In order to inform policies aimed at reducing nutrient emissions to surface waters, it is essential to understand how aquatic ecosystems respond to eutrophication management. Using data from 89 studies worldwide, we examined responses to the reduction or cessation of anthropogenic nutrient inputs relative to baseline conditions. Baseline conditions were pre-disturbance conditions, undisturbed reference sites, restoration targets, or experimental controls. We estimated recovery completeness (% baseline conditions reached) and recovery rate (annual % change relative to baseline conditions) for plant and animal abundance and diversity and for ecosystem functions. Categories were considered fully recovered if the 95% confidence interval (CI) of recovery completeness overlapped 100% and partially recovered if the CI did not overlap either 100% or zero. Cessation of nutrient inputs did not result in more complete or faster recovery than partial nutrient reductions, due likely to insufficient passage of time, nutrients from other sources, or shifting baselines. Together, lakes and coastal marine areas achieved 34% (616% CI) and 24% (615% CI) of baseline conditions decades after the cessation or partial reduction of nutrients, respectively. One third of individual response variables showed no change or worsened conditions, suggesting that achieving baseline conditions may not be possible in all cases. Implied recovery times after cessation of nutrient inputs varied widely, from < 1 yr to nearly a century, depending on response. Our results suggest that long-term monitoring is needed to better understand recovery timescales and trajectories and that policy measures must consider the potential for slow and partial recovery.

1. Current efforts to restore and create ecosystems require greater understanding of ecosystems' responses to commonly used physical and biological intervention approaches to overcome ecological and technological limitations. 2. We estimated effect sizes from measurements of biotic assemblage structure and biogeochemical functions at 628 restored and created wetlands globally, in comparison with 499 reference wetlands. We studied the recovery trajectories of wetlands where different restoration or creation approaches were used under different environmental settings. 3. Although the variance explained by a linear mixed-effects models was low (6-7%), the study of recovery trajectories showed that the restoration or creation approach had no significant effects in most environmental settings. 4. In particular, wetlands where surface modification and flow re-establishment were used followed similar recovery trajectories regardless of whether they were revegetated or not. We even found potential detrimental effects of biological manipulations on the recovery of the plant assemblage, particularly in cold climates and in wetlands restored or created in agricultural areas. 5. Since physical interventions are required to recover or create the hydrological conditions of degraded or new wetlands, and given the high cost (22-73%) of biological interventions (i.e. revegetation), the need for biological interventions is, in most cases, unclear. 6. Our results highlight the urgent need to increase our understanding of the long-term effects of restoration and creation actions in our aim to engage in large-scale ecosystem management strategies for wetlands. 7. Synthesis and applications. These results suggest that, currently, the recovery and development processes of restored and created wetlands can be driven by spontaneous processes rather than by the response of wetlands to human interventions other than those targeted to restore hydrological conditions that existed prior to disturbance. However, given the synthetic nature of the data set, the mixed nature of available data and the limited number of measures we found to estimate recovery, caution must be exercised when adapting the results presented here to the planning and execution of specific ecosystem restoration projects.

Ecological restoration is key to counteracting anthropogenic degradation of biodiversity and to reducing disaster risk. However, there is limited knowledge of barriers hindering the wider implementation of restoration practices, despite high-level political priority to halt the loss of biodiversity. In Europe, progress on ecological restoration has been slow and insufficient to meet international agreements and comply with European Union Nature Directives. We assessed European restoration experts' perceptions on barriers to restoration in Europe, and their relative importance, through a multiple expert consultation using a Delphi process. We found that experts share a common multi-dimensional concept of ecological restoration. Experts identified a large number of barriers (33) to the advancement of ecological restoration in Europe. Major barriers pertained to the socio-economic, not the environmental, domain. The three most important being insufficient funding, conflicting interests among different stakeholders, and low political priority given to restoration. Our results emphasize the need to increase political commitment at all levels, comply with existing nature laws, and optimize the use of financial resources by increasing funds for ecological restoration and eradicate environmentally harmful subsidies. The experts also call for the integration of ecological restoration into land-use planning and facilitating stakeholders' collaboration. Our study identifies key barriers, discusses ways to overcome the main barriers to ER in Europe, and contributes knowledge to support the implementation of the European Biodiversity Strategy for 2030, and the EU 2030 Restoration Plan in particular.