This paper presents an experiment on lampenflora removal in show caves located in a tropical monsoon climate in southeast Asia. Lampenflora thrive in wet conditions on surfaces directly illuminated by white light. They colonize different levels in show caves, from the cave ceiling, with a biota characterized of mainly cyanobacteria (Oscillatoria, Spirulina), algae (Chlorella, Oedoclarium), and mosses (Cyathodium, Thuidium), to near the cave floor, with a more complex biota including higher plants like ferns (Asplenium) and flowering plants (Centella). Mature lampenflora mats also harbor non-phototrophic fungi and bacteria. With the use of environmental scanning electron microscopy, speleothem surfaces were found severely damaged by lampenflora and their associates. In this study, we used H 2 O 2 as an environmentally friendly chemical to exterminate lampenflora. The applied solution should be at least 15% H 2 O 2 to efficiently destroy microbiota such as green algae, diatoms, and bacteria. For a complex community including mosses, fungi, and vascular plants, repeated spraying of chemical and, if possible, water jet washing at carefully selected places are required to recover the aesthetic characteristics of speleothems. Only a combination of such cleaning practices, and then some modification of the illumination regime, can minimize lampenflora development in show caves.
Organic fertilizer application is often touted as an economical and effective method to increase soil fertility. However, this amendment may increase dissolved organic carbon (DOC) runoff into downstream aquatic ecosystems and may consequently alter aquatic microbial community. We focused on understanding the effects of DOC runoff from soils amended with compost, vermicompost, or biochar on the aquatic microbial community of a tropical reservoir. Runoff collected from a series of rainfall simulations on soils amended with different organic fertilizers was incubated for 16 days in a series of 200 L mesocosms filled with water from a downstream reservoir. We applied 454 high throughput pyrosequencing for bacterial 16S rRNA genes to analyze microbial communities. After 16 days of incubation, the richness and evenness of the microbial communities present decreased in the mesocosms amended with any organic fertilizers, except for the evenness in the mesocosms amended with compost runoff. In contrast, they increased in the reservoir water control and soil-only amended mesocosms. Community structure was mainly affected by pH and DOC concentration. Compared to the autochthonous organic carbon produced during primary production, the addition of allochthonous DOC from these organic amendments seemed to exert a stronger effect on the communities over the period of incubation. While the Proteobacteria and Actinobacteria classes were positively associated with higher DOC concentration, the number of sequences representing key bacterial groups differed between mesocosms particularly between the biochar runoff addition and the compost or vermi-compost runoff additions. The genera of Propionibacterium spp. and Methylobacterium spp. were highly abundant in the compost runoff additions suggesting that they may represent sentinel species of complex organic carbon inputs. Overall, this work further underlines the importance of studying the off-site impacts of organic fertilizers as their impact on downstream aquatic systems is not negligible.
Abstract:In this study, air, water, and host rock in show caves in a Vietnam's karst region was monitored and analyzed to identify the ventilation regime and track the cave air CO 2 sources. In general, the studied caves are well ventilated. In dynamic -multiple entrance caves, air ventilation is described with the use of U shape model. In static -single entrance cave, air circulation is explained by cold air trap model. Both ventilation models suggest that air is more circulated in winter than in summer. Seasonally, the cave air CO 2 increases from early spring to summer. Value in the deepest part of the single-entrance cave is approximately 1,000 ppmv and 8,000 ppmv in early spring and summer, respectively. In multiple-entrance and wet caves, CO 2 level is fairly constant all over the show section, increasing from 500 ppmv in early spring to 2,000 ppmv in summer. Data of microclimate, CO 2 content, and particularly δ 13 C show that cave air, particularly in single entrance cave, has higher CO 2 concentration during summer due to a stagnation of cave air circulation and an elevated CO 2 input from soil and epikarst. The cave air CO 2 increase is also observed after intense rainfalls. A factor that increase cave air CO 2 in show caves during the festive days could probably be huma n exhaling but the extent of human factor in these studied cave systems should be further investigated. Cave waters including cave pools and streams mediate CO 2 level in wet caves. Above all, the atmospheric fraction of CO 2 is always dominant (>60%) in all cave sections.Phong Nha -Ke Bang, microclimate, cave air ventilation, soil air CO 2 , human exhaling
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