Sr/Sr Ratios in Ground Water in and around Cedar Bog, Ohio

Abstract

Isotopic ratios of Sr/Sr were measured in 57 ground and surface water samples taken from in and around Cedar Bog in an effort to determine the provenance of the bog waters. Cedar bog lies in Champaign County, southwest Ohio, and it and its surrounding area are underlain by a variety of glacial deposits. The aim of this study is to delineate which of these deposits is the source of the water in the bog. Strontium was separated from the water samples and the isotopic ratios determined using standard methods. The range of values for this ratio is 0.00117 (0.70826 0.70943), which is more than 50 times the precision of an individual ratio as measured by modern mass spectrometry. Analyses of waters collected from a single site, however, show that these ratios vary over a small but measurable range through time. Such variations are most likely caused by local differences in the amounts of silicate and carbonate material in the glacial units and by local variations in precipitation and runoff, and they form a background noise in studies such as these. Efforts to characterize the individual glacial units by the Sr/Sr ratios in their ground waters are hampered by this noise and by uncertainties, when sampling water wells, as to which glacial units yield the water in the wells. Although these factors make it difficult to trace the ground waters back to individual glacial units, the data do indicate that Cedar Bog waters are most likely derived from the area northeast of the bog and that they are unlikely to be derived entirely from the Mad River outwash. OHIO J. SCI. 93 (1): 27-34, 1993 INTRODUCTION Cedar Bog, a Natural Landmark of the National Park Service and a nature preserve managed by the Ohio Historical Society, is located in Champaign County in western Ohio (Fig. 1). In spite of its name, Cedar Bog is actually a fen. Because the name is well-established and in order to avoid confusion, it will be referred to as a bog in this report. Today, it covers approximately 2.4 ha (6 a) and is a remnant of a rapidly-vanishing postglacial bog. This bog once covered a much larger area and is the home of many rare and endangered species. The nearest bogs similar to it today are found in northern Michigan, several hundred km to the north. Cedar Bog has been the subject of many studies through the years. The most recent description of its history, biology, and geology is found in the symposium edited by Glotzhober et al. (1989). The bog and its local ecosystem are preserved by the influx of cool ground water which arises as springs in the bog, and the future existence of the bog and its environment is dependent on the continued supply of such waters. In densely-populated southwestern Ohio, such a continued supply cannot be assumed and is likely to be interrupted by developments such as highways and new construction. The issue of the continued existence of the bog came to a head in the early 1970s when proposals were made to widen U.S. Highway 68 from two to four lanes and to relocate it along the eastern boundary of the bog. Such construction was postponed through the intervention of environmental groups who were concerned about the impact of the construction on the bog, although once again plans for widening the highway are now being considered. Knowledge of the source area of the bog waters would clearly be of great value in future planning Manuscript received 25 March 1992 and in revised form 27 January 1993 (#92-09). for the area so that developments and construction can proceed in such a way as to protect the bog. Several studies, cited later, indicate that the ground water enters from the east or northeast of the bog. The present study describes the use of strontium isotope geochemistry in an attempt to add further evidence to this concept. Strontium Isotope Geochemistry and its Application to Cedar Bog: Principles and Earlier Work The principles and systematics of the use of strontium isotopes as a geochemical indicator and tracer are firmly established and fully described in the literature (Faure 1986). Briefly, the dissimilar geochemical behavior of rubidium and strontium causes variable Rb/Sr ratios in different rock and soil types. These variable ratios and differences in age of the rock and soil types cause various Sr/Sr ratios to form within the rocks and soils. Each ratio is characteristic of a particular combination of age and Rb/ Sr ratio. The soluble portion of the strontium in these units can be dissolved by meteoric water, and the dissolved strontium will then have a Sr/Sr ratio identical to that of the soluble strontium. If the water emerges as a spring downstream, determination of the Sr/Sr of the dissolved strontium can place limits on the types of rocks and soils through which the water flowed and, therefore, its provenance. Strontium isotope geochemistry was used in an attempt to determine the provenance of Cedar Bog waters in an earlier study (Price and Pushkar 1987, 1989; Price 1987). This study was based on only 19 ground water samples and four leachates made in the laboratory from glacial units, but was able to show that the range of Sr/Sr ratios in the waters was sufficient (0.70837 0.70943) to be measured with modern mass spectrometers. The present study presents data from 38 additional ground water samples from within the bog and its surroundings and is SR/SR IN CEDAR BOG GROUND WATER VOL. 93 a more detailed continuation of this study. It has been presented in preliminary form elsewhere (Ste. Marie 1990, Ste. Marie and Pushkar 1990). Geology of Cedar Bog The Cedar Bog area is underlain by early Paleozoic carbonate units dipping gently to the east away from the axis of the Cincinnati arch. Most of these Paleozoic units are covered by Pleistocene glacial deposits. Those that are exposed are mostly upper Silurian (Quinn and Goldthwait 1979). The carbonate bedrock units are overlain by a variety of Pleistocene, mostly Wisconsin, glacial units (Figs. 2, 3A). During the last glacial advance, the continental glacier was divided into two sublobes by the Bellefontaine Outlier, a topographic high a few tens of kilometers north of Cedar Bog in Champaign and Logan counties. Cedar Bog lies between the two sublobes and, because of the many minor advances and retreats of the two sublobes, is covered by a complex series of moraines and outwash sheets (Fig. 3A). Quinn and Goldthwait (1979) describe these deposits in detail and only a brief synopsis is given here. In these descriptions, moraines are ridges of unsorted deposits laid down directly by the glaciers and are generally considered to be impermeable to groundwater flow. Outwash sheets are aquifers made up of coarse, sorted materials deposited by glacial melt water. The oldest glacial unit is a silty clay, commonly identified as the Minford silt of pre-Wisconsin age, and which does not outcrop in the area (Fig. 2). In the area east of Cedar Bog, the Cable moraine overlies the Minford silt but pinches out westward. In most of the study area, the Minford silt is overlain by a sequence of two ..outwash sheets, with the Urbana overlying the Kenard. The Urbana outwash sheet is overlain by the Springfield moraine, which forms a north-south band across the study area. A second moraine, the West Liberty moraine, forms a parallel band west of the Springfield moraine but is found only to the north of the study area. In the area west of Cedar Bog, the Minford silt is overlain by the Farmersville ground and terminal moraine. The youngest glacial unit in the area is the Mad River outwash sheet which was deposited in a north-south valley cut by the Mad River at the time of glacial retreat. The valley transects the Kennard and Urbana outwash sheets so that the Mad River outwash sheet is in hydrological continuity with them (Fig. 2). Cedar Bog lies on top of the Mad River outwash. The presence of the two outwash sheets to the east of the bog, the presence of the impermeable Farmersville moraine to the west, and the absence of any outwash material to the west makes it very probable that any ground water entering the bog does so from the east. This conclusion is supported by Hillman and Kenoyer (1989) who report that the water table in the vicinity of the bog slopes to the west. Data from other ground water geochemistry and flow-modelling studies support the same conclusion (Price and Pushkar 1989, Ricketts et al. 1989, Kenoyer and Hillman 1989). FIGURE 1. Location of Cedar Bog and the study area, Champaign County, OH. OHIO JOURNAL OF SCIENCE D. J. STE. MARIE AND P. PUSHKAR

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@inproceedings{Marie2017SrSrRI, title={Sr/Sr Ratios in Ground Water in and around Cedar Bog, Ohio}, author={Marie and Dan J. Ste and Pushkar and Paul}, year={2017} }