RECONECT monitors the benefits of Nature-based Solutions in Aarhus, Denmark

Authors: Alix Aliaga (Biologist, eDNA specialist), Signe Iversen (Landscape Manager and Climate Adaption Coordinator in Aarhus Municipality), Marzenna Rasmussen (Project Manager on behalf of AMPHI)

The RECONECT demonstrator site in Denmark (an already existing NBS site, established before the start of RECONECT) is located in the North of Aarhus, Denmark’s second-largest city, and consists of two connected areas:

  • an artificial lake (Egå Engsø), created on low lying parts of the Egå river valley on the former seabed from the last ice age. The lake is surrounded by approximately 50 hectares of wet meadows;
  • and ten interlinked sites in the residential area of Lystrup, lying on a hillslope north of the lake in the catchment of the river Egå.

Both areas deal with hydro-meteorological hazards, mainly flooding. The area is protected from high coastal water level by a dike and a lock with a pumping station further downstream.

Figure 1: A look at the demonstrator areas

Which Nature-based Solutions have been implemented?

The artificial wetland Egå Engsø was established in 2006 as part of the Danish fulfilment of the European Water Framework Directive. The purpose of its implementation was to reduce nitrogen and phosphorus levels in Aarhus Bay, caused by agricultural and wastewater discharges so as to avoid eutrophication of the coastal ecosystem.

The Egå Engsø wetland also improved the natural conditions of Egådalen (the valley of Egå) and provides the basis for recreational activities of the area. The wetland reduces flood risk from the river Egå to the lower-lying residential areas functioning as a retention basin. The wetland’s absorption capacity is continuously monitored and can be followed live on RECONECT’s online platform TeleControlNet. In effect, the Nature-based Solution, ie the wetland, greatly boosts the performance of the engineered solutions, the dike and pumping station.

The sites in Lystrup (Climate Change Adaptation or CCA sites) were implemented between 2015 and 2017. The main purpose of the measures was reducing flood risk from heavy rainfall. Since the storage capacity of Egå Engsø is reduced if the water level in the lake is already high, the delayed water runoff from the Lystrup area also helps to maintain the storage capacity of the Egå Engsø. Another purpose was to increase biodiversity on the project sites, as well as to increase stakeholder involvement of the inhabitants in design, maintenance, and recreational utilization of the sites.

How is NBS monitoring proceeding?

The RECONECT monitoring activities connected to water and nature indicators have started in Egå Engsø and Lystrup in 2020. Flora and fauna connected to Egå Engsø were originally monitored by the municipality in 2007, right after the lake was established. The parameters were monitored again via RECONECT in 2020, the re-monitoring is a valuable way of showing the development of the natural and biodiversity status of Egå Engsø. Some of the parameters monitored so far are:

EGÅ ENGSØ

  • Water: Water level in the inlet and outlet of lake Egå.
  • Nature: Cover of vascular plants; Degree of overgrowth with trees and shrubs; Humidity conditions; Species occurrence for breeding birds, mammals, invertebrates.

LYSTRUP

  • Water: Water level, oxygen content and temperature in water pond in Hovmarksparken, Lystrup.
  • Nature: Occurrence of terrestrial and aquatic plant species, macroinvertebrates and protected species of amphibians (Great Crested Newt, or Triturus cristatus).

The monitoring in Egå Engsø and Lystrup will provide data to assess different indicators, split into the three categories Nature, Water and People. In Lystrup, preliminary results already show increased plant biodiversity in plots where CCA solutions were implemented. These sites were monitored in August 2020, based on descriptions of vegetation plots with and without application of CCA solutions, 28 plots in total.

The presence of Triturus cristatus is considered an indicator of good habitat quality. The population size is assessed with two methods: traditional catching and environmental DNA. Figure 2: e-sampling for Triturus Cristatus in Lystrup, June 2020. Figure 3: AMPHI partner doing water sampling for eDNA.
Figure 4: Project sites in Lystrup for vegetation monitoring (terrestrial part). 10 Climate Change Adaptation sites in Lystrup were implemented between 2015–2017. Figure 5: The adjacent area of the lake and islands were split into 22 sub-sites in Egå Engsø. In July and August 2020, all sub-sites, except 20 and 21 were revisited, remapped and species list updated.

In the future, will new monitoring parameters be added?

Especially the social impact of NBS is of interest for the municipality, since it links the water and nature parameters to the citizens’ perception and usage of NBS. In the coming years, the social impact of Egå Engsø and Lystrup will be monitored by carrying out surveys among users and by counting the numbers of visitors. Also, it is planned that further selected physical parameters will be monitored in Lake Egå like sedimentation, surface water temperature and water velocity. These parameters can tell us more about the general state of the lake’s health and the conditions for fish and birds.

What has been the main lesson in working on RECONECT?

RECONECT gave us a unique chance to create evidence for the importance of implementing NBS by allowing us to do a large monitoring program by looking at ecological, hydrological, and social impacts. The co-creation between local authorities, universities and other professionals has given us the possibility to dig deeper into the effects of NBS, which gives us crucial knowledge of both expected and unexpected consequences of establishing such areas. This knowledge is important as more NBS sites are planned to reduce flood risks like in Lake Egå and Lystrup. It is also important because it gives us the possibility to communicate the impact of NBS to people, based on strong evidence.

What have been key enablers and barriers to implementing NBS in Denmark?

The focus and attention towards NBS is growing in Denmark. This focus is definitely inspired by the Paris Agreement and a growing political wish to halt the biodiversity crisis. Nevertheless, the implementation of NBS requires space. One of the most frequent barriers is to get agreements with private landowners since a lot of suitable spaces for creating NBS are situated on private cultivated areas. Financial issues can also be a barrier since it can be expensive to buy private land or to compensate landowners for reduced agricultural income. Financial compensation from the local and national authorities will enable to provide subsidies to private landowners.

What achievements you are most proud of?

One of our main political goals in the Aarhus Municipality is to couple climate change adaption with the creation of more nature and biodiversity. Simultaneously, we are working to create recreative spaces for the citizens and better access to nature. Lake Egå has shown to be such a place with space for both water, nature and people. Shortly after the establishment, lots of different species — including birds, vegetation, invertebrates and mammals — emerged in and around the lake, making the site one of the most popular bird watching sites in this part of Denmark! The citizens of Aarhus have welcomed the area, which quickly became one of the most popular recreational areas on the outskirts of the city. People come here to go for a walk, take a run or meet friends and family on the nature playground on the banks of the lake.

In Lystrup, the citizens’ involvement process was rather intense during the design of the climate change adaption projects and has strengthened local awareness of the project sites. One of the successful spin-offs from the projects are the local cow grazing guild, where locals ‘share’ a few cows that also maintain and conserve the nature on one of the project sites.

For more information, please contact Ms Signe Iversen, Landscape Manager and Climate Adaption Coordinator in Aarhus Municipality

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The RECONECT project demonstrates the effectiveness of Nature-Based Solutions for hydro-meteorological risk reduction in rural and natural areas www.reconect.eu

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The RECONECT project demonstrates the effectiveness of Nature-Based Solutions for hydro-meteorological risk reduction in rural and natural areas www.reconect.eu

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