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: Browsing tree structures

authors: Apperley, Mark

subjects: computer science

abstract: Graphic representations of tree structures are notoriously difficult to create, display, and interpret, particularly when the volume of information they contain, and hence the number of nodes, is large. The problem of interactively browsing information held in tree structures is examined, and the implementation of an innovative tree browser described. This browser is based on distortion-oriented display techniques and intuitive direct manipulation interaction. The tree layout is automatically generated, but the location and extent of detail shown is controlled by the user. It is suggested that these techniques could be extended to the browsing of more general networks.

text: Browsing tree structures Graphic representations of tree structures are notoriously difficult to create, display, and interpret, particularly when the volume of information they contain, and hence the number of nodes, is large. The problem of interactively browsing information held in tree structures is examined, and the implementation of an innovative tree browser described. This browser is based on distortion-oriented display techniques and intuitive direct manipulation interaction. The tree layout is automatically generated, but the location and extent of detail shown is controlled by the user. It is suggested that these techniques could be extended to the browsing of more general networks.

year: 1999-05

title: Traittore; Traduttore: Cultural integrity and translation involving Maori and other indigenous languages

authors: Roa, Tom

subjects: Ethics of translation

abstract: Traittore; Traduttore is Italian for Traitor; Translator. I argue here that translation from or into an indigenous language such as Māori is always, whatever the content and function of the source text, a political act and that, therefore, a Code of Ethics grounded in indigenous perspectives is essential if the ever-present danger of cultural betrayal is to be avoided.

text: Traittore; Traduttore: Cultural integrity and translation involving Maori and other indigenous languages Traittore; Traduttore is Italian for Traitor; Translator. I argue here that translation from or into an indigenous language such as Māori is always, whatever the content and function of the source text, a political act and that, therefore, a Code of Ethics grounded in indigenous perspectives is essential if the ever-present danger of cultural betrayal is to be avoided.

year: 2004