These measurements were made from Totnes to Dittisham on a falling tide. The wind was light southerly throughout.
| Time | Place |
|---|---|
| 11:48 UTC | leave Totnes |
| 11:55 UTC | High Tide at Totnes |
| 14:45 UTC | arrive Dittisham |
The following graphs show the measurements made as a function of time.
... click on an image for a full size graph ...
By combining observations made from the kayak the with position-time information from a GPS the location of each measurement can be determined. These values can then be plotted on an interactive map.
In the maps below measurements from the kayak are presented as colour coded circles. By clicking on a circle the actual measurements can be examined.
The nitrate ion selective sensor (ISE) attempts to measure the concentation of nitrate ions. However other ions (principally chloride and nitrate) are also detected. The manufacturer indicates that the sensor is about 1000 times less sensitive to these other ions.
The nitrate and salinity curves above show a very similar form - with fluctuations in one being closely matched by the other. The following graph shows the measured concentration of salinity in ppt divided by the measured nitrate concentration in ppm.
After 12:40, when the salinity has increased to 5 ppt (0.5%), the ratio measured nitrate (ppm) / measured salinity (ppt) stabilises at about 2.0.
Thus
'nitrate (ppm)' ~ 0.002 * salinity (ppm)
Thus in the nitrate graph above the 'measured' nitrate values which are compromised by the higher values of salinity are shown in red.
