Light eutrophication in show caves and other light-
deprived humid environments, such as mines, tunnels 
and catacombs, can support visible growth of microbial 
mats, with photoautotrophs as the dominant group of or-
ganisms. Photosynthetic pigments of aerophytic cyano-
bacteria and eukaroytic algae impose a greenish patina 
upon surfaces to which – with other community mem-
bers – they adhere strongly. For example, sequencing 
of lampenflora DNA from the Škocjan Caves, Slovenia, 
UNESCO World Heritage Site, revealed a relative domi-
nance of Cyanobacteria (~70%) among prokaryotes, over 
Proteobacteria (~10%), Bacterioidetes (~10%) and other 
groups that represented the remaining ~10% (Plancto-
mycetes, Firmicutes, Acidobacteria, Chlamydiae, Verru-
momicrobia, Actinobacteria). Diverse eukaryotic algae, 
fungi, flagellates and amoebozoans were also identified 
within the community. These “human induced diversity 
hotspots” in caves are responsible for the biodeterioration 
of colonized surfaces that is a common result of the syn-
ergistic effects of phototrophs and heterotrophs. When 
sites become colonized by higher plants, such as moss-
es, liverworts and ferns in species succession, irrevers-
ible biodeterioration impact on rocks and speleothems 
becomes an even more urgent issue. Historical inscrip-
tions and rock-art paintings are particularly sensitive to 
biodeterioration. Lampenflora also affects components 
of the cave fauna, which not only graze upon it, but also 
facilitate its dispersal to other parts of the caves. It can be 
considered a direct indicator for light eutrophication and 
of the available energy within the cave ecosystem. 
There is a need for appropriate monitoring to pro-
vide alerts that will prompt timely action against lampen-
flora before it starts to affect the substrate integrity irre-
versibly, attract excessive and unwanted fauna or become 
encrusted and armoured against subsequent treatment 
and removal. Such monitoring could also be expanded 
to help estimate the efficiency of lampenflora removal in 
caves where this is carried out routinely. Regular moni-
toring can facilitate the delimitation of zones within a 
cave on the basis of the local susceptibility to lampenflora 
colonization. 
Spectrophotometric survey of cave surfaces can 
cover all of the above-mentioned aspects without adverse 
effects on the surfaces. Such methods are used widely in 
the printing, automotive, food, cosmetic, paint, construc-
tion, paper and packaging industries, etc. In the field of 
cultural heritage, the technique is applied to measure the 
difference in appearance of historical material before and 
after treatment with different preservative, protective or 
consolidative materials. 
One feasible approach to colorimetric analysis is 
based on a chromacity system CIEL
*
a
*
b
* 
(where L
*
 stands 
for luminosity, a
*
 being the red–green parameter and b* 
being the blue–yellow parameter). This system enables 
easy calculation of colour changes over time or between 
individual sites. Several sites in the show cave sections 
SPECTROPHOTOMETRIC MONITORING OF SURFACES  
IN SHOW CAVES AS A PART OF MANAGEMENT PLANS  
FOR CONTROLLING LAMPENFLORA GROWTH
Janez MULEC
1
, Samo ŠTURM
2
, Andreja PONDELAK
3
 & Alenka MAUKO PRANJIĆ
3
UDC 582.3:551.435.84
1
Karst Research Institute, Research Centre of the Slovenian Academy of Sciences and Arts, Titov trg 2, SI-6230 Postojna, Slovenia
2
Park Škocjanske jame, Slovenija, Škocjan 2, 6215 Divača, Slovenia
3
Slovenian National Building and Civil Engineering Institute, Dimičeva ulica 12, SI-1000 Ljubljana, Slovenia
Received/Prejeto: 18.11.2019 DOI: 10.3986/ac.v49i1.7677
ACTA CARSOLOGICA 49/1, 141-142, POSTOJNA 2020
COBISS: 1.03

of the Škocjan Caves were monitored to track surface 
colour changes after the adoption of LED lighting and 
treatment of the rock surfaces with hydrogen peroxide 
to remove lampenflora. Results of the oxidizing effect 
of hydrogen peroxide treatment on surfaces affected by 
lampenflora were observed clearly, with the most notable 
contributions from the red–green parameter followed by 
luminosity. 
Interpretation of the colorimetric results obtained 
using this system should consider several factors: fresh 
colonization of lampenflora, increase/decrease of popu-
lation density due to the application of biocides, encrus-
tation of pre-existing lampenflora (and consequently 
higher initial values of the green parameter), and fresh 
deposition of calcite and/or other (coloured) minerals 
between measurements. It seems that lampenflora grows 
faster on coloured (e.g., grey-brown) surfaces, that can 
be attributed to the presence of nutrients or other growth 
factors. Sites commonly exhibited reduced green colour 
after being treated with hydrogen peroxide. Although 
spectrophotometric survey can provide valuable data 
about the monitored surfaces, sometimes a second step, 
to identify the key phototrophs by “time consuming” cul-
turing or the quantification of key indicator species, e.g., 
by quantitative Polymerase Chain Reaction (qPCR), is 
still needed.
Results of spectrophotometric monitoring of rock 
surfaces can be related directly to the progress of lam-
penflora proliferation or removal. Initially, monitoring 
sites should be selected carefully, particularly if there are 
already naturally existing green minerals, if the rate of 
flowstone deposition outstrips the rate of lampenflora 
growth, or if an encrusted microbial mat is already pres-
ent. Particular attention should be given to the inhomo-
geneous nature of surfaces, their unevenness or varying 
colour, and the presence of water droplets and/or seep-
ages.
In show caves catering for large numbers of visi-
tors, necessitating long periods of illumination, spectro-
photometric monitoring of surfaces should become an 
essential part of the management plan for controlling 
lampenflora growth. In some caves preventative actions 
include imposition of a restricted lighting regime with a 
low light intensity, i.e., with a low photosynthetic pho-
ton flux density – PPFD. Sometimes this is cross-coupled 
with the installation of tuneable, low energy-consuming 
LED lamps with emission spectra that lie outside the 
absorption peaks of the main photosynthetic pigment – 
chlorophyll a. Generally, these measures are insufficient 
to prevent initial colonization and further propagation 
of lampenflora in the underground. Show cave manag-
ers already employ some measures to help the recovery 
of affected sites in caves, for example by application of 
biocides based on hydrogen peroxide or sodium hypo-
chlorite. 
Early stages of lampenflora colonization with a low 
population density of microscopic phototrophs cannot 
be detected by subjective “visual inspection” of critical 
surfaces; for this reason, application of a spectrophotom-
etry-based monitoring strategy seems a practical and 
non-invasive initial approach to avoiding the develop-
ment of green mats on illuminated surfaces. Lampenflo-
ra represents a critical issue for cave management world-
wide, and the accompanying problems are likewise com-
mon. That is why the need for good-practice exchange 
was one of the key issues pursued at the recent meeting 
on “Sustainable Management of Show Caves”, held at 
Škocjan Caves, 07–09 October 2019. 
The authors acknowledge David Lowe for language 
editing assistance.
JANEZ MULEC, SAMO ŠTURM, ANDREJA PONDELAK & ALENKA MAUKO PRANJIĆ
ACTA CARSOLOGICA 49/1 – 2020 142