Land Use and Hydrology
The most apparent transformation that has occurred in the Seven Mile Creek Watershed over the past 150 years has been the change in land use and natural land cover. This is clearly illustrated in the two GIS images shown here, depicting land cover prior to settlement and land cover as surveyed in 1992. Today the most prominent feature is cultivated agricultural fields (under two-year corn/soybean rotation), where prairie once dominated the landscape. The Big Woods are effectively extinct in this area, the oak savannah has been almost entirely depleted, and much of the wetlands, including the lake in the western reaches, have been drained. This has all occurred in an attempt to make the land more suited to farming. In addition to 86% of the land in cultivation, the watershed is home to 20 feedlots, the average size of which is roughly 900 acres and supporting about .4 animals per acre. Currently, Northern Plains Dairy (NPD) is constructing a facility in the watershed which will confine 3000 dairy cows on a 103 acre lot. Manure from feedlots is spread on fields throughout the watershed for fertilizer, and with added wastes from NPD, spreading acreage is predicted to increase by 50%. While fertilizer is good for crops, spreading too much manure on a field can do more harm than good to the waterhsed as a whole.
This is a picture of an agricultural field innundated by a recent flooding event. Any manure spread on the area now under water, will be carried away from the field and into nearby open ditches and streams. Manure contamination is associated with increased concentrations of nitrates, phosphates, and fecal coliform bacteria in the water supply.
The increase in farming in the region brought about another change in the appearance of the watershed. Though not as visible, agricultural drainage tiling has probably had the most significant effect on the naturally functioning processes of the watershed. (At the University of Minnesota's online drainage resource site you can learn more about agricultural drainage and tiling.) Throughout the watershed, an extensive network of underground tiles and open drainage ditches cooperate to remove any overabundance of water away from the fields, so as to not drown crops. Shortly after the turn of the century, drainage efforts in Minnesota were funded with public money, in an attempt to attract settlers and aid already established farmers. Since the advent of drainage, 24 miles of open ditching has been carved and 15 miles of public tiling has been installed within the SMC Watershed. The amount of private tiling is estimated at three to four times that of the public system.
Here are two GIS images showing the installation of the public drainage ditch network in SMC Watershed throughout the last century.
At the next stop on the tour, we will look at the impact tiling has had on the hydrology of SMC and it's watershed.