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Abstract Coastal salt marsh, one of the blue carbon ecosystems that can adapt and mitigate climate change influence, is drawing global attention due to its high carbon sequestration capability. In China, however, coastal salt marsh has suffered great losses. Nation-wide analysis of salt marsh trends and management is critical to ecosystem protection and restoration. Thus, by analyzing previous coastal salt marsh studies, we found that the extent of coastal salt marsh varied greatly among the Liao River Delta, the Yellow River Delta, the middle coast of Jiangsu Province, Chongming Dongtan and Jiuduansha in Shanghai, with a 59% overall loss of salt marsh extent from the 1980s to the 2010s. The rate of salt marsh loss slowed down after the year 2000. Coastal land-claim (reclamation) is the most dominant driver of salt marsh loss. Climate change and coastal erosion, invasive species, and vegetation dynamics driven by competition and succession have also led to various effects on salt marsh extent and the ecological services they provide. Sea level rise, reclamation pressure and environmental pollution are the main factors, as negative drivers, together with conservation and restoration policies, as positive ones, affecting future trends in salt marshes. China has implemented several measures to protect and restore salt marshes, such as setting up protected areas, drawing marine ecological redline, and making strict regulations on reclamation. However, stronger legal protection for wetlands, more effective enforcement, and participation by local communities can further enhance salt marsh restoration, conservation and management. Graphical abstract Image 1 Highlights • Great losses (59%) of salt marshes occurred in China from the 1980s to the 2010s due to a few main drivers. • Salt marshes in China face natural and anthropogenic threats. • China has taken even tougher measures to conserve and restore salt marshes. • Legal basis for wetland protection, more effective enforcement and public participation are needed. [ABSTRACT FROM AUTHOR]

Seaweed aquaculture is an important industry with great social and eco-environmental values. This study assessed the water quality and phytoplankton community during the four seasons around the Taohua Island where seaweed aquaculture has been practiced for near 70 years. Sampling was conducted in Laminaria japonica culturing area. Significant seasonal effects were observed among measured environmental factors and phytoplankton community. The species number and density of phytoplankton were positively correlated with temperature (T), Secchi depth (SD) and total nitrogen (TN) but were negatively correlated with dissolve oxygen (DO). In spring (the late culturing period), the seaweed culture increased pH, DO and salinity, while slightly reduced total phosphorous (TP). The phytoplankton abundance was lower in the culturing area than in control area, whereas the Shannon-Wiener diversity were found to be higher. Our study demonstrated that seasonal environment changes (especially T, SD, TN and DO) had strong influence on the functional characteristics of the phytoplankton community and L. japonica cultivation can absorb the nutrients and enhance phytoplankton diversity, thus alleviating eutrophication and reducing the risk of algal blooms. This is of significance to remediate the coastal eutrophicated and to restore the ecosystem. [Display omitted] • In summer, the density of Rhizosolenia setigera ranged from 2.4–6.3 × 105 cells/L, showed extremely high HAB risk. • In culturing area, the seaweed slightly increased salinity, pH and DO, but reduced TP. • Seaweed culturing reduced phytoplankton abundance, slightly increased Shannon-Wiener diversity. • Seaweed culture may be a way to alleviate the HABs problem that China has been experiencing in its coastal waters. • Temperature, Secchi depth and TN showed a positive correlation with the phytoplankton density. [ABSTRACT FROM AUTHOR]

The coastal plain of Cixi City, China, has experienced over 1000 years of reclamation. With the rapid development of agriculture and industry after reclamation, successive inputs into agricultural soils have drastically modified the soil environment. To determine the spatial distribution of heavy metals and to evaluate the influence of anthropogenic activities, a total of 329 top soil samples were taken along a transect on the coastal plain. The samples collected across 11 sea dikes, were selected by a nested sampling methodology. Total Cu, Fe, Mn, Ni, Pb, and Zn concentrations, as well as their diethylenetriamine penta-acetic acid (DTPA) extractable (available) concentrations were determined. Results indicated that except for Zn concentrations, there was neither heavy metals pollution nor mineral deficiency in the soils. Heavy metals exhibited considerable spatial variability, obvious spatial dependence, and close relationships on the reclaimed land. For most metals, the reclamation history was the main influencing factor. Metals concentrations generally showed discontinuities around the position of sea dikes, and the longer reclamation histories tended to have higher metals concentrations than the recently reclaimed sectors. As for Cu and Zn total concentrations, stochastic factors, like industrial waste discharge, fertilization and pesticide application, probably led to the high nugget effect and altered this relationship. The 6th and 10th zones generally had the highest total metals concentrations, due to the concentration of household appliance manufacturers in these reclaimed areas. The first two zones were characterized by high available metals concentrations, probably due to the alternant flooding and emergence, low pH values and high organic matter contents in these paddy field soils. From the 3rd to 7th zones with the same land use history and soil type, metals concentrations, especially available concentrations, showed homogeneity. The nested sampling method adopted demonstrated that the 500-m interval was enough to capture the spatial variation of the metals. These results were useful in evaluating the variation in the environment quality of the soils under long-term reclamation and to formulate plans for future reclamation projects. [ABSTRACT FROM AUTHOR]