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A Short History of a Flat Place: Three Centuries of Geomorphic Change in the Croatan National Forest
Abstract
Despite flat terrain, extensive forests, and little urbanization, there has been extensive landscape change in the Croatan area of North Carolina's lower coastal plain in the past 300 years. Culturally-accelerated erosion, sedimentation, and geomorphic change are documented, including mean historic upland surface lowering of 15 to 25 cm, and historic alluvial sedimentation of 70 to more than 200 cm. This recent environmental history is significant beyond the Croatan because it illustrates three critical points. First, human agency can result in rapid and significant geomorphic change, even in geologically stable areas where traditional geomorphic risk factors such as slope and climate variability are low. Second, geomorphic change may not leave obvious visible clues. The scarcity of apparent landform change in the coastal plain has traditionally left the impression that culturally-induced geomorphic change has been minimal, when in fact such changes are comparable to those in other regions generally recognized as having undergone serious land degradation. Third, the impacts of human agency on geomorphic processes can be difficult to recognize when those impacts are intertwined with other geomorphic changes. In the Croatan, some human impacts are similar to those associated with Holocene sea level rise, though greatly accelerated. This makes historic change difficult to distinguish from longer-term Quaternary environmental changes.
... In North Carolina (NC) coastal plain counties, there has been a population increase of 32% from 197732% from to 199732% from and 16% from 199032% from -200032% from (Street et al., 2005Mallin et al., 2000). The growth in coastal areas has increased the anthropogenic effects on these systems, including the degradation of many water bodies due to increased amounts of land-based nutrients and other pollutants like heavy and trace metals, wastewater, herbicides, and pesticides (Paerl, 2006;Buzzelli et al., 2001;Hyland et al., 2000;Pearl et al., 1998;Phillips, 1997;Riggs et al., 1991;Schropp et al., 1990). Water quality was first addressed as a national problem in the 1970s with the passage of the Water Quality Pollution Control Act and the Clean Water Act (USEPA, 2006). ...
... The sediments found in typical coastal plain terraces and scarps are highly weathered sands and clays with very little labile material or minerals (Phillips, 1992). These sediments are classified as low erosion sediments due to their high infiltration capacity, low slopes, and the relatively low sediment yields seen in the coastal plain when compared to Piedmont sediment properties (Phillips, 1997(Phillips, , 1992. The floodplains adjacent to the coastal water bodies are broad areas that are frequently inundated and are important for sediment trapping (Langland and Cronin, 2003;Phillips, 1997). ...
... These sediments are classified as low erosion sediments due to their high infiltration capacity, low slopes, and the relatively low sediment yields seen in the coastal plain when compared to Piedmont sediment properties (Phillips, 1997(Phillips, , 1992. The floodplains adjacent to the coastal water bodies are broad areas that are frequently inundated and are important for sediment trapping (Langland and Cronin, 2003;Phillips, 1997). ...
... Although there has been some assessment of suspended sediment in larger drainage basins on the Coastal Plain (Simmons, 1976Simmons, , 1988), few data are available for small streams, particularly those with drainage areas less than about 10 km 2 . Similarly, the role of drainage ditches as sediment sinks remains poorly studied (Phillips, 1997; Moore et al., 2001; Cooper et al., 2002; Landwehr and Rhoads, 2003). These artificial channels may be important because of recent studies suggesting that little of the soil eroded from uplands is transported very far downstream or, perhaps, even beyond individual agricultural fields (Phillips et al., 1999a,b; Slattery et al., 2002). ...
... Nevertheless , the 4.25-yr record of storage in agricultural drainage ditches at Littlefield is longer than any other reported in the region. While the need to re-excavate makes it obvious that agricultural drainage ditches are aggrading in the region and there has been some documentation of sedimentation rates in artificial channels in wetlands of eastern North Carolina (Belk and Phillips, 1993; Phillips, 1997 ), with the exception of Slattery et al. (2002), we have no knowledge of any other measurements of ditch sedimentation in an agricultural setting. ...
... For example, little evidence exists in the region to suggest that bank erosion is significant (Slattery et al., 2002), and we observed little evidence to suggest its importance at Littlefield. Similarly, colluvial storage at field edges is likely, but these deposits cannot easily be distinguished from accumulations resulting from tillage (Phillips, 1997). Even if our measured sediment yield is unreliably low, or our extrapolation of measured ditch storage to the entire drainage network inflates (or deflates ) that component, the sediment delivery ratio still remains low. ...
Field measurements of drainage ditch sedimentation and suspended sediment transport were used to construct a simple sediment budget and relate seasonal variations in vegetation and the hydrological characteristics of storms to sediment dynamics in a small agricultural watershed in North Carolina. Results indicate that seasonal variations in crop coverage and vegetation in drainage ditches influence sediment delivery. Following the harvesting of crops and mowing of drainage ditches in late autumn, conditions are favorable to soil erosion and sediment transport through early spring. Storms need not be very intense or produce large rainfall totals to transport significant sediment loads. The maturation of field crops and ditch vegetation in spring produces conditions less conducive to both soil erosion and sediment transport. Intense summer thunderstorms, however, are capable of mobilizing and transporting significant amounts of sediment. The computed sediment yield of 0.1 Mg/ha/yr probably represents a low estimate that, nevertheless, is an order of magnitude less than measured ditch storage and more than two orders of magnitude less than regional estimates of soil loss on Coastal Plain croplands. The results show that headwater ditches may be decoupled from slopes so that much of the eroded soil is stored within small watersheds rather than being transported out of the basin.
... It is widely acknowledged that land disturbance associated with Euro-American settlement produced significant changes in river systems (e.g., Beach, 1994;Costa, 1975;James & Lecce, 2013;Knox, 1977Knox, , 1987Lecce, 1997a;Phillips, 1997;Trimble, 1981;Wilkinson & McElroy, 2007), including adjustments of channel geometry (e.g., Simon, 1989). These changes represent adjustments to changing streamflow and sediment inputs during the Anthropocene (e.g., Knighton, 1998;Labbe, Hadley, Schipper, Leuven, & Gardiner, 2011;Leopold, Wolman, & Miller, 1964;Richards, 1982;Zalasiewicz, Williams, Haywood, & Ellis, 2001). ...
... Although the geomorphic literature is replete with studies showing that land disturbance associated with Euro-American settlement produced significant changes in river systems (e.g., Beach, 1994;Costa, 1975;James & Lecce, 2013;Knox, 1977Knox, , 1987Lecce, 1997aLecce, , 1997bPhillips, 1997;Trimble, 1981;Wilkinson & McElroy, 2007), one of the challenges in quantifying these changes is establishing a reference for conditions prior to settlement (see for example Rhoads & Herricks, 1996). The approach adopted here relied on archival data recorded in the original General Land Office (GLO) survey notes to reconstruct pre-settlement channel conditions during the 1830s. ...
Discharge and bank resistance have long been considered two of the more important factors controlling downstream changes in stream channel geometry. Although stream power has been shown to have an important impact on many components of the fluvial system, it has received little use as an explanatory variable in the consideration of questions related to channel geometry. This study examines spatial and temporal changes in channel geometry and stream power in a moderate-sized watershed in the Driftless Area of Wisconsin, USA. Pre-settlement (~1830) channel geometry and stream power estimates derived from General Land Office survey notes were compared with conditions obtained from modern field surveys. Comparison of pre-settlement and modern channels shows that channel width and cross-sectional area have increased considerably during the post-settlement period, producing on average a threefold increase in cross-sectional stream power. When compared to discharge, slope, and bank sediment variables, cross-sectional stream power is more strongly associated with channel shape, explaining a maximum of 47% of the variance in one of the four study reaches. These results are compared with a reanalysis of previously published data from the midwestern USA, in which cross-sectional power also explains more of the variance in channel shape than discharge or bank sediment.
... Rapid and persistent historical change in the fluvial system has been documented in Europe (e.g., Brown 1987;Gurnell, Downward, and Jones 1994;Taylor and Lewin 1996;Coulthard and Macklin 2001;Macklin and Lewin 2003;Zolitschka, Behre, and Schneider 2003) and the United States (e.g., Magilligan 1985;Huckleberry 1994;Phillips 1997;Knox 2001;Urban and Rhoads 2003). In the dry western United States, where vegetation is relatively sparse and channels are often sandy, channel change can be especially dramatic (Evans 1980;Huckleberry 1994;Waters and Haynes 2001). ...
... Channel change in subhumid and semiarid climates has often been linked to climate fluctuations (Graf 1978;Hereford 1984Hereford , 1986Martin and Johnson 1987;Balling and Wells 1990;Huckleberry 1994;Waters and Haynes 2001). Land-use change, which has been identified as a major factor driving historical channel change in the eastern half of the United States (e.g., Knox 1977Knox , 2001Magilligan 1985;Beach 1994;Magilligan and Stamp 1997;Phillips 1997), has played less of a role in driving channel change in subhumid and semiarid climates. ...
Little is known about historical channel change along rivers on the Great Plains of the United States. Focused on a 113 km reach of the Cimarron River, southwestern Kansas, this study revisits the site of Schumm and Lichty's (1963)38.
Schumm , S. A. and
Lichty , R. W. 1963. Channel widening and flood-plain construction along Cimarron River in southwestern Kansas, Washington, DC: U.S. Geological Survey. Professional Paper 352-D. View all references work that documented channel changes between 1874 and 1960. Based on field and archival evidence from Seward and Morton Counties, Kansas, we find that channel narrowing, which began in the 1940s, continues to the present. Between 1953 and 2001, the mean channel width of the Cimarron River decreased by 114 m, or 75 percent, although channel narrowing and the expansion of riparian vegetation were more pronounced in some locations than in others. The channel changes and increase in riparian vegetation both appear to have been caused by a decrease in annual peak flows, which favored in-channel sedimentation and the expansion of riparian vegetation. The decrease in annual peak flows coincided with a reduction in the annual variation in moisture conditions, as measured by the Palmer Drought Severity Index. Agricultural practices and groundwater withdrawals have likely contributed to the decline in peak flows since 1970.
... So, we assessed agricultural, forested, and freeway roadside drainage ditches in North Carolina's Coastal Plain for signs of sustained wetness, soil carbon, and regional wetland indicator statuses of their plant communities (USACE 2010). The at, humid landscape of the North Carolina Coastal Plain remains wet despite heavy drainage for forestry, agriculture, and development, (Phillips 1997). So, we gured that if any ditches anywhere exhibit the full suite of wetland traits, some of these ditches likely would. ...
The drainage ditches of the North Carolina Coastal Plain retain some ecological structural characteristics of the wetlands they often replace. We surveyed 32 agricultural, freeway, and forested ditch reaches across this region for hydrologic indicators, soil organic matter, and plants. All showed at least some hydrologic indicators and had soil organic matter, especially swampy forests. Twenty-nine of 32 had hydrophytic herbaceous plant assemblages according to US Army Corps of Engineers wetland delineation standards. These herbaceous assemblages differed significantly across site types, and responded to both landscape level factors, like nearby development coverage, and local level factors, like apparent mowing. The US National Hydrography Dataset and the National Wetlands Inventory did not include most sample sites, and mischaracterized most they did include as natural waterbodies. Despite limited information about extent of these ditches, high variability and apparent management impact suggest that human potential to design wetland structure of these manmade aquatic ecosystems throughout the North Carolina Coastal Plain, and beyond, could be large.
... Each of the sites are in the Atlantic Coastal Plain geological province, where geomorphologic changes have occurred [31] . Fort Matanzas NM is located on the Southeastern Coastal Plain geologic province, specifically in the east central Floridan aquifer system ( Figure 1). ...
Changes in sea level along the coastal southeastern United States (U.S.) influence the dynamic coastal response. In particular, the Southeast Coastal Network (SECN) of the National Park Service (NPS) has exhibited evidence of fluctuations in sea level which caused coastal erosion. Airborne LiDAR acquired from NOAA for Fort Matanzas National Monument, Fort Pulaski National Monument, Charles Pinckney National Historic Site, and Cape Lookout National Seashore were analyzed to identify changes in both elevation and the spatial volume of unconsolidated sedimentary material in the coastal southeast over time. Areas that exhibited an increase (deposited material) or decrease (eroded material) in elevation were mapped across the study area from 2006 to 2018. Results indicate a quasi-cyclic process where unconsolidated sediment distribution and the morphodynamic equilibrium changes with time. The coastal zones are steadily oscillating between the process of erosion and deposition affecting the coastal geomorphological dynamic. The use of LiDAR for evaluating coastal sustainability and resiliency due to this environmental phenomenon is clear.
... Suspended sediment is cited as the most prolific water pollutant (USEPA 2004(USEPA , 2006 and therefore studying sediment dynamics within coastal tributaries and estuaries is critical to better management. It is commonly found that sediments introduced to coastal systems are chemically and physically bound with terrestrially based nutrients and other sediment associated pollutants (e.g., heavy and trace-metals, herbicides, pesticides) and ultimate degradation of these water bodies (Schropp et al. 1990;Riggs et al. 1991;Phillips 1997;Paerl et al. 1998;Hyland et al. 2000;Buzzelli et al. 2001;Paerl 2006;). In shallow coastal tributaries and estuaries, there is continuous exchange and deposition of particlereactive materials between the water column and bed sediment (Giffin and Corbett 2003). ...
Urbanization and human-led development have increased more rapidly along shorelines and in coastal watersheds than inland regions over the past century. The result of major land use changes for both urban tracts and agriculture to serve the urban areas, as well as infrastructure development is increased runoff carrying sediments, nutrients, pollutants, pharmaceuticals, and toxins downstream to estuarine systems. The increased runoff levels are only the tip of the iceberg, with human development resulting in increased fecal bacteria from urbanization and excess nutrients from agriculture leading to harmful algal blooms. Estuaries act as a natural filter between land and sea, but have been overloaded by the influx of sediments and pollutants in recent decades. As a result, there have been a variety of impacts to estuarine ecosystems and water quality including increased sediment load, eutrophication, harmful algal blooms, fecal bacteria, as well as shellfish and fisheries declines. In some estuarine systems, the reduction in light penetration to the benthos has led to the loss of seagrasses. In others, seasonal hypoxia is a visible symptom of prolonged eutrophication. There is a need to augment long-term monitoring techniques with new technologies and data processing methods to better understand the current state of estuaries and work towards mitigating human impacts on estuarine ecosystems and water quality.
... Finally, the effects of historical human alterations have in some cases been forgotten if the activity that triggered the alteration is no longer occurring (e.g., Phillips, 1997). Forgotten in this context refers to society as a whole. ...
Logging, urbanization, and dam building are a few ways people have significantly altered natural river ecosystems. Understanding that influence is a grand challenge of our time.
... Finally, the effects of historical human alterations have in some cases been forgotten if the activity that triggered the alteration is no longer occurring (e.g., Phillips, 1997). Forgotten in this context refers to society as a whole. ...
Legacies are persistent changes in natural systems resulting from human activities. Legacies that affect river ecosystems can result from human alterations outside of the river corridor, such as timber harvest or urbanization, or from alterations within the river corridor, including flow regulation, river engineering, and removal of large wood and beaver dams. Human alterations of river ecosystems have been occurring for thousands of years in some parts of the world and are now ubiquitous, yet both river scientists and the public may be unaware of the persistent effects of historical activities. Failure to recognize the legacy of historical activities that no longer occur can skew perceptions of river process and form and the natural range of variability in river ecosystems. Examples come from rivers of the Mid‐Atlantic Piedmont and the Pacific Northwest regions of the United States. Mid‐Atlantic Piedmont streams in which legacy sediment accumulated behind now‐abandoned mill dams experienced a complete transformation from wide, shallow, marshy valleys to sinuous rivers lined with tall cutbanks, but the existence and the cause of this river metamorphosis was not widely recognized until the first decade of the 21st century. Rivers of the Pacific Northwest from which large wood was removed have changed during the past century from spatially heterogeneous, multichannel systems closely connected to their floodplains via frequent channel avulsion and lateral migration to single‐thread channels with more homogeneous floodplains and less lateral connectivity. Again, this river metamorphosis has only been recognized within the past two decades. In each of these regional examples, river process and form have changed so substantially that the river ecosystems can be described as having assumed an alternative state. In these and many other examples, the alternative state provides lower levels of ecosystem services such as habitat, biodiversity, and attenuation of downstream fluxes of water, sediment, organic carbon, and nutrients. River management designed to enhance and restore these ecosystem services can be more effective if the continuing effects of these historical legacies are recognized. The grand scientific challenges resulting from historical human alterations of river ecosystems include the following: (1) to recognize the existence of a legacy that continues to affect river ecosystem process and form; (2) to understand the source of the legacy with respect to chronology, type, spatial extent, and intensity of human activities; (3) to understand the implications of the legacy regarding how river process and form and river ecosystem services have changed; and (4) to design management or restoration strategies that can mitigate the loss of river ecosystem services. In summary, the existence of forgotten legacies challenges river scientists to recognize the continuing effects of human activities that have long since ceased and also poses challenges for the application of scientific understanding to resource management. Societal expectations for attractive, simple, stable rivers are commonly at odds with scientific understanding of rivers as dynamic, spatially heterogeneous, nonlinear ecosystems. Knowledge of how human actions, including historical actions that have long since ceased, continue to alter river ecosystems can help to bridge the gap between societal and scientific perceptions of rivers.
... The CNF was created in 1936 by Theodore Roosevelt as part of a New Deal program to shift land from agricultural use to timber production (Jacobs 2002). The forest has been successfully managed for wood products up to the present date, with significant areas used for loblolly pine (Pinus taeda) production in 30-35 year rotations (Phillips 1997). Although the forest continues to produce timber, the most recent Land and Resource Management Plan (LRMP) for the CNR places a great deal of emphasis on ecological restoration and preservation, as well as on recreation and non-timber forest products. ...
... The dam can be a small milldam or water-supply weir that backs up water for a distance that is only a few times longer than the average channel width (Walter and Merritts, 2008;Pizzuto and O'Neal, 2009) or the dam can be a very large structure taller than 15 m that creates a backwater extending for tens of kilometers upstream. Smaller dams might seem inconsequential, but they are seldom built in isolation: river networks with these structures are likely to have tens to hundreds of them (Phillips, 1997;Walter and Merritts, 2008;Pizzuto and O'Neal, 2009). The amount of sediment accumulating behind any dam reflects the rate at which sediment is supplied to the reservoir, the trapping efficiency of the reservoir (i.e., the ratio of deposited sediment to the total sediment inflow for a given period, which is typically a function of drainage area and reservoir storage capacity), the number of upstream reservoirs trapping sediment (e.g., Yang and Lu, 2014), and the length of time the dam has been in place. ...
Legacy effects on river sediments are those which alter the location and volume of sediments and/or presence of contaminants within the sediments as a result of human activities. This review broadens the typical definition of legacy sediments and discusses human activities that create legacy effects on sediments in terms of three categories: activities that reduce sedimentation within river corridors – defined as channels, floodplains and riparian zones, and hyporheic zones; activities that enhance sedimentation in river corridors; and activities that contaminate river sediments with diverse pollutants. People reduce sedimentation within river corridors via three basic mechanisms: reducing sediment supply to the river corridor through changes in land cover or by trapping and storing sediment within the river corridor; increasing the ability of a river to transport sediments downstream by either increasing water supply to the channel or reducing physical channel complexities that promote flow separation, hydraulic resistance, and sedimentation; and disconnecting channels from floodplains, which are typically sediment storage zones and sediment sources for the channel. Conversely, enhanced sedimentation within river corridors results from increased sediment supply from uplands or upstream river segments and from decreased ability of a river to transport sediments downstream. Contamination of river sediments can result from nearly every conceivable human activity within a drainage basin (e.g., deforestation, agriculture, urbanization, industrial facilities, wastewater treatment). Contaminants can also enter a drainage basin from sources outside the basin boundaries because of contaminant transport within the tissues of migratory animals and via atmospheric deposition. Because many contaminants travel adsorbed to sediments, these pollutants can be concentrated within river corridors by activities that enhance sediment deposition. Legacy effects on sediments are now ubiquitous and abundant within river corridors around the world and can continue to alter river form and function long after cessation of the human activity that created the legacy. River management must be informed by accurate knowledge of the distribution and characteristic of legacy effects on sediments and geoscientists can contribute specialized knowledge to understanding and managing these sediments.
... The conversion of forests to agricultural and urban lands has altered runoff and sediment transport within the Coastal Plain (Phillips, 1997;Hupp, 2000). In the Tables 1 and 2. Cross-sections and more detailed site maps are provided in Soban (2007). ...
Stream channel response to urban land use has not been well documented for southeastern Coastal Plain streams. In this study, urban channel response was evaluated in small Inner Coastal Plain watersheds (<5 km2) in eastern North Carolina. Reaches were selected across a range of watershed total impervious area (0-67% TIA). Channel dimensions and sediment grain size data were collected along 20 urban (>10% TIA) and 20 rural reaches (<10% TIA), and at 10 stormwater outfall sites (180 cross-sections). Urban cross-sectional area, channel incision ratio, and channel grain size (gravel%, D50, and D84) were greater, relative to rural channels. Bankfull cross-sectional areas were approximately 1.78 times greater for urban watersheds than for rural watersheds. Channels in urban watersheds were incised and had median full-channel capacities approximately 3.4 times greater than channels draining rural watersheds. Watershed TIA explained 65-72% of channel capacity enlargement. Urban expansion in the region began in the 1960s, with major urbanization occurring over the last 25 years. Channels draining urban watersheds are still responding to this land use change by downcutting and widening. Urban channel incision has frequently cut off streams from their floodplains, reducing floodplain sediment retention and water quality functions.
... My own metamorphosis stories are characteristic of another common variety, explicating landscape transformations driven by human agency (e.g., Phillips, 1997). ...
Reporting results and promoting ideas in science in general, and Earth science in particular, is treated here as storytelling. Just as in literature and drama, storytelling in Earth science is characterized by a small number of basic plots. Though the list is not exhaustive, and acknowledging that multiple or hybrid plots and subplots are possible in a single piece, eight standard plots are identified, and examples provided: cause-and-effect, genesis, emergence, destruction, metamorphosis, convergence, divergence, and oscillation. The plots of Earth science stories are not those of literary traditions, nor those of persuasion or moral philosophy, and de-serve separate consideration. Earth science plots do not conform those of storytelling more generally, imply-ing that Earth scientists may have fundamentally different motivations than other storytellers, and that the basic plots of Earth Science derive from the characteristics and behaviors of Earth systems. In some cases preference or affinity to different plots results in fundamentally different interpretations and conclusions of the same evidence. In other situations exploration of additional plots could help resolve scientific contro-versies. Thus explicit acknowledgement of plots can yield direct scientific benefits. Consideration of plots and storytelling devices may also assist in the interpretation of published work, and can help scientists improve their own storytelling.
... Landscape-scale groundwater fluxes from the flat upland interfluves toward the valley side slopes has effects on soil chemistry, morphology, and results in some cases in the formation of valley side ferricretes (Daniels et al., 1975; Phillips et al., 1997; Phillips, 2000). Historically, at least, soil erosion and deposition is also active in truncating or thickening soil profiles (Cooper et al., 1987; Phillips, 1993; Phillips, 1997b; Phillips et al., 1999a,b; Slattery et al., 2002). In the study sites, soils are formed above the zone of water table fluctuation for the most part, and the development of vertical textural contrasts is not directly influenced. ...
Soils and weathering profiles in a wide variety of parent materials and environmental settings exhibit coarse-over-fine vertical textural contrasts. Where these cannot be attributed to inherited texture contrasts or erosion–deposition, the most common explanations are based on translocation (eluviation–illuviation) which removes clays from surface layers and deposits them in the subsoil; or bioturbation, where preferentially fine material is delivered to the surface by organisms, from whence erosional winnowing creates a coarse surface layer. In some soils of the lower coastal plain of North Carolina, U.S.A., neither explanation is sufficient to explain the observed texture contrasts. A heuristic model based on a combination of translocation of fine material from surface to subsoil, and bioturbation-driven delivery and recycling of material to the surface can explain the observed vertical textural contrasts. The key elements in the model are coastal plain sediments which include some fine material; eluviation–illuviation by percolating water; delivery of additional fine and mixed grain size material to surface by bioturbation, making it available for translocation; concentration of fine material originally scattered throughout the parent material in a B horizon; and maintenance of vertical moisture fluxes by bioturbation. The model is supported by morphological evidence of the key mechanisms, argillic horizons that are finer than both the surface layers and underlying parent material, evidence that argillic horizon formation is not limited by the rate of clay synthesis, and the absence of texture contrasts in nearby soils formed from dune sands which lack fines.
... Instead, most of the soil may be redistributed within individual fields or stored very near the source in headwater portions of the drainage network. In agricultural landscapes on the Coastal Plain, these headwater networks consist of drainage ditches and canals whose roles as sediment sinks remains poorly understood (Phillips, 1997;Moore et al., 2001;Cooper et al., 2002). ...
This paper examines the role that slope-channel linkages and seasonal vari- ations in vegetation play in explaining spatial and temporal variations in sediment flux through agricultural drainage ditches in eastern North Carolina. We used biannual cross- sectional surveys of drainage ditches to assess erosion/deposition during a five-year period in the headwaters of a small agricultural watershed. Although net accumulations of sedi- ment were observed in three-fourths of the cross sections surveyed, the rate of sedimenta- tion varied considerably from ditch to ditch and cross section to cross section. The ditches were sediment sinks during the growing season in summer and autumn when they became choked with dense vegetation growth, and more hydraulically efficient after removal of vegetation in December during annual maintenance operations. The ditches experienced erosion or modest deposition while the vegetation was dormant during the late winter/ early spring. Sediment was delivered to the ditches from isolated gullies that linked the primary source of sediment, soil eroded on agricultural fields, to the channels. Except for these isolated linkages, ditches and fields are largely decoupled. (Key words: drainage ditches, sedimentation, Coastal Plain, North Carolina.)
... G eographic research has extended our understanding of the temporal and spatial scales of human action in shaping landscapes formerly considered natural or little altered (Denevan 1992;Phillips 1997;Cowell and Dyer 2002) and the ways that human-altered nature can be defined and related to culture and environmental issues (Fall, Lines, and Falconer 1998;Eden 2001). It is now difficult to say that the vegetation and landforms in any landscape presently devoid of humans have not been at least partly altered by direct human action on site in the past or by indirect human action off site. ...
The surface characteristics and dimensions of many beaches reflect past inputs of sediment due to human activity in tributary drainage basins. Subsequent control of erosion in drainage basins, changes in flow regimes of streams, and construction of shorefront structures have reduced sediment input and eliminated beach area in many coastal segments, leading to calls for artificial beach nourishment. This study evaluates the compatibility of sediments delivered as a result of human activity in terms of the appearance and utility of beaches by comparing sites on Elba Island, Italy. Beach morphology, mineralogy, grain size, and roundness of sediments were determined for five sites where sediments were introduced by artificial nourishment, by erosion of spoils from iron mines, and by stream flow through agricultural or mining lands. Size, sorting, angularity, and color of sediments determine their acceptability by beach users. These characteristics were determined by evaluating the mineralogy and method of delivery of sediment (rivers, bluff erosion, and artificial replenishment) and subsequent modification by wave and human action. Wave energy and time are critical to the reworking of sediments to achieve more natural characteristics, but these constraints can be overcome by more careful selection of the mineral characteristics of fill sediments, prewashing fill sediments to remove silts and clays to reduce turbidity, grading nourished beaches to cycle sediments into the wave and swash zones to cause better rounding of sediments, or raking the beach to create the sandy backbeach that is favored by beach users.
... Over the last 300 years, the conversion of forest to agricultural land in the North Carolina Coastal Plain has resulted in significant erosion from upland areas (Phillips, 1997). Many of the floodplain forests along the Atlantic Coastal Plain experienced substantial aggradation in the 18th and 19th Centuries following deforestation and agricultural conversion (Hupp, 2000). ...
This study evaluates the effects of urban land use on stream channels and riparian ground-water levels along low-order Inner Coastal Plain streams in North Carolina. Six sites with stream catchments of similar size (1.19-3.46 km2) within the Tar River Basin were selected across an urban land use gradient, as quantified by a range of catchment total impervious area (TIA; 3.8-36.7%). Stream stage and ground-water levels within three floodplain monitoring wells were measured manually and using pressure transducers from May 2006-June 2007. Channel incision ratio (CIR), the ratio of bank height to bankfull height, was also measured at each monitoring site and along stream reaches within the study area (12 urban and 12 rural sites). Riparian ground-water levels were inversely related to catchment TIA (%). As TIA (%) and stormwater runoff increased, the degree of stream channel incision increased and riparian ground-water tables declined. In urban floodplains (>15% TIA), the median ground-water level was 0.84 m deeper than for the rural settings (<15% TIA). This has resulted in a shift to drier conditions in the urban riparian zones, particularly during the summer months. CIR was found to be a reliable surface indicator of “riparian hydrologic drought” in these settings.
... This leads to the essential question, at what point did streams incise? Certainly, in cases where low-head dams played a role in sediment storage [28,29], this incision begins with the breaching of dams whether during the malaria scares in the mid 1800s [30] or in the recent push to re-establish free flowing hydrologic systems [31,32]. However, the accumulation of floodplain sediment occurred throughout the Piedmont, even in areas without extraordinary dam density [33]. ...
Hydrologic science has largely built its understanding of the hydrologic cycle using contemporary data sources (i.e., last 100 years). However, as we try to meet water demand over the next 100 years at scales from local to global, we need to expand our scope and embrace other data that address human activities and the alteration of hydrologic systems. For example, the accumulation of human impacts on water systems requires exploration of incompletely documented eras. When examining these historical periods, basic questions relevant to modern systems arise: (1) How is better information incorporated into water management strategies? (2) Does any point in the past (e.g., colonial/pre-European conditions in North America) provide a suitable restoration target? and (3) How can understanding legacies improve our ability to plan for future conditions? Beginning to answer these questions indicates the vital need to incorporate disparate data and less accepted methods to meet looming water management challenges.
... Land use changes have dramatically altered the Coastal Plain landscape and its hydrology. Over the last 300 years, the conversion of forest to agricultural land resulted in significant erosion from upland areas (Phillips, 1997). Many of the floodplain forests along the Atlantic Coastal Plain experienced substantial aggradation in the eighteenth and nineteenth centuries following deforestation and agricultural conversion and subsequent channel incision leaving floodplains relatively " high and dry " (). ...
... The Newport River is a third-order blackwater stream in eastern North Carolina, U.S.A. that enters the Atlantic Ocean at Beaufort Inlet (Fig. 1). The 310 km 2 watershed drains unconsolidated late Cretaceous to Holocene sandy sediments (Phillips 1997); overall channel gradient from headwaters to estuary is 0.4 m km -1 . The 34 km 2 non-tidal upper watershed has predominantly agricultural and silvicultural land use. ...
Tidal freshwater zones (TFZ) of coastal rivers link terrestrial watersheds to the ocean and are characterized by large, regularly
inundated riparian zones. We investigated the effect of riparian denitrification on nitrogen flux in the TFZ Newport River,
North Carolina (U.S.A.) by developing an empirical model of denitrification and parameterizing it using measured denitrification
rates, sediment oxidation-reduction potential dynamics, and riparian topography. Denitrification rates were measured monthly
in laboratory-incubated sediment cores by using a membrane inlet mass spectrometer to assess net water-borne N2 flux from the cores. Annual average rates of denitrification in three intertidal riparian habitats, emergent marsh, mudflat,
and hardwood forest, were 1864, 1956, and 2018μgm−2h−1, respectively. Laboratory experiments and in-situ monitoring revealed that the temporal lag between tidal inundation and
reduced, denitrifying conditions was 4–5h. Field measurements and remotely sensed data showed that the inundated surface
area during high tide was three times greater than that at low tide. By combining data on denitrification, oxidation-reduction
potential, and topography, the model predicted that the daily denitrification flux constituted 2–15% of the daily riverine
nitrate flux during most of the year and >100% during low discharge periods. Current regional and global nitrogen budgets
thus may overestimate nitrogen delivery to the ocean by not accounting for the TFZ denitrification.
... On geological time scales, sea level oscillations, erosion of the Appalachian Mountains, accretion of the continental shelf, and tectonic uplift led to the formation of a series of marine terraces (Phillips, 1997). These processes continue today and through evolutionary change have drowned stream valleys of the drainage systems to form the large coastal zone of sounds and estuaries seen today (Corbett et al., 2008;Riggs & Ames, 2003). ...
Hyde County lies southeast on the flat coastal plain of North Carolina, part of the Albemarle-Pamlico Peninsula. It encompasses nationally recognized wildlife refuges and provides vital habitat for endangered, threatened, and sensitive species and natural communities. The low topography makes it extremely vulnerable to sea level rise, especially as the isostatic rates are double the global average at 0.2 - 0.4 cm per year. Climatic changes have impacted the ecosystems through rapid erosion rates. Here I measured the estuarine shoreline rate-of-change and identify priority areas, and investigated environmental predicator variables potentially explaining the erosion variability. By delineating the estuarine shorelines of 1999, 2006, and 2009 from aerial photographs in ArcMap, I was able to measure the rate-of-change for the entire study shoreline area. Three distinct areas experienced relatively higher average erosion rates, -2 m yr-1 to -3 m yr-1. Forty percent of the total shoreline length experienced moderate rates, -1 m yr-1 to -1.9 m yr-1, and 50% experienced low rates, 0 m yr-1 to -0.9 m yr-1. Classification and regression tree (CART) analysis selected directional orientation and ditch variables as influencing variables for 1999-2009 interval and 1999-2006 sub-interval. In particular, northeast and east facing shorelines with ditches exhibited the highest erosion rates. In comparison, directional orientation and percent land cultivated were selected for the 2006-2009 sub-interval. Northeast and east and southeast and south facing shorelines with associated greater than 15% cultivated land exhibited relative highest erosion rates. The CART results only explained 10% of the variance within the dataset, which suggests additional environment factors are influencing erosion rates. The most influential predictor variables varied during the latter time period, which suggests changes in landscape interactions greatly determine erosion vulnerability. Further studies should be conducted to evaluate additional environmental variables. Together, these findings and the spatial distribution of vulnerable areas allow The Nature Conservancy to prioritize shoreline areas and focus adaptation strategies to reach overall Climate Change Adaptation Project goals.
... Shorezones occupy a variety of geomorphic settings as sea level intersects land. In low-lying coastal areas of North Carolina, USA, these inherited settings can be roughly grouped into river valleys and interstream divides, or flats (sensu Wells 1928, Daniels 1978, Phillips 1997, the latter dominating the region. Shorezones are well developed on these settings because of their inherently low slope. ...
This study examines the ecological effects of sea-level rise on shorezone in the Neuse River estuary and western Pamlico Sound, NC. Shorezone is defined here in an ecohydrological context as the area of wetland that extends from an estuarine shoreline landward to where the hydrologic influence of sea level diminishes and terrestrial hydrology dominates. The thesis is structured into three chapters, each highlighting a particular scale of analysis (e.g., landscape, shorezone, and plant community). At the landscape scale, the first chapter investigates geomorphology, hypsography, wetland types, and average landscape slope of successive interstream divide units that are submerging relative to rising sea level. A geographic information system (GIS) was used to identify differences between units and translate them into a space-for-time framework consisting of four temporal stages of shorezone transgression: early - upstream migration, intermediate - non-migration, late - over-flat migration, and terminal - non-migration. The framework is intended to provide a better understanding of processes that have led to the current position of shorezones and to anticipate where effects of rising sea level will be the greatest. In the second chapter, species composition and abundance, soil properties and elevation were analyzed at a plant community scale. Communities were arranged into a hierarchical classification according to hydrogeomorphic wetland type (landscape scale), followed by cover type (shorezone scale), and then community type (plant community scale). A detrended correspondence analysis ordination was performed to analyze samples across an apparent salinity gradient. Analyses revealed a strong relationship between soil porewater salinity and the sequence and distance at which plant communities occur between the shoreline and the landward margin of shorezone. The results suggest that these irregularly flooded shorezones simultaneously exhibit mosaic and zonal patterns of vegetation. At the shorezone scale, changes in cover type over time were estimated for an interstream divide unit in the outer estuary. Cover type classes were ranked to detect the extent, direction (e.g., landward vs. seaward migration), and magnitude (e.g., differences in rank) of vegetation change between 1958 and 1998 using the GIS to analyze aerial photographs. Results show that seaward migration of cover types (517 ha) is more than twice that of landward migration (234 ha). This occurs in spite of an estimated 249 ha landward expansion of shorezone (i.e., transgression) caused by an approximate 15 cm rise in local sea level over the 40 yr study period. This information suggests that at shorter temporal scales, landward migration of shorezone vegetation is not aligned with sea-level rise. M.S.
... The average sediment accumulation rates determined for cores from the NRE, Slocum Creek, and Hancock Creek are moderate and reasonable (0.29, 0.36, and 0.36 cm y À1 , respectively; Table 1) compared to previous work. Based on historical alluvium layers, Phillips (1997) estimated sedimentation at a mill dam site within Slocum Creek to be greater than 0.3 cm y À1 , and these sediments were sourced from the adjacent upland areas. Previous studies conducted in the NRE have measured sediment accumulation rates between 0.1 and 0.6 cm y À1 (Cooper et al., 2004;Giffin and Corbett, 2003). ...
The drainage ditches of the North Carolina Coastal Plain retain ecological structural characteristics of the wetlands they often replace. We surveyed 32 agricultural, freeway, and forested ditch reaches across this region for hydrologic indicators, soil organic matter, and plants. All showed at least some hydrologic indicators and had soil organic matter, especially swampy forests. Twenty-nine of 32 had hydrophytic herbaceous plant assemblages according to US Army Corps of Engineers wetland delineation standards. These varied and rich herbaceous assemblages differed among site types, and sorted according to influences including apparent human restriction of vegetation growth, wetness, and surrounding land use. These results suggest that management can nudge agricultural and freeway ditch herbaceous communities to resemble those of forests, which were typically more hydrophytic and native. The US National Hydrography Dataset and the National Wetlands Inventory excluded most sample sites, and mischaracterized most they did include as natural waterbodies. This lack appears not to arise from technical limitations; data and tools to resolve it are well established. These ditches’ underrecognized but likely vast extent, wide ranges of variability, and apparent response to management suggest that humans’ ability to cultivate wetland structure in these manmade aquatic ecosystems throughout the North Carolina Coastal Plain and beyond is already immense, with even larger potential.
The fluvial‐estuarine transition zone (FETZ) of the Neuse River, North Carolina features a river corridor that conveys flow in a complex of active, backflooded, and high‐flow channels, floodplain depressions, and wetlands. Hydrological connectivity among these occurs at median discharges and stages, with some connectivity at even lower stages. Water exchange can occur in any direction, and at high stages the complex effectively stores water within the valley bottom and eventually conveys it to the estuary along both slow and more rapid paths. The geomorphology of the FETZ is unique compared to the estuary, or to the fluvial reaches upstream. It has been shaped by Holocene and contemporary sea‐level rise, as shown by signatures of the leading edge of encroaching backwater effects. The FETZ can accommodate extreme flows from upstream, and extraordinary storm surges from downstream (as illustrated by Hurricane Florence). In the lower Neuse—and in fluvial‐to‐estuary transitions of other coastal plain rivers—options for geomorphological adaptation are limited. Landscape slopes and relief are low, channels are close to base level, sediment inputs are low, and banks have high resistance relative to hydraulic forces. Limited potential exists for changes in channel depth,width, or lateral migration. Adaptations are dominated by formation of multiple channels, water storage in wetlands and floodplain depressions, increased frequency of overbank flow (compared to upstream), and adjustments of roughness via vegetation, woody debris, multiple channels, and flow through wetlands.
The hydrogeomorphic impacts of land use have important ramifications for the fluvial system at all scales, but particularly for small headwater catchments. Most types of land use tend to decrease infiltration capacities and increase storm flows in small watersheds, with hydrologic response being proportionally greater for smaller, more frequent events than for larger ones. Anthropogenic increases in erosion and sedimentation activity are mediated by the sensitivity of watershed sub-systems to disturbance, and sub-system connectivity. This article reviews hydrogeomorphic changes caused by human activities in small watersheds (< 500 km²) over centennial timescales (the past 300 years).
The hydrogeomorphic impacts of land use have important ramifications for the fluvial system at all scales, but particularly for small headwater catchments having stronger hillslope-channel coupling than points further downstream. The focus of this chapter is the impact of widespread, primarily distributed land-use types, including timber production, crop agriculture, grazing, and urban land uses at the small watershed scale. An overview of hydrogeomorphic systems is presented first, followed by a systematic description of hydrogeomorphic impacts of each of the major land-use types, beginning in upland areas and subsequently tracing the propagation of these impacts downstream to and through channel networks. The major impacts are illustrated using important case studies that also serve to demonstrate both commonalities and key differences in watershed responses to different land uses, as well as their range of variability. Most types of land use tend to decrease infiltration capacities and increase storm flows in watersheds, and magnify the effects of small storm events more so than large ones. Among the current ideas and potential directions for future research suggested by this synthesis are refining concepts and analyses of connectivity among watershed elements and sensitivity of different elements to land-use change, in addition to continuing to monitor and/or reconstruct the long-term adjustment of fluvial systems to major historical land disturbances.
Prior research has highlighted the potential for using soil magnetism as a rapid estimator of total cumulative soil loss on cultivated land. In this study, the influences of particle size, choice of magnetic measurement and initial conditions on a proposed model linking surface soil magnetism and soil loss are described and evaluated. Output model curves are generated for several parameter sets corresponding to different model assumptions and physical scenarios. Output is also compared to a new high-resolution surfacial magnetism data set from a cultivated site, Gilbert Farm in northwestern Alabama (USA), to further evaluate the model. Magnetic susceptibility values at Gilbert Farm range from 150 to 220 (×10−8) m3 kg−1 in a control soil profile. The original model output ranges from 180 to 192 (×10−8) m3 kg−1 and many magnetism values in the cultivated area fall outside this range. Introduction of a particle-size sorting correction factor decreases the range of output values and results in even greater numbers of out-of-range observations. However, there is evidence suggesting that particle-size distributions in the upper soil at this site are not strongly affected by differences in water erosion mechanism. Lower tillage depths cause magnetic susceptibility values to come in range, but may be unrealistic and create a twin-value problem for complex magnetic profiles. Use of the remanence (SIRM)/volume susceptibility (κlf) ratio profile, with values ranging from 35 to 120 mA m−1/10−5 SI, instead of magnetic susceptibility as used in the original model, was found to eliminate out-of-range and twin value. Anomalous magnetism values were identifiable and treatable on the high resolution magnetism maps, but other types of natural spatial variation remain at issue.
As geospatial technologies increasingly figure into resource management activities, there is a corresponding need to provide commensurately detailed high resolution spatial data. This study addresses the capacity of rapidly and cheaply acquired mineral-magnetic data to provide detailed spatially distributed assessments of long-term cumulative soil loss from agricultural fields. Model output from a simple distributed implementation of the Revised Universal Soil Loss Equation (RUSLE) and from a field-data-oriented soil magnetism-based erosion model are compared for a small Alabama (USA) farm lot. An undisturbed reference soil toposequence is used as input to the magnetism model, in contrast with earlier studies that relied on a single reference soil profile. Results from this procedure, while likely to be more dependable, proved primarily to further emphasize spatial patterns noted in prior studies. In addition, the use of a toposequence decreased the area over which RUSLE and magnetism models were in agreement. RUSLE underpredicted denudation relative to magnetism-model results over upper slopes, and overpredicted it on lower slopes. The locations of former access roads may explain underprediction on the upper slopes. The differences between the two method outcomes are discussed with regard to the potential for spatial variability in parent materials, the efficacies of non-fluvial soil redistribution processes, and the availability of detailed land use records for the 100+ years of agricultural activities at the site.
Distributed assessments of total soil loss from agricultural fields are important for understanding both on-site and off-site consequences of historical and current erosion. In this study, the potential for using cheap and rapid measurements of soil magnetism to identify relative degrees of total soil loss is tested in a fallow field in northern Alabama. This is accomplished by defining and mapping erosion categories based on two different magnetic measurements, and an existing soil magnetism model describing soil loss in a nearby field. Surface soil magnetism patterns generally accord with Revised Universal Soil Loss Equation soil loss estimates, but may contain more useful information regarding historical soil redistribution (mass balance at a point) for the fallow field tested. Due to current limitations of the technique and the intrinsic complexity of soilscapes, the best use of magnetic surveying at this time is likely to be in rapid erosion reconnaissance.
Until recently a neglected region, renown for limited exposures, the southern United States is becoming an area of geomorphic discovery. This article presents an overview of current geomorphic research in this region, suggesting that despite past problems, academic geographers have made significant contributions to the geomorphology of the South in recent years. Research topics published on the region are highly varied, with some spatial bias as well as topical bias toward fluvial systems. Yet because of the limited historical work, much is unknown about these unique landscapes and their susceptibility to natural and human disturbances, and much benefit is to be gained from both applied and theoretical study of them.
Although many once-deforested areas of the eastern United States are now revegetated, impacts of this disturbance on watershed processes may persist. In this study, lake sediment stratigraphy and magnetism were used to assess the recovery of a small watershed in the southern Blue Ridge Mountains following abrupt reduction of human impacts. Average sediment yields were found to be higher than those of less disturbed basins nearby, and lower than those reported from the early twentieth-century Piedmont Province. Temporal trends in sediment yield appear to reflect both meteorological and land-use histories. Although most of the lake sediment is magnetically similar to bottomland sources, two instances of local upland sediment input, possibly related to human activities, are evident in the record. Interpreting relationships between sediment yield and changing environmental influences is impeded by poor temporal control in the methodology as well as by the intrinsic dynamics of the fluvial system.
Providence Canyon, one of a series of large gullies in the upper Coastal Plain of the southeastern United States, formed as a result of deforestation and agricultural development in the early 1800's. Sediment eroded from the canyon aggraded the floodplain downstream, dammed tributary valleys, and formed North and South Glory Hole lakes (NGH, 4.8 ha and SGH, 2.5 ha). Sedimentary sequences in these lakes include a basal unit (I) of layered sand and clayey-sand overlain by 0.05-0.1 m of mud, fine sand and organic matter, with large fragments of wood (Unit IIa). An upper unit (IIb) 0.29-1.61 m thick consists of silt and clay containing discrete layers of sand. We interpret Unit I as floodplain alluvium deposited before the lakes were dammed, Unit IIa as sediment deposited during the early phase of the lakes when detritus from trees killed by flooding was abundant, and Unit IIb as lacustrine mud deposited after lake levels stabilized, with periodic pulses of sand eroded from Providence Canyon introduced to the lake by backflooding events. Basal dates extrapolated from a 210Pb chronology for the upper part of SGH core suggests that development of the canyon and formation of the lakes began in the 1840's, and that lake levels stabilized by about 1880. Although consistent with historical accounts of the age of Providence Canyon, these dates must be considered as approximate because of uncertainty in extrapolating dates to the bottom of the core.
In contrast, the 210Pb chronology for the upper portion of the core (post 1930) is validated independently using historical climatic records, and indicates that lacustrine sedimentation faithfully records recent land-use change visible in historical aerial photography. An 8-fold increase in lacustrine sedimentation occurred after the clearing of forest near SGH in the 1930's and 1940's, and a 1.5-fold increase occurred because of road construction in the l950's. Individual sand layers deposited between 1830 and 1957 correlate with erosion at Providence Canyon during major storm events. Since then, downcutting and headward incision by the stream draining Providence Canyon have reduced backflooding to the Glory Hole lakes. As a result, the thickness of individual sand layers decreased, although increases in mass sedimentation rates for mud correspond more directly with large precipitation events after channel incision cut off the major source of sediment from Providence Canyon. The results of this study illustrate the value of the lacustrine sedimentary record in assessing geomorphic, climatic, and human-induced environmental change in heavily disturbed landscapes.
A number of hypotheses and conceptual models, particularly those emphasizing nonlinear dynamics and self-organization, postulate increases or decreases in complexity in the evolution of drainage basins, topography, soils, ecosystems, and other earth surface systems. Accordingly, it is important to determine under what circumstances and at what scales either trend might occur. This paper is concerned with changes in soil landscape complexity due to redistribution of sediment by fluvial, aeolian, and tillage processes at historical time scales in an agricultural field system near Grifton, North Carolina. Soil mapping and soil stratigraphic investigations were used to identify and map soil changes associated with erosion and deposition by water, wind, and tillage; reconstruct the pre-agricultural soil pattern; and identify transformations between soil types. The Kolmogorov entropy of the pre- and post- agricultural landscapes was then compared. The soil transformations associated with erosion and deposition created four distinct new soils and made possible new transformations among soil series, increasing the number of soil types from seven to 11 and the number of possible transformations from 14 to 22. However, the entropy and complexity of the soil landscape decreased, with associated increases in information and redundancy. The mass redistributions created a lower-entropy landscape by concentrating particular soils and soil transformations in specific landscape settings. This result is contrary to studies showing a trend toward increasing pedological complexity at comparable spatial scales, but over much longer time scales. These results point to the importance of temporal scale, and to the fact that environmental complexity is influenced by factors other than the number of different landscape units present.
Hydrological drainage/river basins constitute highly heterogeneous systems of coupled natural and anthropogenic water and pollutant flows across political, national and international boundaries. These flows need to be appropriately understood, quantified and communicated to stakeholders, in order to appropriately guide environmental water system management. In this thesis, various uncertainties about water and pollutant flows in drainage/river basins and their implications for effective and efficient water pollution abatement are investigated, in particular for mine-related heavy metal loadings in the Swedish Dalalven River basin and for nitrogen loadings in the Swedish Norrstrom drainage basin. Economic cost-minimization modeling is used to investigate the implications of pollutant load uncertainties for the cost-efficiency of catchment-scale abatement of water pollution. Results indicate that effective and efficient pollution abatement requires explicit consideration of uncertainties about pollution sources, diffuse contributions of the subsurface water system to downstream pollutant observations in surface waters, and downstream effects of different possible measures to reduce water pollution. In many cases, downstream load abatement measures must be used, in addition to source abatement, in order to reduce not only expected, but also uncertainties around expected pollutant loads. Effective and efficient environmental management of water systems must generally also consider the entire catchments of these systems, rather than focusing only on discrete pollutant sources. The thesis presents some relatively simple, catchment-scale pollutant flow analysis tools that may be used to decrease uncertainties about unmonitored water and pollutant flows and subsurface pollutant accumulation-depletion and diffuse loading to downstream waters.
Changes in land use practices following European settlement in the 1830s produced accelerated sedimentation on virtually all valley floors in the Blue River Watershed, Wisconsin. The contamination of sediments by Pb and Zn mining allowed us to calculate cross-valley rates of flood plain sedimentation for three time periods: the pre-mining period (1830–1900), the mining period (1900–1920), and the post-mining period (1920–1997). Most of the eight valley floors examined contained multiple presettlement surfaces. Significantly higher rates of sedimentation occurred on the lower flood plain surfaces, while the terraces were high enough to prevent sedimentation from most floods. Higher rates of sedimentation on the lower surfaces eventually reduced valley floor relief and, consequently, lateral differences in sedimentation rates.Tributaries and larger valleys downstream exhibited differences in the timing and rates of historical flood plain sedimentation. While rates of sedimentation were high during the pre-mining period in tributary valleys, the lower valleys were receiving little or no pre-mining alluvium. Little pre-mining alluvium was found in mid-basin reaches, suggesting that most of the pre-mining sedimentation was limited to headwater locations. During the mining period, lateral channel migration and the development of meander belts increased the conveyance capacity of tributary and mid-basin channels, which decreased overbank flooding and produced lower rates of sedimentation during the post-mining period. The meander belt channels also had an effect on the lower portion of the watershed by increasing flood magnitudes and the transport of sediment downstream, thereby shifting the locus of sedimentation from the tributaries to the larger, lower valleys. Sedimentation rates in the largest, most downstream site were an order of magnitude higher during the post-mining period than any of the sites upstream.
Soil stratigraphy and morphology in a small agricultural watershed on the coastal plain at Clayroot, North Carolina, indicate long-term, decadal-scale patterns of the redistribution of sediment. The most dramatic truncation of the soil profile occurs on convex upper slopes, and suggests tillage and aeolian erosion as the major processes of soil loss. Thicker soils immediately downslope from convexities are consistent with redistribution by tillage, but significant aeolian soil loss also occurs from some fields. Thinner, apparently truncated soils were also associated with relatively steeper lower slope areas where contemporary rilling was observed. The presence of thicker, cumulic soils at toeslopes where small fans are observed at rill termini and about a half meter of alluvium in drainage ditches indicates that water erosion is also quite prominent. Distinctive soil stratigraphy is found in areas of aeolian deposition, where podzolization in sandy surface deposits has created compound soil profiles. On convex slopes, tillage and wind erosion result in net soil loss, with the former dominating on wetter soils and when plowing occurs, and aeolian processes dominating on drier hilltops and when no-till or minimum tillage practices are followed. Soils are thicker immediately downslope from convexities, with thinner soils and rill erosion on lower slopes. Thickened soils and colluvial deposition in the form of thin fan deposits occur at toeslopes and in depressions. The borders of fields often have thicker soils because of aeolian deposition. Water, wind, and tillage processes are all significant in soil redistribution at the Clayroot site, with relative importance in space and time controlled by topography, soil properties, seasonal moisture and vegetative cover, and tillage practices.
Sampling along the River Lahn, a major tributary to the River Rhine that flows through an agrarian region of west-central Germany, reveals that heavy metal pollution occurs outside major industrial regions and mined landscapes. Along a 60-km reach of the river between Marburg and Wetzlar, mean concentrations of Cu, Pb and Zn at depths of 5 and 15 cm in four floodplain transects were greater than background levels. Concentrations declined sharply between 15 and 25 cm. Laterally, concentrations peaked at the bank top and in the near-channel zone of the floodplain. Beyond the near-channel zone (generally up to 100 m from the channel) concentrations were much less and fairly uniform to the valley wall. The clustering of metals close to the channel suggests that they are a fluvial rather than an eolian deposit. During floods of a moderate magnitude, sediments and attached metals are deposited soon after the river overtops its banks. Although the overall store of metals in the valley is less than that along the Rhine, near-channel metal concentrations are similar to those along rivers draining major industrial and mined areas.
With continued climate change, sea-level rise, and coastal development, concern about shoreline dynamics has expanded beyond oceanfront areas to encompass more protected coastal water bodies, such as estuaries. Because estuaries are critically important ecosystems, understanding coastline changes in these areas is necessary for evaluating resource risks. Throughout the recent decades various methods have been developed to calculate shoreline change and multiple parameters have been hypothesized to correlate with estuarine erosion, including fetch, wave energy, elevation, and vegetation. A transect-based approach is commonly used to quantify shoreline change on linear (i.e., ocean) shorelines; however, due to the complex morphology of the estuarine environments, a point-based approach was developed and applied in this study. Shoreline-change rates and additional parameters (i.e., wave energy and shoreline composition) were determined using 1958 and 1998 aerial photography and available datasets. From these data the average shoreline change of Cedar Island, NC is determined to be -0.24 m yr[superscript]-1, with 88% of the shoreline eroding. Of the parameters analyzed, shoreline composition appears to have an important control on shoreline erosion along Cedar Island, whereas wave energy is not significantly correlated with shoreline-change rates. The point-based approach was applied to the trunk of the Neuse River Estuary to analyze parameters associated with estuarine erosion at two contrasting scales, regional (whole estuary) and local (estuary partitioned into 8 sections, based on orientation and exposure). With a mean shoreline-change rate of -0.58 m yr[superscript]-1, the majority (93%) of the Neuse River Estuary study area is eroding. Although linear regression analysis at the regional scale did not find significant correlations between shoreline change and the parameters analyzed, trends were determined at the local scale. Local-scale analysis determined higher erosion rates, higher elevation, and lower exposure and fetch up-estuary. Erosion rates, fetch, and wave exposure increase, while elevation decreases moving eastward, down-estuary. The general trends found at the local scale highlight the importance of the spatial distribution on shoreline-change rates and parameters analyzed within a complex estuarine system, like the Neuse River Estuary. Linear regression analysis between mean fetch and mean shoreline-change rates at the Local Scale determined an equation to predict shoreline-change rates. Predicted shoreline-change rates overestimate erosion on extremely high fetch shorelines and underestimate erosion on shorelines classified as sediment bank. Overall, the model is conservative in predicting shoreline-change rates by underestimating erosion and accretion within the Neuse River Estuary. Further analysis of mean fetch by specific vegetation type may offer additional insight into the influencing forces on estuarine shoreline change. M.S.
Rivers crossing coastal plains are often inefficient conveyors of sediment, so that changes in upstream sediment dynamics are not evident at the river mouth. Extensive accommodation space and low stream power often result in extensive alluvial storage upstream of estuaries and correspondingly low sediment loads at the river mouth. However, gaging stations with sediment records are typically well upstream of the coast, and thus tend to overestimate sediment yields by under-representing the lower coastal plain and because there is often a net loss of sediment in lower coastal plain reaches. Studies of alluvial sediment storage have generally focused on accommodation space, but, using examples from Texas, we show that low transport capacity controlled largely by slope is a crucial factor.
Spatial variability of soil types and surface horizon thickness were investigated along a 0.2 km transect near an upland valley side slope in the North Carolina Coastal Plain. Previous studies have shown a variable but systematic pattern of soil properties and surface thickness near such "dry edges." The edge effect model successfully predicts the highly variable pattern of soil cover found at the study site, and explains the generally thick (mean ~1 m) surface horizon thickness on the upland portion of the site. It does not explain the 10-fold variation in A and E-horizon thickness (15 to 152 cm) over less than 200 m, the irregular spatial pattern, and the lack of any trend with respect to distance from the dry edge. The broad-scale patterns governed by drainage and topographic factors have superimposed short-range variability, probably associated with biological factors such as tree throw and faunalturbation.
It has been suggested that sediment dynamics of the upper and lower basins of large rivers of the North Carolina Coastal Plain are decoupled. The argument depends in part on sediment discharge from coastal plain uplands sufficient to account for observed alluvial storage and to dilute upper basin sediment. A synthesis of recent work shows extensive historical upland erosion in the region, coupled with limited sediment delivery to estuaries. This points to extensive storage. Further, estimates of slope-to-stream sediment delivery in the coastal plain, based on threshold drainage areas, suggest that sediment discharge is sufficient to account for the upper 70 cm of all flood plains having a mineral soil and a dominantly coastal plain sediment source. This supports upper and lower basin decoupling, but suggests that it may be unique to the historic period.
The loss of mesic hardwood forests on the North Carolina coastal plain has attracted little notice. The area of hardwood forests before European contact was greater than that covered by longleaf pine forest. Remnants of mature longleaf pine ecosystems are present, but mature hardwood ecosystems are almost eliminated from well-drained soils. A case study of three North Carolina counties shows that virtually all the virgin or mature upland forests have been lost. No more than 25 percent of that area is capable of succeeding to mature forest within a century. Landuse trends suggest that few uplands now succeeding to hardwoods will remain undisturbed.
Dendrogeomorphic techniques were used to describe and interpret the spatial and temporal patterns of sedimentation in the
Black Swamp, located along the Cache River in eastern Arkansas. At 30 sites along four transects, 148 trees were examined
for depth of sediment accretion and cored for age determination. Tree-ring and geomorphic analyses indicated that mean sedimentation
rates were significantly related to site elevation, topographic position, and the distribution of tupelo gum and bald cypress.
Maximum mean rates of sedimentation, as high as 0.60 cm/yr, generally occurred in sloughs, areas low in elevation, and where
tupelo gum and bald cypress grow. Mean sedimentation rate appeared to have a negative exponential relation with increasing
elevation. Tree-agc class data indicated a significant increase in sedimentation rate since about 1945, from a mean at or
below 0.01 cm/yr to a mean of 0.28 cm/yr for the past 19 years. Dendrogeomorphic techniques provide valid estimates of sedimentation
rate and allow for the integration of decades of depositional processes in the rate calculation.
Sediment budget for four large (> 1000 km2) drainage basins in the Piedmont physiographic province of North Carolina were estimated from data compiled during erosion and sedimentation surveys. Budgets for the Upper Tar, Upper Neuse, Haw and Deep River basins showed broadly similar trends in allocation of eroded sediment among yield and storage. Sediment yield as a percentage of mean annual gross erosion within the basins averaged 10%. This was less than the rate of alluvial storage, which averaged 14% of annual gross erosion. About 76% of the mean annual erosion was stored as colluvium on hillslopes. There are relatively small differences in sediment delivery and storage ratios among the study basins. This suggests that the relative order of magnitude of the allocation of eroded sediment for southern Piedmont rivers is colluvial storage, alluvial storage and yield. Of the sediment that does reach the streams, more than half is stored as alluvium on an average-annual basis. Aggrading channels and floodplains, siltation of benthic habitats and sediment pollution problems are thus likely to persist unless dramatic reductions in upland erosion or in sediment delivery to streams are realized. With respect to longer-term basin evolution, results point to the need for an improved understanding of the temporal scales of colluvial and alluvial sediment storage.
Since 1492, when Columbus 'discovered' America, the world has been moving toward an increasingly integrated global economy, higher population levels and consequently greater resource demands, and an increasingly precarious state of the biosphere. These developments play a major part in both modern history and in daily life. Understanding their interrelationships and development is crucial to the future of humanity and of the Earth, and is the unifying theme of this collection of readings.
Tables of precipitation probabilities, extremes, and gamma distribution parameters are presented for climatological weekly, biweekly, and triweekly periods for 76 North Carolina location. Calculations are based upon an algorithm which estimates the parameters of the incomplete gamma distribution based on 30 or 50 years of daily rainfall data obtained from the HISARS data acquisition system.
The Atlantic Coastal Plain of the United States has long been considered to have negligible soil erosion owing to low relief and permeable soils. Several recent studies point to a need for reassessment. Post-settlement erosion on the North Carolina Coastal Plain was estimated at the regional scale based on soil-profile truncation of a representative upland soil (Norfolk series). Apparent post-settlement soil-profile truncation ranges from 2.5 to 30 cm (mean 14.5 cm), implying a minimum regional average rate of 0.55 mm/yr since the region was settled in the 1700s. This amounts to a conservative estimated average rate of 9.3 t/ha/yr, a rate of the same general magnitude as estimated erosion rates in the North Carolina Piedmont, long recognized as a problem erosion area. Results imply accelerated water erosion despite the low slopes and permeable soils, and suggest the possibility of significant eolian erosion in the region. This rapid erosion in an area noted for its geological stability is a testament to the importance of vegetation cover and human agency in landscape evolution in the Coastal Plain.
Sediment delivery ratios (SDR) were computed for a 1736 ha, mixed land use, agricultural Coastal Plain watershed, based on observed sediment yield and computed gross erosion by the USLE method and an experimentally determined soil erodibility factor. Considerable seasonal variation in SDR values was observed. This variation was not adequately explained by seasonal variation in rainfall and/or runoff.-from Authors
High-resolution seismic data suggest that portions of depositional sequences representing as many as 18 Quaternary sea-level highstands are preserved within 60 m of Quaternary deposits in northeastern North Carolina. High-frequency, sea-level cyclicity dominated the depositional patterns of the resulting Quaternary sediment sequences. As high-energy coastal systems moved repeatedly across the low-gradient continental shelf, sediment units that had previously been deposited in coastal and shelf environments were significantly modified. During each glacial episode, fluvial channels extensively dissected previously deposited coastal facies. Subsequent deglaciation and transgression flooded the channels, backfilling them with fluvial and estuarine sediments. The infilled channel facies were then partially truncated by shoreface erosion, which also eroded portions of previously deposited coastal sequences. During sea-level highstands, a new sequence of coastal facies was deposited over the ravinement surface cut into remnants of older and similar Quaternary sequences and the associated channel-fill systems. -from Authors
Morphologic analysis of sinuosity, width-depth ratios, and convergence characteristics reveals three compartments: 1) bay-mouth, 2) estuary funnel and 3) meander zone. Each compartment exhibits a characteristic lithofacies reflecting different proportions of wave, tidal and fluvial energy. These lithofacies form a longitudinal tripartite pattern, ie, sand-mud-sand, with coarse-grained sediment at the energetic ends of the system. -from Authors
Two approaches were used: 1) deposition estimates based on changes in depth to the argillic horizon along transects from fields to streams and 2) calculations of mass of deposition derived from estimated 100yr upland erosion based on the universal soil loss equation and a sediment delivery ratio. The average annual rate of sediment deposition on this watershed during the 1880-1979 period was 35 to 52Mg ha-1yr-1. These data suggest that riparian ecosystems are important sinks for sediments. -from Authors
A review of advances in the management of soil erosion under natural meterological conditions during the last decade. Headings are: 1) erosion plots; 2) surveying techniques (a) erosion pins and profilometers, b) photogrammetry); 3) tracers (largely 137Cs). -K.Clayton
Contents
Chapter I. Introduction
Chapter II. The Limited Extent of Erosion on the Piedmont at the Time of European Settlement
Chapter III. The Settlement of the Piedmont by Europeans and Associated Increasing Erosive Land Use, 1700–1860
Chapter IV. The Period of Greatest Erosive Land Use, 1860–1920
Chapter V. The Decrease of Erosive Land use from 1920 to the Present
Chapter VI. Summary, Conclusions, and Prospects
Appendix A. Discussion of Erosive Land Use Data by Years
Appendix B. Changes in Soil Conservation Techniques, 1700–1967
Appendix C. The Importance of Abandoned Land to Erosive Land Use
Appendix D. The Relation of Slavery and Plantation Agriculture to Erosive Land Use
Appendix E. The Relation of Tenancy to Erosive Land Use
Appendix F. Determination of CountyAreas, 1840–1920
Despite extensive reclamation efforts emplaced in 1936, widespread gully erosion continues to affect loess bluffs which were deforested and cultivated between 1850 and 1935. The geomorphic instability introduced into the system by the increased runoff and sediment yield is burying historical materials in the larger gully bottoms. Radiocarbon-dated wood indicates that sedimentation rates have increased 20-fold in the last 100 years and are almost three magnitudes greater than during the period 4000-2000 BP. -Author
Two principal theories have been proposed to explain the origin of stone-lines in Quaternary landscapes, namely the erosion-pedimentation-pedisedimentation theory and the dynamic denudation-soil evolution-biomantle theory. These theories, each of which has its advocates, are compared by means of schematic chronograph analysis. We conclude that the dynamic denudation model best explains stone-line genesis and the soils in which stone-lines occur on many interfluves in mid-latitudes and on many saprolite landscapes in the subtropics and tropics. [Key words: biomantle, chronograph, denudation, landscape evolution, pedimentation, pedogenesis, soil evolution, saprolite.]
Soil erosion and deposition were estimated using Cs-137 activity within a 7.25-ha field/forest system in the southeastern coastal plain. Sol eroded from the field was deposited both in the riparian forest ecosystem and in downslope areas of the field. Total activity, depth to peak activity, and depth to zero activity increased downslope from field to stream. Erosion and deposition rates, estimated by changes in activity per unit area from a reference undisturbed forest site, showed that about twice as much total deposition had taken place as total erosion. Excess deposition was attributed to deposition from the upstream portions of the watershed. Erosion and deposition rates estimated with this method were about 63 and 256 Mg/ha/yr, respectively. Erosion and deposition rates estimated by two different calculation techniques were nearly identical. These rates were considerably higher than rates estimated in an earlier study. The rates may be overestimated because the differential rates of Cs-137 movement on clay particles were not considered. The riparian ecosystem acted as a very efficient sediment trap. 19 refs., 5 figs., 3 tabs.
The study area consists of a first-order drainage basin about 10 ha in size. The hillslopes have mean gradients of 6 to 10% with overland flow the primary contributor to erosion. A detailed geomorphic map of the watershed was constructed on a 1-m topographic survey base map. Map units were delineated based on slope shape, gradient, and USDA erosion class. Erosion classes were determined for the transect pedons by comparison with two uneroded and uncultivated pedons in area cemeteries with similar slope gradient, slope shape, slope length, and landscape positions. The A horizon thickness and organic C content decreased and clay content increased as a consequence of cultivation and erosion. Transect data for all hillslope geomorphic units showed the erosion classes near the shoulder to be either slightly or moderately eroded. The lower backslopes and upper footslopes, just above the sediment basin, were either severely or very severely eroded, suggesting slope length to be the dominant factor affecting erosion. The geomorphic units with concave across-slope shapes were found to be less eroded than those with convex across-slope shapes. -Authors
We have developed a new x-ray spectrograph procedure for quantifying the extent of soil loss from erosion. As a soil erodes, the mass absorption coefficient line is altered. This procedure was tested using soils with argillic horizons and should be useful for soil erosion studies in areas having Alfisols, Ultisols, and Mollisols with argillic horizons. -from Authors
The hydrologic effects of three methods of intensive site preparation—brush chopping, shearing and windrowing, and bedding on contour—were measured during the 1976 and 1977 water‐years on three small watersheds on steep terrain in northern Mississippi. After site preparation, the treated watersheds were fertilized, limed, sown with clover ( Trifolium subterranean L.), and planted with loblolly pine seedlings ( Pinus taeda L.). An undisturbed watershed served as a control. Site preparation exposed soil on 37% of the chopped watershed, on 53% of the sheared and windrowed watershed, and on 69% of the bedded watershed. First‐year sediment losses for the chopped, sheared, bedded, and control watersheds were 12.5, 12.8, 14.2, and 0.6 metric tons/ha, respectively. Sediment concentrations for the four watersheds were 2,471, 2,837, 2,808, and 2,127 mg/liter of stormflow. Most of the first‐year sediment losses occurred during months of highest stormflows, November, January, February, and March. Stream channel scouring was a major source of sediment on the site prepared watersheds.
Second‐year sediment yields from the chopped, sheared, and bedded watersheds decreased to 2.3, 2.2, and 5.5 metric tons/ha, while sediment from the control watershed decreased to 0.1 tons/ha. Sediment concentrations were 670, 794, 2,346, and 393 mg/liter for the four watersheds. In relation to annual precipitation, total stormflow decreased on all treated watersheds the second year.
A stratigraphic and geomorphic study of surficial sediments in the Neuse drainage was completed as part of a general study of the relations between geomorphology and soils in the Coastal Plain of North Carolina. The depositional‐erosional surfaces on the interstream divides have been stable since they were formed, or there have been no recognizable additions or removals on these surfaces except for minor amounts of aerosols. The oldest geomorphic surfaces in the Neuse drainage are in the upper Coastal Plain and are (?) Miocene‐Pliocene, i.e., they may range from >5 to >3.3 million years. The surfaces in the middle Coastal Plain are Pliocene to early Pleistocene, i.e., they range from >5 to 0.5 million years. Surfaces in the lower Coastal Plain are all Pleistocene and are from about 400 to 115, possibly as young as 50 to 35 thousand years. Holocene surfaces, <10 thousand years, are the organic areas of pocosins and most of the valley slopes throughout the Coastal Plain. The Holocene valley slope surfaces are extensive in the middle and upper Coastal Plain, but occupy minor areas of the lower Coastal Plain.
The (?) Miocene‐Pliocene‐Pleistocene ages of the Coastal Plain surfaces are estimates of when subaerial weathering of the sediments and soil formation started. These are the time frames against which all changes produced by soil formation must be measured.
Sediment yield from flat (0.2% slope) delta fields was measured during a 33‐month study. Annual erosion rates were higher than anticipated, ranging from a maximum 12 metric tons ha −1 for a year of above normal rainfall to a minimum 5 metric tons ha −1 for a year of slightly below normal rainfall. Highest sediment concentrations in runoff occurred in the spring during the seedbed preparation and planting season when the soil was bare of vegetative cover, freshly plowed, and highly susceptible to erosion. Lowest concentrations occurred in September and October when vegetative cover was good.
Sediment particle size data from selected storms showed that about 83% of the sediment removed from the fields was < 2 µ m in diameter and nearly all, 98% was < 16 µ m. Field soils were composed of 24% clay, 23% silt, and 53% sand, so considerable enrichment of fine particles occurred during the erosion process. This indicates that most sediment deposits in streams and lakes of the area are composed of fine materials and that gradual enrichment of coarse particles in the soils is occurring over long periods of time.
Extensive low-lying marine deposits border the southeastern United States Atlantic Coastal Plain. Some units are fossiliferous and contain corals as isolated fragments in sediments of a detrital character. These corals are subject to alteration processes such that suites of related samples must be examined to determine the suitability of these coral samples for reliable uranium-series dating. With the exception of those from one location, most samples appear to have remained closed systems with respect to the isotopes of uranium and thorium throughout their geologic history. Extraneous **2**3**0Th has been detected in some of the corals due to incorporation of some detrital materials into their skeletons. For these samples, different methods are applied to correct for the initial **2**3**0Th contamination. Continued sampling and analyses have resulted in 55 individual uranium-thorium determinations. Measurement and analytical results are discussed in the paper. Refs.
A study of surficial deposits in the Piedmont province of Maryland has made it possible to construct a balance equation of sediment production and deposition since erosive agricultural land use began in the 1700s. Truncated Piedmont upland soil profiles imply approximately 0.15 m of soil erosion. In Western Run, a basin 155 km2, consisting of 85 percent Chester and Manor soils, this amounts to 130 × 10-3 hm3/km2 of eroded sediment. Reservoir sedimentation rates imply that 34 percent of the eroded sediment has been carried out of the system. The rest of the sediment remains in the watershed as alluvium in the upper 1 m of flood plains and as colluvium and sheetwash deposits on hillslopes. Agricultural sediment stored in flood plains constitutes 14 percent of the estimated soil erosion. The sediment was deposited mostly by overbank deposition at rates as high as 1.6 cm/yr. The remaining 52 percent of the eroded sediment occurs as colluvium and sheetwash deposits on hillslopes and as fan-shaped colluvial-alluvial deposits at junctures of headwater tributaries. Wood from such deposits was radiocarbon dated at 290 ± 100 yr. A buried junk pile in a flood plain yielded license plates whose dates imply that after 1925 the dump was buried by overbank deposition at rates as high as those for a basin undergoing urbanization. Piedmont basins less than 26 km2 have statistically longer bankfull recurrence intervals than streams with drainage areas greater than 26 km2. This suggests that since the decline of agricultural land use in the early 1900s, small upland tributaries have adjusted to decreased sediment loads by entrenchment into and erosion of sediment deposited since the initiation of colonial agricultural land use.
The adoption of the kandic horizon for use in recognizing the predominance of low activity clay has resulted in reclassification of several major soil series on the Atlantic Coastal Plain of the Southeastern U.S. To provide a more definitive basis for predicting the geographic distribution of the kandic feature, 41 sites correlated to successive geomorphic surfaces in North Carolina were sampled and characterized. The locations represented five defined Coastal Plain surfaces encompassing the Upper, Middle, and Lower Coastal Plain. Well to poorly drained upland soils were included. Results indicate that both the cation exchange capacity 7 and the effective cation exchange capacity requirement for the kandic horizon were consistently satisfied only in the well drained soils on the Upper Coastal Plain surface. Soil with greater wetness and soils on lower, younger geomorphic surfaces (Middle and Lower Coastal Plain) did not consistently satisfy requirements for the kandic horizon.
The appearance of the third volume in Donald Meinig's magisterial historical geography of the Americas is a major publishing event. To mark the occasion, the editors of theJournal of Historical Geographyinvited Professor Meinig to deliver a special lecture on his ambitious project at the 1998 Annual Meeting of the Association of American Geographers in Boston. The following is the text of his presentation. It is followed by two commentaries also delivered in Boston, by Cole Harris and Carville Earle.
Despite high erosion rates in the North Carolina Piedmont and extensive sediment delivery to Coastal Plain reaches of Piedmont-draining streams, sediment budget studies and estuarine sedimentology suggest that relatively little Piedmont-derived sediment reaches the lower Coastal Plain. Dominant sources of alluvium in the lower Coastal Plain reaches of Piedmont-draining rivers were inferred from alluvial floodplain soils. Piedmont-derived alluvial soils are characterized by mixed mineralogy and presence of mica flakes. Alluvial soils derived from erosion of Coastal Plain uplands are characterized by siliceous mineralogy and an absence of mica flakes. The Coastal alluvial soils which occur in fluvial/estuarine transition zones being drowned by rising sea level are organic or buried organic soils. The distribution of these soils along the Tar and Neuse Rivers in the lower Coastal Plain shows almost complete domination of fluvial-estuarine transition zones by soils of the Coastal group, and by soils of the Coastal Plain and Coastal groups for 40 km or more inland of the upper estuaries. No soils of the Piedmont group were found in fluvial-estuarine transition zones or lowermost fluvial reaches. This suggests that the Piedmont is a relatively insignificant source of alluvium in the lower reaches of the rivers. The absence of Piedmont sediment in the lower Coastal Plain is attributed to extensive sediment storage upstream, dilution by Coastal Plain sediments, and Coastal Plain erosion rates which may be higher than was previously believed.
Textural, geochemical, and mineralogic study of soils and weathering profiles has led to the practice of applying varioys weathering parameters as relative age indicators. In our studies examined the entire thickness of weathered sediment (i.e., the weathering profile) for evidence of weathering-induced changes in both sand- and clay-sized mineralogy, and used two techniques for relative age determinations. These techniques were developed as tools to support geologic mapping.One of our techniques for determining relative ages is based on the depth of weathering as recorded by progressive loss of denrital sand-sized minerals upward in the weathering profile. This is our preferred tool, especially in areas where weathering profiles have been truncated. We have found a gradual trend of increasing loss of labile sand-sized minerals (e.g., hornblendes, feldspars) and increasing depth of weathering with increasing age of the deposit. Of significance to many research programs, this technique does not require expensive instruments such as an X-ray diffractometer.Our other technique depends on accumulation of stable, secondary clay-sized minerals in the upper part of the weathering profile. In our study area on the Atlantic Coastal Plain of the United States, the stable assemblage consists of vermiculite, kaolinite, gibbsite, and iron oxides and hydroxides. This technique can be effective for relative age determinations where profiles have not been truncated, and can provide useful information on depositional and erosional history. However, in areas of widespread erosion and profile truncation, such as the Carolinas, the utility of this technique for relative age determinations is limited. There, soils were partially or completely removed in many localities in relatively recent times.
Riparian buffer areas are known to trap sediment leaving agricultural fields, but little quantitative data on this process are available. This study was inititiated to determine the amount of sediment deposited in riparian areas of two watersheds during the last 200 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 **1**3**7Cs data and sediment-soil morphology. At the field-forest edge 15 to 50 cm of **1**3**7Cs sediment accumulated while less than 5 cm of **1**3**7Cs sediment was deposited in the flood plain swamp downstream. Although only a thin ( less than equivalent to 5 cm) layer of sediment accumulated in the flood plain swamp, the large area available made this an important depositional area. 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.
Soil eroded from slopes and sediment added to stream systems as non-point pollution from a small watershed in southeastern Nebraska were quantified. Thickness and areal extent of soil loss were used to calculate weight and volume of soil moved from the slopes as well as the sediment that remained near its source on the landscape. The method described suggests a way in which soil survey mapping units may be characterized in order to quantify the amount of sediment in storage due to past erosion of agricultural land. -from Authors
This paper provides an overview of what is known about forest soil erosion in eastern United States. By most accounts, erosion from undisturbed as well as carefully managed forest land is 0.05 to 0.10 ton/acre/year; that is less than the geologic norm (0.18 to 0.30) and far less than maximum tolerable rates for agricultural land (1 to 5 tons/acre/year). Eroded material is about equal parts of particulate and dissolved matter. Responsibly managed timber harvest causes only minor increases in forest soil erosion, usually from channels and logging roads, but irresponsible timber harvest can increase erosion of particulate matter to unacceptable levels.
A palustrine water tupelo (Nyssa aquatica L.)-baldcy-press (Taxodium distichum (L.) Rich.) swamp in southwestern Alabama was subjected to three types of disturbance, including helicopter logging, rubber-tired skidder logging simulation, and helicopter logging followed by an herbicide application. An adjacent undisturbed stand served as a control area. Post-harvest collection of sedimentation data revealed that the herbaceous and woody vegetation regrowth within the helicopter and skidded clearcut areas trapped more sediments than did the control or herbicide treatment areas. Clearcutting, followed by plant regrowth, improved the wet-land's capacity to remove sediments from overbank flow flood waters.
The Chickahominy River, arising near Richmond, Virginia, flows southeast toward Newport News, which impounds the river for much of its water supply. Much of the bottomland between the two cities is flooded for extended periods annually. Sediment-deposition rates estimated from tree rings were used in conjunction with multi-element analyses of sediments and of selected growth rings from oak trees to estimate amounts of trapped sediment and trace elements. Mean rates of deposition at eight study sites range from 0.7 to 5.7 mm/yr and are related to stream gradient, stream power, percent wetland, hydroperiod, and land use. Deposition rates are highest downstream from the confluence of upper basin tributaries near Richmond, where stream power is low and there is a high percentage of emergent/shrub-scrub wetlands; rates decrease, along downstream reaches toward the Chickahominy reservoir. Tree-ring data suggest that mean sedimentation rates were greater during the last 50 years than during the previous 3-year period, possibly because of urban expansion in the upper basin. Sites nearest the urban area have the highest rates of sedimentation and the highest concentrations of most trace elements in sediments. Trace elements concentrated in sediment include zinc, lead, chromium, copper, nickel, tin, and cadmium. Concentrations in tree rings of zinc, copper, nickel, and lead were generally proportional to those in sediment at a site, and some inter-site correlations were also observed. Unusually high concentrations of zinc were detected in some tree rings, including some that formed before 1950. Concentrations of zinc and lead in the most recently formed rings of those trees suggest that sediment concentrations of those elements may have declined relative to earlier periods. The trapping of substantial amounts of sediment and trace elements by these forested wetlands demonstrates their importance in the maintenance of water-quality.
Drastic changes in sediment production in drainage basins can have significant impacts on sediment yield to estuaries. However, significant but less spectacular changes in fluvial sediment regimes have not greatly influenced sediment output of some rivers in the United States Atlantic Drainage. The limited influence of moderate or incremental changes in fluvial sediment systems on estuarine sediment delivery may be attributable to the large proportion of eroded sediment which is stored within the basins, and the transport-limited nature of long-term sediment yields. A sediment budget for the Pee Dee River basin and Waccamaw River/Winyah Bay estuary of the Carolinas shows that only a small proportion of gross eroded sediment within the basin (about 4%) reaches the estuary on an average-annual basis. Because the system appears to be transport-limited, it is estimated that an 88% reduction in the quantity of eroded sediment reaching streams would be necessary to produce significant change in sediment yield to the estuary. Any increase in sediment production would not be reflected at all in the estuary unless it was accompanied by a corresponding increase in fluvial sediment conveyance capacity. Estuarine sedimentary records thus may not reflect some significant changes in fluvial sediment systems.
Relative to its size and in terms of its sedimentary processes, the Albemarle-Pamlico Lagoonal system is one of the least studied coastal lagoons in the United States. A synthesis of the current knowledge about sedimentation in the Albemarle-Pamlico system is presented, based on archived data published over the last 30 years and new, unpublished data, collected over the past two years. The literature reflects considerable past research effort on sediment grain size and mineralogy, but very little on sediment dynamics or flux of suspended particulate material.The physiographic complexity of the system, which includes barrier islands, a deep central basin, four river systems and extensive fringing embayments, does not appear to be reflected in the form of sedimentologic complexity. In general, the surficial cover of sediments ranges from medium sands in the inlets and on the shoals of the Outer Banks to fine silts and organic-rich clays in the central basin and embayed river mouths and channels. The transition zones from sands to muds are typically sharp and are usually related to bathymetry.It is concluded that (1) parts of the Albemarle-Pamlico lagoonal system may have high sedimentation rates relative to rates of sediment input and that rapid vertical flux by large aggregates offers an explanation for the fluid-mud deposits that would otherwise be absent, (2) fine-grained sediments that escape the estuarine sediment “trap” are confined to Pamlico Sound by the Outer Banks barrier islands and are simply recycled until finally coming to rest in the deep basin, (3) short-term advective processes are secondary to longer term processes (such as sea-level rise and barrier island migration) in the net advection of Albemarle-Pamlico sediments, and (4) at the present rate of terrigenous sediment input and relative sea-level rise, the Albemarle-Pamlico lagoonal system will never reach a sediment-filled state.
Dendrogeomorphic techniques were used to describe and interpret patterns of sedimentation rates at two forested wetland sites in West Tennessee. Fifty-five sampling stations were established along transects upstream and downstream from bridge structures, and 515 trees were examined for depth of sediment accretion and cored for age determination. Temporal variation in sedimentation rate may be related more to stream channelization and agricultural activity than to bridge and causeway construction. Sedimentation rates have increased substantially in the last 28 years, although channelized streams may have overall lower rates than unchannelized streams. Comparisons of sedimentation rates from deposition over artificial markers (short term) with those determined from tree-ring analysis (long-term) indicate that trends are similar where hydrogeomorphic conditions have not been altered substantially. No tendency for increased sedimentation upstream from bridges was observed. Deposition rates were inversely correlated with elevation and degree of ponding. Downstream deposition of sand splays appears to be related to flow constrictions and may be extensive. Mean overall rates of sedimentation (between 0.24 and 0.28 cm year−1), determined dendrogeomorphically, are comparable with other published rates.
The Piedmont and Coastal Plain physiographic provinces comprise 80 percent of the Atlantic Coastal states from New Jersey to Georgia. The provinces are climatically similar. The soil moisture regime is udic. The soil temperature regime is typically thermic from Virginia through Georgia, although it is mesic at altitudes above 400 m in Georgia and above 320 m in Virginia. The soil temperature regime is mesic for the Piedmont and Coastal Plain from Maryland through New Jersey. The tightly folded, structurally complex crystalline rocks of the Piedmont and the gently dipping “layer-cake” clastic sedimentary rocks and sediments of the Coastal Plain respond differently to weathering, pedogenesis, and erosion. The different responses result in two physiographically contrasting terrains; each has distinctive near-surface hydrology, regolith, drainage morphology, and morphometry.
The results of an integrated study comprising litho- and biostratigraphic investigations, uranium-series coral dating, amino acid racemization in molluscs, and paleomagnetic measurements are compared to ascertain relative and absolute ages of Pleistocene deposits of the Atlantic Coastal Plain in North and South Carolina. Four depositional events are inferred for South Carolina and two for North Carolina by all methods. The data suggest that there are four Pleistocene units containing corals that have been dated at about 100,000 yr, 200,000 yr, 450,000 yr, and over 1,000,000 yr. Some conflicts exist between the different methods regarding the correlation of the younger of these depositional events between Charleston and Myrtle Beach. Lack of good uranium-series dates for the younger material at Myrtle Beach makes the correlation with the deposits at Charleston more difficult.
Paleontologic and paleomagnetic investigations were conducted on several hundred Pliocene and Pleistocene marine samples from five regions of the emerged Atlantic Coastal Plain: (1) the Delmarva Peninsula, (2) eastern Virginia, (3) central and northern North Carolina, (4) southern North Carolina and northeastern South Carolina, and (5) the Charleston area, South Carolina. Molluscan and ostracode interval and assemblage zonations, which are the primary means of regional correlation, have been calibrated using planktic biochronologic, paleomagnetic, radiometric and amino-acid recemization data. These multiple dating criteria were used to determine the age and, where possible, the duration of marine transgressive/regressive sequences. A correlation chart illustrates the age relationships of 27 formations from five regions. One important conclusion is some of the Yorktown Formation of Virginia and North Carolina (including the “Duplin” Formation), and some of the Raysor of South Carolina are late Pliocene in age. The late Pliocene Chowan River Formation of North Carolina is older than the early Pleistocene Waccamaw Formation of South Carolina, which in turn may be older than the James City Formation of North Carolina. During the last 1.0 million years, multiple marine transgressions occurred in each region, but the age of these middle and late Pleistocene formations often may differ from one area to the next.A significant result of the study is the evidence for the lack of time equivalence of formations in the five different regions; that is, the sequence of marine transgressions in one region does not necessarily correspond to that in another. This appears to be the result of differing subsidence and uplift histories, the patchiness of the depositional record, and the limitations of the dating techniques in light of the rapidity and frequency of sea-level fluctuations.
The Neuse River estuary is part of the large Albemarle/Pamlico estuarine/lagoonal system (APES) of North Carolina. Exchange between the APES and the open ocean is restricted to inlets in the Outer Banks barrier islands. Freshwater discharge of the Neuse River is low in relation to the size of its estuary, so that the estuary is normally brackish over most of the area which accumulates fine-grained sediments. Mud (silt + clay) accumulation rates are low (⩽ 6 mm year−1).From the mud distribution and the dynamics of suspended sediment in the estuary it has been inferred that the Neuse retains fines efficiently, with probable episodic (high discharge) losses seaward, to Pamlico Sound.As part of a study of particle transport, deposition, and accumulation in the Neuse estuary, we have collected radiochemical data (10 cores) and chemical data (seven cores) on sediment cores from the main channel of the estuary between New Bern, North Carolina and the estuary mouth. K/Al increases in the lower estuary, consistent with earlier reports of increasing illite in the clay fraction. Landward transport of sediment from Pamlico Sound is the most plausible explanation for the increasing K/Al (illite). A marine sediment source may, therefore, be important for the lower estuary.The distribution of sediment inventories (quantities per cm2 of sediment column) of particle-reactive radionuclides is consistent with the hypothesis of landward sediment transport. Inventories of excess 210Pb, 137Cs, and 239,240Pu are coherent through the estuary and show the effects of particle redistribution processes on regionally uniform inputs. To obtain excess (anthropogenic) Zn and Cu, we use metal/Al normalization to estimate natural backgrounds. Anthropogenic metal inputs are concentrated at the head of the estuary, and sediment inventories of excess Zn and Cu generally decrease seaward. Normalization of the excess Zn and excess Cu inventories to excess 210Pb inventories corrects the raw metal inventories for effects of lithology and sediment redistribution. The normalized excess Zn inventory decreases smoothly seaward, while the normalized excess Cu inventory shows an unexplained mid-estuary maximum. Low normalized inventories of anthropogenic metals at the estuary mouth indicate that little modern riverine sediment is stored there.Increasing K/Al (illite) and decreasing anthropogenic Zn and Cu in the lower estuary are thus both consistent with a predominantly marine sediment source. We conclude that landward transport of muds from Pamlico Sound has contributed significantly to the sediment balance of the lower Neuse estuary.
Soil survey reports and soil maps of 11 second-order watersheds on the Keuper marls in Luxembourg were used to establish the extent to which soils were modified by accelerated erosion and colluviation, and to calculate the volume of colluvium. The amount of truncation of the soil profiles in the eroded area is on average 55 cm, of which the equivalent of 36 cm remains in the watersheds as colluvium. The 34% of the eroded soil material that has left the watersheds represents the longterm sediment-delivery ratio.Landuse exerted a more powerful control on the production of colluvium than geomorphology. The area occupied by colluvial soils (C, ha) which offer good quality land can be predicted from the area under agriculture (L, ha) with the equation C= .74L− 56. Comparison with palynologically dated colluvium produced figures for sediment yield of the source areas in the range between 700 and 1800 kg/ha · year.
Thesis--University of South Carolina. Includes bibliographical references (leaves 91-94). Photocopy of typescript.
Thesis--University of South Carolina. Includes bibliographical references (leaves 145-151). Photocopy of typescript. Ann Arbor. Mich. : University Microfilms International, 1979. -- 21 cm.