Coastal Plain Of Alabama Research Articles

Assessing Vulnerability of Regional-Scale Aquifer-Aquitard Systems in East Gulf Coastal Plain of Alabama by Developing Groundwater Flow and Transport Models

Groundwater vulnerability assessment helps subsurface water resources management by providing scientific information for decision-makers. Rigorous, quantitative assessment of groundwater vulnerability usually requires process-based approaches such as groundwater flow and transport modeling, which have seldom been used for large aquifer-aquitard systems due to limited data and high model uncertainty. To quantify the vulnerability of regional-scale aquifer-aquitard systems in the East Gulf Coastal Plain of Alabama, a three-dimensional (3D) steady-state groundwater flow model was developed using MODFLOW, after applying detailed hydrogeologic information to characterize seven main aquifers bounded by aquitards. The velocity field calibrated by observed groundwater heads was then applied to calculate groundwater age and residence time for this 3D aquifer-aquitard system via backward/forward particle tracking. Radioactive isotope data (14C and 36Cl) were used to calibrate the backward particle tracking model. Results showed that shallow groundwater (<300 ft below the groundwater table) in southern Alabama is mainly the Anthropocene age (25–75 years) and hence susceptible to surface contamination, while the deep aquifer-aquitard systems (700 ft or deeper below the groundwater table) contain “fossil” waters and may be safe from modern contamination if there is no artificial recharge/discharge. Variable horizontal and vertical vulnerability maps for southern Alabama aquifer-aquitard systems reflect hydrologic conditions and intermediate-scale aquifer-aquitard architectures in the regional-scale models. These large-scale flow/transport models with coarse resolutions reasonably characterize the broad distribution and vertical fluctuation of groundwater ages, probably due to aquifer-aquitard structures being captured reliably in the geology model. Parameter sensitivity analysis, vadose zone percolation time, wavelet analysis, and a preliminary extension to transient flow were also discussed to support the aquifer vulnerability assessment indexed by groundwater ages for southern Alabama.

A new, narrowly endemic species of swamp-dwelling dusky salamander (Plethodontidae: Desmognathus) from the Gulf Coastal Plain of Mississippi and Alabama.

We describe a new, narrowly endemic species of swamp-dwelling dusky salamander (Plethodontidae: Desmognathus pascagoula sp. nov.) from the Gulf Coastal Plain of southeastern Mississippi and southwestern Alabama based on linear morphometrics, mitochondrial DNA, and single nucleotide polymorphisms from 881 loci produced using genotype-by-sequencing. Some populations of the new species were historically referred to as D. auriculatus, a polyphyletic assemblage of at least three species in the Atlantic and Gulf Coastal Plain from Texas to North Carolina. Populations of D. auriculatus from the Gulf Coastal Plain in Louisiana and Mississippi were recently described as D. valentinei. The new species includes populations that were tentatively referred to D. valentinei, but we find it is morphologically, genetically, and geographically distinct. It is smaller, has a more defined dorsal color pattern, more irregular whitish portholes in up to three rows on the lateral surfaces of the body and tail, and a brighter orange or yellowish orange postocular stripe. At present, the new species is known from only six extant populations in the lower Pascagoula, Escatawpa, and Mobile drainages. The latter represents a distinct phylogeographic lineage. We also refer a historical collection from the northeastern side of the Mobile-Tensaw River Delta to this species, suggesting a much broader range in the past. We suspect that more populations remain to be discovered in the area, and their potential species-level distinctiveness should be tested further. This discovery increases knowledge of the biodiversity in the southeastern United States Coastal Plain, a candidate region meeting the global criteria for a biodiversity hotspot, and underscores the amount of cryptic diversity likely remaining to be discovered and described in Nearctic salamanders.

Drivers of ecosystem vulnerability to Corbicula invasions in southeastern North America

Invasive species introduction is one of the major ongoing ecological global crises. Identifying factors responsible for the success of invasive species is key for the implementation of effective management actions. The invasive filter-feeding bivalve, Corbicula, is of particular interest because it has become ubiquitous in many river basins across North America and elsewhere. Here we sampled bivalve assemblages, environmental indicators, and land cover parameters in the Ouachita highlands in southeastern Oklahoma and southwestern Arkansas, and in the Gulf Coastal Plain of Alabama to test three working models (using structural equation modeling, SEM) based on a priori scientific knowledge regarding Corbicula invasions. Our models tested three competing hypotheses: (1) Native mussel declines are related to land use changes at the watershed level and subsequent Corbicula colonization is a result of an empty niche; (2) Corbicula abundance is one of the factors responsible for native mussel declines and has an interactive effect with land use change at the watershed level; (3) Native mussel declines and Corbicula success are both related to land use changes at the watershed level. We found no evidence for the first two hypotheses. However, we found that environmental indicators and land cover parameters at the watershed scale were robust predictors of Corbicula abundance. In particular, agricultural land cover was positively related with Corbicula density. These results suggest that further improvement of conventional agricultural practices including the optimization of fertilizer delivery systems may represent an opportunity to manage this species by limiting nutrient inputs to stream ecosystems. Preservation of extensive floodplain habitats may help buffer these inputs by providing key ecosystem services including sediment and nutrient retention.

Improving Coastal Plain Hardwoods for Deer and Turkeys with Canopy Reduction and Fire

ABSTRACTPrescribed fire and canopy reduction are accepted forest management practices used to increase forage and cover for white‐tailed deer (Odocoileus virginianus) and wild turkeys (Meleagris gallopavo) in pine systems throughout the southeastern United States. However, use of prescribed fire to improve conditions for deer and turkeys has not been evaluated in upland hardwood forests of the Coastal Plain, and some land managers remain skeptical of the utility of fire in this ecoregion. We designed a manipulative experiment to measure deer and turkey habitat components following canopy reduction and prescribed fire in 4 upland hardwood stands in the Coastal Plain of Alabama, USA, during 2018 and 2019. Specifically, we used herbicide to kill trees with low value to deer and turkeys and retained oaks (Quercus spp.) and other species considered important as part of a forest stand improvement (FSI) operation to reduce canopy coverage. We then applied low‐intensity prescribed fire to half of each treatment unit. One unit in each replicate served as a control. We measured total understory plant coverage, biomass of deer forage, and turkey brooding cover for 2 years following canopy reduction and one year after fire. Coverage of herbaceous plants increased by 134% in FSI/Burn, and coverage of woody and semiwoody plants increased by 33% and 97%, respectively, following FSI only. Deer forage biomass was greater in both FSI and FSI/Burn compared to control, but there was no difference in deer forage biomass between FSI and FSI/Burn. FSI/Burn provided better turkey brooding cover than FSI or control. No overstory trees were killed by fire. We detected minor cambium damage to 13% of water oaks (Quercus nigra) in the FSI/Burn units; other species only showed light bark charring or no sign of burning. We recommend FSI and low‐intensity prescribed fire in Coastal Plain hardwoods to improve brooding cover for turkeys and understory forage for deer while retaining acorn production. © 2020 The Wildlife Society.

Challenges Calibrating Hydrology for Groundwater-Fed Wetlands: a Headwater Wetland Case Study.

This study aims to adapt the Soil and Watershed Assessment Tool (SWAT), a ubiquitously used watershed model, for ground-water dominated surface waterbodies by accounting for recharge from the aquifers. Using measured flow to a headwater slope wetland in Alabama's coastal plain region as a case study, we present challenges and relatively simple approaches in using the SWAT model to predict flows from the draining watershed and relatively simple approaches to model groundwater upwelling. SWAT-simulated flow at the study watershed was limited by precipitation, and consequently, simulated flows were several times smaller in magnitude than observed flows. Thus, our first approach involved a separate stormflow and baseflow calibration which included the use of a regression relationship between observed and simulated baseflow (E NASH = 0.67). Our next approach involved adapting SWAT to simulate upwelling groundwater discharge instead of deep aquifer losses by constraining the range of deep losses, β deep parameter, to negative values (E NASH = 0.75). Finally, we also investigated the use of artificial neural networks (ANN) in conjunction with SWAT to further improve calibration performance. This approach used SWAT-calibrated flow, evapotranspiration, and precipitation as inputs to ANN (E NASH = 0.88). The methods investigated in this study can be used to navigate similar flow calibration challenges in other groundwater dominant watersheds which can be very useful tool for managers and modelers alike.

Effects of longleaf pine planting density and other factors on stand structure and associated wildlife habitat

The primary objective of many longleaf pine (Pinus palustris) restoration programs is to enhance or restore habitat for wildlife dependent on herbaceous plant communities. Because herbaceous cover is inversely related to canopy cover, restoration programs often place restrictions on longleaf pine planting density. However, the influence of planting density on understory plant communities has been inadequately evaluated. Therefore, we initiated a study to examine the relative influences of planting density and other factors on overall understory composition and forage availability for white‐tailed deer (Odocoileus virginianus) and northern bobwhite (Colinus virginianus) in nine longleaf pine stands throughout the Coastal Plain of Alabama during 2017–2018. We found that coverage of herbaceous plants decreased 3.5%, coverage of woody plants decreased 2.4%, and coverage of northern bobwhite forage plants decreased 1.9% for each 1 m2/ha increase in longleaf pine basal area. However, planting density was not a significant predictor of current basal area, nor coverage of any functional group of plants we examined, likely because current longleaf pine density averaged only 46% (range = 30–64%) of seedling planting density. We did not detect an effect of prescribed fire on stand condition or understory plant communities, likely due to variability in fire timing and frequency. Our findings related to planting density were likely a function of low longleaf pine survival, which is not uncommon. Because of this and the inherent variability in growth rates for young longleaf pine stands, restoration programs should consider placing greater emphasis on post‐planting monitoring and management than planting density.

No-tillage and noninversion tillage comparisons across wheat nitrogen rates in Alabama

Minimizing surface and deep tillage operations for wheat (Triticum aestivum L.) production may promote soil quality, but productivity and nitrogen (N) rate requirements need to be examined for these systems across Alabama Coastal Plain soils. A three-year experiment was conducted at three locations to (1) compare noninversion and no-tillage wheat production and (2) determine if N requirements across tillage systems should be modified. Each experiment (nine site-year comparisons) consisted of a split-plot design with tillage as the main plot and six fall and spring applied N fertilizer combinations as subplots, replicated four times. Tiller densities, tiller N concentrations, tiller biomass, wheat yields, grain crude protein, grain N use efficiency, and net returns were evaluated. Tillage system and fall N had no effect on tiller density or tiller N concentrations, except for 8% greater tiller N concentrations (P = 0.0842) for noninversion tillage compared to no-tillage at one location. Noninversion tillage also produced 23% more tiller biomass (P = 0.0040) compared to no-tillage at only one location. At two of the three locations, wheat yield response (P = 0.0764; P = 0.0313) varied up to 12%, but was inconsistent between tillage systems, while tillage system had no effect on grain crude protein and grain N use efficiency. The 134 kg N ha−1 rate produced 17% (P ≤ 0.0001) and 30% (P ≤ 0.0001) yield increases, averaged over tillage systems, for the 67 and 101 kg N ha−1 rates at the tillage responsive locations. No-tillage produced 11% greater net returns (P = 0.0238) than noninversion tillage for one location, while noninversion tillage produced net returns nearly six times greater (P = 0.0434) than no-tillage for the other location. Although net returns for the 101 and 134 kg N ha−1 rates were equivalent, net returns were nearly double for the 134 kg N ha−1 rate compared to the 101 kg N ha−1 rate at one location. No-tillage produced equivalent yields compared to noninversion tillage at two of the three locations, but net returns for no-tillage were only positive for one location. The 134 kg N ha−1 rate was required to maximize wheat production, but net returns indicated no advantage for additional N at the responsive locations, despite differences between N rates. No-tillage may enhance soil quality benefits, but yield increases and net returns were negligible compared to noninversion tillage across the Coastal Plain of Alabama.

Effects of basal area on survival and growth of longleaf pine when practicing selection silviculture

Aim of study: Uneven-aged (UEA) management systems can achieve multiple-use objectives, however, use of UEA techniques to manage longleaf pine (Pinus palustris Mill.) forests are still open to question, because of the species’ intolerance of competition. It was our aim to examine the influence of different levels (9.2, 13.8 and 18.4 m2 ha-1) of residual basal area (RBA) on longleaf pine seedling survival and growth following three growing seasons.Area of study: This study was conducted at the Escambia Experimental Forest, located on the Southern Coastal Plain of Alabama, in the southeastern United States.Material and Methods: Selection silviculture was implemented with the Proportional-Basal Area (Pro-B) method. Prescribed burning was conducted before seed dispersal and in the second year after germination. Photosynthetically active radiation (PAR) was measured under the canopy in the study plots. Survival and growth of longleaf pine seedlings were observed for three growing seasons.Main results: An inverse relationship was found between the number of germinants and RBA, but the mortality of germinants and planted seedlings was not affected by RBA. At age three, an inverse relationship was observed between root-collar diameter (RCD) growth of the germinants and RBA, but RCD growth of planted seedlings was not affected by RBA. Most of the study plots contained more than the projected number of seedlings needed to sustain the target diameter structure.Research highlights: Long-term continuous monitoring of seedling development and recruitment into canopy is required to determine the efficacy of UEA management. However, current data suggest that UEA methods may be a viable alternative to the use of even-aged (EA) methods in longleaf ecosystems.

Mapped Fractures and Sinkholes in the Coastal Plain of Florida and Georgia to Infer Environmental Impacts from Aquifer Storage and Recovery (ASR) and Supply Wells in the Regional Karst Floridan Aquifer System

The regional Floridan aquifer system (FAS) extends from the submerged carbonate platform of the Atlantic Ocean, Gulf of Mexico, and Straits of Florida in the southeastern United States (US), throughout Florida and the coastal plain of Alabama, Georgia, and South Carolina. This carbonate aquifer system is characterized by bedding planes, fractures, dissolution cavities, and other karst features that result in preferential flow of ground water, particularly in response to anthropogenic perturbations such as groundwater withdrawals and aquifer injections. The FAS was divided into six sub-regions for groundwater-modeling purposes in 1989, with results concluding that breaches of those groundwater divides had occurred and those breaches were attributed to large withdrawals of ground water in the US southeastern coastal plain. Those results suggest the model did not elucidate preferential flow conditions through fractures and other karst conduits. We hypothesized that incorporating fractures and sinkholes into groundwater models could improve results and predict adverse impacts to environmentally sensitive areas. We analyzed extensive fracture networks and sinkholes previously mapped throughout Florida and in Dougherty County, Georgia. Some of those fractures extend from one sub-region into an adjacent sub-region of the FAS and may be facilitating the breaching of groundwater divides described in the 1989 groundwater model for this regional aquifer system. The greater total fractures and fracture density in Dougherty County (1,225 and 141.3/100 km2, respectively) compared to 21 north-Florida counties (10-91fractures per county and 0.6-3.8/100 km2, respectively) presumably is due to the scale of fracture mapping and shorter mean lengths of mapped fractures in Dougherty County (1.2 km), compared to north Florida counties (26-118 km), rather than to orders of magnitude increases in fracture densities in that part of the FAS. The number of sinkholes identified in Dougherty County in a recent, unrelated project using 2011 Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images, was approximately an order of magnitude greater than the number of sinkholes mapped in analog form in that county and published in 1986. Extension of the dense network of those fractures that occurred within the boundaries of a Priority Amphibian and Reptile Conservation Area (PARCA) that encompassed Dougherty County covered the Elmodel Wildlife Management Area (WMA) and ASR demonstration well in Baker County, Georgia. Those extensions also passed through numerous agricultural areas with center-pivot irrigation wells in southwest Georgia; intersected other Georgia PARCAs near the Florida-Georgia state line; and clumped in two areas of dense sinkhole clusters in northwest Florida. No determination has been made regarding the contributions of pirated water from the Apalachicola-Chattahoochee-Flint (ACF) River Basins and Wakulla Springshed from the magnitude and extent of agricultural, municipal, and industrial groundwater withdrawals in Georgia’s coastal plain, that exceed groundwater withdrawals in Florida for that area of the FAS, to the increase in sinkholes in Dougherty County and the dense clusters of sinkholes in northwest Florida, via preferential flow through fractures. Similarly, the survival and recovery of at least 24 animal species in Georgia that are either federally listed or high-priority state species may be jeopardized by adverse direct, indirect, and cumulative impacts from preferential flow through fractures, sinkholes, and other karst conduits in response to aquifer injections and withdrawals that have not been evaluated. Currently no regional groundwater model has been constructed to evaluate such preferential groundwater flow in the FAS. A model incorporating preferential flow via mapped fractures and sinkholes is essential to determine the magnitude and extent of environmental impacts from ASR wells and other supply and disposal wells in this regional aquifer system, such as pirated water from the ACF and other river basins, alterations in submarine groundwater discharge to Apalachicola Bay and other coastal areas, saltwater intrusion, upconing of saline ground water and resulting impacts to federally endangered and threatened species and high-priority state species.

Rhizocorallium in estuarine Ingersoll shale (Upper Cretaceous Eutaw Formation, Eastern Alabama coastal plain)

The ichnofossil Rhizocorallium—an oblique to horizontal U-shaped spreiten burrow—has been recognized in a broad range of Phanerozoic continental, marginal marine, and shallow to deep marine facies. Nonetheless, occurrences of this ichnotaxon in Cretaceous estuarine deposits are rarely described. Herein we document Rhizocorallium in the Ingersoll shale, a carbonaceous clay lens within an estuarine succession contained in the Upper Cretaceous (Santonian) Eutaw Formation exposed in the eastern U.S. Gulf coastal plain. The Ingersoll Rhizocorallium specimens, assigned to R. commune var. irregulare based on their basic morphology, horizontal disposition, dimensions, and actively filled spreiten, record a change in depositional conditions and substrate consistency linked to transgression. The Ingersoll shale accumulated rapidly in a restricted tidal channel in a bayhead delta setting and hosts an impoverished resident ichnofauna reflecting soupground conditions. In contrast, attributes of Rhizocorallium (e.g., burrow wall bioglyphs) and associated Thalassinoides in the upper part of the Ingersoll shale reflect firm substrates (i.e., Glossifungites ichnofacies). Firmground development and colonization reflect burial dewatering and subsequent exhumation by bay-shoreline ravinement of clays and the concomitant shift to estuarine central bay deposition. The biological affinity of the Rhizocorallium trace makers cannot be confidently established. However, based on relatively straight and seemingly current-aligned axes, passive burrow fills, lack of associated fecal pellets, and emplacement in firm clay, these structures were likely produced by suspension-feeding organisms—either crustaceans or worms—that took advantage of wave- or tide-induced currents in shallow areas near the estuary head.

Equilibrium Concentrations of Major Cations and Total Alkalinity in Laboratory Soil-Water Systems

Three soils and four waters were used to prepare laboratory soil-water mesocosms. Soil-water mesocosms contained 5-cm-deep layers of soil and 21 L of water from each of the four sources: artificial rainwater, stream water, saline well water, and seawater. Water pH, conductivity, major cations, and total alkalinity were measured at intervals for 200 days. In some instances, equilibrium was not attained during the trial. Soils from the Coastal Plain and Blackland Prairie regions of Alabama caused greater increases in intensities of variables in rain and stream water than did Piedmont Plateau soil, while conductivity, calcium, sodium, and total alkalinity in rain and stream water increased most in mesocosms with Blackland Prairie soil; magnesium increased most in mesocosms with Coastal Plain soil. In mesocosms with saline well water and Blackland Prairie soil, there were changes in all measured variables other than pH and conductivity. In mesocosms with seawater and Blackland Prairie soil, only calcium, magnesium, and potassium in the water were different from the original source water. Shaker experiment revealed that equilibrium concentrations of water quality variables increased as the ratio of soil to water increased.

Web 2.0 for Disaster Response and Recovery

Successful disaster response is an exercise in managing human resources under very difficult conditions. Catastrophic disasters can disrupt both the physical communication networks and the social networks critical to efficient response and recovery. While a well-designed disaster plan serves as a framework, it often requires communication and collaboration between responders to adapt it to the situation at hand. Displacement of library staff adds to the chaotic nature of post-disaster communications, increasing the need for collaborative Web spaces to adapt to changing situations. Using case studies of catastrophic disaster response at libraries, this article begins with an analysis of human resource management problems common to disaster response coordinators worldwide. It then discusses Auburn University Libraries’ uses of free Web 2.0 applications in support of library disaster preparation, response, and recovery. While Auburn University's location on the coastal plain of Alabama is vulnerable to both hurricanes and tornadoes, Auburn has so far only needed to respond to small-scale disasters. The devastation suffered by libraries in the paths of Hurricanes Katrina and Rita served to propel Auburn toward a more comprehensive preparedness stance. Disaster planning at Auburn has embraced Web 2.0 applications, such as Google Documents and Google Talk, to introduce redundant communication channels and to allow for efficient collaboration regardless of the location of library responders. By identifying key Web 2.0 applications and properties that are useful for response and recovery efforts, the research in this article may assist other libraries in improving their disaster preparedness.

Structure and composition changes following restoration treatments of longleaf pine forests on the Gulf Coastal Plain of Alabama

Longleaf pine ( Pinus palustris Mill.) forests of the Gulf Coastal Plain historically burned every 2–4 years with low intensity fires, which maintained open stands with herbaceous dominated understories. During the early and mid 20th century however, reduced fire frequency allowed fuel to accumulate and hardwoods to increase in the midstory and overstory layers, while woody shrubs gained understory dominance. In 2001, a research study was installed in southern Alabama to develop management options that could be used to reduce fuel loads and restore the ecosystem. As part of a nationwide fire and fire surrogates study, treatments included a control (no fire or other disturbance), prescribed burning only, thinning of selected trees, thinning plus prescribed burning, and herbicide plus prescribed burning. After two cycles of prescribed burning, applied biennially during the growing season, there were positive changes in ecosystem composition. Although thinning treatments produced revenue, while reducing midstory hardwoods and encouraging growth of a grassy understory, burning was needed to discourage regrowth of the hardwood midstory and woody understory. Herbicide application followed by burning gave the quickest changes in understory composition, but repeated applications of fire eventually produced the same results at the end of this 8-year study. Burning was found to be a critical component of any restoration treatment for longleaf communities of this region with positive changes in overstory, midstory and understory layers after just three or four burns applied every 2 or 3 years.

Effects of prescribed fire and other plant community restoration treatments on tree mortality, bark beetles, and other saproxylic Coleoptera of longleaf pine, Pinus palustris Mill., on the Coastal Plain of Alabama

Treatments to restore understory plant communities of mature (50–80-year old) longleaf pine ( Pinus palustris Mill.) and reduce risks of wildfire were applied to 10 ha plots that had a substantial shrub layer due to lack of fire. Plots were located in the Coastal Plain of Alabama and treatments consisted of: (1) untreated control, (2) growing season prescribed burn, (3) thin only, (4) thin plus growing season burn, and (5) herbicide plus growing season burn. Thin plus burn plots had significantly higher tree mortality compared to burn only and control plots and, overall, fire was the primary cause of tree death. Most tree mortality occurred within 1-year of treatment. From 2002 to 2004, we captured 75,598 Coleoptera in multiple funnel traps comprising 17 families and 130 species. Abundance of all Coleoptera combined was not different among treatments. Species richness was significantly higher on thin plus burn plots compared to thin only and control plots. Scolytinae (Coleoptera: Curculionidae) were more abundant on thin plus burn plots compared to control plots in fall 2002 but in fall 2003 they were more abundant on thin plus burn, thin only, and herbicide plus burn compared to controls. Among Scolytinae, Dendroctonus terebrans (Olivier), Xyleborinus saxeseni (Ratzeburg), Xyleborus sp. 3, and Hylastes tenuis (Eichhoff), showed varying responses to the treatments. Other Curculionidae were significantly more abundant on thin only and herbicide plus burn plots compared to all other treatments in spring 2003 and in spring 2004 they were more abundant on herbicide plus burn plots compared to thin plus burn treatments. Among Cerambycidae, Xylotrechus sagittatus (Germar) was higher in abundance in fall 2003 on thin plus burn plots compared to all other treatments except herbicide plus burn plots. Within the predator complex, Trogositidae were higher on thin plus burn plots compared to all other treatments except thin only plots in spring 2003, and Cleridae abundance was higher in spring 2004 on burn only plots compared to all other treatments. Linear regression analyses of dead trees per plot versus various Coleoptera showed captures of Buprestidae, Cerambycidae, Trogositidae, Acanthocinus nodosus (Fabricius), Temnochila virescens (Fabricius), and X. saxeseni increased with increasing number of dead trees. Our results show that the restoration treatments tested did not cause increased bark beetle-related tree mortality and they did not negatively affect populations of early successional saproxylic beetle fauna.

Origin of modern quartzarenite beach sands in a temperate climate, Florida and Alabama, USA

Quartzarenite coastal sands extending from eastern Louisiana eastward to Apalachee Bay, Florida, are anomalous: their position 7° north of the Tropic of Cancer contrasts with most other known modern quartzarenites, most of which are in a tropical setting. To determine the origin of these quartzarenite beach sands, we compared the mineralogy of samples taken from Alabama and Florida beaches, rivers that supply sand to the coast, and well cuttings representative of sandstone bedrock exposed in the Alabama coastal plain. To help assess the abundance of recycled quartz, and accepting the conventional wisdom that rounded sand-size quartz grains are recycled, we quantified the roundness of quartz grains in thin sections of river, beach, and well samples. We also determined the abundance of recycled grains with authigenic quartz using cathodoluminescence. River sands on Precambrian and Paleozoic bedrock in the study area have subarkose and sublitharenite compositions. However, as far as 200 km inland from the coast, river sands have attained quartzarenite composition and all rivers are presently delivering sand with at least 97% quartz to the coast. Rivers develop quartzarenite sand composition where they traverse poorly consolidated Tertiary sandstones, all of which we sampled are composed of > 95% quartz. Published experimental work indicates that abrasional rounding of sand-size quartz by rivers is insignificant and rounding in beaches is extremely slow. Hence, the abundance of quartz grains with some degree of rounding (96% for beaches; > 75% for rivers) further attests to the abundance of recycled quartz.

Simulating Field‐Scale Soil Organic Carbon Dynamics Using EPIC

Simulation models integrate our knowledge of soil organic C (SOC) dynamics and are useful tools for evaluating impacts of crop management on soil C sequestration; yet, they require local calibration. Our objectives were to calibrate the Environmental Policy Integrated Climate (EPIC) model, and evaluate its performance for simulating SOC fractions as affected by soil landscape and management. An automated parameter optimization procedure was used to calibrate the model for a site‐specific experiment in the Coastal Plain of central Alabama. The ability of EPIC to predict corn (Zea mays L.) and cotton (Gossypium hirsutum L.) yields and SOC dynamics on different soil landscape positions (summit, sideslope, and drainageway) during the initial period of conservation tillage adoption (5 yr) was evaluated using regression and mean squared deviations. Simulated yield explained 88% of measured yield variation, with the greatest disagreement on the sideslope position and the greatest agreement in the drainageway. Simulations explained approximately 1, 34, and 40% of the total variation in microbial biomass C (MBC), particulate organic C (POC), and total organic C (TOC), respectively. The lowest errors in TOC simulations (0–20 cm) were found on the sideslope and summit. We conclude that the automated parameterization was generally successful, although further work is needed to refine the MBC and POC fractions, and to improve EPIC predictions of SOC dynamics with depth. Overall, EPIC was sensitive to spatial differences in C fractions that resulted from differing soil landscape positions. The model needs additional refinement for accurate simulations of field‐scale SOC dynamics affected by short‐term management decisions.

USING REMOTE SENSING DATA TO EVALUATE SURFACE SOIL PROPERTIES IN ALABAMA ULTISOLS

Evaluation of surface soil properties via remote sensing could facilitate soil survey mapping, erosion prediction, and allocation of agrochemicals for precision management. The objective of this study was to evaluate the relationship between soil spectral signature and surface soil properties in conventionally managed row crop systems. High-resolution remote sensing data were acquired over bare fields in the Coastal Plain, Appalachian Plateau, and Ridge and Valley provinces of Alabama using the Airborne Terrestrial Applications Sensor multispectral scanner. Soils ranged from sandy Kandiudults to fine textured Rhodudults. Surface soil samples (0 to 1 cm) were collected from 161 sampling points for gravimetric soil water content, soil organic carbon, particle size distribution, and citrate dithionite extractable iron content. Surface roughness and crusting were also measured during sampling. Two methods of analysis were evaluated: (1)multiple linear regression using common spectral band ratios and (2)partial least-squares regression. Our data show that thermal infrared spectra are highly, linearly related to soil organic carbon, sand and clay content. Soil organic carbon content was the most difficult to quantify in these highly weathered systems, where soil organic carbon was generally <1.2%. Estimates of sand and clay content were best using partial least-squares regression at the Valley site, explaining 42 to 59% of the variability. In the Coastal Plain, sandy surfaces prone to crusting limited estimates of sand and clay content via partial least-squares and regression with common band ratios. Estimates of iron oxide content were a function of mineralogy and best accomplished using specific band ratios, with regression explaining 36 to 65% of the variability at the Valley and Coastal Plain sites, respectively.

IKONOS Imagery to Estimate Surface Soil Property Variability in Two Alabama Physiographies

Knowledge of surface soil properties is used to assess past erosion and predict erodibility, determine nutrient requirements, and assess surface texture for soil survey applications. This study was designed to evaluate high resolution IKONOS multispectral data as a soil‐mapping tool. Imagery was acquired over conventionally tilled fields in the Coastal Plain and Tennessee Valley physiographic regions of Alabama. Acquisitions were designed to assess the impact of surface crusting, roughness, and tillage on our ability to depict soil property variability. Soils consisted mostly of fine‐loamy, kaolinitic, thermic Plinthic Kandiudults at the Coastal Plain site and fine, kaolinitic, thermic Rhodic Paleudults at the Tennessee Valley site. Soils were sampled in 0.20‐ha grids to a depth of 15 cm and analyzed for percentages of sand (0.05–2 mm), silt (0.002–0.05 mm), clay (&lt;0.002 mm), citrate‐dithionite extractable Fe, and total C (TC). Four methods of evaluating variability in soil attributes were evaluated: (i) kriging of soil attributes, (ii) cokriging with soil attributes and reflectance data, (iii) multivariate regression based on the relationship between reflectance and soil properties, and (iv) fuzzy c‐means clustering of reflectance data. Results indicate that cokriging with remotely sensed (RS) data improved field scale estimates of surface TC and clay content compared with kriging and regression methods. Fuzzy c‐means worked best using remotely sensed data acquired over freshly tilled fields, reducing soil property variability within soil zones compared with field scale soil property variability.

Evaluation of Multispectral Data for Rapid Assessment of Wheat Straw Residue Cover

Crop residues influence near surface soil organic carbon (SOC) content, impact our ability to remotely assess soil properties, and play a role in global carbon budgets. Methods that measure crop residues are laborious, and largely inappropriate for field‐scale to regional estimates. The objective of this study was to evaluate high spectral resolution remote sensing (RS) data for rapid quantification of residue cover. In March 2000 and April 2001, residue plots (15 by 15 m) were established in the Coastal Plain and Appalachian Plateau physiographic regions of Alabama. Treatments consisted of five wheat (Triticum aestivum L.) straw cover rates (0, 10, 20, 50, and 80%) replicated three times. Spectral measurements were acquired monthly via a handheld spectroradiometer (350–1050 nm) and per availability via the Airborne Terrestrial Applications Sensor (ATLAS) (400–12500 nm). Overall, treatment separation was influenced by soil water content and percentage of total organic carbon (TOC) of the residue (degree of decomposition). Results showed that atmospherically corrected visible and near‐infrared ATLAS data can differentiate between residue coverages. Similar results were obtained with the handheld spectroradiometer, although treatment differentiation was less consistent. Thermal infrared ATLAS imagery best discriminated among residue treatments due to differing heat capacities between soil and residue. Results from our study suggest airborne thermal infrared (TIR) imagery can be used for crop residue variability assessment within the southeastern USA.

Groundwater and microbial processes of Alabama coastal plain aquifers

We integrate groundwater geochemistry, microbiology, and numerical modeling techniques to study the origin of elevated salinity and chemical evolution of groundwaters in the coastal plain aquifers of Alabama. Our field data indicate that chemical composition of groundwater evolves by various geochemical and microbial processes as it moves deeper into the subsurface. Sequential peaks of Ca2+, Mg2+, K+, and Na+ along flow paths indicate that separation of ions may be driven by cation exchange. Microbial‐mediated reactions are important for the formation of several discrete hydrochemical zones containing Fe2+, Mn2+, Sr2+, and SO42− rich groundwaters. Elevated Fe2+, Mn2+, and Sr2+ concentrations may be derived from bacterial iron and manganese reduction. High sulfate concentrations observed a short distance from the recharge may be partly explained by microbial sulfur oxidation and nitrate reduction (denitrification). The presence of denitrifying and sulfur‐oxidizing bacteria in water further supports these reactions. Major ion compositions and δD and δ18O values are used to determine the source of salinity and the nature of mixing of different groundwaters. Three water types were identified; these include carbonate groundwater, brines associated with evaporites, and groundwater of meteoric origin. Groundwater age differences and flow velocities were calculated using the 36Cl/Cl ratios. Calculated groundwater flow velocities within the Eutaw and Tuscaloosa aquifers are about 0.20 m/yr and 0.15 m/yr, respectively. We modeled basin‐scale hydrologic and solute transport processes in a cross section extending from the aquifer outcrops to the Gulf Coast. The modeling result shows that the buried Jurassic Louann Salt can significantly increase groundwater salinity in the overlying coastal plain aquifers by density‐driven advection and hydrodynamic dispersion. The modeling results are consistent with Cl/Br ratios and O/H isotope signatures, which indicate that salinity of the groundwater could be derived from seawater that has been evaporated beyond halite saturation. The predicted groundwater flow pattern reveals the mixing of meteoric water, carbonate groundwater (from the Ordovician Knox Group), and saline brines associated with the Louann Salt. The hydrologic model is consistent with the hydrochemical facies distribution in the Alabama coastal plain.