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Water resources of the Apostle Islands National Lakeshore, northern Wisconsin

January 1, 1988

The Apostle Islands National Lakeshore consists of 21 islands, part of the Bayfield Peninsula, and the adjacent waters of Lake Superior. Selected water resources of the Apostle Islands National Lakeshore were assessed to aid the National Park Service in developing and managing the Lakeshore and to provide a data base against which future changes can be compared. This summary of water-resources data, collected by the U.S. Geological Survey during 1979-84, provides a qualitative description of selected hydrologic components of the Lakeshore.

Streamflow in the Lakeshore area is characterized by typical seasonal fluctuations. Flow in Sand River at State Highway 13 ranged from 3.9 to 1,630 cubic feet per second. The recurrence interval of the maximum observed discharge was about 4 years. The minimum observed 7-day low flow was 3.86 cubic feet per second.

The greatest concentrations of most chemical constituents in Bayfield Peninsula streams occurred during base flow.

Annual sediment loads in Sand River at State Highway 13 ranged from 977 tons in 1980 water year to 24,600 tons in 1984 water year.The average annual sediment load transported by Bayfield Peninsula streams to the National Lakeshore area of Lake Superior is estimated to be 44,000 tons. Annual phosphorus loads ranged from 1,400 pounds in 1980 water year to 11,100 pounds in 1984 water year. The average annual phosphorus load transported by Bayfield Peninsula streams to the National Lakeshore area of Lake Superior is estimated to be 21,500 pounds.

Few island streams flow perennially, but Oak Island streams generally yield more base-flow runoff than Stockton Island streams. The base flow of Oak Island streams is dominated by ground-water discharge, whereas Stockton Island stream base flow is sustained by seepage from wetlands and beaver ponds.

There are two major lagoons in the Lakeshore, the Outer Island Lagoon's area is 53 acres and its maximum depth is 7 feet. Dominant inflow to the lagoon is from precipitation on its surface and seepage from an adjacent bog. Outflow during open-water periods is dominated by evaporation. Ground-water seepage from the lagoon toward Lake Superior occurs yearround. The lagoon's water is acidic and has low specific conductance and generally small concentrations of most chemical constituents.

The Michigan Island Lagoon is about 4 acres in area and its maximum depth is 6.5 feet. The most significant sources of inflow appear to be precipitation and wave washover from Lake Superior.

Water from four deep-water monitoring sites in Lake Superior revealed concentrations of total phosphorus, organic carbon, and recoverable mercury ranging from <0.01 to 0.02 milligrams per liter, 1.1 to 5.3 milligrams per liter and <0.1 to 0.1 micrograms per liter, respectively. Neither pesticide residues nor fecal coliform bacteria were detected in the water column. Total phosphorus concentrations in bottom sediment ranged from 50 to 470 milligrams per kilogram and were related directly to the percentage of fine-grained (< 0.0625 millimeters) sediment particles. Traces of only two pesticide residues- DDE and DDT were detected in sediment. The most abundant benthic macroinvertebrate was Pontoporeia affinis, which was found in densities of from 960 to 2,100 organisms per square meter.

No adverse affects resulting from visitor use were detected in the shallow-water, heavy-use areas in Presque Isle Bay off Stockton Island or in the waters between Rocky and South Twin Islands. Phosphorus and organic-carbon concentrations were similar to those observed in the deep-water area; mercury was not detected in water from either area.

Ground-water use in the National Lakeshore is primarily for consumption by Lakeshore visitors and employees. Of 14 wells constructed from 1979-84, 4 were finished in glacial sand and gravel, and 10 were finished in sandstone. Specific capacities ranged from 0.63 to 50 gallon per minute per foot. Average concentrations of dissolved solids are moderate and concentrations of heavy metals did not exceed Wisconsin's primary health standard.

Publication Year 1988
Title Water resources of the Apostle Islands National Lakeshore, northern Wisconsin
DOI 10.3133/wri874220
Authors W. J. Rose
Publication Type Report
Publication Subtype USGS Numbered Series
Series Title Water-Resources Investigations Report
Series Number 87-4220
Index ID wri874220
Record Source USGS Publications Warehouse
USGS Organization Wisconsin Water Science Center