Excess sediment and nutrient export from agricultural fields with steep slopes is a major concern linked to surface water quality in Korea. In this study, the export of suspended sediment (SS), total nitrogen (TN), and total phosphorus (TP) and their event mean concentrations (EMCs) in surface runoff from a highland mixed land use (61% forested, 30% cropped, 9% other) watershed were quantified. In 2007, the Korean Ministry of Environment (MoE) declared the study area as a priority region for non-point source (NPS) pollution management and initiated various best management practices (BMPs) in the study watershed. SS, TN, and TP concentrations in Mandae Stream were monitored for 5 years (2009-2013) to evaluate the effectiveness of BMPs. Average EMCs for SS, TN, and TP were as high as 986, 3.4 and 0.8 mg/L, respectively. The agricultural export coefficients of agricultural land in the study watershed for SS, TN, and TP were 5611, 171, and 6.83 kg/ha/year, respectively. A comparison with results from other studies shows that both EMCs and agricultural export coefficients in the study watershed were much higher than most of the results reported for watersheds in other regions. The results show that sediment and nutrient export from intensive agriculture areas with steep slopes continue to be a major concern for the downstream reservoir, Lake Soyang. Remedial strategies should be directed towards controlling sources of SS, TN, and TP to improve downstream water quality in sloping highland agricultural areas in Korea.

We investigated the carbon and nitrogen stable isotope composition of particulate organic matter (POM) and zooplankton to understand the effects of highly variable hydrologic inputs with the onset of the summer monsoon season in Lake Soyang, Korea. The main characteristic separating pre-monsoon and post-monsoon seasons in Lake Soyang is the dramatic difference in hydrologic inflow. Pre-monsoon 13 C-POM (range À32.4 to À21.8%) was lower than post-monsoon 13 C-POM (range À25.5 to À19.9%). Epilimnetic 13 C-POM was higher postmonsoon compared to pre-monsoon, except in 2007. In the metalimnion, pre-monsoon 13 C-POM varied among years, while the variation in 13 C-POM post-monsoon was small and was related to the inflow of organic matter during summer monsoon storms.13 C-zooplankton was lower post-monsoon (range À31.9 to À24.4%) compared to pre-monsoon (range À19.4 to À17.7 %), while 15 N-zooplankton showed the opposite pattern (pre-and post-monsoon average 6.6 AE 2.0% and 4.3 AE 1.5%, respectively). In Lake Soyang, the seasonal variation in 13 C-zooplankton was closely related to annual succession in the phytoplankton community and 13 C-phytoplankton. Thus, the results of this study provide some insights into the use of 13 C and 15 N measurements for understanding linkages between varying hydrologic characteristics and seasonal variation in the stable isotope composition of zooplankton. The dramatic seasonal change in hydrologic inputs in the monsoonal climate and consequent changes in turbid surface water inflow is linked with changes in the phytoplankton and zooplankton communities in Lake Soyang.

Despite increased attention to the need for sustainable agriculture, fertilizer application rates above crop requirements remain common agricultural practices in South Korea, causing eutrophication of freshwater and coastal ecosystems. The aim of this study is to quantify phosphorus (P) inputs, outputs, and retention in a forested-agricultural watershed. The P budget showed that the combined use of chemical fertilizer and organic compost was the largest source of P (97.6% of the total) followed by atmospheric wet deposition (2.1% of the total P), whereas forest export (0.2% of the total) and sewage treatment plants (STPs) (0.1% of the total) were negligible. The P outputs were crop harvesting and hydrologic export to surface water. The P balance showed that P inputs are higher than the P outputs; approximately 87% of the total P input was retained in the soils within the watershed. However, P concentrations in drainage water were still high enough to cause eutrophication of downstream reservoirs. The results provide important details on the proportion of P export and retention in the watershed. This will help efforts to improve water quality and design better management strategies for agricultural nonpoint source pollution.

The decomposition rates of organic nitrogen and organic phosphorus in lakes and rivers can be important parameters in water quality model calibrations. Commonly, decomposition rate coefficients are calibrated by observing the changes in each component in the field survey. However, in natural field conditions, production and decomposition occur at the same time, and the calibrations may result in uncertainties. In this study, water samples collected from six major rivers in Korea were incubated for 20 days in a dark incubator and the decomposition rates of POP, DOP, LDOP, PON, DON, LPON, LDON, ammonia, and nitrite were determined. By excluding the interference of photosynthesis, animal grazing, and excretion, the decomposition rate coefficients were determined with less uncertainty than in natural conditions. The decomposition data were fit to first-order models of several decomposition pathways, including POP ! DIP,The decomposition rates of dissolved forms were five-seven times higher than particulate forms. And the rates of organic P (0.149 day �1 for LPOP and 0.718 day �1 for LDOP) were 1.6 times higher than those of organic N (0.093 day �1 for LPON and 0.472 day �1 for LDON). Traditionally, the decomposition rates of organic phosphorus and organic nitrogen are not discriminated; the same rate is applied to organic carbon, nitrogen, and phosphorus. The result of this study shows that organic phosphorus and nitrogen should be given different decomposition rates for more accurate models. The rate coefficients measured in this study will provide a guide to the selection of model parameters for water quality modeling.

(1) Background: During the coronavirus disease 2019 (COVID-19) pandemic, the prevalence of obesity or severe obesity has increased worldwide to the point that it has even been referred to as a new disease. However, the impacts of the pandemic on obesity or severe obesity remain unclear, thus requiring a thorough examination of the leading factors of obesity and severe obesity during this time. (2) Methods: The required dataset for this study was extracted from the eighth (2019–2020) Korea National Health and Nutrition Examination Survey (KNHNES). The survey’s data for 2019 and 2020 were analyzed to confirm the leading factors of obesity and severe obesity before and after the outbreak of COVID-19. The samples were weighted, and the data were analyzed using multiple logistic regression. (3) Results: In 2020, the prevalence of obesity and severe obesity in the Korean adult population aged 19 and over, compared with the normal weight group, showed significant increases of 2.5% and 1.4%, respectively, compared with those rates in 2019 (p < 0.05). The main variables affecting the obesity prevalence in Korean adults aged 19 and over in 2020 were gender, age, sitting time per day, and walking time per day, and the factors affecting severe obesity were gender and age. Meanwhile, the daily energy intake variable had no impact on the prevalence of obesity and severe obesity. (4) Conclusions: These findings will serve as a basis to help the present management directions and treatment approaches for individuals with obesity or severe obesity in the post-COVID-19 era.