Research@Lincoln
Research@Lincoln is an open access institutional repository collecting the research produced by Lincoln University staff and students. You may also be interested in Data@Lincoln or Lincoln University Living Heritage.
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Item Open Access Elucidating phosphorus removal dynamics in a denitrifying woodchip bioreactor(Elsevier B.V., 2024-03-20)Denitrifying woodchip bioreactors (DBRs) are an established nitrate mitigation technology, but uncertainty remains on their viability for phosphorus (P) removal due to inconsistent source-sink behaviour in field trials. We investigated whether iron (Fe) redox cycling could be the missing link needed to explain P dynamics in these systems. A pilot-scale DBR (Aotearoa New Zealand) was monitored for the first two drainage seasons (2017–2018), with supplemental in−field measurements of reduced solutes (Fe²⁺, HS⁻/H₂S) and their conjugate oxidised species (Fe³⁺/SO₄²⁻) made in 2021 to constrain within-reactor redox gradients. Consistent with thermodynamics, the dissolution of Fe³⁺(s) to Fe²⁺(aq) within the DBR sequentially followed O₂, NO₃− and MnO₂(s) reduction, but occurred before SO²‾₄ reduction. Monitoring of inlet and outlet chemistry revealed tight coupling between Fe and P (inlet R² 0.94, outlet R² 0.85), but distinct dynamics between drainage seasons. In season one, outlet P exceeded inlet P (net P source), and coincided with elevated outlet Fe²⁺, but at ⁓50 % lower P concentrations relative to inlet Fe:P ratios. In season 2 the reactor became a net P sink, coinciding with declining outlet Fe²⁺ concentrations (indicating exhaustion of Fe³⁺(s) hydroxides and associated P). In order to characterize P removal under varying source dynamics (i.e. inflows vs in-situ P releases), we used the inlet Fe vs P relationship to estimate P binding to colloidal Fe (hydr)oxide surfaces under oxic conditions, and the outlet Fe²⁺ concentration to estimate in-situ P releases associated with Fe (hydr)oxide reduction. Inferred P-removal rates were highest early in season 1 (k = 0.60 g P m³ d⁻¹; 75–100 % removal), declining significantly thereafter (k = 0.01 ± 0.02 g P m³ d⁻¹; ca. 3–67 % removal). These calculations suggest that microbiological P removal in DBRs can occur at comparable magnitudes to nitrate removal by denitrification, depending mainly on P availability and hydraulic retention efficiency.Publication Open Access Earth science field trips in the age of Covid-19: A case study of the SOSC223 virtual field trip : A thesis submitted in partial fulfilment of the requirements for the Degree of Master of Applied Science at Lincoln University(Lincoln University, 2024)Undergraduate earth science education emphasises the role of field trips in student learning and development. Thus, when the Covid-19 pandemic caused teaching to shift online, many educators developed replacement virtual field trips (VFTs) to deliver the field components of their courses. Such was the case with SOSC223, a second-year geomorphology course at Lincoln University, where the 2021 Covid-19 lockdown saw us replace the scheduled field trips with a VFT to the same locations. In this thesis, I investigate instructor and student experiences developing and learning from the SOSC223 VFT in order to evaluate what may have been lost or gained through the rapid shift from a traditional field trip (TFT) to virtual. I conducted semi-structured interviews with students and staff involved with the VFT and analysed the interview data for themes relating to 1) student and instructors’ perceptions of the VFT, 2) the strengths and weaknesses of the trip, and 3) how the VFT compared to a TFT. Thematic analysis of participants’ interview transcripts revealed different overall attitudes between the students and instructors. Instructors' reflections heavily featured the limitations and frustrations of developing the trip during lockdown. They felt the VFT was an adequate resource given the circumstance yet nevertheless saw potential benefits to VFTs as a whole. Students were apprehensive at the outset of the VFT but appreciated having the computerised replacement to the TFTs. Although most would have preferred attending a TFT, they felt the VFT benefitted their learning given the circumstances. The weaknesses of the VFT included its lack of easy interpersonal interaction, its reliance on technology like fast computers and stable internet, and the resourcing requirements to integrate multimedia and scaffold the content of the trip. Despite these challenges, the flexibility and repeatability of the VFT benefitted all participants, and the trip demonstrated clear potential for well-designed interactive multimedia to facilitate students' visual connection to place and ability to visualise complex processes. The SOSC223 VFT differed from TFTs in the logistical constraints and affordances of each and how the mode of delivery impacted students' social and physical immersion within the learning experience. Through conducting this research, it became clear that VFTs can add value to course design when thoroughly resourced and thoughtfully integrated. Whether they are used to augment or replace TFTs or incorporated into a course as standalone activities, VFTs should be designed in a way that builds on their flexibility and repeatability, minimises the impact of their lack of sociality, and builds visual connection through well-resourced, well-integrated multimedia.Item Open Access The effects of soil acidity and aluminium on the root systems and shoot growth of Lotus pedunculatus and Lupinus polyphyllus(Multidisciplinary Digital Publishing Institute (MDPI), 2024-08)Lotus pedunculatus (lotus) and Lupinus polyphyllus (Russell lupin) persist in the upland grasslands of New Zealand, where soil acidity and associated aluminium (Al) toxicity impede conventional pasture legumes. This experiment investigated the response of lotus and Russell lupin to soil acidity and Al. The species were sown in 20 cm tall 1.2 L pots of acidic upland soil. A mass of 4.5 or 6.7 g lime (CaCO₃)/L was added to either the top or bottom or both soil horizons (0–9 cm and 9–18 cm), resulting in six treatments across six randomised blocks in a glasshouse. The soil pH was 4.4, 4.9, and 5.4; the exchangeable Al concentrations were 24, 2.5, and 1.5 mg/kg for 0, 4.5, and 6.7 g lime/L. At 16 weeks post-sowing, the plants were divided into shoots and roots at 0–9 cm and 9–18 cm. Root morphology, shoot and root dry matter (DM), shoot nitrogen (N), and nodulation were measured. The total plant DM and shoot-to-root DM ratio were higher, and the shoot %N was lower for the lotus plants than the Russell lupin plants for the various lime rates (13.2 vs. 2.9 g plant‾¹, 5.6 vs. 1.6, and 2.4 vs. 3.3%, p < 0.05). No response to lime in terms of total DM or total root morphology parameters was exhibited in either species (p > 0.05). Root morphology adjustments in response to acidity between soil horizons were not observed. The results indicated that lotus and Russell lupin are tolerant to high soil acidity (pH 4.4–5.4) and exchangeable Al (1.5–24 mg kg‾¹), highlighting their considerable adaptation to grasslands with acidic soils.Item Open Access Model simplification to simulate groundwater recharge from a perched gravel-bed river(Elsevier, 2024-11)Gravel-bed rivers are an important source of groundwater recharge in some regions of the world. Their interactions with groundwater are complex and highly variable in space and time, with considerable water storage in the riverbed sediments. In losing river sections, where most of the groundwater recharge occurs, the river can be separated from the regional groundwater system by an unsaturated zone (i.e., perched). The complexity of groundwater–surface water interactions in these environments calls for the use of 3D fully integrated hydrological models to represent them, but their computational intensity limits their practicality for parameter inference, uncertainty quantification and regional scale problems. On the other hand, the simple groundwater–surface water exchange functions currently implemented in regional scale groundwater models are not suited to represent complex gravel-bed river systems such as braided rivers. There is therefore a need for developing groundwater–surface water exchange functions tailored to gravel-bed rivers that can be used in regional scale models. To address this issue, we developed a model simplification framework that combines a 3D integrated surface and subsurface hydrological model, a 2D cross-sectional river-aquifer model and a 1D conductance-based analytical model. We aim at broadly simplifying the 3D model while ensuring the appropriate simulation of groundwater recharge. We demonstrate our modelling approach on the Selwyn River (New Zealand) using piezometric data and groundwater recharge estimates derived from field observations and satellite imagery. Our results indicates that groundwater recharge from this river can be simulated using a simple 1D analytical model, which can easily be implemented in regional groundwater models (e.g., MODFLOW models). However, to represent properly the time variability of groundwater recharge, it is essential to use the groundwater level in the shallow aquifer associated with the river as input to the regional groundwater model. Our approach is generally transferable to other gravel-bed rivers but requires some observations of river losses for proper calibration.Item Open Access Probing biological nitrogen fixation in legumes using Raman spectroscopy(MDPI, 2024-08)Biological nitrogen fixation (BNF) by symbiotic bacteria plays a vital role in sustainable agriculture. However, current quantification methods are often expensive and impractical. This study explores the potential of Raman spectroscopy, a non-invasive technique, for rapid assessment of BNF activity in soybeans. Raman spectra were obtained from soybean plants grown with and without rhizobia bacteria to identify spectral signatures associated with BNF. δN¹⁵ isotope ratio mass spectrometry (IRMS) was used to determine actual BNF percentages. Partial least squares regression (PLSR) was employed to develop a model for BNF quantification based on Raman spectra. The model explained 80% of the variation in BNF activity. To enhance the model’s specificity for BNF detection regardless of nitrogen availability, a subsequent elastic net (Enet) regularisation strategy was implemented. This approach provided insights into key wavenumbers and biochemicals associated with BNF in soybeans.
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