Preface

Estuaries and their surrounding wetland regions are among the most productive ecosystems in the world, and among the most populated, with more than half of humanity inhabiting their shores. Anthropogenic factors make estuaries highly susceptible to ecosystem degradation due to the influences of industrialization, overfishing, and pollution. Coastal waters are closely connected with human activity, and their dynamic processes may greatly affect coastal environments. It is believed that sea level rise can threaten coastal living conditions with higher probabilities of flooding and inundation, possibly amplified by local tidal changes in response to water level modifications. Estuaries are a transition zone between riverine and maritime environments, and their ecology is sensitive to physical, chemical, or biological changes. Many estuaries also discharge freshwater river plumes that may further influence coastal zone dynamics on all levels. This book provides a compendium of studies of estuarine dynamics, river plumes, and coastal water dynamics, as well as studies that have investigated the changes in estuarine and coastal zones in response to sea-level rise and other environmental factors. This book also provides a section on issues related to coastal environmental management. Topics covered in this section include consensus-based policies for the fishery industry, and efficient balancing of coastal erosion concerns with public utilization of recreation zones along the coast.

There are three sections in this book. The first section is "Coastal Tide and Sea Level Change", focusing on tide and sea level change in coastal waters. In Chapter 1 of the first section, tide, currents, and other physical properties in Elkhorn Slough waters of Monterey Bay, California, USA are analyzed to reveal the variations in a recent ~30-year period from 1970 to the early 2000s. Due to frictional effects and extensive mud flats and Salicornia marsh, tidal distortion increases, produces overtides, and compound tides; maximum tidal currents in Elkhorn Slough have increased from 0.75 to 1.50 m s−1 since 1970 mainly because of the increase in tidal prism between 1956 and 2003. The man-made changes and continued tidal erosion are the major reason of the tidal prism change. The second chapter reveals correlated changes in sea levels and ocean tides in the Pacific and Atlantic Oceans, and a detailed result of tide and sea level correlations in the Hong Kong coastal waters, suggesting tidal changes are likely to have the greatest effect on coastal locations, especially estuarine regions, which are often highly-developed, densely-populated, and environmentally sensitive. In Chapter 3, using numerical simulations, the influence of sea level rise (SLR) on storm responses is identified for Saco Bay, which is characterized by gentle coastal slopes, and Casco Bay, which is sheltered by barrier islands and peninsulas with steep shorelines. By comparing changes in inundation, storm currents, and salinity distribution between the two bays, the step-like bottom relief at the shoreline of Casco Bay sets up nonlinear responses to SLR. In contrast, storm responses in Saco Bay varied significantly with SLR due to alterations in river dynamics attributed to SLR-induced flooding. The conventional objections by satellite altimeters are normally inaccurate in the coastal waters due to the land effects on the return waveform; in Chapter 4, a promising technology, coastal altimetry, is described. It employs a new methodology to process the waveform from coastal waters. In a case study of the Hong Kong offshore water, it is found that the coastal

sea level trend is about twice as much as the one observed further offshore, suggesting that in the Hong Kong region, the short-term sea level trend significantly increases when approaching the coast.

The second section focuses on studies of the coastal and estuarine water with a title of "Observation and Analysis of Coastal Waters and Estuaries". The first chapter clarifies the dynamics of small river plumes, which are significantly different from that of plumes generated by large rivers. Small plumes exhibit more energetic temporal variability in response to external forcing, such as wind forcing and river discharge, the interaction between neighboring small plumes, and the generation of high-frequency internal waves in coastal ocean by small rivers. In the second chapter, a cruise survey of the Pearl River Estuary (PRE) and adjacent coastal water from May 3–11, 2014 was reported. Using the cruise data, a "sandwich" structure of the lateral salinity distribution and a two-layer structure of longitudinal circulation were identified. The Finite-Volume Community Ocean Model (FVCOM) is configured and run with high spatial resolution of 100 m in the PRE, which reveals that there is a strong neap-spring cycle for the PRE de-tided circulation. Chapter 3 analyzes the sampling data from six bimonthly surveys between November 2011 and September 2012 in the Jansen Lagoon, which is located to the northwest of São Luís Island (northern Brazil), with a significant urban influence. High levels of dissolved oxygen (DO), pH, total phosphorus, and chlorophyll-a were observed in the lagoon waters. The water quality indexes showed that the Jansen Lagoon has a poor water quality due to elevated DO and pH as well as high concentration of surfactants and phenols. Chapter 4 studies in-situ measurements of chromophoric dissolved organic matter (CDOM) absorption during a spring cruise survey in the Pearl River Estuary (PRE). The surface CDOM has higher absorption and lower spectral slope than the bottom. Horizontal transport is suggested to be the dominant hydrodynamic mechanism affecting CDOM distribution pattern in the PRE. Using an algorithm developed for the PRE environment, a time series of CDOM absorption and spectral slope in the PRE and the Hong Kong waters in spring from 2012 to 2018 is produced based on satellite images obtained by four sensors with different spatial and spectral resolutions. In Chapter 5, wind-driven coastal upwelling east of Hainan Island (UEH) in the northwestern South China Sea (SCS) is found to be sensitive to multiple scales of atmospheric forcing that are either very short-term or sudden impact, i.e., typhoon passages, or long-term variability associated with El Niño events. The study suggests that UEH has significant responses to the atmospheric forcing, and the ocean circulation also plays an important role in the modulation of the coastal upwelling.

Section 3 is "Coastal Environment Management". Chapter 1 emphasizes the importance of the coastal areas on potential of fisheries that can contribute greatly to the national economic growth. Good management requires a well-structured plan that takes into account geographical conditions and the sustainability of the plan in the future for the role of marine spatial planning. The dialogue between elite sectors of society and the public are important for the coherence and synergy of spatial planning, and consensus can be achieved based on potential spatial data integration between official spatial data and crowdsourced geographic information, which predominantly look from nontechnical perspectives. In Chapter 2, coastal environment issues such as coastal erosion, sea cliff collapses, etc. are discussed for the coasts along Northeast Brazil and northern Colombia, and how they can damage local economies. It is necessary to better plan for the occupation and uses of these coastal areas, in order to promote a sustainable development.

The chapters of this book provide detailed information on studies of coastal and estuarine environments and may help to inspire in-depth investigations in future. We are grateful to the authors and the publishing staff of IntechOpen for their excellent contributions to this book.

> **Professor Jiayi Pan and Professor Adam T. Devlin** Jiangxi Normal University, Nanchang, Jiangxi, China

Section 1
