Christian F. Lenhart

The Role of Hydrologic Alteration and Riparian Vegetation Dynamics in Channel Evolution along the Lower Minnesota River

Abstract. The Minnesota River carries the largest load of sediment to the Mississippi River in Minnesota, most of which comes from channel sources. This study investigates bank retreat in the lower Minnesota River since 1938. Specifically we asked, How have changes to river form influenced sediment transport and deposition in the lower Minnesota River and how did hydrological and ecological processes affect channel change? It was hypothesized that channel straightening, reduction in floodplain access, and streamflow increases contribute to increased channel-derived sediment load and decreased point bar deposition. Secondly, it was hypothesized that hydrologic changes have reduced woody riparian vegetation on sandbars, further promoting channel widening. To quantify channel sediment and phosphorus loading rates in the lower Minnesota River, we analyzed historic aerial photos for evidence of channel change, we performed long-term monitoring of erosion and deposition rates within the river corridor, and we calculated channel sediment transport rates. Results from this study showed that the Minnesota River has widened by 52% between Mankato and St. Paul since 1938, on average contributing 280,000 Mg of sediment per year and 153 Mg total phosphorus. The river also shortened by 7% since 1938, increasing bankfull shear stress and stream power. Sediment deposition rates in the floodplain have increased since European settlement by an order of magnitude. Ecohydrological studies showed that establishment of woody riparian plants has been inhibited on sandbars by prolonged summer flow duration and scour at high flow, reducing potential point bar growth. Findings from this study will be useful in prioritizing sediment and vegetation management actions.

A Preliminary Review of NOAA's Community-Based Dam Removal and Fish Passage Projects

Dams and other stream blockages prevent anadromous fish from accessing large areas of key habitat. The NOAA Community-Based Restoration Program (CRP) supports habitat restoration projects, including 53 dam removal and fish passage projects from 1996 to 2002. This article provides a preliminary review of the biological benefits provided by the first 18 CRP dam removal and fish passage projects supported between 1996 and 1999. These 18 projects improved access to over 160 km of river habitat for many anadromous fish species, especially river herring (Alosa spp.) on the east coast and salmonids (Oncorhynchus spp.) on the west coast. While fish ladders provide targeted fish species access to key habitat areas, dam removal can improve the health of entire stream ecosystems and provide fish passage to fish species unable to utilize ladders. The CRP complements existing federal regulatory programs by providing a cooperative process at the local level that can restore habitats efficiently and effectively while encouraging long-term stewardship.

Attenuating Excessive Sediment and Loss of Biotic Habitat in an Intensively Managed Midwestern Agricultural Watershed

Portions of the 700 km 2 Elm Creek watershed in southern Minnesota have undergone watershed and channel improvements over the past decade to mitigate turbidity and biota impairment. Increased row cropping, artificial drainage, channel modifications and precipitation have cumulatively contributed to impairment and channel instability. Uplands that were once a prairie pothole landscape are now predominately drained cornsoybean fields, providing little hydrologic storage and sediment attenuation during peak runoff. Riparian degradation and channel discontinuity characterize much of lower Elm Creek. Wetlands have been restored in the upper watershed to reduce runoff and nutrient loading from croplands. Downstream, a 750 meter riparian corridor of Elm Creek was restored and the channel improved by oxbow reconnection, bluff and streambank protection. Monitoring will document erosion and sediment deposition within the reach and Index of Biotic Integrity (IBI) data will be collected to characterize fish and invertebrate communities in the stream.

Restoration of Wetland and Prairie on Farmland in the Former Great Black Swamp of Ohio, U.S.A.

A restoration project was initiated in 2004 to re-establish wet prairie, swamp forest, and oak savanna on 16.2 ha of farmland in northwestern Ohio along a post-glacial lake beach ridge that marked the edge of the Great Black Swamp. The goals were to restore rare and declining plant communities and species and provide nutrient load reduction to Lake Erie. Plant inventories over time and wetland outflow monitoring were used to assess project success. In total 80 species were established in the prairie including six state-listed threatened or endangered plants and < 1% invasive species coverage. Forest restoration efforts established 435 trees with a 31% seedling survival over nine years. Wetland outflow was zero during the monitoring period of April–December in 2012 and 0.4% of total rainfall during 2013, suggesting a large reduction in nutrient outflow. Difficulties with tree plantings in the clay soils of the lake plain include frost heave, low organic matter content, deer grazing, and decline of the two swamp forest dominants: American elm (Ulmus americana) and ash (Fraxinus spp). The restoration of forest on private lands is a long-term process challenged by maintenance and funding issues. This project provided information on restoration alternatives and challenges for farmland within a glacial lake plain setting. Lessons learned will help improve future restoration projects in similar settings to reduce nutrient loading into Lake Erie.

Riparian corridor-channel restoration and management in Elm Creek, Minnesota.

tolerance by reed canarygrass and that roots of tolerant individuals had increased ATPase and ability to sustain water potential and potassium uptake under NaCl stress. Greater NaCl tolerance would help explain reed canarygrass abundance in salt-laden roadside ditches and urban wetlands. Where road salts flow into wetlands, invaders could colonize canopy gaps and outcompete stressed native plants. Salt-mediated invasion would not be unique to this species. In Massachusetts, road salt enhanced invasion of a fen by another salt-tolerator, common reed (Phragmites australis) (Richburg et al. 2001). Throughout Wisconsin, common reed, cattails (Typha angustifolia, T. × glauca), and reed canarygrass are common in roadside ditches where water and road salt likely accumulate. While their distributions might be due to other disturbances (grading, sedimentation, nutrients), the precautionary principle leads us to suggest that icy streets and highways be kept safe using less toxic alternatives to road salt ( Jull 2009).

Factors impacting the variability of effectiveness of agricultural best management practices (BMPs) in Minnesota

Abstract. In the development of nutrient reduction strategies for agricultural watersheds in the TMDL process, effectiveness values are frequently used from the Agricultural BMP Handbook for Minnesota. However, BMP effectiveness is highly variable due to differences in hydrologic pathways, biogeochemical cycles, landscape position and management. In the updated manual the objective was to describe the primary causes and relative amounts of variability for managers so more realistic TMDLs goals are set. A database of BMP effectiveness studies was used to compare variability of effectiveness values by BMP type, landscape position and target nutrient, nitrogen, phosphorus and sediment, with; n = 17-100. The coefficient of variation (c.v.) was used to compare between studies. There were no significant differences in variability by landscape position or flow path. However there was a significant difference in the c.v of dissolved vs. particulate pollutant efficiency. Dissolved phosphorus had the highest variability with a c.v. of 1.98 for 31 studies while sediment and particulate phosphorus had c.v. values

Restoration of the Mississippi River Gorge: Issues and Research Needs

The Mississippi River Gorge has long been of central importance ecologically and economically to the Twin Cities, Minnesota region. It was unique for its high-gradient, boulder-cobble bed along the Mississippi that was valuable for fish and mussel habitat prior to alteration by locks and dams. Gorge restoration is increasingly discussed, as the river corridor is used more for recreation, commercial, and residential purposes rather than industrial uses. This study was intended to provide a synthesis of existing restoration work in the Gorge, an initial feasibility assessment of restoration actions, and to recommend next steps for restoration and research. We reviewed existing restoration activities and assessed the feasibility of restoring components of the ecosystem for ecological, historical, recreational and economic reasons, using the TELOS framework as an analytical tool. Some components of the Gorge ecosystem can be reestablished without removing the Ford Dam, which submerges part of the Gorge, including islands and historic and cultural features. However, some goals require dam removal, particularly fish and aquatic mussel passage. Future restoration is also limited by reservoir sedimentation. Some steps could be undertaken immediately to increase awareness of the Gorge’s historical and ecological value and to collect further information required for restoration activities. More information is needed on the nature of sediment deposits, contaminants, and existing streambed materials before doing intensive ecological restoration. As the Ford Dam ages and maintenance costs increase while demand for parkland increases, the benefits of removal will increase.

Streambank Erosion and Channel Evolution Processes in the Minnesota River Basin

The Minnesota River Basin (MRB) is the largest contributor of sediment and nutrients to the Upper Mississippi River in Minnesota and is impaired for turbidity and nutrients over much of its length. Several recent studies indicate that the majority of sediment in the river originates from channel erosion of ravines, bluffs or streambanks. The objectives of the studies synthesized in this report were: to quantify sources of sediment to the Minnesota River; to determine channel evolutionary processes and stages; and to quantify the impacts of direct channel modification on sediment transport efficiency of the lower Minnesota River.