While there are a multitude of ways to track a parcel of water, few are as intuitive as dye tracing. Scientists can inject dye into the environment and use it as a proxy for water or contaminants within the water. Tracking the movement and dispersal of the dye allows them to estimate the subsequent impact a parcel of water can have on the environment.

Of course, tracking a plume of dye as it disperses into a large body of water is no easy feat. As science has evolved from in vitro to in situ measurements to conduct dye studies, so has the preference to use Rhodamine WT, and to a lesser extent, fluorescein, as the dye of choice. In vitro measurements, though they can provide accurate data, have drawbacks. They can be expensive—someone has to monitor the study and collect the samples—and are therefore prone to human error. In situ measurements allow for unattended, continuous measurements.

Enter the fluorometer – your in-situ subsurface eyes on the dye. These sensors can go beyond a qualitative “dye is present” or “dye is not present” observation and provide quantitative data on dye concentration. These can be deployed in two different ways with different results:

• Moored Sensors: Continuous data collection using moored instruments allows for a more accurate determination of pollutant buildup. No longer tied to a spot sample, continuous data allows users to track changes in dye concentration over time.
  • Enables simultaneous data collection across multiple study sites
  • Allows sampling when/where boats cannot access.
  • Gives significantly more data than a single data point achieved by taking a water sample.
• Profiling sensors: shipboard profiling can determine the movement of dye-tagged water and determine the total area exposed to the dye. Doing so allows for determination of concentration over a larger spatial extent, as well as comparison of dye concentration by depth via vertical mixing.

Combining fluorometers with backscatter/turbidity meters has the added advantage of filtering out the effect of bubbles and sediment on the dye measurement, further enhancing the measurement. Sea-Bird Scientific offers a variety of combination fluorometer/backscatter sensors designed for dye tracing.

Read More

• Case Study: Identifying Oil In Water With The Seaowl UV-A™ Fluorescence and Backscattering Instrument, Ian Walsh, March 2018