THE WORLD’S OLDEST MAN-MADE BIOLOGICAL EXPERIMENT - ANCIENT STONE JARS AS NATURAL MESOCOSMS FOR STUDYING ECOLOGICAL STRUCTURE IN TEMPORARY AQUATIC ECOSYSTEMS

Biological experiments are often short-lived, yet effects on communities and processes require time to emerge. Consequently, conclusions become more robust with longer durations. A striking real-world example can be found in central Laos, where thousands of large stone jars are scattered throughout the landscape. For ~2000 years, rainwater interacting with jar geology and varying tree cover has created unique and replicated aquatic ecosystems. Their clustered layout enables testing of ecological and evolutionary questions. Here, we report how these ancient mesocosms can be used to test ecosystem responses to local abiotic variation and disturbance. The jars contained between 5 to 254 liters, but the capacity of the jars was substantially larger (from about 45 to over 1,000 liters). We show that tree cover dominates every jar ecosystem’s state, with variations in tree cover density creating gradients in oxygen (O₂) and nutrient concentrations among jar ecosystems. Litter contribution to aquatic ecosystems leads to higher nutrient levels and lower O₂ concentration, even in systems under different long-term selection, in the oldest man-made ecosystems ever analyzed. The jar communities, obtained from environmental DNA, reveal very distinct composition in each jar shaped by abiotic conditions and a seemingly high degree of idiosyncrasy. This system provides a rare long-term perspective on how alternate wetting and drying together with terrestrial inputs influence aquatic ecosystems, providing insights into resilience, biodiversity, and ecosystem function in a changing world.

Presentation Preference: Standard Oral (12 Minutes)

Primary Presenter: Laura Käse, Copenhagen University (kaese.laura@gmail.com)

Authors:

Laura Käse, University of Copenhagen, Department of Biology, Section for Freshwater Biology, Denmark  (laura.kaese@bio.ku.dk)

Chanvilay Somvongsa, National University of Laos (NUoL), Department of Biology, Center of Excellence in Biodiversity (CoEB), Lao PDR  (chanvilaysomvongsa@gmail.com)

Khamla Inkhavilay, National University of Laos (NUoL), Department of Biology, Center of Excellence in Biodiversity (CoEB), Lao PDR  (khamla.inkhavilay@nuol.edu.la)

Banchai Malavong, National University of Laos (NUoL), Department of Biology, Center of Excellence in Biodiversity (CoEB), Lao PDR  (banchaimlv@gmail.com)

Ida Nielsen, University of Copenhagen, Globe Institute, Section for GeoGenetics, Denmark  (ida.broman.nielsen@sund.ku.dk)

Sander Nielsen, University of Copenhagen, Department of Biology, Section for Freshwater Biology, Denmark  (sanderbn@hotmail.com)

Claus Christensen, AquaDiscover, Denmark  (claus@aquadiscover.com)

Lars Iversen, McGill University, Department of Biology, Canada  (lars.iversen@mcgill.ca)

Ole Pedersen, University of Copenhagen, Department of Biology, Section for Freshwater Biology, Denmark  (opedersen@bio.ku.dk)

Lars Baastrup-Spohr, University of Copenhagen, Department of Biology, Section for Freshwater Biology, Denmark  (lbaastrupspohr@bio.ku.dk)