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h1. H1130 - Estuaries
h1. General
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|| General characteristics || ||
| Common name and group |Estuary|
| Region | The Netherlands |
| Water systems | coastal waters|
| Nature parameter |Vegetation and habitat types  |
|HR nr|H1130 |
| Fact sheet by |K.E. van de Wolfshaar |{column}{column:width=20%}
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h1. Description habitat



h3. General occurrence


Well-developed estuaries can be found in two locations in The Netherlands, namely the Ems-Dollard estuary in the Wadden Sea and the Westerschelde estuary. The New Waterway near Rotterdam is an artificial estuary. [#1].


h3. Environmental boundary conditions
Estuaries are the downstream parts of a river valley, subject to the tide and extending from the limit of brackish waters. Contrary to the habitat type [H1160 - Grote baaienLarge shallow inlets and bays], there is a substantial freshwater influence. The mixing of freshwater and sea water results in a salt and fresh gradient. The farthest upstream influence of salt water forms the boundary of the estuary, the farthest influence of downstream fresh water forms the boundary of the marine system. An estuary forms an ecological unit with the surrounding terrestrial coastal habitat types (salt marshes and tidal marshes). These habitats, located at the boundary of the estuary, have been described as independent habitat types ([H1310 - Zilte pionierbegroeiingen], [H1320 - Spartina swards] and [H1330 - Atlantic salt meadows]) and are thus not considered under the type "estuary".
Estuaries contain a large variety of plants and animals thanks to the fresh and salt gradient and the mostly sheltered location. Estuaries contain more species than accompanying coastal areas, due to the environmental variation, the large amount of food and, a lower predation pressure for fish. Examples of species who are dependent on this brackish transitional environment are the worms Tubifex costatus_ and _Paranais litoralis_. [#1]. 

h3. Control and growth opportunities 
This habitat type is mainly sensitive to changes in velocity and flooding frequency. In addition, a change in the influence of salt water as well as fresh water alters the surface of the estuary. 


h1. Dose-effect relations
Estuaries are landscape elements that are difficult to capture with habitat factors. However, the occurrence of dwarf eelgrass and common eelgrass can be predicted with the aid of habitat factors. These two species are found frequently in estuaries. 

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h4. Flow chart
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h4. Dose-effect relations
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{chart:type=bar|title=tidal influence|xlabel=tidal influence|yLabel=HAI |dataDisplay=true|dataOrientation=vertical|legend=false}
||tidal influence || HAI ||
| absent | 0 |
| present | 1 |

{chart}
Reference: [#1]
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{chart:type=bar|title=Ecodistrict|xlabel=district|yLabel=HAI |dataDisplay=true|dataOrientation=vertical|legend=false}
||district || HAI ||
| Estuary district | 1 |
|different|0|
{chart}
Reference: [#1]
note: this concerns the division of Flora districts according to Van Soest/Weeda. 
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h5. Occurrence of characteristic species
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Dwarf eelgrass and common eelgrass are an important food source for many organisms. The occurrence of eelgrass is thus beneficial for this habitat type. Therefore, common eelgrass and dwarf eelgrass are included as additional dose-effect relations. You can find the dose-effect relations for both types of eelgrass on the pages [Common eelgrass - Zostera marina] and [Dwarf eelgrass - Zostera noltii]
{chart:type=XYline|title=Occurrence common and dwarf eelgrass|xlabel=Common and Dwarf eelgrass (HAI)|yLabel=HSI |dataDisplay=true|dataOrientation=vertical|legend=false}
|| Common eelgrass or dwarf eelgrass (HAI) ||HAI ||
| 0 | 0 |
| 1.0|1.0|
{chart}
Reference: [#1]
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h1. Uncertainty and validation
(!) These dose-effect relations have not been validated. 


h1. Applicability
To describe a landscape element according to habitat factors is very difficult. Therefore, it is more informative to determine if an area that is defined as an estuary is suitable for eelgrass. This will give an indication of the quality of the estuary, as eelgrass is a food source for many fish, birds and sea mammals and also provides shelter for fish. The occurrence of eelgrass is thus beneficial for an estuary.  

h1. Example project
At present, there is no example of a project available.  


h1. References
1 {anchor:1} [http://www.minlnv.nl/natura2000]