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Whitford, Philip; Whitford, Kathryn (ed.) / Transactions of the Wisconsin Academy of Sciences, Arts and Letters
volume 74 (1986)

Keough, Janet R.
The Mink River- a freshwater estuary,   pp. 1-11 PDF (4.8 MB)


Page 3

Fig. 3. Mean annual level of Lake Michigan, 1935-1981 (from N.O.A.A. 1981).
0 
-J 
w 
> 
w 
-J 
cc 
 2400 600 1200 1800 2400 600 1200 1800 2400 600 1200 1800 2400 
  May 21    May 22    May 23 
Fig. 4. Measurement of water level fluctuation in one of the headwater creeks,
approximately 100 meters from a bedrock spring, taken between May 21-23,
1983. While the amplitude varies, the period is constant throughout the icefree
season. 
1986] Keough—Mink River Estuary 3 
These fine grey sediments and the sandy soils of the surrounding area were
probably deposited during this post-glacial lake stage. Declining lake level
and land rebound have raised the old beaches and also separated the Mink
River watershed from Green Bay (Figure 2). 
HYDROLOGY 
 Hydrologic aspects of the watershed are the most important factors contributing
to the character of the Mink River wetland. There are three primary sources
of water: 
precipitation, groundwater springs, and Lake Michigan. Surface runoff from
the small watershed is limited by lowland forest vegetation. 
 Springs located in the lowland forest surrounding the marsh discharge into
the 
wetland creeks throughout the year. Springs also emerge within the wetland;
these have been observed as open pools in February surrounded by the snow-covered
marsh. Weathered limestone is exposed at the bottom of the headwater springs,
attesting to their origin in the bedrock aquifer. 
The channels connecting the headwater springs to the river appear well entrenched
in the substrate. A review of past aerial photographs (1938, 1952, 1962,
1967, 1974, 1978) indicates that location of the channels has not changed
appreciably in almost 50 years. Sherrill (1978) suggested that the drift
overlying the bedrock around and under the Mink River is shallow. The main
channel of the Mink River forms a distinct and apparently unchanging bend
as it flows near an upland bedrock knoll. Although most of the depression
containing the river and wetland appears to have been filled by lake sediments
and beach deposits, the channel forms suggest bedrock control of the major
channels. 
 Rainfall is moderate; the NOAA station on nearby Washington Island records
an average annual precipitation of 29 inches. Approximately half of this
amount falls during the growing season. 
 Precipitation and spring flow vary little from year to year. However, Lake
Michigan plays a dominant role in wetland dynamics. The level of the lake
has varied widely in historic time (Figure 3). Aerial photographs 


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