A Study of Ephemeral Wetland Types According to Water Level Changes in Lava Forests

Abstract

Jeju Island is a basalt volcanic island located in Korea, and lava forests are distributed in the east and west of the island. Wetlands play a more significant role in lava forest than other forests, due to high volume of underground water as a result of high rainfall permeability rates averaging 67%. In particular, the lava forests of eastern Jeju Island is designated as a protected Ramsar wetland, featuring both a few permanent wetlands and several ephemeral wetlands. Notably, ephemeral wetlands show higher species diversity than permanent wetlands. A study was conducted to understand the types of ephemeral wetlands and investigate the characteristics. Water level sensors were installed in five wetlands for three years beginning in 2020. A three-type classification system was created: rugged topography with many large stones (Wetland ‘Type A’), concave topographies (Wetland ‘Type B’), and sedimentary topographies (Wetland ‘Type C’). The highest water levels were recorded in 2020 at all study sites. ‘Type A’ had the highest water levels (1.5m; 2.7m) before quickly draining (2.9mm/h; 5mm/h), and was the first to zero out. ‘Type B’ achieved the mid-range of recorded water levels (0.7m; 0.8m), and drain rate (1.3mm/h; 1.4mm/h). ‘Type C’ had the lowest highest water level (0.4 m), and the slowest drain rate (0.8 mm/h). In the same 2020 observation period, water levels were maintained at 0.1m for both Type A wetlands were maintained for 72 days and 40 days, ‘Type B’ for 111 days and 92 days, and ‘Type C’ for 221 days. The submersion period during which wetlands were submerged decreased by 7% in 0.1m water level and 19% in 0.25m water level in 2021 compared to 2020, and 37% in 0.1m water level and 42% in 0.25m water level in 2022 compared to 2020. Additionally, there was no observed difference in total annual precipitation in 2020 and 2021, but there was variation in maximum daily rainfall. In 2022, the total annual precipitation was 35% lower than in 2020. Therefore, ephemeral wetland environment change every year, as the amount of level of ephemeral wetlands seems to be affected not only by both total annual precipitation and but also by how concentrated rainfall is within shorter time periods. These factors have a significant impact on the distribution of rare and special plants and the diversity of herbaceous species distributed by the wetland types.