Letteratura scientifica selezionata sul tema "Biogeomorphology"

Floodplains are unique ecosystems because of their linear form, the sometimes extreme dynamism of their geomorphology and because they process large fluxes of energy and materials from upstream areas. This article focuses on the importance of hydrological inputs to floodplains through 1) their influence on the arrangement of landforms and vegetation communities and 2) the connections between flooding regimes and the regeneration and turnover time of floodplain vegetation. Many researchers have demonstrated close links between the arrangement of vegeta tion communities and sedimentary landform types, elevation, soil characteristics, tolerance to flooding and availability of soil moisture. It is suggested that plants on floodplains are found along a combined gradient of available moisture and oxygen which can be viewed simultaneously as a flooding frequency gradient and a complex soil moisture gradient. Discussion of experi mental work on floodplains demonstrates the importance of these gradients to a range of flood plain species in different environments. The relationships between these environmental gradients and the apparent high level of overlap between planform patterns of landforms and vegetation communities on floodplains are related to lag times in different parts of vegetation communities. Flood regimes greatly influence the availability of areas suitable for vegetation regeneration from year to year and the age structure of floodplain communities over decadal time frames. Biotic factors also influence biogeomorphological relationships on floodplains and range from sediment- trapping by vegetation to the impacts of beaver and grazing animals on floodplain hydrology and vegetation. Restoration of floodplains is high on the agenda in many countries and it is argued that, for sustainable results, restoration of hydrological pathways is essential. Planned flood releases below dams in several African countries have had varied success rates but the develop ment of models for managing flows to achieve different restoration targets is the start of an integrated approach to restoring complex floodplain ecosystems.

Thesis (PhD (Conservation Ecology and Entomology))--University of Stellenbosch, 2011.
AFRIKAANSE OPSOMMING: Min aandag is al gegee aan biogeomorfologiese interaksies in glasiale en periglasiale omgewings. Nietemin is hierdie interaksies, wat op die skeidingsvlak tussen ekologie en geomorfologie fokus, baie belangrik in hierdie omgewings, waar organismes in noue verband met die abiotiese omgewing saamleef. In hierdie tesis bestudeer ek die interaksies tussen die vaskulêre plantspesies met die hoogste voorkoms op sub-Antarktiese Marion Eiland, Azorella selago Hook. (Apiaceae), en die omringende geomorfologiese landskapsvorme, -prosesse en meettegnieke. Verder verskaf die tesis voorstelle om toekomstige geïntegreerde biogeomorfologiese navorsing te vergemaklik. Om die gevolge van A. selago-plante vir sedimentbeweging en -verspreiding te verstaan, het ek die verspreiding van sedimentgroottes om hierdie plante gemeet deur middel van 'n kombinasie van fotografiese analise-metodes. Deur as sedimentbewegingsobstruksies te dien, het plante 'n waarneembare effek op die omringende sedimentverdeling. Dit is veral belangrik om hierdie interaksies tussen A. selago en sy omgewing te verstaan in die lig van onlangse klimaatsverandering op die eiland, omdat sedimentgrootte belangrike grondeienskappe soos waterretensiekapasiteit en vriesgevoeligheid beïnvloed. Om die effek wat A. selago plante op die omringende mikroklimaat het beter te verstaan, is die kleinskaalse variabiliteit in grondtemperature om A. selago plante bestudeer. Grootskaalse grondligting as gevolg van fors is gemeet, ten spyte van relatief ligte forseienskappe. Dit dui daarop dat naaldys ook by temperature bo -2°C kan vorm. Wintergrondtemperature aan die oostekant van plante was effens laer en minder veranderlik as aan die westekant van plante, waarskynlik as gevolg van laer windsnelhede en/of sneeu wat ophoop aan die oostelike, lykant van plante. Die resultate benadruk dat A. selago plante 'n belangrike rol speel in die verandering van mikroklimate en dat dit belangrik is om die gevolge van sulke veranderings, soos die skep van mikrohabitatte vir grondorganismes, te verstaan. Daar word vermoed dat positiewe plantinteraksies negatiewe interaksies oorheers in omgewings met hoe abiotiese druk. Gevolglik wys ek dat daar 'n positiewe verband bestaan tussen A. selago plante en saailinge van beide A. selago self, asook van die meerjarige gras Agrostis magellanica Lam. (Poaceae). Ek stel voor dat beide plante en klippe sade, wat deur wind, reenval en/of afdraande sedimenttransportering as gevolg van vriesprosesse vervoer word, opvang. Verder dui verhoogde A. selago saailinggetalle om plante, maar nie om klippe nie, daarop dat plante een of ander biologiese voordeel aan A. selago saailinge bied. Dit is bekend dat die verspreidingspatrone van plantspesies as gevolg van abiotiese stresgradiente varieër. Met hierdie bevinding in gedagte, is moontlike faktore verantwoordelik vir A. selago saailinggetalle en -verspreidingspatrone, soos hoogte bo seespieël en substraatbedekking, bestudeer. Alhoewel dit wil voorkom asof daar 'n verband tussen saailinggetalle en hoogte bo seespieël is, is saailinggetalle en verpreidings meestal afhanklik van ongemeette perseel-spesifieke eienskappe. Plante kan die omringende geomorfologie beïnvloed, maar ook geomorfologiese meettegnieke. Om die potensiaal van kosmogeniese dateringsmetodes as geomorfologiese hulpmiddels in fellfield habitatte te verken, is die akkumulasietempo van die kosmogeniese isotoop ¹ºBe onder en langs 'n A. selago plant bepaal. Die resultate dui daarop dat ¹ºBe nie ten volle in die grondprofiel behoue bly nie en verskeie potensiële redes word bespreek. Verder dui die resultate daarop dat ¹ºBe konsentrasies in fellfield habitatte versigtig geïnterpreteer moet word, aangesien A. selago plante effektief ¹ºBe opvang in hulle grondryke kern. Om vordering in biogeomorfologie te vergemaklik, is dit belangrik om bewus te wees van die verskillende metodes wat geomorfoloë en ekoloë volg. Ekologiese benaderings is dikwels op strenger statistiese tegnieke gebaseer, terwyl geomorfoloë eerder fokus op 'n meer beskrywende benadering en teoretiese beredenering. Ek verduidelik hoekom die twee velde sulke uiteenlopende benaderings volg, benadruk moontlike struikelblokke en verskaf voorstelle om samewerking te vergemaklik.
ENGLISH ABSTRACT: There are few scientific publications that relate to biogeomorphological interactions in glacial and periglacial environments. Interactions that focus on the interface between ecology and geomorphology are very important in these environments, as a tight coupling often exists between organisms and their abiotic surroundings. In this thesis the interactions between the dominant vascular cushion plant species on sub-Antarctic Marion Island, Azorella selago Hook. (Apiaceae), and the surrounding geomorphological landforms, processes and measuring techniques were studied. In addition, the thesis provides suggestions to facilitate future integrated biogeomorphological research. To understand the consequences of A. selago cushions for substrate movement and sorting, the grain size distribution of sediment surrounding these cushions was quantified using a combination of image analysis approaches. Through obstructing frost-related sediment transport, A. selago cushions are shown to affect the grain size sorting of the surrounding sediment. Particle size affects soil properties such as water-holding capacity and frost susceptibility. It is therefore important to understand the interactions between A. selago cushions and sediment distributions, especially in the light of recent warming and drying on the island. Fine scale variability in soil temperature parameters was studied around cushions to improve understanding on how A. selago affects the surrounding soil microclimate. Despite the mild frost climate, extensive frost heave occurred in the study area, indicating that needle ice forms above the previously suggested required temperature of -2°C. Lower and less variable winter temperatures were found on eastern than on western cushion sides, probably as a result of lower wind speeds or leeside snow accumulation on eastern cushion sides. These research findings highlight the importance of A. selago cushions in modifying site microclimates. Such modifications could have important potential consequences, such as providing microhabitats for soil microorganisms and seedlings. Positive plant interactions have been suggested to dominate over negative interactions in environments with high abiotic stress. Positive associations were found between A. selago and both its own seedlings and those of the perennial grass, Agrostis magellanica Lam. (Poaceae) on Marion Island. It is suggested that both cushions and rocks trap seeds dispersed by wind, runoff and/or downslope sediment transport through frost creep. In addition, increased A. selago seedling numbers around cushions, but not around rocks, suggest that cushions provide a biological nurse effect to seedlings of their own kind. Plant species' distributions have been known to vary in response to abiotic stress gradients. In light of this, determinants of A. selago seedling distributions and abundance, such as altitude and substrate cover, were explored. Although there appears to be some altitudinal trend, seedling distributions and abundance patterns were largely attributed to unaccounted variation between sites. Plants can affect the surrounding geomorphology, but also geomorphological measuring techniques. To explore the potential of cosmogenic dating techniques as geomorphological tools in fellfield habitats, accumulation rates of the cosmogenic isotope ­¹ºBe were assessed underneath and adjacent to an A. selago cushion. The results show that ¹ºBe is not fully retained in the soil profile and various reasons are discussed. Furthermore, the results suggest that ¹ºBe concentrations should be interpreted cautiously in fellfield habitats, as A. selago cushions effectively intercept the isotope in their soil-rich core. To facilitate the integration of geomorphological and ecological principles, as was attempted in this thesis, it is important to understand the philosophies behind the different research approaches that ecologists and geomorphologists employ. Ecologists often employ a more statistics-based approach, whereas geomorphologists focus on a more descriptive approach and reasoning based on established theories. I attempt to explain why the two fields follow such different approaches, highlight some potential challenges and provide suggestions to facilitate progress in the interdisciplinary field of biogeomorphology.

Natural interactions between riparian vegetation, large woody debris (LWD) and the fluvial geomorphology of forest streams in North America and Europe have been well researched. In southeastern Australia, where rainfall and runoff are highly variable, where riparian vegetation species are unique and where many streams have been altered since European settlement, there is a paucity of research on such biogeomorphic interactions. This thesis aimed to partly address this knowledge gap by undertaking detailed case studies of four undisturbed streams that varied in their degree of lateral confinement by materials of limited erodibility, i.e. differences in the size and nature of the valley floor trough. These included a laterally and vertically bedrock-confined channel flanked by a series of discontinuous inchannel benches but with no floodplain (Mogo Creek); a laterally bedrock-confined channel flanked by a discontinuous high vertically accreted floodplain and a series of discontinuous in-channel benches (Wheeny Creek); a partially bedrock- and terrace-confined channel discontinuously flanked by pockets of floodplain (Bruces Creek); and a slightly terraceconfined channel continuously flanked by floodplain (Tonghi Creek). Extensive radiocarbon dating of floodplain charcoal at each site highlighted the fact that episodic, rainfall-generated cataclysmic floods have occurred during the late Holocene. These floods totally removed alluvial landforms, including the floodplain forest, from within the valley floor trough. Riparian vegetation communities that have colonised the landforms that redeveloped in the erosional void exhibit a distinct lateral and vertical zonation of species that is determined by the degree of resistance of different species to natural flood disturbance. More flood-resistant tree species, such as Tristaniopsis laurina, are able to grow and survive within the channel and on the channel banks and in—channel benches; possess the ability to reshoot from epicormic buds following high-energy flood disturbance; and can rapidly colonise recently formed alluvial landforms. Less flood—resistant species, such as the Eucalyptus species, grow on higher parts of the floodplain or on remnant Pleistocene river terraces where flood flows are of lower energy and occur less frequently. Measured LWD loadings ranged from 47 m3ha‘I at Mogo Creek to 751 m3ha‘l at Bruces Creek and varied in relation to specific stream power, the relaxation period between cataclysmic floods and the age-structure of the riparian vegetation community from which the LWD was recruited. Large woody debris recruitment processes varied in relation to the geomorphic setting and zonation of riparian vegetation. Episodic bank erosion, undercutting and senescence were identified as the dominant LWD recruitment processes from T. laurina trees growing along the banks of Tonghi and Bruces Creeks, while episodic windthrow was identified as the LWD recruitment process from Eucalyptus trees growing on the floodplains and terraces at these sites. At Mogo and Wheeny Creeks, destruction of in—channel benches by catastrophic floods was identified as the dominant LWD recruitment process from T. laurina and Leptospermum polygalifolium shrubs, while episodic windthrow was the dominant LWD recruitment process from the Eucalyptus trees growing on the high floodplains, where present, and adjacent hillslopes. The longitudinal distribution, orientation and hydraulic impacts of LWD pieces, and the development of log-steps were strongly influenced by the energy of flows experienced and the ratio of tree and LWD size to channel size. Due to high timber densities LWD tends to sink and become partially or completely buried by bedload. It is only in streams with high LWD loadings, low to medium energy bankfull flows and high LWD size to channel size ratios, such as Bruces Creek, that interlocking, wedged pieces of LWD form closely spaced debris dams. The maximum residence time for LWD identified by radiocarbon dating was 980 years on Eucalyptus timber in Wheeny Creek and was interpreted as representing the relaxation period following the most recent cataclysmic flood. Biogeomorphic evidence indicates that riparian vegetation and large woody debris can exert a significant influence on the fluvial geomorphology of sand-bed, forest streams in southeastern Australia by contributing to processes such as pool formation, stream energy dissipation, bank strength, sediment storage patterns, bed stability, oblique bank accretion, in—channel bench and mid-channel bar formation. However, rainfall—generated cataclysmic floods, capable of totally obliterating all landforms within the valley floor trough, including the floodplain forest, have occurred during the late Holocene. Cataclysmic floods exceed vegetationcontrolled thresholds of channel and floodplain stability and resultant specific stream powers of at least 2500 Wm‘2 enable the flood to erode the channel and floodplain to bedrock. Such floods occur more frequently in flood variable regions on high energy streams in narrow valley floor troughs. The width and nature of the valley floor trough, specific stream power and the relaxation period between floods are identified as important factors determining the subsequent influence of riparian vegetation and LWD on the stability of the landforms that redevelop in the erosional void.

Thesis (Ph. D.)--School of Geosciences, Faculty of Science, University of Sydney, 2004.
Degree awarded 2004; thesis submitted 2003. Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Geosciences, Faculty of Science. Title from title screen (viewed 13 January 2009). Includes bibliographical references. Also available in print form.

Abstract The main goal of this study is to examine mechanisms controlling valley asymmetry development at two locations with distinctly differing environmental parameters and to develop a model for the two locations. As a secondary aim the knowledge gained from the main goal is thought to help understand the very uncertain glacial past of the high Drakensberg as it can be compared to the much accepted glacial history of Abisko. Parameters studied were slope angle, landforms, vegetation cover, block abundance, available moisture, bedrock characteristics, temperature and soil moisture. Some parameters were not studied in the field due to time issues; these were instead gathered by literature study. These parameters were structural weakness, soil depth and glaciation. Results show that the environmental differences noted between each sites north and south facing slope are clear. The side facing the equator is at both locations less steep, warmer and has more diverse vegetation. Temperature development with elevation was statistically analyzed and showed no correlation or not statistically significant correlation on all slopes. The expectation the south facing side of the Sani Pass transect showed where a statistically significant decline in temperature with elevation. The main conclusion drawn is that valley asymmetry development at both locations is controlled by the increased intensity of denudational processes on the side facing the equator as a result of the larger input of radiative energy there. It is also suggested that internal feedback mechanisms are related to the hastening of asymmetric development. The main constraint of the study is that not large enough data sets were gathered and that some important parameters like soil depth could not be included in the study. More research is needed in the field of vegetation’s role in interacting with physical processes on mountain slopes. The role of vegetation as an enhancer or retarder of geomorphic processes is not sufficiently understood.
Sammanfattning Denna studies huvuduppgift var att undersöka de mekanismer som kontrollerar uppkomsten av dalgångsasymmetri vid två områden som innehar vitt skilda naturliga förutsättningar och att skapa en modell för platserna. Informationen som ges från huvuduppgiften tros kunna hjälpa förstå den osäkra glaciala historien för Sani Pass eftersom den då direkt kan jämföras med Abiskos väldokumenterade historia. Undersökta parametrar vid båda platserna är sluttningsvinkel, landformer, vegetation, blockmängd, vattenmängd, berggrundskaraktär, temperatur och markfukt. Vissa parametrar kunde inte mätas i fält och fick därför hämtas från facklitteratur. Exempel på sådana parametrar är svagheter i berggrunden, jorddjup och glacial historia. Resultaten visar att det finns tydliga skillnader mellan nord och sydsluttningarna vid båda platser. Den sida som vetter mot ekvatorn har lägre sluttningsvinkel, är varmare och har mer varierande vegetation. Temperaturutveckling vid ökande höjd över havet undersöktes statistiskt där resultaten inte påvisade någon signifikant korrelation mellan ökande höjd och lägre temperatur vid alla områden utom en. Denna plats, Sani Pass nordliga sluttning, påvisades en statistiskt signifikant sänkning av temperaturen med stigande elevation. Den huvudsakliga slutsatsen som utgår från studien är den att utvecklingen av dalgångsassymetri vid båda platserna är kontrollerad av den ökade intensiteten av de nedslitande processerna på den sida som vetter mot ekvatorn. Detta sker på grund av den större mängd solenergi som denna sida mottar. Interna feedback processer verkar även vara kopplade till skapandet av dalgångsasymmetri. Den största motgången i denna studie är att inte nog med data har samlats samt att vissa viktiga parametrar som jorddjup inte kunnat studeras. Mer forskning behövs inom vegetations roll i interaktionen med fysiska processer på bergssluttningar. Om vegetation intensifierar eller motverkar dessa geomorfiska processer är inte tillräckligt förstått.

Urbanisation is increasingly recognised as a major ecological pressure at the coast. By 2035, the Department for Environment, Food and Rural Affairs will have to spend £1 billion each year on flood defence and erosion control infrastructure if current levels of protection are to be sustained in England and Wales; this represents a substantial commitment to building new hard structures. Ecological research has shown that structures like seawalls, breakwaters, and harbour and port infrastructure are poor surrogates for undisturbed rocky shores. This, alongside substantial international policy drivers, has led to an interest in the ways in which structures might be enhanced for ecological gain. Virtually all of this research has been undertaken by ecologists, while the contribution of geomorphological understanding has not been fully recognised. This thesis presents an assessment of the two-way interactions between colonising organisms and the materials used to build hard coastal structures under a framework of biogeomorphology. The influence of material type and small-scale surface texture on early colonisation is assessed alongside detailed observations of the ways in which biota are involved in the alteration of substratum properties and behaviours through weathering and erosion in the intertidal zone. The research demonstrates that biotic (organisms) and abiotic (material substrata) components of coastal structures are inherently linked at various spatial and temporal scales through complex biogeomorphic interactions and feedbacks. Importantly, these interactions have consequences for the subsequent operation of ecological and geomorphological processes that are of relevance to urban marine ecology, weathering and rock coast geomorphology, and engineering. This thesis demonstrates the considerable potential to manipulate substratum-biota interactions on artificial structures for ecological gain, both directly and indirectly. More broadly, the explicitly interdisciplinary methodological approach adopted shows the value and necessity of integrated research for achieving useful, applied outcomes.

Recent studies within the past decade or so have shown the importance of algae in geomorphic and hydrologic processes of lotic systems. However, the ecohydraulic role of algae in bedrock systems has largely been ignored. In addition, the utility of algae as indicators of channel dynamics have often been assumed by geomorphologists, but relatively few studies have examined this relationship. The purpose of this study was to determine whether algae, specifically diatoms, are useful indicators of channel geomorphological dynamics, and to examine if distinct habitats or biotopes typical in fluviokarst and bedrock systems provide unique habitat space for diatoms, and to address the potential ecohydraulic implications. The investigation was performed in a 100 m reach of Shawnee Run, a limestone, fluviokarst tributary to the Kentucky River in Mercer County, KY. The results of the study showed that periphyton are not useful indicators of channel dynamics, and that biotopes and other distinct habitats, including riffles, bedforms, and fine sediment, do not provide unique habitat in terms of diatom community composition.

The eruption of Mount St. Helens in 1980 severely impacted the woody vegetation within the geomorphic floodplain as well as the morphology of the Upper South Fork Toutle River. Historic aerial imagery and LiDAR data were used in combination to create snapshots of the channel and vegetation in 1980, 1983, 1996, 2003, and 2014. This data was mapped and analyzed using GIS, with the primary focus on 2D channel change, vegetation change, and channel-vegetation interactions from 1980 to 2014. No vegetation was discernable in 1980-83 but the vegetation present in 1996 increased in area and in density from 1996 to 2014. The number of channels locations were dependent on vegetation density and presence while vegetation growth occurred predominately in areas previously occupied by the channel.

Abstract Bioerosion is a complex set of physical and chemical processes of rock removal, driven by the interrelationships between (1) ‘biological corrosion’, a solutional process (accounting for 10-30 per cent of total erosion) largely engineered by Cyanobacteria, and (2) ‘biological abrasion’, the removal of these micro-organisms and particulate debris, notably by boring sponges and bivalve molluscs, burrowing echinoids, and grazing amphineurids and gastropods (70-90 per cent of total erosion). Rates of biological abrasion, although largely derived from either live coral surfaces or unconsolidated reef sediments and thus not readily transferable to lithified substrates, have been established through studies of in situ surface modification, experimentation with block transplants and through the collection of sedimentary products. Mean rates of general surface-lowering characteristically range between 0-5-1-0 mm yr-1. As cyanobacterial zonation, and thus erosion rate, varies with position on the littoral profile, and as this zonation changes with exposure, it is possible to explain the characteristic notched form to the littoral profile and its evolution on rocky shores. However, bioerosion rates do not necessarily increase on progressively higher energy coasts: under microtidal regimes, encrustations of coralline algae and vermetid gastropods on surf platforms act as protective structures, sealing the underlying bedrock from bioerosional processes.

ABSTRACT Developing wildfire biogeomorphology as an integrative science is fundamental toward understanding the dynamic processes of adjustment that must occur after wildfires to support heterogeneity, biodiversity, and resilience in fluvial ecosystems. This GSA Special Paper introduces and synthesizes several key points derived from interdisciplinary studies. First, post-wildfire sediment pulses that change the physical elements of fluvial habitat may be transitory or long-lasting, depending on variations in post-wildfire climate conditions. Second, biological processes and feedback may alter post-wildfire geomorphic responses and enhance ecosystem resilience. Third, a greater emphasis on integrated approaches, as encompassed by the discipline of wildfire biogeomorphology, is necessary to adapt ecosystem management strategies. New approaches toward conservation, restoration, and wildfire management that incorporate the variable and dynamic post-wildfire geomorphic responses, the feedbacks between biological and geomorphic processes, and the multiple possible disturbance and recovery trajectories will facilitate sustainable fire management practices in the future.