Floodplain Swamp Research Articles

A palynological reconstruction of pre‐European riparian vegetation at Wollombi, New South Wales and its application to stream bank management and revegetation

Summary A palynological investigation was conducted on sediments from three small floodplain swamps on upper Wollombi Brook in the Hunter Valley NSW in order to reconstruct pre‐European riparian vegetation composition and community structure. Pre‐European riparian plant communities on upper Wollombi Brook were characterized by wet sclerophyll forest associations with rainforest elements (most likely close to the channel). Major changes in both the nature and extent of riparian vegetation have been associated with European settlement. The pre‐European pollen spectra assists the identification of a suite of native taxa potentially suitable for use in riparian revegetation operations, particularly in highly cleared streambank sites where protection of water quality and aquatic habitat is an important goal but where insufficient local remnants are available to indicate pre‐existing plant species. The research emphasizes the use of palaeoenvironmental evidence as a tool for contemporary environmental management.

Effects of Environmental Hypoxia Associated with the Annual Flood Pulse on the Distribution of Larval Sunfish and Shad in the Atchafalaya River Basin, Louisiana

The Atchafalaya River basin (ARB) is a hardwood floodplain swamp associated with the Atchafalaya River in Louisiana. When the ARB is inundated by the river's annual spring flood pulse, the decomposition of organic matter causes hundreds of hectares to become hypoxic (dissolved oxygen (DO) ≤ 2.0 mg/L). During this time hypoxic conditions are variable, but they often persist from April through June in more than 50% of the lower ARB. Because for most fishes in the ARB reproduction occurs on the floodplain during the flood pulse, hypoxic conditions may severely impact larval fish abundances. We examined the relationships between larval fish abundance and hypoxic conditions in the ARB during 1994 and 1995. Of the 5,389 larval fishes from 14 taxa that were collected, sunfish Lepomis spp. (73.9%) and shad Dorosoma spp. (19.1%) dominated the assemblage during both years. Overall, there was a strong positive relationship between DO level and the presence of larval sunfish and shad. Higher DO levels were most strongly associated with the presence of larval sunfish in 1994 but with the presence of larval shad in 1995. These abundance patterns appear to be related to differences in ARB inundation during the 1994 and 1995 flood pulses. The mean monthly river stage for 1994 was consistent with a 34-year average, but the mean monthly river stage in 1995 was significantly lower in April and higher in June. These differences in timing and duration of the flood pulse appeared to have important consequences for the reproduction of sunfish and shad in the ARB. Both sunfish and shad larvae were collected almost immediately after local conditions (e.g., turbulence and increasing primary production) caused hypoxic areas to become normoxic (DO > 2.0 mg/L). These abundance patterns suggest that larvae were present in adjacent littoral macrophytes that served as DO refugia. Because widespread hypoxia limits the nursery potential of large areas of the inundated floodplain, the reproductive success of many ARB fishes would benefit from a water management plan designed to increase the exchange of water between the main channel and backwater areas.

Development of potential acid sulfate paleosols in Paleocene floodplains, Bighorn Basin, Wyoming, USA

Floodplain paleosols in the Paleocene Fort Union Formation in the Bighorn Basin are distinguished by a dark claystone interval with yellow jarosite mottles, relatively high total organic carbon values, and woody debris and leaves along bedding planes. The paleosols also have various redoximorphic features, including low matrix chromas, grey root mottles, and local concentrations of goethite and hematite, especially associated with roots and other organic matter. Jarosite is usually an oxidation product of pyrite, which forms under waterlogged conditions when sulfate and organic matter are available. The former presence of pyrite and the redoximorphic features suggest that the Fort Union paleosols first developed as potential acid sulfate soils ( Brinkman and Pons, 1973). The dark claystones with jarosite are interpreted as permanently reduced or Gr horizons. The Gr horizon is overlain by mudstone that is lighter colored and lacks jarosite. This represents an ancient Bg horizon or A/Bg sequence. The jarosite indicates that the paleosols underwent a subsequent episode of oxidation and acidification. Those processes require that the soils be drained, which probably did not occur during Paleocene time and may be a recent event. Rather, the soils were probably buried as the Fort Union Formation continued to aggrade, and the waterlogged soils were pushed even farther below the groundwater table. Only with late Cenozoic excavation of strata in the basin and exposure of the Fort Union deposits, did jarosite precipitate. Pedogenic and paleobotanical features suggest that the soils formed in floodplain swamps dominated by coniferous trees. The high organic content and clay-rich nature of the Gr horizons suggest that the floodplain swamps were not close to the active channel. The bipartite nature to the profiles (Bg horizon or A/Bg sequence above a Gr horizon) probably resulted from two different kinds of floodplain deposition. Grain size trends indicate that the Gr horizons formed on sediment deposited by overbank flooding. The impermeable, fine-grained sediment and its low topographic position led to waterlogging. The overlying A/Bg or Bg horizons formed on coarser sediment that was probably deposited during channel avulsion. The greater permeability and higher topographic position of this sediment caused it to be better drained than the Gr horizon. The paleosols are unusual because they formed in a freshwater setting, whereas modern potential acid sulfate or acid sulfate soils form in coastal areas where sulfate is readily available. The source of the sulfate may have been Cretaceous marine shales, exposed along the flanks of mountains rising around the Bighorn Basin during Paleocene time. Other Upper Cretaceous and Paleocene formations in the Rocky Mountain area contain similar rocks, suggesting that sulfidic soils were relatively common in the mid-continent at this time. Most of these other examples probably reflect deposition associated with the retreating Western Interior Seaway and humid climates.

The relationship between inundation history and baldcypress stem form in a Virginia floodplain swamp

Algorithms that quantitatively define the stem buttress and the magnitude of stem hypertrophy were developed and used to determine the relationship between tree form and surface water hydrologic regime in baldcypress (Taxodium distichum). Regression analysis using inundation index (I; defined as the average number of inundation days per year over a 49-year period) as the independent variable and extent of buttress (B e ) as the dependent variable described the relationship byB e =52.84+0.111I. The equation (P<0.001) explains approximately 68% of the variation in the relationship. Mean stem form of upland control populations was not significantly different from the stem form predicted from the equation for inundation indices equal to zero (the y-intercept, which corresponds to an upland situation). The use of stem form algorithms ofT. distichum shows promise as a source of historical hydrologic information useful in research and management situations.

Growth of Crustacean Meiofauna in a Forested Floodplain Swamp: Implications for Biomass Turnover

Microcrustaceans are common in the meiobenthos of many freshwater habitats including wetlands. Quantification of their functional roles, including determination of secondary production, has lagged behind our understanding of macrobenthos because microcrustaceans are small animals with nearly continuous reproduction and often short generation times. Such noncohort populations necessitate independent estimates of growth to quantify secondary production. Growth rates of 3 benthic microcrustaceans from a forested floodplain swamp in Alabama were measured on a diet of natural food at temperatures of 10, 15, 20, and 25°C, which span much of the annual range. For Chydorus brevilabris (Cladocera:Chydoridae), somatic growth rates were as high as 20%/d at all temperatures, and total growth rate (including egg production) was roughly twice the somatic growth rate in the larger size classes. For reproductive-sized individuals, eggs represented >60% of the growth within an instar and >60% of an individual's lifetime production. Multiple regression using individual size and temperature as independent variables explained 76% of the variation in somatic growth rates and 49% of the variation in total growth rates. Somatic growth rates were also measured for Physocypria pustulosa (Ostracoda:Cyprididae) and Cypridopsis vidua (Ostracoda:Cypridopsidae). The ostracod species had lower somatic growth rates than the chydorid, but growth rates of all 3 taxa increased with temperature and decreased with increasing size. Somatic growth rates for ostracods were <20%/d in most size classes, and multiple regressions, using individual mass and temperature as independent variables, explained 50% of the variation in somatic growth for Cypridopsis vidua and 33% for Physocypria pustulosa. Growth rates measured in this study under natural conditions suggest that freshwater meiofauna can have higher annual turnover rates (i.e., >15) than is generally assumed.

Influence of Taxonomy, Ecology, and Seasonality in River Stage on Fish Contamination Risks in Floodplain Swamps of the Lower Mississippi River

We compared contamination levels in fish from contaminated and uncontaminated floodplain swamps of the lower Mississippi River to assess differences in contamination risks between swamps, across different taxonomic and ecological groupings of fishes within and between swamps, and with seasonality in river stage. Fish tissue levels of inorganic contaminants were substantially lower than environmental levels in both swamps, suggesting either that fish were not uptaking these contaminants, or they were effectively eliminating the contaminants from their bodies. Tissue levels of organic contaminants were high relative to environmental levels, suggesting that these contaminants were bioaccumulating. Organic contaminants were significantly higher in fish from the contaminated swamp (Devil's Swamp) than in fish from a reference swamp up river (Tunica Swamp). Because the organic contaminants were largely confined to sediments, we expected bottom-oriented fishes to have higher concentrations than pelagic fishes. Assuming that uptake was primarily through the food chain, we expected top predators to exhibit higher concentrations than low-level consumers. We also expected year- round swamp residents to exhibit higher accumulations than more transitory users of backswamp habitat. However, organic contaminant levels did not differ in the directions expected for any of these groupings. We did observe differences in organic contaminant levels within and between swamps for different taxonomic groupings of fishes (species and genera). Some taxa occupying low to middle positions in the food web (e.g., gizzard shad, Lepomis spp.) exhibited higher concentrations than taxa near the top of the food web. Within Devil's Swamp, organic contaminant levels were significantly higher at low river stage, when fish were confined to the swamp, than at high river stage, when fish were free to move between the river and the swamp. We caught more species and more fish per unit effort in Devil's Swamp than in Tunica Swamp, contrary to expectations if contaminants in the former were negatively impacting population and community structure. Species richness differences between swamps were a consequence of catch differences, with higher catch corresponding to inclusion of more rare species. The lower catch in Tunica Swamp may have resulted from physical modifications of its waterways to support agriculture and hunting. The results of this study underscore the importance in factoring information on the taxonomy and ecology of organisms, and seasonal changes in environmental conditions, into assessments of contamination risks.

Differential recovery of a deepwater swamp forest across a gradient of disturbance intensity

On the Savannah River Site, South Carolina, USA, large areas of floodplain swamp forest of baldcypress (Taxodium distichum) and water tupelo (Nyssa aquatica) were destroyed by the cumulative impacts of cooling-water discharges over a 35-year period of nuclear reactor operations. In one floodplain area, four years after thermal discharges ended, we analyzed the pattern of forest recovery across a disturbance gradient spanning from a site of chronic thermal impact and extensive sediment deposition to sites of intermittent thermal impact and little substrate change. Across this spatial gradient, we measured density and size structure of cypress and tupelo and assessed regeneration success in relation to density of surviving canopy trees and to substrate changes. Compared with undisturbed forest, canopy tree density was lower in all disturbed sites and decreased progressively with greater site disturbance. Density of trees regeneration decreased in parallel with declining canopy tree density; however, regeneration was particularly low in the site of chronic impact, where very few canopy trees had survived and where substrate had been modified by sedimentation. Size structures suggested that tree recruitment had occured synchronously during a 5-year period of regional drought and minimal river flooding. Thus, cypress-tupelo recovery was influenced both by availability of seed sources and by site conditions, but floodplain hydrology also affected regeneration. The pattern of differential recovery across the disturbance gradient has allowed the use of natural regeneration potential in efforts to restore the pre-disturbance forest, and it also illustrates several key factors in wetlands design.

A Regional Analysis of the Physical Characteristics of Streams

in blackwater rivers of the Coastal Plain, southeastern United States. Pages 249-276 in C.D. Becker and D.A. Neitzel (editors). Water quality in North American river systems. Battelle Press, Columbus, Ohio. MEYER, J. L., AND R. T. EDWARDS. 1990. Ecosystem metabolism and turnover of organic carbon along a blackwater river continuum. Ecology 71:668677. PULLIAM, W. M. 1991. Carbon dioxide and methane exports from a southeastern floodplain swamp: patterns, pathways, and sensitivity to climate. PhD Dissertation, University of Georgia, Athens. PULLIAM, W. M. 1993. Carbon dioxide and methane exports from a southeastern floodplain swamp. Ecological Monographs 63:29-53. PULLIAM, W. M., AND J. L. MEYER. 1992. Methane emissions from floodplain swamps of the Ogeechee River: long-term patterns and effects of climate change. Biogeochemistry 15:151-174. SABATER, E, J. L. MEYER, AND R. T. EDWARDS. 1993. Longitudinal patterns of dissolved organic carbon concentration and suspended bacterial density along a blackwater river. Biogeochemistry 21: 73-93.

Growth and reproduction of the cladoceran Ceriodaphnia dubia from a forested floodplain swamp

Microcrustaceans are abundant in many freshwater wetlands, including forested floodplain swamps, but little has been done to assess their secondary production and functional role in these systems. Since standard cohort approaches to estimating secondary production are impossible with continuously growing and reproducing microcrustaceans, it is necessary to obtain independent determinations of their growth and reproductive characteristics under environmental conditions encountered in their natural habitat throughout the year. The growth and reproduction of Ceriodaphnia dubia fed natural swamp seston were measured at 10, 15, 20, and 25°C—temperatures which span much of the annual temperature range in southeastern floodplain swamps. Somatic biomass growth rates were as high as 61% d−1. Total growth rates (somatic tissue and egg mass) reached 95% d−1. Both somatic growth rates and total growth rates could be described as functions of individual size and temperature. High egg production, particularly in the larger instars, resulted in individuals maintaining high total growth rates (&gt;20% d−1 at most temperatures) over the lifespan. Lifetime egg production accounted for &gt;50% of biomass produced by individuals at all temperatures and &gt;80% for temperatures ≥20°C. Somatic growth rates for C. dubia fed swamp seston were within the range of literature estimates for other species of Ceriodaphnia under various food conditions.

Nutrient Flux in a Landscape: Effects of Coastal Land Use and Terrestrial Community Mosaic on Nutrient Transport to Coastal Waters

Long-term interdisciplinary studies of the Rhode River estuary and its watershed in the mid-Atlantic coastal plain of North America have measured fluxes of nitrogen and phosphorus fractions through the hydrologically-linked ecosystems of this landscape. These ecosystems are upland forest, cropland, and pasture; streamside riparian forests; floodplain swamps; tidal brackish marshes and mudflats; and an estuarine embayment. Croplands discharged far more nitrogen per hectare in runoff than did forests and pastures. However, riparian deciduous hardwood forest bordering the cropland removed over 80 percent of the nitrate and total phosphorus in overland flows and about 85 percent of the nitrate in shallow groundwater drainage from cropland. Nevertheless, nutrient discharges from riparian forests downslope from croplands still exceeded discharges from pastures and other forests. The atomic ratio of nitrogen to phosphorus discharged from the watersheds into the estuary was about 9 for total nutrients and 6 for inorganic nutrient fractions. Such a low N:P ratio would promote nitrogen rather than phosphorus limitation of phytoplankton growth in the estuary. Estuarine tidal marshes trapped particulate nutrients and released dissolved nutrients. Subtidal mudflats in the upper estuary trapped particulate P, released dissolved phosphate, and consumed nitrate. This resulted in a decrease in the ratio of dissolved inorganic N:P in the estuary. However, the upper estuary was a major sink for total phosphorus due to sediment accretion in the subtidal area. Bulk precipitation accounted for 31 percent of the total nongaseous nitrogen influx to the landscape, while farming accounted for 69 percent. Forty-six percent of the total non-gaseous nitrogen influx was removed as farm products, 53 percent either accumulated in the watershed or was lost in gaseous forms, and 1 percent entered the Rhode River. Of the total phosphorus influx to the landscape, 7 percent was from bulk precipitation and 93 percent was from farming. Forty-five percent of the total phosphorus influx was removed as farm products, 48 percent accumulated in the watershed, and 7 percent entered the Rhode River. These nitrogen and phosphorus discharges into the Rhode River, although a small fraction of total loadings to the watershed, were large enough to cause seriously overenriched conditions in the upper estuary.

Methane emissions from cypress knees in a southeastern floodplain swamp.

Methane emissions were observed from knees of baldcypress (Taxodium distichum) in floodplain swamps of the Ogeechee river, a blackwater river in the lower coastal plain of Georgia, USA Emissions were sampled on 10 dates from March 1988 to September 1989, with small chambers placed over single knees. Methane emission rates from individual knees averaged 0.90 mg/d, corresponding to an average of 0.14 mg m-2 d-1 for the whole floodplain. In the habitat with the highest knee density (0.42 knees/m2), the average rate was 0.55 mg m-2 d-1. Spatial patterns in emissions from knees were similar to those of overall methane emissions from the swamp surface, though because of their low density were a minor contribution (0.42%) to total methane emissions from this system.

Methane emissions from floodplain swamps of the Ogeechee River: long-term patterns and effects of climate change

Patterns and rates of wetland methane emissions and their sensitivity to potential climate change are critical components of the global methane cycle. In this study, we use empirical simulation models to investigate these processes in floodplain swamps of the Ogeechee River in Georgia, U.S.A. We developed statistical models that relate methane emissions to monthly climate and river flow based on field observations of methane emissions from this system made during 1987–1989. Models were then applied to observed climate and hydrograph for 1937–1989 and to simulated altered climates. Altered climates were generated from the present-day climate by changing monthly temperatures by a constant amount and/or changing monthly precipitation by a constant proportion, thus altering long-term averages and preserving year-to-year variation.

Microtopography and Woody Plant Regeneration in a Hardwood Floodplain Swamp in Florida

TITus, J. H. (Savannah River Ecology Laboratory, Drawer E, Aiken, SC 29802). Microtopography and the regeneration of woody plants in a hardwood floodplain swamp in Florida. Bull. Torrey Bot. Club 117: 429-437. 1990.-Seedling distribution in relation to 18 different microtopographic features, relative elevation, and percent canopy cover was determined for woody species c 100 cm tall in a Fraxinus caroliniana Mill, Nyssa sylvatica var. biflora (Walt.) Sarg., and Sabal palmetto (Walt.) Lodd. dominated floodplain swamp in northern Florida. Distribution patterns of 25 woody species corresponded to the duration of inundation by flood waters and microsite substrate type. Although the elevational range in the study area was only 1.5 m, microsite elevation was the environmental factor most strongly correlated with seedling distribution. Microsite substrate type was also closely correlated with species presence. Percent canopy cover differences over different species' seedlings were very slight and were interpreted as biologically insignificant. Large light gaps were not found in the study site and tip-up mounds, although present, were not common. Tip-up mounds were generally poor sites for seedling survival, those created by S. palmetto appeared to present a poorer surface for seedling establishment and survival than tip-up mounds of other tree species.

Aircraft MSS data registration and vegetation classification for wetland change detection

Abstract Portions of the Savannah River floodplain swamp were evaluated for vegetation change using high resolution (5·6 m) aircraft multispectral scanner (MSS) data. Image distortion from aircraft movement prevented precise image-to-image registration in some areas. However, when small scenes were used (200–250 ha), a first-order linear transformation provided registration accuracies of less than or equal to one pixel. A larger area was registered using a piecewise linear method. Five major wetland classes were identified and evaluated for change. Phenological differences and the variable distribution of vegetation limited wetland type discrimination. Using unsupervised methods and ground-collected vegetation data, overall classification accuracies ranged from 84 per cent to 87 per cent for each scene. Results suggest that high-resolution aircraft MSS data can be precisely registered, if small areas are used, and that wetland vegetation change can be accurately detected and monitored.

Phosphorus Redistribution from Cultivated Fields into Riparian Areas

AbstractThe accumulation of P in sediments deposited within riparian areas was measured to study the role of these areas as P sinks. The sediments originated from the cultivated fields and forests of the uplands and were deposited during the last 20 to 25 years. The riparian areas were studied in the Atlantic Coastal Plain and consisted of four field‐forest edges, four ephemeral streams and four flood plains of intermittent streams that flowed into a flood plain swamp. Selective sorting and deposition of sand and silt near the field‐forest edge (0–20 m) and clay deposition downstream (1–4 km) on the flood plains and swamps explained much of the total P distribution in the riparian areas. The P in the sediments increased with percent clay, R2 = 0.80. Laboratory measurements of the equilibrium phosphorus concentration (EPC) in flood plain swamp sediments were two to three times higher than P concentrations in the overlying water (1.0 vs. 0.4 µmol P L−1) during high flow stages of winter and spring. During summer and fall the ortho‐P concentrations of isolated pools and base flow ranged from 1.0 to 1.3 µmol P L−1. Approximately 260 kmol of P were deposited in the riparian areas of the 1850 ha watershed during the past 20 to 25 years. The amount of P deposited was equal to the amount estimated to have been removed from the watershed in the drainage water. Thus about 50% of the P leaving agricultural fields appeared to be removed from the runoff water in the riparian areas. Riparian areas between the field edge and a perennial stream were sinks for P because of the continual deposition of fresh sediment from upland areas.

Riparian Areas as Filters for Agricultural Sediment1

Riparian buffer areas are known to trap sediment leaving agricultural fields, but little quantitative data on this process are available. This study was initiated to determine the amount of sediment deposited in riparian areas of two watersheds during the last 20 yr. These watersheds contained approximately 800 and 1400 ha, and about half of each watershed was cultivated land. The areal extent and thickness of the sediment were mapped and described using 137Cs data and sediment-soil morphology. At the field-forest edge 15 to 50 cm of 137Cs sediment accumulated while <5 cm of 137Cs sediment was deposited in the flood plain swamp downstream. Although only a thin (≤5 cm) layer of sediment accumulated in the flood plain swamp, the large area available made this an important depositional area. The full potential of the flood plain swamp for sediment deposition has not been utilized. About 80% of the 137Cs sediment measured in the watershed was deposited above the flood plain swamp with >50% of this sediment deposited within 100 m of the exit location from the cultivated fields. Sand dominated the deposition at the forest edge while high silt and clay contents occurred in the flood plain swamp. Sediment delivery estimates for Coastal Plain watershed indicated that 84 to 90% of the sediment removed from the cultivated fields remained in the watershed. It is concluded that riparian areas serve a valuable function by trapping sediment from agricultural fields.

Mapping of Wood Stork Foraging Habitat with Satellite Data

Potential foraging sites for an endangered species, the wood stork, were identified using Landsat thematic mapper data for a section of north central Georgia and the Savannah River floodplain swamp in South Carolina. This was accomplished using innovative clustering techniques applied to known wood stork foraging sites around the Birdsville Colony in Georgia. The signatures for known sites were then geographically extended to a 1520-square-kilometer region surrounding the Birdsville Colony. Thematic maps were produced and foraging area acreages computed providing a regional assessment of existing and potential wood stork foraging sites. Approximately 1744 hectarea of potential shallow water and macrophyte foraging habitat were identified in the area surroundings the Birdsville Colony. 14 refs., 3 figs.

Leaf Litter Decomposition across Broad Thermal Gradients in Southeastern Coastal Plain Streams and Swamps

ABSTRACT A 16 week study of leaf decomposition for sweetgum (Liquid-ambar styraciflua), American sycamore (Platanus occidentalis), and baldcypress (Taxodium distichum) was conducted during winter 1983–1984 in thermal and non-thermal streams and floodplain swamps in South Carolina. Mean daily temperatures ranged from 7.6 to 49.0 C in streams and from 10.5 to 29.8 C in swamps. Sweetgum leaves consistently decomposed more rapidly than sycamore leaves and leaf decomposition rates for sweetgum and sycamore tended to be inversely related to thermal regimes. Cypress leaves showed relatively uniform, slow losses over all temperature ranges. The highest processing rates for all leaf types were found in non-thermal, closed-canopy swamp habitat, where the shredding caddisfly, Pycnopsyche sp., was relatively abundant.

A 450-year drought reconstruction for Arkansas, United States

A 450-year reconstruction of the June Palmer Drought Severity Index1 (PDSI) has been derived for Arkansas using annual tree-ring chronologies from selected old-growth baldcypress trees (Taxodium distichum (L.) Rich.) found in floodplain swamps. This is the first palaeoclimate reconstruction achieved with baldcypress, and is some 150 years longer than any previous dendroclimatic estimate for eastern North America. The reconstruction is characterized by substantial fluctuation in the intensity and duration of past wet and dry spells, and is well verified against independent climate data. While there has been some very limited previous use of wet site species for dendrochronology2,3, this is the first verified climate reconstruction based exclusively on a swamp-grown species. Several 500–800-year-long baldcypress chronologies are under development, and some may be extended into mid- to late-Holocene times with tree-ring records from preserved subfossil cypress logs4.

Paleoenvironmental Control of Accumulation and Quality of Upper Freeport Coal Bed (Allegheny Formation, Middle Pennsylvanian), Castleman Coalfield, Maryland: ABSTRACT

The upper Freeport is generally a thick, widespread coal bed in the north-central Appalachian basin. It is a principal bed mined in the Castleman coalfield, Garrett County, Maryland, as delineated on a new geologic map of the coalfield. In the northern part of the coalfield, the upper Freeport is 21-48 in. (53-122 cm) thick and thickens toward the northwest, where the ash and sulfur contents are generally 7-10 wt. % and less than 1.5 wt. %, respectively. This coal bed thins southward and eastward and is absent from a large area in the central part of the coalfield, where its position is occupied by a carbonaceous claystone or flint clay. Toward the south and east, the upper Freeport coal bed generally contains 12-15 wt. % ash and 1.5-6.2 wt. % sulfur. Lithofacies analysis of the floor rocks and their lateral equivalents indicates deposition of the upper Freeport coal bed in floodplain swamps. Limestone and limy claystone floor rocks in the northwest represent distal floodplain lake deposits. Where the coal is unminable or absent to the south, proximal overbank floodplain shale, siltstone, and silty claystone grade laterally into channel sandstone. The gradation of thin coal into carbonaceous claystone to the south indicates increased oxidation and shoaling in a well-drained swamp. There, the coal has the highest ash and sulfur contents, which probably reflect the influx of detritus and iron-rich clays. Thus, the upper Freeport is thickest and has the lowest ash and sulfur contents where the paleoenvironment was a poorly drained, di tal floodplain swamp. End_of_Article - Last_Page 1924------------