Richard B. Brugam

A diatom-inferred water depth reconstruction for an Upper Peninsula, Michigan, lake

Transects of surface sediment samples were taken in 4 lakes from the Sylvania Wilderness Area, Upper Peninsula of Michigan. These surface samples were compared with diatom samples from a core taken in the Northwest basin of Crooked Lake, also from the Sylvania Wilderness Area. Weighted Averaging calibration was used to reconstruct lake depths in Crooked Lake using the diatom microfossils from the core and the surface samples to infer past lake depth. During the early Holocene the lake was dominated by planktonic species and diatom-inferred water depth was large – approx. 13 m. At about 6700 BP inferred water depth was 2 m and samples were dominated by Fragilaria construens var. venter – a species characteristic of shallow parts of the surface sample transects. From 6700 to 5000 BP reconstructed water level was at its shallowest. From 5000 to 3000 BP it increased. This rise in water level was marked by increasing abundances of Aulacoseira ambigua and occurred at the same time increasing percentages of hemlock pollen indicate increasing available moisture. Modern water depth was reached about 3000 BP. The water level changes at Crooked Lake are consistent with regional climate changes in the Upper Midwest during the Holocene. The lake was shallowest during the mid-Holocene warm period documented by other investigators. It deepened as the Midwestern climate became cooler and wetter during the late Holocene.

The relationship between fossil diatom assemblages and limnological conditions

Fossil diatom assemblages from the sediment/water interface in 105 Minnesota lakes were compared with measurements of alkalinity, sulphate, total phosphorus, transparency, and water depth at the sample site. Similar assemblages were placed together using cluster analysis and comparisons of environmental variables between diatom clusters were made using an analysis of variance. Total alkalinity and transparency showed the greatest difference among clusters. Samples from shallow eutrophic prairie lakes were dominated by Melosira granulata, Stephanodiscus niagarae and, occasionally, by Stephanodiscus hantzschii. Deep oligotrophic lakes had modest percentages of Cyclotella comta. Dilute acid lakes were dominated either by Melosira distans and M. italica or by Tabellaria fenestrata, Cyclotella stelligera, and in some cases C. glomerata. Assemblages with Cyclotella glomerata and Synedra nana were found in naturally meromictic lakes. Stephanodiscus hantzschii showed a preference for extremely eutrophic lakes. The relationships between recently deposited diatom assemblages and the lake environmental conditions studied here can be used to evaluate the extent of past environmental change in lakes.

Holocene lake-level rise in the Upper Peninsula of Michigan, USA, as indicated by peatland growth

We examined one sediment core from Kerr Lake and eight cores from the adjacent peatland in the Sylvania Wilderness Area of the Upper Peninsula of Michigan, USA. Radiocarbon dating of the interface between peat and the underlying glacial till showed that the peatland grew by paludification of the surrounding uplands, implying a rising water level in the lake. Pollen analysis of the cores showed that the peatland began expanding just before the arrival of Tsuga in the surrounding forests. The most rapid growth of the peatland occurred between 3900 and 3000 BP. This is also the time when the forests were being transformed from dry Pinus strobus-dominated woodlands to moister Tsuga- and Acer saccharum-dominated northern hardwoods. Our results imply an increase in available moisture at the time of Tsuga colonization.

Diatom indicators of peatland development at Pogonia Bog Pond, Minnesota, USA

Sediment cores were taken from the central pond and fringing mat of a Sphagnum peatland located in the Big Woods vegetation type. Pollen analysis of the pond core spanning 12 000 cal. BP to the present indicated a mid-postglacial warm period (10 000 to 3900 cal. BP at this site), when the area was covered by open oak woodland and prairie. From 3900 to 300 cal. BP oak forest expanded. At 300 cal. BP (ad 1650) Big Woods species (e.g., Tilia, Ostrya, Ulmus and Acer) increased as a result of ‘Little Ice Age’ cooling. Diatoms indicating water of high acid-neutralizing capacity (e.g., Stephanodiscus hantzschii) dominated the lake during the mid-Holocene. At 2100 cal. BP these species were succeeded by Aulacoseira distans and A. perglabra, indicating water of low acid-neutralizing capacity and marking peatland initiation. Transfer functions derived from diatoms in surface-sediment samples from Minnesota and the Upper Peninsula of Michigan suggest that this change was associated with reduced acid-neutralizing capacity in Pogonia Bog Pond. This decline was probably caused by peat accumulation around the Pond. The development of peatland at Pogonia Bog is late relative to sites farther north and east, indicating that the climate of the site has become conducive to peat accumulation in the last 2200 years and that the initiation of peatland development represents a time-transgressive boundary that has moved across central North America.

The neutralization of acidic coal mine lakes by additions of natural organic matter: a mesocosm test

Cylindrical polyethylene enclosures 3 m in length and 1 m in diameter reaching from the surface to the bottom were constructed in an acid (pH=3.1) lake on a coal surface mine in southern Illinois. Wheat straw was added to the enclosures to test the effects of dissimilatory sulfate reduction on water chemistry. Added straw increased sulfide concentrations, raised pH to 6.5, reduced O2 and increased acid neutralizing capacity of the enclosed water columns when compared with a control enclosure and with the open lake. Generation of acid neutralizing capacity exceeded the standing stock of sulfide indicating that sulfide was removed either by precipitation of FeS or outgassing of H2S. The pH and acid neutralizing capacity within the enclosures eventually returned to the level of the surrounding lake because of water exchange around the enclosure walls. Our results show that additions of organic matter to acid surface mine lakes result in the generation of acid neutralizing capacity.

Holocene environmental changes in Lily Lake, minnesota inferred from fossil diatom and pollen assemblages

Abstract A postglacial core was taken from Lily Lake, a soft-water lake, located on carbonate-poor till in eastern Minnesota. Pollen analysis allowed the reconstruction of watershed vegetation change. Diatom assemblages from the core were compared with 255 surface sediment assemblages from Minnesota, Maine, Labrador, and the Canadian arctic. Late-glacial assemblages were similar to Canadian arctic lakes. During the mid-postglacial period of warmer and drier climate, fossil diatom assemblages at Lily Lake were similar to those in the surface sediment of modern eutrophic hardwater lakes in Central Minnesota. The shift to hardwater diatom assemblages coincided with a shift to prairie species in fossil pollen assemblages at about 8000 yr B.P. At about 3400 year B.P. the fossil diatom assemblage that characterized presettlement times was established.

Continental-scale climate forcing factors and environmental change at Glimmerglass Lake in the upper Peninsula of Michigan

Previous palaeoecological studies have shown that there have been major range shifts in Tsuga (hemlock) during the middle and late Holocene that seem to indicate climatic cooling and an increase in available moisture. We examined lake-level changes and peatland growth at Glimmerglass Lake and peatland in the Sylvania Wilderness Area to determine if the mid-Holocene increase in moisture indicated by the pollen record also influenced lakes and wetlands. Sphagnum peat began accumulating at the site at 6240 cal. yr BP. Diatom-inferred depth reconstructions show that the lake level rose 2 m and the peatland expanded out of its basin at 5300 cal. yr BP. All of these changes occurred as the last remnant of the Laurentide Ice Sheet disappeared and orbital forcing reduced seasonality relative to the early Holocene. We conclude that these continental-scale factors caused increased moisture availability in the Upper Peninsula of Michigan, resulting in rising lakewater levels and peatland expansion.

Sediment chemistry of lakes formed by surface-mining for coal in the midwestern U.S.A.

Sediment from lakes on abandoned coal mines in the Midwestern U.S.A. was examined to determine the factors controlling chemical composition and the role the sediment plays in lake neutralization. Sediment concentrations of many cations, (especially heavy metals) are strongly correlated with sediment sulfide concentration, but poorly correlated with the pH of the overlying water. Leaching the sediment of one lake with 1 N ammonium acetate, 0.1 N HCl, and 6 N HCl revealed that cations were mostly bound in weak acid-leachable and strong acid-leachable forms. The weak acid-leachable form is likely to be metal sulfides and calcium carbonate. The sulfide-poor sediments of extremely acid lakes contained few weak acid-leachable cations. Raw mine-spoil contained large amounts of easily leached cations. There is little relationship between changes in sediment chemistry over time determined from cores of lake sediment and past lake pH. Rates of sulfide deposition were examined in sediment cores because sulfate reduction and deposition has been suggested as a major source of alkalinity in lakes influenced by acid precipitation. Although the rate of sulfate deposition in surface mine lakes is high, it alone seems to be insufficient to cause neutralization.

Historical development of the Cypress/Tupelo swamp at Horseshoe Lake, Alexander County, Illinois, USA

Horseshoe Lake, Alexander County, Illinois, is a shallow floodplain lake that lies at the northern range boundary of Taxodium distichum var. distichum (L.) L.C. Rich (bald cypress) in the Mississippi River Valley. About 35% of the lake surface is occupied by a flooded forest of Taxodium distichum and Nyssa aquatica L. (water tupelo). Pollen in two sediment cores was examined to determine the time of arrival of the forest at the site. Taxodium and Nyssa pollen increased in sediment deposited in 1850. The Modern Analogue Technique (MAT) showed that samples dating from before the arrival of Taxodium were most similar to sites in a variety of locations with high Quercus (oak) and Carya (hickory) and low Pinus (pine) percentages without Taxodium. For sediment deposited after the increase in Taxodium, the most similar modern analogues came from Taxodium/Nyssa swamps in the lower Mississippi River Valley and Virginia. Ring analysis of extant trees suggested an increase in reproduction and growth after 1850. The MAT results were consistent with the hypothesis that the Taxodium/Nyssa forest first colonized the lake around 1850 when American farmers developed the upland loess soils of the watershed for agriculture. We suggest that agricultural development on the uplands surrounding the lake encouraged the growth of the Taxodium/Nyssa forest by increasing sedimentation rate and producing large shallow areas of seasonally flooded eroded material.

Chemisty of lake water and groundwater in areas of contrasting glacial drifts in Eastern Minnesota

The water chemistry of 28 lakes from both sides of the border between glacial drifts of the Grantsburg lobe (high CaC03) and Superior lobe (low CaCO3) in east-central Minnesota was examined to determine if drift type influences lake-water chemistry. Similar analyses were performed on groundwater samples taken from wells near each lake. Concentrations of Ca++, Mg++, HC0inf3sup-, SOinf4sup- were significantly higher in lakes of the Grantsburg lobe, whereas K+, Si02, and HCO 3- were significantly higher in samples of groundwater from the Grantsburg lobe. There was no correlation between groundwater concentrations of particular ions and lake-water concentrations of the same ions, implying that the sources of dissolved ions in lake water are shallow groundwater and soil leachates rather than the deeper groundwater sampled here. Na+ and Cl- concentrations in some lakes appear to be strongly influenced by the use of de-icing salt on highways in winter rather than by differences in drift lithology.