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.
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.
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.
This textbook describes some of the most effective and straightforward quantitative techniques for modeling Earth surface processes. By emphasizing a core set of equations and solution techniques, ...the book presents state-of-the-art models currently employed in Earth surface process research, as well as a set of simple but practical research tools. Detailed case studies demonstrate application of the methods to a wide variety of processes including hillslope, fluvial, aeolian, glacial, tectonic, and climatic systems. Exercises at the end of each chapter begin with simple calculations and then progress to more sophisticated problems that require computer programming. All the necessary computer codes are available online at www.cambridge.org/9780521855976. Assuming some knowledge of calculus and basic programming experience, this quantitative textbook is designed for advanced geomorphology courses and as a reference book for professional researchers in Earth and planetary science looking for a quantitative approach to Earth surface processes.
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.
Multi-temporal elevation (MTE) analysis is used to study topographic changes at specific intervals. Barrier-island complexes are often studied using this MTE analysis to quantify changes to the ...environment after hurricanes to understand how dynamic landscapes respond to different forcings. The Sandy Pond spit (SPS) is a north-south trending barrier island on the eastern shore of Lake Ontario, New York, which responds dynamically to fluctuations in water levels, ice cover, and storms. Prior research reconstructed the geomorphic history of the SPS from 1878–2013, determining that the most significant factor affecting decadal change is the lake-water elevation. In the summers of 2017 and 2019, anomalously high precipitation and lake levels resulted in increased erosion along the SPS, and flooding in neighboring communities. In this study I used shoreline position, foredune crest position and elevation and volume of deposition and erosion to determine the dominant force of geometric change on the SPS before, during and after the high water events in 2017 and 2019, using the study period 2001–2020. Lidar data and small uncrewed aerial system images are used to generate digital elevation models (DEMs) and DEMs of difference (DoDs) from surveys conducted in May 2001, July 2007, June 2011, October 2015, May 2018, September 2018, July 2020 and August 2020. Results indicated water level was the most significant factor altering the topography of the SPS. Large storm events although erosive, were not as destructive to the shore environment as the long duration elevated summer water levels. From 2001–2015 the shoreline advanced an average of 0.25 m/year. From 2015–2018 and 2018–2020 the shoreline retreated 0.62 m/year, and 3.27 m/year respectively. The foredune position and elevation altered due to erosion of the dune toe caused by wave action and shoreline retreat from 2015–2020 compared to 2001–2015. To study volumetric changes, the SPS was split into seven ecogeomorphic zones that characterize the barrier-spit system at large. From 2007–2015 net deposition was recorded at five of the seven zones when applying a 95% confidence interval. The zones recording erosion were characterized by high dune complexes with sparse vegetation to anchor sand. From 2015–2018 net erosion was recorded in all seven zones, indicating water level had a statistically significant effect on the rate and volume of geomorphic change to this ecosystem.
Patterned ground is a ubiquitous landform in periglacial regions of Earth and is also present across the mid to high latitudes of Mars. The association of terrestrial patterned ground to the presence ...of subsurface water ice in the form of permafrost that develops a seasonal ‘wet’ active layer during the summer thaw prompted further investigation of patterned ground on Mars. The Phoenix spacecraft was sent to the surface of the north polar plains of Mars to investigate an area of patterned ground where water ice was predicted to occur. The confirmation of subsurface water ice at the Phoenix landing site confirmed the hypothesis that water ice and patterned ground on Mars are intricately linked, however outstanding questions remain regarding the mode of formation of martian patterned ground. Dry modification via sublimation and thermal-driven processes are possible under present-day climate conditions, however warmer climate conditions are predicted to have occurred during past periods of high obliquity and could have supported periglacial freeze-thaw modification of patterned ground on Mars. Understanding the extent to which liquid water may have been available in the recent geological history of Mars is important to constraining past habitability as well as identifying resources for future long-duration human exploration. It is suggested that if patterned ground on Mars experienced periglacial modification in the past, then it currently exists in a relict form. This research examines the morphometry and surface roughness parameters of active and relict terrestrial patterned ground sites in conjunction with evaluations of martian patterned ground to identify parameters that may assist with ongoing efforts to determine the age and modes of historical modification of patterned ground on Mars.
The coastal system provides habitat, storm protection, and economic value. In particular, Florida’s beaches are subject to chronic coastal erosion resulting from natural and anthropogenic influences. ...The most common mitigation response is the nature-based solution of beach nourishment. While this method is widely considered effective, quantifying changes from the dredge and placement on the physical environment is critical to ensure best management practices. The first step in addressing the need to identify gaps in knowledge relating to natural and human-induced changes to the continental shelf, a comprehensive literature review of the US East and Gulf coast continental shelves was conducted identifying needs for more expansive sand searches, a greater understanding of storm impacts on shelf morphodynamics, planning for long-term use of offshore sediment sources, and the impact of dredging on habitats. This study then evaluated the northern Palm Beach County beaches adjacent to the Jupiter Inlet over multiple years to understand the effects of natural and human influence on the morphology and sedimentology of the beach-nearshore environment. Beach sediment was coarser near the Inlet and finer downdrift (south). Seasonal changes in the nearshore from storms decreased the grain size and eroded beaches, whereas nourishment increased grain size and expanded beach width. Influences of physical characteristics of the beach-nearshore environment on the ecosystem were examined based on two important marine species: loggerhead sea turtles and blacktip sharks. No adverse impacts from restoration activities were found on loggerhead reproductive success. However, the active 2020 hurricane season resulted in lower reproductive success metrics. The blacktip shark migration coincides with the typical nourishment construction window. High turbidity in the nearshore was documented in association with multiple nourishment events during the two-year study. The blacktip sharks were quantified in the nearshore south of the nourishment; however, whether the turbidity was influencing the shark aggregates or habitat preference remains unknown. These results support numerous benefits of beach nourishment but suggest further research is needed to evaluate how project construction may impact nearshore fauna. The findings of this study are important for coastal managers who may consider reviewing best management practices of the beach-nearshore system.
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