All seminars are held Thursday afternoons in 108 Clark Hall at 4:00 PM. Reception at 3:30 PM in foyer in front of Clark 108.

JAN 29 TH
Paul Stackhouse (NASA Langley Research Center),
Temporal and Spatial Variability of the Earth's Surface Radiation Budget,
Host Amber Hill

Brief abstract:
The radiative exchange of energy at the Earth's surface is a critical component of the Earth's energy balance and intimately linked to regional and global climate. The NASA/GEWEX (Global Energy and Water Cycle Experiment) Surface Radiation Budget project uses satellite and other ancillary information about the atmosphere and surface to derive a time history of the surface radiation budget of the Earth. In this talk, I present an overview of the Earth's surface radiation budget in terms of its importance to climate. Then we explore the inter- and intra-annual variability of the recent SRB Release 2 spanning from July 1983 through October 1995 using various tools such as an EOF (Empirical Orthogonal Function) analysis. Comparisons against surface measurements will be presented to quantify the uncertainties of the datasets identifying areas of largest uncertainty for future emphasis. Lastly, a brief overview of some renewable energy applications of these datasets will be presented.

FEB 5 TH
Charles Gallegos (Smithsonian Institute),
Linking Land Use and Light Penetration in Small Estuarine Segments,
Host Eric Bricker

Brief abstract:
An optically based indicator of habitat suitability for submerged aquatic vegetation (SAV) has been derived and applied to mesohaline subestuaries of Chesapeake Bay (Maryland and Virginia) with differing land uses, and in the North River, North Carolina. The indicator utilizes concentrations of optically active water quality parameters to determine whether sufficient light penetrates the water column for growth of SAV. Differences in indicator values between vegetated and non-vegetated sites are found to be attributable both to differences in water quality concentrations and to site-specific differences in mass-specific optical properties of the suspended particulate matter. Sites classified as developed watersheds consistently exhibit lower indicator scores, while forested and agricultural watersheds show only minor differences. Difficulties in ascribing causality to land use are discussed in relation to scales of watershed influences in subestuaries and processes that determine the mass-specific absorption and scattering coefficients.

FEB 12 TH
Tom Torgersen (University of Connecticut),
Finding Process in the Earth/environmental sciences.
Host George Hornberger

FEB 19 TH
Matt Goode (University of Arizona),
Ecology and Conservation Issues of the Tiger Rattlesnake (Crolalus tigris) in the Sonoran Desert,
Host Tom Biggs

Brief abstract:
For the past 8 years, my assistants and I have been studying tiger rattlesnakes (Crotalus tigris) in the Sonoran Desert near Tucson, Arizona. To date, we have marked 282 individuals, 66 of which have been implanted with radiotelemeters to facilitate intensive autecological research. In my presentation, I will attempt to summarize various aspects of tiger rattlesnake ecology and life history, and describe how we have used this information in a conservation and management context. Specifically, I will discuss spatial ecology, mating system dynamics, foraging ecology, conservation genetics, and various other aspects of tiger rattlesnake ecology. We are using the results of our research to develop coherent management strategies for rattlesnakes, especially in urban areas where they frequently come in contact with humans. Recent research is focused on determining the effects of a large urban development on tiger rattlesnakes using a before-after-control-impact (BACI) study design. We also developed a comprehensive educational program based on our research that emphasizes coexistence with rattlesnakes.

FEB 26 TH
Oliver Chadwick (UC Santa Barbara),
Use of Silicon Isotopes to Characterize Si Residence Time in Soil,
Host Greg Okin

Brief abstract:
The rate of chemical weathering of Earth's continental crust, and the long-term carbon cycle are controlled in part by tectonic activity. Quiescent areas are characterized by low relief, thick residual soils, and low weathering rates. Active areas have high relief, rapid erosion and weathering. Chemical weathering unlocks elements from the lithosphere allowing them to participate fleetingly in dynamic biogeochemical reactions. Silicon (Si) is the second most abundant element in the Earth's crust and the dominant solute in rivers that drain continents, supplying at least 80% of the dissolved Si entering oceans. Silicon's abundance, chemical reactivity, and the variation in the structural stability of its host minerals ensure that it persists in soils even as its loss supports downstream ecosystems and as it accumulates in sedimentary deposits. In the first systematic measurements of natural abundances of Si stable isotopes associated with weathering, we demonstrate that 30Si/28Si ratios in soils and connected riverine systems provide a tracer of Si residence time on continental surfaces, its movement into aquatic ecosystems, and potentially of long-term continental tectonic patterns stored in ocean sediments.

Silicon isotope ratios ( 30Si, 30Si/28Si relative to a standard) are an untapped resource for understanding the linkages among continental weathering profiles, rivers and oceans. Terrestrial igneous rocks, the ultimate source of dissolved Si to rivers and oceans, have a narrow range of 30Si values of 1.4‰ (-1.0 to +0.4‰), whereas dissolved Si in rivers has a total 30Si variation of 3.0‰ (+0.4 to +3.4‰). The positive shift of 30Siaqeous in rivers compared to parent rock implies a significant isotopic fractionation somewhere in the terrestrial ecosystem. In addition, the terrestrial processes must lead to residual products with even more negative 30Si values than the parent rocks. Riverine 30Siaqeous values may change with weathering intensity, which implies that changes in weathering caused by regional differences in tectonic histories controls the silicon isotopic composition of soils and soil waters. The weathering connection between continental tectonics and riverine Si isotope input to the oceans has ultimate control over the distribution of marine 30Siaqueous signatures, and, therefore, also the marine diatom and sedimentary opal 30Si records.

In this study, we simulated different tectonic states and their effect on humid environment weathering profiles by sampling soils on gently sloping, stable portions of Hawaiian shield volcanoes ranging in age from 0.3 to 4,100 kyr. Differences in lava age act as a proxy for differences in erosion rate because soils on young flows are dominated by primary minerals and rapid weathering rates, soils on old flows are dominated by relatively inert secondary minerals for many meters below the surface, and intermediate age sites provide an idea of the progressive changes that can be expected for varying levels of erosion and landscape rejuvenation. We measured the Si isotopic composition of fresh basalt, soil (<2 mm-size fraction), and soil-water, as well as in samples from three Hawaiian rivers draining large watersheds with underlying lava ages of 20 kyr, 800 kyr, and 4,100 kyr.

MAR 4 TH
Lee Macdonald (Colorado State University),
Post-fire Erosion in the Colorado Front Range,
Host Jeff Chanat

Abstract:
Over the past few years there has been a large increase in the number of acres burned by wildfires in the Western U.S. In addition to the loss of life and property, there is considerable concern over the effects of these fires on runoff and erosion rates, and how these changes affect downstream water resources and domestic water supplies. For the past four years we have been intensively studying the effects of wild and prescribed fires on runoff and erosion rates in the Colorado Front Range. Our primary objectives have included: (1) assessing the strength and persistence of post-fire soil water repellency; (2) using a rainfall simulator to compare plot-scale runoff and erosion rates between sites and over time; (3) measuring hillslope-scale sediment production rates and developing a series of predictive models; (4) measuring runoff and sediment production rates at the small watershed scale (2-5 km2); and (5) evaluating the effectiveness of post-fire emergency rehabilitation techniques.

High-intensity convective storms on severely burned areas are the dominant cause of erosion in mid-elevation forests in the Colorado Front Range. Burning at high severity increases runoff and erosion rates in forested areas by at least 1-2 orders of magnitude. Erosion rates are 5-25 times greater for sites burned at high severity than sites burned at moderate or low severity. These high rates can be attributed to both the development of a water repellent layer and the loss of surface cover. Both wild and prescribed fires generate a shallow, relatively strong water repellent layer in the soil. This decays within 1-2 years; however, post-fire erosion rates decline only slightly in the second year after burning despite the marked reduction in soil water repellency. Soil water repellency explains about 30% of the observed variability in runoff rates at the small plot and hillslope scale, while percent ground cover explains 50-80% of the variability in erosion rates. Empirical curves are being developed to predict ground cover as a function of fire severity and time since burning.

Mulching is the most effective treatment to reduce post-fire erosion rates, and this further emphasizes the importance of percent cover. Other treatments are largely ineffective or effective only for smaller storms. Severe droughts are the primary cause of these fires, and it is not clear that extensive forest thinning can greatly reduce the risk of large, high-severity wildfires, or that we can readily mitigate the observed increases in post-fire runoff and erosion rates.

MAR 17 W
Jenn Rosinski (UVA),
Controls on benthic biodiversity and trophic interactions in a nutrient enriched coastal lagoon

MAR 18 TH
Malcolm Hughes (University of Arizona),
The wise use of tree-rings as records of past climate: myths and distractions?,
Host Michael Mann

Abstract:
The current state of dendrochronology's contributions to climatology is surveyed, with an emphasis on the extent to which its actual and potential strengths are being used, and its weaknesses recognized and surmounted. After recent growth in climatologists' interest in the potential of dendrochronology to contribute to their field is described, strengths and weaknesses of tree rings as natural archives of climate variability are discussed.
The greatest strengths are: the capability to date tree rings to the calendar year with a very high degree of confidence; the existence of large geographic-scale patterns of common year-to-year tree-ring variability; the development of very extensive, shared networks of tree-ring chronologies meeting common standards; the surprising effectiveness of very simple linear models of tree-ring/climate relationships; and the growing understanding of the mechanisms leading to variability in tree-ring features. The greatest weaknesses are that: tree-ring chronologies only capture a fraction of climate variability; their response may be limited to specific seasonal "windows", although, contrary to common supposition, not necessarily in the "growth season"; some do not respond directly to a single monthly or even seasonal climate variable; they may not record the climate variables of interest to climatologists; their use to reconstruct past climate is based on the assumption that the same factors, acting in the same way, controlled the formation of tree rings in the past as in the twentieth century; and, the techniques used to remove non-climatic variability, such as that caused by tree age/size trend and interactions with neighbors, limit the faithful representation of climate variations on centennial and longer time scales in many cases, although not in all cases. The manner in which these strengths have been used, and these weaknesses addressed is discussed.

MAR 24 W
Janna Levin (UVA),
Colloid mobilization in unsaturated soils under transient physical and chemical conditions

Abstract:
Measuring the effect on colloid mobilization of changes in environmental conditions in unsaturated soils is central to enhancing our quantitative understanding of pedogenesis and colloid-facilitated transport of contaminants above the water table. Among the key factors likely to affect colloid mobilization in unsaturated soils are the capillary-pressure head and the pore water ionic strength. We performed laboratory experiments on unsaturated, intact, silt-loam soil cores to examine the impact on the mean level of the colloid mass flux of changes in the capillary-pressure head and ionic strength. Typical colloid concentrations measured in the effluent suspension from the intact core were on the order of 5 mg L-1. Mean mass fluxes ranged from 0.0588 mg h-1 to 0.197 mg h-1. Less negative values of the capillary-pressure head and low ionic strength conditions significantly enhanced colloid mobilization. The greatest changes in the mean level of the mass flux of 0.079 and 0.050 mg h-1 coincided with changes in the magnitude of the capillary-pressure head, suggesting that transient flow conditions enhanced colloid release. Observations of colloid mobilization under unsteady flow conditions are scarce and, as a result, the impact of transient flow on colloid mobility in a field setting remains unclear. We completed a sequence of nine infiltration experiments at the Eastern shore of Virginia to evaluate the magnitude and timing of the colloid breakthrough within the sandy soil. Colloid concentrations during field experiments ranged from 1 to 180 mg L-1. Typical concentrations were on the order of 5 mg L-1. Peak concentrations were observed at the beginning and end of each infiltration event, suggesting that mobile air-water interfaces associated with the wetting fronts facilitated colloid mobilization. Elevated mass flux values of about 6.3 mg min-1 coincided with peak flow rates on the order of 10's to 100's of mL min-1. During some infiltration events, colloid mobilization rates decreased by about an order of magnitude over the length of the experiment. We compared the timing and magnitude of the colloid breakthrough from field experiments to results from successive infiltration experiments on intact soil cores collected at the Eastern shore of Virginia. Colloid concentrations and mass fluxes from laboratory experiments were comparable to those observed during field experiments. For most infiltration experiments on intact cores, colloid mobilization rates decreased by about an order of magnitude over the course of the experiment. This work enhances our quantitative understanding of the impact on colloid mobilization of changes in physical and chemical conditions which may occur, for example, when wetting fronts migrate through the soil during rainfall events. Quantification of increases or decreases in colloid release associated with changes in physical and chemical conditions may facilitate resolution of some water quality and soil management issues.

MAR 25 TH
Jeff Chanat (UVA),
Hydrologic Mechanisms Underlying Episodic Concentration-Discharge Relationships for Acid Neutralizing Capacity in Three Headwater Catchments in Shenandoah National Park, Virginia

APR 1 TH
Jan Kleissl (Michigan Technological University - Candidate for the Dept of Envi Sci faculty vacancy in hydrology)
"Measurements and Simulations of Atmospheric Turbulence: From Pollen Dispersion to Mountain Meteorology"

APR 7 W
Open

APR 8 TH
MOORE LECTURE: Peter Webster (Georgia Tech),
The Monsoons in a Warming World: Racing with the Four Horsemen,
Host Mike Garstang

Abstract:
The climate and weather variability of the South Asia may be understood to a large degree in terms of the coupled land-ocean-atmosphere system. This description also allows an explanation (and the prediction) of the oscillations which occur naturally through South Asia and regional aspects such as the flood occurrence in the Brahmaputra-Ganges catchment and the Bangladesh delta.

It is noted that the Bangladesh region is especially susceptible to natural climate variability. Being a flat region (Bangladesh rises only 1 m in the first 250 km from the coast) relatively small variations in sea level can lead to major coastal changes, inundation and an increased susceptibility to storm surges. Furthermore, the natural variability in rainfall over the Brahmaputra- Ganges catchment causes major oscillations in flood intensity, duration and extent. Thus, it is troublesome to contemplate what may occur if the global warming scenario of sea level increase and more intense and variable regional precipitation were to occur. We develop a picture of the changes, which may occur in the climate and climate variability in Bangladesh during the next century. However, these forecasts must be considered in tandem with natural climate variability, the expected increases in population and the manner in which humans react to change. It is concluded that even without global warming that life in regions such as Bangladesh are probably not sustainable principally because of population increases and the loss of arable land.

APR 14 W
Ross Irwin III (UVA),
Paleolakes and the Highland/Lowland Boundary on Mars

APR 15 TH
MOORE LECTURE: David Aubrey (Woods Hole),
Thirty Years of War in the Middle East: Environmental Consequences,
Host Bob Dolan

Brief abstract:
In 1991, Iraq invaded Kuwait, triggering an immediate international response in support of Kuwait. As Iraq was driven from Kuwait, vast areas of desert, coastal areas, and the marine environment were affected by the activity. Oil installations were set on fire creating great plumes of smoke and soot lasting over 200 days. Oil released from scuttled tankers (up to 20 million barrels) spread along 800 km of the Arabian Sea as far as the Saudi/Kuwait border. Military activity spoiled vast areas of fragile desert environment in Saudi Arabia and Iraq. Immediate actions were undertaken to mitigate the damage to the coastal environment in the form of cleanup of oil at sea and on the beaches; however, the scale of the damage was so great that full cleanup was not practicable. Twelve years later, the Kingdom of Saudi Arabia has re-assessed the damages remaining from the Gulf War. This talk will focus on the ecological impacts to coastal habitats, impacts that remain to this day, and a comparison of risks to the environment, assuming either natural attenuation or active remediation. Important habitats of concern include salt marshes, rocky shorelines, and sandy beaches/tidal flats. This talk will also discuss the novel approach taken by the United Nations to address these acts of environmental sabotage.

APR 16 FR
MOORE LECTURE: David Aubrey (Woods Hole),
"The Environmental Costs of War in the Middle East",
Host Bob Dolan

Brief abstract:
From the Arab consolidation of the Middle East in the seventh century to the 1991 Gulf War, the environment has been used as a receptor of military activities. Extending from the Tigris-Euphrates river catchments south to Qatar, the effects of war remain to this day. These effects include desertification of a vast area that was once a thriving agricultural belt, "oiling" of 800 kilometers of shoreline along the Arabian Gulf, the re-routing of rivers, the elimination of vast marshlands, and damage to coastal fisheries, inter alia. In this lecture I will trace the fingerprints of such war damages using specific examples from wars through time. Based on the persistence of the war-related damages, predictions of the future environmental recovery can be made using various scenarios of remediation/restoration. Left to nature's processes, centuries may be required to restore some of the ecological functions in this cradle of civilization.

APR 21 W
Amanda Joy Knoff (UVA),
A stable isotope approach to the study of bottlenose dolphin population structure along the Atlantic coast of the U.S.

APR 22 TH
Serita Frye (Univ. of New Hampshire),
Above ground-belowground interactions: relating plant and microbial community composition and diversity to wetland ecosystem processes,
Host Linda Blum

APR 22 FR
Mads Thomsen (UVA),
"Do the Invasive Macroalgae Codium Fragile Ssp. Tomentosoides Perform Better Than Native Algal Species?",


Brief abstract:
Codium fragile have been a successful invader in numerous lagoons and estuaries worldwide, and have been suggested to have superior traits. In the talk I compare distribution patterns, biomechanical properties, species interactions, growth rates and recruitment efficiencies of C. fragile to varies native algal species, in Hog Island Bay, a shallow tidal lagoon.

Environmental Sciences Department 291 McCormick Rd Charlottesville, Virginia (434) 924-7761