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The Role of Urea as a Key Nitrogen Source Driving Phytoplankton Blooms in the Nitrogen-Limited South Coast of Korea

질소 제한 환경인 한국 남해안에서 식물플랑크톤 대발생을 유도하는 주요 질소원으로서 요소의 역할

Yeonju Kim1
,
Tae-Hoon Kim1*
김 연주1
,
김 태훈1*
1Department of Earth Systems and Environmental Sciences, Chonnam National University, Gwangju 61186, Korea
1전남대학교 자연과학대학 해양학과 (61186) 광주광역시 북구 용봉로 77
*Corresponding Author
4 November 2025. pp. 1-8
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Abstract

This study investigates the role of urea as an alternative nitrogen (N) source for phytoplankton and its potential to create conditions conducive to harmful algal blooms (HABs) in the N-limited coastal ecosystems of the South Coast of Korea. Three cruises were conducted during the 2023 summer monsoon to analyze spatio-temporal nutrient dynamics. The study area exhibited N-limited conditions, with a mean dissolved inorganic nitrogen (DIN) to dissolved inorganic phosphate (DIP) ratio of 11.2, a value lower than the Redfield ratio. Following intense rainfall, urea concentrations increased significantly, and the ratio of urea to dissolved organic nitrogen (DON) consistently exceeded the accepted bioavailability threshold. This indicates that urea represents a readily available fraction of the large DON pool. Statistical analysis linked this urea pulse to the creation of biogeochemical conditions known to favor HABs (ANOVA, p < 0.05). Principal Component Analysis (PCA) identified urea and DIN loading as the primary driver shifting the ecosystem state towards conditions favorable for bloom initiation. Following the nutrient pulse in July, a significant increase in phytoplankton-derived organic matter in August was confirmed by a positive correlation between dissolved organic carbon (DOC) and protein-like fluorescent DOM. These findings suggest that large-scale urea input, supplied by terrestrial runoff, acts as a key triggering mechanism that creates the prerequisite conditions for the recurrent summer phytoplankton blooms in this N-limited system. The study concludes that urea should be included in nutrient monitoring and management strategies to mitigate HAB risk.

Keywords
urea
dissolved organic nitrogen (DON)
harmful algal blooms (HABs)
nitrogen limitation
nutrient dynamics
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Information
  • Publisher :Korea Institute of Ocean Science and Technology
  • Publisher(Ko) :한국해양과학기술원
  • Journal Title :Ocean and Polar Research
  • Journal Title(Ko) :Ocean and Polar Research
  • Volume : 47
  • Pages :1-8
  • Received Date : 2025-08-11
  • Revised Date : 2025-09-24
  • Accepted Date : 2025-10-14
  • Published Date : 2025-11-04
  • DOI :https://doi.org/10.4217/OPR.2025015
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