Enhancing ecological integrity while preserving ecosystem services: constructing soft-sediment islands in a shallow lake.
Ecosystems are increasingly managed to provide multiple benefits to humans, which often degrades their ecological integrity. This strongly applies to aquatic ecosystems, inwhich 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 fiveisland archipelago from the lake's own soft-sediments called the 'MarkerWadden'. 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.