Dissolved organic matter (DOM) is a key component in the biogeochemical cycling in freshwater ecosystem. However, it has been rarely explored, particularly complex river watershed dominated by natural and anthropogenic sources, such as various effluent facility and livestock. The current research developed a new analytical method for TOC/TN (Total Organic Carbon/Total Nitrogen) stable isotope ratio, and distinguish DOM source using stable isotope value (δ13C-DOC) and spectroscopic indices (fluorescence index [FI] and biological index [BIX]). The TOC/TN-IR/MS analytical system was optimized and precision and accuracy were secured using two international standards (IAEA-600 Caffein, IAEA-CH-6 Sucrose). As a result of controlling the instrumental conditions to enable TOC stable isotope analysis even in low-concentration environmental samples (<1 mgC L-1), the minimum detection limit was improved. The 12 potential DOM source were collected from watershed, which includes top-soils, groundwater, plant group (fallen leaves, riparian plants, suspended algae) and effluent group (pig and cow livestock, agricultural land, urban, industry facility, swine facility and wastewater treatment facilities). As a result of comparing characteristics between 12 sources using spectroscopic indices and δ13C-DOC values, it were divided into four groups according to their characteristics as a respective DOM sources. The current study established the TOC/TN stable isotope analyses system for the first time in Korea, and found that spectroscopic indices and δ13C-DOC are very useful tool to trace the origin of organic matter in the aquatic environments through library database.

Recently, quantitative analyses of food web structure based on carbon and nitrogen stable isotopes are widely applied to environmental assessments as well as ecological researches of various ecosystems, particularly rivers and streams. In the present study, we analyzed carbon and nitrogen stable isotope ratios of POM (both planktonic and attached forms), zooplankton, benthic macroinvertebrates and fish collected from 6 sites located at Nakdong River. Samples were collected from upstream areas of 5 weirs (Sangju, Gangjeong- Goryeong, Dalseong, Hapcheon-Changnyeong, and Changnyeong-Haman Weirs) and one downstream area of Hapcheon-Changnyeong Weir in dry season (June) and after rainy season (September). We suggested ranges of their carbon and nitrogen stable isotope ratios and calculated their trophic levels in the food web to compare their temporal and spatial variations. Trophic levels of organisms were relatively higher in Sangju Weir located at upper part of Nakdong River, and decreased thereafter. However, the trophic levels were recovered at the Changnyeong-Haman Weir, the lowest weir in the river. The trophic level calculated by nitrogen stable isotope ratios showed more reliable ranges when they were calculated based on zooplankton than POM used as baseline. The suggested quantitative ecological information of the majority of biological communities in Nakdong River would be helpful to understand the response of river food web to environmental disturbances and can be applied to various further researches regarding the quantitative approaches for the understanding food web structure and function of river ecosystems as well as restoration.

To elucidate occurrence patterns of C4 plants in agroecosystems, we surveyed flora inside fields and embankments in 222 sites in farming lands in summer and fall, 2013. We also observed Kranz anatomy and analyzed carbon stable isotope to classify photosynthesis types. Our study observed total 54 species of C4 plants in 33 genera and 9 families of vascular plants besides cultivated crops occurring in farming fields. The most common species was Portulaca oleracea L. followed by Digitaria ciliaris and Echinochloa crusgalli (L.) P. Beauv. var. crusgalli among the C4 plants. The ratios of C3 and C4 species number to total number of species tended to maintain constant regardless of survey times and habitat types. The proportion of C4 species to the total number of species were more influenced by the number of C3 species than those of other types in the surveyed sites. Sizes of cultivation areas did not affect the proportions of C4 plants. Increasing number of simultaneous weeding methods, especially with cutting method, appeared to decrease the number of C3 plants. On the other hand, as the number of cultivated crops increased, both C3 and C4 plants increased but the proportions of C4 species remained. We interpret our results that proportion of C4 species in agroecosystems, appear to be dependent on the number of C3 species, which in turn, appear to be affected by cultivation methods.

태백산 분지에 분포하는 탄산염 및 규질쇄설성 혼합 퇴적물로 구성된 세송층(late Middle Cambrian to Furongian)은 δ 13 C값이 1.14에서 2.81‰을 갖는 SPICE (Steptoean positive carbon excursion)를 15 m 두께의 층서구간 에서 보여준다. SPICE는 Fenghuangella laevis대, Prochuangia mansuyi대 그리고 Chuangia대로 구성된 삼엽충 생물대 에서 산출되며 이는 Paibian Stage의 하부에 해당된다. 세송층은 엽층리 이암, 단괴상 셰일, 엽층리 사암, 균질사암, 석 회역암, 석회암-셰일 쌍을 포함한 6개의 암상으로 구성된다. 세송층은 폭풍파도기저면 아래의 외대륙붕에서 퇴적된 것 으로 알려져 있다. 시기적으로 Paibian Stage에 속하는 SPICE는 세송층에서 고수위 퇴적계 다발, 대비 정합면과 해침 퇴적계 다발에서 발견된다. SPICE의 최대 안정 탄소 동위원소 값은 상대적인 해수면 하강에 의해 형성된 대비 정합면 과 일치한다. 세송층에서 SPICE의 산출은 SPICE가 화석의 산출이 결여된 지층의 전세계적 대비를 위해 사용될 수 있 는 도구임을 암시한다.

본 연구는 탄소 및 질소 안정동위원소비를 이용하여 하천에서 환경변화의 지표로 활용할 수 있는 부착조류의 먹이원으로서 기여도를 파악하고자 하였다. 연구지역인 탐진강은 지류를 통해 유입되는 외래기원물질의 영향으 로 상류에서 하류로 갈수록 높은 영양염의 농도를 나타 냈으며 이와 더불어 상위섭식자인 어류의 질소 안정동위 원소비의 증가가 관찰되었다. 또한 탐진강에서 채집된 저 서성대형무척추동물과 어류의 δ13C 값이 상류에서 하류 로 이동하면서 무거워지는 경향을 나타내었다. 이는 탐진 강 하류 수역에서 무거운 δ13C 값을 보였던 암석 부착조 류가 먹이원으로서의 기여도가 높아진 결과로 판단된다.

The Steptoean Positive Carbon Isotope Excursion (SPICE) is found in the Machari Formation which was interpreted to have been deposited on the middle to outer carbonate ramp environment. The Machari Formation is the Middle to Late Cambrian in age and distributed in the Yeongweol area, Gangweon Province, Korea. The SPICE event in the Machari Formation begins with the first appearance datum of trilobite Glyptagnostus reticulatus and ends with the first appearance of datum of trilobite Irvingella. The SPICE is found in approximately 120 m thick sequence and δ13C values in the SPICE interval range from 0.6 to 4.4‰. The SPICE in the Machari Formation is interpreted to be caused by burial of organic matter in the sea floor and subsequent increase of 13C isotope of the Late Cambrian ocean. The SPICE interval in the Machari Formation corresponds to the highstand to transgressive systems tracts.