As an important part of the global carbon cycle, dissolved inorganic carbon (DIC) concentration and its stable carbon isotopic composition (δsup.13Csub.DIC) have been used to constrain the sources of ...DIC in rivers. In this study, we systematically investigated the water chemistry, DIC contents, and δsup.13Csub.DIC values in a tropical agricultural river in northeast Thailand. The water temperature ranged from 20.3 to 31.3 °C, and water pH values ranged from 6.4 to 8.4, with seasonal variations. Based on the major ion compositions, the hydro-chemical type of the Mun River water was a unique Na–Ca–Cl–HCOsub.3 type, controlled by evaporite and silicate weathering. Seasonal variation of DIC concentrations and its carbon isotopic composition was obvious; DIC and δsup.13Csub.DIC were significantly lower in the wet season (135 to 3146 μmol/L and −31.0‰ to −7.0‰) compared to the dry season (185 to 5897 μmol/L and −19.6‰ to −2.7‰). A high level of sup.12C-enriched DIC/COsub.2 from soil respiration and organic matter oxidation may cause the low pH values, δsup.13Csub.DIC values, and high partial pressure of COsub.2 (pCOsub.2) in the middle and lower reaches during the wet/rainy season compared to the dry season. This may be responsible for the seasonal and spatial variations of DIC concentrations and δsup.13Csub.DIC values in the Mun River. According to the relationship between pCOsub.2 and δsup.13Csub.DIC values, COsub.2 outgassing may be more significant in the dry season, due to the greater influx of groundwater with higher pCOsub.2 levels; and the rapid COsub.2 diffusion into the atmosphere will continuously increase the δsup.13Csub.DIC values and decrease pCOsub.2 levels. These results show that riverine biologic effects and COsub.2 outgassing play important roles in the DIC and δsup.13Csub.DIC evolution of this typical agriculturally-dominated watershed.
Geomorphometry Tomislav Hengl, Hannes I. Reuter
2008, 2008-11-01, Letnik:
v.Volume 33
eBook
Geomorphometry is the science of quantitative land-surface analysis. It draws upon mathematical, statistical, and image-processing techniques to quantify the shape of earth's topography at various ...spatial scales. The focus of geomorphometry is the calculation of surface-form measures (land-surface parameters) and features (objects), which may be used to improve the mapping and modelling of landforms to assist in the evaluation of soils, vegetation, land use, natural hazards, and other information. This book provides a practical guide to preparing Digital Elevation Models (DEM) for analysis and extracting land-surface parameters and objects from DEMs through a variety of software. It further offers detailed instructions on applying parameters and objects in soil, agricultural, environmental and earth sciences. This is a manual of state-of-the-art methods to serve the various researchers who use geomorphometry.Soil scientists will use this book to further learn the methods for classifying and measuring the chemical, biological, and fertility properties of soils and gain a further understaing of the role of soil as a natural resource. Geologists will find value in the instruction this book provides for measuring the physical features of the soil such as elevation, porosity, and structure which geologists use to predict natural disasters such as earthquakes, volcanoes, and flooding. * Technical details on a variety of software packages allow researchers to solve real-life mapping issues* Provides soil and agronomy researchers best practice techniques for soil data analysis to assist in enhanced land-use and planning* Offers geologists essential tactics for better environmental management by providing a comprehensive analysis of the physical features of soil * Companion website includes access to the latest technological advancements previously unpublished in any other comprehensive source: geomorphometry software, DEM data sources, and applications
This thesis develops analytical frameworks for evaluating the validity of MBES data with comparable ground truthing and hydrodynamic data with respect to geomorphology and marine biodiversity in two ...Special Areas of Conservation (SAC) in the Malin-Hebrides Sea off the north-Irish coast. First, a modelling framework based on Generalised Linear Modelling (GLM) is developed to test the validity of multi-frequency MBES backscatter data (30, 95, 300 kHz) to characterise sediment grain size in the Hempton's Turbot Bank (HTB) SAC. The results demonstrate that the single-frequency sources have a marginal gain on the multi-frequency model, with the 30 kHz model driving the significance of the multi-frequency model, and the inclusion of the higher frequencies diminishes the level of agreement. Secondly, a combination of K-Means unsupervised classification and GLM based on MBES backscatter (95, 300 kHz) and bathymetry analysis are successfully used to predict different levels of sandeel Hyperoplus lanceolatus densities with respect to geomorphology in the HTB SAC. The study demonstrates that the lower frequency source is more adept at capturing the variety inherent in shallow sub-surface sedimentary environments, which this species prefers. Finally, multidisciplinary modelling and analysis approaches using MBES data, hydrodynamic data and theodolite tracking observations are used to assess the spatial dynamics of harbour porpoise Phocoena phocoena in the Skerries and Causeway SAC. Generalised Additive Modelling (GAM) identifies that slope, aspect and backscatter intensity are the most statistically significant variables accounting for the highest deviance in porpoise sighting density. Models predict a high probability (> 0.6) of porpoise encounters in nearshore areas, particularly concentrated around headlands where local flow acceleration results in coarser beds. The robust workflows developed in this thesis, provides a proof of concept for developing robust monitoring strategies for Marine Protected Areas and associated species. Respective recommendations will inform marine policy, marine spatial planning and management.
The trajectory of geomorphology Church, Michael
Progress in physical geography,
06/2010, Letnik:
34, Številka:
3
Journal Article
Recenzirano
Modern geomorphology was founded in the nineteenth century as an exercise of historical interpretation of landscapes. After the mid-twentieth century it dominantly became a quest to understand the ...processes by which landscapes are modified. This focused attention on the measurement of sediment fluxes on synoptic timescales and on a reductionist, Newtonian programme of construction of low-order theories about those fluxes, largely imported from engineering science. The period also saw the emergence of an applied geomorphology. Toward the end of the twentieth century the subject was dramatically transformed by improved technologies for remote sensing and surveying of Earth’s surface, the advent of personal computation and of large-scale computation, and important developments of absolute dating techniques. These technical innovations in turn promoted recognition of geomorphology as a ‘system science’ and facilitated the reintegration of tectonics into geomorphology, opening the way for a renewed consideration of the history of the landscape. Finally, increasing recognition of the dominance of human agency in contemporary modification of Earth’s terrestrial surface has become a significant theme. Important influences on the continuing development of the subject will include the search for physically sound laws for material fluxes; reconciling geomorphological information and process representations across spatial and temporal scales, in both observation and theory; comprehending complexity in geomorphological processes and landform histories; incorporating the geomorphological role of living organisms, particularly micro-organisms; understanding the role of climate in geomorphology, both in the contemporary changing climate and in the long term; and fully admitting the now dominant role of humans as geomorphic agents. Geomorphology is simultaneously developing in diverse directions: on one hand, it is becoming a more rigorous geophysical science — a significant part of a larger earth science discipline; on another, it is becoming more concerned with human social and economic values, with environmental change, conservation ethics, with the human impact on environment, and with issues of social justice and equity.
A debris rich ice core was collected from a buried ice mass in Ong Valley, located in Transantarctic Mountains in Antarctica. Measured cosmogenic nuclide concentrations in quartz obtained from the ...ice core were used to determine the age of the buried ice mass and infer the processes responsible for the emplacement of the debris currently overlaying the ice. Such ice masses are valuable archives of paleoclimate proxies; however, the preservation of ice beyond 800 kyrs is rare and therefore much effort has been recently focused on finding ice that is older than 1 Ma. In Ong Valley, the large, buried ice mass has been previously dated at > 1.1 Ma. In order to further constrain the age, this research focuses on a novel forward model that predicts the accumulation of the cosmic-ray produced nuclides 10Be, 21Ne, and 26Al in quartz in the Ong Valley englacial and supraglacial debris. Large observed downcore variation in measured cosmogenic nuclide concentrations suggests that the englacial debris is sourced both from subglacially-derived material and recycled surface debris that has experienced surface exposure to cosmic rays prior to entrainment. Modeled results show that the upper section of the ice core is 2.95 +0.18/-0.22 Myrs. The average ice sublimation rate during this time period is 22.86 +0.10/-0.09 m Myr-1, and the surface erosion rate of the debris is 0.206 +0.013/-0.017 m Myr-1. Burial dating of the recycled paleo surface debris suggests that the lower section of the ice core belongs to a separate, older ice mass which is estimated to be 4.3-5.1 Myrs old. The ages of these two stacked, but temporally separate ice masses can be directly related to glacial advances of the Antarctic ice sheet and potentially coincide with two major global glaciations during the early and late Pliocene Epoch when global temperatures and CO2 were higher than present. These ancient ice masses represent new opportunities for gathering information on past climates.
Large wood (used interchangeably with the term “instream wood”), which refers to trees, logs and other wood within a channel, is beneficial to river ecosystems and is being used more frequently as a ...component of river restoration projects. The process of large wood becoming stable within a river channel, inducing floodplain formation, and eventually providing large wood back to the system is known as the ‘floodplain large-wood cycle’ hypothesis (Collins et al., 2012). In a stream restoration context, this process can be viewed as an indicator of a self-sustaining cycle.The ‘floodplain large-wood cycle’ hypothesis was formulated in the Pacific Northwest. To investigate this process in other regions, I used the Merrimack Village Dam (MVD) study site in southern New Hampshire. The study site provided a location where instream wood was recruited to the river from an adjacent terrace as a consequence of erosion associated with a dam removal. Assessment of wood in this scenario was used to evaluate the ‘floodplain large-wood cycle’ (Collins et al., 2012), and to compare MVD to “passive” large wood restoration and deliberate, and potentially engineered, large wood restoration sites throughout New England.To assess multiple sites, I identified metrics to evaluate the effectiveness of large wood to promote ecological and geomorphic complexity within channels. The metrics were quantified at the MVD site and several other sites in New England with natural or placed large wood. I also collected additional data at the MVD site using methods implemented during previous studies, including cross section surveys and repeat photographs (Collins et al., 2017; Pearson et al., 2011).The study assessed habitat and geomorphic effects of large wood within river systems in the northeastern U.S. and provided information to evaluate the use of large wood during river restoration. Overall, only 33%, 33%, and 20% of surveyed sites are consistent with hypotheses formulated regarding significant differences in depth variability, velocity variability, and median velocity between test and reference reaches, respectively. With evidence for and against each hypothesis at both passive and active sites, large wood structures did not cause the geomorphic and hydraulic changes I expected to see. The availability of sand in a channel and the stream slope influencing sediment transport seem to be important factors in determining whether or not large wood has the ability to impact the geomorphic and hydraulic characteristics of a channel. At the MVD site, where sand is available, up to 0.90 m of sediment deposition is seen on top of the surface eroded by a March 2010 flood, surrounding recruited trees. Evaluation of historical aerial imagery further indicates that evidence of the ‘floodplain large-wood cycle’ hypothesis is present at the MVD06 cross section on the Souhegan River in New Hampshire.
It is well-understood that the physical state of a river is a combination and culmination of present processes and past trajectories. Similarly, conceptualizations of fluvial connection hold that ...various aspects of a given river reach—ecologic, geomorphic, hydrologic—do not operate in isolation, but rather as components within a linked system, both influencing and influenced by upstream and downstream conditions. To expand understanding of the river system as an intrinsically linked network of both process and form, here I establish connections between the processes of historical tributary erosion and distal downstream channel migration and floodplain forest establishment in the Yampa and Green River Basin. I then additionally summarize the extensive body of literature concerning the geomorphic response to sediment supply increases in low-gradient, alluvial rivers to further emphasize that the translation of sediment through the landscape can catalyze myriad responses that manifest across a continuum of scales. Concentrating initially on the investigation of historical erosion, examination of historical documents and aerial photos suggests that three key sediment contributing tributaries of the Yampa River—Sand Creek, Muddy Creek, and Sand Wash—underwent substantial historical erosion from 1880-1940. Using field investigation to determine historical channel location and field surveys of present-day dimensions, I then calculate that historical arroyo incision within the latter two tributary watersheds injected 30 × 106 tons of sediment into the mainstem Little Snake and Yampa Rivers during this time. Taking present-day annual sediment loads as an approximate background for the pre-erosion sediment regime, this represented a sizable increase in the sediment load of the Yampa River during the period of historical erosion. Moving downstream, results of dendrochronologic analysis of tree cores from three separate forest locations—Deerlodge Park on the Yampa River, Island Park and Tuxedo Bottom on the Green River—indicate that major portions of these forests established during the same time period of elevated historical erosion. Moreover, channel change analysis suggests that the channel at this time was relatively more dynamic than it has been since, and the area of forest dating to the historical period is much greater than can be explained by high flows alone. Viewed collectively, these findings suggest tributary erosion played a vital role in successful downstream forest establishment. Additional sediment fingerprinting analysis further supports this process link between geomorphic and ecologic process. Using sediment samples taken at the rooting surface of the cottonwood forest in Deerlodge Park, geochemical analysis indicates that the majority of this sediment was sourced from those tributaries—Muddy Creek and Sand Wash—that were undergoing enhanced erosion via arroyo incision during the historical period. Overall, the temporal overlap between the timing of historical tributary erosion and the establishment of substantial portions of downstream floodplain forest, in conjunction with the fact that floodplain sediment is dominantly sourced from watersheds that experienced enhanced historical erosion, together indicates a demonstrable link between the geomorphic process of historical erosion and the ecologic process of downstream floodplain forest establishment. From a summary of existing studies concerning the geomorphic adjustment of low-gradient, alluvial rivers to increased sediment supply, it is additionally clear that tributary erosion that injects substantial amounts of sediment into a river system can result in the requisite channel change necessary for successful forest establishment. The fluvial system is thus best understood as not just a physically coupled network, but a collectively connected web of processes that together regulate and are regulated by one another. Such an understanding emphasizes that management of large watersheds must be holistic and undertaken at the basin scale in order to ensure that vital riverine ecosystems endure.
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