Oxygen depletion and the response of organic matter in Laoyehai, a lagoon with strong aquaculture activities
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摘要: 老爷海是海南岛东岸的一处潟湖, 受强烈人类活动（尤其是养殖活动）影响, 其水体富营养化并伴随低氧. 在选取的旱季和洪季（2010年4月和2011年8月）, 老爷海适值低氧期间, 对老爷海开展了针对溶解氧和有机质的采样与观测. 结果显示, 春季潟湖低氧强烈, 个别站位表层水溶解氧也仅为50%, 夏季则在底层也存在低氧. 在这样的背景下, 春季有机质浓度明显高于夏季, 颗粒有机质的C/N值(C与N的比值)也表现为春季高于夏季（平均值春季为9.7, 夏季为7.7）. 氨基酸所指征的有机质成分暗示春季有机质有较强的细菌降解信号; 夏季有机质的低C/N值和高氨基酸碳、氮归一化产量显示现场生产相对活跃, 有机质主要来自海源浮游植物, 表层水供氧充分. 在水体发生氧亏损时, 溶解和颗粒有机质的降解程度存在差异. 整体而言, 颗粒有机质的降解程度随着水体中溶解氧浓度的下降而增加, 说明颗粒有机质的降解消耗氧气是造成潟湖低氧的重要驱动因素; 溶解有机质成分的变化和溶解氧关联不显著.Abstract: Laoyehai is a lagoon located on the east coast of Hainan and is impacted heavily by human activities (especially those related to aquaculture). Laoyehai is characterized by its eutrophic and hypoxic waters. During previous dry and flood seasons (specifically, April 2010 and August 2011), when hypoxia occurred, field work was conducted to observe the dissolved oxygen (DO) and to collect organic matter. Hypoxia was significant in the spring season with surface DO as low as 50%, while the bottom hypoxic water prevailed in both seasons. In the spring season, the C/N ratio of particulate organic matter was higher than that observed in the summer season (C/N in the spring: 9.7, C/N in the summer: 7.7). Organic matter composition indicated by amino acids showed that there was strong in situ production in the spring relative to that in the summer. Lower C/N values and higher carbon and nitrogen yields of amino acids (AA C yield, AA N yield) in the summer showed active in situ production, suggesting that organic matter was mainly derived from phytoplankton. This also explains the sufficient surface DO in the summer. The degradation of particulate organic matter increased with the decrease of dissolved oxygen, indicating that the particulate organic matter and its degradation were the key driving factors for oxygen consumption in the lagoon. Meanwhile, we found that the relationship between dissolved organic matter components and DO was not significant.
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Key words:
- Laoyehai /
- lagoon /
- hypoxia /
- organic matter /
- amino acid
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图 1 老爷海的地理位置(a)和采样站位(b)
Fig. 1 Geographic position of Laoyehai (a) and sampling stations (b)
图 2 2010年4月和2011年8月老爷海温度、盐度和溶解氧的表底层空间分布
Fig. 2 Spatial distribution of temperature, salinity, and DO of the surface and bottom water layers in April 2010 and August 2011, Laoyehai
图 3 春季和夏季L-5站位温度、盐度和pH值的剖面变化
Fig. 3 Temperature, salinity and pH profiles at the L-5 station in the spring and summer
图 4 春季和夏季老爷海表底层pH值与DO的变化相关性
Fig. 4 Relationship between pH and DO of the surface and bottom water layers during the spring and summer season, Laoyehai
图 5 2010年4月和2011年8月老爷海表层TSM、颗粒有机质（POC%、PN%、POC、PN）和C/N值的空间分布
Fig. 5 Spatial distribution of TSM and particulate organic matter (POC%, PN%, POC, PN) and C/N ratio of surface water in April 2010 and August 2011, Laoyehai
图 6 2010年4月和2011年8月颗粒和溶解态氨基酸在老爷海表底层的空间分布
Fig. 6 Spatial distribution of particulate amino acids and dissolved amino acids at the surface and bottom water layers in April 2010 and August 2011, Laoyehai
图 7 颗粒态氨基酸的碳、氮归一化产量（AA C yield、AA N yield）、降解指数（DI）与C/N值的关系
Fig. 7 Relationships between AA C yield, AA N yield, DI of THPAA, and C/N radio
图 8 老爷海春夏季C/N值、AA C yield、AA N yield随POC%的变化趋势图
Fig. 8 Relationships between AA C yield, AA N yield, C/N ratio, and POC%
图 9 表层颗粒态氨基酸参数随环境变量的散点变化趋势
Fig. 9 Surface THPAA plotted against environmental variables
图 10 溶解态表层氨基酸参数随溶解氧和pH值的变化趋势
Fig. 10 Variation between surface THDAA parameters and DO, pH
图 11 溶解态底层氨基酸参数随AOU和pH值的变化趋势
Fig. 11 Variation between bottom THDAA parameters and AOU, pH
表 1 本研究涉及的氨基酸和指征参数中英文对照表
Tab. 1 Amino acids and parameters used in this study
氨基酸 氨基酸指征参数 英文缩写 中文名 英文缩写 中文名 THPAA 颗粒态氨基酸 AA C yield 氨基酸的碳归一化产量 THDAA 溶解态氨基酸 AA N yield 氨基酸的氮归一化产量 Asp 天冬氨酸 DI 降解指数 Glu 谷氨酸 D-AA% D型氨基酸在总氨基酸中的比例 Asn 天冬酰胺 Gly% 甘氨酸在总氨基酸中的比例 Ser 丝氨酸 D/L-Ala D型丙氨酸与L型丙氨酸的比值 Gln 谷氨酰胺 Thr 苏氨酸 Gly 甘氨酸 Arg 精氨酸 Ala 丙氨酸 GABA γ -氨基丁酸 Tyr 酪氨酸 Aba 氨基丁酸 Val 缬氨酸 Met 蛋氨酸 Trp 色氨酸 Phe 苯丙氨酸 ILE 异亮氨酸 Leu 亮氨酸 Lys 赖氨酸 
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表 2 2010年4月和2011年8月老爷海表底层水体的水质参数
Tab. 2 Water quality parameters of the surface and bottom water layers in April 2010 and August 2011, Laoyehai
温度/℃ 盐度 pH值 DO/(mg·L–1) DO% AOU/(mg·L–1) 2010.4 表层 max 30.1 33.0 9.28 13 164% 3.8 min 27.0 13.8 7.92 3 38% –6.0 mean 28.5 23.5 8.42 7 86% 0.1 2011.8 表层 max 34.1 27.5 8.51 9 128% 3.1 min 29.9 7.2 7.42 4 49% –2.4 mean 31.9 16.5 8.05 6 90% 0.2 2010.4 底层 max 29.6 33.0 8.92 8 101% 6.8 min 27.1 18.8 7.68 0.2 2% –0.7 mean 28.1 24.8 8.22 4 50% 2.9 2011.8 底层 max 32.1 32.3 8.21 6 81% 6.6 min 30.1 16.4 7.45 0 0% 0.7 mean 31.1 21.7 7.85 3 46% 3.2
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表 3 2010年4月和2011年8月老爷海表层水体的总悬浮颗粒物、颗粒有机质浓度和C/N值
Tab. 3 Total suspended matter (TSM), particulate organic matter, and C/N ratio in April 2010 and August 2011, Laoyehai
TSM/(mg·L–1) POC% PN% POC/(µmol·L–1) PN/(µmol·L–1) C/N 2010.4 max 42 14% 1.5% 434 40 11.7 min 24 2% 0.3% 41 6 7.3 mean 34 6% 0.7% 172 17 9.7 2011.8 max 60 4% 0.6% 129 16 8.4 min 17 1% 0.2% 19 3 6.6 mean 36 3% 0.4% 78 10 7.7
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表 4 2010年4月和2011年8月老爷海表底层水体的氨基酸浓度和相关参数
Tab. 4 Amino acids of the surface and bottom water layers in April 2010 and August 2011, Laoyehai
THPAA THDAA CONC/
(mg·L–1)AA C
yieldAA N
yieldDI D-AA% D/L-Ala Gly% CONC/
(mg·L–1)DI D-AA% D/L-Ala Gly% 2010.4表层 max 5.9 16% 30% 0.7 7.4% 0.14 14% 3.2 5.1 16% 0.75 50% min 0.2 1% 3% – 0.2 5.1% 0.03 6% 0.3 – 0.4 0% 0.13 38% mean 1.3 4% 9% 0.3 6.1% 0.09 10% 2.1 1.2 8% 0.25 44% 2011.8表层 max 2.4 10% 22% 1.9 11.3% 0.06 13% 3.4 3.4 10% 0.39 48% min 0.1 2% 4% 0.2 4.4% 0.05 8% 0.4 – 0.7 0% 0.25 34% mean 1.2 6% 13% 0.9 8.4% 0.05 9% 1.5 1.4 5% 0.31 40% 2010.4底层 max 3.3 1.1 11% 0.67 73% min 0.2 – 2.3 5% 0.11 42% mean 1.8 – 0.2 8% 0.25 50% 2011.8底层 max 1.5 1.6 11% 0.51 41% min 0.1 0.8 9% 0.26 36% mean 1.0 1.2 10% 0.34 39%
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表 5 2010年4月和2011年8月老爷海内湾和外湾水体中氨基酸的优势单体
Tab. 5 Dominant monomers of amino acids in the inner and outer gulf in April 2010 and August 2011, Laoyehai
AA C yield AA N yield THPAA THDAA L-Glu% L-Asp% L-Ala% Gly% Gly% L-Ala% L-Asp% L-Thr% 2010.4 内湾（网箱养鱼） 5% 13% 14% 13% 12% 9% 44% 11% 8% 6% 外湾（岸滩养虾） 8% 16% 7% 8% 13% 9% 39% 9% 10% 5% 2011.8 内湾（网箱养鱼） 2% 4% 13% 14% 12% 11% 52% 7% 6% 4% 外湾（岸滩养虾） 3% 6% 7% 9% 13% 9% 40% 9% 8% 5%
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表 6 剖面站L-5站位春季和夏季的溶解氧和氨基酸含量
Tab. 6 Profile of DO and amino acids at the L-5 station in the spring and summer
季节 深度/m DO/(mg·L–1) AA C yielda AA N yielda DIa DIb Gly%b 春季 0 4.0 2% 7% 0.05 0.2 43% 3 0.3 6% 13% 0.6 2.2 37% 4 0.2 0.9 45% 5 0.2 0 47% 夏季 0 9.1 2 2.3 1.1 41% 4 0.0 1.4 38% 注: a 为基于 THPAA 计算得出, b 为基于 THDAA 计算得出.
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