Caves are well known tourist attractions which differ both by the number of visitors and by their impact on caves which occasionally leads to the sizeable negative effect of tourism on vulnerable cave environments (Baker and Genty, 1998). Manita peć Cave (NP Paklenica, Croatia) is relatively small show cave adapted for visitors in 1937 for its exceptional interior. Preliminary report of ongoing study on tourist impact on variation in cave air CO 2 concentration in Manita peć Cave (Croatia) Matea Kulišić 1,2 , Maša Surić 1 , Robert Lončarić 1 , Lukrecija Sršen 1,2 1 Department of Geography, University of Zadar 2 Speleology club Liburnija, Zadar INTRODUCTION 26 th International Karstological School "Classical Karst": Show Caves and Science (on the occasion of the 200 th anniversary of Postojna Cave System's discovery) 18-22 June 2018, Postojna, Slovenia STUDY SITE Speleothems chamber Platform Bottom stairways Water tower First curve Top stairways Table Entrance Last chamber Speleothems chamber Main chamber Entrance Due to its morphology (descending channel) the innermost part acts as a 'cold pocket’ (Surić et al., 2017). Given these settings and increasing number of visitors, new monitoring campaign has been initiated in February 2018, aimed at the variation in cave air CO 2 concentration, in order to estimate and/or prevent possible negative impact of anthropogenic CO 2. 0 100 200 300 400 500 600 700 800 900 Annual variation of CO 2 concentration along the Manita peć cave Viewpoint Entrance Table Top stairways First curve Water tower Bottom stairways Platform Right end RESULTS Top First Water Bottom Right end stairways curve tower stairways of chamber 04.01.2018. 325 339 325 351 348 400 397 398 421 30.01.2018. 414 411 404 441 444 407 464 414 413 01.03.2018. 354 373 412 411 422 412 413 415 415 06.04.2018. 391 387 400 414 415 422 414 415 441 01.05.2018. 378 380 452 524 505 512 510 502 551 01.06.2018. 463 535 693 814 825 812 816 821 845 Measuring point Date Viewpoint Entrance Table Platform Measuring points Measuring during tourist groups before after Table 452 577 Top stairways 524 600 First curve 505 614 Water tower 512 607 Bottom stairways 510 602 Platform 502 612 First set of the measurements from January to June 2018 showed seasonal variation in cave air CO 2 concentration with winter situation characterized by minimal spatial and temporal variations (325-464 ppm). By the beginning of the summer season CO 2 concentration is already doubled in the first third of the cave and stays more or less stable down to the end of the cave. This natural increase of cave air CO 2 concentration is due to diffusion of the summer CO 2 -rich epikarst air through the bedrock discontinuities and it is expected to rise till September. However, although increased, these CO 2 concentrations are much lower in comparison with adjacent Modrič Cave where the June values are already 9-fold higher than surface concentration due to the pure ventilation (Sršen et al., 2018). During the tourists visits, additional measurements were made before and after the tourists passed by. After tourist visit the concentration of CO 2 increased approximately 100 – 150 ppm. METHODS From the February 2017 cave air CO 2 concentration is planned to be measured in front of the cave and additionally at 7 measuring points along the visitor path on monthly basis throughout the year, with occasional measurements before and after touristic groups. Measurements are conducted by AZ 7755 portable CO 2 meter (AZ Instrument), with simultaneous cave air temperature and relative humidity recording. The device has an audible alarm that gives warnings when the CO 2 concentration exceeds the limit (1000 ppm) and emits an acoustic signal (about 80 dB). Also, the unit is calibrated at the factory to 400 ppm CO 2 standards. VISITORS 0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 Number of visitors Year Annual number visitor in cave (per year) After the decade of relative stagnation in number of tourists visiting cave, last year the number of visitors increased to 12,955, although these numbers are still modest in comparison with other well-known show caves (e.g. Postojna Cave with 600,000 visitors per year; Prelovšek et al., 2018). The cave is open every day between 10 and 14 only from July to September, while in May, June and October the cave is open just three days a week, and in April only on Saturday. Such regime is the combination of the interest of tourist (mainly in summer season) and precaution to protect the cave atmosphere. Accordingly, the peak of the visitors overlaps with the natural summer increase of the CO 2 in the cave air. CONCLUSION Preliminary results of the 5-months measurement of cave air CO 2 concentrations point to the seasonal variations with summer increase caused by elevated biogenic activity on the surface and the diffusion of CO 2 -rich epikarst air through the bedrock fissures. However, due to the spacious chambers, relatively big entrance and quite fractured bedrock, Manita peć Cave is relatively well ventilated, and the variations are not as large as in e.g. adjacent Modrič Cave which has significantly different morphology. Anthropogenic impact from tourist respiration is notable (100-150 ppm increase immediately after the group passes), but short-lasting. Further measurements during the highest tourist season will confirm the exact impact of tourist visits on CO 2 concentration and we shall be able to offer some concrete proposal for the conservation of the speleological facility itself. REFERENCES Baker, A., Genty, D. (1998): Environmental pressures on conserving cave speleothems: effects of changing surface land use and increased cave tourism, Journal of Environmental Management, 53, 165-175. Kuhta, K., 2010. Manita peć Cave, NP Paklenica – Report on topographic survey and establishing of the cryptoclimatological parameters monitoring, Hidrogeos d.o.o., Zagreb (in Croatian). Prelovšek, M., Šebela, S., Turk, J., (2018.): Carbon dioxide in Postojna Cave (Slovenia): spatial distribution, seasonal dyna mics and evaluation of plausible sources and sinks, Springer-Verlag GmbH Germany, part of Springer Nature 2018. Sršen, L., Lončarić, R., Surić, M., Kulišić, M., 2018. Monitoring of the cave environmental settings in Modrič show cave (Croatia), 26 th International Karstological School. Surić, M., Lončarić, R., Lončar, N., Buzjak, N., Bajo, P., Drysdale, R.N., 2017a. Isotopic characterization of cave environments at varying altitudes on the eastern Adriatic coast (Croatia) – Implications for future speleothem-based studies, Journal of Hydrology 545, 367-380. ACKNOWLEDGEMENTS For their kind support and assistance we are grateful to the staff of the Paklenica National Park, mostly to Natalija Andačić (director of the Park), Gordan Lukač (conseravtion manager) and Dragica Jović (head of the Department of Promotional and Hospitality & Tourist Activities). 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 Number of visitors per month in cave, in 2005 and 2017 2005 2017 Manita peć Cave is located on the flank of the Paklenica canyon in Velebit Mountain at an altitude of 570 m a.s.l. It is relatively small cave (67,510 m 3 ; Kuhta, 2010) formed in Upper Jurassic limestone and consists of simple descending spatial chambers with the heights up to 35 m. Overbourden is relatively shallow (ca. 80 m) and surface is covered with sparse terra rossa and brown soils. Due to the vicinity to the Adriatic Sea (3.7 km) and the altitude of 570 m a.s.l., temperate humid climate with warm summer prevails (Cfb). Mean annual air temperature (MAAT) measured in front of the cave (Feb 2014 – Feb 2015) was 13.7 °C, while the cave MAAT measured in the innermost part of MP (July 2012 – July 2014) was 9.04 °C (Surić et al., 2017), due to the ‘cold pocket’ effect. Manita peć Cave CO 2 meter