title: The relative importance of water motion on nitrogen uptake by the subtidal macroalga adamsiella chauvinii (rhodophyta) in winter and summer

authors: Kregting, Louise T.

subjects: Adamsiella chauvinii

abstract: The influence of seawater velocity (1.5–12 cm • s⁻¹) on inorganic nitrogen (N) uptake by the soft-sediment perennial macroalga Adamsiella chauvinii (Harv.) L. E. Phillips et W. A. Nelson (Rhodophyta) was determined seasonally by measuring uptake rate in a laboratory flume. Regardless of N tissue content, water velocity had no influence on NO₃⁻ uptake in either winter or summer, indicating that NO₃⁻-uptake rate was biologically limited. However, when thalli were N limited, increasing water velocity increased NH₄⁺ uptake, suggesting that mass-transfer limitation of NH₄⁺ is likely during summer for natural populations. Uptake kinetics (Vmax, Ks) were similar among three populations of A. chauvinii at sites with different mean flow speeds; however, uptake rates of NO₃⁻ and NH₄⁺ were lower in summer (when N status was generally low) than in winter. Our results highlight how N uptake can be affected by seasonal changes in the physiology of a macroalga and that further investigation of N uptake of different macroalgae (red, brown, and green) during different seasons is important in determining the relative influence of water velocity on nutrient uptake.

text: The relative importance of water motion on nitrogen uptake by the subtidal macroalga adamsiella chauvinii (rhodophyta) in winter and summer The influence of seawater velocity (1.5–12 cm • s⁻¹) on inorganic nitrogen (N) uptake by the soft-sediment perennial macroalga Adamsiella chauvinii (Harv.) L. E. Phillips et W. A. Nelson (Rhodophyta) was determined seasonally by measuring uptake rate in a laboratory flume. Regardless of N tissue content, water velocity had no influence on NO₃⁻ uptake in either winter or summer, indicating that NO₃⁻-uptake rate was biologically limited. However, when thalli were N limited, increasing water velocity increased NH₄⁺ uptake, suggesting that mass-transfer limitation of NH₄⁺ is likely during summer for natural populations. Uptake kinetics (Vmax, Ks) were similar among three populations of A. chauvinii at sites with different mean flow speeds; however, uptake rates of NO₃⁻ and NH₄⁺ were lower in summer (when N status was generally low) than in winter. Our results highlight how N uptake can be affected by seasonal changes in the physiology of a macroalga and that further investigation of N uptake of different macroalgae (red, brown, and green) during different seasons is important in determining the relative influence of water velocity on nutrient uptake.

year: 2008

title: Inflow reconnection solutions in incompressible visco-resistive plasmas

authors: Craig, Ian J.D.

subjects: magnetic reconnection

abstract: The development of a visco-resistive length scale for the thickness of a reconnecting current sheet would have significant consequences for the physics of magnetic reconnection in solar flares. In this paper, planar magnetic reconnection in an incompressible visco-resistive plasma is investigated analytically and numerically. Relaxation simulations are performed in an "open" geometry that allows material to enter and exit the reconnection volume. Solutions of two types are identified depending on the strength of the external flow that drives the reconnection. For sufficiently strong flows separate resistive and viscous layers develop in the reconnection region. In this case merging rates are found to be largely independent of viscosity. However, when the flow is too weak to produce a localized current layer, an equilibrium lacking any small-scale structure is obtained. The central conclusion is that neither of these steady-state solutions provide evidence of a visco-resistive length scale.

text: Inflow reconnection solutions in incompressible visco-resistive plasmas The development of a visco-resistive length scale for the thickness of a reconnecting current sheet would have significant consequences for the physics of magnetic reconnection in solar flares. In this paper, planar magnetic reconnection in an incompressible visco-resistive plasma is investigated analytically and numerically. Relaxation simulations are performed in an "open" geometry that allows material to enter and exit the reconnection volume. Solutions of two types are identified depending on the strength of the external flow that drives the reconnection. For sufficiently strong flows separate resistive and viscous layers develop in the reconnection region. In this case merging rates are found to be largely independent of viscosity. However, when the flow is too weak to produce a localized current layer, an equilibrium lacking any small-scale structure is obtained. The central conclusion is that neither of these steady-state solutions provide evidence of a visco-resistive length scale.

year: 2012

title: Spot sampling of nutrient concentrations in the Puarenga catchment, Rotorua

authors: Abell, Jonathan Michael

subjects: New Zealand

abstract: The Centre for Biodiversity and Ecology Research was approached by Tūhourangi Tribal Authority for assistance with measuring water quality in streams in the Puarenga Stream catchment. Water sampling was subsequently undertaken on 18 July 2011 and samples were analysed to determine concentrations of total and dissolved fractions of nitrogen and phosphorus. 
Nitrogen and phosphorus are both essential plant nutrients which, when present in excess, can cause eutrophication and associated water quality decline of freshwaters. High concentrations of dissolved forms of nitrogen can also be toxic to aquatic organisms. Excessive nitrogen and phosphorus concentrations are typically the result of pollution due to human activities, although groundwater in the Central Volcanic Plateau region can have elevated concentrations of phosphorus arising from natural geological sources.
This report summarises the methods used, presents the results and places measured concentrations in context by drawing comparisons with both guideline and regional mean values.

text: Spot sampling of nutrient concentrations in the Puarenga catchment, Rotorua The Centre for Biodiversity and Ecology Research was approached by Tūhourangi Tribal Authority for assistance with measuring water quality in streams in the Puarenga Stream catchment. Water sampling was subsequently undertaken on 18 July 2011 and samples were analysed to determine concentrations of total and dissolved fractions of nitrogen and phosphorus. 
Nitrogen and phosphorus are both essential plant nutrients which, when present in excess, can cause eutrophication and associated water quality decline of freshwaters. High concentrations of dissolved forms of nitrogen can also be toxic to aquatic organisms. Excessive nitrogen and phosphorus concentrations are typically the result of pollution due to human activities, although groundwater in the Central Volcanic Plateau region can have elevated concentrations of phosphorus arising from natural geological sources.
This report summarises the methods used, presents the results and places measured concentrations in context by drawing comparisons with both guideline and regional mean values.

year: 2011-09