IT IS not just modern farming methods that degrade the environment. Farmers living 750 years ago in Canada polluted a lake to such an extent that its ecology has not recovered to this day, a sediment core has revealed.
The study is the second to show the impact Native Americans had on their environment. Earlier this year, researchers showed that Inuit hunters polluted freshwater ecosystems by littering them with whale bones and carcasses.
Iroquois subsistence farmers arrived at Crawford Lake, Ontario, in 1268. In 1325 they built a village close to the lake. Their slash-and-burn farming methods soon changed the lake by increasing the run-off of nutrients into the water. Algal populations rose, along with levels of organic and inorganic carbon, and the lake bottom became deprived of oxygen, according to measurements made by Erik Ekdahl, now at the University of Nebraska, and colleagues (Geology, vol 32, p 745).
Advertisement
Nutrient inputs dropped after the Iroquois stopped farming in the area in 1486. But water at the bottom of the lake remained anoxic for hundreds of years, and the microbial ecology of the lake remains different today. Such lakes 鈥渁re extremely susceptible to even small amounts of nutrients or disturbance鈥�, Ekdahl told New 杏吧原创. He thinks it likely early farmers changed the ecology of many lakes and rivers.