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Journal of Tropical Oceanography

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Distribution characteristics of iron forms and their control on phosphorus release in surface sediments of coastal areas in the Maowei Sea

MO Xiarong1, PAN Hongbo1, YANG Bin1,2,3*, XU Cheng2, KANG Zhenjun1,3, WANG Lingyan1, HUANG Haifang1,3,4   

  1. 1. College of Resources and Environment/Guangxi Key Laboratory of Marine Environmental Disaster Processes and Ecological Protection Technology, Beibu Gulf University, Qinzhou 535011, China;

    2. Key Laboratory of Coastal Salt Marsh Ecosystems and Resources, Ministry of Natural Resources/Jiangsu Key Laboratory of Marine Biotechnology, Jiangsu Ocean University, Lianyungang 222005, China;

    3. Pinglu Canal and Beibu Gulf Coastal Ecosystem Observation and Research Station of Guangxi, College of Marine Sciences, Beibu Gulf University, Qinzhou 535011, China

    4. Key Laboratory of Marine Chemistry Theory and Technology, Ocean University of China, Qingdao, 266100, China



  • Received:2026-02-01 Revised:2026-03-30 Accepted:2026-04-07
  • Supported by:

    Guangxi Natural Science Foundation (2025GXNSFHA069112; 2025GXNSFAA069339); Jiangsu Provincial Natural Science Foundation of China (BK20241962); Guangxi Key Laboratory of Marine Environmental Change and Disaster in Beibu Gulf, Beibu Gulf University (2024KF01); Beibu Gulf Marine Ecological Environment Field Observation and Research Station of Guangxi (23-026-271)

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Abstract: The sequential extraction method was utilized to extract and measure the contents of various iron (Fe) and phosphorus (P) forms in surface sediments of coastal areas in the Maowei Sea. Combining sediment physicochemical parameters to elucidate the distribution characteristics of Fe forms and their influencing factors, and explore the role of Fe in controlling P release. The results showed that the contents of various Fe forms in the surface sediments follows the order of residual Fe (Fe-5) > Fe-Mn oxide-bound Fe (Fe-3) > organic-bound Fe (Fe-4) > carbonate-bound Fe (Fe-2) > exchangeable Fe (Fe-1). The contents of Fe-5 and Fe-3 accounted for 64.28%% and 25.05%% of the total Fe (∑Fe) content, respectively. The high-value areas of ∑Fe and various Fe forms in sedments were located in the estuaries of the Qinjiang River, Maolingjiang River, and Dalanjiang River. Inorganic P (IP) was the primary speciation of total P (∑P), and Fe-bound P (Fe-P) was the main form of IP in the surface sediments. The high-value areas of ∑P and its various P forms in the surface sediments were mainly located in the Maolingjiang River estuary region. Fe-3, Fe-4, Fe-5, bioavailable Fe (BFe), and ∑Fe exhibited significant positive correlations with salinity, moisture content, total organic carbon (TOC), total nitrogen (TN), and silt content in the sediments (P<0.05), while displaying significant negative correlations with sand content (P<0.05), suggesting that salinity, TOC, TN, and moisture content were main environmental factors. Additionally, Fe-3, Fe-5, BFe, and ∑Fe exhibited significantly positive correlations with exchangeable P, Fe-P, detrital P (De-P), IP, organic P, and ∑P in the sediments (P<0.05), Fe-2 and Fe-4 displayed significantly positive correlations with De-P (P<0.05). These findings suggested a synchronous coupling relationship between various forms of Fe and P in sediments, with Fe serving as a crucial regulatory factor in the P cycling. The mass ratio of ∑Fe/∑P ranged from 47.22 to 128.76, all of which were greater than 20. The high ratio values were found at the bay mouth. These findings indicated that Fe exerted significant regulatory control on P release in surface sediments of coastal areas in the Maowei Sea, particularly in the bay mouth region.

Key words: iron forms, phosphorus forms, distribution characteristics, surface sediments, Maowei Sea