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Nonpoint Pollution in the St. Louis River Watershed
Since European settlement, point source pollution (pollution that comes from a discharge or other point source) has been the primary degrader of water quality in the St Louis River basin. Most point sources were cleaned up 20 years ago with tighter restrictions on the waste coming from sewer pipes and industrial outfalls. Since that time water, quality has improved drastically.
In spite of this progress, nonpoint source (NPS) pollution problems persist, and have caused more subtle impacts affecting the river, bay and lake in different ways. We have made significant progress over the last 10 years in reducing NPS pollution, but much work remains.
Erosion and Sedimentation
Eroded soil particles are the most common NPS pollutant in the St. Louis River basin. Sediment degrades aquatic habitat in streams by smothering gravel needed by fish (for reproduction) and aquatic insects (for habitat). Many tributaries in the basin are trout streams, which are very sensitive to sedimentation. Eroded soil particles also carry chemicals and nutrients that, in turn, degrade water quality further. In addition, the importance of erosion control is heightened by the expense and concern associated with the dredging that is needed to maintain shipping channels in the harbor and river.
The primary sources of sediment impacting St. Louis Bay are streambank erosion and construction site erosion.
Streambank Erosion
Soil erosion and related sedimentation have been impacting the bay since the original forest vegetation was cleared. In a 1987 report by Minnesota Sea Grant, underwater core samples taken from St. Louis Bay showed a marked increase in sedimentation rates that coincided with early logging in the area. Early logging, loss of duff layers to forest fires, and changes in forest cover were no doubt hard on stream banks, because they accelerated the rate of stormwater runoff. This increased runoff, plus the damage caused by historic log drives down area rivers increased streambank erosion. We believe that the St. Louis River watershed is still experiencing accelerated streambank erosion rates today.
The Nemadji River Basin Project report (Erosion and Sedimentation in the Nemadji River Basin, published in 1998) grew out of RAP recommendations and gives an excellent overview of changes that have taken place in the watershed. The report also covers recommendations for treatments to minimize continuing landuse impacts.
Construction Site Erosion
Construction sites have also been a major contributor of sediment to the St. Louis River system. Steep slopes in and around the city of Duluth have resulted in soil losses measured at 100 tons per acre from individual storm events. The high stream gradients throughout this sensitive area result in nearly 100% delivery of eroded sediment to the St. Louis River, St. Louis Bay, Superior Bay and/or to Lake Superior.
A heightened awareness of this problem has occurred over the last ten years. State laws require erosion control at construction sites larger than five acres. Even for smaller sites, the City of Duluth has enacted an erosion and sediment control ordinance to address construction site problems. The use of effective erosion control practices such as silt fences and sediment basins are readily apparent today on nearly every site. The success of this effort is in large part due to problem identification by the RAP.
Agricultural Runoff
Sheet and rill erosion from cropland is generally not a problem in the St. Louis River watershed. The cool, wet climate and short growing season keeps most cropland in long hay rotations. This means there is not a lot of bare, exposed soil.
Dairy and beef farms continue to operate here and there throughout the watershed. Most livestock operations are on sites selected by earlier generations and are near or on streams. Feedlot runoff contains nutrients and bacteria, and can be a serious NPS pollutant. Encouraging systems to manage waste and nutrients is a high priority of conservation agencies. The Soil and Water Conservation Districts in Minnesota and the Land Conservation Department in Wisconsin offer programs to help livestock farmers plan design and apply NPS pollution control practices.
Urban Storm Water
Stormwater runoff, created as rainfall and snowmelt run off streets, parking lots and rooftops, carry many types of NPS pollutants into streams and ultimately into Lake Superior. Oil, grease, road salt and sand are common examples of such pollutants. In summer, rainwater falling on hot pavement and parking lots can unnaturally heat area streams, causing thermal pollution.
Miller Creek, which flows through Hermantown and Duluth, supports a population of wild brook trout, but is threatened by urban stormwater runoff. Concern over the creek and these fish have grown along with development of the Miller Hill retail corridor since the 1970s. The RAP, Miller Creek Task Force and now the Miller Creek Joint Powers Board continue to work on stream inventory, restoration and preservation efforts.
Inflow and infiltration related to urban storm water can cause sewage bypasses into the Duluth/Superior harbor and Lake Superior. Inflow occurs when rainwater is channeled into sanitary sewers rather than into the stormwater system by means roof drains, footing drains and sump pumps. Infiltration is the leakage of groundwater into sanitary sewers through old or defective pipes. When large volumes of stormwater are channeled into sanitary sewers during rainstorms, sewage pump stations can't handle the increased flow. This results in overflows of untreated sewage directly into area waterways. Much of the awareness of this problem is due to the RAP. The City of Duluth is involved in a major program to reduce this problem.
The CAC's NPS Pollution Committee
The CAC's NPS Pollution Committee has developed a number of recommendations to reduce NPS pollution in the St. Louis River AOC. It is currently assessing the progress made to date on the existing recommendations that deal with NPS pollution.