Earth & Environmental Sciences
Testate Amoebae as Indicators of the Magnitude of Seasonal Moisture Variability in Sphagnum Peatlands
Numerous proxies have been developed over the past few decades to reconstruct the paleohydrology of peatland systems, including testate amoebae, a group of moisture-sensitive protozoa. Testate amoebae have been successfully used to infer patterns of multi-decadal moisture variability; however, variability at shorter timescales may also influence community composition. The objectives of this study were to determine if the composition of testate amoeba communities is influenced by seasonal moisture variability and, if so, develop models to infer the magnitude of seasonal moisture variability from fossil assemblages.
Testate amoebae and surface moisture conditions, including hourly measurements of relative humidity within the upper few centimeters of Sphagnum, were examined throughout the growing season at 78 sites within eleven peatlands of Pennsylvania and Wisconsin. Cluster analysis and non-metric multidimensional scaling (NMS) were used to describe patterns in community composition, and these patterns were compared to environmental variables to assess controls on testate amoebae. Results suggest that testate amoebae can not only be used as indicators of mean water-table depth, as in previous studies, but also seasonal variability, with particular species and communities characteristic of highly variable environments. The calibration data from this study was used to identify time periods of exceptionally high moisture variability in late Holocene testate amoeba records from the Great Lakes region, using a series of modern analogue based models. These reconstructions suggest that this new tool, when used in tandem with mean water-table depth reconstructions, can provide insights into the fine-scale structure of late Holocene moisture changes.
Mutlidecadal Hydroclimatic Fluctuations Trigger the Initiation and Episodic Expansion of a Floating Kettlehole Peatland
Floating Sphagnum-dominated kettle-hole peatlands are common features of glaciated landscapes. Ecologists have long been interested in these systems as archives of post-glacial environmental change and have sought to understand the processes governing floating peatland initiation and expansion. The widely accepted, though seldom tested, developmental model invokes climate-independent succession of pond-marginal plant communities and lateral expansion of floating vegetation over open water. In contrast, we hypothesize that floating mat expansion is episodic and driven by multidecadal hydroclimatic fluctuations. Under this model, drought exposes organic sediments to colonization by sedges and/or wetland shrubs, subsequent increases in water level cause floatation of peat, and the resulting hydrologic stability is conducive to Sphagnum colonization. We have conducted a preliminary test of this hypothesis by reconstructing the developmental history of a floating kettle-hole peatland in Erie County, Pennsylvania (Titus Bog) using multi-core, multi-proxy paleoecological analyses and comparing spatiotemporal patterns of peatland initiation and expansion to independent records of past hydroclimate. Results indicate that Titus Bog transitioned from a pond to a floating peatland at the western margin around 870 50 yr BP, coincident with a period of major hydroclimatic fluctuations during the Medieval Climate Anomaly. The floating peatland rapidly expanded throughout the rest of the basin several hundred years later (390 75 yr BP) during another interval of prolonged drought recorded in tree ring records from much of North America, including western Pennsylvania. Our results suggest that transient high-magnitude droughts may force kettle-hole ecosystems over critical thresholds, permanently transforming their structure and function.
Retention and Release of Cryptosporidium parvum Oocysts by Experimental Biofilms Composed of Natural Stream Microbial Communities
Cryptosporidium is a group of waterborne protozoan parasites that cause significant gastrointestinal disease in humans. The potential exists for these parasites to accumulate in stream or pipe surface biofilms and to be subsequently released to contaminate the water supply. Natural microbial assemblages were collected from three streams for three seasons (fall, winter, and spring) and used to grow biofilms in laboratory microcosms. These biofilms were then exposed to Cryptosporidium parvum oocysts via continuous inflow to determine daily influx, efflux, and biofilm retention and sloughing. Daily oocyst counts showed that oocysts attached to the biofilm quickly (within hours) and released slowly (within days). In these experiments, at least 40% of the oocysts added to the system attached to the biofilm in the first 72 hours, and at least 20% of the oocysts remained attached to the biofilm beyond 72 hours after the oocyst supply was removed. Although variation across site and season exists, likely as a result of variable microbial communities, all biofilms captured at least 40% of the oocysts and retained some of those oocysts for at least five days. The biofilm attachment and detachment dynamics of C. parvum oocysts have important implications for public health and suggest that biofilm monitoring should be included in routine water supply monitoring.
The interaction between climate, tectonics, and topography in the San Juan Mounains, southwestern Colorado
Alpine glaciers have been found to produce rapid denudation rates that are capable of keeping pace with orogenic rock uplift, leading researchers to characterize glaciers as “buzzsaws” effectively limiting the altitude of developing orogens that intersect the glacial threshold. Research has concentrated on regions of maritime climate and convergent tectonics, leaving the impact of glaciation on intracontinental mountain ranges poorly understood. In the San Juan Mountains of southwestern Colorado, we examined the impact of extensive Quaternary glaciation on topography using swath profiles and morphologic characteristics of relief and slope in relation to glacial thresholds; in addition, apatite (U-Th)/He thermochronology was used to investigate the spatial variation of exhumation throughout the range. The northwestern region had cooling ages of 3-10 Ma, moderate correlation between mean elevation and glacial thresholds, and regionally high values for relief and slope above cirque floors. The southern region, by contrast, had cooling ages of 19-39 Ma, no correlation between mean elevation and glacial thresholds and low values for relief and slope above cirque floors. Lithologic constrains on total denudation imply that active tectonism, not erosionally induced isostatic rebound, was responsible for the difference in cooling ages. In addition, modern climate patterns and late Quaternary glacial extent are similar for the northwest and southern regions and, therefore, climatic variations between the regions and fluvial erosion models cannot account for the differences observed. In the San Juan Mountains it appears that the presence of glacial ice alone does not result in the control of topographic development by glacial thresholds. The data implies that more recent tectonic activity in the northwestern region (related to the Aspen anomaly?) resulted in greater glacial modification of the landscape and suggests that topographic controls imposed by glacial thresholds are dependent on tectonic processes.
Using GIS in the Classroom to Investigate Energy
The National Educational Technology Standards for Students called for a classroom that is student-centered, with collaborative work in a multisensory, multimedia-based information exchange, where active inquiry-based learning and critical thinking are fundamental (International Society for Technology in Education [ISTE], 2000).
The purpose of this session is to illustrate how a Geographic Information System (GIS) can be incorporated into the classroom to support science and geographic inquiry and promote spatial thinking skills. According to the National Research Council (2006), spatial thinking is the knowledge, skills, and habits of mind to use concepts of space, tools of representation, and processes of reasoning in order to structure problems, find answers, and express solutions to those problems. › Continue reading