Annex 7: Data calculations

1. Conversion from ions to elements
2. Calculation with L-flags in data series
3. Calculation of mean of pH
4. Calculation of weighted means
5. Calculation of sea-salt corrected values
6. Biodiversity indices

1 Conversion from ions to elements

Calculate the results to be reported in S, N and P using the formula

concentration of element = factor x concentration of ion

eg.
conc SO2S = 0.5005 x (conc SO2)
conc SO4S = 0.3338 x (conc SO4)
conc NO2N = 0.3045 x (conc NO2)
conc NO3N = 0.2259 x (conc NO3)
conc NH4N = 0.7765 x (conc NH4)
conc PO4P = 0.3261 x (conc PO4)

2 Calculation with L-flags in data series

If the primary data-series contains values below the detection limit (quality flag L), these values are compensated by 0.5 x the detection limit value prior to statistical mean calculations and no quality flag is reported with the mean values. Additional information on flags in Chapter 4 (4.3.3).

3 Calculation of mean of pH

The original pH values must be converted to conc H⁺ before calculations - the mean concentration H⁺ is then reconverted to a pH-value

4 Calculation of weighted means

Volume weighted means for precipitation (precipitation, throughfall and stemflow) chemistry are calculated using the formula:

Flow weighted means for runoff, soil water and groundwater chemistry are calculated using the formula:

5 Calculation of sea-salt corrected values

In the IM programme sulphate values are reported as uncorrected sulphur - not sea-salt corrected anthropogenic sulphur. A method for sea-salt correction is given here. Sea-salt corrected values are marked with an asterisk (*) and calculated as:

[Ca*] = [Ca] - 0.037 [Cl]
[Mg*] = [Mg] - 0.198 [Cl]
[Na*] = [Na] - 0.858 [Cl]
[K*] = [K] - 0.018 [Cl]
[SO4*] = [SO4] - 0.103 [Cl]

where [ ] is concentration expressed in µeq/l.

6 Biodiversity indices

Shannon-Wiener index of species diversity