Knowledge Hub for Water | Nature-based solutions (2024)

What are nature-based solutions?

The European Union is committed to develop nature-based solutions, and supports variousinitiatives in this direction including research andinnovation projects:“Nature-based solutions are innovations inspired and supported by nature, which arecost-effective, simultaneously provide environmental, social and economic benefits and helpbuild resilience. They bring more, and more diverse, nature and natural features andprocesses into cities, landscapes and seascapes, through locally adapted, resource-efficientand systemic interventions. Nature-based solutions must benefit biodiversity and support thedelivery of a range of ecosystem services.”

What are nature-based solutions? What they can do for us?

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• Nature-based solutions

Nature-based solutions are supported in many different contexts, by very different actors in theworld. Examples:

1. TheWorld Bank:“Nature-based solutions are actions to protect, sustainably manage, or restorenatural ecosystems, that address societal challenges such as climate change, humanhealth, food and water security, and disaster risk reduction effectively andadaptively, simultaneously providing human well-being and biodiversity benefits. Forexample, a common problem is the flooding in coastal areas that occurs as a resultof storm surges and coastal erosion. This challenge, traditionally tackled withmanmade (grey) infrastructure such as sea walls or dikes, coastal flooding, can alsobe addressed by actions that take advantage of ecosystem services such as treeplanting.”
2. The International Union for the Conservation of Nature (IUCN):“Nature-based solutions are actions to protect, sustainably manage, and restorenaturaland modified ecosystems that address societal challenges effectively and adaptively,simultaneously benefiting people and nature. Nature-based solutions address societalchallenges through the protection, sustainable management and restoration of bothnatural and modified ecosystems, benefiting both biodiversity and human well-being.Nature-based solutions are underpinned by benefits that flow from healthyecosystems.They target major challenges like climate change, disaster risk reduction, food andwater security, biodiversity loss and human health, and are critical to sustainableeconomic development.”

Nature-based solutions for better watermanagement

Nature-based solutions may be cost-effective in addressing water management issues inagriculture.

Treatment wetlands enable the removal of excess nutrients from manure in areas with limitationsto fertilizers application. Reed beds may be a cheap and operationally simple option for thetreatment of sludge, producing a compost that can be used to increase the organic matter contentof soils. When treating domestic wastewater sludge with little runoff and industrialcontributions, likely to contain low levels of metals and other persistent contaminants, thelong retention time of reed beds ensures degradation of the less persistent chemicals, hencepotentially a sludge of good chemical quality that could be a valuable soil conditioner. Thesesolutions may be often financially self-sustainable.

Buffer strips and ponds are effective ways to control diffuse pollution. Their broadimplementation may be cost-effective in reducing nutrient and pesticide loads to the receivingwater bodies. However, they require public investments or anyway payments to farmers, as theyrepresent net costs for them. Similarly, while ponds to store water for irrigation may besustainable investments for farmers, their design oriented to support biodiversity entails extracosts that should be compensated in order to make them feasible. Similar considerations apply toin-stream retention measures such as two-stage design of drainagechannels.

In some cases, there can be opportunities to restore valuable ecosystems while improving watermanagement, although usually measures at the scale of the catchment require public support totrigger the investments needed to deliver the full benefits. An example of this is therestoration of Lake Karla as a multi-purposereservoir. Finally, in other cases it may bepossible to obtain significant benefits with relatively simple management changes, entailinglimited costs, as suggested by the example of blocking the drainage of headwater streams in theKyll river basin in Germany .

The implementation of NBS requires an assessment of costs and benefits in comparison with their“grey” alternatives, and the definition of appropriate “business models” to secure their broaduptake and sustainable operation.

Annexes to JRC Science for Policy Report

Potential to implement nature-basedsolutions in Europe

Here we address selected typologies of nature-based solutions (NBS), including:

• treatment wetlands for the removal of excess nutrients frommanure and the stabilization of sludge;
• buffer strips, ponds and vegetated drainage ditches fordiffuse pollution control;
• ponds for water storage and managed aquifer recharge toaddress irrigation demand.

We propose criteria to map the favourability to investments in the above NBS typologies foragricultural water management, their costs and effectiveness. We identify areas where eachtypology can be implemented, taking into account various constraints.

We introduce indicators representing the intensity of "demand" for NBS, i.e. presence of diffusepollution loads, excess manure and sewage sludge, soil erosion and pesticide loads, summerdeficit of precipitation with respect to potential evapotranspiration, lack of biodiversity atthe landscape scale, and intensity of extreme precipitation requiring flood buffering.

Treatment wetlands

Treatment wetlands (TW) are a well-established NBS for wastewater and sludge, particularly forthe treatment of domestic effluents in small agglomerations or for the polishing of secondarywastewater treatment plant effluents. They are typically designed as free-surface water ponds ortanks, or tanks filled with gravel (“beds”) through which water may percolate and flow eitherhorizontally or vertically.

Buffer strips and ponds

Control of pollution due to excess nutrients from agricultural fields, as well as othercontaminants such as pesticides and suspended sediments, can be achieved through a series ofdiffuse elements, including buffer strips, vegetated drainage ditches and free surface wetlandponds, intercepting runoff before it is discharged to the receiving water bodies. This type ofinterventions becomes particularly effective when implemented systematically over a catchment,thus intercepting a significant percentage of the total runoff thereby produced.

Free water surface wetlands and vegetated drainage ditches operate the removal of nutrients andsediments by providing conditions for the settling of suspended solids, nutrient uptake by theaquatic vegetation, and denitrification by microorganisms in a complex ecosystem reproducing theconditions of natural wetlands. Buffer strips operate on the same principle, but through theuptake of nutrients by plant roots, entrapment of sediments and denitrification in soils. Bufferstrips may be designed to intercept surface flow, subsurface or groundwater flow, or both.

Water storage

Nature-based solutions for the collection and storage or retention of water can provide benefitsin terms of water harvesting, flood mitigation or a combination of the two. Each aspect dependsstrictly on the volume of water available for these purposes. Depending on how the storagevolumes areimplemented, they may associate their hydrological function to an ecological, as well as asocioeconomic function. Among NBS for water storage we consider three strategies for waterretention solutions that have a catchment-scale relevance: small farm-scale reservoirs in theform of ponds; large reservoirs restoring natural lake habitats; and restoration of theretention capacity of soils.

Maps and info tools

A research project led by JRC suggests an approach to using the above information to buildscenarios ofimplementation of NBS, which can be applied for the appraisal of programmes of measures at theregional and European scale.

Annexes to JRC Technical Report

Case studies

Usually NBS are designed on a case-by-case basis. It is very difficult to propose general designprinciples, and the economic, social and ecological benefits must be evaluated in the specificcontext. While guidance documents exist, it is oftenuseful to take inspiration from availablecase studies. Here we present a few cases where NBS have been analysed in-depth in theirtechnical, economic and social/ecological aspects.