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.

Coastal exploitation and human‐mediated modifications have markedly altered the community composition and functioning of coastal wetlands worldwide. Although recent work has shown that harnessing positive density‐dependent feedbacks can greatly enhance the recovery of habitat‐modifying species in degraded wetlands, the role of these intraspecific feedbacks in explaining the persistence of altered, unfavorable plant communities remains largely unexplored. Here, we experimentally tested whether intraspecific facilitation may explain the persistence of common reed (Phragmites australis) in human‐modified coastal wetlands. We performed a full‐factorial mesocosm experiment crossing low‐density pioneer versus high‐density established development stages with saline (20 psu) versus freshwater conditions. Results showed a clear shift in plant growth response from intraspecific competition under freshwater conditions to self‐facilitation in saline treatments. We identified two positive feedback mechanisms enabling the established treatment to overcome salinity stress: (1) Enhanced root oxygenation of the sediment at higher plant density decreased accumulation and intrusion of phytotoxic sulfide, and (2) density‐dependent rainwater infiltration into the soil lowered salinity in the dense root mat, preventing salt stress. Our study demonstrates that intraspecific facilitation can be an important factor in explaining the persistence of Phragmites australis in coastal wetlands. We emphasize the importance of integrating positive interactions in coastal restoration but argue that they should either be harnessed when restoring vegetation or broken when eradication of nontarget species is the management objective.

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This is an open access article under the terms of the Creat ive Commo ns Attri bution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Abstract 1. Grazing can significantly impact spatial heterogeneity and conservation value of ecosystems. Earlier work revealed that overgrazing may stimulate persistent vegetation collapse in low-productivity environments where vegetation survives by concentrating scarce resources within its local environment. However, it remains unclear whether grazer fluctuations may cause persistent vegetation changes in high-productivity systems where dense stands facilitate their own survival by hampering grazer access.2. Here, we experimentally tested how the release from grazing by greylag geese (Anser anser) affects spatial vegetation structure in a highly productive, brackish marsh in which dense reed (Phragmites australis) stands and bare roosting areas coexist. Next, we assessed the resilience of the change in vegetation patterning by reintroducing the geese after a 2-year exclosure period.3. During herbivore exclusion, vegetation rapidly colonized the bare areas, while reintroduction of herbivores generated a clear species-specific response. Specifically, the pioneer species, Bolboschoenus maritimus, was immediately eradicated, while the dense and high structure of P. australis facilitated its own persistence by limiting grazer access. Surface accretion (~1 cm/year) during herbivore exclusion further amplified this herbivore-inhibiting feedback, because greylag geese primarily rely on waterlogged conditions for grubbing. Synthesis and applications.Our results indicate that temporary reductions in herbivore numbers may induce persistent unfavourable changes in the spatial structure of a high-productivity system. It is therefore important to first assess whether vegetation changes are naturally reversible or persistent. If state shifts are indeed persistent, sufficiently high grazer densities must be maintained to warrant the favourable heterogeneous system. If changes in vegetation structure negatively impact grazer densities, active management such as sod cutting or mowing may be required to restore ecosystem structure and functions. 1818 | Journal of Applied Ecology REIJERS Et al.