In non-irrigation or lack irrigation seasons, the shallow water table provides moisture for the soil and crops. This part is about 10% of total discharge in irrigation area. Other 45% of discharge is surface drainage, which decreases at the 2000s because of sediment in drainage system (Fig.7). The very important part is irrigation area groundwater discharge to discharge area, which shows groundwater flows from irrigation area to non-irrigation area (subsurface drainage). This part is about 45% of irrigation system discharge and is about 70% of non-irrigation area recharge, which dominates the ecosystem out of irrigation area.
Discharge from farmland increased because waste land was reclaimed. Discharge to wilding land increased from about 150 millions cubic meters in the 1980s to 300 millions cubic meters in the 2000s. This should be contributed from the groundwater from farmland and canal loss because most wilding land surrounds irrigation area in the study area. On the contrary, discharge to sandy wasteland decreases from about 300 millions cubic meters in the 1980s to about 160 millions cubic meters in the 2000s. This was because sandy wasteland area decreased much in this period. The irrigation area subsurface drainage decreased during this period and lessened the wetland recharge (Fig.6, Fig.7). This makes the wetland area continuously shrinking. Since the Aiximan wetland acts as water and salt discharge area in the local hydrological system and is ecological valuable area, actions are needed to stop the shrinking.
Salt movement in surface drainage is calculated from 10 drainage gauging stations and salt in subsurface drainage is calculated from over 20 groundwater observation wells. Salt movement in surface drainage and subsurface drainage is shown in Fig.8. The salt in surface drainage that moves out of irrigation area is up to 800 thousand tons per month in summer and the salt in subsurface drainage can reach 500 thousand tons per month. The groundwater from irrigation area to non-irrigation area acts as subsurface drainage for irrigation area, which not only drain surplus water but also desalinate irrigation area. Further study is needed to investigate where the salt accumulates in non-irrigation area and how the water quality in the wetland will be changed by subsurface drainage from irrigation area.