fine sediment
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2022 ◽  
Author(s):  
Stephen P Lound ◽  
Gavin F Birch ◽  
Deirdre Dragovich

Abstract Middle Harbour is a drowned-river valley located adjacent to the larger Sydney estuary, Australia. Extensive, high-resolution seismic data were correlated with borehole, land use, topographical, and geological data to calculate the mass of genetically different sediment deposits in Middle Harbour. The Harbour follows a well-defined drowned river-valley structure featuring small fluvial bedload delta deposits in the upper reaches of the embayments, a deep, central extensive mud basin overlying transgressive basal accumulations and a large flood-tide delta at the entrance. Deposits of an estimated 5,094 t of bedload, 21,143 t of suspended sediment and 5,947 t of transgressive basal material located in the estuary provided sedimentation rates of 0.68 t y-1, 1.29 t y-1, and 2.86 t y -1 respectively. These rates, determined from measured accumulations, were surprisingly low and substantially smaller than modelled rates. However, low sedimentation rates for suspended material may be due to fine sediment escaping over the top of the marine tidal delta, which effectively traps all bedload material from exiting the Harbour. Results of this study indicate that Holocene bedload sedimentation in Middle Harbour was slow and regular until a rapid increase after urbanisation commenced in the catchment. Most pre-Holocene material was eroded from Middle Harbour during the Last Glacial period with sediment currently present in the estuary having been deposited since sea-level recovery.


2022 ◽  
Vol 134 ◽  
pp. 108502
Author(s):  
Morwenna McKenzie ◽  
Judy England ◽  
Ian Foster ◽  
Martin Wilkes
Keyword(s):  

10.1142/12473 ◽  
2022 ◽  
Author(s):  
Johan C Winterwerp ◽  
Thijs van Kessel ◽  
Dirk S van Maren ◽  
Bram C van Prooijen
Keyword(s):  

2021 ◽  
Author(s):  
Jessica Droujko ◽  
Peter Molnar

Abstract Fine sediment transport in rivers is important for catchment nutrient fluxes, global biogeochemical cycles, water quality and pollution in riverine, coastal and marine ecosystems. Monitoring of suspended sediment in rivers with current sensors is challenging and expensive and most monitoring setups are restricted to few single site measurements. To better understand the spatial heterogeneity of fine sediment sources and transport in river networks there is a need for new smart water turbidity sensing that is multi-site, accurate and affordable. In this work, we have created such a sensor, which detects scattered light from an LED source using two detectors in a control volume, and can be placed in a river. We compare several replicates of our sensor to different commercial turbidity probes in a mixing tank experiment using two sediment types over a wide range of typical concentrations observed in rivers. Our results show that we can achieve precise and reproducible turbidity measurements in the 0-4000 NTU or 0-16g/L range. Our sensor can also be used directly as a suspended sediment sensor and bypass an unnecessary calibration to Formazin. The developed turbidity sensor is much cheaper than existing options of comparable quality and is especially intended for distributed sensing across river networks.


2021 ◽  
Author(s):  
◽  
Debbie Mair

<p>This ecological and geomorphological assessment of Horokiri Stream and Ration Creek was conducted across four longitudinal zones to explore the effects of sediment delivery, run-off, channel form, riparian and in-stream habitat. The Horokiri Stream channel has moved approximately 7 metres westward over the last 20 years, with both banks now covered in long grass, flaxes, natives with a mix of tall canopy trees. Looking at stream, Spearman’s for Ration at Figure 27 (n = 16, rho -0.243, p = 0.36) as deposited sediment increased, MCI decreased, non-significant. Spearman’s for Horokiri at Figure 28 (n = 16, rho 0.247, p = 0.35) as MCI increased with sediment, non-significant. Results from upstream of the riparian zones showed more deposited fine sediment. However, within both the riparian zones the sediment deposition was much lower. The native riparian planting along the stream banks had a positive effect on reducing sedimentation. The findings support the concept that the restoration of riparian zones with buffer widths exceeding 10 metres can improve stream habitat and invertebrate health. There was no relationship between flow and deposition rate P(X2>241.84) = 0.24. Figure 24 shows deposited sediment on MCI depending on land use groups (X2 = 11.81, df = 4, p = 0.019). No statistically significant differences were found (comparing the effect of sediment between different land use management groups).  An experiment investigated a disturbance hypothesis in both Ration Creek and Horokiri Stream was conducted during February 2019. The experiment was designed to be long enough to study the effects of four weekly pulse flushing events created by scrapping the stream bed with a drain drag tool and the effects of a press sustained disturbance on the macroinvertebrate community. I measured the sediment and the macroinvertebrate captured in each trap within the experiment site every seven days. My prediction was that macroinvertebrate communities subject to sustained fine sediment delivery (press disturbance) are affected by simulated pulse flushing events (pulse disturbance). A comparison of sediment depositional rate before and after the manipulative experiment (Figure 36) showed higher sediment deposition after the pulse flushing events (1.55 W/A/D) compared to before during the assessment phase (0.88 W/A/D) in Horokiri (t = 2.35, df = 8.95, p = 0.04), but no significant difference before (1.57 W/A/D) or after (1.38 W/A/D) in Ration (t = -0.818, df = 7.71, p = 0.44). It appeared that the smaller riparian buffer width of 2-5m at Ration Creek did not limit sediment deposition. The effects of sediment disturbance in the experiment reflect the rapid ability of macroinvertebrates to respond to sediment by drifting out of unsuitable areas. The weekly pulse disturbance events resulted in increased sediment deposition compared to the background levels of sediment deposition (indicative of a press disturbance) in both streams. As pulse disturbance events increased, the number of macroinvertebrate taxa decreased. Horokiri Stream invertebrate communities declined by 33% compared to Ration Creek which declined by 50%.</p>


2021 ◽  
Author(s):  
◽  
Debbie Mair

<p>This ecological and geomorphological assessment of Horokiri Stream and Ration Creek was conducted across four longitudinal zones to explore the effects of sediment delivery, run-off, channel form, riparian and in-stream habitat. The Horokiri Stream channel has moved approximately 7 metres westward over the last 20 years, with both banks now covered in long grass, flaxes, natives with a mix of tall canopy trees. Looking at stream, Spearman’s for Ration at Figure 27 (n = 16, rho -0.243, p = 0.36) as deposited sediment increased, MCI decreased, non-significant. Spearman’s for Horokiri at Figure 28 (n = 16, rho 0.247, p = 0.35) as MCI increased with sediment, non-significant. Results from upstream of the riparian zones showed more deposited fine sediment. However, within both the riparian zones the sediment deposition was much lower. The native riparian planting along the stream banks had a positive effect on reducing sedimentation. The findings support the concept that the restoration of riparian zones with buffer widths exceeding 10 metres can improve stream habitat and invertebrate health. There was no relationship between flow and deposition rate P(X2>241.84) = 0.24. Figure 24 shows deposited sediment on MCI depending on land use groups (X2 = 11.81, df = 4, p = 0.019). No statistically significant differences were found (comparing the effect of sediment between different land use management groups).  An experiment investigated a disturbance hypothesis in both Ration Creek and Horokiri Stream was conducted during February 2019. The experiment was designed to be long enough to study the effects of four weekly pulse flushing events created by scrapping the stream bed with a drain drag tool and the effects of a press sustained disturbance on the macroinvertebrate community. I measured the sediment and the macroinvertebrate captured in each trap within the experiment site every seven days. My prediction was that macroinvertebrate communities subject to sustained fine sediment delivery (press disturbance) are affected by simulated pulse flushing events (pulse disturbance). A comparison of sediment depositional rate before and after the manipulative experiment (Figure 36) showed higher sediment deposition after the pulse flushing events (1.55 W/A/D) compared to before during the assessment phase (0.88 W/A/D) in Horokiri (t = 2.35, df = 8.95, p = 0.04), but no significant difference before (1.57 W/A/D) or after (1.38 W/A/D) in Ration (t = -0.818, df = 7.71, p = 0.44). It appeared that the smaller riparian buffer width of 2-5m at Ration Creek did not limit sediment deposition. The effects of sediment disturbance in the experiment reflect the rapid ability of macroinvertebrates to respond to sediment by drifting out of unsuitable areas. The weekly pulse disturbance events resulted in increased sediment deposition compared to the background levels of sediment deposition (indicative of a press disturbance) in both streams. As pulse disturbance events increased, the number of macroinvertebrate taxa decreased. Horokiri Stream invertebrate communities declined by 33% compared to Ration Creek which declined by 50%.</p>


2021 ◽  
Author(s):  
◽  
Dayanitha Damodaran

<p>Mass mortality events (MMEs) occur when a disproportionate part of a population dies in a single event. The frequency of MMEs is increasing globally. In the past, MMEs have been linked to starvation, changes in environmental conditions and disease outbreaks. However, it is often unclear what the underlying cause of these events are. In New Zealand several MMEs have occurred in the bivalve species Austrovenus stutchburyi (Wood 1828) and Paphies subtriangulata (Wood 1828) with little known about the cause. Both of these species are recreationally harvested for consumption in New Zealand and have cultural significance.  In order to better understand MMEs in these species we must first gain a better understanding of stress expression. Bivalves have few observable features and it is difficult to classify them as healthy or stressed without investigating immune change which can be quite costly. Some research has looked into how different cell types change in response to pollutants but few studies have researched how cell types change in response to environmental conditions. The aim of this research was to find novel ways of assessing if shellfish were healthy or stressed. Little is known about how shellfish respond to environmental stressors and this is the first study to look at several novel stress expressions simultaneously, in New Zealand shellfish.  Histological, morphological and behavioural responses were measured in both A. stutchburyi and P. subtriangulata after treatment with increased temperature, lowered salinity and increased fine sediment input for up to 5 weeks. Temperature stress was the main stressor for P. subtriangulata (85% of overall mortality occurred in the heat treatment), salinity was the main stressor for A. stutchburyi (46% of overall mortality occurred in the salinity treatment), and fine sediment stress did not seem to have an effect on either species in this study. Overall, A. stutchburyi were more robust to the treatments, but low mortality occurred in both species (≤8%). Mortality correlated with time of year and was believed to be related to spawning in P. subtriangulata (48% of overall mortality occurred from October-November). Both species had a single histological marker, in A. stutchburyi this was change in gill morphology, and in P. subtriangulata this was change in digestive gland morphology. Several individual morphological features were identified as potential stress markers in A. stutchburyi and P. subtriangulata. Additionally, when removed from aquaria P. subtriangulata had impeded foot retraction time in the salinity treatment. The differences in stress markers shows the diversity of reactions to stressors even within New Zealand bivalves. This study provides a useful baseline in investigating how P. subtriangulata and A. stutchburyi respond to environmental stress. The histological slides produced during this investigation are an invaluable resource that can be used in future studies and in comparisons with archived specimens from known MMEs. Knowing how to detect signs of stress in these bivalves will help to predict MMEs in the future and aid in implementing processes to combat these events.</p>


2021 ◽  
Author(s):  
◽  
Dayanitha Damodaran

<p>Mass mortality events (MMEs) occur when a disproportionate part of a population dies in a single event. The frequency of MMEs is increasing globally. In the past, MMEs have been linked to starvation, changes in environmental conditions and disease outbreaks. However, it is often unclear what the underlying cause of these events are. In New Zealand several MMEs have occurred in the bivalve species Austrovenus stutchburyi (Wood 1828) and Paphies subtriangulata (Wood 1828) with little known about the cause. Both of these species are recreationally harvested for consumption in New Zealand and have cultural significance.  In order to better understand MMEs in these species we must first gain a better understanding of stress expression. Bivalves have few observable features and it is difficult to classify them as healthy or stressed without investigating immune change which can be quite costly. Some research has looked into how different cell types change in response to pollutants but few studies have researched how cell types change in response to environmental conditions. The aim of this research was to find novel ways of assessing if shellfish were healthy or stressed. Little is known about how shellfish respond to environmental stressors and this is the first study to look at several novel stress expressions simultaneously, in New Zealand shellfish.  Histological, morphological and behavioural responses were measured in both A. stutchburyi and P. subtriangulata after treatment with increased temperature, lowered salinity and increased fine sediment input for up to 5 weeks. Temperature stress was the main stressor for P. subtriangulata (85% of overall mortality occurred in the heat treatment), salinity was the main stressor for A. stutchburyi (46% of overall mortality occurred in the salinity treatment), and fine sediment stress did not seem to have an effect on either species in this study. Overall, A. stutchburyi were more robust to the treatments, but low mortality occurred in both species (≤8%). Mortality correlated with time of year and was believed to be related to spawning in P. subtriangulata (48% of overall mortality occurred from October-November). Both species had a single histological marker, in A. stutchburyi this was change in gill morphology, and in P. subtriangulata this was change in digestive gland morphology. Several individual morphological features were identified as potential stress markers in A. stutchburyi and P. subtriangulata. Additionally, when removed from aquaria P. subtriangulata had impeded foot retraction time in the salinity treatment. The differences in stress markers shows the diversity of reactions to stressors even within New Zealand bivalves. This study provides a useful baseline in investigating how P. subtriangulata and A. stutchburyi respond to environmental stress. The histological slides produced during this investigation are an invaluable resource that can be used in future studies and in comparisons with archived specimens from known MMEs. Knowing how to detect signs of stress in these bivalves will help to predict MMEs in the future and aid in implementing processes to combat these events.</p>


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