2.4 Data collection
A total of nine hundred standard tablets were buried in four types of
land cover (forest, cropland, shrubland, and grassland) in three
experiment sites for different periods. The specific buried pattern of
the standard tablet was shown in Figure 2. In forest and cropland, three
layers (-5 cm, -25 cm, and -35 cm of underground) of standard tablets
are buried for five experiment periods (30 days, 60 days, 90 days, 120
days, and 365 days), respectively. While in shrubland and grassland, due
to the thickness of the soil layer is too thin, only two layers (-5 cm
and -25 cm of underground) of standard tablets were buried. Of the three
experiment sites, Site A experimented from August 6, 2017, to August 5,
2018, Site B experimented from August 13, 2017, to August 12, 2018, and
Site C experimented from August 1, 2017, to July 31, 2018, respectively.
When the burial time reaches 30 days, the first batch of standard
tablets shall be taken back for three sites, and so on for the rest of
the set of tablets.
To protect the safety of field experiments, we hired local people to
manage the experiment sites. After the experiment, 892 out of 900
standard tablets were retrieved from three field experiment sites. Of
the eight lost tablets, six of them are broken, and two of them were not
found. After the treatment of retrieved tablets, the first data we get
is the weight of the standard tablet after the experiment, and the
following formula could calculate the karst dissolution amount (Yuan &
Cai, 1988).
\(D_{w}=(W_{2}-W_{1})\times 1000\times S^{-1}\) (1)
Where \(D_{w}\) refers to the karst dissolution amount (mg
cm-2), \(W_{1}\) is the weight of after experimenting
with the tablet (g), \(W_{2}\) is the initial weight of tablet (g),\(S\) is the superficial area of the tablet (cm2).
The karst dissolution loss caused by different intensity droughts are
calculated:
\(D_{L}=D_{\text{wn}}-D_{\text{wt}}\) (2)
Where \(D_{L}\) is the amount of karst dissolution loss caused by
drought (mg cm-2), \(D_{\text{wn}}\) is the karst
dissolution amount of normal state (mg cm-2),\(D_{\text{wt}}\) is the amount of karst dissolution of drought
treatment (mg cm-2).
Removed the broken and missing tablets, each soil layer comprises three
tablets in one experiment time. Every dissolution data we obtained from
different periods is contained of three or two tablets on average. This
method can eliminate some noise of experiment data to a certain extent.
Furthermore, it is important to note that the present study is focused
mainly on the karst dissolution loss caused by different intensity
droughts, rather than accurately measuring the dissolution amounts of
karst.