2023 Vol. 42, No. 8
Display Method:
2023, 42(8): .
Abstract:
2023, 42(8): 1-23.
doi: 10.1007/s13131-023-2211-9
Abstract:
Submarine groundwater discharge (SGD) is an important part in the land-sea interactions, which mainly contains three components: submarine fresh groundwater discharge (SFGD), tidal flat recirculated saline groundwater discharge (tidal flat RSGD) and subtidal recirculated saline groundwater discharge (subtidal RSGD). In order to make a more accurate assessment of the impact of SGD on coastal ecological environment, it is necessary to distinguish the main components of SGD. In this study, the Maowei Sea, located in the northern part of the Beibu Gulf, was selected as the study area. Based on the radium (Ra) tracing method, we present a new analytical method for distinguishing the three main components of SGD in this area combined with field data. The average daily flow along the coastline of the Maowei Sea of tidal flat RSGD was slightly higher than that of SFGD, and both two were on the magnitude of 1×105 m3/d. The average daily flow for the subtidal RSGD of the entire subtidal zone of the Maowei Sea reached to the magnitude of 1×106–1×107 m3/d. The long-term variation trend of terrestrial SGD is a valuable information for the study of the influence of terrigenous material on the coastal ecological environment. Based on the results of four sampling periods, it is found that the fluxes of SFGD and tidal flat RSGD in the Maowei Sea had good linear correlation with the net precipitation. As an example, January 2015 to August 2022 were selected as the study periods, and the variation trends of SFGD and tidal flat RSGD were calculated by linear function with net precipitation as the independent variable. The results showed that the flux of tidal flat RSGD was slightly higher than that of SFGD, and the difference between the two is larger in flood season while smaller in dry season. In general, in the coastal range of China, the total SGD flux in the Maowei Sea area is at a high level, and the SFGD flux is at a medium level.
Submarine groundwater discharge (SGD) is an important part in the land-sea interactions, which mainly contains three components: submarine fresh groundwater discharge (SFGD), tidal flat recirculated saline groundwater discharge (tidal flat RSGD) and subtidal recirculated saline groundwater discharge (subtidal RSGD). In order to make a more accurate assessment of the impact of SGD on coastal ecological environment, it is necessary to distinguish the main components of SGD. In this study, the Maowei Sea, located in the northern part of the Beibu Gulf, was selected as the study area. Based on the radium (Ra) tracing method, we present a new analytical method for distinguishing the three main components of SGD in this area combined with field data. The average daily flow along the coastline of the Maowei Sea of tidal flat RSGD was slightly higher than that of SFGD, and both two were on the magnitude of 1×105 m3/d. The average daily flow for the subtidal RSGD of the entire subtidal zone of the Maowei Sea reached to the magnitude of 1×106–1×107 m3/d. The long-term variation trend of terrestrial SGD is a valuable information for the study of the influence of terrigenous material on the coastal ecological environment. Based on the results of four sampling periods, it is found that the fluxes of SFGD and tidal flat RSGD in the Maowei Sea had good linear correlation with the net precipitation. As an example, January 2015 to August 2022 were selected as the study periods, and the variation trends of SFGD and tidal flat RSGD were calculated by linear function with net precipitation as the independent variable. The results showed that the flux of tidal flat RSGD was slightly higher than that of SFGD, and the difference between the two is larger in flood season while smaller in dry season. In general, in the coastal range of China, the total SGD flux in the Maowei Sea area is at a high level, and the SFGD flux is at a medium level.
2023, 42(8): 24-31.
doi: 10.1007/s13131-023-2181-y
Abstract:
Submarine groundwater discharge (SGD), which can be traced using naturally occurring radium isotopes, has been recognized as a significant nutrient source and land-ocean interaction passage for the coastal waters of the Daya Bay, China. However, uncertainties in assessing SGD fluxes must still be discussed in detail. In this study, we attempted to utilize the Monte Carlo method to evaluate the uncertainties of radium-derived SGD flux in the northeast and entirety of the Daya Bay. The results show that the uncertainties of the SGD estimate in the northeast bay are very sensitive to variations in excess radium inventories as well as radium inputs from bottom sediments, while the uncertainties of the SGD estimate for the entire bay are strongly affected by fluctuations in radium inputs from bottom sediments and radium end-members of SGD. This study will help to distinguish the key factors controlling the accuracy of SGD estimates in similar coastal waters.
Submarine groundwater discharge (SGD), which can be traced using naturally occurring radium isotopes, has been recognized as a significant nutrient source and land-ocean interaction passage for the coastal waters of the Daya Bay, China. However, uncertainties in assessing SGD fluxes must still be discussed in detail. In this study, we attempted to utilize the Monte Carlo method to evaluate the uncertainties of radium-derived SGD flux in the northeast and entirety of the Daya Bay. The results show that the uncertainties of the SGD estimate in the northeast bay are very sensitive to variations in excess radium inventories as well as radium inputs from bottom sediments, while the uncertainties of the SGD estimate for the entire bay are strongly affected by fluctuations in radium inputs from bottom sediments and radium end-members of SGD. This study will help to distinguish the key factors controlling the accuracy of SGD estimates in similar coastal waters.
2023, 42(8): 32-39.
doi: 10.1007/s13131-023-2236-0
Abstract:
As an important land-ocean interaction process, submarine groundwater discharge (SGD) is composed of multiple dynamical processes at different scales and plays an important role in the study of coastal ocean geochemical budgets. However, most of the existing studies focus on the quantification of the total groundwater discharge, few studies are about the differentiation and quantification of groundwater discharge processes at different scales (i.e., short-scale SGD and long-scale SGD). As a world-class river, the Huanghe River is highly turbid and heavily regulated by humans. These natural and anthropogenic factors have a significant impact on groundwater discharge processes in the Huanghe River Estuary (HRE). In this study, the distribution patterns of the natural geochemical tracer radium isotopes (224Ra and 223Ra) and other hydrological parameters in the HRE were investigated during four cruises. By solving the mass balance of 224Ra and 223Ra in the HRE, the long-scale SGD flux was quantified as 0.01−0.19 m/d, and the short-scale SGD flux was 0.03−0.04 m/d. The rate of short-scale SGD remained essentially constant among seasons, while the rate of long-scale SGD varied considerably at different periods and showed a synchronous trend with the variation of river discharge. The results of this study are significant for understanding the SGD dynamics in the HRE and the contribution of SGD to the ocean geochemical budgets.
As an important land-ocean interaction process, submarine groundwater discharge (SGD) is composed of multiple dynamical processes at different scales and plays an important role in the study of coastal ocean geochemical budgets. However, most of the existing studies focus on the quantification of the total groundwater discharge, few studies are about the differentiation and quantification of groundwater discharge processes at different scales (i.e., short-scale SGD and long-scale SGD). As a world-class river, the Huanghe River is highly turbid and heavily regulated by humans. These natural and anthropogenic factors have a significant impact on groundwater discharge processes in the Huanghe River Estuary (HRE). In this study, the distribution patterns of the natural geochemical tracer radium isotopes (224Ra and 223Ra) and other hydrological parameters in the HRE were investigated during four cruises. By solving the mass balance of 224Ra and 223Ra in the HRE, the long-scale SGD flux was quantified as 0.01−0.19 m/d, and the short-scale SGD flux was 0.03−0.04 m/d. The rate of short-scale SGD remained essentially constant among seasons, while the rate of long-scale SGD varied considerably at different periods and showed a synchronous trend with the variation of river discharge. The results of this study are significant for understanding the SGD dynamics in the HRE and the contribution of SGD to the ocean geochemical budgets.
Simulation of transport mechanism of radium isotopes in aquifer on the southern coast of Laizhou Bay
2023, 42(8): 40-48.
doi: 10.1007/s13131-022-2096-z
Abstract:
Naturally occurring radium (223Ra, 224Ra, 226Ra, and 228Ra) isotopes have been widely applied as geochemical tracers in marine environments, especially when estimating the submarine groundwater discharge (SGD). In this sense, the influencing factors and transport mechanism of radium isotope activity in aquifers can be key information for SGD estimation. This work evaluates the adsorption/desorption behavior of 224Ra and 226Ra in the solid-liquid phase through a leaching experiment and analysis of field data. The results suggested that radium isotope activity was positively correlated with salinity and grain size, in the case of abundant sediments. Through ion analysis, we found that the ions (Na+, Ca2+, Mg2+, and Ba2+) exchanged with radium isotopes in the process of transport. A 1-D reactive transport model was established to simulate the transport process of radium isotope in aquifers. The model successfully simulated the variation of radium isotope desorption activity with salinity and was subsequently verified in the field. This study contributes to the understanding of the geochemical behavior of radium isotopes in aquifers and provides guidance for selecting a suitable groundwater endmember in SGD estimation.
Naturally occurring radium (223Ra, 224Ra, 226Ra, and 228Ra) isotopes have been widely applied as geochemical tracers in marine environments, especially when estimating the submarine groundwater discharge (SGD). In this sense, the influencing factors and transport mechanism of radium isotope activity in aquifers can be key information for SGD estimation. This work evaluates the adsorption/desorption behavior of 224Ra and 226Ra in the solid-liquid phase through a leaching experiment and analysis of field data. The results suggested that radium isotope activity was positively correlated with salinity and grain size, in the case of abundant sediments. Through ion analysis, we found that the ions (Na+, Ca2+, Mg2+, and Ba2+) exchanged with radium isotopes in the process of transport. A 1-D reactive transport model was established to simulate the transport process of radium isotope in aquifers. The model successfully simulated the variation of radium isotope desorption activity with salinity and was subsequently verified in the field. This study contributes to the understanding of the geochemical behavior of radium isotopes in aquifers and provides guidance for selecting a suitable groundwater endmember in SGD estimation.
2023, 42(8): 49-60.
doi: 10.1007/s13131-023-2255-x
Abstract:
In this paper, for the first time, we investigated the combined effect of subsurface dams and a typical stratified aquifer (two high-permeability layers with a low-permeability layer between them) on groundwater flow and salinity distribution in a tidally influenced coastal unconfined aquifer. Subsurface dams can inhibit the invasion of saltwater, and the low-permeability layer (LPL) and tide action can increase the effect of subsurface dams and the removal rate of residual saltwater. Through sensitivity analysis, it was discovered that shifting the dam location towards the inland resulted in a reduction in the effective heights of the dam. The upper saline plume contracted with increasing dam height, and the upper boundary of LPL was moved to shallower regions. And the natural removal time increased significantly with increasing dam height and the bottom boundary of LPL was moved to deeper regions. In addition, if the dam location was close to the sea boundary and the bottom boundary of LPL was moved to deeper regions, we could increase the subsurface dam height to reduce the risks of control of saltwater intrusion. This study provides us a comprehensive understanding of the complex hydrodynamics of saltwater intrusion and provides guides for the design of subsurface dams aimed at saltwater intrusion control in stratified coastal aquifers.
In this paper, for the first time, we investigated the combined effect of subsurface dams and a typical stratified aquifer (two high-permeability layers with a low-permeability layer between them) on groundwater flow and salinity distribution in a tidally influenced coastal unconfined aquifer. Subsurface dams can inhibit the invasion of saltwater, and the low-permeability layer (LPL) and tide action can increase the effect of subsurface dams and the removal rate of residual saltwater. Through sensitivity analysis, it was discovered that shifting the dam location towards the inland resulted in a reduction in the effective heights of the dam. The upper saline plume contracted with increasing dam height, and the upper boundary of LPL was moved to shallower regions. And the natural removal time increased significantly with increasing dam height and the bottom boundary of LPL was moved to deeper regions. In addition, if the dam location was close to the sea boundary and the bottom boundary of LPL was moved to deeper regions, we could increase the subsurface dam height to reduce the risks of control of saltwater intrusion. This study provides us a comprehensive understanding of the complex hydrodynamics of saltwater intrusion and provides guides for the design of subsurface dams aimed at saltwater intrusion control in stratified coastal aquifers.
2023, 42(8): 61-76.
doi: 10.1007/s13131-023-2234-2
Abstract:
Mangrove and salt-marsh wetlands are important coastal carbon sinks. In order to quantify carbon export via pore water exchange and to evaluate subsequent fate of the exported carbon, we carried out continuous observations in a mangrove-Spartina alterniflora ecozone in the Zhangjiang River Estuary, China. The carbon fluxes via pore water exchange were estimated using 222Rn and 228Ra as tracers to be (2.15 ± 0.63) mol/(m2∙d) for dissolved inorganic carbon (DIC) and (–0.008 ± 0.07) mol/(m2∙d) for dissolved organic carbon (DOC) in the wet season and (3.02 ± 0.65) mol/(m2∙d) for DIC and (–0.15 ± 0.007) mol/(m2∙d) for DOC in the dry season in the mangrove-dominated creek (M-creek), while (2.52 ± 0.82) mol/(m2∙d) for DIC and (0.02 ± 0.09) mol/(m2∙d) for DOC in the dry season in the S. alterniflora-dominated creek (SA-creek). The negative value means that pore water was a sink of DOC in the creek. The total carbon via pore water exchange in the tidal creeks in the mangroves accounted for 41%–55% of the net carbon fixed by mangrove vegetation and was 3–4 times as much as the soil carbon accretion in the mangroves. The exported carbon in the form of DIC contributed all of the carbon outwelling from the M-creek and 79% of the carbon outwelling from the SA-creek, implying effective fixation of carbon by the wetland ecosystem. Moreover, it resulted in 54% in the dry season, 75% in the wet season of the carbon dioxide released from the M-creek to the atmosphere, and 84% of the release from the SA-creek. Therefore, quantification of pore water exchange and related soil carbon loss is essential to trace the fate of carbon fixed in intertidal wetlands.
Mangrove and salt-marsh wetlands are important coastal carbon sinks. In order to quantify carbon export via pore water exchange and to evaluate subsequent fate of the exported carbon, we carried out continuous observations in a mangrove-Spartina alterniflora ecozone in the Zhangjiang River Estuary, China. The carbon fluxes via pore water exchange were estimated using 222Rn and 228Ra as tracers to be (2.15 ± 0.63) mol/(m2∙d) for dissolved inorganic carbon (DIC) and (–0.008 ± 0.07) mol/(m2∙d) for dissolved organic carbon (DOC) in the wet season and (3.02 ± 0.65) mol/(m2∙d) for DIC and (–0.15 ± 0.007) mol/(m2∙d) for DOC in the dry season in the mangrove-dominated creek (M-creek), while (2.52 ± 0.82) mol/(m2∙d) for DIC and (0.02 ± 0.09) mol/(m2∙d) for DOC in the dry season in the S. alterniflora-dominated creek (SA-creek). The negative value means that pore water was a sink of DOC in the creek. The total carbon via pore water exchange in the tidal creeks in the mangroves accounted for 41%–55% of the net carbon fixed by mangrove vegetation and was 3–4 times as much as the soil carbon accretion in the mangroves. The exported carbon in the form of DIC contributed all of the carbon outwelling from the M-creek and 79% of the carbon outwelling from the SA-creek, implying effective fixation of carbon by the wetland ecosystem. Moreover, it resulted in 54% in the dry season, 75% in the wet season of the carbon dioxide released from the M-creek to the atmosphere, and 84% of the release from the SA-creek. Therefore, quantification of pore water exchange and related soil carbon loss is essential to trace the fate of carbon fixed in intertidal wetlands.
2023, 42(8): 77-86.
doi: 10.1007/s13131-023-2212-8
Abstract:
Subterranean estuaries (STE) are important seawater-groundwater mixing zones with complex biogeochemical processes, which play a vital role in the migration and transformation of dissolved materials. In this study, we first investigated the spatial distributions of dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorous (DIP), dissolved inorganic silicon (DSi) and metal elements (As, Ba, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) in STE including upper intertidal, seepage face and subtidal zones. We then estimated submarine groundwater discharge (SGD) and associated nutrient and metal element fluxes. From the generalized Darcy’s law method, SGD was estimated to be 30.13 cm/d, which was about 7 times larger than the inflow (4.16 cm/d). The nutrient and metal fluxes from SGD were estimated to be (5.33 ± 4.99) mmol/(m2·d) for DIN, (0.22 ± 0.03) mmol/(m2·d) for DIP, (16.20 ± 2.05) mmol/(m2·d) for DSi, (1325.06 ± 99.10) μmol/(m2·d) for Fe, (143.41 ± 25.13) μmol/(m2·d) for Mn, (304.06 ± 81.07) μmol/(m2·d) for Zn, (140.21 ± 13.33) μmol/(m2·d) for Cu, (84.49 ± 2.94) μmol/(m2·d) for Pb, (37.38 ± 5.51) μmol/(m2·d) for Ba, (27.88 ± 3.89) μmol/(m2·d) for Cr, (10.10 ± 6.33) μmol/(m2·d) for Ni, and (6.25 ± 3.45) μmol/(m2·d) for As. The nutrient and metal fluxes from SGD were relatively higher than those from the inflow, suggesting that nearshore groundwater acted as the sources of nutrients and metal elements discharging into the sea. The environmental potential pollution of coastal seawater was evaluated by pollution factor index (Pi), comprehensive water quality index (CWQI), and ecological risk index (ERI). Pb mainly caused potential danger of nearshore environment with considerable contamination (Pi = 5.78 ± 0.19), heavy pollution (CWQI = 4.09) and high ecological risk (ERI = 18.00). This study contributed to better understanding the behavior of nutrients and metal elements and improving the sustainable management of STE under the pressure of anthropogenic activities and climate change.
Subterranean estuaries (STE) are important seawater-groundwater mixing zones with complex biogeochemical processes, which play a vital role in the migration and transformation of dissolved materials. In this study, we first investigated the spatial distributions of dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorous (DIP), dissolved inorganic silicon (DSi) and metal elements (As, Ba, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) in STE including upper intertidal, seepage face and subtidal zones. We then estimated submarine groundwater discharge (SGD) and associated nutrient and metal element fluxes. From the generalized Darcy’s law method, SGD was estimated to be 30.13 cm/d, which was about 7 times larger than the inflow (4.16 cm/d). The nutrient and metal fluxes from SGD were estimated to be (5.33 ± 4.99) mmol/(m2·d) for DIN, (0.22 ± 0.03) mmol/(m2·d) for DIP, (16.20 ± 2.05) mmol/(m2·d) for DSi, (1325.06 ± 99.10) μmol/(m2·d) for Fe, (143.41 ± 25.13) μmol/(m2·d) for Mn, (304.06 ± 81.07) μmol/(m2·d) for Zn, (140.21 ± 13.33) μmol/(m2·d) for Cu, (84.49 ± 2.94) μmol/(m2·d) for Pb, (37.38 ± 5.51) μmol/(m2·d) for Ba, (27.88 ± 3.89) μmol/(m2·d) for Cr, (10.10 ± 6.33) μmol/(m2·d) for Ni, and (6.25 ± 3.45) μmol/(m2·d) for As. The nutrient and metal fluxes from SGD were relatively higher than those from the inflow, suggesting that nearshore groundwater acted as the sources of nutrients and metal elements discharging into the sea. The environmental potential pollution of coastal seawater was evaluated by pollution factor index (Pi), comprehensive water quality index (CWQI), and ecological risk index (ERI). Pb mainly caused potential danger of nearshore environment with considerable contamination (Pi = 5.78 ± 0.19), heavy pollution (CWQI = 4.09) and high ecological risk (ERI = 18.00). This study contributed to better understanding the behavior of nutrients and metal elements and improving the sustainable management of STE under the pressure of anthropogenic activities and climate change.
2023, 42(8): 87-98.
doi: 10.1007/s13131-023-2233-3
Abstract:
The transport and diffusion of substances in seawater are limited by the mixing motion of water bodies, while the main forms of mixing in offshore water bodies are advection and eddy diffusion. The eddy diffusion process of water indicates the possible transport direction of dissolved substances. However, the complex environment in the coastal zone makes it difficult to quantitatively assess the water diffusion process. 222Rn is a useful tool to trace the diffusion process of water bodies. However, studies on the 222Rn distribution and its behavior in the Beibu Gulf are scarce. In this study, the activity distribution characteristics of 222Rn in surface seawater of the Guangxi shelf area of the Beibu Gulf were measured. Based on the one-dimensional, steady-state model, the vorticity diffusion coefficient of 222Rn in the horizontal direction was calculated as (0.42−2.13) × 108 m2/d, and the offshore fluxes of 222Rn under the influence of water mixing were calculated as 2.00 × 1012 Bq/d. Correspondingly, the horizontal transport fluxes of silicate, phosphate, nitrite and nitrate were 6.28 × 10−3 mol/(m2·d), 0.10 × 10−3 mol/(m2·d), 0.20 × 10−3 mol/(m2·d) and 4.15 × 10−3 mol/(m2·d), respectively. These results indicate that the study of eddy current diffusion in offshore marine water facilitates a deeper understanding of the water mixing process and nutrient transport and migration.
The transport and diffusion of substances in seawater are limited by the mixing motion of water bodies, while the main forms of mixing in offshore water bodies are advection and eddy diffusion. The eddy diffusion process of water indicates the possible transport direction of dissolved substances. However, the complex environment in the coastal zone makes it difficult to quantitatively assess the water diffusion process. 222Rn is a useful tool to trace the diffusion process of water bodies. However, studies on the 222Rn distribution and its behavior in the Beibu Gulf are scarce. In this study, the activity distribution characteristics of 222Rn in surface seawater of the Guangxi shelf area of the Beibu Gulf were measured. Based on the one-dimensional, steady-state model, the vorticity diffusion coefficient of 222Rn in the horizontal direction was calculated as (0.42−2.13) × 108 m2/d, and the offshore fluxes of 222Rn under the influence of water mixing were calculated as 2.00 × 1012 Bq/d. Correspondingly, the horizontal transport fluxes of silicate, phosphate, nitrite and nitrate were 6.28 × 10−3 mol/(m2·d), 0.10 × 10−3 mol/(m2·d), 0.20 × 10−3 mol/(m2·d) and 4.15 × 10−3 mol/(m2·d), respectively. These results indicate that the study of eddy current diffusion in offshore marine water facilitates a deeper understanding of the water mixing process and nutrient transport and migration.
2023, 42(8): 99-112.
doi: 10.1007/s13131-023-2235-1
Abstract:
Phosphorus (P) is an essential nutrient for many organisms in the ocean, which plays a central role in the stability of ecosystems and the evolution of the environment. The distribution, occurrence and source-sink process of P in offshore waters are highly influenced by mariculture activities. P transformation in water-sediment system is the key process in P cycling, however, the mechanism is poorly documented in the coastal sea which is influenced by human activities. Based on the comprehensive surveys in the adjacent waters outside Rushan Bay in May, July and August 2014 and February 2015, the form and transformation of P in the suspended particulate matter (SPM) and surface sediment were analyzed. The results showed that contents of total P, authigenic P and organic P of SPM increased with the increase in distance from the shoreline off Rushan Bay, and the detrital-P decreased. The partition coefficient of P between water and SPM was related to the chemical activity of different forms of P, and a higher reactivity of inorganic P associated with SPM was observed. Hypoxia induced by mariculture changes the distribution and morphological composition of P in SPM and sediment in this typical aquaculture area, which can result in a conversion of sink to source of P in the sediment, thereby having a significant impact on the regional nutrient budget and associated with eutrophication.
Phosphorus (P) is an essential nutrient for many organisms in the ocean, which plays a central role in the stability of ecosystems and the evolution of the environment. The distribution, occurrence and source-sink process of P in offshore waters are highly influenced by mariculture activities. P transformation in water-sediment system is the key process in P cycling, however, the mechanism is poorly documented in the coastal sea which is influenced by human activities. Based on the comprehensive surveys in the adjacent waters outside Rushan Bay in May, July and August 2014 and February 2015, the form and transformation of P in the suspended particulate matter (SPM) and surface sediment were analyzed. The results showed that contents of total P, authigenic P and organic P of SPM increased with the increase in distance from the shoreline off Rushan Bay, and the detrital-P decreased. The partition coefficient of P between water and SPM was related to the chemical activity of different forms of P, and a higher reactivity of inorganic P associated with SPM was observed. Hypoxia induced by mariculture changes the distribution and morphological composition of P in SPM and sediment in this typical aquaculture area, which can result in a conversion of sink to source of P in the sediment, thereby having a significant impact on the regional nutrient budget and associated with eutrophication.
2023, 42(8): 113-124.
doi: 10.1007/s13131-023-2232-4
Abstract:
Submarine groundwater discharge (SGD) plays a major role as a conveyor of metals to coastal waters. However, the seasonal change of metal fluxes derived through SGD is unclear. Here, we evaluated the behaviours and fluxes of trace metals (Mn, Fe, Ba, Pb, U, Cr, Zn, Cu) in an estuary under different seasonal conditions. The behaviours of trace metals revealed that SGD was the source of Mn (3.51 mmol/(m2·d)), Fe (0.174 mmol/(m2·d)) and Ba (0.024 mmol/(m2·d)), but the Cu sink (−0.55 μmol/(m2·d)) and other metals exhibited a seasonal source‒sink conversion. The seasonal variation of dissolved organic matter and the fresh groundwater proportion in subterranean estuaries may have an important effect on metals fluxes especially for the Fe, Mn and Ba. Our result shows that the single seasonal metal fluxes estimation applied to the annual scale will cause a large deviation, up to 3.6 times for Fe, 5.5 times for Mn, and 15 times for Ba. Therefore, the influence of seasonal fluctuations on SGD-derived metal fluxes cannot be ignored, and our findings will be important for comprehending the metal budget and cycle in nearshore environment.
Submarine groundwater discharge (SGD) plays a major role as a conveyor of metals to coastal waters. However, the seasonal change of metal fluxes derived through SGD is unclear. Here, we evaluated the behaviours and fluxes of trace metals (Mn, Fe, Ba, Pb, U, Cr, Zn, Cu) in an estuary under different seasonal conditions. The behaviours of trace metals revealed that SGD was the source of Mn (3.51 mmol/(m2·d)), Fe (0.174 mmol/(m2·d)) and Ba (0.024 mmol/(m2·d)), but the Cu sink (−0.55 μmol/(m2·d)) and other metals exhibited a seasonal source‒sink conversion. The seasonal variation of dissolved organic matter and the fresh groundwater proportion in subterranean estuaries may have an important effect on metals fluxes especially for the Fe, Mn and Ba. Our result shows that the single seasonal metal fluxes estimation applied to the annual scale will cause a large deviation, up to 3.6 times for Fe, 5.5 times for Mn, and 15 times for Ba. Therefore, the influence of seasonal fluctuations on SGD-derived metal fluxes cannot be ignored, and our findings will be important for comprehending the metal budget and cycle in nearshore environment.
2023, 42(8): 125-133.
doi: 10.1007/s13131-023-2256-9
Abstract:
Hypoxia is a common phenomenon in the sea adjacent to the Changjiang River Estuary (CJE), one of the global major estuaries. Submarine groundwater discharge (SGD) is a widely recognized pathway for terrestrial materials entering the sea, and has been found to be significant off the CJE. We used a 222Rn mass balance model to estimate the SGD fluxes off the CJE and showed that it is linked to seasonal dissolved oxygen (DO) variations. Average SGD fluxes were estimated to be (0.012 ± 0.010) m3/(m2·d) in winter, (0.034 ± 0.015) m3/(m2·d) in summer, and (0.020 ± 0.010) m3/(m2·d) in autumn. We found a significant negative correlation between DO concentrations and SGD rates with groundwater discharge being highest in the summer flood season. In addition, distribution patterns of SGD and hypoxia zones in summer are spatially overlapped, indicating that SGD is an important contributor to summer hypoxia in this region.
Hypoxia is a common phenomenon in the sea adjacent to the Changjiang River Estuary (CJE), one of the global major estuaries. Submarine groundwater discharge (SGD) is a widely recognized pathway for terrestrial materials entering the sea, and has been found to be significant off the CJE. We used a 222Rn mass balance model to estimate the SGD fluxes off the CJE and showed that it is linked to seasonal dissolved oxygen (DO) variations. Average SGD fluxes were estimated to be (0.012 ± 0.010) m3/(m2·d) in winter, (0.034 ± 0.015) m3/(m2·d) in summer, and (0.020 ± 0.010) m3/(m2·d) in autumn. We found a significant negative correlation between DO concentrations and SGD rates with groundwater discharge being highest in the summer flood season. In addition, distribution patterns of SGD and hypoxia zones in summer are spatially overlapped, indicating that SGD is an important contributor to summer hypoxia in this region.
2023, 42(8): 134-146.
doi: 10.1007/s13131-023-2146-1
Abstract:
In order to characterize the features of radium isotopes in estuaries of Tianjin, a continuous survey and sampling of typical estuaries were conducted from 2013 to 2017 in this study. The activities of natural radioactive radium isotopes (223Ra, 224Ra, and 228Ra) in groundwater and surface water were measured by the radium-delayed coincidence counting (RaDeCC) system. The non-conservative behavior of the radium isotopes was investigated under hydrogeochemical conditions and urbanization. The results indicated that in terms of horizontal distribution, the activities of radium in groundwater (Hangu, Tanggu, and Dagang) showed an upward trend from north to south and demonstrated a higher figure than surface water (Haihe River and Duliujian River). Concerning the vertical distribution, the activitives of radium at a 15 m burial depth was higher than that at a 30 m burial depth in all measurements. The activities of radium isotopes in the study area increased with the increase of total dissolved solids, and their desorption behavior on Fe-Mn oxides was constrained by the redox intensity. Different hydrogeological conditions resulted in variations in the vertical profile of radium activities. The activity of radium was regulated by seasonal variation and precipitation in groundwater and surface water. In addition, the rapid urbanization has caused a significant impact on the features of radium isotopes in typical estuaries of Tianjin. Meanwhile, radium isotopes can be applied to reflect the impact of urbanization on surface water-groundwater systems. Clarifying and cleverly utilizing the relationship between behavior of radium isotopes and urbanization will promote the development of the Tianjin Binhai New Area in a healthy way.
In order to characterize the features of radium isotopes in estuaries of Tianjin, a continuous survey and sampling of typical estuaries were conducted from 2013 to 2017 in this study. The activities of natural radioactive radium isotopes (223Ra, 224Ra, and 228Ra) in groundwater and surface water were measured by the radium-delayed coincidence counting (RaDeCC) system. The non-conservative behavior of the radium isotopes was investigated under hydrogeochemical conditions and urbanization. The results indicated that in terms of horizontal distribution, the activities of radium in groundwater (Hangu, Tanggu, and Dagang) showed an upward trend from north to south and demonstrated a higher figure than surface water (Haihe River and Duliujian River). Concerning the vertical distribution, the activitives of radium at a 15 m burial depth was higher than that at a 30 m burial depth in all measurements. The activities of radium isotopes in the study area increased with the increase of total dissolved solids, and their desorption behavior on Fe-Mn oxides was constrained by the redox intensity. Different hydrogeological conditions resulted in variations in the vertical profile of radium activities. The activity of radium was regulated by seasonal variation and precipitation in groundwater and surface water. In addition, the rapid urbanization has caused a significant impact on the features of radium isotopes in typical estuaries of Tianjin. Meanwhile, radium isotopes can be applied to reflect the impact of urbanization on surface water-groundwater systems. Clarifying and cleverly utilizing the relationship between behavior of radium isotopes and urbanization will promote the development of the Tianjin Binhai New Area in a healthy way.
2023, 42(8): 147-157.
doi: 10.1007/s13131-023-2257-8
Abstract:
Subterranean estuaries, i.e., the mixing zone between terrestrial groundwater and recirculated seawater, host a wide range of microbiota. Here, field campaigns were conducted at the mouth of the subterranean estuary at the Sanggou Bay (Shandong Province, China) over four consecutive seasons at a seepage face (0−20 cm depth). The diversity of benthic microbiome was characterized via 16S rRNA gene sequencing and metagenomics, combined with physic-chemical parameters, e.g., organic carbon, total nitrogen and sulfate contents in sediments. During spring, the dominant species were assigned to the phylum Proteobacteria. Important opportunistic species was assigned to Acidobacteria, Actinobacteria and Bacteroidetes. The key components were identified to be species of the genera Pseudoalteromonas, Colwellia and Sphingobium, indicating the involvement of sediment microbiota in the degradation of sedimentary organic carbon, particularly that of pelagic origin, e.g., phytoplankton detritus and bivalve pseudo-feces. During spring, the microbial community was statistically similar along the depth profiles and among the three sampled stations. Similar spatial distributions were obtained in the remaining seasons. By contrast, the dominant species assemblages varied significantly among seasons, with key genera being Thioprofundum and Nitrosopumilus during summer and autumn and Thioprofundum and Ilumatobacter during winter. Network analysis revealed a seasonal shift in benthic nitrogen and sulfur metabolism associated with these variations in microbial community composition. Overall, our findings suggested that macro elements derived from pelagic inputs, particularly detrital phytoplankton, shaped the microbial community compositions at the seepage face, resulting in significant seasonal variations, while the influence of terrestrial materials transported by groundwater on the sediment microbiota at the seepage face found to be minor.
Subterranean estuaries, i.e., the mixing zone between terrestrial groundwater and recirculated seawater, host a wide range of microbiota. Here, field campaigns were conducted at the mouth of the subterranean estuary at the Sanggou Bay (Shandong Province, China) over four consecutive seasons at a seepage face (0−20 cm depth). The diversity of benthic microbiome was characterized via 16S rRNA gene sequencing and metagenomics, combined with physic-chemical parameters, e.g., organic carbon, total nitrogen and sulfate contents in sediments. During spring, the dominant species were assigned to the phylum Proteobacteria. Important opportunistic species was assigned to Acidobacteria, Actinobacteria and Bacteroidetes. The key components were identified to be species of the genera Pseudoalteromonas, Colwellia and Sphingobium, indicating the involvement of sediment microbiota in the degradation of sedimentary organic carbon, particularly that of pelagic origin, e.g., phytoplankton detritus and bivalve pseudo-feces. During spring, the microbial community was statistically similar along the depth profiles and among the three sampled stations. Similar spatial distributions were obtained in the remaining seasons. By contrast, the dominant species assemblages varied significantly among seasons, with key genera being Thioprofundum and Nitrosopumilus during summer and autumn and Thioprofundum and Ilumatobacter during winter. Network analysis revealed a seasonal shift in benthic nitrogen and sulfur metabolism associated with these variations in microbial community composition. Overall, our findings suggested that macro elements derived from pelagic inputs, particularly detrital phytoplankton, shaped the microbial community compositions at the seepage face, resulting in significant seasonal variations, while the influence of terrestrial materials transported by groundwater on the sediment microbiota at the seepage face found to be minor.
2023, 42(8): 158-170.
doi: 10.1007/s13131-023-2185-7
Abstract:
Subterranean estuaries (STEs) are characterized by the mixing of terrestrial fresh groundwater and seawater in coastal aquifers. Although microorganisms are important components of coastal groundwater ecosystems and play critical roles in biogeochemical transformations in STEs, limited information is available about how their community dynamics interact with hydrological, geochemical and environmental characteristics in STEs. Here, we studied bacterial and archaeal diversities and distributions with 16S rRNA-based Illumina MiSeq sequencing technology between surface water and groundwater in a karstic STE. Principal-coordinate analysis found that the bacterial and archaeal communities in the areas where algal blooms occurred were significantly separated from those in other stations without algal bloom occurrence. Canonical correspondence analysis showed that nutrients and salinity can explain the patterns of bacterial and archaeal community dynamics. The results suggest that hydrological, geochemical and environmental characteristics between surface water and groundwater likely control the bacterial and archaeal diversities and distributions in STEs. Furthermore, we found that some key species can utilize terrestrial pollutants such as nitrate and ammonia in STEs, indicating that these species (e.g., Nitrosopumilus maritimus, Limnohabitans parvus and Simplicispira limi) may be excellent candidates for in situ degradation/remediation of coastal groundwater contaminations concerned with the nitrate and ammonia. Overall, this study reveals the coupling relationship between the microbial communities and hydrochemical environments in STEs, and provides a perspective of in situ degradation/remediation for coastal groundwater quality management.
Subterranean estuaries (STEs) are characterized by the mixing of terrestrial fresh groundwater and seawater in coastal aquifers. Although microorganisms are important components of coastal groundwater ecosystems and play critical roles in biogeochemical transformations in STEs, limited information is available about how their community dynamics interact with hydrological, geochemical and environmental characteristics in STEs. Here, we studied bacterial and archaeal diversities and distributions with 16S rRNA-based Illumina MiSeq sequencing technology between surface water and groundwater in a karstic STE. Principal-coordinate analysis found that the bacterial and archaeal communities in the areas where algal blooms occurred were significantly separated from those in other stations without algal bloom occurrence. Canonical correspondence analysis showed that nutrients and salinity can explain the patterns of bacterial and archaeal community dynamics. The results suggest that hydrological, geochemical and environmental characteristics between surface water and groundwater likely control the bacterial and archaeal diversities and distributions in STEs. Furthermore, we found that some key species can utilize terrestrial pollutants such as nitrate and ammonia in STEs, indicating that these species (e.g., Nitrosopumilus maritimus, Limnohabitans parvus and Simplicispira limi) may be excellent candidates for in situ degradation/remediation of coastal groundwater contaminations concerned with the nitrate and ammonia. Overall, this study reveals the coupling relationship between the microbial communities and hydrochemical environments in STEs, and provides a perspective of in situ degradation/remediation for coastal groundwater quality management.
2023, 42(8): 171-177.
doi: 10.1007/s13131-023-2152-3
Abstract:
In the open ocean, radium isotopes are useful tracers of residence time and water-mass mixing. However, limited by the measurement resolution of commonly used gamma counters, the low activity of radium in the open ocean makes it necessary to enrich radium from large volumes of seawater and pretreat radium-enriched carriers prior to measurements. The commonly applied method of radium enrichment and pretreatment, however, has limitations of uneven coating of MnO2 on cartridges, relatively expensive cartridges, time-consuming issues during cartridge-ashing, ash loss during transfer, and changes of gamma counters efficiency caused by different ash weights. To address these issues, in this study we optimized the enrichment and pretreatment of low-activity radium prior to measurements. Firstly, we replaced commonly used acrylic cartridges with cheaper polypropylene cartridges, which took 6 h to be ashed, 42 h shorter than for acrylic cartridges. Secondly, MnO2-coated cartridges were prepared with a circulating hot acidic KMnO4 solution to ensure homogeneous coating. The radium extraction efficiency of this MnO2-coated cartridge was 20%–61% higher than that prepared by directly immersing cartridges in the solution. The radium delayed coincidence counter efficiency for MnO2-coated cartridge was stable with a moisture content of 0.05–1. Lastly, after ashing cartridges, instead of directly transferring the ash to a measurement vial, a mixture of hydroxylamine hydrochloride and hydrochloric acid was used to completely leach the ash for long-lived radium, followed by coprecipitation by BaSO4, to avoid potential loss of ash during transfer and variations in measurement geometry due to different ash weights. And the recovery of long-lived radium pretreatment was 94%–102%, which improved by 11% compared with the common method. In addition, the radium extraction efficiency of the MnO2-coated cartridge varied from 3% to 4% within the in situ pump working flow rate of 4–7 L/min, which fell within the measurement errors.
In the open ocean, radium isotopes are useful tracers of residence time and water-mass mixing. However, limited by the measurement resolution of commonly used gamma counters, the low activity of radium in the open ocean makes it necessary to enrich radium from large volumes of seawater and pretreat radium-enriched carriers prior to measurements. The commonly applied method of radium enrichment and pretreatment, however, has limitations of uneven coating of MnO2 on cartridges, relatively expensive cartridges, time-consuming issues during cartridge-ashing, ash loss during transfer, and changes of gamma counters efficiency caused by different ash weights. To address these issues, in this study we optimized the enrichment and pretreatment of low-activity radium prior to measurements. Firstly, we replaced commonly used acrylic cartridges with cheaper polypropylene cartridges, which took 6 h to be ashed, 42 h shorter than for acrylic cartridges. Secondly, MnO2-coated cartridges were prepared with a circulating hot acidic KMnO4 solution to ensure homogeneous coating. The radium extraction efficiency of this MnO2-coated cartridge was 20%–61% higher than that prepared by directly immersing cartridges in the solution. The radium delayed coincidence counter efficiency for MnO2-coated cartridge was stable with a moisture content of 0.05–1. Lastly, after ashing cartridges, instead of directly transferring the ash to a measurement vial, a mixture of hydroxylamine hydrochloride and hydrochloric acid was used to completely leach the ash for long-lived radium, followed by coprecipitation by BaSO4, to avoid potential loss of ash during transfer and variations in measurement geometry due to different ash weights. And the recovery of long-lived radium pretreatment was 94%–102%, which improved by 11% compared with the common method. In addition, the radium extraction efficiency of the MnO2-coated cartridge varied from 3% to 4% within the in situ pump working flow rate of 4–7 L/min, which fell within the measurement errors.
2023, 42(8): 178-184.
doi: 10.1007/s13131-023-2238-y
Abstract:
Radon is recognized as a powerful tracer of certain geophysical processes in marine and aquatic environments. In the past few decades, the instruments and methods for measuring radon concentration in water have been developed to some extent but still lack underwater in-situ measurements. Here we present an in-situ detection equipment for radon-in-water (pulsed ionization chamber (PIC)-radon) to measure dissolved radon in ocean and groundwater settings. The equipment has been successfully deployed in the Jiaozhou Bay in July 2022 and has achieved 14 d of unattended underwater in-situ observation. Then it was successfully placed in a groundwater monitoring well in the Laizhou Bay in November 2022 and monitored radon activities for over 30 d. The results showed that this instrument had a good indication of submarine groundwater discharge. The PIC-radon detector takes advantage of smaller size, lower power consumption, and is barely influenced by humidity, making it particularly suitable for long-term in-situ measurement, especially in harsh environments with limited human care or deployment spaces.
Radon is recognized as a powerful tracer of certain geophysical processes in marine and aquatic environments. In the past few decades, the instruments and methods for measuring radon concentration in water have been developed to some extent but still lack underwater in-situ measurements. Here we present an in-situ detection equipment for radon-in-water (pulsed ionization chamber (PIC)-radon) to measure dissolved radon in ocean and groundwater settings. The equipment has been successfully deployed in the Jiaozhou Bay in July 2022 and has achieved 14 d of unattended underwater in-situ observation. Then it was successfully placed in a groundwater monitoring well in the Laizhou Bay in November 2022 and monitored radon activities for over 30 d. The results showed that this instrument had a good indication of submarine groundwater discharge. The PIC-radon detector takes advantage of smaller size, lower power consumption, and is barely influenced by humidity, making it particularly suitable for long-term in-situ measurement, especially in harsh environments with limited human care or deployment spaces.
2023, 42(8): 185-189.
doi: 10.1007/s13131-023-2183-9
Abstract:
Radon (Rn) is a naturally occurring radioactive inert gas in nature, and 222Rn has been routinely used as a powerful tracer in various aquatic environmental research on timescales of hours to days, such as submarine groundwater discharge. Here we developed a new approach to measure 222Rn in discrete water samples with a wide range of 222Rn concentrations using a Pulsed Ionization Chamber (PIC) Radon Detector. The sensitivity of the new PIC system is evaluated at 6.06 counts per minute for 1 Bq/L when a 500 mL water sample volume is used. A robust logarithmic correlation between sample volumes, ranging from 250 mL to 5000 mL, and system sensitivity obtained in this study strongly suggests that this approach is suitable for measuring radon concentration levels in various natural waters. Compared to the currently available methods for measuring radon in grab samples, the PIC system is cheaper, easier to operate and does not require extra accessories (e.g., drying tubes etc.) to maintain stable measurements throughout the counting procedure.
Radon (Rn) is a naturally occurring radioactive inert gas in nature, and 222Rn has been routinely used as a powerful tracer in various aquatic environmental research on timescales of hours to days, such as submarine groundwater discharge. Here we developed a new approach to measure 222Rn in discrete water samples with a wide range of 222Rn concentrations using a Pulsed Ionization Chamber (PIC) Radon Detector. The sensitivity of the new PIC system is evaluated at 6.06 counts per minute for 1 Bq/L when a 500 mL water sample volume is used. A robust logarithmic correlation between sample volumes, ranging from 250 mL to 5000 mL, and system sensitivity obtained in this study strongly suggests that this approach is suitable for measuring radon concentration levels in various natural waters. Compared to the currently available methods for measuring radon in grab samples, the PIC system is cheaper, easier to operate and does not require extra accessories (e.g., drying tubes etc.) to maintain stable measurements throughout the counting procedure.
