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The Wild Nemadji
The Nemadji River and its
tributaries flow through Minnesota and Wisconsin, draining approximately
433 square miles. Approximately 40% of the drainage basin is in
Wisconsin. According to the Carlton, MN Soil and Water Conservation
District (CSWCD), approximately 192,000 acres of the land is forested, or
69% of the watershed, with 53% of forested land consisting of deciduous
trees greater than 45 years old.
The lower Nemadji River
flows in a narrow, steep-sided valley when it enters the heavily
industrialized and urbanized portion of the City of Superior; from there it
empties into Allouez Bay and the Duluth-Superior Harbor near the Burlington
Northern Ore Docks (WDNR). The major development near the river is a
Burlington Northern Santa Fe Railroad taconite storage facility. Taconite pile rainfall runoff is
collected on site where it passes into a series of detention ponds and
discharges to the Nemadji River through a pipe. Detention ponds on the Nemadji Gold Course also detain
surface runoff and provide management of area flows (CTE Surface Water
Management Plan). Even within the
City of Superior, the steep clay bluffs that confine the valley are
generally undeveloped and forested in some places, creating a buffer
between the river system and surrounding urban areas. A series of
emergent marshes occur along the inside of the well-developed meanders that
are characteristic of this river. These marshes are separated from the main
channel by weedy natural levees, which support a mixture of tall wetland
shrubs and small lowland hardwoods (WDNR).
The mouth of the Nemadji
River is an area of side-channel wetlands that extend for about a mile
upstream. Wetlands at the mouth of the Nemadji cover about 90 acres
and support the spawning beds of over 60 warm water fish species, including
muskellunge, perch, bass, walleye, northern pike, and salmon. Lamprey also occur in the river.
This area is identified by the Lake Superior Binational Program as
important habitat to the Lake Superior ecosystem for coastal wetlands as
well as fish and wildlife spawning and nursery grounds.
The Murky Nemadji
The Nemadji River is famous
for its turbid, clay-filled water. About 33% of the river’s basin is
covered in red clay, sometimes up to 200 feet thick; this layer was
deposited during a geologic period when glacial lakes covered the region
(CSWCD). Though red clay erosion is natural, human activities on the
land in the last century have accelerated the natural process, and the
river has cut deep valleys into the surrounding bluffs. According to
the Natural Resources Conservation Service (NRCS), movement of soil material
downhill due to gravity (slumping) is severe. Nearly 90% of the fine
sediment in the river is due to bluff erosion and slumping, and 74% of this
sediment ultimately ends up in Lake Superior (CSWCD).
The major human activities
that have had a significant impact on the hydrology of the Nemadji River
basin are the early logging practices dating back to the mid 1800s. Logging converted forest to permanent
agriculture, streams were cleared to efficiently transport logs to the
sawmills,, and roads and railroads cut through the basin. This all led to efficient hydrologic
pathways for water to get to the river quickly (Nemadji River Basin
Project). While approximately 70%
percent of the watershed is now reforested, the deciduous trees adjacent to
streams may not be an effective sediment filter, or may not form a sturdy
enough root system to hold soils in place. Many red clay slumps in
the watershed move downhill despite tree cover, likely due to shallow
groundwater movement beneath the root zone. The riparian areas along
the stream vary dramatically in width and quality (NRCS).
Transport of pollutants
attached to settled bottom material has created a “storehouse” of toxins in
the lower reaches of the harbor. Pollutants include mercury, dioxins, and
polychlorinated biphenyls.
Re-suspension and/or dredging of this material can lead to elevated
toxin levels in the biota. Increased sedimentation also decreases the
river’s fisheries. Even so, the
Minnesota portion of the Nemadji watershed contributes 40% of Lake
Superior’s migratory trout and salmon spawning habitat in Minnesota. In
addition, fine-grained sedimentation degrades the quality of spawning bed
habitat by covering fish eggs with fine-grained sediment (Nemadji River
Basin Project).
The Expensive Nemadji
The Duluth-Superior Harbor is
shallow, so it must be dredged to maintain channels deep enough for ship
traffic. Approximately 33,000 tons of Nemadji River sediment is
dredged annually by the U.S. Army Corps of Engineers to maintain adequate
depth for shipping traffic in Superior Bay. The annual cost for this
portion of the total dredging within the Duluth-Superior Harbor area is
approximately $260,000 (WDNR Basin Plan). The Nemadji River deposits
approximately 131,100 tons of sediment per year into the Harbor; of that
amount, between 94,000 and 117,000 tons are silt and clay. This is
the equivalent of 17 dump truck loads of silt and clay being unloaded into
Lake Superior daily. Sedimentation can cause choking of spawning beds
and carry contaminants and nutrients with them that can degrade aquatic
habitat. (NRCS)
In addition, damage due to the
instability of red clay results in frequent and expensive maintenance
schedules for road cut and embankment situations. The most extensive study
of damage to the ecosystem was done during the Red Clay Project in the
1970s. Property damage from slumping is relatively small due to the
low population density in the watershed (WDNR Basin Plan).
The Susceptible Nemadji
As the Nemadji flows into the
City of Superior, several railroads and highways cross over it. The
susceptibility of the river to waste discharges and spills became clear
when several Burlington-Northern railway cars fell from the Highway 35
Bridge into the river on June 30, 1992. One tank car ruptured,
releasing 34,000 gallons of a chemical mixture known as aromatic
concentrates. Benzene makes up about 45 percent of the chemical
mixture. Approximately 30,000 people in the Superior area had to
evacuate as a cloud of chemical vapors drifted over the city, portions of
Duluth, and the western tip of Lake Superior (WDNR Basin Plan).
However, human health was not immediately threatened, though Superior
Police Department prevented public access to the affected area and the
Douglas County rescue squad patrolled the Nemadji River (EPA). Dying
and distressed fish were observed in conjunction with the spill.
Mortality estimates suggest thousands of fish died, including game, forage,
and rough species. Distressed fish rose to the water’s surface where they
were exposed to the sheen of raw chemicals and vulnerable to predation by
the many gulls observed feeding on them (WDNR Basin Plan).
Stormy weather and safety
issues hampered spill response. Heavy rains following the spill
may have helped disperse the materials and cold weather reduced
vaporization. Containment booms helped recover some chemicals at the
31st St Bridge, but rising water levels and mixing during the
16-mile run downstream inhibited recovery. Most of material reached
Superior Harbor within 30 to 50 hours after the spill. Most
contaminants quickly volatized or were carried away in the river, while
some substances bound to sediments, where they dissipated more
slowly. While many were concerned that residuals of the chemicals
would linger in the river sediments, tests one year later showed no
significant results (WDNR Basin Plan).
The City’s Comprehensive Plan
suggests that approximately 500 new residential units will be constructed
along the Nemadji River by 2020.
The new impervious area could increase sediment loads to Superior
Bay and create larger peak runoff rates and volumes (CTE Water Management
Plan).
Rehabilitating the Nemadji
The Nemadji River is part of
the St. Louis River Area of Concern (AOC), which was designated by the
Great Lakes Water Quality Agreement (WQA) between the United States and
Canada in 1972. Nine beneficial use impairments have been recognized:
1) Restrictions on fish and
wildlife consumption;
2) Degradation of fish and
wildlife populations;
3) Fish tumors or other
deformities;
4) Degradation of benthos;
5) Restrictions on dredging
activities;
6) Eutrophication or
undesirable algae;
7) Beach closings;
8) Degradation of aesthetics;
and
9) Loss of fish and wildlife
habitat.
The Remedial Action Plan (RAP)
was developed in 1987 to restore beneficial uses of this area. The
goal of the RAP is to define problems and their causes, and then recommend
actions and timetables to restore all beneficial uses of the AOCs.
Restoring uses is to be achieved through implementation of programs and
measures to control pollution sources and remediate environmental problems
(St. Louis River Citizens Action
Committee).
In 1993, the Citizen’s
Advisory Committee of the RAP requested the Natural Resources Conservation
Service identify methods for reducing sedimentation in the Nemadji River
(Nemadji River Basin Project, Phase II). The Nemadji River Basin
Project (NRBP) began in October 1993. The effort is led by the
Natural Resources Conservation Service, which applied for the funds with
local sponsors (Carlton County Board, Douglas County Board, Carlton County
Soil & Water Conservation District, Duluth/Superior Metropolitan
Interstate Committee).
The RAP advised that agencies
secure funding to implement recommendations generated by the NRBP.
These recommendations will forward the goal of reducing sediment input from
the Nemadji River watershed. The RAP calls for a basin project to
reduce erosion and sedimentation, with a watershed-wide focus,
determinations of the extent and causes of runoff problems, and strategies
to implement practices that would reduce erosion and sedimentation.
The NRBS builds on previous work of the Red Clay Project, which focused on
engineering solutions to streambank erosion – they concluded that 90
percent of the sediment discharged to Lake Superior originated in 2 percent
of the area, namely streambanks, channels, and gullies (WDNR Basin
Plan). As part of the NRBP, the WDNR has been involved in developing
practices for land use, soil management, and forestry that will help
protect and improve water quality condition. A detailed sediment
budget was also developed for the watershed. Data provided by the
project will be used to rank the basin for priority watershed selection,
with the knowledge that the watershed could benefit from priority watershed
status (Nemadji River Basin Project, Phase II).
Though the lower Nemadji
system has suffered many abuses, it has retained significant natural features
and should be a prime candidate for remedial attention. Protecting and rehabilitating the Nemadji River corridor is a
priority, because it harbors ecologically unusual rich mesic hardwood
forests, floodplain forests, and marshes.
The marshes are representatively diverse, dominated by
native species, appear reasonably functional, and support uncommon resident
birds. Exotic plants are still quite localized, associated mostly with the
disturbed levees and formerly dredged areas near U.S. Highway 2. The Nemadji
River Bottoms are also identified as a Lake Superior Basin Priority Site
due to its high quality floodplain wetlands and the erodability of the
soils in this area.
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