title: Pore water chemistry and early diagenesis in sediments of Lake Rotorua, New Zealand

authors: Motion, Olivia Jane

subjects: pore water

abstract: To gain an understanding of the transfer of nutrients and trace elements from sediment pore waters to surface waters of eutrophic Lake Rotorua and the early diagenetic processes controlling the transfer, pore water chemistry in the sediments of Lake Rotorua was investigated over a one year period in 2006 by collection of sediment cores on three occasions and deployment of pore water equilibrators on two occasions. Pore water concentrations of Fe2+, Mn2+, S, PO4, NH4, As, Cd, and Pb were analysed. Phosphate and ammonium fluxes to the water column from the sediments were calculated from measured concentration gradients by Fick's law of diffusion. Gas present in the sediments was analysed for composition, and source, and its ebullition rate measured.
Anaerobic oxidation of organic matter is indicated by negative Eh values. Sulfate reduction was indicated near the sediment-water interface and releases of Fe2+, Mn2+, PO4 and NH4 into the pore water from particulate material were associated with the reducing conditions. Peaks in concentration of nutrients and elements occurred at the sediment surface over summer and deeper in the pore water profile over the cooler months of May and September.
Sampling with peepers at fine scales immediately above the sediment-water interface indicated the presence of a nepheloid layer where elements are actively being recycled. Sulfate reduction appears to occur in the layer above the sediment-water interface, indicating that dissolved oxygen has already been reduced. Phosphorus is possibly being removed by iron and manganese oxide/hydroxide precipitation 5 to 15 cm above the sediment-water interface.
Pore water saturation calculations indicate that sulfides may be controlling concentrations of iron and possibly other metals in the pore water by formation of pyrite in the zone of sulfate reduction. Below the zone of sulfate reduction, siderite and vivianite may be precipitating and acting as an additional sink for iron and phosphorus.
ii
Nutrient release rates based on Fick's law of diffusion indicated 430 tonnes of dissolved phosphorus and 1150 tonnes of ammonium were released to Lake Rotorua's water column in 2006, suggesting nutrient release from the sediments is the dominant flux of nutrients to the water column of Lake Rotorua.
Methanogenesis, from acetate fermentation, occurs below the zone of sulfate reduction, where it becomes the dominant process in organic matter degradation. Ebullition of gas was measured at 126 ml m-2 d-1 and this gas was comprised dominantly of methane.
Possible remediation techniques that could reduce the internal load of nutrients released from the lake sediments include sediment removal by dredging or capping the sediments with an adsorbent or sealing layer. Capping the sediments could be compromised by ebullition of gas that would disrupt the capped layer, opening up pathways that allow more readily for exchange between pore water nutrients and the water column. Dredging is likely to stimulate the ebullition of most of the trapped gas and result in a rapid efflux of much of the nutrient rich pore water into the lake, however dredging the top 10 to 20 cm of the sediments may partially reduce phosphorus in the pore waters but would not substantially reduce ammonium and fluxes would remain similar to current levels. Improving redox conditions in the sediments could reduce pyrite formation improving phosphorus binding with iron.

text: Pore water chemistry and early diagenesis in sediments of Lake Rotorua, New Zealand To gain an understanding of the transfer of nutrients and trace elements from sediment pore waters to surface waters of eutrophic Lake Rotorua and the early diagenetic processes controlling the transfer, pore water chemistry in the sediments of Lake Rotorua was investigated over a one year period in 2006 by collection of sediment cores on three occasions and deployment of pore water equilibrators on two occasions. Pore water concentrations of Fe2+, Mn2+, S, PO4, NH4, As, Cd, and Pb were analysed. Phosphate and ammonium fluxes to the water column from the sediments were calculated from measured concentration gradients by Fick's law of diffusion. Gas present in the sediments was analysed for composition, and source, and its ebullition rate measured.
Anaerobic oxidation of organic matter is indicated by negative Eh values. Sulfate reduction was indicated near the sediment-water interface and releases of Fe2+, Mn2+, PO4 and NH4 into the pore water from particulate material were associated with the reducing conditions. Peaks in concentration of nutrients and elements occurred at the sediment surface over summer and deeper in the pore water profile over the cooler months of May and September.
Sampling with peepers at fine scales immediately above the sediment-water interface indicated the presence of a nepheloid layer where elements are actively being recycled. Sulfate reduction appears to occur in the layer above the sediment-water interface, indicating that dissolved oxygen has already been reduced. Phosphorus is possibly being removed by iron and manganese oxide/hydroxide precipitation 5 to 15 cm above the sediment-water interface.
Pore water saturation calculations indicate that sulfides may be controlling concentrations of iron and possibly other metals in the pore water by formation of pyrite in the zone of sulfate reduction. Below the zone of sulfate reduction, siderite and vivianite may be precipitating and acting as an additional sink for iron and phosphorus.
ii
Nutrient release rates based on Fick's law of diffusion indicated 430 tonnes of dissolved phosphorus and 1150 tonnes of ammonium were released to Lake Rotorua's water column in 2006, suggesting nutrient release from the sediments is the dominant flux of nutrients to the water column of Lake Rotorua.
Methanogenesis, from acetate fermentation, occurs below the zone of sulfate reduction, where it becomes the dominant process in organic matter degradation. Ebullition of gas was measured at 126 ml m-2 d-1 and this gas was comprised dominantly of methane.
Possible remediation techniques that could reduce the internal load of nutrients released from the lake sediments include sediment removal by dredging or capping the sediments with an adsorbent or sealing layer. Capping the sediments could be compromised by ebullition of gas that would disrupt the capped layer, opening up pathways that allow more readily for exchange between pore water nutrients and the water column. Dredging is likely to stimulate the ebullition of most of the trapped gas and result in a rapid efflux of much of the nutrient rich pore water into the lake, however dredging the top 10 to 20 cm of the sediments may partially reduce phosphorus in the pore waters but would not substantially reduce ammonium and fluxes would remain similar to current levels. Improving redox conditions in the sediments could reduce pyrite formation improving phosphorus binding with iron.

year: 2007

title: To report or not to report? Understanding the impacts of reporting decisions for family and sexual violence in Aotearoa New Zealand

authors: Cording, Jacinta

abstract: Most victims of family violence (FV) and sexual violence (SV) do not report their criminal victimisation to police, but instead their experiences remain part of the ‘dark figure of crime’, or the proportion of actual crimes committed that remain officially unrecorded. The gap between victimisation and reported victimisation has a number of broad consequences for the policies and practices of government.
In this report we combine New Zealand Crime and Victims Survey (NZCVS) and other Integrated Data Infrastructure (IDI) data to consider two broad questions. First, what individual, community and offence-related factors predict non-reporting of FV and SV offences to Police (RQ1)? Second, is reporting or not associated with differences in wellbeing outcomes (RQ2)? Our analyses help to contextualise research and policy that relies on reported crime, and to identify areas where, as a result, reporting-associated policy responses may have potential shortcomings.

text: To report or not to report? Understanding the impacts of reporting decisions for family and sexual violence in Aotearoa New Zealand Most victims of family violence (FV) and sexual violence (SV) do not report their criminal victimisation to police, but instead their experiences remain part of the ‘dark figure of crime’, or the proportion of actual crimes committed that remain officially unrecorded. The gap between victimisation and reported victimisation has a number of broad consequences for the policies and practices of government.
In this report we combine New Zealand Crime and Victims Survey (NZCVS) and other Integrated Data Infrastructure (IDI) data to consider two broad questions. First, what individual, community and offence-related factors predict non-reporting of FV and SV offences to Police (RQ1)? Second, is reporting or not associated with differences in wellbeing outcomes (RQ2)? Our analyses help to contextualise research and policy that relies on reported crime, and to identify areas where, as a result, reporting-associated policy responses may have potential shortcomings.

year: 2025-04-02

title: The use of functionalised biochar to enhance phosphorus removal in woodchip bioreactors. The integration of mātauranga Māori to enhance the cultural aspects of woodchip bioreactors.

authors: Taoho, Brandon

subjects: Woodchip bioreactor

abstract: Nutrient pollution, resulting from excessive releases of nitrogen (N) and phosphorus (P) into waterways, poses a significant threat to aquatic ecosystems worldwide. Elevated nutrient levels can result in eutrophication, which can have detrimental effects on the health of waterbodies and their biota. Woodchip bioreactors are effective, edge-of-field technologies that can help mitigate nutrient pollution by lowering nutrient concentrations in agricultural drainage systems known to carry leached N and P into waterways. However, one limitation to their design is their ineffectiveness at removing P. The inclusion of functionalised biochar is one potential solution to enhance P removal in woodchip bioreactors. There is a growing need to mitigate nutrient pollution in New Zealand that does not depend on a western-centric perspective only. Integration of mātauranga Māori and western science into the design and operations of a woodchip bioreactor is one approach to incorporate both knowledge systems to the goal of mitigating nutrient pollution. In this dissertation, a column experiment was used to compare the P removal efficiencies of two treatments of functionalised biochar, and one treatment of woodchips when subjected to stream water spiked with P. Subsequently, a single phosphate extraction was done to determine the phosphate absorption capacities of each treatment. The results showed that the two functionalised biochar treatments had the highest efficacy in reducing P concentrations in the P-spiked stream water compared to the woodchip-only treatment. Both treatments also showed higher P absorption, evidenced from the Fe-P/Feox ratio, within the phosphate extraction experiment. A wānanga was organised at Matahuru Marae, Lake Waikare, to share mātauranga Māori on how to culturally enhance woodchip bioreactors from a Te Ao Māori perspective. Participants recommended that native woodchips be incorporated into woodchip bioreactors because of their inherent association to the land and people. Overall, the results implied that functionalised biochar is an effective solution to enhance P removal in woodchip bioreactors due to their biophysical properties to absorb and retain P. Secondly, incorporating native woodchips into woodchip bioreactors systems potentially offers a sustainable and culturally respected alternative to conventional wood chips, aligning with Māori values and tikanga

text: The use of functionalised biochar to enhance phosphorus removal in woodchip bioreactors. The integration of mātauranga Māori to enhance the cultural aspects of woodchip bioreactors. Nutrient pollution, resulting from excessive releases of nitrogen (N) and phosphorus (P) into waterways, poses a significant threat to aquatic ecosystems worldwide. Elevated nutrient levels can result in eutrophication, which can have detrimental effects on the health of waterbodies and their biota. Woodchip bioreactors are effective, edge-of-field technologies that can help mitigate nutrient pollution by lowering nutrient concentrations in agricultural drainage systems known to carry leached N and P into waterways. However, one limitation to their design is their ineffectiveness at removing P. The inclusion of functionalised biochar is one potential solution to enhance P removal in woodchip bioreactors. There is a growing need to mitigate nutrient pollution in New Zealand that does not depend on a western-centric perspective only. Integration of mātauranga Māori and western science into the design and operations of a woodchip bioreactor is one approach to incorporate both knowledge systems to the goal of mitigating nutrient pollution. In this dissertation, a column experiment was used to compare the P removal efficiencies of two treatments of functionalised biochar, and one treatment of woodchips when subjected to stream water spiked with P. Subsequently, a single phosphate extraction was done to determine the phosphate absorption capacities of each treatment. The results showed that the two functionalised biochar treatments had the highest efficacy in reducing P concentrations in the P-spiked stream water compared to the woodchip-only treatment. Both treatments also showed higher P absorption, evidenced from the Fe-P/Feox ratio, within the phosphate extraction experiment. A wānanga was organised at Matahuru Marae, Lake Waikare, to share mātauranga Māori on how to culturally enhance woodchip bioreactors from a Te Ao Māori perspective. Participants recommended that native woodchips be incorporated into woodchip bioreactors because of their inherent association to the land and people. Overall, the results implied that functionalised biochar is an effective solution to enhance P removal in woodchip bioreactors due to their biophysical properties to absorb and retain P. Secondly, incorporating native woodchips into woodchip bioreactors systems potentially offers a sustainable and culturally respected alternative to conventional wood chips, aligning with Māori values and tikanga

year: 2023