Progress on nutrient biogeochemistry in a typical coastal bay affected by intensive mariculture

Recently, a new manuscript entitled “Nutrient Budget and Biogeochemical Dynamics in Sansha Bay, China: A Coastal Bay Affected by Intensive Mariculture” by  Drs. Aiqin Han, Hui Lin, Shuh-Ji Kao and etc. was published in Journal of Geophysical Research: Biogeosciences (IF:3.822). This study was supported in part by the National Natural Science Foundation of China, the Scientific Research Foundation of Third Institute of Oceanography, Ministry of Natural Resources, China, and the Natural Science Foundation of Fujian Province of China.

Sansha Bay is a coastal bay that undergoes intensive mariculture activities, and is influenced by China Coastal Current in winter and by South China Sea Warm Current in summer. Nutrient biogeochemistry is therefore complex, in addition, there is a lack of information from system scale biogeochemical studies.

Using the Land-Ocean Interaction Coastal Zone (LOICZ) mass balance model, the external DIN and DIP additions ratio was estimated, ~21.8-20.4:1, while Si(OH)4 addition/removal occurred seasonally. Potential N biogeochemical processes were also explored. Using a three end-member mixing model, nutrient biogeochemistry (regeneration/uptake, denoted by d) within the aquaculture ecosystem was estimated separately from complex physical mixing effects. In winter, nutrient regeneration dominated (dDIN:dDIP ~20:1; dSi(OH)4:dDIN <1:2), likely due to remineralization of particles (phytoplankton with a 16:1 Redfield ratio and/or fish feed/faeces with a non-Redfield ratio). In contrast, nutrient consumption dominated in summer (dDIN:dDIP ~13.5:1; dSi(OH)4:dDIN ~2.4:1).

This study is one of the first attempts to use a combination of field observations, the LOICZ budget model and three end-member mixing model to characterize external nutrient addition/removal and internal nutrient uptake/regeneration in a complex shelf system subjected to intensive mariculture activities, riverine input, and the influence of adjacent coastal seawater, and is important in defining the mariculture ecosystem in terms of a river-shelf continuum.

Conceptual schematic illustrating the nutrient dynamics of DIN, DIP, Si(OH)4, DON, and PN in Sansha Bay affected by intensive mariculture and under the influence of both river nutrient inputs and those from adjacent coastal waters. Briefly, (a) organic matter appeared to be remineralized and regenerated in the bay in winter; (b) both nutrient regeneration and consumption occurred in the water column in summer, although DIN and DIP showed an apparent net addition.

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