title: Phosphorus and arsenic distributions in a seasonally-stratified, iron- and manganese-rich lake: microbiological and geochemical controls

authors: Hartland, Adam

abstract: Seasonal stratification in temperate lakes greater than a few metres deep provides conditions amenable to pronounced vertical zonation of redox chemistry. Such changes are particularly evident in eutrophic systems where high phytoplankton biomass often leads to seasonally-established anoxic hypolimnia and profound changes in geochemical conditions. In this study, we investigated the behaviour of trace elements in the water column of a seasonally-stratified, eutrophic lake. Two consecutive years of data from Lake Ngapouri, North Island, New Zealand, demonstrate the occurrence of highly correlated profiles of phosphorus (P), arsenic (As), iron (Fe) and manganese (Mn), all of which increased in concentration by 1-2 orders of magnitude within the anoxic hypolimnion. Stoichiometric and mass-balance considerations demonstrate that increases in alkalinity in hypolimnetic waters were consistent with observed changes in sulfate, Fe and Mn concentrations with depth, corresponding to dissimilatory reduction of sulfate, Fe(III) and Mn(IV) hydroxides. Thermodynamic constraints on Fe, Mn and Al solubility indicate that amorphous Fe(III), Mn(IV) hydroxides most probably controlled Fe and Mn in the surface mixed layer (~0 to 8 m) while Al(III) hydroxides were supersaturated throughout the entire system. Surface complexation modelling indicated that iron hydroxides (HFO) potentially dominated As speciation in the lake. It is likely that other colloidal phases such as allophanic clays also limited HPO42- activity, reducing competition for HAsO42- adsorption to iron hydroxides. This research highlights the coupling of P, As, Fe and Mn in Lake Ngapouri, and the apparent role of multiple colloidal phases in affecting P and As activity within overarching microbiological and geochemical processes.

text: Phosphorus and arsenic distributions in a seasonally-stratified, iron- and manganese-rich lake: microbiological and geochemical controls Seasonal stratification in temperate lakes greater than a few metres deep provides conditions amenable to pronounced vertical zonation of redox chemistry. Such changes are particularly evident in eutrophic systems where high phytoplankton biomass often leads to seasonally-established anoxic hypolimnia and profound changes in geochemical conditions. In this study, we investigated the behaviour of trace elements in the water column of a seasonally-stratified, eutrophic lake. Two consecutive years of data from Lake Ngapouri, North Island, New Zealand, demonstrate the occurrence of highly correlated profiles of phosphorus (P), arsenic (As), iron (Fe) and manganese (Mn), all of which increased in concentration by 1-2 orders of magnitude within the anoxic hypolimnion. Stoichiometric and mass-balance considerations demonstrate that increases in alkalinity in hypolimnetic waters were consistent with observed changes in sulfate, Fe and Mn concentrations with depth, corresponding to dissimilatory reduction of sulfate, Fe(III) and Mn(IV) hydroxides. Thermodynamic constraints on Fe, Mn and Al solubility indicate that amorphous Fe(III), Mn(IV) hydroxides most probably controlled Fe and Mn in the surface mixed layer (~0 to 8 m) while Al(III) hydroxides were supersaturated throughout the entire system. Surface complexation modelling indicated that iron hydroxides (HFO) potentially dominated As speciation in the lake. It is likely that other colloidal phases such as allophanic clays also limited HPO42- activity, reducing competition for HAsO42- adsorption to iron hydroxides. This research highlights the coupling of P, As, Fe and Mn in Lake Ngapouri, and the apparent role of multiple colloidal phases in affecting P and As activity within overarching microbiological and geochemical processes.

year: 2015

title: Testing the synchroneity of pollen signals using tephrostratigraphy

authors: Newnham, Rewi M.

subjects: pollen signals

abstract: Since the advent of radiocarbon dating, the concept of synchronous pollen-vegetation events extending across broad regions such as the British Isles, which had emerged from earlier pollen-stratigraphic studies, has been largely refuted. Nevertheless the assumption that pollen profiles within a geographically coherent area should exhibit broadly comparable and synchronous pollen signals still holds currency among some palynologists. This assumption is tested here by comparing pollen spectra between lateglacial and postglacial sites in northern New Zealand, until recently unaffected by human activity, where independent correlations are obtained by tephrochronology. At sites of similar size, morphology, and depositional environment within the same phytogeomorphic region, it is possible to achieve accurate palynological correlations, provided local taxa and those representing ecologically disparate source species are omitted from the pollen datasets. However, anomalous correlations may still occur and are more likely when sites with different depositional environments or at greater distances are compared. These results suggest that the concept of synchronous pollen signals, even between nearby sites with similar depositional setting, is not universally applicable and it is possible that erroneous palynostratigraphic correlations have been made in the past.

text: Testing the synchroneity of pollen signals using tephrostratigraphy Since the advent of radiocarbon dating, the concept of synchronous pollen-vegetation events extending across broad regions such as the British Isles, which had emerged from earlier pollen-stratigraphic studies, has been largely refuted. Nevertheless the assumption that pollen profiles within a geographically coherent area should exhibit broadly comparable and synchronous pollen signals still holds currency among some palynologists. This assumption is tested here by comparing pollen spectra between lateglacial and postglacial sites in northern New Zealand, until recently unaffected by human activity, where independent correlations are obtained by tephrochronology. At sites of similar size, morphology, and depositional environment within the same phytogeomorphic region, it is possible to achieve accurate palynological correlations, provided local taxa and those representing ecologically disparate source species are omitted from the pollen datasets. However, anomalous correlations may still occur and are more likely when sites with different depositional environments or at greater distances are compared. These results suggest that the concept of synchronous pollen signals, even between nearby sites with similar depositional setting, is not universally applicable and it is possible that erroneous palynostratigraphic correlations have been made in the past.

year: 1999

title: Viewing the world through a wider lens: Māori and council planning documents

authors: Kennedy, Nathan

subjects: New Zealand

abstract: My effort to convey an iwi perspective on environmental resource management - what we call kaitiakitanga – should highlight for new planners about to enter the profession that the environmental perspectives of hapū  and iwi (which are provided for in the RMA), are currently not well covered in either mainstream local government planning or education.

text: Viewing the world through a wider lens: Māori and council planning documents My effort to convey an iwi perspective on environmental resource management - what we call kaitiakitanga – should highlight for new planners about to enter the profession that the environmental perspectives of hapū  and iwi (which are provided for in the RMA), are currently not well covered in either mainstream local government planning or education.

year: 2008-07-30