Carolina Bay geoarchaeology and Holocene landscape evolution on the Upper Coastal Plain of South Carolina

Surface water on the mainly dry, upland interfluves of the Upper Coastal Plain of South Carolina occurs currently as a sporadic distribution of shallow ponds held within Carolina bays and other small, isolated basins. At seven bays on the U.S. Department of Energy's Savannah River Site on the Upper Coastal Plain of South Carolina, we investigated Holocene changes in bay morphology, ecology, and prehistoric human activity. At Flamingo Bay, we employed archaeological survey and testing, shovel and auger testing, sediment analysis, and ground-penetrating radar to document stratigraphy and chronology of the sand rim on the eastern side of the bay. Artifact assemblage indicate changes in intensity of human use of the bay. Radiocarbon dates from a sediment core establish time scales for depositional processes at the center of the basin. Ground-penetrating radar data from the other bays indicate that the stratigraphy of all seven bays is broadly similar. We conclude that: (1) Significant modification of the bays, including rim development and basin infilling, occurred during the Holocene; (2) ponds on the early Holocene landscape were larger and more permanent than at present; (3) early Holocene climate, as indicated by both depositional processes and human activity, was not characterized by prolonged periods of extremely dry conditions; and (4) fluvial-centric models of terminal Pleistocene—early Holocene human adaptations require revision to include intensive use of isolated upland ponds. © 1996 John Wiley & Sons, Inc.     

Multiple-method estimation of recharge rates at diverse locations in the North Carolina Coastal Plain, USA

Recharge rates determined at diverse study sites in a shallow, unconfined aquifer differed from one another depending on the analytical method used and on each method’s applicability and limitations. Total recharge was quantified with saturated-zone methods using water-table fluctuations at seven sites in North Carolina, USA and using groundwater-age dating at three of the seven sites; at two of the sites, potential recharge was quantified with an unsaturated-zone method using Darcy’s law; and at five of the sites, net recharge was quantified with a stream hydrograph-separation method using streamflow-recession curves. Historical mean net recharge was 25 to 69% of the historical total recharge rates. The large disparity is attributed to groundwater losses between recharge and discharge areas, primarily by evapotranspiration and seepage to underlying aquifers. The spatial distribution of historical mean annual total recharge did not vary between landscape units, as suggested in a previous study. Similarly, total recharge did not correlate significantly with mean annual rainfall, mean annual water table depth, or the surficial soil properties of percent clay and bulk density. Total recharge did correlate significantly with the surficial soil properties of percent sand and percent silt.

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Résumé Les taux de recharge déterminés sur divers sites d’études dans un aquifère phréatique libre, varient les uns par rapport aux autres selon la méthode analytique utilisée et les limites et l’applicabilité de chaque méthode. La recharge totale a été quantifiée avec des méthodes en zone saturée utilisant les fluctuations des nappes sur sept sites de la Caroline du Nord, USA, et en utilisant les datations des eaux souterraines sur trois des sept sites ; sur deux des sites, la recharge potentielle a été quantifiée avec une méthode en zone non-saturée utilisant la loi de Darcy, et sur deux sites, la recharge nette a été quantifiée suivant une méthode de séparation des hydrographes de cours d’eau utilisant les courbes de récession du débit. La moyenne historique de la recharge nette est comprise entre 25 et 69% des taux historiques de recharge totale. L’importante disparité est attribuée aux pertes en eaux souterraines entre les zones de recharge et les zones d’exutoire, d’abord par évapotranspiration et ensuite par infiltration vers les aquifères sous-jacents. La distribution spatiale de la recharge historique moyenne annuelle et totale ne varie pas selon les unités paysagères, comme cela était suggéré dans une étude antérieure. De même, la recharge totale n’est pas corrélée significativement avec la moyenne annuelle des précipitations, la moyenne annuelle de la profondeur de la nappe, ou les propriétés de surface des sols que sont le pourcentage d’argile ou la densité apparente. La recharge totale est corrélée significativement avec les propriétés de surface du sol et les teneurs en sable et en silt.

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Resumen Las tasas de recarga determinadas en diversos sitios de estudio en un acuífero somero no confinado difieren entre sí dependiendo del método analítico usado y de las limitaciones y aplicabilidad de cada método. Se cuantificó la recarga total con métodos de zona saturada usando fluctuaciones del nivel freático en siete sitios en Carolina del Norte, Estados Unidos, y usando datación de edades de agua subterránea en tres de los siete sitios; en dos de los sitios se cuantificó la recarga potencial con un método de zona no saturada usando la Ley de Darcy y en cinco de los sitios se cuantificó la recarga neta con el método de separación hidrográfica usando curvas de recesión de flujo en arroyos. La recarga neta media histórica varió entre 25 y 69% de las tasas de recarga total histórica. La diferencia tan grande se atribuye a pérdidas de agua subterránea entre áreas de descarga y recarga, principalmente por evapotranspiración y escurrimiento hacia acuíferos subyacentes. La distribución espacial de la recarga total anual media histórica no varió entre las unidades de paisaje, como ya se había sugerido en un estudio previo. De modo similar, la recarga total no guarda correlación significativa con la lluvia media anual, la profundidad media anual del nivel freático, o las propiedades superficiales del suelo, particularmente porcentaje de arcilla y densidad volumétrica. La recarga total si tuvo una correlación significativa con las propiedades superficiales del suelo tal como porcentaje de arena y porcentaje de limo.

     

Wet early to middle Holocene conditions on the upper Coastal Plain of North Carolina, USA

A peat core from a cutoff paleochannel of Little River on the upper Coastal Plain of North Carolina provides a continuous pollen record of environmental change for the past 10,500 years and includes a sedimentary record of overbank floods. Palynological and sedimentary data indicate that the early to middle Holocene was wetter than previously suggested from lake sites in the southeastern United States. The period from 9000 to 6100 cal yr B.P. is characterized by high pollen percentages of Nyssa and Quercus, but low percentages of Pinus. Fifteen large overbank flood events are present within this period (5 floods/1000 yr). In contrast, only 6 large overbank flood events occurred since 6100 cal yr B.P. (1 flood/1000 yr). The increases in moisture and flood events probably were controlled by changes in atmospheric circulation related to shifts in the position of the Bermuda High, sea surface temperatures, and El Niño activity that together may have affected the frequency of large floods generated from tropical storms in the region.     

Reexamination of postglacial vegetation history in northern Idaho: Hager Pond,Bonner Co.

Hager Pond, a mire in northern Idaho, reveals at least five pollen zones since sediments formed after the last recession of continental ice (>9500 yr BP). Zone I (>9500-8300 yr BP) consists mainly of diploxylon pine, plus low percentages of Abies, Artemisia, and Picea. SEM examination of conifer pollen at selected levels in the zone reveals that Pinus albicaulis, P. monticola, and P. contorta are present in unknown proportions. The zone resembles modern pollen spectra from the Abies lasiocarpa-P. albicaulis association found locally today only at high elevation. Presence of whitebark pine indicates a cooler, moister climate than at present, but one which was rapidly replaced in Zone II (8300-7600 yr BP) by warmer, drier conditions as inferred by prominence of grass with diploxylon pine. Zone III (7600-3000 yr BP) was probably dominated by Pseudotsuga menziesii, plus diploxylon pine and prominent Artemisia and denotes a change in vegetation but continuation of the warmer drier conditions. Beginning at approximately 3000 yr BP Picea engelmannii, Abies lasiocarpa, and/or A. grandis and diploxylon pine were dominants and the inferred climate became cooler and moister concomitant with Neoglaciation. The modern climatic climax (Zone V), with Tsuga heterophylla as dominant, has emerged in approximately the last 1500 yr.     

Non-monotonic Responses of Phytoplankton Biomass Accumulation to Hydrologic Variability: A Comparison of Two Coastal Plain North Carolina Estuaries

Freshwater inputs often play a more direct role in estuarine phytoplankton biomass (chlorophyll a) accumulation than nitrogen (N) inputs, since discharge simultaneously controls both phytoplankton residence time and N loading. Understanding this link is critical, given potential changes in climate and human activities that may affect discharge and watershed N supply. Chlorophyll a (chla) relationships with hydrologic variability were examined in 3-year time series from two neighboring, shallow (<5?m), microtidal estuaries (New and Neuse River estuaries, NC, USA) influenced by the same climatic conditions and events. Under conditions ranging from drought to floods, N concentration and salinity showed direct positive and negative responses, respectively, to discharge for both estuaries. The response of chla to discharge was more complex, but was elucidated through conversion of discharge to freshwater flushing time, an estimate of transport time scale. Non-linear fits of chla to flushing time revealed non-monotonic, unimodal relationships that reflected the changing balance between intrinsic growth and losses through time and along the axis of each estuary. Maximum biomass occurred at approximately 10-day flushing times for both systems. Residual analysis of the fitted data revealed positive relationships between chla and temperature, suggesting enhanced growth rates at higher temperatures. N loading and system-wide, volume-weighted chla were positively correlated, and biomass yields per N load were greater than other marine systems. When combined with information on loss processes, these results on the hydrologic control of phytoplankton biomass will help formulate mechanistic models necessary to predict ecosystem responses to future climate and anthropogenic changes.     

Quaternary vegetation history of the Mississippi embayment

Nonconnah Creek, located in the loess-mantled Blufflands along the eastern wall of the Lower Mississippi Alluvial Valley in Tennessee displays a sedimentary sequence representing the Altonian Substage through the Woodfordian Substage of the Wisconsinan Stage. The site has a biostratigraphic record for the Altonian and Farmdalian Substages that documents warm-temperate upland oak-pine forest, prairie, and bottomland forest. At 23,000 yr B.P., white spruce and larch migrated into the Nonconnah Creek watershed and along braided-stream surfaces in the Mississippi Valley as far as southeastern Louisiana. The pollen and plant-macrofossil record from Nonconnah Creek provides the first documentation of a full-glacial locality in eastern North America for beech, yellow poplar, oak, history, black walnut, and other mesic deciduous forest taxa. During the full and late glacial, the Mississippi Valley was a barrier to the migration of pine species, while the adjacent Blufflands provided a refuge for mesic deciduous forest taxa. Regional climatic amelioration, beginning about 16,500 yr B.P., is reflected by increases in pollen percentages of cooltemperate deciduous trees at Nonconnah Creek. The demise of spruce and jack pine occurred 12,500 yr B.P. between 34° and 37° N in eastern North America in response to postglacial warming.     

Time series analyses of suspended sediment concentrations at North Inlet,South Carolina

Daily water samples have been collected at three stations in the North Inlet (South Carolina) marshestuary system since February 1981 as part of the NSF Long-Term Ecological Research (LTER) project. As a result of this sampling regime, nearly continuous time series of inorganic and organic suspended sediment, particulate organic carbon (POC), Secchi disk, salinity, and water temperature are now available. Power spectrum analysis of these data reveals that most of the explainable variance in the inorganic suspended sediment, POC, and Secchi disk data is related to a yearly cycle that is strongly coherent with water temperature such that high turbidity is associated with high water temperature. Only a small fraction of the explainable variance is associated with frequencies that can be related to the semidiurnal tide. Simple correlation analysis also indicates that turbidity is more closely associated with water temperature than with tide height or salinity. The ratio of POC to inorganic suspended sediment shows no discernible power spectra peaks and is weakly, but inversely, correlated with temperature. From these results we hypothesize that temperature-regulated bioturbation is the main factor controlling turbidity variations in the system. The lack of a strong inverse correlation between turbidity and salinity suggests that river runoff has little immediate impact on the suspended sediment of nearshore coastal waters in systems similar to North Inlet.     

Chronology of Inland Eolian Dunes on the Coastal Plain of Georgia, USA

Most inland eolian dunes associated with rivers on the Georgia Coastal Plain probably date to glacial periods. Direct dating of the dune sand by optically stimulated luminescence dating, combined with limiting ages from radiocarbon dating, shows that dunes formed during isotope stage 2, stage 3, the transition between stages 4 and 5, and isotope stage 6 or earlier. Most of the dates indicate dune activity between 30,000 and 15,000 years ago. Holocene activity included limited and local reworking of the crests of some thick dunes along streams that flow from the Piedmont.     

Late-glacial and Holocene vegetation and climatic history of the Cass Basin, central South Island, New Zealand

Lithology, pollen, macrofossils, and stable carbon isotopes from an intermontane basin bog site in southern New Zealand provide a detailed late-glacial and early Holocene vegetation and climate record. Glacial retreat occurred before 17,000 cal yr B.P., and tundra-like grassland–shrubland occupied the basin shortly after. Between 16,500 and 14,600 cal yr B.P., a minor regional expansion of forest patches occurred in response to warming, but the basin remained in shrubland. Forest retreated between 14,600 and 13,600 cal yr B.P., at about the time of the Antarctic Cold Reversal. At 13,600 cal yr B.P., a steady progression from shrubland to tall podocarp forest began as the climate ameliorated. Tall, temperate podocarp trees replaced stress-tolerant shrubs and trees between 12,800 and 11,300 cal yr B.P., indicating sustained warming during the Younger Dryas Chronozone (YDC). Stable isotopes suggest increasing atmospheric humidity from 11,800 to 9300 cal yr B.P. Mild (annual temperatures at least 1°C higher than present), and moist conditions prevailed from 11,000 to 10,350 cal yr B.P. Cooler, more variable conditions followed, and podocarp forest was completely replaced by montane Nothofagus forest at around 7500 cal yr B.P. with the onset of the modern climate regime. The Cass Basin late-glacial climate record closely matches the Antarctic ice core records and is in approximate antiphase with the North Atlantic.     

Albian to Coniacian zonation of the Western Coastal Plain of Israel

A planktonic biozonation of the Albian to Coniacian stages for the Western Coastal Plain of Israel, is proposed. Ten zones are described, based on the succession of the following genera: Ticinella, Thamanninella, Rotalipora and Marginotruncana. Chronostratigraphic position of the zones and comparison with both, regional and worldwide biozonation, are discussed.     

Quaternary coastal evolution and vegetation history of northern New South Wales, Australia, based on dinoflagellates and pollen

The Richmond River Valley of northern N.S.W. contains a late Pleistocene succession dating back to approximately 250,000 yr B.P. Dinoflagellate and spore-pollen assemblages from the lowest interval, the lower “Dungarubba Clay” of Drury (1982), indicate deposition in a restricted estuarine environment at approximately 250,000 yr. Deposition in the overlying interval, the upper “Dungarubba Clay” and “Gundurimba Clay”, at approximately 120,000 yr B.P., began in a restricted estuary, but rising sea level caused inundation and deposition in a more open, marine-dominated environment. Dinoflagellate cyst assemblages from the last interglaciation (stage 5) are interpreted by analogy with those from the morphologically similar, modern Broken Bay, N.S.W. They are indicative of an open, marine-dominated environment and imply that barrier formation in the Richmond River Valley, and possibly elsewhere in northern N.S.W., did not commence until after the initial postglacial transgression. Synchronous changes in sea level and rainforest development suggest that there was no significant time lag between climate and sea-level change.     

Quaternary Stratigraphy and Paleogeography of the Galilee Coastal Plain, Israel

The Quaternary deposits in the Galilee coastal plain comprise alternating calcareous sandstone, red loam, dark clay, and uncemented sand. The calcareous sandstone in the lower part of the sequence represents a Pliocene to early Pleistocene marine transgression, and is covered unconformably by the late Quaternary sequence. The base of this sequence has an estimated age of 500,000 yr. It is covered unconformably by marine calcareous sandstone in the west, which represents the global high sea-level stand of isotope stage 7.1, and is known as one of the “Tyrrhenian” events in the Mediterranean area. The overlying members represent the low sea-level stand of stage 6, the first a red paleosol indicating a relatively wet phase and the second an eolianite unit representing a drier phase. The eolianite forms longitudinal, subparallel ridges that formed contemporaneously. The overlying marine sandstone, which contains one of the diagnostic fossils of the “Tyrrhenian” events, the gastropodStrombus buboniusLMK, accumulated during the global high stand of stage 5.5. The last glacial period left no sedimentary record. The Holocene is represented by a marine clay unit that is covered by sand. The present study establishes a complete and detailed chronostratigraphic sequence for an eastern Mediterranean beach, which contains the gastropodS. buboniusLMK.S. buboniuson the Galilee coast is attributed to stage 5.5 and, therefore, establishes an east–west Mediterranean correlation, which can be used for linking Mediterranean events to paleo-sea levels and global climate changes.     

Geoheritage values of consanguineous wetland suites on the Swan Coastal Plain,Western Australia

A wide range of wetland types occur on the Swan Coastal Plain of Western Australia. They vary from basins, and flats, to slopes and channels, and vary in size, shape, water characteristics, sediment types, stratigraphy, vegetation, origin, and maintenance processes. The wetlands range from large linear lakes to small round or irregular seasonally damp wetland basins to seasonally flooded flats, to seasonally flooded or permanently flowing channels. Salinity ranges from fresh to saline to hyposaline; and recharge mechanisms from perching of surface-water to wetting and inundation by groundwater, as determined by regional features such as geology, geomorphology, soils, climate and hydrology, and local physical/chemical processes. The Swan Coastal Plain presents a bewildering array, diversity, and complexity of wetlands, but patterns and ordering can be recognised if the wetlands are aggregated into natural groups. The wetlands, in fact, have been aggregated into natural groupings termed ‘consanguineous suites’, resulting in some 30 different formally named wetland suites related to geomorphic setting varying, for instance, from interdune depressions on a beach-ridge plain (the Becher Suite), to karst-formed linear lakes in limestone-ridge country (the Yanchep Suite), to irregular to round, semi-interconnected basins on a quartz sand subdued dune system (the Jandakot Suite), to linear and round basins formed along the hydrological contact between limestone and quartz sand (the Bibra Suite), among others. The variety of wetland types on the Swan Coastal Plain represents geodiversity that needs to be addressed in geoheritage assessments of the State of Western Australia. Further, as repositories of Holocene to Pleistocene sedimentary sequences, the wetlands present significant reservoirs of information on wetland history, climate changes, and hydrochemical history, and are templates on wetland maintenance and functioning, diagnostic for their geologic/geomorphic setting useful for management of wetlands in Western Australia, nationally, and globally. From a global perspective, the diversity and array of consanguineous suites of the Swan Coastal Plain is unique. An understated aspect of the approach in identifying consanguineous suites of wetlands of the Swan Coastal Plain is that in their geological, geomorphological, and hydrological/hydrochemical setting they provide profound insights into gradual and uninterrupted wetland development, sedimentary filling and ecological functioning because, for a given east–west transect, they are located in the same climate setting but in different geologic/geomorphic and hydrochemical settings. They appear to be unrepresented globally, and therefore, in terms of geoheritage, are internationally significant.     

Land subsidence and sea level rise on the Atlantic Coastal Plain of the United States

Land subsidence due to decline in head in confined aquifers, related to municipal and industrial water pumpage, is widespread in the Atlantic Coastal Plain. Although not a major engineering problem, subsidence greatly complicates adjustment of precise leveling and distorts prediction of future sea-level rise. When preconsolidation stress equivalent to about 20 m of head decline is exceeded compaction of fine-grained sediments of the aquifer system begins, and continues until a new head equilibrium is attained between fine and coarse units. The ratio subsidence/head decline is quite consistent, ranging from 0.0064 in southeastern Virginia to 0.0018 at Dover, Delaware and Atlantic City, New Jersey. Higher values are related to the occurrence of montmorillonite as the predominant clay mineral present. Review of tide gauge records indicates that gauges not affected by land subsidence or other local secular effects have been sinking relative to sea level since 1940 at rates averaging about 2.5 mm/yr, of which 0.6 mm/yr is ascribed to glacio-isostatic adjustment to unloading of North America resulting from melting of late Pleistocene glaciers, and about 0.9 mm/yr is ascribed to steric sea-level rise related to ocean warming. The residual 1 mm/yr of relative sea-level rise is not well understood, but may be related to regional tectonic subsidence of the Atlantic coast.     

Holocene vegetation history of the Okanogan Valley,Washington

Haploxylon pine(s) and Artemisia dominated the initial vegetation in front of the receding Okanogan Lobe until ca. 10,000 yr B.P., as revealed by two pollen records in north-central Washington. After 10,000 yr B.P. the macroclimate became warmer throughout the Okanogan drainage as diploxylon pines and Artemisia increased. The Mount Mazama eruption at ca. 6700 yr B.P. is recorded as two stratigraphically separate and petrographically distinct tephra units at Bonaparte Meadows. While there are apparent short-term changes in the vegetation coincident with the ashfall(s), Artemisia continues to dominate the Okanogan Valley until ca. 5000 yr B.P. By 4700 yr B.P. the modern vegetation, dominated by Pseudotsuga menziesii, had become established around Bonaparte Meadows.     

Modelling water-table depth in a primary aquifer to identify potential wetland hydrogeomorphic settings on the northern Maputaland Coastal Plain,KwaZulu-Natal,South Africa

The primary aquifer on the Maputaland Coastal Plain in northern KwaZulu-Natal, South Africa, is the principal source of water for rivers, lakes and most of the wetlands in dry periods, and is recharged by these systems in wet periods. Modelling hydrologic conditions that control regional water-table depth can provide insight into the spatial patterns of wetland occurrence and of the persistence of wet conditions that control their character. This project used a groundwater model (MODFLOW) to simulate 10-year water-table fluctuations on the Maputaland Coastal Plain from January 2000 to December 2010, to contrast the conditions between wet and dry years. Remote sensing imagery was used to map “permanent” and “temporary” wetlands in dry and wet years to evaluate the effectiveness of identifying the suitable conditions for their formation using numerical modelling techniques. The results confirm that topography plays an important role on a sub-regional and local level to support wetland formation. The wetlands’ extent and distribution are directly associated with the spatial and temporal variations of the water table in relation to the topographical profile. Groundwater discharge zones in the lowland (1–50 masl) areas support more permanent wetlands with dominantly peat or high organic soil substrates, including swamp forest and most of the permanent open water areas. Most temporary wetlands associated with low-percentage clay occurrence are through-flow low-lying interdune systems characterised by regional fluctuation of the water table, while other temporary wetlands are perched or partially perched. The latter requires a more sophisticated saturated-unsaturated modelling approach.     

典型滨海平原区地下水流系统水化学场演化及成因:以杭嘉湖平原为例

滨海平原地区地下水流系统水化学场演化过程复杂,同时受古海侵咸化以及现代人类活动影响,当前对其专门分析的研究较少.以杭嘉湖平原为例,综合运用多元统计和水化学分析方法,对采集的78个深层孔隙承压水样品水化学数据进行解译.研究表明:区内水化学分区可划分为"古海侵区"、"径流排泄区"、"海水咸化区",水化学类型依次为Na-Cl...