Beware Greeks bearing tillers: research into soil erosion shows agriculture’s impact
In a paper published in Nature Scientific Reports this week,researchers from the University of Wollongong lay claim to uncovering the earliest evidence of agriculture’s impact on the environment. By examining changing chemical isotopes in sediment samples taken from Lake Dojran in modern-day Macedonia and Greece, scientists found evidence of a significant erosion event about 3200 years ago that they links directly to the spread of farming to the region. “What we show for the first time now is how deep the impact [from farming] was on the environment,” said Leo Rothacker, a PhD student and lead author of the paper. “Our data indicates that the soil has been pretty much been completely stripped from the landscape.” The research was able to separate the human fingerprint from the natural climate variations covering a period from 12,300 years ago up to the arrival of agriculture some eight millenia later. The depletion of soils appears to have occurred over a period of as long as a few hundred years before societal impacts began showing up, or around the time of the start of the so-called Greek Dark Ages, Mr Rothacker said. “[This was] a time where population declined rapidly, agriculture suffered, the metallurgy of bronze and the ability to write were forgotten,” he said.“Lakes are excellent archives to unravel the environmental variability in the geological past,” co-author Alexander Francke said. “In particular, relatively small and shallow lakes (such as Dojran) are highly sensitive to environmental variability. The suitability of the site was also aided by the lake’s relatively small catchment area of 275 square kilometres. “[That] provides a more direct connection between hillslope erosion and sediment deposition in the basin, and the local paleoclimatic conditions have already been extensively studied,” Dr Francke said. “This allows us to directly link erosion to climate and thus to unravel natural and human causes of accelerated hillslope erosion.” Mr Rothacker said the link between soil health and agricultural output would have shown up rapidly. “Without soil, you basically lack the key component in the eco-system to grow food,” he said. “If you don’t have mature soils any more, you can’t grow that food and you can’t supply a large population.” While pastoral activities in the region may have contributed to the erosion identified in the sediment, changes in pollen data suggest the spread of plant cultivation and other agriculture – and later deforestation – were the “most significant factor” in the observed erosion, the paper said. Demand for wood was boosted by the emergence of regional trade, “when large amounts of high quality Macedonian timber were required for shipbuilding and construction”, metal smelting and then warfare, the paper said. Mr Rothacker said other links between agriculture and soil erosion have been identified elsewhere, such as in China, but as much as 1000 years later than the finding from Greece. He said it is likely the earliest date for such links will be pushed back further as other suitable sites are examined. The research may also have implications for modern societies, which have become ever more dependent on agriculture to meet rising demand from swelling populations that were also becoming wealthier. “It should make us aware of how we use our landscape,” Mr Rothacker said. “In order to sustain soil resources, which are an essential part of our ecological system, we need to be aware of how we use our soils.” “The main message is that we have to be more and more aware of our natural resources if we want to use them in the future,” he said. “By learning from the past, we might not make the same mistakes again.” Anthony Dosseto, another of the authors and a leader of UoW’s School of Earth and Environmental Sciences team, said the work provides evidence the Anthropocene – the proposed geological period that marks the start of significant human impact on the Earth’s geology and ecosystems – began much earlier than the beginning of the Industrial Revolution as is often touted by advocates of the new era. “Some have proposed that [the Anthropocene] started as early as the emergence of agriculture during the Neolithic Revolution (or about 12,000 years ago), however, supporting observations are scarce.” Professor Dosseto said. “This [study] supports that the Anthropocene – and thus a deep human impact on the environment – started as early as a few thousand years ago,” he said. The tools developed in the research are being applied elsewhere, including Australia and New Zealand, and will also help researchers understand how soil resources respond to climate change, Professor Dosseto said.