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.

The nitrogen isotope value in both ammonium and nitrate ion were determined at 9 stations during both June and August 2016, in order to understand the origin of DIN at the Han river. δ15N-NO3 and δ15N-NH4 values in 8 stations (CP, SB, MHC, P4, SJ, SBC, P2, SC) were no significant variation. However δ15N-NO3 and δ15N-NH4 values in KK (Kyeongan stream) showed significant different in comparison with 8 stations, with an apparent increase of nitrogen isotope values. These results indicate that antropogenic nitrogen source influence on KK station. Also the δ13C and δ15N isotope ratio of phytoplankton (Diatom and Cyanobacteria) in KK (Kyeongan stream) showed heavier values, compared to other study stations. These results indicate that nitrogen isotope value in phytoplankton effects by different nitrogen source in study sites. These results suggest that the analysis of stable isotope ratios is a simple but useful tool for the identification of dissolved inorganic nitrogen origin in aquatic environments.

Nitrogen (N) loading from domestic, agricultural and industrial sources can lead to excessive growth of macrophytes or phytoplankton in aquatic environment. Many studies have used nitrogen stable isotope ratios to identify anthropogenic nitrogen in aquatic systems as a useful method for studying nitrogen cycle. In this study to evaluate the precision and accuracy of Kjeldahl processes, two reference materials (IAEA-NO-3, N-1) were analyzed repeatedly. Measured the δ¹⁵N-NO₃and δ¹⁵N-NH₄values of IAEA-NO-3 and IAEA-N-1 were 4.7±0.2‰ and 0.4±0.3‰, respectively, which are within recommended values of analytical uncertainties. Also, we investigated spatial patterns of δ¹⁵N-NO₃and δ¹⁵N-NH₄in effluent plumes from a waste water treatment plant in Han River, Korea. δ¹⁵N-NO₃and δ¹⁵N-NH₄values are enriched at downstream areas of water treatment plant suggesting that dissolved nitrogen in effluent plumes should be one of the main N sources in those areas. The current study clarifies the reliability of Kjeldahl analytical method and the usefulness of stable isotopic techniques to trace the contamination source of dissolved nitrogen such as nitrate and ammonia.

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.

To investigate the possibility of discrimination between organic and non-organic rice using stable isotope nitrogen of natural abundance, organic rice of 17 samples and non-organic rice of 13 samples grown at adjoining organic rice field were collected in 2008. Rice was grinded into brown rice, milled rice and hull, and samples were analysed for nitrogen and δ¹⁵N at NICEM. Authors also made inquiries about N source for both farmers who conduct organic- and non-organic rice cultivation. In order to know whether the δ¹⁵N can be used in discrimination between organic and non-organic rice, discriminant analysis were made with SPSS and logistic method. 1. Organic farmers used manure, rice bran, used mushroom culture, fermented fertilizer (company products), and oil cake, but non-organic farmers applied compound fertilizer. Rice straws were remained in organic rice field while moved out in non-organic field. 2. There were difference in δ¹⁵N among organic rice and its byproduct(7.760‰ in hull, 6.720‰ in rice), but significant difference was not found between them. And the trend was same between province. Non-organic rice showed similar results. 3. Significant difference of δ¹⁵N were found between organic rice and non-organic rice (p＜0.01) and between hull of organic rice and that of non-organic rice hull (p＜0.05). δ¹⁵N seemed to be useful criteria for discrimination of organic and non-organic rice. 4. When applied discrimination analysis of SPSS and logistic, there were significant difference between organic rice, non-organic rice and its byproducts except brown rice and hull in SPSS method. Hull can be used as the most useful component for unknown sample prediction with 83.3% probability.