Periodic Reporting for period 1 - DYNOX (Dynamics of nitrous oxide release to the atmosphere under coastal hypoxia)
Berichtszeitraum: 2022-10-01 bis 2024-09-30
Context
The DYNOX project aimed to elucidate the role of seasonal hypoxia as a driving mechanism for the exchange of the potent greenhouse gas (GHG) nitrous oxide (N2O) across the sediment-water-air interfaces in anthropogenically impacted coastal regions. To this end, we employed a comprehensive and innovative observational approach in Lake Grevelingen (Netherlands), which is a saline coastal reservoir that experiences seasonal hypoxia as a result of limited water exchange after two dams were built in the 60s-70s. The measurement strategy consisted of novel shipboard measurements, laboratory-based incubation experiments and analysis of archived samples. This comprehensive approach allowed an unprecedented analysis of the fluxes of N2O from a shallow eutrophic coastal ecosystem and its natural variability in response to the onset of seasonal hypoxia. The results of DYNOX aimed not only close gaps in data and fundamental understanding in the field of Earth and Environmental Sciences, but also provided valuable data to the Essential Ocean Variables Framework of the Global Ocean Observing System, and will serve as a scientific basis for issuing recommendations to local authorities on priority locations for cost-effective environmental monitoring. Hence, the project results are a direct contribution to the research and innovation framework programme “Horizon Europe”, within the mission area “Healthy oceans, seas, coastal and inland waters”, as well as to the UN Sustainable Development Goals (SDG) by addressing SDG 13 “Climate Action” and SDG 14 “Life Below Water”.
Main goals
Considering the substantial lack of understanding of the biogeochemical cycling of N2O within marine sediments and the influence of seasonal hypoxia on the emissions of this gas towards the atmosphere, DYNOX employed a multidisciplinary approach to elucidate the role of seasonal hypoxia as a driving mechanism for the exchange fluxes of N2O across the sediment-water-air interfaces in an anthropogenically impacted coastal system, thereby addressing a central task in the improvement of predictions of the ocean’s role under future climate scenarios. To this end, DYNOX addressed the following specific objectives:
Objective 1: Ascertain the spatial and temporal variability of sources and sinks of N2O within coastal sediments in response to the seasonal onset of hypoxia.
Objective 2: Constrain the water column budget of N2O and its variability under seasonally changing environmental settings, as well as the vertical distribution in association with different production pathways.
Objective 3: Quantify the transfer of N2O across the sea-air interface and its temporal and spatial variability.
The DYNOX project aimed to elucidate the role of seasonal hypoxia as a driving mechanism for the exchange of the potent greenhouse gas (GHG) nitrous oxide (N2O) across the sediment-water-air interfaces in anthropogenically impacted coastal regions. To this end, we employed a comprehensive and innovative observational approach in Lake Grevelingen (Netherlands), which is a saline coastal reservoir that experiences seasonal hypoxia as a result of limited water exchange after two dams were built in the 60s-70s. The measurement strategy consisted of novel shipboard measurements, laboratory-based incubation experiments and analysis of archived samples. This comprehensive approach allowed an unprecedented analysis of the fluxes of N2O from a shallow eutrophic coastal ecosystem and its natural variability in response to the onset of seasonal hypoxia. The results of DYNOX aimed not only close gaps in data and fundamental understanding in the field of Earth and Environmental Sciences, but also provided valuable data to the Essential Ocean Variables Framework of the Global Ocean Observing System, and will serve as a scientific basis for issuing recommendations to local authorities on priority locations for cost-effective environmental monitoring. Hence, the project results are a direct contribution to the research and innovation framework programme “Horizon Europe”, within the mission area “Healthy oceans, seas, coastal and inland waters”, as well as to the UN Sustainable Development Goals (SDG) by addressing SDG 13 “Climate Action” and SDG 14 “Life Below Water”.
Main goals
Considering the substantial lack of understanding of the biogeochemical cycling of N2O within marine sediments and the influence of seasonal hypoxia on the emissions of this gas towards the atmosphere, DYNOX employed a multidisciplinary approach to elucidate the role of seasonal hypoxia as a driving mechanism for the exchange fluxes of N2O across the sediment-water-air interfaces in an anthropogenically impacted coastal system, thereby addressing a central task in the improvement of predictions of the ocean’s role under future climate scenarios. To this end, DYNOX addressed the following specific objectives:
Objective 1: Ascertain the spatial and temporal variability of sources and sinks of N2O within coastal sediments in response to the seasonal onset of hypoxia.
Objective 2: Constrain the water column budget of N2O and its variability under seasonally changing environmental settings, as well as the vertical distribution in association with different production pathways.
Objective 3: Quantify the transfer of N2O across the sea-air interface and its temporal and spatial variability.
1) Activities performed
1.1) Training
* Microprofiler usage with microsensors for chemical measurements within sediments (8-9 April 2023, Unisense, Aahrus, Denmark)
* Collection of sediment samples with UWITEC coring device, as well as set up of ship-based experiments with sediment cores (1-4 March 2023, Radboud University and research vessel "Navicula", The Netherlands)
* Measurements of inorganic nutrients in seawater samples (March-April 2023, Radboud University)
* Operation and deployment of floating chamber for trace gas flux measurements
1.2) Field campaigns
* Participation on research cruise to Lake Grevelingen/Veerse Meer (R/V Navicula Cruise N2302, 28 February - 5 March 2023)
* Participation on research cruise to Lake Grevelingen (R/V Navicula Cruise N2315, 12-14 September 2023)
* Participation on research cruise to coastal waters off Angola-Namibia (R/V Meteor Cruise M189, 16 April -13 May 2023)
1.3) Student supervision
* One master student from the Biology Programm at Radboud University
* One master student from the Marine Geosciences Programm at Utrecht University
2) Main achievements
* Acquisition of new expertise in sampling and analysis of sediment samples
* Direct experience in the deployment of floating chambers for measurments of different trace gases
* Comprehensive data set of nitrous oxide concentrations in sediments and water column, as well as ancillary measurements
* First assessment of nitrous oxide dynamics in Lake Grevelingen as a response of seasonal hypoxia
1.1) Training
* Microprofiler usage with microsensors for chemical measurements within sediments (8-9 April 2023, Unisense, Aahrus, Denmark)
* Collection of sediment samples with UWITEC coring device, as well as set up of ship-based experiments with sediment cores (1-4 March 2023, Radboud University and research vessel "Navicula", The Netherlands)
* Measurements of inorganic nutrients in seawater samples (March-April 2023, Radboud University)
* Operation and deployment of floating chamber for trace gas flux measurements
1.2) Field campaigns
* Participation on research cruise to Lake Grevelingen/Veerse Meer (R/V Navicula Cruise N2302, 28 February - 5 March 2023)
* Participation on research cruise to Lake Grevelingen (R/V Navicula Cruise N2315, 12-14 September 2023)
* Participation on research cruise to coastal waters off Angola-Namibia (R/V Meteor Cruise M189, 16 April -13 May 2023)
1.3) Student supervision
* One master student from the Biology Programm at Radboud University
* One master student from the Marine Geosciences Programm at Utrecht University
2) Main achievements
* Acquisition of new expertise in sampling and analysis of sediment samples
* Direct experience in the deployment of floating chambers for measurments of different trace gases
* Comprehensive data set of nitrous oxide concentrations in sediments and water column, as well as ancillary measurements
* First assessment of nitrous oxide dynamics in Lake Grevelingen as a response of seasonal hypoxia
The main findings of the project are:
* Lake Grevelingen is an overall source of atmospheric nitrous oxide, albeit its seasonal variability. Yet, there is also nitrous oxide depletion in both high and low-oxygen conditions. Whereas depletion under low oxygen conditions is the result of denitrification (fuelled by the microbial decomposition of high loads of organic material to the lake), the mechanisms behind nitrous oxide depletion are not fully clarified and should be investigated in future studies.
* The main source of nitrous oxide that is emitted to the atmosphere is the vertical displacement of low-oxygen waters containing high concentrations of nitrous oxide, with the implication that increased stratification and deoxygenation will potentially enhance the nitrous oxide emissions of the lake. Thus, hypoxia (i.e. oxygen depletion) is the main driver of the seasonal variability in production and emissions of nitrous oxide.
* There are elevated concentrations of nitrous oxide in bottom waters adjacent to the sediments. However these concentrations did not have a noticeable effect on the budget of nitrous oxide in the water column because of the strong stratification. This finding is important because any processes altering the stratification of the lake could therefore exacerbate its emissions to the atmosphere.
* Lake Grevelingen is an overall source of atmospheric nitrous oxide, albeit its seasonal variability. Yet, there is also nitrous oxide depletion in both high and low-oxygen conditions. Whereas depletion under low oxygen conditions is the result of denitrification (fuelled by the microbial decomposition of high loads of organic material to the lake), the mechanisms behind nitrous oxide depletion are not fully clarified and should be investigated in future studies.
* The main source of nitrous oxide that is emitted to the atmosphere is the vertical displacement of low-oxygen waters containing high concentrations of nitrous oxide, with the implication that increased stratification and deoxygenation will potentially enhance the nitrous oxide emissions of the lake. Thus, hypoxia (i.e. oxygen depletion) is the main driver of the seasonal variability in production and emissions of nitrous oxide.
* There are elevated concentrations of nitrous oxide in bottom waters adjacent to the sediments. However these concentrations did not have a noticeable effect on the budget of nitrous oxide in the water column because of the strong stratification. This finding is important because any processes altering the stratification of the lake could therefore exacerbate its emissions to the atmosphere.