What will it take to keep a sunken Civil War ship from succumbing to wood decay? Decomposition caused by fungi, bacteria, and other natural agents is a natural part of forest life cycles, breaking down dead and dying trees to return nutrients to the soil for use by other living organisms. However, wood decay creates challenges for those working to preserve historic wooden artifacts for posterity. A go-to expert in both forest health and historical preservation is Bob Blanchette, the UMN forest mycology professor who also has aided with historical preservation in such storied locations as Beijing’s Forbidden City, King Midas’s tomb, Ernest Shackleton’s Antarctic research sites, and Chilean historic churches.
Ninety-eight years underwater can do a lot of structural damage to a wooden ship. The USS Cairo, was one of the first Civil War casemate ironclads and part of the Union City Class Mississippi river squadron, sunk after hitting a mine in 1862. It then sat at the bottom of the Yazoo River, undergoing soft rot attack by fungi and then bacterial degradation as it increasingly became covered by river sediment. Salvage efforts in the 1950s found Cairo very decayed and difficult to lift with cables and wires—its softened wood “cut as if one were to cut through cheese with a wire.” After its eventual recovery, the Cairo sat outdoors in the Mississippi weather for 15 years until funding was secured to preserve the ship at the Vicksburg National Military Park in Mississippi, where it has remained for 40 years. It has been displayed outdoors under a covered structure and received some wood treatments to aid preservation. However, to preserve this ship as it continues to age and degrade, more information is needed on the wood degradation taking place.
In collaboration with conservators Claudia Chemello and Paul Mardikian from Terra Mare Conservation, and the Vicksburg National Military Park, Blanchette and Ben Held are using wood microbiology and pathology skills to diagnose this ailing ship. Using 66 small wooden samples from the Cairo, Blanchette and Held isolated the available fungal cultures, which then underwent DNA extraction and sequencing for molecular identification. This revealed 115 unique taxa of fungi present, many of which were known to cause soft rot, such as select species of Alternaria, Curvularia, Chaetomium, Cladiosporum, and Xylaria. Also present were aggressive white rot fungi. Many of these have received little study. Using microscopic analysis, they identified the wood samples as oak, pine, and yellow poplar. Additionally, a subset of wood samples underwent Inductively Coupled Argon Plasma Optical Emission Spectrometry to compare elements present, versus newer wood pieces used as control. The Cairo samples showed abnormally high concentrations of boron, copper, lead, zinc, among others. For full results and process, see the publication in Journal of Fungi.
These findings provide a specific molecular description of the environment- and fungal-induced changes undergone by the Cairo, which for the first time, provide a more detailed understanding of the deterioration history and current condition of this landmark. From there, the team is providing guidance on long-term conservation measures for the Cairo. A key recommendation arising from the study is an urgent need to enclose the ship in a controlled environment to mitigate decay. More broadly, these findings provide a case study on how fungi can interact with wood and other elements, as well as in the impact of chemical treatments that had been used to try and preserve the Cairo in the past. There is now a baseline of information that opens opportunities to further analyze how soft rot and white rot fungi interact with aging wood that has been treated for preservation, an area in which more information is needed to improve best practices.
Blanchette, R.A.; Held, B.W.; Chemello, C.; Mardikian, P. Evaluation of Wood Decay and Identification of Fungi Found in the USS Cairo, a Historic American Civil War Ironclad Gunboat. J. Fungi 2025, 11, 732. https://doi.org/10.3390/jof11100732