Green riparian zones and wet biotopes
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As opposed to traditional, reinforced banks, nature-friendly riparian zones form a gradual transition from shore to water. On the dry shore, land and shore vegetation can establish itself, in the shallow water marsh vegetation and in deeper water there is place for various water plants. Nature-friendly shores with an ecologically sound structure form excellent living areas for many plants, birds, insects, amphibians, fish and mammals. It is desirable to partly plant the shore vegetation and to create as much variation as possible in order to prevent reeds/rushes to develop over the entire shore length, which would cause a monoculture.
Nature-friendly riparian zones have a positive impact upon water quality. Reeds and rushes absorb nutrients and floating particles settle on them, as a result of which the clarity of the water improves. A nature-friendly riparian zone also is safer for children. Due to the less sudden transition from land to water, small children fall less easily in the water and can climb out more easily if they do.
cross-section of a nature-friendly bank
‘Nature-friendly riparian zones’ is a broad concept. By shaping shores in a nature-friendly or ecological manner, living areas are created for different plants and animals. This can be done in various ways, for the sake of different groups of animals or plant communities. When nature-friendly riparian zones are desired, it is important to establish first what can be expected and what is desired and what is not.
‘Below is a bulleted list of general guidelines for the establishment of nature-friendly riparian zones.
- The width of the riparian zone determines the ecological value of the zone. Up to a width of 6 metres, the number of plant and animal species increases strongly with the width. For widths larger than 6 metres, the increase is less significant.
- When there is limited space for a riparian zone, a single broad riparian zone and one very narrow (reinforced, if necessary) are preferable over two fairly narrow zones.
- When a broad ecological zone is created on only one side, the north shore is preferable, as this shore receives the most sunlight. This enhances the development of larvae and the eggs of amphibians, among others. Many flowering plants also have a preference for sunny locations.
- Shores with a slight slope allow for a gradual transition from water to land; this creates additional opportunities for plants and animals.
- When both the presence of amphibians and fish is desired, a ‘nursery’ needs to be created for the amphibians, for instance in the form of a pond, because multiple fish species eat the eggs and/or larvae.
- In places where the shore is reinforced over a length of 100 metres or more, “exit” areas are needed for amphibians, small mammals and other fauna.
- When bridges and culverts are built, the ability for various species to pass these artefacts should be considered, in order to ensure that the exchange of fauna within and between neighbourhoods is possible.
- By not using straight but curved lines in the development of a riparian zone, places with more and with less sun and wind are created. These variations enhance species diversity. Moreover, riparian zones with a curving shoreline have a more natural appearance.
- Different plant species place different requirements upon their environment. Some species prefer a sandy soil and others clay. Some species may occur in fairly deep water, others only in shallow water. The same is true for variations in the water level: some species need a fluctuating water level, others tolerate it, and still others cannot live with it.
- The management of the plants can have a dominant effect upon the way they look. By mowing in summer, a different species composition develops than when mowing is done in winter. Mowing annually leads to a different vegetation structure than when, for instance, the shoreline is mowed only once every five years.
- Different animal species place different requirements upon the structure of the shoreline vegetation. Some species need grassy vegetation, others rough vegetation. There also are species that are tied to particular plant species’.
De groene ruimte; Pötz et al., 2009