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Geology topics

Thomas G. Huntington

Publications and source records attributed to Thomas G. Huntington.

At least 73 records · Page 4Linked to original sources
USGS2005

Results of the acid rain program: Status and trends of emissions and environmental impacts (1990–2002)

Both SO2 and NOx emissions from power generation sources have significantly declined under Title IV. In 2002, SO2 emissions from Title IV-affected sources totaled 10.2 million tons and NOx emissions from all Title IV-affected sources totaled 4.5 million tons, down 35% and 33% respectively from 1990 levels. Sources in states with the highest emissions continue to reduce their emissions the most, and there have been no significant geographic shifts in emissions. The benefits of these emission reductions include improvements in air quality (which are expected to lead to significant human health benefits), broad-scale reductions in sulfate deposition, and improvements in visibility. While surface waters in some areas have begun to show signs of recovery from acidification, acidification is still occurring in many areas. Although there have been no broad-scale regional reductions in nitrogen deposition, nitrogen deposition has declined in some areas, benefiting some nitrogen-sensitive forests and coastal waters and acid-sensitive lakes and streams.

Book chapter↗
USGS2005

Assessing acid deposition: Advances in the state of science

NAPAP has a long history of conducting research related to acid deposition. Throughout the 1980s NAPAP supported a large number of research projects that confirmed the link between SO 2 and NO x emissions and acidic lakes and streams hundreds of miles away. Recent research is confirming the tight link between emissions of SO 2 and the amount of several different forms of sulfur in the atmosphere and in precipitation, and improving our ability to measure acid deposition. Research has continued since 1990, albeit on a smaller scale, to increase our understanding of how acid deposition affects trees, soils, lakes, streams, coastal waters, and building materials such as stone and copper. Some of the areas where the most research has been done include: the importance of calcium in mediating soil and forest response to acidification; the role of nitrogen in acidification and recovery from acidification; and the role of nitrogen deposition in coastal ecosystems. In addition, substantial advances have been made in understanding the human health impacts of fine particles, including sulfates and nitrates, which are briefly mentioned here.

Book chapter↗
USGS2002

Historical trend in ice thickness on the Piscataquis River in central Maine.

We analyzed a long-term record of ice thickness on the Piscataquis River in central Maine to determine whether there were temporal trends that were associated with climate warming. Trends in ice thickness were compared and correlated with regional time series of winter air temperature, heating degree days (HDD) , date of river ice-out, seasonal center-of-volume date (SCVD) (date on which half of the stream runoff volume during the period 1 Jan and 31 May has occurred), water temperature, and lake ice-out date. All of these variables except lake ice-out date showed significant temporal trends during the 20 th century. Average ice thickness around 28 Feb. decreased by about 23 cm from 1912 to 2001. Over the period 1900 to 1999, winter air temperature increased by 1.7 ˚C and HDD decreased by about 7.5%. Final ice-out date on the Piscataquis River occurred earlier (advanced), by 0.23 days yr –1 over the period 1931 to 2002. The SCVD advanced by 0.11 days yr –1 over the period 1903 to 2001. Ice thickness was significantly correlated with winter air temperature, HDD, river ice-out, and SCVD (P-value < 0.01). These systematic temporal trends in multiple hydrologic indicator variables indicate a coherent response to climate forcing.

Maine↗
USGS2001

Chemical weathering of the Panola Granite: Solute and regolith elemental fluxes and the weathering rate of biotite

Present-day elemental and mineral weathering rates based on solute fluxes are compared quantitatively to past long-term rates determined from solid-state elemental fractionation in a saprolitic granite regolith at Panola, Georgia, USA. Saturated fluid flow across a low-permeability kaolin duripan controls the rate of steady-state unsaturated flow in the underlying saprolite. Water and Cl mass balances and experimental conductivities produce a minimum fluid flux density of 8x10 -2 m yr -1 and a fluid residence time of 12 years. Solute Si flux, based on pore water concentrations and infiltration rates, is 27 mmoles yr -1 , compared to a long-term flux rate of 17 mmoles yr -1 , based on regolith Si loss and reported 36 Cl dating of the regolith surface. Similarities in short- and long-term fluxes imply that parameters influencing silicate weathering, including precipitation, temperature, and vegetative cover, while not necessarily constant, have not significantly impacted Si leaching rates during the last several hundred thousand years. Linear decreases in solid-state Mg with decreasing regolith depth permit the calculation of the long-term biotite weathering rate under isovolumetric steady-state weathering conditions. A rate constant of 3x10 -17 moles m -2 s -1 is up to 5 orders of magnitude slower than that reported for experimental dissolution of biotite, implying very different reaction kinetics during natural weathering. Short-term biotite weathering fails to produce expected increases in solute Mg and K concentrations with increasing depth and fluid residence times in the regolith. This discrepancy indicates that ion exchange disequilibrium and open-system biologic uptake in an aggrading forest ecosystem are of sufficient magnitudes to overwhelm solute fluxes resulting from biotite weathering.

Georgia↗
USGS2000

The potential for calcium depletion in forest ecosystems of southeastern United States: Review and analysis

Biogeochemical mass balance assessments of calcium status in southeastern forests indicate that losses through harvesting and soil leaching often exceed inputs from atmospheric deposition and weathering. Many forest soils of the southeastern United States are particularly sensitive because these soils and the underlying saprolite from which these soils are derived are largely depleted of weatherable calcium. At most of the intensively studied sites in the southeastern United States, it is estimated that calcium depletion has already reduced or will likely reduce exchangeable soil calcium reserves to less than the estimated requirement for a merchantable forest stand in 150 years or less. At most sites, calcium uptake into merchantable wood equals or exceeds soil leaching losses. Chronic atmospheric deposition of sulfate and nitrate and declining atmospheric deposition of calcium are likely to accelerate calcium depletion. The southeastern U.S. regional distribution of soil calcium pools and calcium fluxes (deposition and uptake in merchantable wood) indicates that the depletion status of the intensively studied sites is representative of a substantially larger area. Where weathering inputs are insufficient to replace leaching and uptake losses, there is a potential for a regional problem in forest nutrition over the long term.

Alabama, Arkansas, Florida, Georgia, Louisiana, Ma↗
USGS2000

Panola Mountain, Georgia: A Water, Energy, and Biogeochemical Budgets Program Site

The Panola Mountain Research Watershed (PMRW) is a 41-hectare forested watershed in the southern Piedmont physiographic province near Atlanta, Georgia. The watershed contains a naturally regenerated second-growth forest on abandoned agricultural land, typical of the Piedmont. Research at PMRW has focused on how streamflow is generated, and in particular, on how water and solutes move from hillslopes to the stream. The research shows that streamflow and solute concentrations of precipitation, throughfall, soil water and streamwater change rapidly during rainstorms. Furthermore, these variations are strongly associated with the soil-moisture conditions, the soil type and thickness, and the rainfall intensity, all of which effect the chemical interactions and mixing of water traveling along hydrological pathways over and through the bedrock and soils.

Georgia↗
USGS1999

Dynamic replacement and loss of soil carbon on eroding cropland

Links between erosion/sedimentation history and soil carbon cycling were examined in a highly erosive setting in Mississippi loess soils. We sampled soils on (relatively) undisturbed and cropped hillslopes and measured C, N, 14 C, and CO 2 flux to characterize carbon storage and dynamics and to parameterize Century and spreadsheet 14 C models for different erosion and tillage histories. For this site, where 100 years of intensive cotton cropping were followed by fertilization and contour plowing, there was an initial and dramatic decline in soil carbon content from 1870 to 1950, followed by a dramatic increase in soil carbon. Soil erosion amplifies C loss and recovery: About 100% of the original, prehistoric soil carbon was likely lost over 127 years of intensive land use, but about 30% of that carbon was replaced after 1950. The eroded cropland was therefore a local sink for CO 2 since the 1950s. However, a net CO 2 sink requires a full accounting of eroded carbon, which in turn requires that decomposition rates in lower slopes or wetlands be reduced to about 20% of the upland value. As a result, erosion may induce unaccounted sinks or sources of CO 2 , depending on the fate of eroded carbon and its protection from decomposition. For erosion rates typical of the United States, the sink terms may be large enough (1 Gt yr −1 , back‐of‐the‐envelope) to warrant a careful accounting of site management, cropping, and fertilization histories, as well as burial rates, for a more meaningful global assessment.

Global Biogeochemical Cycles↗
USGS1998

Carbon cycling in terrestrial environments: Chapter 17

This chapter reviews a number of applications of isotopic techniques for the investigation of carbon cycling processes. Carbon dioxide (C0 2 ) is an important greenhouse gas. Its concentration in the atmosphere has increased from an estimated 270 ppm at the beginning of the industrial revolution to &sim; 360 ppm at present. Climatic conditions and atmospheric C0 2 concentration also influence isotopic discrimination during photosynthesis. Natural and anthropogenically induced variations in the carbon isotopic abundance can be exploited to investigate carbon transformations between pools on various time scales. It also discusses one of the isotopes of carbon, the 14 C, that is produced in the atmosphere by interactions of cosmic-ray produced neutrons with stable isotopes of nitrogen (N), oxygen (O), and carbon (C), and has a natural abundance in the atmosphere of &sim;1 atom 14 C per 10 12 atoms 12 C. The most important factor affecting the measured 14 C ages of soil organic matter is the rate of organic carbon cycling in soils. Differences in the dynamics of soil carbon among different soils or soil horizons will result in different soil organic 14 C signatures. As a result, the deviation of the measured 14 C age from the true age could differ significantly among different soils or soil horizons.

Book chapter↗
USGS1998

Soil, environmental, and watershed measurements in support of carbon cycling studies in northwestern Mississippi

Measurements including soil respiration, soil moisture, soil temperature, and carbon export in suspended sediments from small watersheds were recorded at several field sites in northwestern Mississippi in support of hillslope process studies associated with the U.S. Geological Survey's Mississippi Basin Carbon Project (MBCP). These measurements were made to provide information about carbon cycling in agricultural and forest ecosystems to understand the potential role of erosion and deposition in the sequestration of soil organic carbon in upland soils. The question of whether soil erosion and burial constitutes an important net sink of atmospheric carbon dioxide is one hypothesis that the MBCP is evaluating to better understand carbon cycling and climate change. This report contains discussion of methods used and presents data for the period December 1996 through March 1998. Included in the report are ancillary data provided by the U.S. Department of Agriculture (USDA) ARS National Sedimentation Laboratory and U.S. Forest Service (USFS) Center for Bottomland Hardwoods Research on rainfall, runoff, sediment yield, forest biomass and grain yield. Together with the data collected by the USGS these data permit the construction of carbon budgets and the calibration of models of soil organic matter dynamics and sediment transport and deposition. The U.S. Geological Survey (USGS) has established cooperative agreements with the USDA and USFS to facilitate collaborative research at research sites in northwestern Mississippi.

Mississippi↗
USGS1997

Effects of acidic deposition on water quality and forest health in Georgia

Biogeochemical studies at the Panola Mountain Research Watershed near Atlanta, Ga., and in the Coastal Plain Province of Georgia have provided an assessment of some of the potential effects of acid deposition on streamwater quality and forest health in Georgia. Historically, "acid rain" has not been considered a potentially serious problem in the southeastern United States; however, recent studies have raised questions about the sensitivity of forest and aquatic resources to chronic pollutant loading. Intensive streamwater-quality monitoring during storms has shown that episodic acidification presently is occurring and likely will become substantially more severe in future decades. Acidic deposition at current rates does not appear to have direct adverse effects on forest health, but does contribute to the chronic loss of nutrient cations.

Georgia↗
USGS1996

Predicting watershed acidification under alternate rainfall conditions

The effect of alternate rainfall scenarios on acidification of a forested watershed subjected to chronic acidic deposition was assessed using the model of acidification of groundwater in catchments (MAGIC). The model was calibrated at the Panola Mountain Research Watershed, near Atlanta, Georgia, U.S.A. using measured soil properties, wet and dry deposition, and modeled hydrologic routing. Model forecast simulations were evaluated to compare alternate temporal averaging of rainfall inputs and variations in rainfall amount and seasonal distribution. Soil water alkalinity was predicted to decrease to substantially lower concentrations under lower rainfall compared with current or higher rainfall conditions. Soil water alkalinity was also predicted to decrease to lower levels when the majority of rainfall occurred during the growing season compared with other rainfall distributions. Changes in rainfall distribution that result in decreases in net soil water flux will temporarily delay acidification. Ultimately, however, decreased soil water flux will result in larger increases in soil- adsorbed sulfur and soil-water sulfate concentrations and decreases in alkalinity when compared to higher water flux conditions. Potential climate change resulting in significant changes in rainfall amounts, seasonal distribution of rainfall, or evapotranspiration will change net soil water flux and, consequently, will affect the dynamics of the acidification response to continued sulfate loading.

Water, Air, & Soil Pollution↗
USGS1996

Small watershed studies: Analytical approaches for understanding ecosystem response to environmental change

Biogeochemical studies in small watersheds provide an analytical approach to understand how ecosystems respond to natural climatic variations and human-induced environmental change. Small watersheds, usually less than 5 km2, are small enough to permit characterization and understanding of ecosystem processes within relatively simple, homogeneous biological and physical settings; yet they are large enough to incorporate more complex processes and element cycles than can be studied at plot scales. Watersheds comprise discrete hydrochemical environments allowing quantification of hydrologic, element, and energy budgets. Element budgets, or mass balances, can be quantified as the difference between the mass of a solute that enters a watershed in wet and dry deposition and leaves a watershed in streamflow. Element budgets are primary tools used to investigate biogeochemical processes. Monitoring various aspects of element budgets to assess ecosystem health and stability is analogous to measuring the pulse or blood chemistry of a patient. Monitoring streamwater chemistry, basic climate, soil, and biotic variables provide a means to integrate complex biogeochemical processes and evaluate trends in water quality. Small watershed studies provide a scientific basis to develop predictive models of watershed function. Major emphases of small watershed studies include investigation of hydrologic and chemical responses to natural climate variation, anthropogenic stressors, and alternate forest-management practices. The nature and significance of biogeochemical research in small watersheds is reviewed by Moldan and Cerny (1994). The U.S. Geological Survey, U.S. Department of Agriculture Forest Service, and other federal agencies support several long-term small watershed studies to provide insight into a variety of ecosystem processes. Long-term records are essential to distinguish trends resulting from natural climatic variations or other stressors. The following sites, with noted periods of records, are examples of intensively studied forested watersheds in eastern USA supported by federal agencies: ■ Coweeta Hydrologic Laboratory, North Carolina, (1939-present), Swank and Crossley (1988). ■ Hubbard Brook Experimental Forest, New Hampshire, (1956-present), Bormann and Likens (1979). ■ Sleepers River Research Watershed, Vermont, (1958-present), Shanley et al. (1995). ■ Walker Branch Watershed, Tennessee, (1967-present), Johnson and Van Hook (1989). ■ Catoctin Mountains Research Site, Maryland, (1982-present), Rice and Bricker (1995). ■ Catskill Stream Network, New York, (1983- present), Murdoch and Stoddard (1992). ■ Panola Mountain Research Watershed, Georgia, (1985-present), Huntington et al. (1993). Small watershed studies also provide essential baseline information for understanding variations in water quality and element cycling in "pristine" ecosystems that can be used as benchmarks to evaluate anthropogenic impacts and alternate watershed management practices. This paper provides examples of how analytical tools developed through watershed research provide insight into ecosystem processes and can contribute to the management of watershed resources.

Conference Paper↗
USGS1995

Carbon sequestration in an aggrading forest ecosystem in the Southeastern USA

An analysis of C pools at the Panola Mountain Research Watershed (PMRW) near Atlanta, GA, indicates that aggrading forests in the U.S. Southeast are an important regional C sink. The forests in this area were cut in the early 1800s and the land was cultivated until the early 1900s, when farming was abandoned and forest regeneration began. Cultivation resulted in extensive erosion, which depleted soil C pools. The rate of soil C sequestration during the 70-yr period of forest regeneration was estimated to be between 0.34 (standard error [SE] = 0.12) and 0.79 (SE = 0.19) Mg C ha −1 yr −1 . There is a large potential for continued C accumulation in the soil at PMRW based on the difference between current measured soil C pools of 82 Mg C ha −1 at PMRW and 122 Mg C ha −1 at the nearby “undisturbed” Fernbank Forest in Atlanta, GA. The rate of C sequestration in biomass at PMRW was 1.47 Mg C ha −1 yr −1 for the regeneration period, bringing the ecosystem total to between 1.81 and 2.26 Mg C ha −1 yr −1 . Carbon sequestration in temperate forest ecosystems partially mitigates the effects of increased atmospheric loading of CO 2 .

Georgia↗