Studying sediment layers taken from deep under Lake Murten, researchers have managed to reconstruct the environmental conditions from Roman times to show how the environment was being polluted due to population growth and intensive farming.
A team of scientists from the Swiss Federal Institute of Aquatic Science and Technology (Eawagexternal link), led by paleolimnologist Mischa Haas, examined ten-metre long sediment cores extracted from deep under Lake Murten in northwest Switzerland. This enabled them to reconstruct environmental conditions over a period of several centuries.
The cores revealed varves - alternating dark and light sediment layers that arise when neither oxygen nor living things are found at the bottom of the lake – from the period in which Romans inhabited the region around Lake Murten– from 200 BC to 400 AD.
The researchers conclude that even in Roman times, the environment was being polluted by unfiltered wastewater, the mining of metals such as iron or lead, and the clearing of forests.
“We had not expected that signs of the Romans would be so evident in the lake sediment,” Haas said.
During Roman times, the population grew rapidly. Forests were cleared around Lake Murten for firewood, new homes and fields for farming. The resulting erosion of the earth washed many nutrients like phosphorous, nitrogen and iron into Lake Murten, which led to oxygen deprivation for many fish and other organisms.
“It is also interesting that we can see in the sediments exactly when the Roman empire began to fall apart and how the lake reacted to such social revolution,” said Haas.
The lake sediments show that from the 2nd century AD more oxygen was present in the lake depths. However, it took 300 years for the ecosystem to recover, he added.
“Our study shows that human interference in an ecosystem has an effect that can last for hundreds of years,” said Haas.
The research was part of the Paleofarm projectexternal link, financed by the Swiss National Science Foundation (SNSF), which studies lakes in Switzerland, Russia and Greenland, to reconstruct the influence of agriculture on land and lake systems over the past 10,000 years.