Abstract
Suaeda salsa saltmarshes are an important coastal wetland habitat of China’s northern Yellow Sea, which plays a critical role in sequestering carbon (blue carbon), protecting shorelines, maintaining biodiversity, and has substantial economic value (e.g., ecotourism). However, the area of S. salsa has been rapidly declining due to several different threats from reclamation and invasive species that impact its natural succession. Here, we map the changes in the distribution of the S. salsa saltmarshes along the northern Yellow Sea of China (NYSC) at 5-year intervals by applying the supervised maximum likelihood method to analyze Landsat images from 1988 to 2018 and investigate the potential impact of three important factors on habitat change by analyzing the temporal changes in S. salsa saltmarshes with other land covers. S. salsa saltmarsh areas have decreased by 63% (264 km2 ha to 99 km2), and the average loss of S. salsa saltmarshes was 5.5 km2/year along the NYSC over the past three decades. There have been many dramatic declines in the two main distribution areas of S. salsa saltmarshes with a 77% loss of habitat area in Liaodong Bay (from 112 km2 to 26 km2) and a 52% loss in the Yellow River Delta wetland-Guangli-Zhima estuarine wetland (from 137 km2 to 65 km2). Land reclamation is the most important impact factor in the loss of S. salsa saltmarshes, while there have been limited effects of natural succession and smooth cordgrass (Spartina alterniflora) invasion. In light of the important ecological services and economic value of the S. salsa habitat, emergency conservation actions (e.g., habitat restoration, strictly supervision) are needed to limit the rapid habitat loss, which should include the immediate cessation of extensive land reclamation along the NYSC.
Highlights
We first mapped the historical spatial–temporal distribution of S. salsa saltmarsh areas near the northern Yellow Sea of China (NYSC) from 1988 to 2018 by using a long time-series of Landsat images, which revealed that Liaodong Bay and the Yellow River Delta wetland—GuangliZhima estuarine wetlands are the core distribution regions of S. salsa saltmarsh areas
Consistent with other findings on the loss of coastal wetlands, there has been an extensive loss of S. salsa saltmarsh areas on the coast of the NYSC during the past three decades, primarily driven by land reclamation [4,16,24]
During the past several decades, significant areas of coastal wetlands have been lost due to human reclamation and natural changes; for example, tidal flats have declined by 16.02%
Summary
Coastal wetlands, which are composed by multiple natural landscapes connecting mainland and oceanic ecosystems, provide hugely significant ecological services (e.g., buffering ocean storms [1], shoreline protection against rising sea-levels, and maintaining biodiversity [2]) and have critical economic value from the contribution of their vast marine biological resources [3]. In recent decades, coastal wetlands have been under intensive pressure worldwide from land reclamation [4,5], reduced stream discharge and sediment fluxes from rivers [4,6], erosion, and sea-level rise [7]. Reclamation has indirectly negatively impacted local wetland ecosystems through soil compaction [8], heavy mental contamination, oil pollution, and biodiversity loss [9]
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