A global map of saltmarshes

Abstract

BackgroundSaltmarshes are extremely valuable but often overlooked ecosystems, contributing to livelihoods locally and globally through the associated ecosystem services they provide, including fish production, carbon storage and coastal protection. Despite their importance, knowledge of the current spatial distribution (occurrence and extent) of saltmarshes is incomplete. In light of increasing anthropogenic and environmental pressures on coastal ecosystems, global data on the occurrence and extent of saltmarshes are needed to draw attention to these critical ecosystems and to the benefits they generate for people. Such data can support resource management, strengthen decision-making and facilitate tracking of progress towards global conservation targets set by multilateral environmental agreements, such as the Aichi Biodiversity Targets of the United Nations' (UN's) Strategic Plan for Biodiversity 2011-2020, the Sustainable Development Goals of the UN's 2030 Agenda for Sustainable Development and the Ramsar Convention.New informationHere, we present the most complete dataset on saltmarsh occurrence and extent at the global scale. This dataset collates 350,985 individual occurrences of saltmarshes and presents the first global estimate of their known extent.The dataset captures locational and contextual data for saltmarsh in 99 countries worldwide. A total of 5,495,089 hectares of mapped saltmarsh across 43 countries and territories are represented in a Geographic Information Systems polygon shapefile. This estimate is at the relatively low end of previous estimates (2.2-40 Mha), however, we took the conservative approach in the mapping exercise and there are notable areas in Canada, Northern Russia, South America and Africa where saltmarshes are known to occur that require additional spatial data. Nevertheless, the most extensive saltmarsh worldwide are found outside the tropics, notably including the low-lying, ice-free coasts, bays and estuaries of the North Atlantic which are well represented in our global polygon dataset. Therefore, despite the gaps, we believe that, while incomplete, our global polygon data cover many of the important areas in Europe, the USA and Australia.

Fresh groundwater discharge insignificant for the world’s oceans but important for coastal ecosystems

“…Coastal areas with elevated risk include sensitive coastal ecosystems. A comparison with published locations of these ecosystems [42][43][44] shows that 26% (0.4-39%) of the world's estuaries and 17% (0.3-31%) of the salt marshes at risk of eutrophication. In addition, 14% (0.1-26%) of the coastline that is located within 500 m of a coral reef is at risk of eutrophication ( Fig.…”

“…Given the very high sensitivity of coastal ecosystems and especially coral reefs to nitrogen 87 , this threshold value is likely to result in a relatively conservative estimate of eutrophication risk. The calculated locations of sites with high eutrophication risk was compared with the location of sensitive ecosystems such as estuaries 42 , salt marshes 43 , and coral reefs 44 . We acknowledge that eutrophication of marine ecosystems is a complex function of nutrient input, transport, denitrification, and mixing with seawater.…”

Quantifying Bed Level Change at the Transition of Tidal Flat and Salt Marsh: Can We Understand the Lateral Location of the Marsh Edge?

“…Tidal flats and salt marshes are widespread coevolving ecosystems in the coastal region (Marani et al, 2007;Mcowen et al, 2017). They provide multiple ecosystem services like carbon sequestration (Chmura et al, 2003;Duarte et al, 2013), filtering water (Nelson & Zavaleta, 2012), providing a habitat and nursery ground (Irmler et al, 2002;Van Eerden et al, 2005), and improving coastal safety by stabilizing the bed and attenuating waves (Temmerman et al, 2013;Vuik et al, 2016).…”

Carbon Stocks and Accumulation Rates in Salt Marshes of the Pacific Coast of Canada

“…However, consideration of the areal extent of each of these ecosystems is useful for placing the role of blue carbon uptake into perspective for Canadian ecosystems. Estimates of total salt marsh area in Canada range from 44,000 ha (Bridgham et al, 2006) to 111,274 ha (Mcowen et al, 2017). In contrast, the boreal forest ecosystem is one of Canada's largest terrestrial biomes and encompasses approximately 270 million ha (Kurz et al 2013).…”