Sungmin Jung

Variation in carbon and nitrogen stable isotopes in POM and zooplankton in a deep reservoir and relationship to hydrological characteristics

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 δ13C-POM (range −32.4 to −21.8‰) was lower than post-monsoon δ13C-POM (range −25.5 to −19.9‰). Epilimnetic δ13C-POM was higher post-monsoon compared to pre-monsoon, except in 2007. In the metalimnion, pre-monsoon δ13C-POM varied among years, while the variation in δ13C-POM post-monsoon was small and was related to the inflow of organic matter during summer monsoon storms. δ13C-zooplankton was lower post-monsoon (range −31.9 to −24.4‰) compared to pre-monsoon (range −19.4 to −17.7 ‰), while δ15N-zooplankton showed the opposite pattern (pre- and post-monsoon average 6.6 ± 2.0‰ and 4.3 ± 1.5‰, respectively). In Lake Soyang, the seasonal variation in δ13C-zooplankton was closely related to annual succession in the phytoplankton community and δ13C-phytoplankton. Thus, the results of this study provide some insights into the use of δ13C and δ15N 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.

Development of a water quality index model for lakes and reservoirs

Lake water quality and trophic state are evaluated using various parameters which may have different interpretations. Therefore, it is useful to adopt a proxy index that shows normalized values of parameters having different units and distribution characteristics. In this study, a model for integrated water quality index was developed for lakes and reservoirs in Korea. Water quality and phytoplankton were examined in 36 lakes, two natural lakes and 34 artificial lakes. The study lakes were selected to represent the range geographic regions and lake morphology in Korea. After investigating the interrelationships among water quality parameters, four parameters (total organic carbon, chlorophyll-a, total phosphorus, and turbidity) were selected as surrogate indicators of overall water quality. A relative evaluation system was developed by adopting a logistic function index that describes a cumulative distribution function and reflects the relative position of each parameter among the study lakes. The cumulative distribution probability ranging from 0 to 1 was multiplied by 100 and then transformed into the Korean Lake Water Quality Index (LQI) ranging from 0 to 100. A score of 50 was assigned to the median value of the dataset, 0 to the highest concentration value and 100 to the lowest concentration value. Thus, the LQI is an integrated easy-to-understand index that provides information about the relative status of each lake. The results of this study can represent a model to provide a relative evaluation system for lake and reservoir water quality, which can be useful for ecosystem management within an ecoregion or a jurisdictional district.

Dissolved and particulate organic carbon concentrations in stream water and relationships with land use in multiple-use watersheds of the Han River (Korea)

This study examines temporal variation in dissolved organic carbon (DOC) and particulate organic carbon (POC) concentrations in streams in the Han River watershed, Korea. On days without significant antecedent rain, DOC and POC concentrations ranged from 0.87 to 3.23 mg C/L and 0.24 to 2.92 mg C/L, respectively. Following rain events, both DOC and POC concentrations were higher. Soil and compost had δ13C values similar to stream δ13C-DOC and δ13C-POC. These results demonstrate the importance of studies using tracer approaches and the value of research on sources of organic carbon transported in streams in multiple use monsoonal watersheds.

The decomposition rates of organic phosphorus and organic nitrogen in river waters

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, POP → DOP → DIP, LPOP → LDOP → DIP, , and . 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.

Potential effects of sediment processes on water quality of an artificial reservoir in the Asian monsoon region

Abstract Sediment processes in lakes may affect water chemistry through the internal loading of phosphorus, ammonia, and sulfides released under anoxic conditions. Lake Soyang is a deep warm monomictic reservoir with a dendritic shape, located in the Asian summer monsoon region, South Korea. During summer, the lake is stratified and receives a large nutrient input via storm runoff, which forms a turbid intermediate layer with high concentrations of suspended particles. The lake water, the main inflowing stream (the Soyang River), bottom sediment, and porewater of the lake sediments were studied over a 2-year period (2012–2013). After intensive monsoon rain events, particulate organic carbon (POC), total phosphorus (TP), and turbidity were high in the inflowing water (C: 1.21 mg L−1 in June 2013) and in the metalimnion (2.8 mg L−1, 17.6 μg L−1, and 58.5 NTU, respectively in July 2013). Higher concentrations of iron (Fe) and manganese (Mn) were also associated with the turbid intermediate layer (37 and 8 μg L−1, respectively, in July 2013). During the summer stratification period, oxygen started to deplete in the hypoliminion (down to 0.5 mg L−1 in September 2013), and sediment became anoxic, showing negative oxidation redox potential (ORP) in core samples. Diffusion of dissolved inorganic P and ammonia from sediment to the water column can be substantial, considering the concentration difference between the porewater and hypolimnetic water. Fe and Mn were abundant in the sediment porewater at the dam site, implying inorganic nutrients and minerals are well transported along the 60 km long lake axis by the density current of storm runoff. Sulfate and reduced sulfur were larger in the porewater of the top sediment than in the lower layer of the sediment core (below 10 cm). The results show that substantial amounts of inorganic nutrients and minerals are supplied to the lake by storm runoffs during monsoon and distributed through the lake by a density current, controlling the material cycle and flux at the sedimen tsurface.

Methane Gas Emission from an Artificial Reservoir under Asian Monsoon Climate Conditions, with a Focus on the Ebullition Pathway.

The role played by reservoirs in the biogeochemical cycles of elements is a subject of ongoing debate. Recent research has revealed that reservoirs emit significant levels of greenhouse gases. To assess the importance of reservoirs in monsoon climate areas as a source of methane gas into the atmosphere, we investigated variations in organic carbon (OC) input into the reservoir, oxic state changes, and finally the amount of methane emitted (focusing on the ebullition pathway) in Lake Soyang, which is the largest reservoir in South Korea. Total organic carbon (TOC) concentrations were higher during summer after two years of heavy rainfall. The sedimentation rates of particulate organic carbon (POC) and particulate organic nitrogen (PON) were higher in the epilimnion and hypolimnion than the metalimnioin, indicating that autochthonous and allochthonous carbon made separate contributions to the TOC. During stratification, oxygen depletion occurred in the hypolimnion due to the decomposition of organic matter. Under these conditions, H2S and CH4 can be released from sediment. The methane emissions from the reservoir were much higher than from other natural lakes. However, the temporal and spatial variations of methane ebullition were huge, and were clearly dependent on many factors. Therefore, more research via a well-organized field campaign is needed to investigate methane emissions.

The effects of Asian summer monsoons on algal blooms in reservoirs

Abstract An important characteristic of lakes and reservoirs in the East Asian summer monsoon region is the dramatic seasonal difference in hydrologic inputs, with annual rainfall commonly concentrated in a few heavy rain events. In this study, we surveyed the monthly variations of phytoplankton density in 3 large deep reservoirs and 7 small shallow reservoirs and analyzed the effect of large precipitation events on phytoplankton. During heavy rains, stream phosphorus concentrations increased sharply, and phosphorus loadings into reservoirs were not continuous but episodic shock loadings. In deep stratified reservoirs, however, the concentrations of phosphorus and chlorophyll a were much lower than expected from the high total phosphorus levels in the storm runoff. Inflowing storm waters laden with phosphorus flowed into metalimnetic layers because deep reservoirs had strong thermal stratification and the storm water was cooler than the epilimnion. The result was the formation of an ecosystem resilient to phosphorus shock loadings during monsoon. Nutrients in the metalimnion seemed to be dispersed gradually toward the epilimnion, and phytoplankton reached maximum densities, called “monsoon blooms,” after the monsoon. By contrast, shallow reservoirs with short hydraulic residence times had lower chlorophyll a concentrations during the monsoon season because the high flushing rate was the major limiting factor of phytoplankton growth. In conclusion, summer monsoon is the major determinant of phytoplankton density in reservoirs of the East Asian region, but their responses can vary widely depending on hydrologic characteristics.

Recovery of Fish Community and Water Quality in Streams Where Fish Kills have Occurred

본 논문은 최근 몇 년 동안 어류폐사가 발생했던 하천인 월운천, 서천, 장남천 그리고 안양천을 대상으로 어종의 변동을 조사하였다. 어류폐사의 영향을 받은 지역에서 종수의 회복률은 22~86%까지 이르렀는데, 인공구조물과 수질에 의한 영향을 받았다. 장남천에서는 알칼리성 pH로 인해 어류폐사가 발생하였으나 다른 두 하천(월운천, 서천)에 비해 수질의 회복 이후 빠른 종수의 회복을 보였다. 또한, 안양천에서의 낮은 종수는 간헐적으로 발생하는 용존산소고갈로 인한 수질악화의 영향이 크다. 이와 더불어 하천에 설치되어 있는 인공구조물은 특히 저서성 어종의 회복에 부정적인 영향을 주는 것으로 나타났다. 수질 또는 어류개체군의 이동이 회복될 때 어종의 빠른 회복이 예상되지만, 여전히 많은 하천에서 수질의 악화현상과 일부 노후화한 인공구조물의 존재는 어류의 서식환경을 악화시킬 수 있고 어류폐사 이후 하천에서 어종의 회복을 지연시키는 원인이 될 수 있다. 하천에서 어류군집의 보존을 위해서는 어류의 이동을 위한 통로와 유역으로부터의 오염원의 유입을 관리하여야 한다.