A climate adaptation strategy for Mai Po Inner Deep Bay Ramsar site: Steppingstone to climate proofing the East Asian-Australasian Flyway

1.5 m SLR will also result in a loss of 15 to 18% of inland and open water marshes in the north- ern reaches of the wetland conservation area (Table 2, Fig 2). These marshes represent the fish- ponds, and the area bordering the lower reaches of the Shenzhen River and upper estuary, where the river bank is artificially constructed for river training, and there are no coastal man- groves or tidal mudflats. The regularly flooded marshes represent the ponds that support reed- beds in the Nature Reserve, and under a 2 mm/yr accretion rate, over 50% of these marshes will be lost, indicating that some of the ponds that are not connected to the estuary via tidal creeks will also become inundated during low tide under a 1.5 m SLR (Table 2). This likely reflects erosion and subsidence of the tidal flats, allowing sea water intrusion into the nature reserve. Under a more extreme 2 m SLR scenario, the tidal flats and coastal mangroves will still remain relatively unaffected during low tide at accretion rates of 15 mm/yr, but there will be a loss of about 77 and 57%, respectively, of tidal flats and mangroves with an 8 mm/yr accretion rate (Table 2). The regularly flooded marshes in the nature reserve will also lose 56% of area with an 8 mm/yr accretion rate, and the inland open water marshes will lose about 18% of area even with a 15 mm/yr accretion rate. Under the high tide scenarios, with 1.5 m SLR and 15 mm accretion levels about 76% of the tidal flats will become inundated, while the mangroves will remain unaffected (Table 2, Fig 3).

There will be a loss of between 19 to 22% of inland open water marshes during high tide, a marginal increase from the low tide scenario (Table 2). However, over half of the regularly Table 2. Changes to habitats under the 1.5 and 2 m sea level rise scenarios and different accretion rates by 2100 as projected by the SLAMM. 1.5 m Sea Level Rise 2 m Sea Level Rise Low Tide High Tide Low Tide High Tide %Change in Habitat %Change in Habitat 2100 2100 2100 2100 2 mm Accretion Regularly-Flooded Marsh -56 -57 -57 -80 Mangrove -54 -63 -58 -61 Tidal Flat -77 -91 -77 -92 Inland Open Water/ Inland Fresh Marsh -18 -22 -19 -59 4mm Accretion Regularly-Flooded Marsh -1 -57 -57 -79 Mangrove 3 -62 -57 -61 Tidal Flat -77 -77 -77 -92 Inland Open Water/ Inland Fresh Marsh -16 -22 -19 -58 8 mm Accretion Regularly-Flooded Marsh 0 -57 -56 -57 Mangrove 3 -62 -57 -53 Tidal Flat 0 -77 -77 -91 Inland Open Water/ Inland Fresh Marsh -15 -22 -18 -46 15 mm Accretion Regularly-Flooded Marsh 0 0 0 -57 Mangrove 3 0 0 -49 Tidal Flat 0 -76 0 -77 Inland Open Water/ Inland Fresh Marsh -15 -19 -16 -45 Percent losses are given for low and high tide scenarios. https://doi.org/10.1371/journal.pone.0239945.t002 PLOS ONE Climate adaptation strategy for Mai Po Inner Deep Bay Ramsar site PLOS ONE | https://doi.org/10.1371/journal.pone.0239945 October 21, 2020 7 / 16