F. C. Thornton

Aluminum toxicity in forests exposed to acidic deposition: The ALBIOS results

The ALBIOS project was conducted to examine the influence of acidic deposition on aluminum transport and toxicity in forested ecosystems of eastern North America and northern Europe. Patterns of aluminum chemistry were evaluated in 14 representative watersheds exposed to different levels of sulfur deposition. Controlled studies with solution and soil culture methods were used to test interspecific differences in aluminum sensitivity for one indicator species (honeylocust - Gleditsia triacanthos L. ) and six commercial tree species (red spruce - Picea rubens Sarg., red oak - Quercus rubra L., sugar maple - Acer saccharum Marsh., American beech - Fagus grandifolia Ehrh., European beech - Fagus sylvatica, and loblolly pine - Pinus Taeda L. ). Overall, red spruce was the tree species whose growth was most sensitive to soluble aluminum, with significant biomass reductions occurring at Al concentrations of approximately 200–250 umol/L. Analyses of soil solutions from the field sites indicated that the conditions for aluminum toxicity for some species exist at some of the study areas. At these watersheds, aluminum toxicity could act as a contributing stress factor affecting forest growth.

Emissions of NO from soil at a rural site in central Tennessee

Field measurements of soil emissions of NO from a Mountview silt loam soil with three land uses (forest, fertilized pasture, and fertilized corn) were made on a commercial farm during a summer and autumn sampling period. A new automated closed-chamber sampling system was developed to allow simultaneous measurements on five chambers per 100 m2 plot. Individual chambers with hinged tops, covering 0.3 m2 of soil area were pneumatically operated via data logger control to sample soil NO flux every third hour. Spatial variability in emission rates was high. For each land use type the range from the lowest to the highest emitting chamber was approximately threefold. Land use type significantly affected soil NO emissions. The fertilized pasture had the highest mean emission rate (44.1 ng N m−2 s−1), followed by the fertilized corn (27.0 ng N m−2 s−1), and the forest (8.4 ng N m−2 s−1). NO emission rates and soil nitrate levels at the forest plot were considerably higher than at other forest sites in the region, possibly due to runoff from an adjacent fertilized hayfield. The results of this study, when extrapolated to a regional estimate, suggest that emissions of NO from soils could play a significant role in summertime tropospheric ozone photochemistry in the southeastern United States.

Field comparison of static and flow‐through chamber techniques for measurement of soil NO emission

A field comparison of flow-through and static chamber techniques for measuring soil emissions of NO was performed on fertilized soil at a commercial cotton (Gossypium hirsutum L.) farm near Muscle Shoals, Alabama, during July 1992. The purpose of the study was to compare soil NOx. emissions data taken using two different techniques at a common field site. Emission rates with collocated chambers using the two techniques were compared, and spatial means were also compared for 17 National Oceanic and Atmospheric Administration (NOAA) plots and 10 Tennessee Valley Authority (TVA) plots. Emission rates of NO at the site covered a broad spectrum, ranging from less than 1 to greater than 100 ng N m−2 s−1. Data from collocated TVA static and NOAA flow-through chambers showed a correlation coefficient of 0.98 with a linear regression slope of 0.97. A t test indicated that the mean difference was not statistically different than zero. The plot mean emission rates were 17.7 and 18.0 ng N m−2 s−1 for the TVA and NOAA chambers, respectively, for an 8-day comparison period. These findings indicate that data sets collected with these methods are comparable and may be combined without concern for differences in technique. These results also reveal that the techniques used by each group in attempting to characterize overall site mean emissions are remarkably similar, despite differences in chamber size, plot location, extent of areal coverage, and random error associated with the measurements. This finding is significant in that it means that field data used to characterize emissions estimates by both protocols can be pooled to better estimate regional soil NO emission inventories.

NO emissions from soils in the southeastern United States

Biogenic soil emissions of nitric oxide (NO) are important in the formation of tropospheric ozone (O3) in the rural environment. This paper summarizes our recent estimates of soil NO emissions from a wide variety of sites in nine southeastern United States. A total of over 12,000 individual flux measurements was made from crop, pasture, and forests representing major physiographic regions within the southeast. These measurements were used to determine flux algorithms relating NO emissions from land types. Strong relationships were found between NO flux and temperature that explained over 80% of the variation in emissions. Using these relationships and Geographic Information Systems land base information for the states, calculated seasonal emissions for NO are reported. Crop land regulated regional soil NO emissions, accounting for 83% of the emissions in summer, 61% in spring, and 55% in fall. The summertime contribution of soil NO to the overall NO inventory, including anthropogenic sources, averaged 4.1% for the states, ranging from a high of 9.5% for Mississippi to a low of 2.2% for Florida. The importance of high summertime temperatures in controlling soil NO was evident in that emissions on a prototypical summer day were only one fifth the emissions of a hot (36°C, maximum daily high) summer day. Comparisons of the algorithms we developed to those of the current model used by the Environmental Protection Agency, BEIS 2.2, showed reasonable agreement, that is, agreement within a factor of 2, given the inherent temporal and spatial variability of soil NO emissions.

The influence of acid precipitation and ozone on nitrogen nutrition of young loblolly pine

Field grown loblolly pine (Pinus taeda L.) seedlings from two half-sibling families were exposed to three levels of acid precipitation and four levels of O3 in open top chambers at Auburn, AL. At the end of one growing season, dry weight and total N accumulation of seedlings was directly related. to rainfall acidity, possibly indicating a fertilizer response in the N deficient soil. Increasing O3 levels elicited an increase in N content of permanent tissues that was not related to a dry weight response. The origin of this N was believed to be increased internal translocation associated with enhanced premature needle senescence observed at higher O3 levels.

Manganese removal from water using limestone-filled tanks

Abstract A pilot-scale water treatment system, consisting of two limestone-filled tanks followed by a vegetation cell, was constructed to treat drainage water from a coal-ash disposal pond located at a coal-fired fossil plant in Alabama, USA. Inflow water manganese concentration averaged 3.5 mg l −1 (ranging from 0.02 to 5.98 mg l −1 over the 495-day treatment period. The system worked effectively in removing Mn, producing water which averaged 0.49 mg l −1 or an 88% removal efficiency. A black film coated the rocks in the limestone tanks and was assumed to be the chief site of Mn removal via microbial oxidation. This film contained up to 140 g Mn kg −1 , with an average concentration of 61.4 g Mn kg −1 . The results of this study demonstrate an ecotechnological means to treat water that is high in Mn, provided the water does not have high Fe concentrations that would coat rock surfaces.

Estimation of the source strength of soil NO x in the Nashville, Tennessee, urban area

Soil biogenic NOx emissions are an important part of the total global NOx budget. The objective of this study was to investigate the role of the soil NOx source in an urban-metropolitan area. We measured the emissions from soils within the urban-metropolitan land use area of Nashville, Tennessee, and surrounding Davidson County, to estimate the importance of this source in the overall NOx budget of Davidson County. Nashville is currently in nonattainment for ozone (O3), and a State Implementation Plan (SIP) has been promulgated to help achieve compliance of the O3 standard. Using geographic information systems imagery and aerial photographs, we determined the extent of urban-metropolitan soils within the Nashville area. Results indicated that 409 km2, or approximately 34% of the county, was classified as residential or urban, with the predominant vegetation being grass (68%). The residential sector was the largest with 323 km2, the urban area comprising 87 km2, and a total area of 8 km2 of golf courses. Soil NOx emission measurements were made in approximate proportion to the major land use types using static chamber techniques. Results indicated that urban-metropolitan soils were not an important source of soil NOx. Approximately 10 Mg NOx, or 0.003% of the total annual NOx budget of Davidson County, is estimated to be emitted by urban soils annually. Additionally, the remaining soil sources in the county, forests and agricultural land, contributed 179 Mg, or 0.66% of the total annual NOx budget. While soil NOx emissions were concluded to be a negligible component of the Davidson County budget, their contribution to the NOx budget of the surrounding four counties in the SIP area was significant. Extrapolation of soil NOx emissions for three of the four counties within the SIP area indicated that soil biogenic NOx emissions contributed from 7.0 to 9.8% of the daily average NOx budget during the months of June through August. Because of the soil temperature dependence of soil NOx emissions, it was estimated that during the hottest July days the soil biogenic component could contribute over 17% of the total NOx in some SIP counties.