Extent of Sedge/Grass Meadow in a Lake Michigan Drowned-River-Mouth Wetland Dictated by Topography/Bathymetry and Lake Level

Water-level fluctuations are critical in maintaining the diversity of plant communities in Great Lakes wetlands. Sedge/grass meadows are especially sensitive to such fluctuations. We conducted vegetation sampling in a sedge/grass-dominated Lake Michigan drowned-river-mouth wetland in 1995, 2002, and 2010 that followed high lake levels in 1986 and 1997. We also conducted photointerpretation studies in 16 years dating back to 1965 to include responses to high lake level in 1952 and 1974. Topographic/bathymetric data were collected to assess their influence on areal extent of sedge/grass meadow. Dominant species in short emergent and submersed/floating plant communities changed with water availability from 1995 to extreme low lake levels in 2002 and 2010. Sedge/grass meadow was dominated by Calamagrostis canadensis and Carex stricta in all years sampled, but Importance Values differed among years partly due to sampling in newly exposed areas. Photointerpretation studies showed a significant relation between percent of wetland in sedge/grass meadow and summer lake level, as well as the number of years since an extreme high lake level. From the topographic/bathymetric map created, we calculated the cumulative area above each 0.2-m contour to determine the percent of wetland dewatered in select years following extreme high lake levels. When compared with percent sedge/grass meadow in those years, relative changes in both predicted land surface and sedge/grass meadow demonstrated that accuracy of lake level as a predictor of area of sedge/grass meadow is dependent on topography/bathymetry. Our results regarding relations of plant-community response to hydrology are applicable to other Great Lakes wetlands.

Past terrestrial hydroclimate driven by Earth System Feedbacks

Geologic evidence suggests drastic reorganizations of subtropical terrestrial hydroclimate during past warm intervals, including the mid-Piacenzian Warm Period (MP, 3.3 to 3.0 Ma). Despite having a similar to present-day atmospheric CO2 level (pCO2), MP featured moist subtropical conditions with high lake levels in Northern Africa, and mesic vegetation and sedimentary facies in subtropical Eurasia. Here, we demonstrate that major loss of the northern high-latitude ice sheets and continental greening, not the pCO2 forcing, are key to generating moist terrestrial conditions in subtropical Sahel and east Asia. In contrast to previous hypotheses, the moist conditions simulated in both regions are a product of enhanced tropospheric humidity and a stationary wave response to the surface warming pattern, both varying strongly in response to land cover changes. These results suggest that past terrestrial hydroclimate states were driven by Earth System Feedbacks, which may outweigh the direct effect of pCO2 forcing.

Late Pleistocene lake level, glaciation and climate change in the Mongolian Altai deduced from sedimentological and palynological archives

Glacial and lacustrine sediments from the Mongolian Altai provide paleoclimatic information for the late Pleistocene in Mongolia, for which only a few sufficiently studied archives exist. Glacial stages referred to global cooling events are reported for the last glacial maximum (27–21 ka) and the late glacial period (18–16 ka). Sedimentary archives from the first part of the last glacial period are infrequent. We present proxy data for this period from two different archives (88–63 and 57–30 ka). Due to the limitation of effective moisture, an increase of precipitation is discussed as one trigger for glacier development in the cold-arid regions of central Asia. Our pollen analysis from periods of high paleolake levels in small catchments indicate that the vegetation was sparse and of dry desert type between 42–29 and 17–11 ka. This apparent contradiction between high lake levels and dry landscape conditions, the latter supported by intensified eolian processes, points to lower temperatures and cooler conditions causing reduced evaporation to be the main trigger for the high lake levels during glacier advances. Rising temperatures that cause melting of glacier and permafrost ice and geomorphological processes play a role in paleolake conditions. Interpreting lake-level changes as regional or global paleoclimate signals requires detailed investigation of geomorphological settings and mountain–basin relationships.

A Geological Understanding of Lake Michigan's High Lake Levels

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