The CO
2
concentration of the air in Postojna Cave (400–7900 ppm) is found to be induced by CO
2
sources (human respiration contributing ~ 20,000–58,000 ppm per breath, outgassing of dripwater and ...water seeping from the vadose zone/epikarst with a
p
CO
2
values of 5000–29,000 ppm, and underground Pivka River having
p
CO
2
at 2344–4266 ppm) and CO
2
dilution (inflow of outside air with a CO
2
concentration of ~ 400 ppm). Measurements show that sinking Pivka River has the lowest CO
2
concentration among plausible CO
2
sources but still continuously exceeds the surrounding cave air CO
2
concentration. During the winter months, intensive ventilation reduces the cave air CO
2
concentration to outside levels (~ 400 ppm), even in the centre of the cave system. CO
2
dilution is less pronounced in summer (CO
2(min)
≈ 800 ppm), since the ventilation rate is not as strong as in winter and the outside air that enters the cave through breathing holes and fractures is enriched with soil CO
2
. During spring and autumn, the daily alternation of the ventilation regime with a smaller rate of air exchange results in yearly cave air CO
2
peaks of up to ~ 2400 ppm. Some dead-end passages can be much less affected by ventilation, resulting in a cave air CO
2
concentration of up to 7900 ppm. The strongest diurnal CO
2
peaks due to human respiration were recorded during the spring holidays (increase of up to 1300 ppm day
−1
), compared to considerably smaller summer peaks despite peak visits (increase of ~ 600 ppm day
−1
).
Nitrate (NO
3
−
) pollution is a common phenomenon in karst underground rivers, which are important water sources in karst landscapes. For drinking water safety and environmental protection, it is ...crucial to accurately identify NO
3
−
sources and their migration and transformation processes in the Lihu Underground River. In this study, water samples of the Lihu Underground River in Guangxi were collected in May 2014, October 2014, January 2015, and July 2015, and water chemical and dual isotopic (δ
15
N-NO
3
−
and δ
18
O-NO
3
−
) approaches were used to evaluate the NO
3
−
characteristics and sources in the Lihu Underground River. The concentration of NO
3
−
in the Lihu Underground River ranged from 1.16 to 19.78 mg·L
−1
, with an average of 9.30 mg·L
−1
, which is more than 37% of the WHO standard (10 mg·L
−1
). The concentrations of NO
3
−
in the wet season (May 2014 and July 2015) were slightly lower than those in the dry season (from October 2014 to January 2015) at most sampling sites due to dilution effects. The migration and transformation processes of NO
3
−
were analyzed by comparing the measured and calculated concentrations of NO
3
−
in the Lihu Underground River. In the dry season (from October 2014 to January 2015), the variation in NO
3
−
concentration upstream and midstream of the Lihu Underground River was affected by exogenous input and nitrification. From midstream to the outlet of Xiaolongdong, it is affected by self-purification factors, including physical processes, chemical processes, and biological processes. In the wet season (May 2014 and July 2015), the dilution and mixing effects were the main factors controlling the variation in NO
3
−
concentration in the Lihu Underground River. The contribution rates of potential NO
3
−
sources (incl. atmospheric precipitation (AP), NO
3
−
fertilizer (NF), NH
4
+
in fertilizer and rainfall (NFA), soil organic nitrogen (SON), and manure and sewage (M&S)) were quantitatively evaluated by using the IsoSource model. The results showed that in May 2014, the main sources of NO
3
−
were M&S and NF, with contribution rates of 46% and 41%, respectively. In October 2014, NO
3
−
sources were M&S with a contribution rate of 47%, followed by NFA with a contribution rate of 31%. In January 2015, NO
3
−
sources in groundwater were M&S, with a contribution rate of 53%, followed by NFA (34%). In July 2015, the main NO
3
−
sources were M&S and NF, whose contribution rates were 54% and 39%, respectively.
Cave air temperature, carbon dioxide concentrations in the cave air and external air temperature were analysed at several locations in Postojna Cave over the course of six holiday periods in ...2009–2011. The results show that a 1-day increase in visitor numbers from 200 to 3,500 raised the cave air temperature by a maximum of 0.5 °C. The air temperature increases are within the annual range of cave air temperature variations. A fivefold increase in visitor numbers resulted in a carbon dioxide concentration that was at least twice as high as normal. The carbon dioxide concentration increased from 450 to 1,750 ppm (December 2009–January 2010). After 10 days of peak period visits, both the CO
2
concentration and the temperature returned almost to the pre-holiday values. The gradual increase in mean annual air temperature in the cave (2004–2010) is not related to the number of visitors but to outside climate conditions.
We use measurements of dissolution rates of limestone tablets placed along a cave stream to estimate rates of modern incision. Dissolution rates within the stream display a systematic decrease with ...downstream distance. We discuss a variety of mechanisms that could be responsible for the longitudinal decrease in dissolution rates and develop simple mathematical models for each. The dissolutional length scales that arise from each model allow a first-order estimate of the plausibility of each mechanism and motivate further field studies to test each possibility. Water chemistry and other field data suggest that a decrease in the concentration of CO2 along the cave stream is responsible for the observed decrease in dissolution rates. We propose two potential mechanisms that could trigger this reduction in dissolved CO2 and discuss the plausibility of each mechanism in light of the field data collected. Either of these mechanisms introduces a feedback loop whereby the stream profile of a channel in soluble bedrock indirectly influences CO2 concentrations in the water, via either microbial or hydraulic processes. The CO2 concentration in turn effects the incision rates and therefore the future stream profile. This study illustrates the importance of CO2 dynamics in determining incision rates in a soluble channel and points to further modeling and field work that are needed in order to enable the development of realistic stream incision models in soluble strata.
Soil organic carbon (SOC) is a critical measure of soil organic matter (SOM) content. SOM plays a vital role in ecosystem services, soil fertility, soil water retention capacity, and carbon cycling. ...SOC can be partitioned into various carbon fractions, which exhibit diverse stability and chemical compositions that are influenced variably by lithology as well as biological and climatic processes. A better understanding of SOC and the influence of different bedrock types on carbon fractions could facilitate the evaluation of the fate and stability of SOC. The present study is focused on the concentrations and characteristics of different SOC fractions (e.g., Labile organic carbon, LOC; Recalcitrant organic carbon, ROC; Calcium-bound organic carbon, Ca-SOC; Iron/aluminium-bound organic carbon, Fe/AlSOC) in forest soils associated with different bedrock lithology under similar climate conditions in the centre of the 'Classical Karst', and evaluates influence of the geological environment on SOC. SOC and SOC fraction concentrations decreased with an increase in depth in all profiles, indicating stabilized soil profiles. SOC values (9.7-45.5 g-kg-1) were consistent with the findings of other studies on soils in the region. ROC and Fe/Al-SOC (51.5-65.8 % and 68.0-73.3 %, respectively) were the major SOC fractions, while Ca-SOC accounted for a considerably lower proportion (6.4-7.4 %) of the SOC contents. Key factors influencing SOC contents were calcite (expressed as calcium oxide) and clay contents, which represent mineral complexes stabilizing SOC. Overall Fe2O3 and Al2O3 concentration did not explain differences in SOC nor its fractions, potentially due to the importance of chemical/mineral forms of Fe- and Al-related minerals (reactivity). Soils on carbonate rocks, which are richer in clay and CaO, had 6.35 g-kg-1 (28 percentage points) higher concentrations of SOC average when compared with soils on siliciclastic rock, due to higher concentrations of stabilized SOC fractions. The results demonstrate that bedrock lithology and pedogenesis are key factors influencing SOM stabilization.
The comprehensive knowledge of karst surface, caves, waters and biodiversity were examined with special emphasis on planning for environmental management and land use in karst regions using examples ...of projects performed by the staff from the Karst Research Institute ZRC SAZU. Based on the knowledge of karst, karst phenomena, karst waters and karst biodiversity, karstological monitoring was developed throughout the construction of expressways and planning for railways on karst terrain. Newly revealed karst phenomena were properly preserved. Regular climatic and biological monitoring were developed and implemented, as well as karstology consultation with an emphasis on the impact of the use of caves as natural assets. To understand karst, its evolution dynamics and processes, models were developed with which the study of the risk posed by dam site construction in karst areas was possible. Karst aquifers and their protection were studied using tracer tests and different methods of the transfer of contaminants through the vadose zone and underground flow connections. In assessing the vulnerability and contamination risk of groundwater, a comprehensive method was elaborated. Microorganisms and fauna of dripping water in caves were used as monitors of cave ecosystem health. By applying high-quality karstological research results from individual spheres of karstology and interdisciplinary studies, a foundation for sustainable planning of life in karst regions that will consider the natural and cultural characteristics and vulnerability of karst landscapes has been established.
Heaven’s Cave is located in the centre of the Phong Nha-Ke Bang national park, about 500 km southern from the Vietnamese capital and 40 km from the city of Dong Hoi. Phong Nha-Ke Bang national park ...is protected also as a UNESCO world heritage site. Due to weak economic situation in this region as a result of lack of natural resources, karst tourism represents an important opportunity for raising the quality of live in the province. A proposal to adapt non-touristic Heaven’s Cave for tourism was presented to Karst Research Institute ZRC SAZU in 2006. Because the caves are sensitive ecosystems and all activities in them should be carefully implemented, our task was to make basic survey and map the cave, to perform a speleological and touristic research, to propose possible interventions for adapting the cave for tourism and to prepare a strategy for tourism development in this area. The latter should also show us if some interest is present among tourists for new show cave in this region. From this point of view this study does not represent systematic long-term approach for adapting a cave for tourism but rather a short study of a cave with potential to be show cave in remote area of Central Vietnam. Approach used in this study should be used in similar environments as a first step to estimate if weakly known cave is environmentally and economically suitable for development for touristic purposes.Keywords: Heaven’s Cave, Thien Duong Cave, Phong Nha-Ke Bang, Vietnam, show cave.
Hydrodynamic aspect of caves Prelovšek, Mitja; Turk, Janez; Gabrovšek, Franci
International journal of speleology,
01/2008, Letnik:
37, Številka:
1
Journal Article
Recenzirano
Odprti dostop
From a hydrological point of view, active caves are a series of connected conduits which drain water through an aquifer. Water tends to choose the easiest way through the system but different ...geological and morphological barriers act as flow restrictions. The number and characteristics of restrictions depends on the particular speleogenetic environment, which is a function of geological, geomorphological, climatological and hydrological settings. Such a variety and heterogeneity of underground systems has presented a challenge for human understanding for many centuries. Access to many underground passages, theoretical knowledge and recent methods (modeling, water pressure-resistant dataloggers, precise sensors etc.) give us the opportunity to get better insight into the hydrodynamic aspect of caves. In our work we tried to approach underground hydrodynamics from both theoretical and practical points of view. We present some theoretical background of open surface and pressurized flow in underground rivers and present results of some possible scenarios. Moreover, two case studies from the Ljubljanica river basin are presented in more detail. The approach and methodology in each case is somewhat different, as the aims were different at the beginning of exploration. However, they both deal with temporal and spatial hydrodynamics of underground waters.
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