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INTRODUCTION 
 The U.S. shoreline of the Great Lakes is nearly 4000 miles in length. Wetlands
occupy only a small proportion of the coastal region; 1370 coastal wetlands,
comprising an area of 466 square miles, have been identified (Herdendorf
et a!. 1981). Approximately 30°lo of U.S. Great Lake wetlands occur
adjacent
to Lake Michigan. Many rivers that flow into the Great Lakes were once associated
with wetland areas; most of these are now either heavily disturbed or have
been destroyed by urban development. Curtis did not recognize Great Lakes
coastal wetlands as a community type in his Vegetation of Wisconsin (1959).
In recent years, there have been a number of descriptive 
studies of wetlands along the Lower Great Lakes (Williamson 1979, Brant and
Herdendorf 1972, Fahselt 1981, Hanink 1979, Herdendorf et al. 1981, Jaworski
and Raphael 1976, Mudroch 1981, Geis, 1985, Geis and Kee 1977, Stuckey 1971,
1975, LeMay and Mulamoottil 1980, Farney and Bookhout 1982, and Ruta 1981).
The few studies of Wisconsin coastal wetlands deal primarily with those along
Green Bay (Bosley 1976, 1978, Harris et al. 1977, Howlett 1974, and Roznik
1978). 
 The Mink River supports one of the best of the remaining Lake Michigan coastal
wetlands. Located near the tip of the Wisconsin Door County Peninsula, the
Mink River flows southeastward into 
 THE MINK RIVER — A FRESHWATER ESTUARY 1 
JANET R. KEOUGH 
Center for Great Lakes Studies 
University of Wisconsin-Milwaukee 
Abstract 
 The Mink River Estuary is one of the few remaining natural wetlands along
the Lake Michigan coastal zone. The river flows through a bedrock valley
across the Door Co., Wisconsin, peninsula. Surficial materials forming its
watershed are glacial and post-glacial, mainly shoreline material placed
during higher levels of Lake Michigan. 
 The dynamics of Lake Michigan play an important role in the control of wetland
plant communities. Most expand and contract as the lake level falls and rises
over the long-term. Lake seiches cause the water in the wetlands to flow
upstream and downstream in both a daily and hourly cycle, generating a persistent
gradient between the alkaline headwater springs and more neutral lake. 
 Land use adjacent to the river has changed little since presettlement, although
the upland forest in the surrounding watershed has been largely replaced
by farm fields. The estuary consists of several vegetation types. The deep
marsh and shallow marsh types are inhabited by communities of few species,
owing to disturbance by long-term changes in lake water level. The wet meadow,
shrub carr, and lowland forest types are more diverse, largely because they
are more protected from extreme water level change by elevation and, in the
case of wet meadow species, by the development of hummocks by Carex stricta.
Peak above- and below-ground biomass found in herbaceous wetland communities
in 1981 are presented. Perennial species peak in August, while annuals peak
in September; most below-ground accumulation peaks in September.