Dorothy Sack

Hemiarid Lake Basins: Geomorphic Patterns

Geomorphic and stratigraphic patterns, which in lacustrine geoscience differ more in etymology than substance, are the evidence by which hydrographic patterns and underlying hydroclimatic and tectonic patterns are reconstructed in hemiarid lake basins. Regional and local geomorphic patterns are equally important: regional geomorphic patterns are the predictive basis for making local geomorphic observations, and local patterns are the observational basis for building and testing regional models.

SEDIMENT FLUX AND COMPACTION TRENDS ON OFF-ROAD VEHICLE (ORV) AND OTHER TRAILS IN AN APPALACHIAN FOREST SETTING

This research investigates the impact of off-road vehicles (ORVs) on sediment dynamics and compaction in the forested hillslope terrain of southeastern Ohio. A dense network of ground-height change, penetrometer resistance, and penetrometer depth measurements was collected from trails and trail-adjacent forest land at four ORV and, for comparison, two non-ORV trail study sites (hiking, horse-riding). Repeat measurements were made at the height of the ORV season, at the end of the ORV season, and near the end of the off-season. Separate statistical comparisons of ground-height change and penetrometer observations for forest versus trail locations, ORV versus non-ORV study sites, and one time period versus another reveal compaction on all trails, significant surface compaction on the ORV trails, and considerable sediment flux on both the trails and the adjacent forest land at the ORV sites. This flux includes sediment transfer during the riding season from the ORV trails to the adjacent forest land by wash and tire throw. Net erosion that occurred on the ORV trails during the studied part of the riding season was quantitatively offset by off-season aggradation, but the system is primarily one of sediment through-put. Considering the entire riding season, erosion rates on the ORV trails may be as high as 0.11 m3/m2/yr.

Hemiarid Lake Basins: Hydrographic Patterns

Lakes and other mappable bodies of standing water occur at the atmosphere-lithosphere interface. Over short time intervals, water body configurations (hydrography) are directly responsive to atmospheric (hydroclimatic) forcing. Over longer intervals, hydrography also reflects lithospheric (tectonic and volcanic) forcing. In turn, hydrographic patterns in lake basins strongly influence and even control many geomorphic and stratigraphic patterns (e.g. Mabbutt 1977, pp. 180–214). These linked patterns (hydro-climatic + tectonic → hydrographie → geomorphic + stratigraphie) make lakes and kindred water bodies superb instruments for gauging environmental change and recording palaeoenvironmental history.

EXPERIENCES AND VIEWPOINTS OF SELECTED WOMEN GEOMORPHOLOGISTS FROM THE MID-20TH CENTURY

In 1980, as a geomorphology graduate student, I wrote to five senior women geomorphologists in North America and Great Britain requesting information regarding their careers and career experiences. At that time, the number of professionally established women in geomorphology in those countries was very small. The sample consisted of three professors (Borowiecki, King, and Morisawa), one associate professor (Macpherson), and one research scholar (Mammerickx), who had received their doctoral degrees in geomorphology between 1949 and 1966. Each responded to the request for information with a letter and a curriculum vitae. The extent to which they discussed their views regarding, and their personal experiences as, women in geomorphology in the mid-20th century varied widely, as did the amount of biographical information that each provided. Nevertheless this archive reveals some commonalities in their backgrounds, experiences, and views about women in geomorphology. Three of the respondents reported experiencing discrimination early in their careers, while two made career adjustments because of family commitments. Overall the women generally credited their success as professional geomorphologists to a deep appreciation of nature or landscape and to considering themselves as geomorphologists who happened to be women.

The educational value of the history of geomorphology

Abstract The history of geomorphology can be a valuable tool for educating students of geomorphology. The largest and most available record of what geomorphologists thought and did in the past is their original published work. Also available are some fine papers on the history of geomorphology that review and analyze primary sources and past events in the discipline in order to generalize, explain trends, and reveal historical associations. Interest in the history of the discipline varies widely, of course, among geomorphologists. Nevertheless, several educational benefits, in addition to explaining the academic affiliation of geomorphology with two separate disciplines, can be derived from incorporating the history of geomorphology into university-level geomorphology courses. History is a popular subject,and presenting some geomorphic concepts using a historical approach can help to maintain or stimulate student interest. Because of the tendency for older literature to contain more qualitative description and methodological detail than more recent literature, undergraduate students may comprehend some concepts better from older papers. By reading the original literature, students determine for themselves what previous practitioners accomplished, rather than relying solely on the interpretations of others. Reading original literature also helps students realize that older does not mean less intelligent, and that like the critical reading of recent geomorphic literature, the critical reading of historic geomorphic papers can provide a wealth of new research ideas. A thematic set of the historic literature can be used to demonstrate to students the scientific method, the origin, testing, and evolution of hypotheses, how explanations develop in this field, and that science proceeds through individuals working in a sociological context. Including history of geomorphology in the curriculum helps to place contemporary research in the perspective of the past as well as the perspective of the future.

Evidence for Climate Change From Desert Basin Palaeolakes

Lakes have long been recognized as being rich storehouses of environmental information. A lake basin collects water, but also sediment, much of which has been weathered and transported via fluvial processes from the near and far reaches of its drainage basin. The amount of water held in a lake is recorded on the landscape in coastal erosional and depositional landforms created at the water’s edge. The sediments deposited on the bottom of the lake can be clastic, geochemical, or biogenic, and include materials derived within the standing water body itself, such as through coastal erosion, chemical precipitation, or biogenic concentration, as well as those delivered to the lake from the surrounding drainage basin. In most cases only a small percentage of a lake’s sediment load is delivered from outside of the drainage basin as aeolian fallout. Because, under natural conditions, climate is the main determinant of the amount of water in a lake and because it influences some important characteristics of the lacustrine sediments and biota, changing climatic conditions are represented in the suites of abandoned shorelines and accumulations of sediments left by the lake over time (Fig. 25.1). This archival property makes the geomorphic and sedimentologic evidence of present and past lakes valuable as environmental and palaeoenvironmental indicators. Such evidence from late Quaternary palaeolakes, in fact, ranks among of the most complete and accessible sources of palaeoclimatic proxy

Holocene Artemisia-Chenopodiaceae-dominated grassland in North China: Real or imaginary?

The Songnen grasslands were traditionally thought to be dominated by Artemisia and Chenopodiaceae plants as early as the late Pleistocene. However, increasing evidence has called that interpretation into question. To shed new light on the paleovegetation evolution of the arid and semi-arid steppe in North China, phytolith assemblages preserved in the region’s sand-paleosol sequence (section Daike) are used as a proxy for paleovegetation structure. Results show that both the sand and paleosol layers in the Songnen grassland sections contain well-preserved phytoliths attributed to different families of grass. This is the first direct evidence of the nature of the vegetation that existed during the sandy layer episodes. Moreover, the phytolith evidence represented in the samples indicates that plant successions happened within the subfamilies of Poaceae through the time. Referring to phytoliths in modern plants and topsoils, and using statistical analyses, we propose that phytolith assemblages in the section Daike originated from Poaceae-dominant communities rather than an Artemisia-Chenopodiaceae ecosystem. The phytoliths, and evidence from the historical and modern pollen-vegetation relationships, lead to rejection of the hypothesis of a past widespread Artemisia-Chenopodiaceae ecosystem in the Songnen grasslands. Using published radiocarbon and thermoluminescence data, it is proposed that the present Poaceae-dominated grasslands developed as early as the early Holocene. This study also highlights the usefulness of phytolith analysis in paleovegetation reconstruction in arid and semi-arid lands.