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.
Encounters with Confluences Sumner, Ray
Yearbook - Association of Pacific Coast Geographers,
01/2019, Letnik:
81, Številka:
1
Journal Article
Recenzirano
This study examines a selection of river confluences, places that are frequently locations of important physical investigations by hydrologists, geomorphologists, biologists, and engineers, among ...others. In contrast, confluences can also demonstrate a complex interplay of historical, economic, social, and political factors. Many urban stream confluences were sites of prehistoric human settlement; others are more recent historic sites, or important shipping facilities; and some are simply tourist attractions. From the multitude of stream confluences, this paper examines a small selection from the United States of America and Europe, with a focus on the multiplicity of human associations and layers of meaning.
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.
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