Geoscience Reference
In-Depth Information
2 Tracer Experiments
Six tracer experiments were carried out during the autumn of 2009 in the Murray
Burn, which runs through the Heriot-Watt University campus at Riccarton in
Edinburgh. The same stretch of the river had been used during an earlier set of
tracer experiments (see, e.g., Wallis
2005
). A map of the study area is shown in
Fig.
1
. In the 2009 experiments, the tracer (Rhodamine WT) was injected at Site 1
and concentration-time profiles were measured at Sites 3 and 4, which are 183 m
apart. For each experiment, water samples were collected from the centre of the
stream at regular time intervals and taken back to the laboratory for analysis.
The water samples were analysed in a controlled environment laboratory using
the following procedure. Firstly, the water samples and tracer standards (made
by serial dilution from the same stock tracer solution used to prepare the injected
tracer) were stored overnight in the laboratorytoallowthemalltobeatthe
same temperature. Secondly, the following morning, a Turner Designs Field
Fluorometer was calibrated using the standards, and thirdly, the water samples
were analysed. To enable any machine drift or temperature fluctuations to be
taken into account, some of the water samples and calibration standards were
reanalysed at the end of the sample analysis and the laboratory temperature was
recorded several times during the analysis. The calibration of the fluorometer
was linear and it remained stable during the water sample analysis, but it varied
between experiments. The laboratory temperature was stable at about 20
Cforall
the experiments. Initial data analysis consisted of removing the background signal
and converting the resultant fluorescence values to tracer concentrations. The
background signal for each concentration-time profile was estimated from the end
of the trailing edge.
200m
Research Park
N
3
4
2
Student Residences
1
Fig. 1 Map of study area: the
numbers show the sites from
the earlier study
Murray Burn
