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Biogeochemical processes in land-ocean interfaces, surface estuaries, subterranean estuaries and sediment-water interface
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Nutrient biogeochemistry in the Cross River estuary system and adjacent Gulf of Guinea, South East Nigeria (West Africa)
P-C2-02-S
Solomon Felix Dan* , Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 26610, China
Su-Mei Liu, Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 26610, China
Enobong Charles Udoh, State Key Laboratory of Marine Geology, College of Ocean and Earth Science, Tongji University, Shanghai 200092, China
Shuai Ding, Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 26610, China
Presenter Email: solomon.dan86@yahoo.com |
| The Cross River, Calabar River, and Great Kwa River together form a network of an estuary system otherwise known as the Cross River estuary system. Studies of nutrients and water mass dynamics was conducted in February 2017. Nutrients measured included NO3-, NO2-, NH4+, dissolved inorganic phosphate (DIP), total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), dissolved organic nitrogen (DON), dissolved organic phosphorus (DOP) and dissolved silicate (DSi). The rivers were enriched with DSi and depleted in DIP. Dissolved nutrients were elevated in the Great Kwa River than Cross River and Calabar River. The levels of DSi and DIN were less than average global concentration and that of eutrophic tropical systems. DON represented 68% and 84% of TDN in the Calabar River, and Cross River, respectively. DOP also accounted for ~75% and 67% of TDP in the Calabar River and Cross River, respectively. DIN and DIP occupied 76% of TDN and 56% of TDP in the Great Kwa River. Based on nutrient molar ratios, primary production was strongly limited by DIP, while DIN was potentially limiting. Nutrients in the Cross River estuary system behaved both conservatively and nonconservatively and were affected by biogeochemical and physical processes. Preliminary estimate of nutrient budgets using the LOICZ steady-state box model demonstrated that riverine input was the primary source of nutrients to the estuary system. Nutrient input from atmospheric deposition was very limited. The total residence time of water in the estuary system was ~25 day and may have affected biotic processes and nutrient transport to the adjacent shelf. Nonconservative fluxes of dissolved nutrients resulted in the transport of DIP, DOP, DIN, DON, and DSi to the adjacent shelf. The ecosystem metabolism indicated that the Cross River estuary system is heterotrophic and slowly fixing nitrogen more than it is denitrifying during the study period |
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