Nitrous oxide has a much stronger effect on the climate than carbon dioxide. Soils, peatlands and rivers are potential nitrous oxide sources. However, when, where and how much nitrous oxide is emitted into the air has not yet been sufficiently researched. A team led by Gesa Schulz, a doctoral student at the Helmholtz-Zentrum Hereon, has now studied nitrous oxide production in the Elbe estuary in greater detail and discovered real hotspots. The results, which were published in the journal Biogeosciences, can help to better assess the sources of nitrous oxide worldwide.
When it comes to climate change, most people talk about the greenhouse gas carbon dioxide, which is released in large quantities through the combustion of natural gas, crude oil and coal. What is often overlooked is that there are other potent greenhouse gases that have been far less researched. These include nitrous oxide (N2O) in particular, whose effect on the climate is almost 300 times greater than that of carbon dioxide. N2O is released primarily by biological processes and the decomposition of nitrogen compounds in agriculture, but rivers or peatlands can also emit nitrous oxide. However, where, when and how much nitrous oxide escapes into the atmosphere worldwide is still unclear. The Intergovernmental Panel on Climate Change estimates that one percent of the nitrogen that enters rivers rises into the air as nitrous oxide after biochemical conversion. But these are rough estimates.
A team led by Gesa Schulz, a doctoral student in the department Aquatic Nutrient Cycles at the Helmholtz-Zentrum Hereon, has therefore taken a closer look and measured nitrous oxide production in the entire Elbe estuary from Geesthacht, east of Hamburg, to the North Sea over several years and in different seasons. As the scientists write in the journal Biogeosciences, the Elbe estuary releases nitrous oxide throughout the year – although the amount varies from season to season.
In addition, the data that Gesa Schulz and her colleagues have collected are very important for a fundamentally better assessment of nitrous oxide production in estuaries. For the last decades, measurements in the atmosphere and the estimates of the Intergovernmental Panel on Climate Change show a continuous increase of N2O emissions. However, the N2O sources have not yet been identified or accurately measured. “We are contributing to answering these open questions,” says Gesa Schulz. “This also makes it possible to address the problem regionally through targeted measures.” Her research may also help to better calculate nitrous oxide emissions in computer climate models in the future. (Source: Hereon Press Release)
To learn more about the sources of nitrous oxide production and hotspots, read the full Hereon press release and the published study:
==> Estuaries as climate gas hotspots
Schulz, G., Sanders, T., Voynova, Y.G., Bange, H.W., & Dähnke, K. (2023): Seasonal variability of nitrous oxide concentrations and emissions in a temperate estuary. Biogeosciences, 20, 3229–3247, doi:10.5194/bg-20-3229-2023
Abstract:
Nitrous oxide (N2O) is a greenhouse gas, with a global warming potential 298 times that of carbon dioxide. Estuaries can be sources of N2O, but their emission estimates have significant uncertainties due to limited data availability and high spatiotemporal variability. We investigated the spatial and seasonal variability of dissolved N2O and its emissions along the Elbe Estuary (Germany), a well-mixed temperate estuary with high nutrient loading from agriculture. During nine research cruises performed between 2017 and 2022, we measured dissolved N2O concentrations, as well as dissolved nutrient and oxygen concentrations along the estuary, and calculated N2O saturations, flux densities, and emissions. We found that the estuary was a year-round source of N2O, with the highest emissions in winter when dissolved inorganic nitrogen (DIN) loads and wind speeds are high. However, in spring and summer, N2O saturations and emissions did not decrease alongside lower riverine nitrogen loads, suggesting that estuarine in situ N2O production is an important source of N2O. We identified two hotspot areas of N2O production: the Port of Hamburg, a major port region, and the mesohaline estuary near the maximum turbidity zone (MTZ). N2O production was fueled by the decomposition of riverine organic matter in the Hamburg Port and by marine organic matter in the MTZ. A comparison with previous measurements in the Elbe Estuary revealed that N2O saturation did not decrease alongside the decrease in DIN concentrations after a significant improvement of water quality in the 1990s that allowed for phytoplankton growth to re-establish in the river and estuary. The overarching control of phytoplankton growth on organic matter and, subsequently, on N2O production highlights the fact that eutrophication and elevated agricultural nutrient input can increase N2O emissions in estuaries.