Environmental DNA Reveals Reykjavík´s Human and Ecological History
The arrival of Norse settlers on Iceland (Landnám) in the late 9th century CE (Common Era) is said to have triggered an ecological disaster. Here, we revisit this narrative through environmental DNA (eDNA) and multiproxy analyses of sediment cores from Lake Tjörnin in central Reykjavík, one of Iceland's earliest and longest-occupied settlements. Originally a marine embayment, Tjörnin became a freshwater lake around 450 CE. Early settlement around 877 CE brought livestock, barley cultivation, and other introduced taxa that enhanced nutrient cycling and unexpectedly increased local biodiversity. Contrary to the conventional view of rapid deforestation, eDNA shows that birch expanded during the settlement period, likely supported by deliberate management. Pronounced ecological and land use shifts occurred after 1260 CE, but these were coeval with the Little Ice Age cooling and occurring during a period of increased volcanic and environmental variability, rather than anthropogenic degradation. Crop cultivation effectively ceased, tree and shrub taxa (arboreal taxa) retracted, and grazing pressure maintained open landscapes. Even more profound ecological changes came after c. 1890 CE with urbanization and industrialization, as wastewater discharge, heavy-metal pollution, and fossil fuel use reshaped Tjörnin's ecosystem. These findings challenge the prevailing model of Norse-induced environmental collapse, revealing instead a dynamic human–environment relationship shaped by both cultural practices and external stressors. By applying eDNA to a long-occupied urban catchment, we demonstrate the power of genomic methods to refine settlement chronologies, reassess ecological baselines and changes, and integrate natural and cultural histories. This approach offers a model for revisiting human–environment interactions in urban centres worldwide.
The arrival of Norse settlers on Iceland (Landnám) in the late 9th century CE (Common Era) is said to have triggered an ecological disaster. Here, we revisit this narrative through environmental DNA (eDNA) and multiproxy analyses of sediment cores from Lake Tjörnin in central Reykjavík, one of Iceland's earliest and longest-occupied settlements. Originally a marine embayment, Tjörnin became a freshwater lake around 450 CE. Early settlement around 877 CE brought livestock, barley cultivation, and other introduced taxa that enhanced nutrient cycling and unexpectedly increased local biodiversity. Contrary to the conventional view of rapid deforestation, eDNA shows that birch expanded during the settlement period, likely supported by deliberate management. Pronounced ecological and land use shifts occurred after 1260 CE, but these were coeval with the Little Ice Age cooling and occurring during a period of increased volcanic and environmental variability, rather than anthropogenic degradation. Crop cultivation effectively ceased, tree and shrub taxa (arboreal taxa) retracted, and grazing pressure maintained open landscapes. Even more profound ecological changes came after c. 1890 CE with urbanization and industrialization, as wastewater discharge, heavy-metal pollution, and fossil fuel use reshaped Tjörnin's ecosystem. These findings challenge the prevailing model of Norse-induced environmental collapse, revealing instead a dynamic human–environment relationship shaped by both cultural practices and external stressors. By applying eDNA to a long-occupied urban catchment, we demonstrate the power of genomic methods to refine settlement chronologies, reassess ecological baselines and changes, and integrate natural and cultural histories. This approach offers a model for revisiting human–environment interactions in urban centres worldwide.