Sedimentary Ancient DNA Tracks Multi-Kingdom Ecosystem Reorganizations Following Sequential Human Land Use at Crawford Lake.

Abstract

Crawford Lake has an exceptional stratigraphic record that began recording biannual (varved) sedimentation in the lake basin ~750 years ago, preserving evidence of shifting cultural zones and agricultural practices, from Late Woodland Period Indigenous agriculturalists to the impacts of industrialization during the late 19th century. It was selected as the candidate site for the proposed 'Anthropocene' epoch in 2023-a proposal ultimately rejected in 2024-but the lake's significance extends beyond a formal stratigraphic boundary. Its sediments preserve a long record of human-ecosystem entanglement that captures the cumulative, reverberating nature of local human impacts and global change. While many proxies have been studied at the site, the lake's sedimentary ancient DNA (sedaDNA) record has yet to be investigated. Here, we report on sedaDNA preserved at Crawford Lake over the last ~1300 years. Sedentism and agriculture clearly impacted the entire lake ecosystem, with corresponding shifts observable in the sedaDNA of plants, animals, algae, fungi and bacteria. Canada goose (Branta canadensis) roosting on the lake-likely drawn by foraging opportunities in fields cleared for Three/Four Sisters agriculture and sedentism-contributed to repeated eutrophications and algal blooms that permanently shifted the lake's ecological structure. Subsequent impacts during the Euro-Canadian zone furthered anthropogenic succession, although local impacts have been minimal since closure of the sawmill in 1900 ce, allowing for sensitivity to global change. Beyond the molecular ecological history of the lake, we also evaluate the effectiveness of an Arctic/Subarctic bait-set for palaeoecological reconstructions of the Eastern Woodlands, and the preservation of lake sedaDNA.