McVan Analite 395 turbidity probes:
Turbidity is a measure of the decrease in the transparency of a solution due to the presence of sediment particles, coloured organic matter and the water itself which causes incident light to be scattered, reflected and attenuated (Ziegler, 2002). It is the most widely used surrogate for measuring suspended sediment concentration (Gray and Gartner, 2009, Pruitt, 2003). The McVan Analite 390 Digital Series are a range of nephelometers that comply with ISO 7027 standards and are able to operate at depths of up to 100m. They operate by measuring the degree of scattering at an angle of 90° to the incident light beam using a near Infra-red photodiode light source with a wavelength of 860nm (0.86µm) and a spectral bandwidth less than or equal to 60nm with a path length under 10cm, providing accurate turbidity measurements in the range of 0 – 1000 NTU’s with ± 1% precision. At the sub-stations, samples are taken from the river at 15 minute intervals and pumped through a flow through cell, where turbidity measurements are made. By housing the probes in a flow through cell, external effects caused by the presence of large debris and the development of bio-films are reduced. Additional product specifications can be found at:
http://www.planet-ocean.co.uk/PDF/NEP-390.pdf
ISCO 3700 automatic sampler:
Each water quality monitoring stations is equipped with an ISCO 3700 automatic sampler. These samplers consist of a intake, sample distributor, pump, bottle container unit and activation system (Gray et al., 2008), whereby a sample volume which is dependent on the peristaltic pump speed and number of rotations is drawn up from the channel by suction (Newburn, 1988). These samplers are efficient, lightweight, affordable and computer controlled, allowing sampling to be triggered remotely or initiated automatically in response to rainfall, or changes in river level. However, they operate best in fine grained fluvial environments (Lewis and Eads, 2008) due to the samplers inability to collect samples isokinetically. Additional product specifications can be found at:
http://www.isco.com/products/products3.asp?PL=201101030
Time Integrated Mass-flux samplers (TIMs):
Each water quality monitoring stations is equipped with a TIMs. Designed by Phillips et al. (2000); The Time Integrated Mass- flux sampler (TIMs) is anchored to the river bed using metal stakes (or similar), positioned with the 4mm diameter inlet perpendicular to the direction of flow. Water passes through the inlet and into the expansion chamber. Here, the velocity of flow is reduced by a factor of 600 to encourage sedimentation of the sediment particles in transport. The water flows through the expansion chamber and out via the outlet. The apparatus is subject to the full range of flow conditions and sediment fluxes over the sampling period, providing a continuous record fine sediment flux, which will be representative of all events (Walling et al., 2008a). The streamlined design minimises flow intrusion, altering the flow magnitude by no more than 20% in addition to allowing the flow to exit unimpeded, thereby minimising sampling bias which is often inevitable using other methods (Fox and Papanicolaou, 2007).
YSI multi-parameter probe
Each outlet station is equipped with a YSI 6600 V2 Sonde, enabling the simultaneous measurement of conductivity (0 – 100 mS cm-1 ± 0.5%), temperature (-5 to + 50°C ± 0.15°C), pH (0 – 14 units ± 0.2 units), dissolved oxygen (0 – 500% ± 2%), turbidity (0 – 1000 NTU ± 2%) and chlorophyll-a (0 – 400µg L-1). The optical probes are also equipped with self cleaning sensors in order to minimise bio-fouling although this is minimised by housing the probe in a flow through cell. Additional product specifications can be found at:
http://www.ysi.com/media/pdfs/E52-6600V2.pdf
Sontek/YSI Argonaut SW
The outlet stations in the Thackthwaite and Newby catchments are equipped with a Sontek/YSI Argonaut SW (Shallow Water) velocimeter. This instrument measures velocity of flow in 2-D (using 2 acoustic beams). Both the along channel and vertical velocity components of flow are measured. Additionally, water level measurements are using vertical acoustic beam. Due to the range of measurements, this doppler velocitimeter is capable of providing instantaneous discharge measurments when loaded with cross-section information of the channel profile. Additional product specifications can be found at:
http://www.sontek.com/pdf/expdes/Argonaut-SW-Expanded-Description.pdf
Schlumberger Mini-diver
As a means of providing a back-up source of river level data, each water quality monitoring site is equipped with a Schlumberger Mini-diver. These are small, wireless instruments which have enough internal memory to make over 24 000 pressure measurments. When fluctuations in atmospheric pressure is accounted for using a Schlumberger baro, accurate water level measurments can be make at high frequencies. At our sites, measurments are made at 5 minute intervals. Additional product specifications can be found at:
http://www.swstechnology.com/groundwater-monitoring/groundwater-dataloggers/mini-diver
Hack Lange NH4D SC Ammonium Sensor
The Newby and Pow outlet stations are equipped with the Hach NH4D SC Ammonium Sensor. This uses an ion-selective electrode (ISE) to detect ammonium ions (NH4+) directly as ammonium nitrogen (NH4-N). A differential pH electrode is used as the reference electrode for stability. The most significant potential interference is from potassium ions (K+) which is compensated through the use of an integrated potassium ISE to correct the ammonium value. The probe has an operating range of 0.2 to 1000 mg L-1 (with an accuracy of ± 5%). Additional product specifications can be found at:
www.hach.com/asset-get.download-en.jsa?id=7639982041
Hach Lange Nitratax SC
The Newby and Pow outlet stations are equipped with the Hach Lange Nitratax SC Nitrate sensor. This is a self-cleaning process probe for immediate measurement of nitrate(NO3 – N) content of water, which is turbidity compensated through reference measurement. The probe has an operating range of 0.1 – 100 mg L-1 (with an accuracy of ± 3%). Additional product specifications can be found at:
Hach Lange PHOSPHAX sigma
The Newby and Pow outlet stations are equipped with the PHOSPHAX sigma process photometer for the continuous measurement of orthophosphate and total phosphorus concentrations. Analysis is based on the DIN-equivalent molybdenum blue method. The chemo-thermic reaction principle ensures complete breakdown within a few minutes. The operating range is 0.01 – 5.0 mg L-1 for Total- P and 0.01 – 5.0 mg L-1 for PO4 – P. Additional product specifications can be found at:
References
Fox, J. F. and A. N. Papanicolaou (2007). “The use of carbon and nitrogen isotopes to study watershed erosion processes.” Journal of the American Water Resources Association 43(4): 1047-1064.
Gray, J. R. and J. W. Gartner (2009). “Technological advances in suspended-sediment surrogate monitoring.” Water Resour. Res. 45: W00D29.
Lewis, J. and R. Eads (2008). Implementation guide for turbidity threshold sampling: principles, procedures, and analysis. Arcata, CA: USA, Department of Agriculture, Forest Service, Pacific Southwest Research Station.
Newburn, L. H. (1988). Modern sampling equipment: Design and application. Principles of environmental sampling. L. H. Keith. Salem, MA: USA, American Chemical Society: 209 – 220.
Phillips, J. M., M. A. Russell, et al. (2000). “Time-integrated sampling of fluvial suspended sediment: a simple methodology for small catchments.” Hydrological Processes 14: 2589 – 2602.
Pruitt, B. A. (2003). Use of turbidity by state agencies. Turbidity and Other Sediment Surrogates Workshop, April 30 – May 2, Reno, NV.
Walling, D. E., A. L. Collins, et al. (2008). “Tracing suspended sediment and particulate phosphorus sources in catchments.” Journal of Hydrology 350(3-4): 274-289.
Ziegler, A. C. (2002). Issues related to the use of turbidity measurements as a surrogate for suspended sediment. Turbidity and Other Sediment Surrogates Workshop. Reno, NV.