is examined to derive an understanding of how much and why, people value the wetland. A socio-economic profile of the respondents to the survey is generated in order that a judgement can be made on whether the postal survey technique has validly captured a national opinion. The study proceeds to aggregate the national economic benefits of the wetland in the form of Net Present Values (in January 1987 dollar terms, using a 10% discount rate). These values are then compared to illustrate how preservation of the wetland is likely to provide significantly greater social benefits than agricultural development benefits. The study continues by discussing national preferences of wetland use and making recommendations on wetland management in the future. A critique on applying the CVM in a New Zealand context is presented as a conclusion to the thesis.