title: Modelling the relative importance of internal and external nutrient loads on water column nutrient concentrations and phytoplankton biomass in a shallow polymictic lake

authors: Burger, David F.

subjects: lake management

abstract: Lake Rotorua is a large (area 79 km²), shallow (mean depth 10.8 m), polymictic lake in central North Island, New Zealand. The lake is eutrophic, with a mean external aerial load of 18.5 mg m⁻² d⁻¹ for total nitrogen and 1.2 mg m⁻² d⁻¹ for total phosphorus. Blooms of cyanobacteria and occasional anoxia of bottom waters occur during summer (December–March). We used a vertically resolved water quality model, DYRESM–CAEDYM, to examine the relative importance of internal and external nutrient inputs on water column nutrient concentrations and phytoplankton biomass, with particular emphasis on cyanobacteria. External nutrient loads associated with nine major inflows to the lake and three additional inflows representing smaller geothermal and coldwater flows and residual flows, were represented as inputs to the model. Other forcing inputs to the model included local meteorological data, discharge from the only outflow, the Ohau Channel, and measured rates of sediment nutrient release obtained from benthic chamber deployments which were used to prescribe ranges of sediment nutrient release that were simulated dynamically within the model. Profiles of water column nutrient concentrations, surface chlorophyll a concentrations and continuous temperature and dissolved oxygen measurements were used to validate the model. Simulated water column temperature and soluble reactive phosphorus (SRP) and ammonium (NH4) concentrations closely matched field measurements, and captured the timing and duration of stratification events as well as subsequent changes in bottom water nutrient concentrations. Surface water concentrations of chlorophyll a were also similar between simulated and observed data. Model simulations indicate that reductions in sediment nutrient fluxes would be more effective in reducing cyanobacterial biomass than similar proportional reductions in catchment fluxes, due to the coincidence of large sediment nutrient release events with high cyanobacterial biomass. This finding indicates that only a significant and prolonged reduction in external loads, which in turn reduces internal loads, will ultimately reduce cyanobacterial biomass in Lake Rotorua.

text: Modelling the relative importance of internal and external nutrient loads on water column nutrient concentrations and phytoplankton biomass in a shallow polymictic lake Lake Rotorua is a large (area 79 km²), shallow (mean depth 10.8 m), polymictic lake in central North Island, New Zealand. The lake is eutrophic, with a mean external aerial load of 18.5 mg m⁻² d⁻¹ for total nitrogen and 1.2 mg m⁻² d⁻¹ for total phosphorus. Blooms of cyanobacteria and occasional anoxia of bottom waters occur during summer (December–March). We used a vertically resolved water quality model, DYRESM–CAEDYM, to examine the relative importance of internal and external nutrient inputs on water column nutrient concentrations and phytoplankton biomass, with particular emphasis on cyanobacteria. External nutrient loads associated with nine major inflows to the lake and three additional inflows representing smaller geothermal and coldwater flows and residual flows, were represented as inputs to the model. Other forcing inputs to the model included local meteorological data, discharge from the only outflow, the Ohau Channel, and measured rates of sediment nutrient release obtained from benthic chamber deployments which were used to prescribe ranges of sediment nutrient release that were simulated dynamically within the model. Profiles of water column nutrient concentrations, surface chlorophyll a concentrations and continuous temperature and dissolved oxygen measurements were used to validate the model. Simulated water column temperature and soluble reactive phosphorus (SRP) and ammonium (NH4) concentrations closely matched field measurements, and captured the timing and duration of stratification events as well as subsequent changes in bottom water nutrient concentrations. Surface water concentrations of chlorophyll a were also similar between simulated and observed data. Model simulations indicate that reductions in sediment nutrient fluxes would be more effective in reducing cyanobacterial biomass than similar proportional reductions in catchment fluxes, due to the coincidence of large sediment nutrient release events with high cyanobacterial biomass. This finding indicates that only a significant and prolonged reduction in external loads, which in turn reduces internal loads, will ultimately reduce cyanobacterial biomass in Lake Rotorua.

year: 2008

title: Measuring and characterising inbound sessions in residential DSL traffic

authors: Alcock, Shane

subjects: DSL

abstract: It has been assumed that the need for successful NAT traversal discourages residential DSL users from running services or applications that require them to accept connections from remote hosts. However, there are now numerous approaches for NAT traversal but there have been no studies measuring the prevalence of DSL users accepting inbound sessions. This paper presents an analysis of TCP and UDP flows initiated by remote clients to a group of residential DSL users, using packet traces captured from a New Zealand ISP between 2009 and 2011. Our analysis reveals that over half of all measured users accepted at least one inbound TCP or UDP session. There was no dominant port being used to accept sessions and port usage was spread over thousands of different ports. Skype and BitTorrent were the most popular application protocols observed and had increased in popularity over time. We also report on the use of dual SYNs to perform TCP NAT traversal in our data.

text: Measuring and characterising inbound sessions in residential DSL traffic It has been assumed that the need for successful NAT traversal discourages residential DSL users from running services or applications that require them to accept connections from remote hosts. However, there are now numerous approaches for NAT traversal but there have been no studies measuring the prevalence of DSL users accepting inbound sessions. This paper presents an analysis of TCP and UDP flows initiated by remote clients to a group of residential DSL users, using packet traces captured from a New Zealand ISP between 2009 and 2011. Our analysis reveals that over half of all measured users accepted at least one inbound TCP or UDP session. There was no dominant port being used to accept sessions and port usage was spread over thousands of different ports. Skype and BitTorrent were the most popular application protocols observed and had increased in popularity over time. We also report on the use of dual SYNs to perform TCP NAT traversal in our data.

year: 2011

title: The use of Māori words in National Science Challenge online discourse

authors: Calude, Andreea S.

subjects: Maori loanwords

abstract: New Zealand English is well-known for its heavy borrowing of words from Māori. This lexical component, unique to New Zealand English alone has been studied intensely over the last 50 years, particularly in newspaper media. Current research suggests the use is still increasing today, primarily in Māori-related contexts. Here, we analyse a surprising and unexpected use of Māori loanwords in science digital discourse (neither genre being previously investigated), where we discover a strong presence of Māori borrowings in National Science Challenge website and Twitter content. Using corpus linguistics methods, we argue that the use of Māori loanwords in this genre functions as a national identity building tool, used by various authors to signal that the ‘challenges’ the country faces are uniquely New Zealand’s ‘challenges’.

text: The use of Māori words in National Science Challenge online discourse New Zealand English is well-known for its heavy borrowing of words from Māori. This lexical component, unique to New Zealand English alone has been studied intensely over the last 50 years, particularly in newspaper media. Current research suggests the use is still increasing today, primarily in Māori-related contexts. Here, we analyse a surprising and unexpected use of Māori loanwords in science digital discourse (neither genre being previously investigated), where we discover a strong presence of Māori borrowings in National Science Challenge website and Twitter content. Using corpus linguistics methods, we argue that the use of Māori loanwords in this genre functions as a national identity building tool, used by various authors to signal that the ‘challenges’ the country faces are uniquely New Zealand’s ‘challenges’.

year: 2019