Generally, the quality of New Zealand coastal habitats is high by international standards. However, estuaries near urban development are under stress , and action can be taken to alleviate this. All societies affect the environment they live in.
Their customary practices maintained a balance between communities and the environment. Resources were managed sustainably. Some of their practices included:. This shows that the principles of kaitiakitanga were upheld in the early days. Kaitiakitanga means guardianship or protection. Learn more about kaitiakitanga from the work of the Waikato-Tainui people to restore their awa.
Scientific research sometimes reveals environmental problems — such as human impact on estuaries. This can give people the opportunity to respond — becoming science citizens who work with scientists on solutions to the problems. The sheltered waters of estuaries also support unique communities of plants and animals specially adapted for life at the margin of the sea.
Many different habitat types are found in and around estuaries, including shallow open waters, freshwater and saltwater marshes, swamps, sandy beaches, mud and sand flats, rocky shores, oyster reefs, mangrove forests, river deltas, tidal pools and seagrass beds. Estuaries provide us with a suite of resources, benefits and services. Some of these can be measured in dollars and cents, while others cannot. Estuaries provide places for recreational activities, scientific study and aesthetic enjoyment.
Estuaries are an irreplaceable natural resource that must be managed carefully for the mutual benefit of all who enjoy and depend on them. Below are additional ways in which estuaries are important click to expand :.
Thousands of species of birds, mammals, fish and other wildlife depend on estuarine habitats as places to live, feed and reproduce. And many marine organisms, including most commercially-important species of fish, depend on estuaries at some point during their development. Because they are biologically productive, estuaries provide ideal areas for migratory birds to rest and refuel during their long journeys.
Because many species of fish and wildlife rely on the sheltered waters of estuaries as protected spawning places, estuaries are often called the "nurseries of the sea. Estuaries have important commercial value and their resources provide economic benefits for tourism, fisheries and recreational activities. The protected coastal waters of estuaries also support important public infrastructure, serving as harbors and ports vital for shipping and transportation.
This interplay results in a wide variety of hydrodynamic conditions in an estuary, yielding a wide variety of sedimentary systems as well. Primary physical drivers in estuaries are tides. The predominant tidal frequency may be semi-diurnal twice a day or diurnal once a day. Tides influence salinity and oxygen levels and temperature in the estuary.
Strong tidal currents can move sediments such as mud, sand and shells. The volume of water between low and high tide landward of a certain cross-section is known as the tidal prism in that particular cross-section. In short tidal basins, such as coastal lagoons, the tidal prism in the mouth also correlates with the total basin volume below the mean water level and the relative intertidal area in the basin.
Also the influx of fresh river water into an estuary is an important physical driver. The river flow helps maintaining one or more natural outlets to the sea. In areas with a strong seasonal variation of river flows this may even lead to temporary closure of estuaries in times of low flow. Floods and storm events at sea influence the amount of water, sediments and nutrients that are transported from the river into an estuary.
The quantity of fresh river water entering the estuary large determines the salinity distribution in estuarine waters and the degree of vertical stratification. This stratification is caused by the difference in density of fresh and saline water: lighter, fresh water floats on top of heavier saline water. The differences in density hamper the mixing of the water, causing salinity stratification.
The degree of stratification determines the extent to which oxygen can reach deep waters and meet the respiratory needs of benthic communities.
Also, it determines the degree to which the nutrients released from benthic communities in deep water can reach surface waters and become available for uptake by plants. Strong tidal currents or wave motions may force mixing and destratification of the water column. The salinity patterns and gradients in an estuary are the result of stratification and mixing processes. These processes also dominate transport and dispersion within estuaries.
An informative video on mixing can be found here. Estuarine salinity gradients are time-varying at a range of scales, associated with the tidal cycle, day-to-day, seasonal and interannual variations in river discharge and tidal range, the occurrence of storm surges, etc. This time-varying salinity is characteristic of estuaries and strongly influences the ecosystem in these areas. Wind in estuaries, tidal basins and lakes not only causes locally generated wave fields, but also non-tidal circulations, especially in areas with significant depth variations.
If there is sufficient time and space for the waves to become high enough, they are able to move sediment. The growth of locally generated wind waves in estuaries is usually limited by the fetch, i. Intertidal flats, when emerged, limit the fetch and hence the wave growth. When submerged, the flats limit wave growth by dissipating wave energy in the shallow waters on top of them.
In this way, intertidal flats play an important role in the design conditions for the flood defence system bordering the estuary. The wide variety of hydrodynamic conditions in an estuary also yields a variety of sedimentary systems, from sandy channel beds, via mixed intertidal flats to mudflats and muddy marshlands. Sediment originates from rivers, sea and the land surrounding the estuary Day et al. Where saline water and sediment-laden river water meet and mix, the increasing salinity may cause sediments suspended in the fresh water to flocculate , resulting in an estuarine turbidity maximum ETM and a zone of intense sedimentation.
These zones are also known as estuarine entrapment zones or null zones. A simplified conceptual model of shoal formation assumes that the tidal motion tends to build up a shoal, via various asymmetries in the water motion that give rise to a net uphill sediment transport. Waves, on the other hand, tend to erode a shoal, especially its top part. If the equilibrium between tidal and wave action is disturbed, like in the Eastern Scheldt after the construction of the storm surge barrier, this has consequences for the shoal morphology.
The interplay between physical forces and biota is called bio-physical interaction. Intertidal coastal environments are often inhabited by distinct biota such as sea grasses, salt marsh vegetation and epibenthic oyster reefs and mussel beds. These organisms form three-dimensional structures on and in an otherwise bare soft-sediment environment.
These structures interact with the tide- and wave-induced hydrodynamic forces. These reef-building organisms are known as ecosystem engineers , as they are capable to mediate the environment for the entire biological community. The dominant issue in this environment is coastal safety, but most of the times multiple land use issues also play a role. Therefore, decision making about estuaries often involves national, regional and local governance levels.
Furthermore, participation of supranational governance levels may be relevant since activities in an estuary may have their influence upstream. Key actors are national and regional authorities and increasingly also supranational government institutions e. In cases where coastal safety is a matter of national importance and solidarity, the national authority is often in the lead, whereas the decentral governments often have an important say in other issues.
Usually, estuarine management has to comply with a variety of development and management plans, sectorial strategies, international regulations — such as EU Directives — and other regional and national policies. Therefore, integration of plans and structure may be a challenge. In Europe, the increasing interest in an integrated approach of estuarine management requires involvement of many parties of more or less equal importance. Stakeholders groups, when confronted with decisions in which they have had no say, will tend to resist against them and they may have extensive legal means to do so.
Although there seems to be consensus on the usefulness of stakeholder participation, public input is often limited in nature and extent.
For applying innovative approaches like BwN in estuarine areas with a number of stakeholders groups with the same importance of interests, it is certainly important to actively involve them in the planning process so as to meet their interests as much as possible and minimise the chance of time-consuming court cases. For more information on governance processes see Governance.
Estuaries provide multiple resources and processes from which mankind can benefit. These benefits are known as ecosystem services, commonly divided into four categories United Nations Millennium Ecosystem Assessment.
For further reading on ecosystem services see here. Services of estuaries which are necessary for the production of all other ecosystem services, but do not yield direct benefits to society:. The BwN sub-programme for estuaries mainly focuses on the protection and the creation of intertidal areas.
These areas are of key importance to the estuarine ecosystem and in many estuaries their total size has decreased as a result of erosion after dredging, land reclamation, expansion of harbours, dam and barrier building, etc. Below we present some examples of how estuarine dynamics can be used for sustainable eco-engineering.
Within an estuary, currents and locally generated waves determine the erosion, transport and deposition of sediment. The seaward end of the estuary is shaped by erosion and deposition of sediments by wave-driven and tidal currents. A Building with Nature opportunity is to use the forces of currents and waves to redistribute sediments in the estuary.
By redirecting currents and influencing waves by eco- engineered structures, erosion or deposition of sediments can be promoted. This can be used to deepen or maintain discharge channels and shipping routes, or to form new intertidal areas.
These tidal flats can be a prerequisite for provision, regulating and cultural ecosystem services such as food production, water purification, habitat and aesthetic beauty. These vegetation types attenuate waves, fix the bottom and may even trap sediment, thus helping to protect the coast from natural hazards and floods.
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