Riparian buffers are promoted for water quality improvement, habitat restoration, and stream bank stabilization. While considerable research has been conducted on the effects of riparian buffers on water quality and aquatic habitat, little is known about the influence of riparian vegetation on stream bank erosion. The overall goal of this research was to evaluate the effects of woody and herbaceous riparian buffers on stream bank erosion. This goal was addressed by measuring the erodibility and critical shear stress of rooted bank soils in situ using a submerged jet test device. Additionally, several soil, vegetation, and stream chemistry factors that could potentially impact the fluvial entrainment of soils were measured. A total of 25 field sites in the Blacksburg, Virginia area were tested. Each field site consisted of a 2nd-4th order stream with a relatively homogeneous vegetated riparian buffer over a 30 m reach. Riparian vegetation ranged from short turfgrass to mature riparian forest. Multiple linear regression analysis was conducted to determine those factors that most influence stream bank erodibility and the relative impact of riparian vegetation. Results of this research indicated woody riparian vegetation reduced the susceptibility of stream bank soils to erosion by fluvial entrainment. Riparian forests had a greater density of larger diameter roots, particularly at the bank toe where the hydraulic stresses are the greatest. These larger roots (diameters > 0.5 mm) provided more resistance to erosion than the very fine roots of herbaceous plants. Due to limitations in the root sampling methodology, these results are primarily applicable to steep banks with little herbaceous vegetation on the bank face, such as those found on the outside of meander bends. In addition to reinforcing the stream banks, riparian vegetation also affected soil moisture and altered the local microclimate. While summer soil desiccation was reduced under deciduous riparian forests, as compared to herbaceous vegetation, winter freeze-thaw cycling was greater. As a result, in silty soils that were susceptible to freeze-thaw cycling, the beneficial effects of root reinforcement by woody vegetation were offset by increased freeze-thaw cycling. Using the study results in an example application, it was shown that converting a predominately herbaceous riparian buffer to a forested buffer could reduce soil erodibility by as much as 39% in soils with low silt contents. Conversely, for a stream composed primarily of silt soils that are prone to freeze-thaw cycling, afforestation could lead to localized increases in soil erodibility of as much as 38%. It should be emphasized that the riparian forests in this study were deciduous; similar results would not be expected under coniferous forests that maintain a dense canopy throughout the year. Additionally, because dense herbaceous vegetation would likely not develop in the outside of meander bends where hydraulic shear stresses are greatest, the reductions in soil erodibility afforded by the herbaceous vegetation would be limited to areas of low shear stress, such as on gently sloping banks along the inside of meander bends. As the first testing of this type, this study provided quantitative information on the effects of vegetation on subaerial processes and stream bank erosion. It also represents the first measurements of the soil erosion parameters, soil erodibility and critical shear stress, for vegetated stream banks. These parameters are crucial for modeling the effects of riparian vegetation for stream restoration design and for water quality simulation modeling. / Ph. D.

L'obiettivo della ricerca è stato quello di identificare la coltura bioenergetica con il maggior potenziale di sequestro del carbonio (C); sono state considerate tre colture perenni arboree (pioppo, robinia e salice) e tre colture erbacee perenni (canna comune , miscanto e panico ) al sesto anno dal loro impianto e coltivate nello stesso ambiente. In primo luogo sono state misurate le variazioni dei tassi del C organico del suolo (COS) per il primo 1 m, mentre per i primi 30 cm di suolo è stato stimato il grado di stabilita del COS valutando sette frazioni di COS che presentano differenti gradi di stabilizzazione; in secondo luogo, sono stati caratterizzati gli apparati radicali delle sei specie per la stessa profondità di suolo, per valutare dove le specie accumulano la biomassa radicale lungo il profilo di suolo. I risultati confermano che l’impianto di colture bioenergetiche perenni su superfici precedentemente dedite a colture annuali gestite convenzionalmente rappresenta una opzione valida per sequestrare C nel soulo. Tuttavia, è stata osservata una diversa capacità di sequestro di C tra specie arboree ed erbacee: le specie arboree hanno dimostrato aumentre il contenuto di COS nel primo strato di suolo ( 0-10 cm di suolo), ma la loro capacità di allocare biomassa radicale negli strati profondi del suolo è limitata; mentre, la specie erbacee allocano un’alta quantità di biomassa radicale negli strati profondi del suolo, ma solo il panico ed il miscanto hanno aumentato il contenuto di C nel primo strato di suolo. / The objective of the present research was to identify the bioenergy crop with the greatest carbon sequestration potential among three perennial woody crops (poplar, black locust and willow) and three perennial herbaceous crops (giant reed, miscanthus and switchgrass) at the sixth year from plantation and in the same location. First of all the SOC stock variations for the first 1 m soil depth and the quantification of seven soil C fractions related to SOC stabilization level of the first 30 cm of soil were assessed; secondly, a characterization of the root system and the traits which affect the carbon allocation in soil were considered. The results confirm that the establishment of perennial bioenergy crops in previous arable fields can be a suitable option to sequester carbon (C) belowground. However, a different C sequestration capacity was observed between woody and herbaceous crops: woody species showed the greatest SOC sequestration potential in the first soil layer (0-10 cm of soil) but their ability to allocate root biomass in the deeper soil layers was limited; while, the herbaceous species allocated a high amount of root biomass in the deeper soil layers, but only switchgrass and miscanthus sequester C in the first soil layer.

Bioporen werden von Regenwürmern und Pfahlwurzeln geformt und gelten als präferentieller Weg für das Wurzelwachstum in tiefere Bodenbereiche. Jedoch ist bislang unklar, ob dem bioporennahen Unterboden eine besondere Funktion für das Wurzelwachstum, die Nährstoffakquise und den Zugang in den bulk-Boden zukommt. In diesem Bereich fehlt es an einer Quantifizierung von Wurzelwachstum und die Messung von Wurzelaktivität. Mit speziell angefertigtem Beprobungswerkzeug wurde der bioporennahe Unterboden großlumiger, nahezu vertikal verlaufender Bioporen (Durchmesser >5 mm) in kleinteiligen Abständen in 0-2, 2-4 und 4-8 mm auf die Wurzellänge [cm], den Wurzeldurchmesser [mm], die Gesamt-C- und -N-Gehalte [%] (Ct, Nt) sowie den pH-Wert untersucht. Neben der Untersuchung von Bioporen im Feld wurde in Gefäßversuchen der Einfluss des Regenwurms und der Pfahlwurzel auf das Wurzelwachstum separat betrachtet. Für die Untersuchungen wurden Sommergerste, Sommerraps und Ackerbohne eingesetzt zur Abbildung verschiedener Wurzelsysteme. Die Ergebnisse zeigten einen deutlich ausgeprägten lateral abnehmenden Gradienten der Ct- und Nt-Gehalte im Feldversuch. In den Gefäßversuchen gab es keine Unterschiede zwischen den Bioporentypen in den Ct- und Nt-Gehalten. Die Wurzeln wuchsen hauptsächlich im Bioporenlumen und in 0-2 mm, geringer in 2-4 und 4-8 mm des bioporennahen Unterbodens. Der pH-Wert war in der Wurmpore höher als im bulk-Boden. Sommerraps und Ackerbohne zeigten anhand Wurzel-induzierter pH-Wertänderung eine deutliche Stoffwechselaktivität in der Wurzelprägung, während in der Wurmprägung keine signifikante pH-Wertveränderung für die drei Kulturarten sichtbar wurde. Die verminderte laterale Wurzelausdehnung im bioporennahen Unterboden deutet auf ein begrenztes Potenzial der Bioporen als Zugangsweg zum Explorieren des bulk-Bodens hin. Ein erhöhtes Wurzelwachstum in den ersten 2 mm des bioporennahen Unterbodens weist auf eine Verankerung der Wurzeln und eine Nährstoffaufnahme hin. / Biopores are formed by earthworms and taproots and are considered a preferential pathway for root growth into deeper soil layers. However, it is unclear to date whether the biopore sheath has a specific function for root growth, nutrient acquisition and access into the bulk soil. There is a lack of literature on the quantitative measurement of root growth and the measurement of actual root activity in the biopore sheath. Using sampling tools specially made for this type of investigation, the biopore sheath of large-sized, nearly-vertical biopores (diameter >5 mm) were sampled at small-scale intervals in 0-2, 2-4 and 4-8 mm and analyzed for root length [cm], root diameter [mm], total C- and N-contents [%] (Ct, Nt), and pH. In addition to the study of biopores in the field, the influence of earthworm or taproot on root growth was considered separately in pot experiments. Spring barley, spring oilseed rape and faba bean were used for the investigations in order to be able to map different root systems. The results showed a clearly pronounced laterally decreasing gradient of Ct- and Nt-contents in the field experiment. There were no differences between the biopore types in Ct- and Nt-contents in the pot experiments. Roots grew mainly in the biopore and in 0-2 mm, less in 2-4 and 4-8 mm of the biopore sheath. The pH value was higher in the worm type biopore than in the bulk soil. Based on root-induced pH change, spring oilseed rape and faba bean showed significant metabolic activity in root type biopore, while no significant pH change was found in worm type for the three crop species. The laterally decreasing root elongation from biopore surface towards bulk soil is pointing towards a limited potential of biopores as an access path to explore the bulk soil. Increased root growth in the first 2 mm of the biopore sheath indicates root anchorage and nutrient uptake.

Das Wurzelwachstum von Winterweizen wurde erfasst und modelliert, um teilflächenspezifisches Boden- und Düngemanagement zu verbessern. Die Variation von Wurzellängendichten im Feld wurde über zwei Vegetationsperioden hinweg an zwei unterschiedlichen Standorten in Ostdeutschland untersucht. Zur Auswertungserleichterung der hohen Anzahl an Wurzelproben, wurde eine halbautomatische Methode zur Bildanalyse von Wurzeln entwickelt. Der Einfluss von Änderungen bezüglich Bodenwasserstatus und Bodendichte bzw. Durchdringungswiderstand auf das Wurzelwachstum wurde untersucht. Die erhobenen Felddaten dienten gleichzeitig dazu, die Bodenwasser- und Wurzelwachstumsberechnung des Modells CERES-Wheat zu validieren. Das Modell simulierte die unterschiedlichen Bodeneigenschaften sowie die Wurzellängendichten und Bodenwassergehalte nur unzureichend. Der Effekt von Änderungen der Niederschlagsmengen auf die Simulationen von Wurzellängendichten und Bodenwassergehalten wurde anhand einer Unsicherheitsanalyse getestet und war extrem gering. Des Weiteren wurde eine Methode für praktische Zwecke entwickelt, mit der die Generierung von räumlich hoch aufgelösten Bodeninformationen unter Verwendung limitierter Eingangsdaten möglich ist. Die Modellkalkulationen basieren auf der Dempster-Shafer-Theorie. Anhand von multitemporal und multimodal erfassten Bodenleitfähigkeitsdaten, die Eingangsdaten für den Modellansatz sind, wurden Bodentypen und Texturklassen bestimmt. Das Modell generiert eine digitale Bodenkarte, die flächenhafte Informationen über Bodentypen und Bodeneigenschaften enthält. Die Validation der Bodenkarte mit zusätzlich erhobenen Bodeninformationen ergab gute bis sehr gute Ergebnisse. / Winter wheat root growth was measured and modelled to improve site-specific soil and fertilizer management in commercial wheat fields. Field variations in root length densities were analysed at two contrasting sites in East-Germany during two vegetation seasons. A semi-automated root analysing method was developed to facilitate analyses of large numbers of samples. Influences of variations in soil water states, bulk densities and penetration resistances on spatial distributions of roots were quantified. Differences in soil characteristics were large between the two sites and affected root growth considerably. The same field data was used for validating the soil moisture and root growth calculations of the widely applied growth model CERES-Wheat. Simulations of root length densities, soil physical properties and soil water contents were inadequate. The effects of changes of rainfall variabilities on simulated root length densities and soil water contents were tested by uncertainty analysis but were negligible low. A methodology for generating soil information for practical management purposes at a high degree of spatial resolution using limited input information was developed. The corresponding model calculations were carried out based on the Dempster and Shafer theorem. Soil types and texture classes were determined with multimodally and multitemporally captured data of soil electrical conductivities which are required input data of the new model approach. The model generates a digital map with extensive information of spatial variations in soil properties. The validation of the generated soil map with soil data from independent measurements yielded close correlation between measured and calculated values.