Soil Water dynamic and water balance in a coral island: Zhaoshu Island,
Xisha archipelago
Abstract
Study of the soil water dynamic and water balance in coral islands is
important to utilize and manage the limited freshwater resources of
islands. In this study, we studied the soil water dynamic in Zhaoshu
Island, Xisha archipelago using the observed data and the Richards
equation, and analyzed the water balance of this island in the dry and
wet seasons, respectively. The soil water movement showed that there was
a dry soil layer at the depths between 40cm and 160cm of the soil
profile in the dry season. The evaporation (Es) flux was low, but the
transpiration (Er) could still absorb water from the capillary zone to
maintain growth. In the wet season, the infiltration dominated the main
process of soil water movement. The result of water balance showed the
precipitation, the change values of water in the entire flow domain
(△Volume), bottom boundary flux (vBot), Er, Es were 913mm, 10mm, 349mm,
203mm, 351mm, respectively from October 2018 to September 2019.
Precipitation is the only source of the freshwater, about 38% of the
precipitation infiltrated into the groundwater, 22% of the
precipitation was uptaken by the vegetation, and 39% of the
precipitation was evaporated from the land surface. In the dry season,
the evapotranspiration (ETa) was just 44mm/month which was 94% larger
than the precipitation, and about 14mm/month of water was uptaken from
groundwater by the plants. But in the wet season, 56% of the
precipitation infiltrated into the groundwater, 37% of the
precipitation was consumed by ETa. This study can help us well
understand the process of water movement in coral islands, and provide
references for further management in protecting coral island ecologies.