Research article 142 Environmental Geology 31 (3/4) June 1997 7 Q Springer-Verlag Received: 18 December 1995 7 Accepted 10 September 1996 A. Pulido-Bosch (Y) 7 W. Martín-Rosales 7 M. López-Chicano 7 A.Vallejos Department of Geodynamics, Faculty of Sciences. 18071 Granada. Spain C. M. Rodríguez-Navarro Department of Mineralogy, Faculty of Sciences. 18071 Granada, Spain. Human impact in a tourist karstic cave (Aracena, Spain) A. Pulido-Bosch 7 W. Martín-Rosales 7 M. López-Chicano 7 C. M. Rodríguez-Navarro A. Vallejos Abstract Human intrusion on the Cave of Marvels (southwestern Spain) has produced a series of ef- fects on the water (fall in the level of the pools due to pumping from nearby wells), the air (increased temperature and CO 2 concentration as well as de- creased relative humidity) and the rock. In addi- tion, plant colonization, favored by the lighting sys- tem, has irreversibly altered numerous speleothems. The processes of degradation are especially intense in the sectors with less air volume and limited ven- tilation. The analysis of the cave deposits by scan- ning electron microscopy and thin section analysis revealed that floral pollution constitutes one of the most aggressive agents against the calcite and ara- gonite precipitates, being responsible for biochemi- cal and biophysical degradation of the first order. Key words Tourist cave 7 Human impact 7 Speleothem degradation 7 Biological weathering Introduction In recent years, interest in the underground karstic envi- ronment has grown, not only from a speleological or scientific viewpoint, but also from an economic perspec- tive. The profits derived directly and indirectly from the touristic exploitation of caves can acquire substantial im- portance at local level. A good example of this is the Grotta Grande del Vento, one of the most important tou- ristic caves in Italy, which received almost 9 million visi- tors between 1974 and 1990 (Bertolani and others 1991). In Aracena (southwestern Spain), a town of only 6000 in- habitants, the Cave of Marvels has over 160 000 visitors annually, undoubtedly constituting a notable source of income for this small population. However, in some instances, the lack of regulation of the visits or of an adequate maintenance infrastructure can result in a serious threat to the underground environ- ment (Cigna 1993). One of the major problems is the growth and proliferation of microflora (algae, lichens and mosses) as a consequence of inappropriate illumination, gravely damaging the speleothems and secondary carbon- ate deposits (Caumartin 1986). The study of cave conservation in relation to tourism is not simple, since many factors and variables must be si- multaneously taken into account. From the standpoint of the cave itself, the oldest and most common methodolog- ical approach is based on the concept of a speleological network, which treats caves as the only mechanism of transference between the endokarst and the exterior (Trombe 1952; Eraso 1969). Other authors consider a cave to be a closed system (Heaton 1986), using models based on physics to predict environmental variations in- duced by human presence (Villar and others 1984, 1986; Cigna 1987). Mangin and D’Hulst (1995) view the prob- lem from a larger perspective, conceiving caves within their hydrogeological context and considering them as a system in dynamic equilibrium in which the energy in- puts are equal to the outputs; excessive human pressure upsets the balance, producing a progressive environmen- tal degradation. Such imbalance can be identified by cor- relative and spectral analyses of the different variables in- volved. This is a method frequently used in karstic hy- drology and hydrogeology (Mangin 1984; Padilla and Pu- lido-Bosch 1995). The fundamental mechanisms of anthropic alteration of speleothems are related to the processes of evaporation, condensation and augmentation of CO 2 concentration, though biological corrosion can result in more serious degradation by the involuntary introduction of microor- ganisms. The cave and the monitoring network The Cave of Marvels is situated in the southwest corner of Spain (Fig. 1), some 70 km from Portugal. This cave has a known length of 2130 m and, although its develop-