Task: Question Generation
Input (English): Background Paragraph: Groundwater salinization compromises buffering properties. Vegetation clearance, along with irrigation, causes serious issues. Irrigation increases the water table and mobilizes salts, and vegetation clearance allows it to come in contact with water habitats and vegetation. This stresses species not adapted to high salinity. High levels of salinity reduces water uptake in plants, by causing stomatal closure, reducing photosynthesis. Forests undergo decline in areas of high salinity and shallow groundwater depths because these conditions make them more susceptible to droughts. Forests undergo decline in areas of high salinity and shallow groundwater depths making them more susceptible to droughts. 
Story: In the sixteenth century the State of Michigan had forests all over. But that has long been gone. 
Especially, in the state's northeast part the vegetation has been cleared in the twentieth century. 
Wooded areas were replaced by farm lands. All these farmlands were under heavy Irrigation. At one time, in the sixteenth century, plant species like elm and oak used to be plentiful. We still had some elms and oaks in the twentieth century, but they were not great many in number.
Output (English): Which century saw northeast Michigan's water table at decreased level, sixteenth century or twentieth century?