3 results
The loss of karst dissolution caused by different intensity droughts for four types of land cover in three experimental sites is summarized in Table 2. It is apparent from this data that the drought has caused a great loss to karst dissolution. Under the influence of light drought, the forest has a 0.4451 mg cm-2 of karst dissolution loss (range from 0.0276 to 0.6642 mg cm-2), equivalent to 31.83% of the karst dissolution loss on average. Spatially, Site A has the highest loss, followed by Site B, and then Site C has the lowest loss, which only 5.78 percent of karst dissolution was lost. By comparison, the cropland has experienced a lower loss, has a 0.3044 mg cm-2 (27.80%) of karst dissolution loss (range from 0.1695 to 0.4359 mg cm-2) due to light drought. Among the three experimental sites, Site C was the most affected area by drought, followed by Site B, and Site A was the least affected area. For shrubland, the light drought has caused a 0.5580 mg cm-2 of karst dissolution loss (range from 0.1591 to 0.8094 mg cm-2), lost by 39.97% on average. And the spatial distribution of karst dissolution loss is the same as that of the forest. The karst dissolution loss of light drought for grassland was 0.5131 mg cm-2 in mean value, equal to 36.56% of the karst dissolution loss. In space, the highest karst dissolution loss of light drought for grassland was Site B, the second-highest loss was Site A, and the third-highest loss was Site C. These data show that the shrubland has the highest karst dissolution loss under the affected of light drought, followed by grassland and forest, and the cropland has the lowest karst dissolution loss in mean value.
Moderate drought can cause an average loss of 37.66%, 37.96%, 42.06%, and 44.63% of karst dissolution for the forest, cropland, shrubland, and grassland, respectively. The losses of four kinds of land cover in three experimental sites were clearly higher than that of light drought. Specifically, moderate drought has caused, in mean, a 0.6676 mg cm-2 (range from 0.2871 to 0.9651 mg cm-2) of karst dissolution loss for the forest, 0.6203 mg cm-2 (range from 0.2767 to 0.8682 mg cm-2) for cropland, 0.8671 mg cm-2 (range from 0.2663 to 1.3317 mg cm-2) for shrubland, and 0.9062 mg cm-2 (range from 0.2594 to 1.8125 mg cm-2) for grassland, respectively. Qualitatively, the grassland has the highest karst dissolution loss under the impact of moderate drought, followed by shrubland and forest, and the cropland is the least affected land cover types. Regionally, Site B has the highest karst dissolution loss of forest, shrubland, and grassland, followed by Site A, and the Site C is obviously less than that of Site A and Site B. While for cropland, the karst dissolution loss of Site C was the highest, followed by Site B, and the Site A was the lowest.
The mean losses of karst dissolution caused by severe drought were 0.9247 mg cm-2 (range from 0.4601 to 1.3040 mg cm-2) for the forest, 0.8117 mg cm-2(range from 0.3977 to 1.1034 mg cm-2) for cropland, 1.1150 mg cm-2 (range from 0.2906 to 1.6810 mg cm-2) for shrubland, and 1.2372 mg cm-2 (range from 0.2318 to 2.4767 mg cm-2) for grassland, respectively. The loss percentage of four kinds of land cover was over 40%, ranged from 42.80% to 46.80% on average. The karst dissolution loss caused by severe drought, in mean, from high to low was grassland, shrubland, forest, and cropland. By region, the highest dissolution loss of forest occurred in Site B, then Site A, and finally the Site C. To cropland, Site C is the most hit by severe drought, followed by Site B, and the Site A hit by drought lowest. Affected by severe drought, the shrubland of Site A has the highest karst dissolution loss, followed by Site B, and Site C has the lowest loss. About grassland, the regional loss pattern is the same as the forest.
As shown in Table 2, once extreme drought occurs, the forest will suffered a 0.8602 mg cm-2 (range from 0.5742 to 1.1830 mg cm-2) of karst dissolution loss, 0.9316 mg cm-2 (range from 0.5638 to 1.2349 mg cm-2) of loss for cropland, 1.1668 mg cm-2 (range from 0.3770 to 1.8817 mg cm-2) of loss for shrubland, and 1.6108 mg cm-2 (range from 0.2421 to 3.0682 mg cm-2) of loss for grassland, respectively, were lost by 42.00%, 43.27%, 45.19%, and 50.36%, on average. The mean loss of karst dissolution to grassland was the highest, followed by shrubland and cropland, and the forest has the lowest karst dissolution loss in amount and rate. Like severe drought, the spatial loss patterns of karst dissolution caused by extreme drought for four kinds of land cover types are the same as severe drought. From these data, we found an interesting phenomenon. The extreme drought caused the loss of karst dissolution of forest in Site A and Site B, as well as the karst dissolution loss of shrubland in Site B, which is slightly lower than that of severe drought. Besides, although the karst dissolution loss of grassland in Site C caused by extreme drought does not drop in amount compared to the severe drought, it is lower than that of loss of moderate drought. These results suggest that the karst process may be deposited under the influence of extreme drought. Of course, this does not rule out the effect of abnormal experimental data.
Not surprisingly, rare drought has caused the highest loss to karst dissolution. On average, rare drought has caused a 2.0546 mg cm-2 (range from 0.9616 to 2.6323 mg cm-2) of karst dissolution loss for the forest, 1.9405 mg cm-2 (range from 1.0065 to 2.7327 mg cm-2) for cropland, 2.2760 mg cm-2(range from 0.5258 to 3.3794 mg cm-2) for shrubland, and 4.5336 mg cm-2 (range from 0.5500 to 8.3984 mg cm-2) for grassland, which equivalent to 54.55% of karst dissolution loss for the forest, 55.97% of loss for cropland, 48.03% of loss for shrubland, and 64.34% of loss for grassland, respectively. In total, grassland suffered the highest karst dissolution loss under the impact of rare drought, followed by shrubland and forest, and then the cropland has the lowest loss of karst dissolution. In terms of spatial loss, rare drought has the greatest impact on forest and shrubland in Site A, followed by Site B, and the forest and shrubland of Site C have the least effects. While for cropland, Site B has the highest loss of karst dissolution, followed by Site C, and Site A has the lowest loss of karst dissolution. For grassland, Site B suffered the biggest loss of karst dissolution, followed by Site A, and Site C suffered the lowest loss of karst dissolution.
The vertical analysis showed that there had been a clear increase trend in karst dissolution loss with the rise of drought intensity (Figure 3, Figure 4). With the drought intensity increased from light to severe, the karst dissolution losses of almost all land cover types in amount were increased except for the grassland in Site C (Figure 3). When drought intensity rises to the extreme, the dissolution loss of forest in Site A and Site B, and the dissolution loss of shrubland in Site B have a slight drop. The karst dissolution loss of all types of land cover in three experimental sites was increased along with the strengthen of drought intensity. Although the loss percentage of karst dissolution is not consistent with the increase of drought intensity, it also shows a clear upward trend (Figure 4). Regionally, almost all karst dissolution loss of land cover in Site C was clearly lower than Site A and Site B except the cropland. According to the experimental results, the lower amount of karst dissolution loss does not mean that the loss rate is small such as the karst dissolution loss of forest in Site C. It also shows that the influence of drought on karst dissolution loss in different areas is exceptionally related to karst environment.