1. 150 Years of Wetland Loss at Jeffers Petroglyph Site
Minnesota’s landscapes have undergone dramatic, visible changes both in vegetation and hydrology following human disturbances. Wetlands are one affected areas. Historic wetland loss in Minnesota over the last 250 is estimated between 25-50% (Minnesota DNR).Wetlands provide many essential ecosystem functions, providing habitat for wildlife and improving downstream water quality.
The Jeffers area is a very important archaeological area. The Jeffers Petroglyphs are the oldest collection of rock carvings in the North Eastern plains. This area was important to many Native Americans before European settlement in the area and is known as a sacred area now.
150 Years of Wetland Loss at Jeffers Petroglyph Site
Jack Hubler-Dayton, Tom Knee, Evan Pak
Environmental Studies Department, 1520 St. Olaf Avenue, Northfield, MN USA
Abstract
Introduction
Results
The Jeffers Petroglyph site is the largest and oldest collection of rock carving on the North Eastern plains. This project estimates wetlands loss around the Jeffers petroglyph in the last 150 years. In the reference plat maps from the 1850s, aerial photographs from 1950, and modern LIDAR imagery. Our findings indicate a tremendous loss both in wetland number and following anglo-european settlement.
Minnesota’s landscapes have undergone dramatic, visible changes both in vegetation and hydrology following human disturbances. Wetlands are one affected areas. Historic wetland loss in Minnesota over the last 250 years is estimated between 25-50% (Minnesota DNR). Wetlands provide many essential ecosystem functions, providing habitat for wildlife and improving downstream water quality.
The Jeffers area is a very important archaeological area. The petroglyphs are the oldest collection of rock carvings in the North Eastern plains. The area was important to many Native Americans before European settlement in the area and is known as a sacred site now.
From the 1850s to 1950s there was a decrease of approximately 90% in wetland area. Additionally, there was a decrease of approximately 85% between 1950 and the 1980 NWI data. This leads to an overall loss between the 1850s and 1980s of 97.36%.
Study Site
Figure 1. The location of Jeffers. The area straddles the border of Cottonwood and Brown counties in Southwest Minnesota.
Figure 2. LiDAR data of the area. This shows the topography of the area with higher areas being lighter and lower areas darker.
Figure 6. Graph showing the change in acreage of identified wetlands over time
Minnesota’s landscapes have undergone dramatic, visible changes both in vegetation and hydrology following human disturbances. Wetlands are one affected areas. Historic wetland loss in Minnesota over the last 250 is estimated between 25-50% (Minnesota DNR).Wetlands provide many essential ecosystem functions, providing habitat for wildlife and improving downstream water quality.
The Jeffers area is a very important archaeological area. The Jeffers Petroglyphs are the oldest collection of rock carvings in the North Eastern plains. This area was important to many Native Americans before European settlement in the area and is known as a sacred area now
Hypothesis
Discussion
Using historic data given by plat maps and older aerial photos, we assume a large loss over time both in acreage and number of identified wetlands. We hypothesize this rate will be close to the state average loss (25-50% since settlement). The heavy influence of agriculture in the area will cause a changing of locations of some wetlands.
There has been incredibly high wetland area loss in the Jeffers area since European settlement in the area
This loss is due to size loss not number of wetlands
1850s - 31 wetlands identified
1950s - 55 wetlands counted
1980s - 18 wetlands counted
This area is one of the drier in Minnesota (average yearly precipitation 28.06in, state average 28.61in)
The incredibly high wetland loss is not due to precipitation so the loss is anthropogenically caused, most likely caused by agriculture
By determining the location and change in these wetlands we can see the dramatic shift in landscape since European settlement
Despite its significance as a sacred site the preservation of this area is minimal
To rectify, work should be done to return the area to its natural state out of respect for the significance it holds to many Native Americans
Management of Minnesota’s wetlands is a large problem, much of the land has been drained for agricultural use which has negative effects on the quality of soils and water directly as well as on migrating and local animal populations (Halvorson 2002, Lal 2004)
The drying of this area as well as the agricultural use (as shown by the aerial photographs) mean there is a necessity for drainage of groundwater or manipulation of waterways to ensure the crops have enough water to grow which has an effect on a much larger area
Methods
Conclusions
We downloaded the National Wetlands Index and the position of current wetlands present in target area.
We recorded wetlands indicated on the original plat survey maps from the 1850’s.
We georectified and stitched the 1950 aerial photos. Visible features consistent with wetlands were then traced to create polygons (MN Geospatial Information Office).
We then processed LiDAR imagery of our area in ArcMap to predict water sinks based on the topography (ibid).
Figure 3. Plat map from 1858 of the center of the study area. A large wetland is shown off center. Six different plat maps were used in identifying wetlands which gave 31 different wetlands with an average size of 16.2 acres.
Figure 4. These aerial photos were used to identify more wetlands. 55 wetlands were identified with an average size of .9 acres.
Figure 5. This figure shows all the identified wetlands and the associated source data. Overlaps are shown with more recent source data on top. The backing data is a sink map produced with LiDAR data. This shows the lower areas with lighter colors. The sink data gives an idea of where water may pool in a given area.
Limitations
The sink data here shows a clear change in wetland location with many large wetlands completely disappearing over time and new wetlands springing up across the study site.
The individual surveyors creating the maps changed from 1857 to 1858 thereby possibly introducing bias in wetland documentation
Some aerial photographs had spots or other damage, which often appeared similar to wetlands.
Classifying the areas surrounding streams and rivers was difficult, as wetlands had less contrast against the background.
Some of the fields have rock outcroppings which can appear similar to wetlands.
The Jeffers Historic Petroglyph Site and surrounding area is operated by the Minnesota Historical Society. There, they currently manages 33 acres of virgin tallgrass prairie, 47 acres of restored prairie, and 80 acres of prairie undergoing restoration. This habitat supports the largest single population of Brush Prairie Clove, an endangered species. Currently, many native plants are thriving.
Future land management strategies should consider possible wetland restoration, in order to offset past losses.
Bibliography
Status and Trends of Wetlands in Minnesota: Wetland Quantity Trends from 2006 to (n.d.). . Status and Trends of Wetlands in Minnesota: Wetland Quantity Trends from 2006 to rep.
Minnesota Geospatial Information Office.
Halvorson, A. D., B. J. Wienhold, and A. L. Black Tillage, Nitrogen, and Cropping System Effects on Soil Carbon Sequestration. Soil Science Society of America Journal 66:906.
Lal. R Carbon emission from farm operations. Environment International. 30:
Acknowledgements
We would like to thank Professor Charles Umbanhowar for his help with the project. This includes but is not limited to ArcMap help, general guidance, and comic relief. Additionally, we would like to thank St. Olaf College for providing the resources to complete this project.