Enhancing ecological integrity while preserving ecosystem services: Constructing soft‐sediment islands in a shallow lake

Abstract

Ecosystems are increasingly managed to provide multiple benefits to humans, which often degrades their ecological integrity. This strongly applies to aquatic ecosystems, in which engineering can enhance flood protection, drinking water supply, fisheries and recreation. Although these activities typically increase ecosystem functionality to humans, they often impair key aspects of biodiversity and natural functioning. Classical restoration of such degrading freshwater ecosystems can lead to societal opposition, if returning to a former ecosystem state affects previously acquired ecosystem services. Innovative nature‐based solutions are therefore needed that enhance natural values in ecosystems, without affecting existing services. We present a large‐scale project aiming to increase the ecological integrity of a human‐modified freshwater lake while maintaining its services to humans. The freshwater lake Markermeer in the Netherlands was formed by closing off an estuary for flood protection. The ecological integrity of this lake diminished over time, likely because a declining primary productivity impaired biodiversity at higher trophic levels. This decline is associated with a lack of gradual land–water transitions, strong resuspension of fine sediments, low nutrient availability and lack of dynamics typically to be expected in a natural temperate freshwater lake. Restoring the lake to its former marine state would conflict with current ecosystem services. A nature‐based solution was initiated in 2016, consisting of constructing a five‐island archipelago from the lake's own soft‐sediments called the ‘Marker Wadden’. The project aims to increase the lake's primary production by creating gradual land–water transitions, more heterogeneity in water depths and decreasing turbidity by creating shelter and deep sinks reducing fine‐sediment resuspension by the wind – thus introducing currently missing elements that are typical for natural lakes. We present the underlying ecological framework and first scientific results of this innovative ongoing project. Within 4 years, the Marker Wadden project shows how forward‐looking sustainable development of lake ecosystems using a rewilding approach can enhance natural processes and attract birds and fish, without conflicting with existing ecosystem services. This inspires new directions for halting and reversing the degradation of other vital ecosystems worldwide.

Impacts of shelter on the relative dominance of primary producers and trophic transfer efficiency in aquatic food webs: Implications for shallow lake restoration

“…If we also sampled Gastropoda attached on the wall, it only increases the gastropod number in the sheltered treatments, which will not affect the final conclusion. In our study, higher Gastropoda densities seemed related to macrophyte abundance, as we observed also elsewhere on Marker Wadden (van Leeuwen et al., 2021). Furthermore, we found that in the shelter + macrophytes treatment more Corophiidae were found.…”

Nature‐based Solutions to tackle climate change and restore biodiversity

“…Increasing plant diversity in highly modified aquatic systems can also trigger a bottom‐up cascade and increase benefits to humans, as shown by Van Leeuwen et al. (2021) who reports the progress of the restoration of a man‐made freshwater ecosystem in the Netherlands. Lake Markermeer was initially formed by creating an estuary for flood protection.…”

“…Observations must also monitor the entire ecosystem, and not just the target species (such as the plant responsible for carbon storage or the predator of a specific pest). Trophic cascades up and down food chains can destabilise ecosystems, and ignoring these could have negative consequences, as shown by Lake Merkemeer in the Netherlands which was designed for flood protection but ultimately reduced lake biodiversity (Van Leeuwen et al., 2021). It is not trivial to determine the most suitable habitat and location for an NbS.…”

Paai- en opgroeigebieden voor vis in en rond Marker Wadden

“…Het huidige Markermeer kent maar weinig natuurlijke landwaterovergangen -meer dan driekwart van de oevers in het Markermeer is verhard met basaltblokken. Voor een nadere beschrijving van het concept van de aanleg van Marker Wadden en de eerste resultaten wordt verwezen naar KIMA (2021) en Van Leeuwen et al (2021).…”

“…Op termijn kan Marker Wadden uitgroeien tot een voedselrijk moeras met een zodanige omvang dat de effecten uitstralen op een groter gedeelte van het Markermeer. In dat geval kunnen de eilanden een katalyserende functie hebben als organische koolstofbron die bodemprocessen versterkt (Van Leeuwen et al 2021, Van Riel et al 2019, Verdonschot et al 2021 Marker Wadden vormen een schakel in de verdere ontwikkeling van grootschalige, natuurlijke oevers.…”