Wetland flora of the Grand Calumet River in Northwest Indiana: potential impacts of sediment removal and recommendations for restoration

Proceedings of the Indiana Academy of Science, Wntr-Fall, 1999 by Young D. Choi

ABSTRACT

Northwestern Indiana supports unusually diverse floras. However, rapid industrialization and urbanization since the late 19th Century have changed much of the natural character of the wetlands along Grand Calumet River. Of more than 1400 species that occurred historically in the northwestern Indiana, 19 species were identified as extirpated species; and only 653 species, including 1 extirpated, 17 endangered, 14 threatened, and 18 rare species were documented during the recent surveys in the Grand Calumet River wetlands. Over 97% the wetlands along the Grand Calumet River were disturbed by fragmentation, infestation by alien species (120 of 653 species were alien), and anthropogenic disruption of ecosystem processes (e.g., fire suppression, draining, filling, and sedimentation). Among the wetlands along the Grand Calumet River, Roxanna Marsh, DuPont Tract, Clark & Pine East Nature Preserve, and Miller Woods were identified as high quality habitats with special needs of conservation. The proposed sed iment dredging may cause direct physical damage to wetland floras, shoreline erosion along the stream banks, and "probable" drainage by deepening the riverbed. Restoration of ecosystem structure and function is needed to minimize such negative impacts that would potentially be incurred by the proposed sediment dredging.

Keywords: Wetland, flora, dredging, conservation, restoration

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With its 14,000-year geologic history, northwestern Indiana natural areas support unusually diverse biological communities (Reshkin 1990). The diverse flora on the dune-and-swale complex on the southern shore of Lake Michigan has been noted by Cowles' (1899) bench-mark study, followed by Fuller (1935), Olson (1958), and Wilhelm (1990). Many factors caused drastic changes in species of the plant communities along the Grand Calumet River. The geomorphology of this river system has been altered significantly by human activities. The rivers have become straighter and narrower as a result of channelization. In addition, drainage and filling, along with industrial pollution of marshes and ponds adjacent to the river, altered local hydrology (Hiebert et al. 1986; Wilcox et al. 1986; Bowles 1990). This chapter discusses (1) pre-settlement and present-day wetland plant communities, (2) potential impacts of the proposed dredging project on wetland vegetation in the Grand Calumet River basin, and (3) restoration potenti als of native wetland flora in conjunction with sediment removal.

NATIVE FLORA OF PRE-SETTLEMENT TIMES

Extirpated species.--Peattie (1930), in his publication Flora of the Indiana Dunes, estimated that 1400 plant species inhabited the Indiana Dunes area. Nineteen of these species have not been seen in Indiana since Peattie's sightings, and they have now been classified as extirpated species (species that had not been seen in Indiana for 50 years) by Aldrich et al. (1986). They are Betula populifolia (gray birch), Carex scabrata, Corallorrhiza trifida (coral root), Gerardia pedicularia ambigens (clammy false foxglove), Hemicarpa drummondii, Hippuris vulgaris (mare's tail), Lechea stricta (bush pinweed), Lemna perpusilla (least duckweed), Linnaea borealis (twin flower), Lonicera canadensis (American fly honeysuckle), Oryzopsis pungens (short-horned rice grass), Panicum lucidum (bog panic grass), Psilocarya nitens (bald rush), Pyrola secunda (one-sided shinleaf), Scleria reticularis (netted nut rush), Shepherdia canadensis (russet buffaloberry), Trillium cernuum macranthum (nodding trillium), and Utricularia resu pinata (small purple bladderwort).

Historic plant community types.--Bacone et al. (1980) reconstructed the pre-settlement vegetation characteristics of northwestern Indiana by analyzing land survey records that were compiled between 1829 and 1834. The wetland community types recognized by this study are aquatic communities, marshes, swamps, bottomland forests, beach communities, and pannes.

Aquatic communities consist of macrophytes and phytoplankton in standing or running water. The 1829-1834 survey record noted Polygonum spp., Nuphar advena, and Nymphaea tuberosa as typical macrophytes (Bacone et al. 1980). Since European settlement, species composition of this community has been changed significantly by numerous human activities such as loading of nutrients, silts and other pollutants, alteration of local hydrology through channelization, drainage, and filling of the river and its adjacent wetlands.

Marshes are probably the most prominent plant community types along the Grand Calumet River. Marshes are open (non-forested) wetlands that are dominated by sedges and/or grasses communities (Bacone et al. 1980). On the wet end of the moisture gradient, sedge meadow is found directly adjacent to aquatic. At the other extreme, wet prairie overlaps with the borders of mesophytic prairies and savanna complex (Wilhelm 1990). As is indicated by its name, sedge meadow is characterized by abundant sedges (Cyperaceae); wet prairies are dominated by grasses (Poaceae). Typical plant species in this community type include Aster puniceus firmus, Bidens coronata tenuiloba, Carex aquatilis altior, Decodon verticillatus, Polygonum punctatum, and Scirpus acutus. Historically, periodic fires--both natural and man-made--have been a crucial factor in maintaining marshes because fires prohibit the invasion of woody shrubs and trees. Since European settlement, however, most marshes have been heavily disturbed by drainage, by invas ion of woody species facilitated by artificial fire suppression and by intentional or accidental introduction of alien species (Labus et al. 1999).