1. INTRODUCTION

1.1 What are the Ecosystem Services?

Ecosystem services are defined as the various benefits that human societies obtain from ecosystems, from the basic provisioning functions (e.g. food or water supply) to more regulating such as cultural, recreation or other supporting services (MEA 2005). The concept has become a cornerstone in environmental science as it becomes possible to integrate ecological considerations into economic decision-making. Ecosystem services are divided into four broad categories that have been broadly used both by scientists and policymakers.

1. provisioning (goods such as food, fiber, timber and freshwater);

2. regulating (benefits derived from ecosystem processes such as climate regulation, flood control, water purification and pollination);

3. cultural (non-material benefits such as recreation, aesthetic inspiration, spiritual values); and

4. supporting (services that are essential to the ecosystems functioning and indirectly sustain other services such as nutrient cycling, soil formation and primary production).

In 2018, the European Environment Agency developed the “Common International Classification of Ecosystem Services” (CICES), based on “final services” (ecosystem outputs directly used by people). Moreover, CICES was designed in a way that is possible to align ecosystem services accounting with the System of Environmental-Economic Accounting (SEEA). This had as a result to reduce the risk of double-counting when performing economic valuation. In parallel, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) introduced the concept of Nature’s Contributions to People (NCP), aiming to strengthen the science-policy interface for biodiversity and ecosystem services. This framework is rather broader in scope as compared to CICES, even if it is closely related to ecosystem services, trying to respond to the critique that the concept frames nature in strictly utility-based terms. Its base is to incorporate the

diverse views, particularly the local knowledge, into the assessment of how ecosystems contribute to human well-being. NCP is divided to:

● material contributions (e.g., food, energy, raw materials),

● regulating contributions (e.g., water regulation, climate regulation, soil fertility), and

● non-material contributions (e.g., learning, spiritual values, cultural identity).

The policy relevance of ecosystem services is huge. Framing conservation and restoration in terms of the services provided to people has enabled the development of innovative mechanisms, such as Payments for Ecosystem Services (PES) that are listed as one of the mechanisms that should allow societies to pay for the maintenance of these services (Global Environment Facility 2014). For example, the evaluation of wetlands for their water purification function has influenced land-use decisions, while recognition of mangroves as providers of coastal protection has enhanced the efforts for their conservation against aquaculture or urban expansion. Despite its widespread adoption, the ecosystem services framework has been subject to severe

critique as several researchers have pointed out that there is a risk of reducing the complex social–ecological relationships into simplified service units. For example, there are concerns about the

difficulty of non-material monetary evaluation (e.g. cultural values) or about whose benefits are prioritized and who pay the costs of ecosystem degradation or restoration. Nevertheless, this concept

remains central, and it is incorporated in the conservation planning of the UN and EU [UN Sustainable Development Goals (SDGs), the EU Biodiversity Strategy and the SEEA-EA framework for natural capital accounting].

1.2 Categories of Ecosystem Services

Provisioning Services are central to human livelihoods and economic systems. They are related to goods and materials directly obtained from ecosystems, such as food, freshwater, timber, fiber,

medicinal resources and fuel. Examples of provisioning services are fisheries, forests but also agricultural systems dependent on ecosystem functions such as soil fertility and pollination. Provisioning services are the most easily measurable service, often expressed in biophysical units such as tons of grain, cubic meters of water or monetary market values.

Regulating services refer to the benefits derived from the regulation of ecosystem processes. They are vital for maintaining ecosystem stability and resilience. For example, they include climate regulation by forests because of carbon sequestration, water purification or flood mitigation by riparian zones in wetlands and pest and disease regulation by natural predators. These highly important services are usually neglected and become visible only after their degradation occurs. For example, the loss of

wetlands can increase flood risks, while decline in pollinator populations can threaten crop yields. The evaluation of regulating services is often very difficult as they are the expression of complex ecological processes.

Cultural services include the non-material benefits that ecosystems provide. Examples of Cultural services are recreation, tourism, aesthetic appreciation, spiritual fulfilment and cultural heritage.

Natural environments provide opportunities for education, inspiration and recreation. They are thought to be critical for human mental health and quality of life. They are quantified, although not easily, through surveys, participatory methods and several indicators such as visitor numbers. Cultural services include the non-material benefits that ecosystems provide.

Supporting services are those that sustain other ecosystem services through complex ecological functions. Their fundamental role in ecosystem functioning is widely acknowledged. In these services, nutrient cycling, soil formation, primary production and habitat provision for species are included. Although these services do not directly provide benefits to humans, they are the basis for the function of all the other ecosystem services. For example, agricultural productivity is based on nutrient cycling and soil formation. However, measuring supporting services are often treated with caution as there is a risk of double-counting but their fundamental role in ecosystem functioning is widely acknowledged. Several alternative classifications to MEA typology have been proposed in order to define or clarify methodological and conceptual problems. The most known is CICES that focus on the final ecosystem services that are directly used by people. CICES evaluation framework was formed in a way to reduce the lack of clarity in some assessment procedures and the conceptual uncertainty in ecosystem service evaluation. Meanwhile, the IPBES framework on Nature’s Contributions to People (NCP) reorganizes services into three groups: material, regulating, and non-material, with a strong emphasis on pluralistic values and knowledge systems. These frameworks highlight the diversity of ways in which ecosystem services can be conceptualized, measured, and communicated depending on the audience and policy needs.

1.3 Ecosystem Services in River Deltas\

River deltas are among the most environmentally dynamic and productive ecosystems on Earth. The continuous deposition of sediments transferred by the river waters shape them while in parallel create fertile floodplains and extensive wetlands. Globally, they are socio-ecological hotspots of significant importance as they are major centers of population and agriculture. There is a diversity of ecosystems in deltas, such as agricultural lands, freshwater wetlands, mangroves or coastal marshes that support a wide range of ecosystem services. These services are extremely important as deltas provide food, water and livelihoods not only for local communities but also for regional and global economy, while they also offer protection against climate change and environmental hazards such as floods and storm surges. All types of ecosystem services are found in deltas.

● Provisioning Services in Deltas

Freshwater supply is a key provisioning service, as deltaic aquifers and rivers supply drinking water and irrigation to millions of people. In addition, deltas are widely acknowledged as centers of

agricultural and fishery production. The sediments, deposited downstream, create fertile soils that support all kinds of crops and sustain intensive agriculture. Fisheries and aquaculture are important economic activities in deltas while, in parallel, deltas are nurseries for numerous commercially important species. Globally, delta fisheries and aquaculture contribute substantially to the total economic value of fisheries, which is estimated at over $362 billion annually and support the livelihoods of more than 120 million people (FAO 2022).

Timber and fuelwood are harvested from deltaic forests, for building materials or energy sources, while a number of non-timber forest products for millions of households are also provided.

Livestock husbandry also depends on the extensive grazing lands and crop residues in deltas, supporting dairy and meat production. Apiculture in deltas or riparian areas, where hives are

seasonally relocated, is also rather extensive in some areas of the world. It is supported by floral plant diversity in a mosaic of agricultural lands and riparian areas and wetlands that provide nectar

sources for bees.

● Regulating Services in Deltas

Regulating services are central to the resilience of deltas. They provide water purification services as wetlands filter nutrients and pollutants and consequently improve water quality. Furthermore,

carbon sequestration in deltaic ecosystems contributes to global climate regulation. Moreover, wetlands regulate the hydrological flows, floods and buffer storms. Therefore, mangroves and

marshes in deltas act as natural coastal defense systems reducing erosion.

● Cultural Services in Deltas

Deltas are deeply linked with cultural heritage and traditions. They are historically referred to as cradles of civilization as several ancient cities were Delta settlements, such as Cairo on the Nile

Delta, Dhaka in the Ganges-Brahmaputra-Meghna Delta, and Ho Chi Minh City in the Mekong Delta. Tourism and recreation are common activities in deltas.

● Supporting Services in Deltas

Supporting services in deltas include nutrient cycling, soil formation and the provision of habitats for diverse flora and fauna species. The mixture of terrestrial and aquatic ecosystems creates

biodiversity hotspots that conserve biodiversity and offer breeding and nursery habitats for multiple species. These habitats support provisioning and regulating services and directly link

biodiversity to human well-being.

Despite their importance, delta ecosystems face severe and growing pressures. Human activities such as dam construction, sediment extraction or land use changes reduce sediment supply and affect the natural processes that sustain ecosystem services. Climate change increases these pressures, even more, through sea-level rise, salinization and increased storm intensity. Population growth and urbanization further intensify land-use changes threatening both biodiversity and service provision.

1.4 IAS Impact on Deltaic Ecosystem services

Invasive Alien Species (IAS) are referred to as a major driver of biodiversity loss that threaten the sustainable provision of ecosystem services especially on deltaic ecosystems. The reason for this is that IAS can drastically alter the ecological processes and subsequently reduce the ability of ecosystems to support the well-being of human societies. In deltaic ecosystems, the threat caused by IAS is particularly serious, as these ecosystems present both high ecological productivity and intense human use.

1.4.1 Impacts on Provisioning Services

IAS directly affect water availability in deltaic ecosystems and the provision of agricultural services. IAS naturally clog irrigation channels, reduce water flow and outcompete agricultural crops for the

acquisition of vital natural resources such as water and nutrients, leading to reduced agricultural yields and subsequent significant economic losses. In fisheries, IAS, in the role of Invasive predator of deltaic ecosystems, they compete with native fish species mainly through predation (direct effect) or by limiting the available resources that were previously exploited by native fish (indirect effect), thereby reducing the active population size of native fish populations. In this way, fish resources are reduced, affecting the supply of fish catches and ultimately threatening the livelihoods of people who depend on this provisioning service (capture fisheries and aquacultures) from which they derive income. Therefore, IAS increase the chances of food insecurity as thousands of people include the native fish in their diets for decades.

IAS also affect several other provisioning services except for fisheries and agriculture. For example, invasive aquatic plants such as Eichhornia crassipes (water hyacinth) and Phragmites australis can restrict access to freshwater resources used for domestic consumption or irrigation, reducing both quantity and quality of water supplies in deltaic wetlands. IAS plants also compete with native forest and grassland species of deltaic ecosystems, and either directly displace native tree and shrub species or alter regeneration processes in riparian forests. Therefore, they may reduce the availability of timber, fuelwood, and non-timber forest products. The spread of IAS also affects the forage plants population, which are important for reducing livestock production. In deltas where beekeeping and honey production are practiced, invasive plants may reduce the abundance of native flowering species, thereby threatening pollination resources critical to apiculture.

1.4.2 Impacts on Regulating Services

The category of regulating ecosystem services is among the services most strongly affected by IAS. They can dramatically change the morphology of deltaic ecosystems by affecting and trapping bed (delta bed) sediments and stabilizing habitats in new ways, accelerating bed erosion and changing water flow and velocity, degrading flood protection. Another effect of IAS on regulating services in deltaic ecosystems is changes in the water filtration process carried out through the roots of various plant species as some IAS increase the nutrient loading and subsequent eutrophication leading in algal blooms and dissolved oxygen reduction. In addition, other IAS disrupt microbial communities and those of invertebrates that are essential for the pollutant processing and maintaining water quality while they also disrupting the trophic network.

1.4.3 Impacts on Cultural Services

The cultural ecosystem services of deltaic ecosystems such as recreation, heritage events, historical heritage are influenced by the ecological processes which are often disrupted by IAS as the benefits of these services are directly linked to the health and integrity of ecosystems like deltaic ones. Deltaic ecosystems are characterized, like all ecosystems, by some "keystone" species such as endemic species of birds, amphibians, fish or even plant species. Changes in water quality as mentioned above in regulating services as well as reduced habitat accessibility diminish non-material activities such as recreation and ecotourism. For local communities in deltaic ecosystems, the changes caused by IAS represent, in addition to economic losses, the erosion of their historical heritage.

1.4.4 Impacts on Supporting Services

Ecosystem supporting services — nutrient cycling, soil formation and habitat provision to support biodiversity, are often affected by IAS. IAS, as temporally newly introduced into an ecosystem, are

particularly competitive due to the lack of natural enemies or limiting factors (e.g. food) that do not exist in their new environment, thus favoring their establishment and rapid spread. Often these species can also carry parasites or viruses that are exogenous to the new environment, further affecting supporting services. IAS, outcompete indigenous species in acquiring resources and reduce biodiversity, which is a factor in ecosystem stability. In an ecosystem, high biodiversity provides functional redundancy meaning that multiple species perform similar ecological roles. This redundancy acts as an ecological buffer helping to maintain stable ecosystem functioning even if some species are lost. The impacts of IAS on supporting services concern the reduction of biodiversity due to the usual competitiveness against native species that often leads to their displacement in locations where IAS have not yet expanded. For example, Callinectes sapidus is reported to have in some cases displaced native crustacean species. Other impacts on supporting services include changes in pH, organic matter and other physicochemical properties of soils, including changes in biogeochemical cycles as well as changes in the biogeomorphology of ecosystems. Thus, IAS influence ecosystem health not only by monopolizing resources and causing changes in vital biogeochemical cycles, or in soil aeration but also by interacting with mesofauna and microfauna.

1.4.5 Broader Socio-Economic Consequences

The degradation of ecosystem services by IAS has significant socio-economic impacts in deltaic ecosystems reducing provisioning services. With the reduction in provisioning services, both social and economic cohesion are directly affected. Social cohesion concerns the increase in food insecurity, the erosion of cultural services while economic cohesion concerns the reduction in the income of users of ecosystem services, e.g. farmers, fishermen, while tourism activity is also affected. At the same time, the loss of supporting services threatens long-term ecosystem resilience. The above impacts translate into significant economic costs.

1.5 Biodiversity and Human Well-Being

Biodiversity is defined by the Convention on Biological Diversity (United Nations 1992) as “the variability among living organisms from all sources, including terrestrial, marine and other aquatic

ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems.” This formal definition describes biodiversity as a structural feature of the living world. Recently, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES 2019) expand the term defined Biodiversity as “diversity within species, between species and of ecosystems, and it underpins nature’s contributions to people, including ecosystem functions and services that directly and indirectly support human well-being and quality of life”. Therefore, it emphasizes nature’s contributions to people's welfare, directly or indirectly. Human well-being “is assumed to have multiple constituents, including the basic material for a good life, such as secure and adequate livelihoods, enough food at all times, shelter, clothing, and access to goods; health, including feeling well and having a healthy physical environment, such as clean air and access to clean water; good social relations, including social cohesion, mutual respect, and the ability to help others and provide for children; security, including secure access to natural and other resources, personal safety, and security from natural and human-made disasters; and freedom of choice and action, including the opportunity to achieve what an individual values doing and being. Freedom of choice and action is influenced by other constituents of well-being (as well as by other factors, notably education) and is also a precondition for achieving other components of well-being, particularly with respect to equity and fairness”. Following this term, Biodiversity, in relation to ecosystem services, also supports all of these dimensions, directly or indirectly, by providing essential goods, sustaining ecological processes and supporting non-material cultural and spiritual values.

1.5.1 Biodiversity and Provisioning Ecosystem services

The most direct link between biodiversity and human well-being is through the provision of material goods. Biodiversity provides the genetic resources that sustain health, food and industry. Global food security is sustained by the agricultural biodiversity, e.g. crop varieties, livestock breeds and fish species, but non-harvested species that support food provision, such as soil micro-biota or pollinators. The decrease of genetic diversity in agriculture reduces resilience to pests or diseases and thus increased the vulnerability for human populations dependent on crop production.

Fisheries and aquaculture that are sustained by diverse aquatic ecosystems, supply nearly 3.3 billion people with at least 20% of their animal protein intake (FAO). In deltas, fishery supports both local population activity and international market sustaining the economy of millions of people. Moreover, habitats such as wetlands and estuaries serve as nurseries for commercially valuable species, linking ecosystem integrity directly to provisioning services. In parallel, biodiversity provides a significant number of products such as timber, fuelwood, fibers, resins and honey that support rural economies (TEEB 2010). In several Mediterranean and Balkan deltas,

apiculture linked to riparian vegetation contributes honey and wax to local markets while also supporting pollination services. Medicinal biodiversity is equally critical. Thousands of species are used both in traditional and modern medicine as compounds derived from them have formed the basis for essential pharmaceuticals. The loss of biodiversity thus represents a reduction in current and future options for health and innovation.

1.5.2 Biodiversity and Regulating Ecosystem services

The relationship between regulating ecosystem services and biodiversity are often less visible than material goods, although they are equally critical for human welfare. The earth’s climate is regulated by various diverse ecosystems through sequestering carbon. More specifically, vegetated coastal ecosystems (mangrove forests, seagrass beds, salt marshes) are disproportionately important in sequestering carbon dioxide when compared with terrestrial ecosystems. Wetlands filter nutrients and pollutants, improving water quality for downstream users and reducing treatment costs. Soils rich in soil micro-biota sustain nutrient cycling, maintain fertility and reduce erosion, ensuring long-term agricultural productivity. Moreover, riparian forests stabilize sediments, buffer storms and reduce salinity protecting thus both ecosystems and human settlements. Pollination is another key regulating service. 75% of crop species benefit from it. It is referred that

wild pollinators are also a vital part of our crop systems. In more than 40 important crops grown worldwide, wild pollinators improved pollination efficiency, increasing fruit set by twice that facilitated

by honeybees.

The stability of regulating ecosystem services is directly linked to biodiversity. In general, ecosystems with greater biodiversity show higher levels of productivity, resistance to invasion, and

resilience to disturbances. Therefore, the decrease of biodiversity makes societies more vulnerable.

1.5.3 Biodiversity and Regulating Ecosystem services

For thousands of years, humans have attributed cultural significance to biodiversity that was beyond its role as a source of food, materials or labour. This is proved by the numerous plant and animal species that have symbolic value, are national emblems or referred to religious texts. In all human history, biodiverse landscapes inspire art, literature, science and deep emotional connections that strengthen the ties between people and nature. Nature is thought to contribute to quality of life through inspiration and learning. Experiences with nature enhance psychological and physical health, linking biodiversity and nature exposure with human`s health. The significance of this cultural aspect of biodiversity is further reflected in the considerable time and resources invested by people to experience and connect with nature. Therefore, recreation and tourism are among the cultural ecosystem services. Activities such as birdwatching, diving, hiking and wildlife safaris are directly dependent on biodiversity, support the rural economies with significant income.

1.5.4 Biodiversity and Supporting Ecosystem services

Biodiversity is the basis of supporting ecosystem services, such as the primary production, nutrient cycling, soil formation and habitat provision. Biodiversity enhances the efficiency with which ecological communities capture essential resources such as nutrients, water, light and prey, and convert them into biomass, while also promoting decomposition and nutrient recycling through reater diversity in plant litter. Moreover, biodiversity increases the quality, stability and resilience of ecosystems as the different species have complementary roles that enhance ecosystem productivity functioning. Diverse communities include key species, with significant functional impacts that maximize resource capture. Wetland mosaics with various patches of plant and animal communities provide breeding habitats for fish and birds and pollinator diversity increases agricultural productivity and directly supports human welfare. In river deltas, high biodiversity enhances the protective role of deltas as species rich communities are more effective in reducing erosion and the risk from storms and floods. Thus, it is the diversity of life forms, rather than mere vegetation cover, that secures the supporting services on which human well-being depends.

Ecosystem services are shaped not only by the functional traits, distribution and abundance of the species present, but also by climate, resource availability and disturbance regimes. Therefore, human-driven invasions or extinctions often disrupt these processes and reduce the stability of ecosystem service.

1.6 Classification and Measurement of Ecosystem Services

The Millennium Ecosystem Assessment (MEA) was the first classification system for the Ecosystem Services. It was developed under the supervision of the United Nations Environment Programme

(UNEP). Over 1,360 experts worldwide worked from 2001 until 2005 when it was completed. Several other organizations were also involved, including the World Bank, the United Nations Development Programme (UNDP), and the World Resources Institute (WRI). MEA classified the ecosystem Services in 4 broad categories: provisioning, regulating, cultural, and supporting services. This framework was the foundation for subsequent approaches to ecosystem service assessment. Based on MEA, the European Environment Agency developed the Common International Classification of Ecosystem Services (CICES) that is a classification system of the Final Ecosystem Services. Final Ecosystem Services are defined as those ecosystem outputs that directly contribute to human well-being, such as food, water, flood protection or recreation. The primary goal of CICES was to provide a structure that would avoid the double counting of intermediate processes such as nutrient cycling.

Therefore, both MEA and CICES, as classification systems, organize and categorize different types of ecosystem services for consistency and comparability.

CICES has classified the Final Services into three main categories, Provisioning, Regulation Maintenance and Cultural. While this taxonomic clarity is highly valuable for harmonization and meta-

analysis, CICES does not include guidance for mapping, model or measuring the Final services. On the contrary, MAES (Mapping and Assessment of Ecosystems and their Services), developed by the European Commission, goes on step further classification. It is a policy-driven framework designed to help EU Member States not only identify and categorize ecosystem services but also map ecosystems, assess their condition, quantify service flows, and link these results to policy and management needs. MAES is thus implementation-oriented. MAES includes the below key elements:

1. Mapping of ecosystems (identifying where they are and what types they represent).

2. Assessing condition (evaluating ecosystem health and degradation).

3. Measures service flows (quantifying outputs such as food provision, water regulation, or recreation).

4. Connects this information to EU strategies and directives, including the Water Framework Directive, the Habitats Directive, and the Marine Strategy Framework Directive.

Therefore, MAES and CICES complement one another as CICES provides the classification, whereas MAES proposes the implementation process that links ecosystem, service flows and policy.

MAES Workflow

The Mapping and Assessment of Ecosystems and their Services (MAES) workflow can be visualized

as below (Fig. 1). This representation shows MAES five main steps.

1.7 The Use of MAES in Assessing Ecosystem Services

The Ecosystem Services evaluation is essential in order to link the ecosystem ecological functions with human well-being and decision-making. MEA (Millennium Ecosystem Assessment) and CICES (Common International Classification of Ecosystem Services), as Classification systems have provided a framework for describing ecosystem services. However, these frameworks do not explain how and why a service is changing over time or how these changes will be taken into account in management. Therefore, in order for the evaluation to be practical and meaningful, it must be tied to measurements, spatial mapping and indicators that connect ecosystem condition to service provision. Therefore, MAES framework is an essential tool as it introduces a stepwise workflow: mapping ecosystem extent, assessing ecosystem condition, quantifying service flows and linking these results to EU policy frameworks. This allows to detect the existing services, to measure their extent, to monitor their decrease or increase and take the necessary management actions. When we want to evaluate invasive alien species (IAS) effects, the need for a measurement-based assessment is crucial. IAS alter the condition of an ecosystem by changing biodiversity composition, hydrology, or soil fertility and disrupt ecosystem service flows. For example, invasive plants may reduce water availability for irrigation by clogging channels, while invasive fish can reduce native fish populations. Such impacts are only captured only after quantification of the service decline. MAES gives the framework to map the extent of IAS colonization, measure the degraded condition of affected habitats and quantify the reduction in service flows (e.g., decrease in fish catch, reduced flood regulation). In a second step, MAES’s information can directly inform EU biodiversity strategies, IAS regulation and restoration priorities.

1.8 The Central Role of Provisioning Services and Biodiversity in Ecosystem Service Evaluation

The assessment of ecosystem services (ES) necessarily involves choices regarding which services can be measured in detail. This project focuses on provisioning services and biodiversity, as these provide the most direct, measurable and policy-relevant aspects in deltaic ecosystems. The Provisioning services, such as freshwater supply, fisheries, agricultural yields, timber, honey,

and other material products, are the most measurable benefits that ecosystem services give to human societies. They are directly linked to food security, human welfare and economic activity. In deltaic ecosystems, provisioning services support regional and national economies as millions of people depend on deltas for crop production, aquaculture, livestock and freshwater resources. These services are also relatively clear to quantify through biophysical and economic indicators (e.g., tons of fish landed, hectares cultivated, volumes of freshwater supplied). Because of this measurability and their immediate connection to human well-being, provisioning services are prioritized in most ecosystem service assessments. On the contrary, the present methodological assessments for regulating and cultural services are challenging. Regulating services, such as flood control, water purification or climate regulation, are difficult to be measured with precision. They usually require complex models, long time series, and large datasets that are not always available.

Similarly, cultural services, including recreation and aesthetic values, are difficult to quantify. Biodiversity, although not a service, is included because it is the foundation of ecosystem functioning. The diversity of species regulates the stability, resilience, and long-term sustainability of all other services. Higher biodiversity typically ensures that ecosystems are more resistant to disturbances,

including those caused by invasive alien species (IAS) and climate change. In deltas, biodiversity supports provisioning services such as fisheries, pollination and crop, while also reinforcing egulating services like nutrient cycling and water purification.