Lessons learned PART IV: What influences the iFLUX results?

There are some circumstances that have shown an impact in our previous projects. We list what we learned about them here:

• Filter length: Shorter filters give more accurate results when there is a tidal effect. When there is a tidal effect, it can be recommended to first perform real-time measurements with the iFLUX sensor to map these tidal dynamics and improve the passive flux measurements accordingly.
• Soil structure: The filter, in which the cartridges are placed, is preferably only in 1 type of soil layer. Having different soil layers at the height of measurement can cause "turbulent flows" and influence the result. In such cases the chance of "induced" fluxes from other layers is possible through filter pack. 

• Very high flows (e.g. Switzerland large drop) make it more difficult to perform correct measurements. The water will then also flow around the cartridge and not through it. This causes more turbulence in the flow and the measurement is less accurate. 
• High variation: Strongly heterogeneous soils, very large changes at small distances (<20 cm), such as alternating thin layers of sand and clay, make it difficult to obtain representative flux results in the aquifer. In this case it is advised to increase the number of measurements to increase the certainty of the measurements. Alternatively or additionally a pump test can be executed to determine an average mass flux and mass discharge.