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| Minnesota Water Science Center |
U.S. Geological Survey Scientific Investigations Report 2007–5200
By Timothy K. Cowdery and David L. Lorenz, with Allan D. Arntson
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The Nature Conservancy (TNC) owned and managed 24,795 acres of mixed wetland, native prairie, farmland and woods east of Crookston, in northwestern Minnesota. The original wetlands and prairies that once occupied this land are being restored by TNC in cooperation with many partners and are becoming part of the Glacial Ridge National Wildlife Refuge. Results of this study indicate that these restorations are likely to have a substantial effect on the local hydrology.
Water occurs within the study area on the land surface, in surficial aquifers, and in buried aquifers of various depths, the tops of which are 50 to several hundred feet below the land surface. Surficial aquifers are generally thin (about 20 feet), narrow (several hundred feet), and long (tens of miles). Estimates of the horizontal hydraulic conductivity of surficial aquifers were 2.7–300 feet per day. Buried aquifers underlie much of the study area, but interact with surficial aquifers only in isolated areas. In these areas, water flows directly from buried to surficial aquifers and forms a single aquifer as much as 78 feet thick. The surface–water channel network is modified by several manmade ditches that were installed to remove excess water seasonally and to drain wetlands. The channels of the network lie primarily parallel to the beach ridges but cut through them in places. Back–beach basin wetlands delay and reduce direct runoff to ditches.
Recharge to the surficial aquifers (10.97–25.08 inches per year during 2003–5) is from vertical infiltration of rainfall and snowmelt (areal recharge); from surface waters (particularly ephemeral wetlands); and from upward leakage of water from buried aquifers through till confining units (estimated at about 1 inch per year). Areal recharge is highly variable in space and time. Water leaves (discharges from) the surficial aquifers as flow to surface waters (closed basins and ditches), evapotranspiration, and withdrawals from wells. Unmeasured losses (primarily discharge to ungaged (closed) basins) were 53–115 percent of areal recharge during 2003–5, while discharge to ditches that leave the study area was 17–41 percent. Discharge over 100 percent of areal recharge indicates a loss in ground–water storage. During the dry year of 2003, substantial ground water (about one–third of annual areal recharge) was released from aquifer storage but was replenished quickly during the subsequent normal year. Shallow ground–water flow is complex, with water in surficial aquifers, ditches, and wetlands part of a single hydrologic system. The ages determined for surficial ground–water samples were less than 15 years old, and one–third (8 of 24) were less than 5 years old, substantiating the close connection of surficial ground water to the land surface.
During the study, 68–81 percent of water left the area through unmeasured surface–water losses (primarily evapotranspiration), which is 2– to 4–times that leaving through the ditch system. Base flow in ditches (ground–water discharge) was 30 to 71 percent of all ditch flow. Mean annual runoff in all gaged basins except SW3 (2.26 inches per year) was similar (3.69–4.12 inches per year).
The quality of water samples from surficial aquifers and surface water collected in the study area was generally suitable for most uses but was variable. Most ground– and surface–water samples were dominated by calcium, magnesium, and bicarbonate ions. About one–quarter of surficial ground–water samples contained nitrate at concentrations greater than the U.S. Environmental Protection Agency’s (USEPA) Maximum Contaminant Level for human consumption. The median concentration of dissolved phosphorus ranged from 0.0108 milligrams per liter as phosphorus (mg/L–P) to 0.0293 mg/L–P. Nutrient concentrations in ditches were generally above the USEPA nutrient guidelines for reference streams in the area. Water samples contained detectable concentrations of atrazine, acetachlor, metolachlor, pendimethalin, prometon, and terbutryn and 11 of the 19 degradates analyzed. In general, degradates were found more frequently and at higher concentrations than were the parent herbicides. No herbicide or degradate was detected in water samples from buried aquifers, reflecting the protection that clay–rich confining units afford these aquifers.
The restoration of wetlands and prairies in the study area likely will result in more water retained on the land and improved water quality. Increased water retention could raise ground–water levels, but the rise likely would be very local and short–lived. Restorations likely would substantially change ditch–flow characteristics in the study area, but the changes would be insubstantial further downstream. Reduction in agriculture should result in a net decrease in nutrient and pesticide load to the study area.
Effects of the wetland and prairie restorations could be measured in the future, when restorations are complete and the hydrologic system has had time to equilibrate. A comparison between a future assessment and the one documented in this report would quantify the hydrologic changes resulting from wetland and prairie restorations in the Glacial Ridge study area.
Abstract
Introduction
Hydrologic Setting
Climate
Methods
Data Sites
Ground–Water Sites
Surface–Water Sites
Ground–Water Data Analysis
Mass–Balance and Ditch–Data Analysis
Sample Collection, Analysis, and Quality Control
Hydrology
Hydrogeology
Aquifer Descriptions
Surficial Aquifers
Buried Aquifers
Recharge and Discharge
Isotope Evidence for Ground–Water Recharge and Discharge
Discharge and Ground–Water Mass Balance
Ground–Water Levels and Flow
Surficial Aquifers
Buried Aquifers
Ground–Water Age from Dissolved Gases
Surface–Water Hydrology
Description of Daily Flows
Base Flow and Surface–Water Mass Balance
Hydrograph–Recession Slope
Storm–Runoff Hydrograph Modeling
Water Quality
Ground Water
Major Ions
Nutrients
Herbicides and Their Degradates
Variability
Surface Water
Physical Properties and Major Ions
Nutrients and Herbicides
Implications of Wetland and Prairie Restorations
Effects on Ground–Water Flow
Effects on Surface–Water Flow
Effects on Water Quality
Measuring Restoration Effects
Summary
Acknowledgments
References Cited
Appendix 1. Land–Use History
Appendix 2. Site names, numbers, and types
Appendix 3. Detailed Methods
Well construction
Stratigraphic and Water–Level Analysis
Mass–Balance Analysis
Hydrographic Analysis
Synoptic Sampling
Variability Sampling
Appendix 4. Water–Quality Assurance and Control
Appendix 5. Glacial History
1–3. Maps showing:
1. Topography and surficial aquifer extent, Glacial Ridge study area, northwestern Minnesota.
2. Land–use and water–level networks, Glacial Ridge study area, northwestern Minnesota, 2005.
3. Ditch watersheds and water–quality networks, Glacial Ridge study area, northwestern Minnesota, 2005.
4. Graph showing characteristics of water–level network wells, Glacial Ridge study area, northwestern Minnesota.
5. Conceptual hydrogeologic section through the Glacial Ridge study area, northwestern Minnesota.
6. Map showing surficial sand and gravel thickness, Glacial Ridge study area, northwestern Minnesota.
7. Hydrogeologic sections, Glacial Ridge study area, northwestern Minnesota.
8. Graph showing ground–water levels, Glacial Ridge study area, northwestern Minnesota, October–November, 2004.
9. Graph showing water–isotope composition, Glacial Ridge study area, northwestern Minnesota, May–July 2004.
10. Map showing water table, Glacial Ridge study area, northwestern Minnesota, June 2004.
11. Map showing potentiometric surface of buried aquifers, Glacial Ridge study area, northwestern Minnesota, June 2004.
12–18. Graphs showing:
12. Ditch hydrographs, Glacial Ridge study area, northwestern Minnesota, August–October 2004.
13. Base–flow separation of hydrograph from ditch gage SW4, Glacial Ridge study area, northwestern Minnesota,
May 29–June 26, 2004.
14. Water ionic composition, Glacial Ridge study area, northwestern Minnesota, May–July 2004.
15. Nutrient concentrations in water, Glacial Ridge study area, northwestern Minnesota, May–July 2004.
16. Herbicide and degradate concentrations in water, Glacial Ridge study area, northwestern Minnesota, May–July 2004.
17. Ground–water nitrate– and ammonia–concentration variability, Glacial Ridge study area, northwestern Minnesota, 2003–5.
18. Modeled and hypothetical direct runoff using the Clark unit–hydrograph method at ditch gage SW4, Glacial Ridge study area,
northwestern Minnesota, May 2004.
4–1. Graph showing water–quality–control data, Glacial Ridge study area, northwestern Minnesota, 2003–5.
1. Data networks for the Glacial Ridge study, northwestern Minnesota.
2. Characteristics of ditch basins, Glacial Ridge study area, northwestern Minnesota.
3. Precipitation and ground–water recharge, Glacial Ridge study area, northwestern Minnesota, 2003–5.
4. Net ground–water mass balance, Glacial Ridge study area, northwestern Minnesota, water years 2003–5.
5. Ground–water age and related well data, Glacial Ridge study area, northwestern Minnesota, 2004.
6. Flow characteristics of ditch basins, Glacial Ridge study area, northwestern Minnesota, water years 2003–5.
7. Ditch–flow statistics, Glacial Ridge study area, northwestern Minnesota, water years 2003–5.
8. Base–flow separation, Glacial Ridge study area, northwestern Minnesota, 2003–5.
9. Net surface–water mass–balance, Glacial Ridge study area, northwestern Minnesota, water years 2003–2005.
10. Percentage of each basin receiving precipitation from each precipitation gage used in the Clark unit–hydrograph model,
Glacial Ridge study area, northwestern Minnesota, June 2003 and May 2004.
11. Storm–runoff hydrograph model–variable values for final simulated storm hydrographs, Glacial Ridge study area, northwestern
Minnesota, June 2003 and May 2004.
12. Summary statistics of field measurements and major–ion concentrations in ditch–water samples, Glacial Ridge study area,
northwestern Minnesota, 2003–5.
13. Summary statistics of nutrient concentrations in ditch–water samples, Glacial Ridge study area, northwestern Minnesota, 2003–5.
2–1. Site names, numbers, and types.
3–1. Soil map units with parent material interpreted as surficial aquifer deposits, Glacial Ridge study area, northwestern Minnesota.
3–2. Analytical methods.
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Whole report (9.70 MB) – 68 pages (8.5" by 11" paper)
Suggested Citation:
Cowdery, T.K., and Lorenz, D.L, with Arntson, A.D., 2008, Hydrology prior to wetland and prairie restoration in and around the Glacial Ridge National Wildlife Refuge, northwestern Minnesota, 2002–5: U.S. Geological Survey Scientific Investigations Report 2007–5200, 68 p.
For more information about USGS activities in Minnesota, visit the USGS Minnesota Water Science Center home page.
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