title: Surface elevation changes and sediment characteristics of intertidal surfaces undergoing mangrove expansion and mangrove removal, Waikaraka Estuary, Tauranga Harbour, New Zealand

authors: Stokes, Debra J.

subjects: New Zealand

abstract: Since the 1940s mangroves have expanded their areal coverage in many estuaries in the northern half of the North Island of New Zealand. The extent of mangrove colonization in Waikaraka Estuary, Tauranga Harbour, has been documented using photogrammetric analysis, and the impacts of subsequent mangrove removal are analysed. Surface elevation changes in response to mangrove removal are measured using RSETs (Rod Surface Elevation Table) and erosion pins, and sediment accumulation rates were calculated from sediment trap results. Temporal changes to surface sediment texture are analysed. Mangrove physiognomy is described from analysis of mean plant height, plant density and pneumatophore density. Plant heights reflect the shrubby growth form of mangroves growing toward their southern climatic limit, with mean plant heights under 1.5 m. Mangrove coverage has increased from approximately 16,000 m2 in 1943 to 115,000 m2 in 2003. Since May 2005, 9,600 m2 of mangrove vegetation has been removed from the estuary. For the monitoring period of March 2006 to March 2007, rates of surface elevation change in cleared areas ranged from - 9 mm to - 38 mm yr (mean -14 mm yr). Conversely, surface elevation under mangrove forest varied between sites, ranging from -5 mm to 14 mm yr (mean 3 mm yr). Results from RSETs and erosion pins and a coarsening of surface sediment texture at the cleared sites, is consistent with sediment release after mangrove removal.

text: Surface elevation changes and sediment characteristics of intertidal surfaces undergoing mangrove expansion and mangrove removal, Waikaraka Estuary, Tauranga Harbour, New Zealand Since the 1940s mangroves have expanded their areal coverage in many estuaries in the northern half of the North Island of New Zealand. The extent of mangrove colonization in Waikaraka Estuary, Tauranga Harbour, has been documented using photogrammetric analysis, and the impacts of subsequent mangrove removal are analysed. Surface elevation changes in response to mangrove removal are measured using RSETs (Rod Surface Elevation Table) and erosion pins, and sediment accumulation rates were calculated from sediment trap results. Temporal changes to surface sediment texture are analysed. Mangrove physiognomy is described from analysis of mean plant height, plant density and pneumatophore density. Plant heights reflect the shrubby growth form of mangroves growing toward their southern climatic limit, with mean plant heights under 1.5 m. Mangrove coverage has increased from approximately 16,000 m2 in 1943 to 115,000 m2 in 2003. Since May 2005, 9,600 m2 of mangrove vegetation has been removed from the estuary. For the monitoring period of March 2006 to March 2007, rates of surface elevation change in cleared areas ranged from - 9 mm to - 38 mm yr (mean -14 mm yr). Conversely, surface elevation under mangrove forest varied between sites, ranging from -5 mm to 14 mm yr (mean 3 mm yr). Results from RSETs and erosion pins and a coarsening of surface sediment texture at the cleared sites, is consistent with sediment release after mangrove removal.

year: 2009

title: Regulation of phosphorus bioavailability by iron nanoparticles in a monomictic lake

authors: Saeed, Huma

subjects: Science & Technology

abstract: Dissolved reactive phosphorous (DRP) in lake systems is conventionally considered to predominate over other dissolved P species, however, this view neglects an important set of interactions that occurs between P and reactive iron hydroxide surfaces. This study addresses the coupling of P with dispersed iron nanoparticles in lakes, an interaction that may fundamentally alter the bioavailability of P to phytoplankton. We used difusive gradients in thin flms (DGT) and ultrafltration to study Fe-P coupling in the water column of a monomictic lake over a hydrological year. Fe and P were predominantly colloidal (particle diameters>~5nm<~20nm) in both oxic epilimnetic and anaerobic hypolimnetic waters, but they were both DGT-labile under sub-oxic conditions, consistent with difusion and dissolution of Fe-and-P-bearing colloids within the DGT difusive gel. During peak stratifcation, increases in Fe and P bioavailability were spatially and temporally coincident with Fe nanoparticle dissolution and the formation of a deep chlorophyll maximum at 5–8m depth. These results provide a window into the coupling and decoupling of P with mobile iron colloids, with implications for our understanding of the behaviour of nutrients and their infuence on phytoplankton community dynamics.

text: Regulation of phosphorus bioavailability by iron nanoparticles in a monomictic lake Dissolved reactive phosphorous (DRP) in lake systems is conventionally considered to predominate over other dissolved P species, however, this view neglects an important set of interactions that occurs between P and reactive iron hydroxide surfaces. This study addresses the coupling of P with dispersed iron nanoparticles in lakes, an interaction that may fundamentally alter the bioavailability of P to phytoplankton. We used difusive gradients in thin flms (DGT) and ultrafltration to study Fe-P coupling in the water column of a monomictic lake over a hydrological year. Fe and P were predominantly colloidal (particle diameters>~5nm<~20nm) in both oxic epilimnetic and anaerobic hypolimnetic waters, but they were both DGT-labile under sub-oxic conditions, consistent with difusion and dissolution of Fe-and-P-bearing colloids within the DGT difusive gel. During peak stratifcation, increases in Fe and P bioavailability were spatially and temporally coincident with Fe nanoparticle dissolution and the formation of a deep chlorophyll maximum at 5–8m depth. These results provide a window into the coupling and decoupling of P with mobile iron colloids, with implications for our understanding of the behaviour of nutrients and their infuence on phytoplankton community dynamics.

year: 2018

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