Journal of Tropical Oceanography >
Distribution of nutrients and eutrophication characteristics in the surface water around Nan’ao Island
Copy editor: YIN Bo
Received date: 2024-06-05
Revised date: 2024-08-19
Online published: 2024-08-29
Supported by
Science and Technology Planning Project of Guangdong Province(2021B1212050023)
Science and Technology Planning Project of Guangdong Province(2023B1212060047)
National Natural Science Foundation of China(32171548)
Guangdong Basic and Applied Basic Research Foundation(2022A1515010656)
The key environmental factors (nutrients, chlorophyll a (Chl a), chemical oxygen demand (COD), etc.) and eutrophication indexes were investigated in the surface water around the Nan’ao Island in 2022. The seasonal change of nutrients concentration was significant, which gradually declined from northwest to southeast in the surrounding region of the island. The nutrients concentration was significantly higher in winter than in other seasons. During summer, the nutrients concentration was high near the Qin’ao Bay, which possibly originated from the discharge of domestic wastewater. The highest dissolved inorganic nitrogen (DIN) was found near the estuary of the Rongjiang River and the highest dissolved inorganic phosphorus (DIP) was found near a net cage aquaculture zone in the Zhelin Bay. This phenomenon suggested that the river input increased the nitrogen loading and the cage aquaculture increased the phosphorus loading in this region. The seawater showed high Chl a and low nutrients in summer, suggesting the strong bio-assimilation effect of phytoplankton on the nutrients. The structure of nutrients was generally balanced, and no absolute limitation was detected for nitrogen, phosphorus or silicate. Nitrogen nutrients were relatively limited in the offshore region in autumn. According to the eutrophication index (EI), nutrient quality index (NQI) and trophic index (TRIX), the highest eutrophic status was generally located in the Zhelin Bay and the Rongjiang River estuary. However, the region near the Qing’ao Bay showed high eutrophic status in summer. With the rapid development of tourism, the influence of domestic wastewater should be paid more attention to in the Nan’ao Island. The eutrophication indices showed a significantly positive correlation with DIN and a negative correlation with salinity. River discharge should be the main reason for water eutrophication in this region. The eutrophic status could be much underestimated using the EI index for waters with low nutrients and high chlorophyll during summer. The results contribute to a better understanding of the water quality status around the Nan’ao Island and provide basic data for environment management and marine resource utilization.
HUANG Haochen , KE Zhixin , ZHOU Zhixi , ZHOU Weihua . Distribution of nutrients and eutrophication characteristics in the surface water around Nan’ao Island[J]. Journal of Tropical Oceanography, 2025 , 44(2) : 196 -207 . DOI: 10.11978/2024120
图1 南澳岛周边采样站位分布图该地图基于自然资源部国家基础地理信息中心审图号为GS(2024)0568号标准地图制作, 底图无修改 Fig. 1 The sampling stations around Nan’ao Island This map is based on the standard map GS (2024) 0568 approved by the National Basic Geographic Information Center of the Ministry of Natural Resources, with no modifications to the base map |
图2 南澳周边海域表层水体温度(a—d)和盐度(e—h)的季节分布特征a, e: 春季; b, f: 夏季; c, g: 秋季; d, h: 冬季 Fig. 2 Seasonal distributions of water temperature (a)—(d) and salinity (e)—(h) in the surface water around Nan’ao Island a, e: spring; b, f: summer; c, g: autumn; d, h: winter |
表1 南澳周边海域表层水体各季节的主要环境因子和富营养化指数(均值±标准差)Tab. 1 The environmental factors and eutrophication index in the surface water around Nan’ao Island in different seasons (mean ± SD) |
因子或指数 | 春季 | 夏季 | 秋季 | 冬季 |
---|---|---|---|---|
温度/℃ | 23.38 ± 0.46c | 27.07 ± 1.99a | 25.85 ± 0.28b | 17.00 ± 0.21d |
盐度/‰ | 31.71 ± 0.46a | 31.42 ± 2.63a | 32.67 ± 1.77a | 30.78 ± 2.40a |
DIN/(mg·L-1) | 0.10 ± 0.09b | 0.08 ± 0.06b | 0.17 ± 0.10b | 0.49 ± 0.26a |
DIP/(mg·L-1) | 0.014 ± 0.016bc | 0.011 ± 0.009c | 0.030 ± 0.013b | 0.050 ± 0.020a |
DSi/(mg·L-1) | 0.44 ± 0.28b | 0.77 ± 0.52ab | 0.88 ± 0.36ab | 1.06 ± 0.47a |
DIN/DIP | 20.42 ± 15.97a | 21.41 ± 11.80a | 12.08 ± 3.77a | 21.22 ± 6.58a |
Chl a/(μg·L-1) | 2.55 ± 2.24b | 7.05 ± 4.94a | 1.44 ± 0.84b | 1.53 ± 0.43b |
COD/(mg·L-1) | 0.96 ± 0.25b | 1.57 ± 0.26a | 0.68 ± 0.33b | 0.89 ± 0.28b |
DO/(mg·L-1) | 7.15 ± 0.74bc | 7.79 ± 0.71ab | 7.00 ± 0.67c | 8.07 ± 0.16a |
EI指数 | 0.51 ± 0.76b | 0.37 ± 0.48b | 0.98 ± 1.06b | 6.34 ± 7.32a |
NQI指数 | 1.65 ± 0.90b | 2.57 ± 1.00b | 2.10 ± 0.81b | 3.88 ± 1.47a |
TRIX指数 | 4.43 ± 0.89a | 5.08 ± 0.33a | 4.91 ± 0.70a | 4.87 ± 0.47a |
注: 不同字母表示组间在统计上的显著差异(p<0.05)。所有比较均基于单因素方差分析后的Tukey多重比较 |
图3 南澳岛周边海域表层溶解无机氮质量浓度(DIN)(a—d)、溶解无机磷质量浓度(DIP)(e—h)和活性硅酸盐质量浓度(DSi)(i—l)的季节分布a, e, i: 春季; b, f, j: 夏季; c, g, k: 秋季; d, h, l: 冬季 Fig. 3 Seasonal distributions of DIN (a)—(d), DIP (e)—(h), and DSi (i)—(l) in the surface water around Nan’ao Island a, e, i: spring; b, f, j: summer; c, g, k: autumn; d, h, l: winter |
图4 南澳周边海域表层水体中硝态氮( )、亚硝氮( )和氨氮( )相对比例的季节变化a. 春季氨氮比例; b. 夏季氨氮比例; c. 秋季氨氮比例; d. 冬季氨氮比例; e. 各季节不同站位的DIN组成 Fig. 4 Seasonal variations of the percentages of nitrate ( ), nitrite ( ) and ammonia ( ) in the surface water around Nan’ao Island a. Spring ammonia nitrogen ratio; b. Summer ammonia nitrogen ratio; c. Autumn ammonia nitrogen ratio; d. Winter ammonia nitrogen ratio; e. DIN composition at different stations in different seasons |
图6 南澳周边海域表层水体叶绿素a质量浓度(Chl a)(a—d)、化学需氧量(COD)(e—h)和溶解氧(DO)(i—l)的空间分布a, e, i: 春季; b, f, j: 夏季; c, g, k: 秋季; d, h, l: 冬季 Fig. 6 The spatial distribution of Chl a (a)—(d), COD (e)—(h) and DO (i)—( l) in the surface water around Nan’ao Island a, e, i: spring; b, f, j: summer; c, g, k: autumn; d, h, l: winter |
图7 南澳周边海域表层水体富营养化指数(EI)(a—d)、营养质量指数(NQI)(e—h)和营养状态指数(TRIX)(i—l)的分布特征a, e, i: 春季; b, f, j: 夏季; c, g, k: 秋季; d, h, l: 冬季 Fig. 7 The spatial distribution of eutrophication index (EI) (a)—(d), nutrient quality index (NQI) (e)—(h) and trophic index (TRIX) (i)—(l) in the surface water around Nan’ao island a, e, i: spring; b, f, j: summer; c, g, k: autumn; d, h, l: winter |
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