Reference values and background - what to compare results with
One of the most important exercises in interpreting results is finding the right reference point. Because the same number - conductivity, phosphorus, pH - can be entirely typical for one water and worrying for another. Two concepts help with this: reference conditions and background.
Reference conditions
This is the state of waters closest to natural, little changed by people - the reference point against which the assessment of ecological status is compared in the Water Framework Directive. “High” status is in practice “close to the reference conditions for a given type of water”. That is why the assessment always relates to the type of river or lake, not to a single, universal number.
Background (including geochemical)
This is the natural level of a given component, resulting e.g. from the geological structure of the catchment. Water flowing through limestone rocks will have a different hardness and pH than that from crystalline terrain - and this is not any “anomaly” but its background. Assessing a deviation only makes sense against this background.
Your water’s “own norm”
Hence a practical rule: for your site, build your own baseline - the typical range of values at different times and under different conditions. Then:
- you will easily catch real deviations (rather than natural variability),
- you will avoid false alarms,
- you will interpret the result more accurately (see How to interpret results).
Where to get references
- water types and reference conditions - from status-assessment methodologies and monitoring materials (GIOŚ),
- regional context - from open data,
- your own measurement history - the most valuable, because it concerns exactly your point.
In practice
Your own baseline is born of a consistent series at a fixed point. In LimnoLog a station’s measurement history is always at hand on the chart, and you can adjust the guidelines to the reality of your water - not to a universal, often inadequate number.
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