E-Book, Englisch, 322 Seiten, Format (B × H): 152 mm x 229 mm
An Introduction
E-Book, Englisch, 322 Seiten, Format (B × H): 152 mm x 229 mm
ISBN: 978-0-444-63414-6
Verlag: Elsevier Science & Technology
Format: EPUB
Kopierschutz: 6 - ePub Watermark
Estuaries, the intersection of freshwater and coastal ecosystems, exhibit complex physical and biological processes which must be understood in order to sustain and restore them when necessary.
This book demonstrates how, based on an understanding of the processes controlling estuarine ecosystem health, one can quantify its ability to cope with human stresses. The theories, models, and real-world solutions presented serve as a toolkit for designing a management plan for the ecologically sustainable development of estuaries.
- Provides a sound knowledge of the physical functioning of an estuary, a critical component of understanding its ecological functioning
- Ideal reference for those interested in marine biology, oceanography, coastal management, and sustainable development
- Describes the essentials behind conceptual and numerical models of the health of an estuary ecosystem and how to use these models to quantify both human impacts and the value of remediation and management measures
- Chapters are written in an accessible way that encourages collaboration between aquatic, marine, and wetland biologists, ecologists, oceanographers, geologists, geomorphologists, chemists, and ecosystem modelers
- Covers the physical, chemical, and biological elements of estuary environments, indicating that the essence of an estuary's functioning lies in its connectivity with the adjacent catchment and the marine/coastal system
Zielgruppe
Environmental, managers, water resource managers, marine scientists, aquatic ecologists, civil engineers
Autoren/Hrsg.
Fachgebiete
- Naturwissenschaften Biowissenschaften Hydrobiologie
- Geowissenschaften Geologie Geochemie
- Geowissenschaften Umweltwissenschaften Nachhaltigkeit
- Geowissenschaften Geologie Limnologie (Süßwasser)
- Geowissenschaften Geographie | Raumplanung Deltas, Flussmündungen, Küstenregionen
- Geowissenschaften Umweltwissenschaften Umweltmanagement, Umweltökonomie
- Geowissenschaften Geologie Hydrologie, Hydrogeologie
- Geowissenschaften Geologie Geophysik
Weitere Infos & Material
1 Introduction
1.1 What is an estuary?
1.2 Humanity and estuaries
1.3 Ecohydrology as the solution
1.4 Ecohydrological science: The structure of this book
2 Estuarine water circulation
2.1 The tides at sea
2.2 The residence time of water
2.3 The age of water
2.4 Exposure time versus residence time
2.5 Stratification
2.6 Lateral stratification, trapping, and streakiness
2.7 The importance of the bathymetry on currents
2.8 The importance of coastal currents and waves for estuarine flushing
2.9 The importance of storms on the estuarine circulation
2.10 The special case of lagoons
2.11 The influence of the Earth rotation
2.12 Ship waves
3 Estuarine sediment dynamics
3.1 Geomorphological time scales
3.2 Sediment properties and dynamics
3.3 Stability of the banks
3.4 Tidal pumping
3.5 Some engineering implications
3.6 Biological implications of the export of estuarine mud to coastal waters
3.7 Net sediment budgets
3.8 The size of the mouth
3.9 Mud and human health
4 Tidal wetlands
4.1 Description
4.2 Hydrodynamics
4.3 Wave attenuation by wetland vegetation
4.4 Ecological processes within a tidal wetland
4.5 Enhancement of estuarine fisheries
4.6 Groundwater flow
4.7 Wetlands as bioengineers
5 Estuarine ecological structure and functioning
5.1 Simple food webs
5.2 The key role of detritus
5.3 The role of groundwater
5.4 Estuarine connectivity
5.5 Stressed ecosystems
5.6 Estuarine water quality barriers
5.7 The role of estuaries for fishes and their recruitment to estuaries
5.8 The role of birds in estuarine ecohydrology
5.9 The ecology of tideless estuaries, lagoons and ICOLLS
6 Ecohydrology models
6.1 Introduction: Finding a balance between simplicity, complexity, and realism
6.2 Engineering models
6.3 Ecosystem models
7 Ecohydrology solutions
7.1 Ecohydrology as a response to natural and anthropogenic problems
7.2 Freshwater supply to estuaries: Environmental flows, the essence of ecohydrology
7.3 Estuarine and coastal restoration
7.4 Managing human health threats
7.5 Habitat creation/restoration
7.6 Protection against natural hazards
7.7 Biodiversity offsetting: Ecohydrology in practice
7.8 Main lessons in ecohydrology and ecosystem engineering
7.9 What future for estuaries and coastal waters?
References
Index
2 Estuarine water circulation
Publisher Summary
The physical functioning of estuarine water and sediment varies greatly from estuary to estuary because estuaries can take many shapes and sizes, and because the external physical forcings by river flows, sediment, tides, wind, and evaporation also vary for each one. The hydrodynamic regime of estuaries is the combined result of several components, including the currents and mixing processes caused by the interaction between freshwater and seawater; the tides with their semi-diurnal, diurnal, weekly, fortnightly, equinoctial, and annual cycles; the wind, rainfall and evaporation; oceanic events in coastal waters such as an upwelling, the passage of oceanic eddies, and storms; and the spatially and temporally varying bathymetry and geomorphology, so that an estuary is never at a steady state. This chapter details the net result of these features to give the overall water circulation patterns, which form the basic functioning of an estuary. Keywords Currents Diffusion Evaporation Flushing Mixing Residence time Return coefficient River flow Salinity Stratification Storm Temperature Tides Wind It is not possible to either understand or successfully manipulate the ecological structure and functioning of an estuary without understanding the physical functioning of its water and sediment. This functioning varies greatly from estuary to estuary because estuaries can take many shapes and sizes (Figure 1.1), and because the external physical forcings by river flows, sediment, tides, wind and evaporation vary from estuary to estuary. The hydrodynamic regime of estuaries is the combined result of several components, including the currents and mixing processes caused by the interaction between freshwater and seawater, the tides with their semidiurnal, diurnal, weekly, fortnightly, equinoctial and annual cycles, the wind, rainfall and evaporation, oceanic events in coastal waters such as an upwelling, the passage of oceanic eddies, and storms, and the spatially and temporally varying bathymetry and geomorphology, so that an estuary is never at a steady state (Dyer, 1997; Prandle, 2009). This chapter details the net result of these features to give the overall water circulation patterns, which form the basic functioning of an estuary. As shown here, the relative freshwater and seawater dynamics create the current patterns that will control the transport of suspended sediment and particulate organic matter, contaminants and passively moving organisms in estuaries. The dynamics of the estuary cannot be separated from either those of the freshwater catchment or the coastal and marine areas, again emphasising the connectivity in the system (Elliott and Whitfield, 2011). 2.1 The tides at sea
The tides at sea are a sequence of sinusoidal, tidal harmonic components that are different for every location. The dominant tidal constituents are the diurnal constituents, K1, O1, P1, Q1, and S1, with periods of 23.93, 25.82, 24.07, 26.87, and 24.00 h, respectively, and the semidiurnal constituents M2, S2, N2, and S2, with periods of 12.42, 12.00, 12.66, and 11.97 h, respectively. The sum of these sinusoidal curves with slightly different periods yields a spring-neap tide cycle, whereby the tidal range fluctuates from a maximum (spring tide) to a minimum (neap tide) and back to the maximum over a 28-day cycle. Thus, the tidal range changes daily, as does the timing of the high tide that shifts by about 50 min daily (Ippen, 1966). The tides are classified as microtidal (tidal range < 2 m), mesotidal (2 m < tidal range < 4 m), macrotidal (4 m < tidal range < 6 m), and hypertidal (tidal range > 6 m). The rising tide is called the flood tide, the falling tide is the ebb tide and the intermediate periods are the slack water. The tides are distorted as they propagate in the estuary and the point at which they are no longer observed is the tidal intrusion limit or the tidal limit (Figure 1.13; Prandle, 2009). Often the ebb and flood tides in an estuary differ in duration, called asymmetric tides. This is a function of the hydromorphology of the estuary, which is controlled particularly by the bathymetry, bottom friction and the river inflow. 2.2 The residence time of water
The water circulation determines the residence time and its converse term the flushing rate, which are key physical variables determining the resilience of an estuary and the extent to which the health of an estuary is affected by human-induced stresses. For instance, rapid flushing of polluted estuaries may ensure that there is insufficient time for the dissolved oxygen to be depleted and for sediments to accumulate in the estuary. Therefore, well-flushed estuaries are thus intrinsically more robust than poorly flushed estuaries. On the other hand, human-impacted estuaries with a residence time of several weeks often suffer from dissolved oxygen depletion and experience high turbidity that can exceed 5 g l- 1 and may be up to 14 g l- 1 (Uncles et al., 1998a, 1998b); that oxygen depletion is the result of the suspended particulate matter oxygen demand, the shallow depth and increased summer temperatures, the influx of allochthonous and autochthonous detritus, and the biochemical oxygen demand of point source and diffuse anthropogenic organic matter inputs (see Chapter 5). In contrast, the Tweed Estuary, UK, has a residence time of about 13 h, is less sediment rich and receives less anthropogenic inputs and so it suffers no oxygen depletion (Uncles et al., 2006). The bottom waters of Ise Bay, Japan, have a residence time greater than 50 days, and they suffer from oxygen depletion (Fujiwara et al., 2002). The residence time also affects other parameters such as the degree of contamination and consequently the health of an estuary and coastal waters, including dissolved nutrients, heavy metals and other persistent pollutants, suspended particulate matter, plankton retention and the development of harmful algae blooms (Balls, 1994). 2.2.1 Vertically well-mixed estuary
The residence time can readily be estimated for a vertically well-mixed estuary following the simple, yet realistic, LOICZ method (Swaney et al., 2011). In this method, the estuary is the water body between the river mouth and the salinity intrusion limit (Figure 2.1). Upstream of the estuary is the river, including the tidal river; downstream of the estuary are the coastal waters, defined here as the water mass that mixes with the estuary. The freshwater flow into the estuary Qf (m3 s- 1) is what comes from the catchment as river flow plus groundwater (Figure 2.1). The groundwater inflow is often negligible and can often be ignored except in porous substrata such as limestone. The freshwater flow Qr leaving the estuary is r=Qf+rainfall+localinflowsintheestuary–evaporation (2.1) Figure 2.1 Sketch of the water fluxes in and out of an estuary following the LOICZ model. The river has a salinity Sf = 0, the coastal waters have a salinity So and the estuary has an intermediate salinity Se (0 < Se < So) because estuarine water is a mixture between oceanic water and river water. The inflow of seawater in the estuary is calculated as a diffusive flux; that is, it is proportional to (So- Se). Salt is conserved (i.e. what salt comes in has to get out), hence inflow=QxSo-Se=-Saltoutflow=-QrSr (2.2) where r=salinityatthemouthoftheestuary=0.5So+Se. From Equation (2.2) the diffusive inflow from the ocean is then calculated as x=-QrSrSo-Se (2.3) It is then possible to calculate the renewal time (a time scale related to the flushing time) Tr of water in the estuary (what LOICZ calls the residence time) knowing the volume V (m3) of the estuary as r=VQr+Qx (2.4) 2.2.2 Vertically stratified estuary
A vertical stratified estuary is the result of insufficient vertical mixing in the presence of buoyancy effects, whereby the less dense brackish and often warmer water lies over the denser and usually colder seawater. In this case, the simplest way to quantify the residence time is through the use of a single compartment, tidally averaged box model (Figure 2.2). Typically an estuary has a freshwater inflow with a discharge Qf and a salinity Sf (generally Sf = 0); there is an oceanic inflow along the bottom with a discharge Qin and a salinity So; there is an outflow to the ocean near the surface with a discharge Qout and a salinity S1. Mass is conserved, so that the outflow of water is equal to the inflow of water. Neglecting groundwater inflow/outflows as well as...
