title: Density and habitat dependent effects of crab burrows on sediment erodibility

authors: Needham, Hazel Rosemary

subjects: Annular flume

abstract: Despite biological interactions being highlighted as a key process in determining particle fluxes, relatively few studies have attempted to establish the links between burrow building bioturbators and sediment stability. The mud crab Austrohelice crassa, is a key burrowing species in New Zealand estuaries that has shown context-specific interactions with its environment. Here we use annular flumes to test if sediment stability and erodibility were altered as a function of A. crassa burrow density in two contrasting sediment types: a cohesive sandy-mud and a non-cohesive sand. Three burrow density treatments (n=3) reflecting the natural density range in each sediment type (sand; 0-100m-2, sandy-mud; 0-400m-2), were collected from the field and subjected to sequential increases in water flow velocity. Flow profiles were measured and bed shear stresses were calculated for each treatment. Increasing burrow density reduced the mass of sediment eroded at 0.35ms-1(ME-35, gm-2) in cohesive sandy-mud, while in non-cohesive sand a unimodal pattern was observed, whereby erosion rates were greatest at the lowest burrow density (19m-2). In the cohesive sediment, the linear decrease in erodibility with increasing burrow density was likely affected by the sluicing of fine particulates (silt-clay) from burrows when the tide was out creating both a smoothing and consolidating effect on the sediment surface. A reduction in flow velocity due to the increased presence of surficial pellets and greater trapping of bedload transported material was attributed to the reduction in the mass of sediment eroded in sand at high burrow densities. This study demonstrates that burrow builders influence sediment transport by more than just vertical particle mixing and highlights some of the complexities of small-scale sediment processes. Knowledge of different organism-sediment interactions among sediment types and spatial scales will enhance the accuracy of sediment transport models

text: Density and habitat dependent effects of crab burrows on sediment erodibility Despite biological interactions being highlighted as a key process in determining particle fluxes, relatively few studies have attempted to establish the links between burrow building bioturbators and sediment stability. The mud crab Austrohelice crassa, is a key burrowing species in New Zealand estuaries that has shown context-specific interactions with its environment. Here we use annular flumes to test if sediment stability and erodibility were altered as a function of A. crassa burrow density in two contrasting sediment types: a cohesive sandy-mud and a non-cohesive sand. Three burrow density treatments (n=3) reflecting the natural density range in each sediment type (sand; 0-100m-2, sandy-mud; 0-400m-2), were collected from the field and subjected to sequential increases in water flow velocity. Flow profiles were measured and bed shear stresses were calculated for each treatment. Increasing burrow density reduced the mass of sediment eroded at 0.35ms-1(ME-35, gm-2) in cohesive sandy-mud, while in non-cohesive sand a unimodal pattern was observed, whereby erosion rates were greatest at the lowest burrow density (19m-2). In the cohesive sediment, the linear decrease in erodibility with increasing burrow density was likely affected by the sluicing of fine particulates (silt-clay) from burrows when the tide was out creating both a smoothing and consolidating effect on the sediment surface. A reduction in flow velocity due to the increased presence of surficial pellets and greater trapping of bedload transported material was attributed to the reduction in the mass of sediment eroded in sand at high burrow densities. This study demonstrates that burrow builders influence sediment transport by more than just vertical particle mixing and highlights some of the complexities of small-scale sediment processes. Knowledge of different organism-sediment interactions among sediment types and spatial scales will enhance the accuracy of sediment transport models

year: 2013

title: The role of looming and attention capture in drivers’ braking responses

authors: Terry, Hugh R.

subjects: headway distance

abstract: This study assessed the ability of drivers to detect the deceleration of a preceding vehicle in a simulated vehicle-following task. The size of the preceding vehicles (car, van, or truck) and following speeds (50, 70, or 100 km/h) were systematically varied. Participants selected a preferred following distance by engaging their vehicle's cruise control and when the preceding vehicle began decelerating (no brake lights were illuminated), the participant's braking latency and distances to the lead vehicle were recorded. The experiment also employed a secondary task condition to examine how the attention-capturing properties of a looming vehicle were affected by driver distraction. The results indicated that a looming stimulus is capable of redirecting a driver's attention in a vehicle following task and, as with detection of brake lights, a driver's detection of a looming vehicle is compromised in the presence of a distracting task. Interestingly, increases in vehicle size had the effect of decreasing drivers’ braking latencies and drivers engaged in the secondary task were significantly closer to the lead vehicle when they began braking, regardless of the size of the leading vehicle. Performance decrements resulting from the secondary task were reflected in a time-to-collision measure but not in optic expansion rate, lending support to earlier arguments that time-to-collision estimates require explicit cognitive judgements while perception of optic expansion may function in a more automatic fashion to redirect a driver's attention when cognitive resources are low or collision is imminent.

text: The role of looming and attention capture in drivers’ braking responses This study assessed the ability of drivers to detect the deceleration of a preceding vehicle in a simulated vehicle-following task. The size of the preceding vehicles (car, van, or truck) and following speeds (50, 70, or 100 km/h) were systematically varied. Participants selected a preferred following distance by engaging their vehicle's cruise control and when the preceding vehicle began decelerating (no brake lights were illuminated), the participant's braking latency and distances to the lead vehicle were recorded. The experiment also employed a secondary task condition to examine how the attention-capturing properties of a looming vehicle were affected by driver distraction. The results indicated that a looming stimulus is capable of redirecting a driver's attention in a vehicle following task and, as with detection of brake lights, a driver's detection of a looming vehicle is compromised in the presence of a distracting task. Interestingly, increases in vehicle size had the effect of decreasing drivers’ braking latencies and drivers engaged in the secondary task were significantly closer to the lead vehicle when they began braking, regardless of the size of the leading vehicle. Performance decrements resulting from the secondary task were reflected in a time-to-collision measure but not in optic expansion rate, lending support to earlier arguments that time-to-collision estimates require explicit cognitive judgements while perception of optic expansion may function in a more automatic fashion to redirect a driver's attention when cognitive resources are low or collision is imminent.

year: 2008

title: Introduction to tephra-derived soils, North Island, New Zealand: University of Waikato and University of Wisconsin-Platteville post-conference Andisol excursion, 21-23 December, 2016

authors: Lowe, David J.

abstract: Provisional itinerary DAY 1 Wednesday 21 December: Mamaku Plateau-Rerewhakaaitu-Lake Tarawera: 1 Goodwin Farm, Tapapa Rd, Tapapa: welded ignimbrite, tephras, loess, buried soils (Tirau soil) - stratigraphy of sequence (230 ka and younger) and upbuilding pedogenesis - Tirau silt loam 2 Brett Rd, Rerewhakaaitu: Holocene tephras and buried soil (Rotomahana soil) - Volcanic landscape, historical importance of area for NZ soil survey - Stratigraphy of sequence (~9.5 cal ka to 10 June 1886 Tarawera eruption) and upbuilding pedogenesis - Rotomahana sandy loam, 3 Ash Pit Rd, Rerewhakaaitu: tephras and buried soils (Matahina soil) - Matahina gravel - buried spodic/podzol soil features, 4 Okareka Loop Rd tephra section with proximal Rotorua Tephra and buried soils, loess, Buried Village Museum, Te Wairoa, Lake Tarawera (Stoney Point). DAY 2 Thursday 22 December: Otorohanga-Waitomo Caves -Pirongia Mountain: 1 Raynes Road section: Ultisol in composite tephra sequence (Kainui soil), 2 Otorohanga Kiwi House, 3 Waitomo Caves,, 4 Pirongia Mountain: Mangakara forest walk, 5 Evening meal on an Andisol. DAY 3 Friday 23 December: Hobbiton, Hamilton gardens including Te Parapara (ancient Maori garden): 1. Hobbiton tour 10.15 am (2 hrs), 2. Hamilton Gardens incl. Te Parapara Garden and human-modified soils (Tamahere soil).

text: Introduction to tephra-derived soils, North Island, New Zealand: University of Waikato and University of Wisconsin-Platteville post-conference Andisol excursion, 21-23 December, 2016 Provisional itinerary DAY 1 Wednesday 21 December: Mamaku Plateau-Rerewhakaaitu-Lake Tarawera: 1 Goodwin Farm, Tapapa Rd, Tapapa: welded ignimbrite, tephras, loess, buried soils (Tirau soil) - stratigraphy of sequence (230 ka and younger) and upbuilding pedogenesis - Tirau silt loam 2 Brett Rd, Rerewhakaaitu: Holocene tephras and buried soil (Rotomahana soil) - Volcanic landscape, historical importance of area for NZ soil survey - Stratigraphy of sequence (~9.5 cal ka to 10 June 1886 Tarawera eruption) and upbuilding pedogenesis - Rotomahana sandy loam, 3 Ash Pit Rd, Rerewhakaaitu: tephras and buried soils (Matahina soil) - Matahina gravel - buried spodic/podzol soil features, 4 Okareka Loop Rd tephra section with proximal Rotorua Tephra and buried soils, loess, Buried Village Museum, Te Wairoa, Lake Tarawera (Stoney Point). DAY 2 Thursday 22 December: Otorohanga-Waitomo Caves -Pirongia Mountain: 1 Raynes Road section: Ultisol in composite tephra sequence (Kainui soil), 2 Otorohanga Kiwi House, 3 Waitomo Caves,, 4 Pirongia Mountain: Mangakara forest walk, 5 Evening meal on an Andisol. DAY 3 Friday 23 December: Hobbiton, Hamilton gardens including Te Parapara (ancient Maori garden): 1. Hobbiton tour 10.15 am (2 hrs), 2. Hamilton Gardens incl. Te Parapara Garden and human-modified soils (Tamahere soil).

year: 2016-12-21