Comprehensive studies of different types of river mouths (on the example of the river mouths in the north-western part of the Black Sea)

The development of the concept of sea estuaries as separate geographic objects based on a strategy of interdisciplinary research and about 6 million non-equidistant observation data, subject to nonstationarity of estuarine processes and unstable anthropogenic load, made it possible to propose a universal structural and hydrological typification of estuaries; to establish their maritime boundaries in terms of the minimum values of water salinityas Cv, to regionalize water areas from river to maritime boundaries and, on the this basis, to improve scientific terminology. Modern distribution schemes have been obtained and general patterns have been established for the variability of the main characteristics of the state of estuaries, depending on the variability of the river runoff and the water level of estuarine seasides, and new methods for their calculation, invariant for similar estuaries, are proposed. 54 negative phenomena are included in the catalogue; their interrelationships, causes and consequences are established. The analysis of estuarine processes has been carried out, the patterns of variability of their main characteristics from natural and anthropogenic factors have been determined. The ways of solving the problems of nature management in the estuarine regions of the northwestern part of the Black Sea are proposed. The monograph is intended for oceanographers, hydrologists, hydrochemists, ecologists, workers of environmental protection, monitoring and control organizations, as well as teachers, graduate students and students of relevant specialties.

DOM Biological Lability in an Estuarine System in Two Contrasting Periods

Estuarine processes play a key role in determining the amount and quality of land-derived dissolved organic matter (DOM) reaching the oceans. Microbial-mediated reactions can affect the concentration, quality, and bioavailability of DOM within an estuary. In this study, we investigated biological DOM removal in a small estuary and its variability in two contrasting seasons (spring and autumn) characterized by natural differences in the concentration and quality of the riverine DOM. Two incubation experiments were carried out using natural DOM and heterotrophic prokaryotes community collected at the estuary in March and September. Dissolved organic carbon (DOC) concentration, DOM fluorescence, and the heterotrophic prokaryotes abundance (HPA) showed marked differences between the two seasons. These parameters were followed through time for up to two months. Despite the marked differences in the initial conditions, the DOC removal rates were surprisingly similar in the two periods (16 µM DOC month−1 in March and 18 µM DOC month−1 in September), with the biggest removal in the first 48 h. The trend of fluorescent DOM (FDOM) during the incubation showed marked differences between the two periods. In March, the net removal of all the FDOM components was observed consistently with the decrease in DOC; whereas, in September, the net production of humic-like substances was observed.

Amazon Sediment Transport and Accumulation Along the Continuum of Mixed Fluvial and Marine Processes

Sediment transfer from land to ocean begins in coastal settings and, for large rivers such as the Amazon, has dramatic impacts over thousands of kilometers covering diverse environmental conditions. In the relatively natural Amazon tidal river, combinations of fluvial and marine processes transition toward the ocean, affecting the transport and accumulation of sediment in floodplains and tributary mouths. The enormous discharge of Amazon fresh water causes estuarine processes to occur on the continental shelf, where much sediment accumulation creates a large clinoform structure and where additional sediment accumulates along its shoreward boundary in tidal flats and mangrove forests. Some remaining Amazon sediment is transported beyond the region near the river mouth, and fluvial forces on it diminish. Numerous perturbations to Amazon sediment transport and accumulation occur naturally, but human actions will likely dominate future change, and now is the time to document, understand, and mitigate their impacts.

Investigation of Morphological Changes in the Tamsui River Estuary Using an Integrated Coastal and Estuarine Processes Model

This study is to investigate morphological changes in the Tamsui River Estuary in Taiwan driven by multiple physical processes, such as river flows, tides, waves, and storm surges, and then to study the impacts of sediment flushing operated at the Shihmen reservoir upstream on the river estuary. An integrated coastal and estuarine processes model (CCHE2D-Coast) (Center for Computational Hydroscience and Engineering Two-Dimensional-Coast) was validated by simulating these physical processes in the estuary driven by three historical typhoons in 2008. The site-specifically validated model was then applied to simulate morphological changes in the estuary in response to reservoir sediment flush scenarios from the upstream. For the impact assessment of sediment flushing, a synthetic hydrological event was designed by including a historical typhoon and a typical monsoon. It was found that during the typhoon, the sediments will be mostly deposited in the estuarine river reach of Tamsui and the Wazihwei sandy beach. During the monsoon period, most of the sediments tend to be deposited in the second fishing port of Tamsui, the northern breakwater, and the estuary, while the Wazihwei sandy beach in the river mouth would be scoured by backflow. Simulations of the complex flow fields and morphological changes will facilitate the best practice of sediment management in the coastal and estuarine regions.

5. Tidal bores

A tidal bore is perhaps the most spectacular tidal phenomenon that can be readily observed. When a large tide enters a shallow, funnel-shaped estuary with a gently sloping bottom, its waveform is distorted and this can lead to an impressive rolling ‘wall of water’, travelling upriver. ‘Tidal bores’ explains that estuary shape and a large tidal range are important for tidal bore formation. Tidal bores can be smooth, non-breaking ‘undular’ waves or a variety of breaking forms of increasing violence. Famous examples are seen along the Qiantang River in China, the Amazon River in Brazil, and the River Severn in the UK. The impact of tidal bores on estuarine processes and ecosystems is also discussed.