Short-term Vegetation Changes on an Abandoned Mining Site as Determined by Pollen Analysis

Abstract

-The effectiveness of palynology in documenting short-term ( 4 m in height) of the abandoned mine site was dominated by Ulmus rubra, U. americana, Prunus serotina, and less commonly Populus deltoides, Cornus drummondi and Quercus imbricaria. Species important in the shrub layer (1-4 m in height) were Acer negundo, Rhus radicans and C. drummondi (Elzinga, 1984). The second study area, Randolph Lake (37?57.8'N, 89?47.7'W) in Randolph County Conservation Area (419 ha), was a 28.4-ha lake created by stream impoundment in 1960. While forest characterized much of the conservation area (182 ha), land use in the lake's watershed was predominantly agricultural (Illinois Department of Conservation, undated). Major taxa of the tree layer found in woodland surveys were Quercus alba, Q. rubra, Q. stellata, Carya ovata, C. lacinosa and Fraxinus americana; abundant in the shrub layer were Ulmus americana, U. rubra, Cornus florida and Rhus aromatica (Elzinga, 1984). The larger area of this lake as compared to Streamline Lake results in the collection of a greater proportion of regional pollen, thus making it a good site for comparing local vegetation changes around Streamline Lake using the technique of Jacobson (1979). MATERIALS AND METHODS The rodless coring device designed by Hutunen and Marilainen (1975) was used to obtain core samples from Streamline Lake. Brugam et al. (1983) found this device well-suited to the soft sediments of surface mine lakes. Although use of this device was attempted at Randolph Lake, it was ineffective in penetrating the clay-rich sediment. Instead, the coupledrod coring technique described by Wright (1980) was employed. Both lakes were cored in September 1982, recovering a 38-cm core from Streamline Lake and a 75-cm core from Randolph Lake. Laboratory treatment of the sediment followed the general pollen preparatory techniques of Faegri and Iverson (1975), with the modifications of Cwynar et al. (1979). Pollen grains were counted at 400x and identified at 100X with Kapp (1969) and locally collected reference slides. Approximately 300 pollen grains were counted in each sample. Pollen accumulation rates were estimated by adding a Lycopodium spike of a known concentration to each sample and by following the calculations of Davis (1969). The sedimentation rate for Streamline Lake was determined using the lead-210 (Pb-210) dating method (see Brugam and Carlson, 1981). While the Pb-210 dating method was applied to the Randolph Lake core, anomalous Pb-210 activities were evident throughout, thus precluding calculation of a sedimentation rate. However, the presence of numerous regular laminae in the core coupled with the short lacustrine time interval suggested that the sedimentation rate could be estimated. The lacustrine zone, marked by higher diatom concentrations, was determined to be at 57 cm. An average sedimentation rate of 2.85 cm/yr was then calculated by dividing the length of the core above the lacustrine horizon (57 cm) by the known age of the lake (20 yr). RESULTS AND DISCUSSION Sediment dating of the 38-cm Streamline core by Pb-210 revealed a disjunct lacustrine sedimentation regime (Fig. 1); the sediment between 30 and 38 cm represented an 11-yr period, and the top 14 cm of the core represented 24 yr. These periods of sediment deposition cumulatively represented 35 yr and gave an estimate for the date of lake origin as 1947. This date agreed well with the actual lake formation date: 1944-1946 (B. W. Holloway, pers. comm.). The sediment between 15 and 30 cm was marked by anomalous Pb-210 This content downloaded from 207.46.13.160 on Tue, 25 Apr 2017 17:59:36 UTC All use subject to http://about.jstor.org/terms 1988 ELZINGA. ANALYZING VEGETATION CHANGES 373 LnAz = 2.280.054z STREAMLINE S = 0.61 cm/yr 2.5R= -.89 + 1982 1958 4-~~~~~~~~~~~~~~~~4 2.0 + + + > 1947 u) + + + LnAz 3.58-0.042z < 1.5 S =0.79 cm/yr O1958 RR= -.99