The differences between urban and rural streams regarding hydrological process, channel morphodynamics and ecosystem functioning have been highlighted by a number of studies in recent decades. The need to understand lotic ecosystem functioning in these environments at scales relevant to individual organisms has led to research focusing on hydraulic composition and structure over small areas of channel bed. In this study we map and analyze the hydraulic biotope composition of two urban and two rural stream reaches in the North Carolina (USA) Piedmont to determine if urban flow regimes and attendant channel modification processes might translate into important differences in hydraulic environment, and if so, what those differences are. Hydraulic biotope assemblages were found to vary only moderately in diversity per unit stream length between sites, but were distinctly different in composition. One important control on the differences between rural and urban streams was found to be the localized incision of urban channels into bedrock and saprolite. Resistant rock outcrop in the beds of urban streams creates rapid and riffle biotopes and long stretches of upstream pool habitat by impoundment. Urban reaches were found to be more homogeneous than rural reaches in hydraulic composition and were dominated by pools. Rural reaches, characterized by copious sandy alluvium in the bed, were dominated by runs or glides. Quantitative differentiation of biotopes based on four hydraulic indices generally yields coherent associations, although these may vary in content. Comparisons between hydraulic and biotic diversities suggest relationships favoring biotic functional group aggregation over species richness-based indices of diversity. Because the majority of published hydraulic diversity analyses are based on coarse-bed streams, further study of hydraulic diversity in streams with finer substrate is likely to be beneficial.
Conocimiento de la dinámica del proceso y las formas de almacenamiento de los sedimentos en el río es importante para comprender los impactos del cambio climático y cambio en el uso del suelo en la producción de sedimentos, morfología longitudinal y transversal del canal del cauce, y los hábitat acuáticos y de ribera. Entre las formas importantes de almacenamiento de sedimentos están los bancos dentro de los canales: nivel, depósitos fluviales escalonados que ocurren a diferentes alturas sobre el fondo del canal pero por debajo de la superficie del llano de inundación principal. En este estudio, la presencia contemporánea de bancos dentro de los canales en cauces en el Piedmont fue examinada, y las características hidrológicas de las localidades de estudio fueron investigadas como potenciales causantes de la formación del banco. Nueve localidades en el canal del cauce, estudiadas originalmente en 1964, fueron reexaminadas para determinar cambios en el número de niveles en el banco dentro del canal y las características morfológicas actuales del banco. De uno a tres niveles de banco no documentados en 1964 se observaron en varios lugares que tienen áreas de drenaje a menos de 600 km 2 . Se encontró que generalmente los bancos de bajo y medio nivel son altamente discontinuos, dominados casi exclusivamente por vegetación herbácea, y con frecuencia bien estratificadas. A pesar de que instancias específicas de ocurrencia de bancos pueden ser controladas a nivel local, la correspondencia entre las elevaciones de los bancos dentro de los canales y etapas de flujos de periodos de sequía con intervalos de recurrencia similares a las del llano de inundación activo más alto y más grande bajo condiciones hidroclimáticas promedio, sugieren un vínculo entre la morfogénesis del banco y las sequías. El crecimiento reciente de los bancos en la última década de sequía en el Piedmont es demostrable en una localidad, utilizando restos culturales que pueden ser adjudicados a una fecha específica. Sin embargo, la asignación inequívoca de edades específicas a los depósitos del banco sigue siendo problemático.
Despite the growing interest in organic farming, its practice remains limited because of its lower productivity relative to conventional farming. Land suitability evaluation for organic crops can potentially improve productivity, and thus the economic viability of organic farming. The best analytical procedures for such evaluations have not yet been fully explored. This article addresses the evaluation of land suitability of present agricultural lands for organic agriculture of rain-fed winter wheat using Duplin County, North Carolina, a location economically dependent on agriculture, as a case study. A novel land suitability evaluation procedure is developed combined with seventeen suitability criteria from five principal categories including climatic parameters, soil characteristics and qualities, soil chemistry, soil organic matter and fertility, and flood and erosion hazards by using geographic information systems (GIS), multicriteria analysis, and the square root method. Our analysis demonstrates that although 18.6 percent of agricultural lands in Duplin County are highly suitable for organic winter wheat production, a large proportion (76.8 percent) of agricultural lands are also moderately suitable. The method of suitability analysis used in this research, which allows specific consideration of soil organic matter and fertility as particularly critical factors for organic farming, can be easily exported to other locations, for similar applications.
Sediment bodies produced during historical periods of human land use, sometimes referred to as legacy sediment, may be found in various locations within drainage basins, and potentially remobilized by hydrogeomorphic processes accompanying land use change. The amounts and locations of stored legacy sediment can be significant factors in modern drainage basin function and should be accounted for when possible. In this study, late nineteenth-century erosion and sediment storage were investigated and used to construct approximate sediment budgets for two small Blue Ridge Mountain drainage basins in North Carolina (USA). Erosion was quantified using a distributed implementation of the Universal Soil Loss Equation (USLE), and calibrated on the separate bases of soil profile truncation data and recent published rates for long-term erosion in the region. Sediment yield information was reconstructed from pond sediments trapped behind a mill dam. Alluvial sediment storage was quantified using field studies of streambank and floodplain sediment profiles and digital elevation data. Colluvial storage was calculated as a residual in the sediment budget, and further evaluated using soil profile studies of footslope deposits, and soil survey maps. The proportions of erosion accounted for by the different budget terms in the most reliable budget are: 28% sediment yield (i.e., a sediment delivery ratio of 0.28), 69% colluvial storage, and 3% alluvial storage. Blue Ridge basins with low levels of ground disturbance erode like Piedmont basins at high levels of ground disturbance, primarily due to higher slope angles. Sediment delivery ratio is high relative to those given for much larger basins in the adjacent and more frequently studied Piedmont province, and generally in accordance with published sediment delivery curves that reflect higher hydrogeomorphic connectivities within smaller basins. Low values for alluvial storage in Blue Ridge basins may be explained by high sediment transport within steep channels. Colluvial 3 storage values have high uncertainties because of the well known problem of error accumulation in residual budget terms. Field data on colluvial deposits reported here are not sufficient to correct for this problem, and in general, the acquisition of accurate field data on historical colluviation remains an important methodological issue in historical sediment budgeting.
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