Research about Glacial Ridge National Wildlife Refuge

USGS2019

The hydrologic benefits of wetland and prairie restoration in western Minnesota—Lessons learned at the Glacial Ridge National Wildlife Refuge, 2002–15

Conversion of agricultural lands to wetlands and native prairie is widely viewed as beneficial because it can restore natural ecological and hydrologic functions. Some of these functions, such as reduced peak flows and improved water quality, are often attributed to restoration; however, such benefits have not been quantified at a small scale. To inform future restoration efforts, especially in northern prairie settings, the U.S. Geological Survey, in cooperation with the Minnesota Environment and Natural Resources Trust Fund, the U.S. Fish and Wildlife Service, and the Red Lake Watershed District, compared the hydrology of the Nation’s largest wetland and prairie restoration, Glacial Ridge National Wildlife Refuge, before and after restoration. Wetland and prairie restorations resulted in substantial changes in flows through the hydrologic cycle, in reduction of overland runoff and ditch flow during storms, and in improvements in water quality. Wetland and prairie restorations within the six basins characterized in this study resulted in a 14-percent decrease of cropland, a 6-percent increase of wetlands, and a 19-percent increase of native prairie between 2002 and 2015. During the same period, runoff rate decreased 33 percent (as a proportion of precipitation) and ditch flow rate decreased by 23 percent. Areal groundwater recharge rate increased from 30 to 35 percent (16 percent relative change in flow rate). Base flow as a proportion of total ditch flow increased from 25 to 35 percent (a 40-percent relative change). Peak ditch flow from storms decreased, ditch-flow recessions lengthened, and base flow from groundwater discharge increased, though only a small amount in some basins. These changes reduce the amount of ditch water leaving the study area, reducing flows that contribute to downstream flooding. Median surficial groundwater and ditch-water nitrate concentrations decreased by 79 and 53 percent, respectively. Median ditch-water suspended-sediment concentration decreased by 64 percent. Neither the density of restorations nor the beneficial changes in hydrology were evenly distributed in the study area. The amount of hydrologic benefits within an individual ditch basin did not relate directly with the amount of restoration in that basin; however, the landscape characteristics that related most closely with hydrologic benefits were the area of a basin underlain by a surficial aquifer and the area of drained wetlands (indicating the potential for wetland restoration). In western Minnesota, the basins underlain by surficial aquifers that contain large areas of drained wetlands are the uplands of the Alexandria Moraine Complex and the beaches of glacial Lake Agassiz on the eastern side of the western one-third of Minnesota, north of Wilmar, Minnesota. These findings provide resource managers with information that can help focus restoration resources in areas where the greatest hydrologic benefits can be realized.

Minnesota↗

USGS2013

Mercury in wetlands at the Glacial Ridge National Wildlife Refuge, northwestern Minnesota, 2007-9

The Glacial Ridge National Wildlife Refuge was established in 2004 on land in northwestern Minnesota that had previously undergone extensive wetland and prairie restorations. About 7,000 acres of drained wetlands were restored to their original hydrologic function and aquatic ecosystem. During 2007–9, the U.S. Geological Survey, in cooperation with the U.S. Fish and Wildlife Service and the Red Lake Watershed District, analyzed mercury concentrations in wetland water and sediment to evaluate the effect of wetland restoration on mercury methylation. The wetland waters sampled generally were of the calcium/magnesium bicarbonate type. Nitrogen in water was mostly in the form of dissolved-organic nitrogen, with very low dissolved-nitrate and dissolved-ammonia concentrations. About 71 percent of all phosphorus in water was dissolved, with one-half of that in the form of orthophosphorus. Wetland water had total-mercury and methylmercury concentrations ranging from 1.5 to 20 nanograms per liter (ng/L) and 0.2 to 16 ng/L, respectively. Median concentrations were 7.1 and 2.9 ng/L, respectively. About one-half of the mercury in wetland water samples was in the form of methylmercury, but this form ranged from 7 to 81 percent of each sample. Compared to concentrations in stream sediment samples collected throughout the United States, Glacial Ridge National Wildlife Refuge wetland sediment samples contained typical total-mercury concentrations, but methylmercury concentrations were nearly twice as high. The maximum concentration measured in Glacial Ridge National Wildlife Refuge wetland water approached the highest published water methylmercury concentration in uncontaminated waters of which we are aware. However, the upper quartile of water methylmercury concentrations is similar to concentrations reported for some impoundments and wetlands in northwestern Minnesota and North Dakota. Methylmercury concentrations in sampled wetlands were much higher than those from typical lakes or flowing streams throughout the United States. The high concentrations of methylmercury measured in sampled wetlands indicate the potential for substantial methylmercury concentrations in aquatic biota and wildlife that consume those biota. These wetlands also are a methylmercury source for downstream lakes and rivers. The high concentrations of methylmercury in water, its bioaccumulation potential, and its known toxicity in aquatic birds and food webs highlight a need to assess methylmercury in the biota within these ecosystems. Better understanding of factors that control methylmercury production concentrations within aquatic food webs in ecosystems of the Glacial Ridge National Wildlife Refuge would enable resource managers to better understand and manage risk to wildlife.

Minnesota↗