Rock outcrops are widespread across the surface of the earth, particularly in karst environments, and they play an important role in infiltration-runoff processes by triggering preferential flow. However, the characteristics of the preferential flow network at the soil-rock interface and its influencing factors in karst areas remain poorly understood. To clarify how the emergence of outcrops on the land surface affects soil infiltrability and water flow behavior, soil hydraulic conductivity (K) measurements and dye tracing experiments were conducted in a karst area with two contrasting surface features (i.e., rock outcrop plot [RP] and non-rock-outcrop plot [NRP]) in Yunnan Province, Southwest China. Results showed that (i) in the immediate vicinity of rock outcrops in the RP, K values were significantly increased, and other soil properties and plants were also improved when compared with results 1 m away from outcrops and in the NRP; and (ii) in the RP, the soil-rock interface dominated the preferential flow network surrounding outcrops, and the connected conduits produced by plant roots and soil fauna were also involved in this infiltration process. Matrix flow was the dominant flow behavior in the NRP. We concluded that rock outcrops, by improving soil properties and building a well-connected preferential flow network, can greatly change infiltrability and water flow behavior in karst soil. This implied that outcrops will facilitate quick infiltration after most rainfall events and thus reduce rain-induced surface runoff and soil erosion, as well as increasing groundwater recharge and the water supply to nearby plants.
Core Ideas
Runoff simulation was conducted on different sides of rock outcrops.
Rock outcrops shaped the water flow paths differently on their three sides.
Outcrop runoff will contribute greatly to soil loss, rock dissolution, and biodiversity.
Rock outcrops (ROCs), a widespread surface component in a karst landscape, play a unique, hydrological role in the infiltration and redistribution of precipitation. This experiment aimed to explore water pathways of outcrop runoff and their ecological functions in epikarst by applying the dye tracer Brilliant Blue FCF on three sides of rocks—the uphill sides, the downhill sides, and the lateral sides—to simulate the outcrop runoff under a rainfall intensity of 100 mm h−1, combined with a soil loss survey and soil property measurements. Our results showed that the outcrop runoff infiltration in three directions (i.e., lateral flow into the soil, vertical flow, and lateral spread at the soil–rock interface) differed greatly on the three sides of the ROCs. Deep but narrow vertical flow was the most common infiltration pattern on the uphill sides; long but shallow lateral flow toward downslope dominated outcrop runoff movement on the lateral sides. However, on the downhill sides, the vertical flow at the soil–rock interface was quantitatively equal to the lateral flow to soil. The difference in outcrop runoff infiltration at the three sides of ROCs may help to reveal the mechanisms of soil erosion as well as rock dissolution and biodiversity in a karst environment.
Rock outcrop is an important habitat supporting plant communities in karst landscape. However, information on the restoration of higher biotic populations on outcrops is limited. Here, we investigated the diversity, biomass changes of higher vascular plants (VP) and humus soil (HS) on karst outcrops during a restoration process. We surveyed VP on rock outcrops and measured HS reserved by various rock microhabitats in a rock desertification ecosystem (RDE), an anthropogenic forest ecosystem (AFE), and a secondary forest ecosystem (SFE) in Shilin County, southwest China. HS metrics (e.g. quantity and nutrients content) and VP metrics (e.g. richness, diversity and biomass) were higher at AFE than at RDE, but lower than at SFE, suggesting that the restoration of soil subsystem vegetation increased HS properties and favored the succession of VP on rock outcrops. There was significantly positive correlation between VP metrics and HS amount, indicating that the succession of VP was strongly affected by availability and heterogeneity of HS in various rock microhabitats. Thus, floral succession of rock subsystem was slow owing to the limited resources on outcrops, although the vegetation was restored in soil subsystem.
Preferential flow is the most common form of water loss occurring at the interface between rock and soil (hereinafter referred to as “rock–soil interface”) in karst areas, and it is also one of the important factors causing soil water leakage into the underground. Therefore, it is of great significance to cut off the pathway of soil water loss through control of preferential flow. In this experiment, rock film mulching (RFM) was used to control the preferential flow at the rock–soil interface, and its influence on the soil water infiltration pattern and soil water content was analyzed by simulating rainfall, dye tracer tests, and digging soil profiles. The results show that: (1) the RFM can significantly control the soil water loss at the rock–soil interface, (2) so that the water intercepted by the above-ground rocks changed from longitudinal infiltration to transverse diffusion, more water moved into the surrounding soil patches, and (3) the soil water content was significantly increased. These results indicate that the RFM has an important blocking effect on preferential flow at the rock–soil interface, which has important guiding significance for reducing soil water erosion in karst areas.
The research on production of fuels and value‐added chemicals from sustainable feedstocks is of considerable significance. In this study, a solid acid, cucurbit[6]uril‐sulfate (Q[6]‐sulfate) was prepared as an efficient catalyst to produce ethyl levulinate (EL) from various feedstocks, including biomass‐derived carbohydrates (fructose, glucose, and sucrose), expired fructan‐probiotic granules and kitchen waste. Compared to homogeneous mineral/organic acids, the application of solid acid Q[6]‐sulfate reduced the acidic waste effluent and alleviated the corrosion of equipment. Q[6]‐sulfate exhibited higher catalytic efficiency than conventional sulfonic solid acids. After optimizing reaction conditions, EL yields of 97.3 %, 97.1 %, and 76.3 % were obtained from fructose, glucose, and sucrose, respectively. Furthermore, EL was successfully produced by the Q[6]‐sulfate‐catalyzed ethanolysis of expired fructan‐probiotic granules and kitchen waste, and maximum yields of 89.5 % and 43.7 % were obtained respectively. This work provides a sustainable route for the catalytic production of EL and the valorization of biomass‐derived carbohydrates and food/kitchen waste.
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