title: Simulating discharge and pollutants from the Waipa Stream catchment under different irrigation scenarios using the SAWT model

authors: Me, Wang

abstract: The water quality of Lake Rotorua has declined over several decades due to increasing inputs of nitrogen (N) and phosphorus (P). Prior to 1991, the Rotorua City wastewater treatment plant was a significant contributor to this decline through direct discharge of treated municipal wastewater to the lake. In 1991 the Rotorua Lakes Council (RLC) halted wastewater discharge to Lake Rotorua and commenced land disposal of treated wastewater by spay irrigation to 193 ha of the Whakarewarewa Forest. It was intended that plant uptake and microbial denitrification would reduce N levels, and P would be removed through absorption and retention to clay soil particles. The aim was to reduce wastewater nutrient loads to the point that wastewater runoff entering the Waipa Stream, and ultimately Lake Rotorua, would have a minimal impact on the trophic state of Lake Rotorua.
Resource consent conditions for wastewater disposal to the Whakarewarewa Forest restricted total nitrogen (TN) and total phosphorus (TP) wastewater losses to the Waipa Stream to 30 tonnes yr⁻¹ and 3 tonnes yr⁻¹, respectively. Previous assessments of nutrient losses have indicated some non-compliance with the TN consent limit, there has also been an increase in TP loading to the Waipa Stream since 2002. These increases may be caused by a number of factors including the application rate of wastewater, increases in the nutrient load from non-irrigated areas within the catchment, forest operations not associated with wastewater irrigation and altered rainfall patterns. The Rotorua Lakes Council contracted the University of Waikato to provide an assessment of possible causes for the increased nutrient loading, and to investigate how varying the timing of wastewater irrigation regimes could affect nutrient loading to the Waipa Stream.
The Soil and Water Assessment Tool (SWAT) is a GIS based catchment model used to simulate water fluxes and contaminant transport. The model was parameterised using hydrological and water quality values from relevant literature, and values derived from model auto-calibration within fixed ranges using a Sequential Uncertainty Fitting (SUFI-2) procedure followed by manual adjustment. Model results showed a high correspondence (r > 0.8; p < 0.001) between measurements and simulations of discharge. However, the model underestimated several peaks of weekly mean TSS load during high rainfall events which were found to be related to harvesting of forest blocks. Underestimates of weekly mean TP peaks were also observed and appeared to be either a lagged response to high rainfall, high TP concentrations in the irrigated wastewater or harvesting of several forest blocks concurrently. Most peaks in hourly routing of NO₃-N and TN loads averaged to weekly time scale also corresponded to high rainfall as well as to high TN concentrations in the wastewater.
The effects of various wastewater irrigation scenarios on downstream water quality were also simulated using SWAT. Daily wastewater irrigation was the most effective scenario for reducing nutrient leaching and avoiding soil nutrient saturation when compared to weekly irrigation (i.e., identical total volume on a weekly basis). Cessation of irrigation on high rainfall days, with reassignment of the irrigation to the first subsequent low-rainfall day, produced unexpected small increases in annual TP (+5%) and TN loading (+2.5%). Simulations of increased area of irrigation or ceasing irrigation resulted in reductions of nutrient loads to the Waipa Stream.
These results indicate that harvesting of plantation forest blocks in the Waipa sub-catchment and wastewater irrigation during high rainfall were contributing to higher than estimated TSS and TP loading to the Waipa Stream. Modelling of variations in wastewater irrigation frequency showed that reductions in TP and TN loadings to the Waipa Stream could be achieved by switching to a programme of daily rather than weekly irrigation and avoidance of irrigation during or the day following heavy rainfall. These findings support the decision to switch irrigation frequency from weekly to daily and are likely to assist in reducing the impact of anthropogenic nutrient loading on Lake Rotorua.

text: Simulating discharge and pollutants from the Waipa Stream catchment under different irrigation scenarios using the SAWT model The water quality of Lake Rotorua has declined over several decades due to increasing inputs of nitrogen (N) and phosphorus (P). Prior to 1991, the Rotorua City wastewater treatment plant was a significant contributor to this decline through direct discharge of treated municipal wastewater to the lake. In 1991 the Rotorua Lakes Council (RLC) halted wastewater discharge to Lake Rotorua and commenced land disposal of treated wastewater by spay irrigation to 193 ha of the Whakarewarewa Forest. It was intended that plant uptake and microbial denitrification would reduce N levels, and P would be removed through absorption and retention to clay soil particles. The aim was to reduce wastewater nutrient loads to the point that wastewater runoff entering the Waipa Stream, and ultimately Lake Rotorua, would have a minimal impact on the trophic state of Lake Rotorua.
Resource consent conditions for wastewater disposal to the Whakarewarewa Forest restricted total nitrogen (TN) and total phosphorus (TP) wastewater losses to the Waipa Stream to 30 tonnes yr⁻¹ and 3 tonnes yr⁻¹, respectively. Previous assessments of nutrient losses have indicated some non-compliance with the TN consent limit, there has also been an increase in TP loading to the Waipa Stream since 2002. These increases may be caused by a number of factors including the application rate of wastewater, increases in the nutrient load from non-irrigated areas within the catchment, forest operations not associated with wastewater irrigation and altered rainfall patterns. The Rotorua Lakes Council contracted the University of Waikato to provide an assessment of possible causes for the increased nutrient loading, and to investigate how varying the timing of wastewater irrigation regimes could affect nutrient loading to the Waipa Stream.
The Soil and Water Assessment Tool (SWAT) is a GIS based catchment model used to simulate water fluxes and contaminant transport. The model was parameterised using hydrological and water quality values from relevant literature, and values derived from model auto-calibration within fixed ranges using a Sequential Uncertainty Fitting (SUFI-2) procedure followed by manual adjustment. Model results showed a high correspondence (r > 0.8; p < 0.001) between measurements and simulations of discharge. However, the model underestimated several peaks of weekly mean TSS load during high rainfall events which were found to be related to harvesting of forest blocks. Underestimates of weekly mean TP peaks were also observed and appeared to be either a lagged response to high rainfall, high TP concentrations in the irrigated wastewater or harvesting of several forest blocks concurrently. Most peaks in hourly routing of NO₃-N and TN loads averaged to weekly time scale also corresponded to high rainfall as well as to high TN concentrations in the wastewater.
The effects of various wastewater irrigation scenarios on downstream water quality were also simulated using SWAT. Daily wastewater irrigation was the most effective scenario for reducing nutrient leaching and avoiding soil nutrient saturation when compared to weekly irrigation (i.e., identical total volume on a weekly basis). Cessation of irrigation on high rainfall days, with reassignment of the irrigation to the first subsequent low-rainfall day, produced unexpected small increases in annual TP (+5%) and TN loading (+2.5%). Simulations of increased area of irrigation or ceasing irrigation resulted in reductions of nutrient loads to the Waipa Stream.
These results indicate that harvesting of plantation forest blocks in the Waipa sub-catchment and wastewater irrigation during high rainfall were contributing to higher than estimated TSS and TP loading to the Waipa Stream. Modelling of variations in wastewater irrigation frequency showed that reductions in TP and TN loadings to the Waipa Stream could be achieved by switching to a programme of daily rather than weekly irrigation and avoidance of irrigation during or the day following heavy rainfall. These findings support the decision to switch irrigation frequency from weekly to daily and are likely to assist in reducing the impact of anthropogenic nutrient loading on Lake Rotorua.

year: 2017

title: Bundle-driven move analysis: Sentence initial lexical bundles in PhD abstracts

authors: Li, Liang

abstract: Rhetorical moves are discoursal units that perform communicative functions in a given genre. They have been manually identified in many previous studies taking a corpus-based approach, and these studies have provided important contributions to discourse structure theories. However, manual analysis has restricted the scale and quantity of texts under investigation and the identification of moves is likely to be influenced by researchers' prior knowledge. In contrast, a corpus-driven approach, by applying automatic computational technology to process a large number of texts, possibly results in a better representation of the moves in a genre and minimises researcher bias in move identification. This study applies one typical corpus-driven approach, a bundle-driven approach, to analyse rhetorical moves of PhD abstracts, a move-intensive genre. The study focused on 5-word sentence initial bundles. Almost all the generated bundles could be identified as move indicators. The majority of the indicated moves aligned with the moves proposed for research article abstracts in previous studies, and one new move, Structure, was identified. This study indicates the potential of a bundle-driven approach in exploring rhetorical moves and in examining the linguistic features of moves by means of lexical bundles. Pedagogical implications for EAP writing are also suggested.

text: Bundle-driven move analysis: Sentence initial lexical bundles in PhD abstracts Rhetorical moves are discoursal units that perform communicative functions in a given genre. They have been manually identified in many previous studies taking a corpus-based approach, and these studies have provided important contributions to discourse structure theories. However, manual analysis has restricted the scale and quantity of texts under investigation and the identification of moves is likely to be influenced by researchers' prior knowledge. In contrast, a corpus-driven approach, by applying automatic computational technology to process a large number of texts, possibly results in a better representation of the moves in a genre and minimises researcher bias in move identification. This study applies one typical corpus-driven approach, a bundle-driven approach, to analyse rhetorical moves of PhD abstracts, a move-intensive genre. The study focused on 5-word sentence initial bundles. Almost all the generated bundles could be identified as move indicators. The majority of the indicated moves aligned with the moves proposed for research article abstracts in previous studies, and one new move, Structure, was identified. This study indicates the potential of a bundle-driven approach in exploring rhetorical moves and in examining the linguistic features of moves by means of lexical bundles. Pedagogical implications for EAP writing are also suggested.

year: 2020

title: Waitangi Soda Springs alum dosing – bioavailability of aluminium 2013

authors: Ling, Nicholas

abstract: Continuous alum dosing of the Waitangi Soda Springs at Lake Rotoehu commenced in 2010 to reduce inflows of dissolved reactive phosphorus to Lake Rotoehu. Analyses of bioaccumulation in the tissues of kōura and goldfish from Lake Rotoehu were undertaken on animals collected in September 2013 to determine the bioavailability and bioaccumulation of aluminium. Comparative analyses were undertaken on kōura and goldfish collected from Lakes Rotorua and Rotoiti. Lake Rotoehu kōura and goldfish showed slightly elevated aluminium concentrations in the gills indicating enhanced exposure to aluminium but little evidence for significant bioaccumulation in tissues.

text: Waitangi Soda Springs alum dosing – bioavailability of aluminium 2013 Continuous alum dosing of the Waitangi Soda Springs at Lake Rotoehu commenced in 2010 to reduce inflows of dissolved reactive phosphorus to Lake Rotoehu. Analyses of bioaccumulation in the tissues of kōura and goldfish from Lake Rotoehu were undertaken on animals collected in September 2013 to determine the bioavailability and bioaccumulation of aluminium. Comparative analyses were undertaken on kōura and goldfish collected from Lakes Rotorua and Rotoiti. Lake Rotoehu kōura and goldfish showed slightly elevated aluminium concentrations in the gills indicating enhanced exposure to aluminium but little evidence for significant bioaccumulation in tissues.

year: 2015