title: The changing face of Lake Okataina’s ‘phosphorus scape’: Who is the culprit?

authors: Kpodonu, Theodore

abstract: Lake sediments contain a great wealth of data on biogeochemical and limnological processes of historical importance, which can be used to interpret natural ecosystem dynamics, and climatic and anthropogenic impacts. In this study, this information was used to understand the dynamics of phosphorus speciation in deep Lake Okataina, to assist with understanding how changes in the catchment influence lake productivity. A 49-cm sediment core was retrieved from Lake Okataina and its depositional history was dated using 210Pb and tephra chronology. Amongst New Zealand lakes, Okataina may be considered close to a ‘reference’ lake, with 89% native forest and without a significant change in its land use in the past c. 800 years. However, perturbations to the lake during this time may be due to expanding populations of invasive terrestrial mammals, earthquakes, volcanic eruptions and tree felling, which may alter the geochemistry of the soils in the catchment, composition of runoff and, ultimately, the composition of the bottom sediments of the lake. We hypothesised that changes in soil phosphorus geochemistry in the catchment will result in a changing phosphorus species in the lake sediments.

text: The changing face of Lake Okataina’s ‘phosphorus scape’: Who is the culprit? Lake sediments contain a great wealth of data on biogeochemical and limnological processes of historical importance, which can be used to interpret natural ecosystem dynamics, and climatic and anthropogenic impacts. In this study, this information was used to understand the dynamics of phosphorus speciation in deep Lake Okataina, to assist with understanding how changes in the catchment influence lake productivity. A 49-cm sediment core was retrieved from Lake Okataina and its depositional history was dated using 210Pb and tephra chronology. Amongst New Zealand lakes, Okataina may be considered close to a ‘reference’ lake, with 89% native forest and without a significant change in its land use in the past c. 800 years. However, perturbations to the lake during this time may be due to expanding populations of invasive terrestrial mammals, earthquakes, volcanic eruptions and tree felling, which may alter the geochemistry of the soils in the catchment, composition of runoff and, ultimately, the composition of the bottom sediments of the lake. We hypothesised that changes in soil phosphorus geochemistry in the catchment will result in a changing phosphorus species in the lake sediments.

year: 2015

title: Investigating subantarctic ¹⁴C ages of different peat components: site and sample selection for developing robust age models in dynamic landscapes

authors: Thomas, Zoë

subjects: Science & Technology

abstract: Precise radiocarbon (¹⁴C) dating of sedimentary sequences is important for developing robust chronologies of environmental change, but sampling of suitable components can be challenging in highly dynamic landscapes. Here we investigate radiocarbon determinations of different peat size fractions from six peat sites, representing a range of geomorphological contexts on the South Atlantic subantarctic islands of the Falklands and South Georgia. To investigate the most suitable fraction for dating, 112 measurements were obtained from three components within selected horizons: a fine fraction <0.2 mm, a coarse fraction >0.2 mm, and bulk material. We find site selection is critical, with locations surrounded by high-ground and/or relatively slowly accumulating sites more susceptible to the translocation of older carbon. Importantly, in locations with reduced potential for redeposition of material, our results show that there is no significant or systematic difference between ages derived from bulk material, fine or coarse (plant macrofossil) material, providing confidence in the resulting age model. Crucially, in areas comprising complex terrain with extreme relief, we recommend dating macrofossils or bulk carbon rather than a fine fraction, or employing comprehensive dating of multiple sedimentary fractions to determine the most reliable fraction(s) for developing a robust chronological framework.

text: Investigating subantarctic ¹⁴C ages of different peat components: site and sample selection for developing robust age models in dynamic landscapes Precise radiocarbon (¹⁴C) dating of sedimentary sequences is important for developing robust chronologies of environmental change, but sampling of suitable components can be challenging in highly dynamic landscapes. Here we investigate radiocarbon determinations of different peat size fractions from six peat sites, representing a range of geomorphological contexts on the South Atlantic subantarctic islands of the Falklands and South Georgia. To investigate the most suitable fraction for dating, 112 measurements were obtained from three components within selected horizons: a fine fraction <0.2 mm, a coarse fraction >0.2 mm, and bulk material. We find site selection is critical, with locations surrounded by high-ground and/or relatively slowly accumulating sites more susceptible to the translocation of older carbon. Importantly, in locations with reduced potential for redeposition of material, our results show that there is no significant or systematic difference between ages derived from bulk material, fine or coarse (plant macrofossil) material, providing confidence in the resulting age model. Crucially, in areas comprising complex terrain with extreme relief, we recommend dating macrofossils or bulk carbon rather than a fine fraction, or employing comprehensive dating of multiple sedimentary fractions to determine the most reliable fraction(s) for developing a robust chronological framework.

year: 2019

title: Book review: Beyond the scene: Landscape and identity in Aotearoa New Zealand – Edited by Janet Stephenson, Mick Abbott and Jacinta Ruru

authors: Beattie, James John

subjects: book review

abstract: This article reviews the book: “Beyond the scene: Landscape and identity in Aotearoa New Zealand”, edited by Janet Stephenson, Mick Abbott and Jacinta Ruru.

text: Book review: Beyond the scene: Landscape and identity in Aotearoa New Zealand – Edited by Janet Stephenson, Mick Abbott and Jacinta Ruru This article reviews the book: “Beyond the scene: Landscape and identity in Aotearoa New Zealand”, edited by Janet Stephenson, Mick Abbott and Jacinta Ruru.

year: 2010-12