title: Suspended Sediment Monitoring in Remote Aquatic Environments: An Assessment of New and Existing Measurement Techniques in Alluvial Gully Systems
Creators: name: Doriean, Nicholas J
Publisher: name: Griffith University
Year: 2020
Subjects: subject: suspended sediment dynamics
subject: pumped active suspended sediment
subject: Great Barrier Reef
subject: pollutants

description: Our current understanding of suspended sediment dynamics is often limited to accessible aquatic environments that can be monitored using existing techniques. Consequently, there is a lack of data from remote, ephemeral waterways, such as gullies, which are challenging to monitor using conventional approaches originally designed to operate in rivers and streams. Recent research suggests gully erosion is a significant driver of sediment pollution to aquatic environments; for example, greater than 40% of the sediment pollution to the Great Barrier Reef can be attributed to gully erosion. Current deficiencies in our capability to monitor gully water quality require the development of affordable, autonomous monitoring methods that can be deployed at high spatial resolution across a gully network and that can also withstand harsh, remote environments. Therefore, a simple and robust time-integrated device for in situ suspended sediment sampling was developed; the pumped active suspended sediment (PASS) sampler. The PASS sampler operates by drawing water through a settling column using a peristaltic pump at a constant velocity, effectively concentrating the suspended sediment, into a time-integrated sample, from a large volume of sampled water into approximately 4 L. Laboratory testing showed the PASS sampler was capable of retaining over 90% of the suspended sediment in a sample dominated by silt and clay (median particle size = 6.98 [microns]). The device was tested alongside a suite of conventional suspended sediment monitoring techniques (flow proportional discrete sampling, automatic discrete sampling, passive single stage sampling and turbidity measurement) for application in alluvial gully systems and found to provide samples that accurately represented time weighted average suspended sediment concentration and particle size distribution. The suite of evaluated methods was applied to investigate the effect of landscape-scale gully remediation on the water quality of a catchment draining into the Great Barrier Reef. The median suspended sediment concentration of the remediated gully (1429 mg L-1) was greatly reduced compared to a control gully (7123 mg L-1). The application of a novel monitoring network using PASS samplers and other established measurement methods, in conjunction with suspended sediment-associated nutrient analysis, provided a detailed and robust account of the water quality improvements generated by landscape-scale gully remediation and the implications it could have for reducing sediment and associated nutrient pollution to the Great Barrier Reef. Ambient concentrations of pollutants considered most likely to impact the health of Great Barrier Reef ecosystems were also greatly reduced (~75% reduction of fine suspended sediment (&lt; 63 [microns]) and a ~65% reduction in sediment-associated nutrients (nitrogen and phosphorus)).