New progress has been made in the soluble carbon transport mechanism driven by multi-interface hydrological processes in key karst slope zones

Under the action of karst, the dual-dimensional structure of aboveground and underground in the karst area developed, and the hydrological process was mainly
the underground process.
The core zone of the karst critical zone (soil-surface karst zone system) is not only a major reservoir of soluble carbon, but also a hot spot
for hydrological and biogeochemical processes.
However, due to the limitation of observation techniques for underground processes in the karst critical zone, the mechanism of soluble carbon loss of multi-interface runoff components in the soil-surface karst zone system is unclear
。 The karst ecosystem scientific research plots established in this area in the past all draw on the monitoring methods and technical means of surface processes in the loess area and red soil area, which cannot realize the coupling monitoring of aboveground-underground processes unique to karst areas at the same time, and cannot reveal the distribution, migration and transformation mechanism of water, soil and biogenic elements in the three-dimensional space of aboveground-underground multi-interface in key areas of karst area, which is difficult to meet the requirements of vegetation restoration, soil erosion control, groundwater recharge assessment and efficient utilization of water resources, non-point source pollution prevention and control in karst areas.
Major practical needs
such as extreme weather event response.
In view of the above problems, the Huanjiang Karst Ecosystem Observation and Research Station has developed a multi-interface three-dimensional water and soil process monitoring method and platform for the key karst slope zone, which realizes the real-time dynamic monitoring and sample collection of production flow and material migration process at multiple interfaces (atmosphere-soil interface, soil-surface karst zone interface, surface karst zone-bedrock interface) in key karst zone (Figure 1).

Recently, the team of Wang Kelin and Zhang Wei of the Huanjiang Karst Ecosystem Observation and Research Station of the Institute of Subtropical Agroecology, Chinese Academy of Sciences, relied on the multi-interface three-dimensional water and soil process monitoring platform (4 treatments, 3 duplicates, a total of 12 communities) in the key zone of the above karst slope to simultaneously observe the multi-interface production flow processes and soluble carbon loss processes in the soil-surface karst zone system for three consecutive years (2018-2020).
The effects
of structural factors (bare rock rate, soil thickness, soil thickness coefficient of variation, surface karst zone thickness, weathering degree of surface karst zone, bedrock undulation, soil texture, etc.
) and land use patterns (natural restoration of shrubland, pasture, fruit forest, traditional maize) on multi-interface hydrological processes and soluble carbon loss fluxes in key karst zones were analyzed.

The results (Figure 2): 1) show that the hydrological processes in the key zone of karst slope show obvious characteristics of mainly underground processes: lateral infiltration of surface karst zone (70%), middle flow of loam at the rock-soil interface (27%), and surface runoff (3%)
.
In general, with the increase of human utilization intensity, the groundwater recharge of karst slope decreased significantly, and the shallow surface lateral runoff such as surface runoff and the middle flow of rock-soil interface gradually increased, thereby reducing the hydrological regulation and storage function of the soil-surface karst zone system and aggravating the risk of
drought and flood disasters.
2) Soil thickness, bedrock undulation and soil texture are the most important key belt structural factors
to control the multi-interface DOC and DIC loss flux in the key karst zone.
Geotechnical systems with thicker soil layers and flat contact of the soil-surface karst zone are more likely to trigger soluble carbon loss
driven by shallow surface transverse runoff.
However, compared with traditional maize cultivation and fruit forest planting, conservation pasture planting showed significant water retention and carbon retention effects
such as reducing runoff and carbon loss.
3) Extreme rainfall events lead to the loss of soluble carbon in the multiboundary system of the key zone of karst slope as high as 2.
5 times the total annual loss of flat water, and extreme rainfall events are the key prevention and control period
for the loss of key biogenic substances in karst areas.
This study provides a scientific basis
for the loss control of biotic elements in key karst zones and sustainable use of water and soil resources under the background of global change.

The findings were published in Catena under the title Soluble carbon loss through multiple runoff components in the shallow subsurface of a karst hillslope: Impact of critical zone structure and land use
。 The research was supported
by the National Natural Science Foundation of China, the National Natural Science Foundation of China, and the Guangxi Key Research and Development.

Paper link

Fig.
1 Multi-interface three-dimensional soil and water process monitoring platform in key zones of karst slopes

Fig.
2 Multi-interface DOC and DIC loss characteristics and their key influencing factors in key zones of karst slopes