"The Vanishing Prairie'' is a Star Tribune series examining the way that agriculture is profoundly transforming the landscape of the Upper Midwest and its valuable native ecosystems.

Sept. 23: The prairie is an ecological asset of global significance, but it is disappearing rapidly in an era of high grain prices, generous farm subsidies and advances in farm technology.

Nov. 24: A new generation of super-bugs and superweeds is appearing in Midwestern fields, confounding farmers and reflecting the loss of native biological diversity.

Today: Across Minnesota, many wells are contaminated with farm chemicals, in part because native landscapes that filter water have been converted to fertilizer-intensive agriculture.