Scientific methodology
Suspended particle sampling
Plankton nets will be deployed from the river bank or within the stream and left in the stream for an period of time to be determined on site. The actual method of deployment will depend on the configuration of the river at the sampling location. As much as possible, non-plastic sampling equipment will be used.
Two net sizes will be used: 0.053 mm and 0.25 mm.
Any sediment collected in the net will be placed onto a mat and viewed through a microscope to observe the presence or absence of plastic.
Water velocity will be estimated using multiple repeat measurements of transport time for a float over a fixed distance. The mean flow velocity in the river will be estimated as 80% of the surface velocity. From this, and the cross-section of the sampling net, the estimated volume of water sampled will be calculated.
All locations will be recorded using GPS. A qualitative estimate of the turbidity using a turbidity tube will be made at all locations and the sampling set up will be photographed.
Sediment sampling
A fixed volume of sediment will be excavated from separation zones at selected locations. Separation zones will be chosen where fine sand/silt/mud deposits are present as these will have had lowest velocities during deposition.The sediment will be added to a barrel and mixed with water from the river. The aim of this is to remobilise the sediment. Samples will be collected from the water column after a period of time has elapsed. The principle being that higher density mineral sediment will fall to the base of the barrel before any lower density plastic that may be present.
The water/sediment samples will be passed through the plankton nets and the resultant sediment load analysed as for suspended sediment.
Plankton nets will be deployed from the river bank or within the stream and left in the stream for an period of time to be determined on site. The actual method of deployment will depend on the configuration of the river at the sampling location. As much as possible, non-plastic sampling equipment will be used.
Two net sizes will be used: 0.053 mm and 0.25 mm.
Any sediment collected in the net will be placed onto a mat and viewed through a microscope to observe the presence or absence of plastic.
Water velocity will be estimated using multiple repeat measurements of transport time for a float over a fixed distance. The mean flow velocity in the river will be estimated as 80% of the surface velocity. From this, and the cross-section of the sampling net, the estimated volume of water sampled will be calculated.
All locations will be recorded using GPS. A qualitative estimate of the turbidity using a turbidity tube will be made at all locations and the sampling set up will be photographed.
Sediment sampling
A fixed volume of sediment will be excavated from separation zones at selected locations. Separation zones will be chosen where fine sand/silt/mud deposits are present as these will have had lowest velocities during deposition.The sediment will be added to a barrel and mixed with water from the river. The aim of this is to remobilise the sediment. Samples will be collected from the water column after a period of time has elapsed. The principle being that higher density mineral sediment will fall to the base of the barrel before any lower density plastic that may be present.
The water/sediment samples will be passed through the plankton nets and the resultant sediment load analysed as for suspended sediment.