biodiversity for food and agriculture
4.3 Associated biodiversity
4.3.7 Associated biodiversity for water-related ecosystem services
Introduction
Water is vital to all species and to all ecosystem functions and services. While much of the Earth’s estimated 1.4 billion km3 of water is in long-term storage in oceans, ice caps and aquifers, about 41 000 km3 circulates between the atmosphere, the surface of the land, subsurface zones, freshwater
bodies and the ocean (Acreman, 2004). Ecosystems and the living organisms within them influence the hydrological cycle and hence the amount of water available at particular locations at particular points in time: for example, whether or not there is suffi-cient water to meet the needs of plants during the growing season in a cropping area or whether or not a vulnerable area is hit by flooding.
Vegetation and soils are vital to the control of water flows in terrestrial ecosystems. Vegetation promotes the infiltration of water into the soil, thus helping to recharge underground aquifers and lowering flood risk (Acreman, 2004). Soil biota – plants, micro-organisms and invertebrate and vertebrate animals – modifies the structure of the soil and affects the pathways and rates of water infiltration, influencing the capacity of the soil to hold water (BIO Intelligence Service, 2014;
Sans and Meixner, 2016) (see Section 4.3.4 for further information on the status and trends of associated biodiversity contributing to soil-related ecosystem services). Plants also return water to the atmosphere through transpiration (Acreman et al., 2014; Stewart, 1977) and in some cases influ-ence the amount of precipitation that falls in the local area (Spracklen, Arnold and Taylor, 2012;
Wright et al., 2017) (see Box 4.7).
As well as influencing the quantity of water available, biodiversity also influences water quality, including by cycling nutrients within waterbodies and between them and other ecosys-tems. Nutrient-cycling services are essential to the health of aquatic ecosystems. On the one hand, aquatic organisms clearly need to be able to access sufficient quantities of nutrients to allow them to grow and reproduce. On the other, however, waterbodies can become overloaded with nutri-ents, for example in agricultural areas where there is a heavy use of fertilizers, and this can have neg-ative impacts on biodiversity and the supply of ecosystem services (see Chapter 3).
A myriad of interconnected physical, physio- chemical, chemical and biological processes contribute to water-purification and nutrient- cycling services in aquatic ecosystems (Cardinale, 2011; Ostroumov, 2002, 2005). Some species
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Box 4.7
Páramos – a vital provider of water-regulating services under threat
What are páramos?
Páramos are high-altitude ecosystems found mainly in a discontinuous belt stretching along the Andean mountain range from the Cordillera de Merida in the Bolivarian Republic of Venezuela to the Huancabamba depression in northern Peru, passing through Colombia and Ecuador (Buytaert et al., 2006; IUCN, undated). There are separate páramo complexes in Costa Rica and in the Sierra Nevada de Santa Marta, Colombia (Hofstede, Segarra and Mena, 2003).
Páramo ecosystems extend from the upper tree line to the perennial snow border (3 200 to 5 000 metres above sea level) (IUCN, undated). It is estimated that they host around 5 000 different plant species, a high proportion of which are endemic (i.e. found nowhere else) (Buytaert et al., 2006).
Species that occupy the páramos have developed remarkable adaptations to harsh physiochemical and climatic conditions such as low atmospheric pressure, intense ultraviolet radiation and the drying effects of the wind (ibid.).
How do páramos contribute to water regulation?
Páramos play a key role in regulating water flows (Buytaert et al., 2006): rainfall is high and may be supplemented by fog condensation; water consumption is low as the leaves of the tussock grasses are protected against radiation and dry air by accumulated dead leaves and because the herbaceous vegetation consists of xerophytic species (plants adapted to a lack of water); the tussock grasses and dwarf shrubs protect the soil and reduce evaporation. The soils themselves
have extraordinary water-retention capacity (ibid.). Many of the largest tributaries of the Amazon basin have their headwaters in páramo ecosystems,which thus help sustain the lives and livelihoods of millions of people, providing water for domestic, agricultural and industrial consumption and for use in generating hydropower (Buytaert et al., 2006).
Why are páramos under threat?
The country reports mention several threats to the páramos and the ecosystem services they provide. For example, the report from Peru states that the country’s páramos are undergoing a process of transformation, desertification and erosion, mainly as a result of overgrazing, extractive activities, intensive agriculture and pollution. It notes that this is directly affecting the ecosystem’s capacity to moderate extreme events, prevent erosion, maintain soil fertility and maintain genetic diversity. Ecuador mentions that the invasive alien species Kikuyu grass (Pennisetum clandestinum) represents a threat to páramos, as it could outcompete native species and, given its value as a fodder, promote more livestock grazing in mountain areas. Costa Rica reports that, according to a scenario study, climate change will lead to altitudinal shifts in life zones that will potentially result in the disappearance of the country’s páramos in the coming decades.
Sources: Country reports of Costa Rica, Ecuador and Peru (plus the references cited in the text).
Páramos ecosystem on the foothills of Puracé National Park in the Andes, Colombia. © Nigel Dudley.
Espeletia spp., commonly known as frailejones, are typical plants of páramos ecosystems. © Nigel Dudley.
play particularly prominent roles. For example, some plant species, such as the water hyacinth (Eichhornia crassipes), duck weed (e.g. Lemna spp.), aquatic ferns (e.g. Azolla spp.), cattails (Typha spp.) and reeds (Phragmites spp.), are recognized for their ability to remove toxic sub-stances such as heavy metals from waterbodies (Ramsar Convention, 2011a).47 Filter-feeding animals, such as ascidians (sea squirts), cirripeds (barnacles), bryozoans (colony-forming inverte-brates sometimes referred to as moss animals), bivalves (e.g. clams, oysters, mussels and scallops), polychaetes (bristle worms) and sponges, play a conspicuous “cleaning” role in the ecosystem as they remove suspended particles from the water (Ostroumov, 2005). However, virtually all the species in an aquatic ecosystem are involved in water-purification and nutrient-cycling processes, either directly (e.g. by trapping, transforming, accumulating and/or translocating pollutants via their behavioural activities and physiological pro-cesses) or indirectly (e.g. by releasing oxygen into the water, mixing the water column, influencing the physical and chemical properties of the water by contributing organic matter, or influencing the behaviour of other organisms such a prey species) (Ostroumov, 2002, 2005; Vanni, 2002).
In addition to processes occurring within waterbodies themselves, water-purification ser-vices are provided by other ecosystems through which water flows (forests, grasslands, etc.) (FAO, 2007d; Oregon State University, 2008; Ostroumov, 2005). As with water-cycling services, the capac-ity of these ecosystems to purify water is greatly affected by the state of the vegetation and the soils within them – and in turn on a wide range of components of biodiversity that contribute to soil health or help maintain plant communities.48
In response to a question about species managed specifically to promote water-related ecosystem services, countries mention approx-imately 80 species. Examples include willows
47 It should be noted that some of those species are invasive in some regions of the world.
48 See Section 4.5 for further discussion of the status and trends of rangelands, forests and wetlands.
(Salix spp.), cattails (Typha spp.), the oyster mushroom (Pleurotus ostreatus) and bamboos (Bambusa spp.) (see Section 4.3.1). Trees are par-ticularly widely mentioned, as is the importance of soils, wetland ecosystems, forests and riparian areas. For example, the United States of America highlights the importance of the soil as a filter that improves water quality, and also notes the role played by riparian buffers in reducing the amount of fertilizer and other agricultural chemicals passing from farmland into waterways. Countries also note a number of marine and coastal eco-systems as important suppliers of water-purifica-tion services. For example, Norway menwater-purifica-tions kelp forests and Solomon Islands mentions coral reefs, mangroves, seagrass beds and intertidal mud ecosystems. Several groups of aquatic species are noted as contributors to marine water-purifica-tion services, including shellfish and micro-organ-isms (Mexico) and microalgae (Peru).
State of knowledge
As described above, a wide range of taxonomic and functional groups of organisms, across a range of different ecosystems, contribute to water-purification and water-cycling services.
However, although the processes involved may be broadly understood, in many cases little is known about the underlying ecological mechanisms that keep them in operation or about the relationships between the diversity and distribution of BFA and provision of these services (Cardinale, 2011;
Harrison et al., 2014; Ostroumov, 2005).
Water quality itself has not yet been assessed comprehensively at global scale. In 1978, the Global Environment Monitoring System for freshwater (GEMS/Water) was established under the auspices of the United Nations Environment Programme, the United Nations Educational, Scientific and Cultural Organization, the World Health Organization and the World Meteorological Organization (UN Environment, 2016c). The GEMS/Water Data Centre maintains the Global Water Quality database and infor-mation system (GEMStat), which stores data received from a global network of national
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focal points (ibid.). A global assessment of water quality (Meybeck et al., 1989; UNESCO, WHO and UN Environment, 1996) was published in 1988.
However, inconsistencies in spatial and tempo-ral coverage and differences in the ranges of variables reported meant that the assessment relied on sources other than the GEMS/Water database (UN Environment, 2016c). In 2016, UN Environment published A snapshot of the world’s water quality: towards a global assessment (ibid.), a prestudy aiming to provide some of the building blocks of a global assessment and to provide a preliminary estimate of the state of water quality in freshwater ecosystems, with a focus on lakes and rivers in Africa, Asia and Latin America.
The status of relevant ecosystems and groups of species are assessed and monitored under a number of global initiatives. For example, IUCN monitors the conservation status of marine and freshwater invertebrates and how they are being affected by environmental changes (Collen et al., 2012). The IUCN Species Programme Marine Biodiversity Unit assesses extinction risks for marine vertebrates, plants and selected inverte-brates, including those in important ecosystems such as coral reefs, mangroves and seagrass beds (GMSA, 2017). The Global Census of Marine Life,49 conducted between 2000 and 2010 to assess and explain the diversity, distribution and abundance of marine life, resulted in the creation of a global marine-life database (see Chapter 6 for more information). More information on relevant eco-system assessments can be found in Section 4.5.
Regional and national initiatives within the framework of The IUCN Red List have pro-vided detailed reviews of the status of par-ticular groups of aquatic species. For instance, the European Red List of Non-Marine Molluscs (Cuttelod, Seddon and Neubert, 2011) provides information on the state of freshwater bivalves and gastropods. A study of African freshwater biodiversity (Darwall et al., 2011) addresses the state, diversity, distribution and conservation of, inter alia, freshwater molluscs and plants in
49 http://www.coml.org/
a range of ecosystems, including river and arte-sian basins, ancient, montane and crater lakes, saline lagoons, salt-marshes and mangroves.
Other examples include studies of the status of freshwater biodiversity in the Eastern Himalaya (Allen, Molur and Daniel, 2010), Western Ghats (Molur et al., 2011) and Indo-Burma biodiversity hotspots (Allen, Smith and Darwall, 2012).
In as far as the country reports mention research or monitoring programmes addressing the role of biodiversity in the delivery of water-cycling and water-purification services, it is generally to note a lack of knowledge or a lack of studies on relevant components of biodiversity (e.g. micro- organisms), on the capacity of particular ecosys-tems to deliver these services or on trends in the supply of these services. Finland does, however, mention water purification among the ecosystem services for which there has been a rapid growth of research in recent decades.
Status and trends
As discussed above, while water-related support-ing and regulatsupport-ing ecosystem services depend to a large degree on the extent, distribution and general health of relevant ecosystems and on a very wide range of different organisms, some species play particularly prominent roles. In the case of water purification services, these include aquatic plants and various groups of aquatic inver-tebrates. The risk status of species in these cate-gories is, in general, relatively poorly monitored, as compared to that of vertebrates, for example.
Data from The IUCN Red List for some relevant taxa – Maxillopoda (crustaceans such as barnacles and copepods), Holothuroidea (sea cucumbers), Bivalvia (e.g. clams, oysters, mussels and scallops) and Polychaeta (bristle worms) – are summarized in Figure 4.7, disaggregated by class.
Countries’ responses on trends in the supply of water-purification, waste-treatment, water- cycling and nutrient-cycling services in particular production systems are summarized in Table 4.4.
Where water-purification and waste-treatment services are concerned, trends are mixed (i.e.
neither positive nor negative nor stable trends
predominate) in all production systems except live-stock grassland-based and irrigated crop systems, where reports of negative trends predominate.
In the case of water-cycling services, reports of positive trends predominate in planted forest, fed aquaculture and irrigated (non-rice) crop systems.
Although few responses are provided for these production systems, reports of stable trends pre-dominate for non-fed aquaculture and decreas-ing trends for irrigated rice systems. In all the remaining production systems trends are mixed.
Few countries provide information on trends in nutrient-cycling services in aquatic production systems. In the case of fed aquaculture systems, increasing trends predominate. Decreasing trends predominate for culture-based fisheries.
For other aquatic systems, trends are mixed. The various reports of positive trends in aquaculture systems may relate to the proactive introduction of management techniques and strategies aimed at addressing concerns about the environmental impacts of these systems.
Reasons for negative trends are indicated in a number of country reports. The most frequently mentioned drivers include deforestation, expan-sion of the agricultural frontier and increased livestock grazing in riparian or coastal areas.
China reports that water-purification services in the Miyun Reservoir watershed in Beijing have declined substantially as a result of the expan-sion of construction and other land-use changes.
Finland mentions that recent milder winters may have disrupted the water-purification function of vegetation on land surrounding waterbodies, an effect reported to have arisen because soils are increasingly unfrozen during the non-vegetative period when plants are less able to intercept eroded matter. Panama lists water-purification services among those predicted to decrease as a result of a net loss of forest area. The Gambia notes that changes in land use are diminishing the capacity of forests to provide water-purification and waste-treatment services. The Cook Islands mentions that the removal of trees from littoral forests may be increasing algal growth and sedi-mentation in some lagoon areas. Switzerland, in contrast, provides a more positive assessment of trends in water-related ecosystem services, noting that the capacity of lakes and rivers to purify water has probably increased as a result of resto-ration efforts. The capacity of the country’s forests to provide water-purification services is reported to have been secured for decades through appro-priate forest management.
FIGURE 4.7
Global risk status of invertebrates in the classes Bivalvia, Holothuroidea, Maxillopoda and Polychaeta to work with new one (shades of gray
political/conceptual)
© From cover color palette Polychaeta
Note: EX (Extinct); CR (Critically Endangered); EN (Endangered); VU (Vulnerable); DD (Data Deficient); NT (Near Threatened) and LC (Least Concern).
Source: The IUCN Red List version 2017-2.
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