Role of phosphorus in the seasonal deoxygenation of the East China Sea shelf
<p>The Changjiang is the largest river in Asia and the main terrestrial source of freshwater and nutrients to the East China Sea (ECS). Nutrient concentrations have long been increasing in the Changjiang, especially after 1960 with urbanization, the development of industrial animal production,...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2022-12-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/19/5893/2022/bg-19-5893-2022.pdf |
| _version_ | 1811289460896169984 |
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| author | A. Laurent H. Zhang H. Zhang K. Fennel |
| author_facet | A. Laurent H. Zhang H. Zhang K. Fennel |
| author_sort | A. Laurent |
| collection | DOAJ |
| description | <p>The Changjiang is the largest river in Asia and the main
terrestrial source of freshwater and nutrients to the East China Sea (ECS).
Nutrient concentrations have long been increasing in the Changjiang,
especially after 1960 with urbanization, the development of industrial
animal production, and fertilizer application in agriculture, resulting in
coastal eutrophication and recurring summer hypoxia. The supply of
anthropogenic nitrogen (N) exceeds that of phosphorus (P) relative to the
Redfield ratio. This results in seasonal P limitation in the Changjiang
plume. P limitation and its effects on primary production, respiration, and
hypoxia in the ECS have not been studied systematically, although such
knowledge is needed to understand bloom dynamics in the region, to assess
the consequences of altered nutrient loads, and to implement nutrient
reduction strategies that mitigate hypoxia. Using a coupled
physical–biogeochemical model of the ECS that was run with and without P
limitation, we quantify the distribution and effects of P limitation. The
model shows that P limitation develops eastward of the Changjiang Estuary
and on the Yangtze Bank but rarely southward along the Zhejiang coast. P
limitation modifies oxygen sinks over a large area of the shelf by partly
relocating primary production and respiration offshore, away from the
locations prone to hypoxia near the Changjiang Estuary. This relocation
drastically reduces sediment oxygen consumption nearshore and dilutes the
riverine-driven primary production and respiration over a large area
offshore. Our results suggest that the hypoxic zone would be 48 % larger
in its horizontal extent, on average, if P limitation was not occurring.
Results are summarized in a conceptual model of P limitation on the ECS
shelf that is also applicable to other systems. Then we carried out nutrient
reduction simulations which indicate that, despite the effect of P
limitation on hypoxia, reducing only P inputs as a nutrient reduction
strategy would not be effective. A dual N <span class="inline-formula">+</span> P nutrient reduction strategy
would best mitigate hypoxia. The model results suggest that decreasing the
size of the hypoxic zone by 50 % and 80 % would require reductions in
N <span class="inline-formula">+</span> P load of 28 % and 44 %, respectively.</p> |
| first_indexed | 2024-04-13T03:55:18Z |
| format | Article |
| id | doaj.art-31ed829ccd224d5a8df16941f881b0b7 |
| institution | Directory Open Access Journal |
| issn | 1726-4170 1726-4189 |
| language | English |
| last_indexed | 2024-04-13T03:55:18Z |
| publishDate | 2022-12-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Biogeosciences |
| spelling | doaj.art-31ed829ccd224d5a8df16941f881b0b72022-12-22T03:03:39ZengCopernicus PublicationsBiogeosciences1726-41701726-41892022-12-01195893591010.5194/bg-19-5893-2022Role of phosphorus in the seasonal deoxygenation of the East China Sea shelfA. Laurent0H. Zhang1H. Zhang2K. Fennel3Department of Oceanography, Dalhousie University, Halifax, Nova Scotia, CanadaDepartment of Oceanography, Dalhousie University, Halifax, Nova Scotia, CanadaSchool of Marine Science and Technology, Tianjin University, Tianjin, ChinaDepartment of Oceanography, Dalhousie University, Halifax, Nova Scotia, Canada<p>The Changjiang is the largest river in Asia and the main terrestrial source of freshwater and nutrients to the East China Sea (ECS). Nutrient concentrations have long been increasing in the Changjiang, especially after 1960 with urbanization, the development of industrial animal production, and fertilizer application in agriculture, resulting in coastal eutrophication and recurring summer hypoxia. The supply of anthropogenic nitrogen (N) exceeds that of phosphorus (P) relative to the Redfield ratio. This results in seasonal P limitation in the Changjiang plume. P limitation and its effects on primary production, respiration, and hypoxia in the ECS have not been studied systematically, although such knowledge is needed to understand bloom dynamics in the region, to assess the consequences of altered nutrient loads, and to implement nutrient reduction strategies that mitigate hypoxia. Using a coupled physical–biogeochemical model of the ECS that was run with and without P limitation, we quantify the distribution and effects of P limitation. The model shows that P limitation develops eastward of the Changjiang Estuary and on the Yangtze Bank but rarely southward along the Zhejiang coast. P limitation modifies oxygen sinks over a large area of the shelf by partly relocating primary production and respiration offshore, away from the locations prone to hypoxia near the Changjiang Estuary. This relocation drastically reduces sediment oxygen consumption nearshore and dilutes the riverine-driven primary production and respiration over a large area offshore. Our results suggest that the hypoxic zone would be 48 % larger in its horizontal extent, on average, if P limitation was not occurring. Results are summarized in a conceptual model of P limitation on the ECS shelf that is also applicable to other systems. Then we carried out nutrient reduction simulations which indicate that, despite the effect of P limitation on hypoxia, reducing only P inputs as a nutrient reduction strategy would not be effective. A dual N <span class="inline-formula">+</span> P nutrient reduction strategy would best mitigate hypoxia. The model results suggest that decreasing the size of the hypoxic zone by 50 % and 80 % would require reductions in N <span class="inline-formula">+</span> P load of 28 % and 44 %, respectively.</p>https://bg.copernicus.org/articles/19/5893/2022/bg-19-5893-2022.pdf |
| spellingShingle | A. Laurent H. Zhang H. Zhang K. Fennel Role of phosphorus in the seasonal deoxygenation of the East China Sea shelf Biogeosciences |
| title | Role of phosphorus in the seasonal deoxygenation of the East China Sea shelf |
| title_full | Role of phosphorus in the seasonal deoxygenation of the East China Sea shelf |
| title_fullStr | Role of phosphorus in the seasonal deoxygenation of the East China Sea shelf |
| title_full_unstemmed | Role of phosphorus in the seasonal deoxygenation of the East China Sea shelf |
| title_short | Role of phosphorus in the seasonal deoxygenation of the East China Sea shelf |
| title_sort | role of phosphorus in the seasonal deoxygenation of the east china sea shelf |
| url | https://bg.copernicus.org/articles/19/5893/2022/bg-19-5893-2022.pdf |
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