Lake Shihwa suffers from trace-metal pollution discharged from the Banweol stream and the Shihwa Industrial Complex. Installation of floodgates in 2001 increased water exchange and decreased trace-metal content, thereby improving the benthic environment within the lake. We analyzed surface sediments (including grain size, pH, trace-metal concentrations), water-quality data, and the assemblages of, and prevalence of deformities in, the benthic foraminifera, to understand the effects of recent changes in salinity variability. Since spatial and temporal distributions of benthic foraminifera are known to vary in response to both biotic and abiotic environmental variables, they are useful indicators of environmental change.

Since the installation of floodgates, surface-sediment composition coarsened from silt to sandy mud/muddy sand in response to increased water flow. Trace-metal contaminants (Ni, Cu and Zn) have decreased and are close to the Effect Range-Low (ER-L) designation. We identified 15 species of benthic foraminifera (3 agglutinated, 10 calcareous-hyaline, and 2 calcareous-porcelaneous). Buccella frigida and Elphidium albiumbilicatum were dominant, but seven sampling localities formed a nearly abiotic zone. Although trace contaminants have decreased, a high prevalence of test deformities (up to 65%) was observed, mostly in E. albiumbilicatum. Our findings suggest these abnormalities may be strongly related to the effects of seasonal variation of salinity in Lake Shihwa.

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