Changes in the Alhambra Palaces algal biodeterioration after 25 years

Abstract

The architectural complex of the Alhambra in Granada is an important part of our cultural heritage, both for its historical and artistic relevance. Selected as UNESCO World Heritage Site in 1984, it is currently one of the most visited monuments in Europe. In order to preserve it, constant conservation and restoration activities are needed. An important deterioration agent that affects cultural heritage is microalgae, which are capable of colonizing and modifying stone, especially those sites with high humidity or in which water is present, like the numerous fountains, ponds and channels in the Alhambra. Microalgae form biofilms and mats that cause aesthetic alterations on stone, as well as harmful chemical and physical changes like, for instance, mineral crust formation. In the present paper, we analyze the microalgal colonization and the state of conservation of the most relevant fountains in the Nasrid Palaces of the Alhambra, and we compare it with the state of conservation and colonization they presented 25 years ago. Samplings have been carried out to identify the different species present on the fountains and to assess any modification on algal communities after this period of time, during which fountains have been subjected to different treatments and restoration processes. Presence of microalgae on the fountains and the characteristics of their communities after 25 years can serve as an indicator of the utility of the treatments employed for conservation. Despite some fountains have experienced an improvement regarding colonization in relation to the past, there are no significant changes regarding the type of the most persistent and mineralizing microalgae. It should be noted that the problem of algal colonization has not disappeared, and it would be very interesting to address it with an eye to the future.