Effects of different sluice control manipulation on the benthic community structure in the artificial Lake Sihwa, Korea

초록

Coastal environments in Korea have been under increasing pressure during the last five decades as a result of increasing human populations. In January 1994, the Sihwa area of a shallow brackish ecosystem was impounded by the 17.2 km long dyke after seven years of construction that created an artificial Lake Sihwa in the central part of Kyeonggi Bay on the western coast of Korea, by the entrapment of Yellow Sea water. This saline lake water was strongly stratified with freshwater at the surface and entrapped saline water on the bottom. Therefore, the pycnocline, lying usually at a depth of about 6 m, prevents mixing between the two water bodies, and thus generates periodically hypoxic and anoxic conditions in the deeper waters every summer. As a result, the Sihwa Lake suffers from these hypoxia / anoxia events that contribute to the disastrous periodical mass mortality of benthic communities. To ameliorate these circumstances the water inside the lake had been partially exchanged with the natural seawater sporadically by sluice control until 1997 and thereafter the Sihwa Lake was managed under the periodic sluice control as a brackish lake since 2000. Then, the sluice control system was changed in July 2005 from the manipulation of two times per day discharge and inflow system into the control of consecutive three-day discharge and two-day inflow system. The system change of the sluice control revealed that the overall environmental conditions in the Sihwa Lake were enhanced with the increased seawater inflow towards more coastal marine environment by the higher salinity from 27.9 to 30.4 psu, higher dissolved oxygen concentrations from 6.4 to 7.3 mg/l, higher sorting coefficient of the grain size in the surface sediment and diminution of the mud fraction in some part of the lake. Hence, the quality of the benthic environment was improved as well. Therefore, in terms of the benthic community parameters, they showed the higher biodiversity from 83 to 153 species, av