The results of the sediment-core analysis surprised the researchers: “We had not expected that signs of the Romans would be so evident in the lake sediment,” comments Mischa Haas. He is referring to the varves, clearly recognizable in the sediment core and stemming from the period in which the Romans flourished on Lake Murten. Varves are alternating dark and light sediment layers that arise when neither oxygen nor living things are found on the lake bottom.
The results can be traced back to the explosive population growth during Roman times, which led to clear-cutting of numerous forests by the Lake Murten population in order to acquire wood for burning and building and to establish fields for agriculture. The ensuing erosion of the earth washed many nutrients like phosphorous, nitrogen and iron into Lake Murten, which became eutrophied – resulting in oxygen deprivation for many fish and other organisms.