This report has been prepared as part of an effort by IUCN to define its position on Nature-based Solutions (NbS) and plan for future work to advance this concept and support effective implementation of NbS to enhance ecosystem services provision and address societal challenges. The report proposes a definitional framework for NbS, including a set of general principles for any NbS intervention. The report also defines the scope of NbS as an umbrella concept embracing a number of different ecosystem-based approaches.

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Nature-based solutions to address global societal challenges

For many years, estuarine science has been the ‘poor relation’ in aquatic research – freshwater scientists ignored estuaries as they tended to get confused by salt and tides, and marine scientists were more preoccupied by large open systems. Estuaries were merely regarded by each group as either river mouths or sea inlets respectively. For the past four decades, however, estuaries (and other transitional waters) have been regarded as being ecosystems in their own right. Although often not termed as such, this has led to paradigms being generated to summarise estuarine structure and functioning and which relate to both the natural science and management of these systems. This paper defines, details and affirms these paradigms that can be grouped into those covering firstly the science (definitions, scales, linkages, productivity, tolerances and variability) and secondly the management (pressures, valuation, health and services) of estuaries. The more ‘science’ orientated paradigms incorporate the development and types of ecotones, the nature of stressed and variable systems (with specific reference to resilience and redundancy), the relationship between generalists and specialists produced by environmental tolerance, the relevance of scale in relation to functioning and connectivity, the sources of production and degree of productivity, the biodiversity-ecosystem functioning and the stress-subsidy debates. The more ‘management’ targeted paradigms include the development and effects of exogenic unmanaged pressures and endogenic managed pressures, the perception of health and the ability to manage estuaries (related to internal and external influences), and the influence of all of these on the production of ecosystem services and societal benefits.

Challenging paradigms in estuarine ecology and management

This review presents recent concepts, understanding and experience of the restoration, recovery and human-mediated modification of estuarine, coastal and marine ecosystems. It shows that these can be divided into four categories: natural recovery from a natural or anthropogenic change (whether adverse or otherwise); anthropogenic interventions in response to a degraded or anthropogenically changed environment; anthropogenic responses to a single stressor; and habitat enhancement or creation. A conceptual framework for restoration and recovery of marine marginal and semi-enclosed areas is presented after exploring and refining the plethora of terms used in restoration science and management. Examples of management action are given including managed realignment and the restoration of docks, biogenic reefs, saltmarsh, seagrass, beaches and upper estuarine water quality. We emphasise that although recovery techniques are worthwhile if they can be carried out, they rarely (if ever) fully replace lost habitat. Moreover, while they may have some success in marginal or semi-enclosed areas such as coastal bays, estuaries and fringing habitats, they are less relevant to open coastal and marine habitats. Therefore the best option available in the latter can only be to remove the stressor, as the cause of any change, to prevent other stressors from operating and to allow the conditions suitable for natural recovery. This review emphasises that whereas some ecological concepts related to restoration are well understood, for example, the nature of ecosystem structure and functioning, others such as carrying capacity, resilience and ecosystem goods and services are still poorly quantified for the marine and estuarine environments. The linking between these ecological concepts and the management framework is also relatively recent but is required to give a holistic approach to understanding, managing and manipulating these environments.

Estuarine, coastal and marine ecosystem restoration: Confusing management and science – A revision of concepts

Evaluating the ecological performance of wetland restoration in the Yellow River Delta, China.

Many estuarine and coastal marine ecosystems have increasingly experienced degradation caused by multiple stressors. Anthropogenic pressures alter natural ecosystems and the ecosystems are not considered to have recovered unless secondary succession has returned the ecosystem to the pre-existing condition or state. However, depending upon the scales of time, space and intensity of anthropogenic disturbance, return along the historic trajectory of the ecosystem may: (1) follow natural restoration though secondary succession; (2) be re-directed through ecological restoration, or (3) be unattainable. In order to address the gaps in knowledge about restoration and recovery of estuarine and coastal ecosystems, this special feature includes the present overview and other contributions to provide a synthesis of our knowledge about recovery patterns, rates and restoration effectiveness. From the 51 examples collated in this contribution, we refine the recovery from the list of stressors into six recovery mechanisms: (1) recovery from sediment modification, which includes all aspects of dredging and disposal; (2) recovery by complete removal of stressors limiting natural ecosystem processes, which includes tidal marsh and inundation restoration; (3) recovery by speed of organic degradation, which includes oil discharge, fish farm wastes, sewage disposal, and paper mill waste; (4) recovery from persistent pollutants, which includes chemical discharges, such as TBT; (5) recovery from excessive biological removal, related to fisheries and (6) recovery from hydrological and morphological modification. Drawing upon experience both from these many examples and from an example of one comprehensive study, we show that although in some cases recovery can take <5 years, especially for the short-lived and high-turnover biological components, full recovery of coastal marine and estuarine ecosystems from over a century of degradation can take a minimum of 15–25 years for attainment of the original biotic composition and diversity may lag far beyond that period.

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Medium- and Long-term Recovery of Estuarine and Coastal Ecosystems: Patterns, Rates and Restoration Effectiveness

https://www.waterboards.ca.gov/waterrights/water_issues/programs/bay_delta/deltaflow/docs/exhibits/swrcb/swrcb_simenstand2005.pdf

Mark A. Ford

Papers

When is restoration not?: Incorporating landscape-scale processes to restore self-sustaining ecosystems in coastal wetland restoration

Restoring marsh elevation in a rapidly subsiding salt marsh by thin-layer deposition of dredged material

Ecogeomorphology of Spartina Patens‐dominated tidal marshes: Soil organic matter accumulation, marsh elevation dynamics, and disturbance