Wetland Loss/Degradation

Primary reference(s)

Craig, N.J., R.E. Turner and J.W. Day, 1979. Land loss in coastal Louisiana (USA). Environmental Management, 3:133-144.

Olsson, L., H. Barbosa, S. Bhadwal, A. Cowie, K. Delusca, D. Flores-Renteria, K. Hermans, E.
Jobbagy, W. Kurz, D. Li, D.J. Sonwa, L. Stringer, 2019. Land degradation. In: Climate Change and Land: an IPCC Special Report on Climate Change, Desertification, Land Degradation, Sustainable Land Management, Food Security, and Greenhouse Gas Fluxes in Terrestrial Ecosystems. Accessed 21 October 2020.

Ramsar Convention 1971. Convention on Wetlands of International Importance Especially as Waterfowl Habitat, 2 February 1971 (amended 1982 & 1987). Accessed 21 October 2020.

Additional scientific description

The Ramsar Classification of Wetland Type includes 42 types of wetland grouped into three categories: marine and coastal wetlands, inland wetlands, and human-made wetlands. The five major wetland types are generally recognised as: marine (coastal wetlands including coastal lagoons, rocky shores, and coral reefs); estuarine (including deltas, tidal marshes, and mangrove swamps); lacustrine (wetlands associated with lakes); riverine (wetlands along rivers and streams); and palustrine (meaning ‘marshy’ – marshes, swamps and bogs). In addition, there are human-made wetlands such as fish and shrimp ponds, farm ponds, irrigated agricultural land, salt pans, reservoirs, gravel pits, sewage farms and canals (Ramsar, 1971).

Conversion of freshwater wetlands to agricultural land has historically been a common way of increasing the area of arable land (Olsson et al., 2019). However, wetlands with organic and wet soils are crucial in maintaining the Earth’s carbon balance as they contain soils with high organic carbon content. Human activities on wetlands (e.g., drainage, agriculture, forestry, peat extraction, aquaculture) and their effects (e.g., oxidation of soil organic matter) may significantly affect the carbon and nitrogen balance and, thus, the greenhouse gas emissions from these lands. The degradation of peatland ecosystems, for example, is particularly relevant in the context of climate change given their very high carbon storage and their sensitivity to changes in soils, hydrology and/or vegetation. Human activity, either draining or mining approximately takes up 10% of global peatlands, releasing 80.8 Gt carbon and 2.3 Gt nitrogen. This corresponds to an annual greenhouse gas emission of 1.91 (0.31–3.38) Gt CO2-equivalent. that could be saved with peatland restoration. Drainage induces peatland degradation and alters peatlands, globally, from a net sink to a net source of greenhouse gases in the land-use sector (Joosten, 2009; IPCC, 2014; Leifeld and Menichetti, 2018; Olsson et al., 2019).

Wetland loss/degradation results in associated reduction in ecosystem services delivered by wetlands such as: provisioning services including food and freshwater; regulating services such as flood control, storm protection, drought buffering, groundwater recharge and discharge, and carbon sequestration; cultural services such as recreation; and supporting services such as purification of water supplies, shoreline stabilisation and erosion control; retention of nutrients, sediments, and pollutants; and stabilisation of local climate conditions – particularly rainfall and temperature. The ecosystem services related to human health primarily cover supply of water, food, nutrition, and medicine, purification of waste products, and buffering against adverse flooding and climate effects (Ramsar, 2005, 2016).

Metrics and numeric limits

Approximately 1% of the Earth’s surface is freshwater wetlands. They provide a very large number of ecosystem services, such as groundwater replenishment, flood protection and nutrient retention, and are biodiversity hotspots. Over two-thirds of the world’s fish harvest is linked to the health of coastal and inland wetland areas. Agriculture is also impacted by wetlands through the maintenance of water tables and nutrient retention in floodplains. In addition, rice, a common wetland plant, is the staple diet of more than half of the global population. The loss of wetlands since 1900 has been estimated at about 55% globally (Davidson, 2014) and 35% since 1970 (Ramsar, 2016; Hu et al., 2017; Darrah et al., 2019; Olsson et al., 2019).

Coastal wetlands around the world are sensitive to sea level rise. Studies and projections of the impacts on global coastlines are inconclusive, with suggestions that between 0% to 90% (depending on sea level rise scenario) of present-day wetlands will disappear during the 21st century (Olsson et al., 2019).

Despite their importance, coastal wetlands are listed among the most heavily damaged natural ecosystems worldwide. However, coastal wetland restoration and preservation is an extremely cost-effective strategy for society, for example, the preservation of coastal wetlands in the USA provides storm protection services worth 23.2 billion USD per year. Coastal wetlands function as valuable, self-maintaining ‘horizontal levees’ for storm protection (Costanza et al., 2008; Olsson et al., 2019).

Globally, approximately 1.1 Gha of land is affected by salt, with 14% of this categorised as forest, wetland or some other form of protected area (Olsson et al., 2019).

Examples of drivers, outcomes and risk management

Overexploitation of freshwater resources jeopardises human well-being and the environment. Access to safe water, human health, food production, economic development and geopolitical stability are made less secure by the degradation of wetlands driven by the rapidly widening gap between water demand and supply. Even with current attempts to maintain minimum water flows for ecosystems, the capacity of wetlands to continue to deliver benefits to people and biodiversity, including clean and reliable water supplies, is declining. Efforts to support water allocation to ecosystems, such as environmental flow requirements, placing upper limits on water allocations, and new water management legislation, must be strengthened (Ramsar, 2016).

Many Contracting Parties to the Ramsar Convention, recognising the importance of the conservation and wise use of wetlands, have adopted some form of an avoid-mitigate-compensate approach to wetland loss and degradation. In this context, national, regional, and local laws and policies emphasise that negative wetland impacts should be avoided if at all possible. If such negative impacts cannot be avoided or prevented, actions should be taken to mitigate (minimise or reduce) this wetland loss or degradation. Finally, if wetland loss or degradation remains after such mitigation, actions should be taken to compensate for (i.e., offset) these residual impacts (Gardner et al., 2012).

Wetlands constitute a resource of great economic, cultural, scientific and recreational value to human life. Wetlands and people are ultimately interdependent. Furthermore, wetlands are an essential component of the global water cycle and play a key role in climate regulation. As such, the progressive encroachment on and loss of wetlands needs to be stopped, and measures must be taken to conserve and make wise use of wetland resources. To achieve this at a global level requires cooperative, intergovernmental action. The Ramsar Convention on Wetlands provides the framework for such international, as well as for national and local, action (Ramsar, 2016).