Assessing environmental changes in Lake Shihwa, South Korea, based on distributions and d13C of n-alkanes

Abstract

The artificial Lake Shihwa located in South Korea has been typically under the strong anthropogenic pressure with the continuous organic matter inputs from industrial, urban, rural and reed wetland areas. The Shihwa tidal power plant was built in 2011 in order to improve the water quality in Lake Shihwa. In this study, we investigated historical environmental changes in Lake Shihwa and diverse organic matter sources in lake core (n=108) and surface (n=9) sediments and riverbank (n=12) sediments based on bulk (TOC, TN, C/N ratio, δ13CTOC, and δ15NTN) and molecular (relative abundances and δ13C of n-alkanes) parameters. Although the bulk organic parameters showed similar characteristics for all lake surface sediments investigated, the distribution pattern and δ13C of n-alkanes revealed distinctive differences between the 2009 samples and the 2012 and 2016 samples. This change of sedimentary organic matter characteristics can be affected by the operation of the tidal power plant started in 2011. The vertical profiles of bulk and molecular records in lake sediment cores collected in 2009, especially at the site closest to the dike, showed a drastic shift around 1987, indicating that a stronger anoxic sedimentary condition prevailed after 1987. This can be associated with the sea dike construction in 1987, prohibiting a sea-lake water exchange and thus deteriorating the water quality. Accordingly, it appears that lake Shihwa has been experiencing severe environmental changes due to human activities, such as constructing a sea dike and operating a tidal power plant.