Current Issue
2024 Vol. 43, No. 6
Display Method:
2024, 43(6): 1-2.
Abstract:
2024, 43(6): 1-14.
doi: 10.1007/s13131-023-2254-y
Abstract:
Ocean productivity is the foundation of marine food web, which continuously removes atmospheric carbon dioxide and supports life at sea and on land. Spatio-temporal variability of net primary productivity (NPP), sea surface temperature (SST), sea surface salinity (SSS), mixed layer depth (MLD), and euphotic zone depth (EZD) in the northern Bay of Bengal (BoB) during three monsoon seasons were examined in this study based on remote sensing data for the period 2005 to 2020. To compare the NPP distribution between the coastal zones and open BoB, the study area was divided into five zones (Z1−Z5). Results suggest that most productive zones Z2 and Z1 are located at the head bay area and are directly influenced by freshwater discharge together with riverine sediment and nutrient loads. Across Z1−Z5, the NPP ranges from5315.38 mg/(m2·d) to 346.7 mg/(m2·d) (carbon, since then the same). The highest monthly average NPP of 5315.38 mg/(m2·d) in February and 5039.36 mg/(m2·d) in June were observed from Z2, while the lowest monthly average of 346.72 mg/(m2·d) was observed in March from Z4, which is an oceanic zone. EZD values vary from 6−154 m for the study area, and it has an inverse correlation with NPP concentration. EZD is deeper during the summer season and shallower during the wintertime, with a corresponding increase in productivity. Throughout the year, monthly SST shows slight fluctuation for the entire study area, and statistical analysis shows a significant correlation among NPP, and EZD, overall positive between NPP and MLD, whereas no significant correlation among SSS, and SST for the northern BoB. Long-term trends in SST and productivity were significantly positive in head bay zones but negatively productive in the open ocean. The findings in this study on the distribution of NPP, SST, SSS, MLD, and EZD and their seasonal variability in five different zones of BoB can be used to further improve the management of marine resources and overall environmental condition in response to climate changes in BoB as they are of utmost relevance to the fisheries for the three bordering countries.
Ocean productivity is the foundation of marine food web, which continuously removes atmospheric carbon dioxide and supports life at sea and on land. Spatio-temporal variability of net primary productivity (NPP), sea surface temperature (SST), sea surface salinity (SSS), mixed layer depth (MLD), and euphotic zone depth (EZD) in the northern Bay of Bengal (BoB) during three monsoon seasons were examined in this study based on remote sensing data for the period 2005 to 2020. To compare the NPP distribution between the coastal zones and open BoB, the study area was divided into five zones (Z1−Z5). Results suggest that most productive zones Z2 and Z1 are located at the head bay area and are directly influenced by freshwater discharge together with riverine sediment and nutrient loads. Across Z1−Z5, the NPP ranges from
2024, 43(6): 15-31.
doi: 10.1007/s13131-023-2283-6
Abstract:
Highly productive estuaries facilitate intense decomposition of dissolved organic matter (DOM) as a carbon source. However, the specific impacts of typhoons on DOM decomposition in eutrophic bays remain unclear. To address this issue, we investigated the spectral characteristics of DOM before and after Typhoon Ewiniar in Zhanjiang Bay, a eutrophic semi-enclosed bay in the northwestern South China Sea. The results revealed that intense microbial decomposition of DOM occurred during the pre-typhoon period because high nutrient inputs facilitated the mobilization of DOM in the bay. However, the intrusion of external seawater induced by the typhoon diluted the nutrient levels in Zhanjiang Bay, reducing the impact of microbial decomposition on DOM during the post-typhoon period. Nevertheless, the net addition of DOM occurred in Zhanjiang Bay during the post-typhoon period, possibly because of the decomposition of particulate organic matter (POM) and desorption of particulate matter. In addition, an increase in apparent oxygen utilization, a decrease in DO saturation and the reduced level of Chl a indicated that organic matter (OM) decomposition was enhanced and OM decomposition shifted to POM decomposition in Zhanjiang Bay after the typhoon. Overall, our study highlighted the shift in the intense OM decomposition from DOM to POM decomposition before and after typhoons in eutrophic bays, providing new insights into the response of typhoons to biogeochemistry.
Highly productive estuaries facilitate intense decomposition of dissolved organic matter (DOM) as a carbon source. However, the specific impacts of typhoons on DOM decomposition in eutrophic bays remain unclear. To address this issue, we investigated the spectral characteristics of DOM before and after Typhoon Ewiniar in Zhanjiang Bay, a eutrophic semi-enclosed bay in the northwestern South China Sea. The results revealed that intense microbial decomposition of DOM occurred during the pre-typhoon period because high nutrient inputs facilitated the mobilization of DOM in the bay. However, the intrusion of external seawater induced by the typhoon diluted the nutrient levels in Zhanjiang Bay, reducing the impact of microbial decomposition on DOM during the post-typhoon period. Nevertheless, the net addition of DOM occurred in Zhanjiang Bay during the post-typhoon period, possibly because of the decomposition of particulate organic matter (POM) and desorption of particulate matter. In addition, an increase in apparent oxygen utilization, a decrease in DO saturation and the reduced level of Chl a indicated that organic matter (OM) decomposition was enhanced and OM decomposition shifted to POM decomposition in Zhanjiang Bay after the typhoon. Overall, our study highlighted the shift in the intense OM decomposition from DOM to POM decomposition before and after typhoons in eutrophic bays, providing new insights into the response of typhoons to biogeochemistry.
2024, 43(6): 32-37.
doi: 10.1007/s13131-023-2267-6
Abstract:
Marine sediments collected from the Zhujiang (Pearl) River Estuary (ZRE) and South China Sea (SCS) were utilized to study the occurrence and spatial distribution of tetrabromobisphenol A (TBBPA) and hexabromocyclododecane (HBCDD). The levels of TBBPA and HBCDD in sediments ranged from not detected (nd) to 6.14 ng/g dry weight (dw) and nd to 0.42 ng/g dw. TBBPA concentrations in marine sediments were substantially higher than HBCDD. The concentrations of TBBPA and HBCDD in the ZRE sediments were significantly greater than those in the SCS. α-HBCDD (48.7%) and γ-HBCDD (46.2%) were the two main diastereoisomers of HBCDD in sediments from the ZRE, with minor contribution of β-HBCDD (5.1%). HBCDD were only found in one sample from the northern SCS. The enantiomeric fraction of α-HBCDD in sediments from the ZRE was obviously greater than 0.5, indicating an accumulation of (+)-α-HBCDD. The enantiomers of HBCDD were not measured in sediments from the SCS. This work highlighted the environmental behaviors of TBBPA and HBCDD in marine sediments.
Marine sediments collected from the Zhujiang (Pearl) River Estuary (ZRE) and South China Sea (SCS) were utilized to study the occurrence and spatial distribution of tetrabromobisphenol A (TBBPA) and hexabromocyclododecane (HBCDD). The levels of TBBPA and HBCDD in sediments ranged from not detected (nd) to 6.14 ng/g dry weight (dw) and nd to 0.42 ng/g dw. TBBPA concentrations in marine sediments were substantially higher than HBCDD. The concentrations of TBBPA and HBCDD in the ZRE sediments were significantly greater than those in the SCS. α-HBCDD (48.7%) and γ-HBCDD (46.2%) were the two main diastereoisomers of HBCDD in sediments from the ZRE, with minor contribution of β-HBCDD (5.1%). HBCDD were only found in one sample from the northern SCS. The enantiomeric fraction of α-HBCDD in sediments from the ZRE was obviously greater than 0.5, indicating an accumulation of (+)-α-HBCDD. The enantiomers of HBCDD were not measured in sediments from the SCS. This work highlighted the environmental behaviors of TBBPA and HBCDD in marine sediments.
2024, 43(6): 38-48.
doi: 10.1007/s13131-024-2377-9
Abstract:
Zhanjiang Bay is a major aquaculture area in China with many types of mariculture products (such as oysters, fish, and shrimp). The culture area and shrimp output in Zhanjiang Bay are ranked first in China. We investigated the total organic carbon (TOC), total nitrogen (TN), TOC/TN ratio, and stable isotopes (δ13C and δ15N) of the fish and shrimp feed, fish and shrimp feces, and sedimentary organic matter (SOM) in and around different aquaculture areas of northeastern Zhanjiang Bay to study the impact of aquaculture activities on SOM. The average TOC contents of fish and shrimp feed were 39.20% ± 0.91% and 39.29% ± 0.21%, respectively. The average TOC content in the surface sediments of the oyster culture area, the mixed (fish and shrimp) culture area, and the cage fish farm area were 0.66%, 0.88% ± 0.10%, and 0.58% ± 0.19%, respectively, which may indicate that mixed culture had a greater impact on SOM. The relatively high TOC and TN contents and relatively low TOC/TN ratios, and δ15N values in the upper layer of the core sediment in the mixed culture area could also support the significant influence of mixed culture. The average δ13C and δ15N values of fish and shrimp feed were −20.6‰ ± 2.2‰ and 1.8‰ ± 1.2‰, respectively, which were different from the isotopic values of SOM in the study area. δ13C and δ15N values for SOM in different aquaculture areas were different from those of nearby reference stations, probably reflecting the influence of aquaculture. The δ13C and δ15N values in the oyster culture area (−25.9‰ and 6.0‰, respectively) seemed to have reduced δ13C and enriched δ15N relative to those of the reference station (−24.6‰ and 5.8‰, respectively). This may reflect the influence of organic matter on oyster culture. The δ15N value of the station in the mixed culture area (7.1‰ ± 0.4‰) seemed to be relatively enriched in δ15N relative to that of the reference station (6.6‰). Sedimentation and the subsequent degradation of organic matter from mixed cultures may have contributed to this phenomenon. The surface sediment at the cage fish farm area seemed to be affected by fish feces and primary production based on the indication of δ13C and δ15N values. The sediment core at the mixed culture region (NS6) had lower TOC/TN ratios and more positive δ13C and δ15N values than the sediment core at the oyster culture area, suggesting a higher proportionate contribution of marine organic matter in the mixed culture area. In summary, oyster culture, mixed culture, and cage fish culture in northeastern Zhanjiang Bay had a certain degree of impact on SOM, and mixed culture had more significant influences on SOM based on the high TOC contents and the significant vertical variations of TOC/TN ratio and δ15N value in the sediment of this area. This study provides new insights into the impact of aquaculture activities on SOM content.
Zhanjiang Bay is a major aquaculture area in China with many types of mariculture products (such as oysters, fish, and shrimp). The culture area and shrimp output in Zhanjiang Bay are ranked first in China. We investigated the total organic carbon (TOC), total nitrogen (TN), TOC/TN ratio, and stable isotopes (δ13C and δ15N) of the fish and shrimp feed, fish and shrimp feces, and sedimentary organic matter (SOM) in and around different aquaculture areas of northeastern Zhanjiang Bay to study the impact of aquaculture activities on SOM. The average TOC contents of fish and shrimp feed were 39.20% ± 0.91% and 39.29% ± 0.21%, respectively. The average TOC content in the surface sediments of the oyster culture area, the mixed (fish and shrimp) culture area, and the cage fish farm area were 0.66%, 0.88% ± 0.10%, and 0.58% ± 0.19%, respectively, which may indicate that mixed culture had a greater impact on SOM. The relatively high TOC and TN contents and relatively low TOC/TN ratios, and δ15N values in the upper layer of the core sediment in the mixed culture area could also support the significant influence of mixed culture. The average δ13C and δ15N values of fish and shrimp feed were −20.6‰ ± 2.2‰ and 1.8‰ ± 1.2‰, respectively, which were different from the isotopic values of SOM in the study area. δ13C and δ15N values for SOM in different aquaculture areas were different from those of nearby reference stations, probably reflecting the influence of aquaculture. The δ13C and δ15N values in the oyster culture area (−25.9‰ and 6.0‰, respectively) seemed to have reduced δ13C and enriched δ15N relative to those of the reference station (−24.6‰ and 5.8‰, respectively). This may reflect the influence of organic matter on oyster culture. The δ15N value of the station in the mixed culture area (7.1‰ ± 0.4‰) seemed to be relatively enriched in δ15N relative to that of the reference station (6.6‰). Sedimentation and the subsequent degradation of organic matter from mixed cultures may have contributed to this phenomenon. The surface sediment at the cage fish farm area seemed to be affected by fish feces and primary production based on the indication of δ13C and δ15N values. The sediment core at the mixed culture region (NS6) had lower TOC/TN ratios and more positive δ13C and δ15N values than the sediment core at the oyster culture area, suggesting a higher proportionate contribution of marine organic matter in the mixed culture area. In summary, oyster culture, mixed culture, and cage fish culture in northeastern Zhanjiang Bay had a certain degree of impact on SOM, and mixed culture had more significant influences on SOM based on the high TOC contents and the significant vertical variations of TOC/TN ratio and δ15N value in the sediment of this area. This study provides new insights into the impact of aquaculture activities on SOM content.
2024, 43(6): 49-59.
doi: 10.1007/s13131-023-2243-1
Abstract:
Oxygen facilitates the breakdown of the organic material to provide energy for life. The concentration of dissolved oxygen (DO) in the water must exceed a certain threshold to support the normal metabolism of marine organisms. Located in the northern Beibu Gulf, Qinzhou Bay receives abundant freshwater and nutrients from several rivers which significantly influence the level of the dissolved oxygen. However, the spatial-temporal variations of DO as well as the associated driving mechanisms have been rarely studied through field observations. In this study, a three-dimensional coupled physical-biogeochemical model is used to investigate the spatial and seasonal variations of the DO and the associated driving mechanisms in Qinzhou Bay. The validation against observations indicates that the model can capture the seasonal and inter-annual variability of the DO concentration with the range of 5−10 mg/L. Sensitivity experiments show that the river discharges, winds and tides play crucial roles in the seasonal variability of the DO by changing the vertical mixing and stratification of the water column and the circulation pattern. In winter, the tide and wind forces have strong effects on the DO distribution by enhancing the vertical mixing, especially near the bay mouth. In summer, the river discharges play a dominant role in the DO distribution by inhibiting the vertical water exchange and delivering more nutrients to the Bay, which increases the DO depletion and results in lower DO on the bottom of the estuary salt wedge. These findings can contribute to the preservation and management of the coastal environment in the northern Beibu Gulf.
Oxygen facilitates the breakdown of the organic material to provide energy for life. The concentration of dissolved oxygen (DO) in the water must exceed a certain threshold to support the normal metabolism of marine organisms. Located in the northern Beibu Gulf, Qinzhou Bay receives abundant freshwater and nutrients from several rivers which significantly influence the level of the dissolved oxygen. However, the spatial-temporal variations of DO as well as the associated driving mechanisms have been rarely studied through field observations. In this study, a three-dimensional coupled physical-biogeochemical model is used to investigate the spatial and seasonal variations of the DO and the associated driving mechanisms in Qinzhou Bay. The validation against observations indicates that the model can capture the seasonal and inter-annual variability of the DO concentration with the range of 5−10 mg/L. Sensitivity experiments show that the river discharges, winds and tides play crucial roles in the seasonal variability of the DO by changing the vertical mixing and stratification of the water column and the circulation pattern. In winter, the tide and wind forces have strong effects on the DO distribution by enhancing the vertical mixing, especially near the bay mouth. In summer, the river discharges play a dominant role in the DO distribution by inhibiting the vertical water exchange and delivering more nutrients to the Bay, which increases the DO depletion and results in lower DO on the bottom of the estuary salt wedge. These findings can contribute to the preservation and management of the coastal environment in the northern Beibu Gulf.
2024, 43(6): 60-70.
doi: 10.1007/s13131-024-2373-0
Abstract:
Eutrophication in coastal waters has been increasing remarkably, severely impacting the water quality in mariculture bays. In this study, we conducted multiple isotopic measurements on suspended particulate nitrogen (δ15N-PN) and dissolved nitrate (δ15N-\begin{document}${\mathrm{NO}}_3^- $\end{document} ![]()
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Eutrophication in coastal waters has been increasing remarkably, severely impacting the water quality in mariculture bays. In this study, we conducted multiple isotopic measurements on suspended particulate nitrogen (δ15N-PN) and dissolved nitrate (δ15N-
2024, 43(6): 71-85.
doi: 10.1007/s13131-023-2308-9
Abstract:
Understanding the mechanism of harmful algal bloom formation is vital for effectively preventing algal bloom outbreaks in coastal environments. Karenia spp. blooms in the East China Sea show a significant correlation with nutrient regimes. However, the impact of key components of nutrients, especially dissolved organic nitrogen (DON), on the blooms of Karenia spp. is not clear. Quantitative research is still lacking. In this study, the cruise observations, field mesocosm-flask culture experiments, and a multinitrogen-tri-phytoplankton-detritus model (NTPD) are combined to reveal the quantitative influence of nutrient regimes on the shift of Prorocentrum donghaiense and Karenia spp. in the East China Sea. It has a synchronism rhythm of diatom-P. donghaiense-Karenia spp.-diatom loop in the field culture experiment, which is consistent with the results of the cruise observation. The results showed that the processes of terrigenous DON (TeDON) and dissolved inorganic nitrogen (DIN:\begin{document}$\mathrm{NO}_{3}^{-} $\end{document} ![]()
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Understanding the mechanism of harmful algal bloom formation is vital for effectively preventing algal bloom outbreaks in coastal environments. Karenia spp. blooms in the East China Sea show a significant correlation with nutrient regimes. However, the impact of key components of nutrients, especially dissolved organic nitrogen (DON), on the blooms of Karenia spp. is not clear. Quantitative research is still lacking. In this study, the cruise observations, field mesocosm-flask culture experiments, and a multinitrogen-tri-phytoplankton-detritus model (NTPD) are combined to reveal the quantitative influence of nutrient regimes on the shift of Prorocentrum donghaiense and Karenia spp. in the East China Sea. It has a synchronism rhythm of diatom-P. donghaiense-Karenia spp.-diatom loop in the field culture experiment, which is consistent with the results of the cruise observation. The results showed that the processes of terrigenous DON (TeDON) and dissolved inorganic nitrogen (DIN:
2024, 43(6): 86-95.
doi: 10.1007/s13131-024-2375-y
Abstract:
Eutrophication caused by inputs of excess nitrogen (N) has become a serious environmental problem in Hangzhou Bay (China), but the sources of this nitrogen are not well understood. In this study, the August 2019 distributions of salinity, nutrients [nitrate (\begin{document}${{\rm {NO}}_3^-} $\end{document} ![]()
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Eutrophication caused by inputs of excess nitrogen (N) has become a serious environmental problem in Hangzhou Bay (China), but the sources of this nitrogen are not well understood. In this study, the August 2019 distributions of salinity, nutrients [nitrate (
2024, 43(6): 96-106.
doi: 10.1007/s13131-024-2374-z
Abstract:
Ocean fronts play important roles in nutrient transport and in the shaping ecological patterns. Frontal zones in small bays are typically small in scale, have a complex structure, and they are spatially and temporally variable, but there are limited data on how biological communities respond to this variation. Hangzhou Bay, a medium-sized estuary in China, is an ideal place in which to study the response of plankton to small-scale ocean fronts, because three water masses (Qiantang River Diluted Water, Changjiang River Diluted Water, and the East China Sea current) converge here and form dynamic salinity fronts throughout the year. We investigate zooplankton communities, and temperature, salinity and chlorophyll a (Chl a) in Hangzhou Bay in June (wet period) and December (dry period) of 2022 and examine the dominant environmental factors that affect zooplankton community spatial variability. We then match the spatial distributions of zooplankton communities with those of salinity fronts. Salinity is the most important explanatory variable to affect zooplankton community spatial variability during both wet and dry periods, in that it contributes >60% of the variability in community structure. Furthermore, the spatial distributions of zooplankton match well with salinity fronts. During December, with weaker Qiantang River Diluted Water and a stronger secondary Changjiang River Plume, zooplankton communities occur in moderate salinity (MS, salinity range 15.6 ± 2.2) and high salinity (HS, 22.4 ± 1.7) regions, and their ecological boundaries closely match the Qiantang River Diluted Water front. In June, different zooplankton communities occur in low salinity (LS, 3.9 ± 1.0), MS (11.7 ± 3.6) and HS (21.3 ± 1.9) regions. Although the LS region occurs abnormally in the central bay rather than its apex because of the anomalous influence of rising and falling tides during the sampling period, the ecological boundaries still match salinity interfaces. Low-salinity or brackish-water zooplankter taxa are relatively more abundant in LS or MS regions, and the biomass and abundance of zooplankton is higher in the MS region.
Ocean fronts play important roles in nutrient transport and in the shaping ecological patterns. Frontal zones in small bays are typically small in scale, have a complex structure, and they are spatially and temporally variable, but there are limited data on how biological communities respond to this variation. Hangzhou Bay, a medium-sized estuary in China, is an ideal place in which to study the response of plankton to small-scale ocean fronts, because three water masses (Qiantang River Diluted Water, Changjiang River Diluted Water, and the East China Sea current) converge here and form dynamic salinity fronts throughout the year. We investigate zooplankton communities, and temperature, salinity and chlorophyll a (Chl a) in Hangzhou Bay in June (wet period) and December (dry period) of 2022 and examine the dominant environmental factors that affect zooplankton community spatial variability. We then match the spatial distributions of zooplankton communities with those of salinity fronts. Salinity is the most important explanatory variable to affect zooplankton community spatial variability during both wet and dry periods, in that it contributes >60% of the variability in community structure. Furthermore, the spatial distributions of zooplankton match well with salinity fronts. During December, with weaker Qiantang River Diluted Water and a stronger secondary Changjiang River Plume, zooplankton communities occur in moderate salinity (MS, salinity range 15.6 ± 2.2) and high salinity (HS, 22.4 ± 1.7) regions, and their ecological boundaries closely match the Qiantang River Diluted Water front. In June, different zooplankton communities occur in low salinity (LS, 3.9 ± 1.0), MS (11.7 ± 3.6) and HS (21.3 ± 1.9) regions. Although the LS region occurs abnormally in the central bay rather than its apex because of the anomalous influence of rising and falling tides during the sampling period, the ecological boundaries still match salinity interfaces. Low-salinity or brackish-water zooplankter taxa are relatively more abundant in LS or MS regions, and the biomass and abundance of zooplankton is higher in the MS region.
2024, 43(6): 107-118.
doi: 10.1007/s13131-024-2311-1
Abstract:
Massive bodies of low-oxygen bottom waters are found in coastal areas worldwide, which are detrimental to coastal ecosystems. In summer 2020, the response of coastal hypoxia to extreme weather events, including a catastrophic flooding, an extreme marine heatwave, and Typhoon Bavi, is investigated based on multiple satellite, four cruises, and mooring observations. The extensive fan-shaped hypoxia zone presents significant northward extension during July−September 2020, and is estimated as large as 13 000 km2 with rather low oxygen minimum (0.42 mg/L) during its peak in 28−30 August. This severe hypoxia is attributed to the persistent strong stratification, which is indicated by flood-induced larger amount of riverine freshwater input and subsequent marine heatwave off the Changjiang River Estuary. Moreover, the Typhoon Bavi has limited effect on the marine heatwave and coastal hypoxia in summer 2020.
Massive bodies of low-oxygen bottom waters are found in coastal areas worldwide, which are detrimental to coastal ecosystems. In summer 2020, the response of coastal hypoxia to extreme weather events, including a catastrophic flooding, an extreme marine heatwave, and Typhoon Bavi, is investigated based on multiple satellite, four cruises, and mooring observations. The extensive fan-shaped hypoxia zone presents significant northward extension during July−September 2020, and is estimated as large as 13 000 km2 with rather low oxygen minimum (0.42 mg/L) during its peak in 28−30 August. This severe hypoxia is attributed to the persistent strong stratification, which is indicated by flood-induced larger amount of riverine freshwater input and subsequent marine heatwave off the Changjiang River Estuary. Moreover, the Typhoon Bavi has limited effect on the marine heatwave and coastal hypoxia in summer 2020.
2024, 43(6): 119-130.
doi: 10.1007/s13131-023-2244-0
Abstract:
Hypoxia off the Changjiang River Estuary has been the subject of much attention, yet systematic observations have been lacking, resulting in a lack of knowledge regarding its long-term change and drivers. By revisiting the repeated surveys of dissolved oxygen (DO) and other relevant hydrographic parameters along the section from the Changjiang River Estuary to the Jeju-do in the summer from 1997 to 2014, rather different trends were revealed for the dual low-DO cores. The nearshore low-DO core, located close to the river mouth and relatively stable, shows that hypoxia has become more severe with the lowest DO descending at a rate of −0.07 mg/(L·a) and the thickness of low-DO zone rising at a rate of 0.43 m/a. The offshore core, centered around 40-m isobath but moving back and forth between 123.5°–125°E, shows large fluctuations in the minimum DO concentration, with the thickness of low-DO zone falling at a rate of −1.55 m/a. The probable factors affecting the minimum DO concentration in the two regions also vary. In the nearshore region, the decreasing minimum DO is driven by the increase in both stratification and primary productivity, with the enhanced extension of the Changjiang River Diluted Water (CDW) strengthening stratification. In the offshore region, the fluctuating trend of the minimum DO concentration indicates that both DO loss and DO supplement are distinct. The DO loss is primarily attributed to bottom apparent oxygen utilization caused by the organic matter decay and is also relevant to the advection of low-DO water from the nearshore region. The DO supplement is primarily due to weakened stratification. Our analysis also shows that the minimum DO concentration in the nearshore region was extremely low in 1998, 2003, 2007 and 2010, related to El Niño signal in these summers.
Hypoxia off the Changjiang River Estuary has been the subject of much attention, yet systematic observations have been lacking, resulting in a lack of knowledge regarding its long-term change and drivers. By revisiting the repeated surveys of dissolved oxygen (DO) and other relevant hydrographic parameters along the section from the Changjiang River Estuary to the Jeju-do in the summer from 1997 to 2014, rather different trends were revealed for the dual low-DO cores. The nearshore low-DO core, located close to the river mouth and relatively stable, shows that hypoxia has become more severe with the lowest DO descending at a rate of −0.07 mg/(L·a) and the thickness of low-DO zone rising at a rate of 0.43 m/a. The offshore core, centered around 40-m isobath but moving back and forth between 123.5°–125°E, shows large fluctuations in the minimum DO concentration, with the thickness of low-DO zone falling at a rate of −1.55 m/a. The probable factors affecting the minimum DO concentration in the two regions also vary. In the nearshore region, the decreasing minimum DO is driven by the increase in both stratification and primary productivity, with the enhanced extension of the Changjiang River Diluted Water (CDW) strengthening stratification. In the offshore region, the fluctuating trend of the minimum DO concentration indicates that both DO loss and DO supplement are distinct. The DO loss is primarily attributed to bottom apparent oxygen utilization caused by the organic matter decay and is also relevant to the advection of low-DO water from the nearshore region. The DO supplement is primarily due to weakened stratification. Our analysis also shows that the minimum DO concentration in the nearshore region was extremely low in 1998, 2003, 2007 and 2010, related to El Niño signal in these summers.
2024, 43(6): 131-141.
doi: 10.1007/s13131-024-2376-x
Abstract:
The sinking of phytoplankton is critical to organic matter transportation in the ocean and it is an essential process for the formation of coastal hypoxic zones. This study was based on a field investigation conducted during the summer of 2022 in the Changjiang River (Yangtze River) Estuary (CJE) and its adjacent waters. The settling column method was employed to measure the sinking velocity (SV) of different size fractions of phytoplankton at the surface of the sea and to analyze their environmental control mechanisms. The findings reveal significant spatial variation in phytoplankton SV (−0.55–2.41 m/d) within the CJE. High-speed sinking was predominantly observed in phosphate-depleted regions beyond the CJE front. At the same time, an upward trend was more commonly observed in the phosphate-rich regions near the CJE mouth. The SV ranges for different size-fractionated phytoplankton, including micro- (>20 μm), nano- (2–20 μm), and picophytoplankton (0.7–2 μm), were −0.50–4.74 m/d, −1.04–1.59 m/d, and −1.24–1.65 m/d, respectively. Correlation analysis revealed a significant negative correlation between SV and dissolved inorganic phosphorus (DIP), implying that the influence of DIP contributes to SV. The variations in phytoplankton alkaline phosphatase activity suggested a significant increase in SV across all size fractions in the event of phosphorus limitation. Phytoplankton communities with limited photosynthetic capacity (maximum photochemical efficience, Fv/Fm < 0.3) were found to have higher SV than that of communities with strong capacity, suggesting a link between sinking and alterations in physiological conditions due to phosphate depletion. The findings from the in situ phosphate enrichment experiments confirmed a marked decrease in SV following phosphate supplementation. These findings suggest that phosphorus limitation is the primary driver of elevated SV in the CJE. This study enhances the comprehension of the potential mechanisms underlying hypoxic zone formation in the CJE, providing novel insights into how nearshore eutrophication influences organic carbon migration.
The sinking of phytoplankton is critical to organic matter transportation in the ocean and it is an essential process for the formation of coastal hypoxic zones. This study was based on a field investigation conducted during the summer of 2022 in the Changjiang River (Yangtze River) Estuary (CJE) and its adjacent waters. The settling column method was employed to measure the sinking velocity (SV) of different size fractions of phytoplankton at the surface of the sea and to analyze their environmental control mechanisms. The findings reveal significant spatial variation in phytoplankton SV (−0.55–2.41 m/d) within the CJE. High-speed sinking was predominantly observed in phosphate-depleted regions beyond the CJE front. At the same time, an upward trend was more commonly observed in the phosphate-rich regions near the CJE mouth. The SV ranges for different size-fractionated phytoplankton, including micro- (>20 μm), nano- (2–20 μm), and picophytoplankton (0.7–2 μm), were −0.50–4.74 m/d, −1.04–1.59 m/d, and −1.24–1.65 m/d, respectively. Correlation analysis revealed a significant negative correlation between SV and dissolved inorganic phosphorus (DIP), implying that the influence of DIP contributes to SV. The variations in phytoplankton alkaline phosphatase activity suggested a significant increase in SV across all size fractions in the event of phosphorus limitation. Phytoplankton communities with limited photosynthetic capacity (maximum photochemical efficience, Fv/Fm < 0.3) were found to have higher SV than that of communities with strong capacity, suggesting a link between sinking and alterations in physiological conditions due to phosphate depletion. The findings from the in situ phosphate enrichment experiments confirmed a marked decrease in SV following phosphate supplementation. These findings suggest that phosphorus limitation is the primary driver of elevated SV in the CJE. This study enhances the comprehension of the potential mechanisms underlying hypoxic zone formation in the CJE, providing novel insights into how nearshore eutrophication influences organic carbon migration.
2024, 43(6): 142-152.
doi: 10.1007/s13131-024-2372-1
Abstract:
The nutrients from the East China Sea (ECS) through the Tsushima/Korea Strait (TS) strongly impact the ecosystem of the Japan Sea (JS). The complex origins of the Tsushima Warm Current and the various nutrient sources in the ECS result in complex spatial-temporal variations in nutrients in the TS. Using a physical-biological model with a tracking technique, we studied the effects of nutrient sources from the ECS on the TS. Among all the nutrient sources, the Kuroshio has the highest nutrient concentrations in the TS. Its maximum concentration occurs at the bottom, while those of rivers and atmospheric deposition occur at the surface, and that of the Taiwan Strait occurs in the middle layer. The nutrient transport through the TS exhibits similar seasonal variations, as does the volume transport. The transport of nutrients from the Kuroshio accounts for more than 85% of the total. The transport of nutrients from the Taiwan Strait is greater during autumn and winter. The transport of dissolved inorganic nitrogen (DIN) from both rivers and atmospheric deposition through the TS peak in August. Nutrient transport cannot be equated with volume transport. The DIN in the less saline zone originates not only from rivers but also from atmospheric deposition and the Kuroshio. The transport of nutrients from the Taiwan Strait is not as significant as its volume transport in the TS.
The nutrients from the East China Sea (ECS) through the Tsushima/Korea Strait (TS) strongly impact the ecosystem of the Japan Sea (JS). The complex origins of the Tsushima Warm Current and the various nutrient sources in the ECS result in complex spatial-temporal variations in nutrients in the TS. Using a physical-biological model with a tracking technique, we studied the effects of nutrient sources from the ECS on the TS. Among all the nutrient sources, the Kuroshio has the highest nutrient concentrations in the TS. Its maximum concentration occurs at the bottom, while those of rivers and atmospheric deposition occur at the surface, and that of the Taiwan Strait occurs in the middle layer. The nutrient transport through the TS exhibits similar seasonal variations, as does the volume transport. The transport of nutrients from the Kuroshio accounts for more than 85% of the total. The transport of nutrients from the Taiwan Strait is greater during autumn and winter. The transport of dissolved inorganic nitrogen (DIN) from both rivers and atmospheric deposition through the TS peak in August. Nutrient transport cannot be equated with volume transport. The DIN in the less saline zone originates not only from rivers but also from atmospheric deposition and the Kuroshio. The transport of nutrients from the Taiwan Strait is not as significant as its volume transport in the TS.
2024, 43(6): 153-162.
doi: 10.1007/s13131-023-2245-z
Abstract:
Petroleum hydrocarbon pollution is a global concern, particularly in coastal environments. Polycyclic aromatic hydrocarbons (PAHs) are regarded as the most toxic components of petroleum hydrocarbons. In this study, the biomonitoring and ranking effects of petroleum hydrocarbons and PAHs on the marine fish model Oryzias melastigma embryos were determined in the Jiulong River Estuary (JRE) and its adjacent waters in China. The results showed that the levels of petroleum hydrocarbons from almost all sites met the primary standard for marine seawater quality, and the concentrations of the 16 priority PAHs in the surface seawater were lower compared with those in other coastal areas worldwide. A new fish expert system based on the embryotoxicity of O. melastigma (OME-FES) was developed and applied in the field to evaluate the biological effects of petroleum hydrocarbons and PAHs. The selected physiological index and molecular indicators in OME-FES were appropriate biomarkers for indicating the harmful effects of petroleum hydrocarbons and PAHs. The outcome of OME-FES revealed that the biological effect levels of the sampling sites ranged from level Ⅰ (no stress) to level Ⅲ (medium stress), which is further corroborated by the findings of nested analysis of variance (ANOVA) models. Our results suggest that the OME-FES is an effective tool for evaluating and ranking the biological effects of marine petroleum hydrocarbons and PAHs. This method may also be applied to evaluate other marine pollutants based on its framework.
Petroleum hydrocarbon pollution is a global concern, particularly in coastal environments. Polycyclic aromatic hydrocarbons (PAHs) are regarded as the most toxic components of petroleum hydrocarbons. In this study, the biomonitoring and ranking effects of petroleum hydrocarbons and PAHs on the marine fish model Oryzias melastigma embryos were determined in the Jiulong River Estuary (JRE) and its adjacent waters in China. The results showed that the levels of petroleum hydrocarbons from almost all sites met the primary standard for marine seawater quality, and the concentrations of the 16 priority PAHs in the surface seawater were lower compared with those in other coastal areas worldwide. A new fish expert system based on the embryotoxicity of O. melastigma (OME-FES) was developed and applied in the field to evaluate the biological effects of petroleum hydrocarbons and PAHs. The selected physiological index and molecular indicators in OME-FES were appropriate biomarkers for indicating the harmful effects of petroleum hydrocarbons and PAHs. The outcome of OME-FES revealed that the biological effect levels of the sampling sites ranged from level Ⅰ (no stress) to level Ⅲ (medium stress), which is further corroborated by the findings of nested analysis of variance (ANOVA) models. Our results suggest that the OME-FES is an effective tool for evaluating and ranking the biological effects of marine petroleum hydrocarbons and PAHs. This method may also be applied to evaluate other marine pollutants based on its framework.
2024, 43(6): 163-172.
doi: 10.1007/s13131-024-2309-8
Abstract:
The sinking of diatoms is critical to the formation of oceanic biological pumps and coastal hypoxic zones. However, little is known about the effects of different nutrient restrictions on diatom sinking. In this study, we measured the sinking velocity (SV) of Thalassiosira weissflogii using a new phytoplankton video observation instrument and analyzed major biochemical components under varying nutrient conditions. Our results showed that the SV of T. weissflogii under different nutrient limitation conditions varied substantially. The highest SV of (1.77 ± 0.02) m/d was obtained under nitrate limitation, significantly surpassing that under phosphate limitation at (0.98 ± 0.13) m/d. As the nutrient limitation was released, the SV steadily decreased to (0.32 ± 0.03) m/d and (0.15 ± 0.05) m/d, respectively. Notably, under conditions with limited nitrate and phosphate concentrations, the SV values of T. weissflogii significantly positively correlated with the lipid content (P < 0.001), with R2 values of 0.86 and 0.69, respectively. The change of the phytoplankton SV was primarily related to the intracellular composition, which is controlled by nutrient conditions but did not significantly correlate with transparent extracellular polymer and biosilica contents. The results of this study help to understand the regulation of the vertical sinking process of diatoms by nutrient restriction and provide new insights into phytoplankton dynamics and their relationship with the marine nutrient structure.
The sinking of diatoms is critical to the formation of oceanic biological pumps and coastal hypoxic zones. However, little is known about the effects of different nutrient restrictions on diatom sinking. In this study, we measured the sinking velocity (SV) of Thalassiosira weissflogii using a new phytoplankton video observation instrument and analyzed major biochemical components under varying nutrient conditions. Our results showed that the SV of T. weissflogii under different nutrient limitation conditions varied substantially. The highest SV of (1.77 ± 0.02) m/d was obtained under nitrate limitation, significantly surpassing that under phosphate limitation at (0.98 ± 0.13) m/d. As the nutrient limitation was released, the SV steadily decreased to (0.32 ± 0.03) m/d and (0.15 ± 0.05) m/d, respectively. Notably, under conditions with limited nitrate and phosphate concentrations, the SV values of T. weissflogii significantly positively correlated with the lipid content (P < 0.001), with R2 values of 0.86 and 0.69, respectively. The change of the phytoplankton SV was primarily related to the intracellular composition, which is controlled by nutrient conditions but did not significantly correlate with transparent extracellular polymer and biosilica contents. The results of this study help to understand the regulation of the vertical sinking process of diatoms by nutrient restriction and provide new insights into phytoplankton dynamics and their relationship with the marine nutrient structure.
