213 Usage of chem_id and mass_area_id
Usage of keys
In survey litterfall, the keys chem_id and mass_area_id are used to connect dry weights (in table LFD) with chemical values (in table LFC), and with mass area values (in table LFA). The link between LFC/LFA and LFC/LFD is a 1:n link. This means, that while each key may only occur once in the LFC or once in LFA, it can be assigned to multiple dry weights in LFD associated with pooled fractions, pooled tree species or collection periods. Thus, every possible dry weight pooling combination can be clearly assigned to one chemical or one mass/area measurement.
Construction pattern
Keys for linking dry weight values to both chemical and mass/area values follow the same pattern.
| Key | Pattern | Example |
|---|---|---|
| chem_id | C_[partner_code]_[code_plot]_[survey_year]_[consecutive number for each plot-year] | C_50_101_2003_1 |
| mass_area_id | A_[partner_code]_[code_plot]_[survey_year]_[consecutive number for each plot-year] | A_1_84_2014_4 |
Example 1 - Pooling over time
The following overview is based an imaginary example of Plot 12 in Switzerland (code 50) in year 2002. During this time, a total of 8 (pooled) samples were chemically analysed: C_50_12_2002_1 - C_50_12_2002_8.
In this example, samples were pooled over different time periods, but separated by tree species and fractions.
Example 2 - Pooling over fractions and time
The second example shows an imaginary situation of Plot 21 in Belgium (code 102) in year 2015. Here altogether 12 chemical analyses were conducted, identified with chem_ids: C_102_21_2015_1 - C_102_21_2015_12.
In this case, the litterfall from different samples was often mixed across fractions and additionally pooled over time.
In the same way, samples from different tree species can also be pooled and labelled with the same chem_id.
Clear assignment is most important
The order of the consecutive number does not matter. But it is of most imortance that each analyse has a unique key and correctly assigned to the samples in LFD!