Identifying pollution sources of sediment in Lake Jangseong, Republic of Korea, through an extensive survey: Internal disturbances of past aquaculture sedimentation.

Lake sediments are important sinks of various pollutants and preserve historical pollution records caused by anthropogenic activities. Recently, the sediments of Lake Jangseong, South Korea were first detected with high concentrations of organic matter (ignition loss [IL]; total organic carbon [TOC]), nutrients (total nitrogen [TN]; total phosphorus [TP]), and some heavy metals (Zn, Cu, Cd, and Hg). Here, we identified the origins of these concentrations accumulated in the sediments using extensive surveys and various assessments. Sediment pollution assessed by sediment quality guidelines, pollution load index, and potential ecological risk index was found to be of serious concern for IL, TN, TP, and Cd. Thus, we assessed pollution sources through spatial, grid, and vertical distributions and found that the high pollutant concentrations detected in 2020 were confirmed only at a certain location in the lake. Additionally, similar results were detected in the sedimentary layer below a sediment core at a depth of 15.0 cm. The high pollutant concentrations locally occurred around a "hotspot" site that was previously frequently used for aquaculture activities, indicating that the pollutants were accumulated in sediments owing to past cage fish farming rather than from influx of externally sourced pollution. Furthermore, chemical fractionation of phosphorus and heavy metals and assessment of stable isotopes (13C and 15N) of organic matter suggested that the pollutants in the sediments at the "hotspot" sites had different origins than those found at other sites. Accordingly, the by-products discharged after cage fish farming, such as residual feed, fish meal, and waste, accumulated in the sediments and were then exposed to natural internal disturbances caused by the effects of climate change-induced drought. This local distribution and the phosphorus and heavy metal chemical fraction results with low elution potential indicated that the pollutants in the sediments of Lake Jangseong had negligible impact on water quality.

Organic matter and heavy metal in river sediments of southwestern coastal Korea: Spatial distributions, pollution, and ecological risk assessment.

This study identifies the impact of river sediments on coastal ecosystems in the southwestern coastal region of Korea. Surface sediments were analyzed for their spatial distributions of organic matter, nutrients, and heavy metal concentrations. Furthermore, pollutants were identified according to the pollution load index (PLI) and potential ecological risk index (RI). Concentrations did not show serious pollution levels compared to generalized guidelines; however, some sites exceeded the PLI pollution standard, and were also identified as potential ecological risks. Through cluster analyses the sediment sites were classified into three groups: rivers with relatively high concentrations of organic matter and nutrients, rivers affected largely by artificial heavy metal pollution, and rivers with low levels of pollution by organic matter, nutrients, and heavy metals. It is evident that continuous monitoring and management are required to prevent major pollution from industrial complexes, agriculture, and commercial activities in the regions near these rivers.