Ancient DNA From Lake Mud Records 1,000 Years of Human Life and Ecological Change

At the bottom of a small lake in Ontario, Canada, lies one of the most precise environmental archives on Earth, and scientists have now read a full millennium of its contents using fragments of genetic material too small to see with the naked eye. An international team of researchers, including faculty at Binghamton University, has reconstructed a 1,000-year timeline of ecological change and human activity at Crawford Lake, the site that rose to global fame during the scientific debate over the proposed Anthropocene epoch. By extracting and sequencing sedimentary ancient DNA, or sedaDNA, preserved in the lakebed, the team assembled a remarkably detailed, multi-kingdom record of the plants, animals, bacteria, and fungi that lived around the water across ten centuries of shifting human land use. The study, published in the journal Molecular Ecology, demonstrates how genetic fragments shed into the environment can transform a bed of lake mud into a continuously updated chronicle of an entire ecosystem.

Crawford Lake owes its extraordinary preservative powers to an unusual physical quirk. It is a meromictic lake, meaning its water column never fully mixes with the lakebed. Because the deep waters remain undisturbed, sediment settling from the surface is laid down in neat, alternating layers of calcite and organic-rich laminae, each pair representing a single year of deposition. Matthew Emery, co-first author of the study and assistant professor of anthropology at Binghamton University, compared the structure to the growth rings of a tree. Like those rings, each sediment layer can be dated to a specific year, offering an exceptionally well-preserved, year-by-year account of environmental change. That annual resolution, combined with the lake’s status as one of the most intensively studied lakes in the world, gave the sedaDNA team an unparalleled opportunity to test their methods against decades of established palaeoecological evidence.

The technique at the heart of the study descends from methods originally developed to hunt far older quarry. Researchers used capture enrichment, a process in which genetic baits made of RNA are designed to bind to the DNA of target species if those genetic fragments are present in a sample. The RNA baits also attach to magnetic beads, allowing scientists to literally reel in their target DNA with a magnet. Emery noted that these approaches were first engineered to chase down extinct Pleistocene megafauna and extinct hominin relatives such as Neanderthals and Denisovans. Now, they are being applied to lake mud to trace human-environment interactions spanning recent centuries and reaching deep into geological time. Bait sets can be combined to target hundreds or even thousands of species genomes simultaneously, making the approach far more efficient than random shotgun sequencing, and allowing researchers to choose in advance which organisms they want to search for in the archive.

The reconstructed timeline traces a dramatic arc of human influence. In the period before local agriculture, the sedaDNA records a landscape shaped only by natural processes. Between the 1200s and the 1500s, the genetic evidence confirms the presence of Indigenous peoples farming maize and sunflowers near the lake, a finding that aligns with archaeological evidence of Longhouse Peoples villages at the site. The data also captures site abandonment and the ecological succession that followed, and then documents the Euro-Canadian period, with renewed impacts from logging, lumbering, milling, and farming, culminating in the unmistakable global markers of industrialization in the upper layers, including fossil fuel remnants, plastics, artificial fertilizers, acid rain, and even plutonium. It was precisely this well-preserved contamination record that made Crawford Lake a leading candidate among geologists supporting the Anthropocene as a new geological epoch, a designation that was ultimately rejected even as the scientific debate continues.

Among the study’s most striking results is the recovery of genetic evidence invisible to traditional palaeoecological techniques. Cattle DNA appears in sediments dating to the early 1800s, providing new proof of cattle in the surrounding landscape that left no trace in the fossil or pollen record. Even more remarkably, the analysis detected two of the so-called Four Sisters crops, maize and sunflower, directly from lake core samples for the first time. Three Sisters agriculture is an Indigenous farming technique introduced to the Great Lakes region during the Late Woodland Period, roughly 1000 to 1650 CE, in which maize, beans, and squash are planted side by side in mutually beneficial combinations. When sunflower is added, the grouping becomes the Four Sisters. While fossil and pollen studies had previously confirmed beans and squash at the Crawford Lake village site, those two crops were absent from the lake sediments, a puzzle the researchers attribute to the dietary preferences of an unexpected intermediary.

That intermediary is the Canada goose. The sedaDNA record shows a sharp increase in Canada goose DNA during the periods of Indigenous agriculture, a pattern consistent with geese foraging in cultivated maize and sunflower fields and then roosting on Crawford Lake. Their droppings would have carried both nutrients and traces of the crops they had eaten into the water, likely driving repeated algal blooms from nutrient influxes that are also visible in the sedimentary genetic record. These eutrophication events, caused by excess nutrients in the water, may even have contributed to the abandonment of the site, which occurred on more than one occasion according to the timeline. After abandonment in the 1500s, the lake’s ecology gradually rebounded, with the record showing a return of pine trees, rabbits, deer, beavers, and loons, and a notable disappearance of maize. Today, similar blooms are more often driven by artificial fertilizers, but the Crawford Lake record shows that nutrient-driven algal booms have deep human roots.

The study also delivered surprises about the physics of DNA decay itself. One of the biggest revelations, according to co-first author Tyler Murchie, lead scientist of Biodiversity Genomics: Ancient DNA at the Hakai Institute and adjunct assistant professor of anthropology at McMaster University, is that older DNA is not necessarily more damaged. Some of the roughly 500-year-old lake sedaDNA from plants and animals at Crawford Lake proved more degraded than DNA tens to hundreds of thousands of years old recovered from permafrost sites in northwestern Canada, demonstrating that preservation conditions matter far more than age alone. The chemistry of a burial environment, whether frozen, waterlogged, mineral-rich, or oxygenated, can determine whether genetic fragments survive intact for millennia or crumble into unreadable noise within a few centuries. For a small lake in southern Ontario, the cold, still, stratified water column turned out to be an unexpectedly generous custodian of molecular history.

The research was not without technical limitations, and the team has been candid about them. The bait set used in the analysis, the PaleoChip Arctic v1.0, was designed for Pleistocene and early Holocene sites far older than the period of human activity at Crawford Lake, and the absence of beans and squash in the results may reflect a gap in that panel or the geese’s preference for maize and sunflower. The researchers are already working to improve their bait sets for better capture enrichment, with Murchie emphasizing the need for an Eastern Woodland panel for future targeted ancient DNA research in the region. The effort has momentum behind it: in January, co-senior author Hendrik Poinar, professor of anthropology at McMaster University, and Murchie received an NSERC Alliance grant to develop improved sedaDNA methods for permafrost and marine sediments, support the reconstruction of long-term terrestrial and marine ecosystem dynamics, and build the Canadian Ancient DNA Network.

Beyond its technical achievements, the study underscores the collaborative nature of modern environmental science. Poinar noted that the work was only possible through the combination of genetics, archaeology, traditional Indigenous knowledge, lake chemistry, and geochemistry, disciplines that together make the unknown a little more tangible and the past recoverable, almost like magic. The international team included scientists from McMaster University, the Hakai Institute, Brock University, the University of Alberta, and the University of British Columbia in Canada; Binghamton University and Arizona State University in the United States; and Stockholm University in Sweden. Emery described the layered sediment as a filing cabinet and a time capsule, each stratum holding the plants and animals that lived around the lake when it formed, readable straight down through the centuries as long as nothing has shuffled the order. As the debate over the Anthropocene continues, Crawford Lake’s genetic archive now offers a thousand-year benchmark against which humanity’s accelerating transformation of the natural world can be measured, one annual layer at a time.

Subject of Research: Sedimentary ancient DNA analysis reconstructing 1,000 years of human-environment interactions at Crawford Lake, Ontario

Article Title: Ancient DNA reveals 1,000 years of human–environment interactions at Crawford Lake

Article References: Ancient DNA reveals 1,000 years of human–environment interactions at Crawford Lake. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: ancient DNA, sedaDNA, Crawford Lake, Anthropocene, Indigenous agriculture, Three Sisters, eutrophication, capture enrichment, molecular ecology, palaeoecology, meromictic lake, environmental change