Chemical And Physical Characteristics Of Shallow Ground Waters In Northern Michigan Bogs, Swamps, And Fens

Fifteen chemical and physical characteristics were examined in samples of shallow ground water taken in midsummer at 15-30 cm below the surface in six bogs, 15 swamps, and six fens. The wetland types were identified on the basis of their vegetation. Three groups of covarying water characteristics were identified by factor analysis. Factor I included Ca, Mg, Si, pH, alkalinity, conductivity and to a much lesser extent Na, and reflects the degree of telluric water influence in the wetland. Factor 2 included reactive-P, total-P, NH3-N, and to a lesser extent K, and consists of elements that primarily enter interstitial water via organic matter decomposition. Factor 3 included Na, Cl, and to a much lesser extent K. The wetlands formed two distinct groups with respect to water chemistry: weakly minerotrophic (pH 3.8-4.3) including all bogs and moderately to strongly minerotrophic (pH 5.5-7.4) including all swamps and fens. The bogs had very low values for Factor I characteristics and moderate values for the remaining characteristics. The swamps and fens had moderate to high values for Factor 1 characteristics and showed considerable overlap in this respect. The fens had consistently low values for Factor 2 characteristics but overlapped with some swamps which also had low Factor 2 scores. Failure to completely separate the vegetationally very distinct swamps and fens from each other on the basis of their physical and chemical water characteristics indicates that another factor, probably water level regime, is of major importance in determining their vegetation type. NORTHERN MICHIGAN BOGS, conifer swamps, and fens differ strongly in floristics, species density, proportion of evergreen species, role of symbiotic nitrogen fixing species, and role of Sphagnum spp. (Schwintzer, 1981). Considerable evidence indicates that the ionic balance and cation content of wetland waters strongly influence wetland floristics and vegetation type (DuRietz, 1954; Sjors, 1961; Gorham, 1967; Heinselman, 1970; Moore and Bellamy, 1974; Pietsch, 1976; and others). Based on water chemistry two main classes of wetland are recognized: 1) ombrotrophic; and 2) minerotrophic. Ombrotrophic wetlands are dependent on precipitation for water and minerals. Consequently their waters are highly deficient in telluric mineral ions (ions leached from mineral soils and bedrock by percolating water) 1 Received for publication 6 June 1981; revision accepted 9 August 1981. We thank Kent 0. Jones for extensive help in the field, Jerry Krausse for water chemistry analyses, Harold F. Hemond for helpful comments on the manuscript, and Frances O'Brien for typing the manuscript. This work was supported by NSF-RANN Grant No. AEN72-03483 to the University of Michigan Biological Station and by Harvard Forest and represents a contribution from the University of Michigan Biological Station. 3 Present address: Dept. Botany and Plant Pathology, University of Maine. Orono, ME 04469. and have low metal-ion saturation of the peat and low pH. In contrast at least some telluric water enters minerotrophic wetlands. Here metal-ion saturation of the peat and pH depend on the amount of telluric water entering the wetland and the nature of the underlying strata in the region. Little is known about shallow ground waters in northern Michigan wetlands and wetlands in other parts of the Laurentian Mixed Forest ecoregion (Bailey, 1976). The available information is limited to relatively complete descriptions of a bog in northern Michigan (Schwintzer, 1978a) and a fen in central Michigan (Richardson et al., 1978); and partial descriptions of shallow ground water in a variety of northern Wisconsin wetlands (Wilde and Randall, 1951) and northern Minnesota peatlands (Heinselman, 1970). The present study examines shallow ground waters in or near the rooting zone in bogs, swamps and fens in northern Michigan to determine: 1) the nature of the waters found in the wetlands of this region; and 2) the extent of linkage between characteristics of shallow ground waters and wetland vegetation type. Five macronutrients (N, P, K, Ca, and Mg) and other ions as well as pH, alkalinity, conductivitv., and color were measured in bogs.