The effect of future global climate and land-use change on greenhouse gas fluxes and microbial processes in salt marshes

Project Information

MarshFlux

Grant agreement ID: 838296

DOI

10.3030/838296

Project closed

EC signature date 26 April 2019

Start date 4 January 2020

End date 3 January 2023

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 276 498,24

EU contribution

€ 276 498,24

Coordinated by

THE UNIVERSITY OF BIRMINGHAM
United Kingdom

Periodic Reporting for period 2 - MarshFlux (The effect of future global climate and land-use change on greenhouse gas fluxes and microbial processes in salt marshes)

Reporting period: 2022-01-04 to 2023-01-03

Summary of the context and overall objectives of the project

Coastal wetlands are globally important ecosystems providing valuable ecosystem services, such as carbon (C) sequestration over long timescales, affecting global C cycling and climate modulation. The amount of C sequestered, and therefore the net long-term global cooling potential of coastal marshes, however, is affected by complex biogeochemical reactions in marsh soils, which may produce and/or consume all three of the major greenhouse gases (GHGs) (carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O)). The magnitude and direction of these fluxes, and whether marsh soils act as a source or sink of GHGs, is affected by a variety of environmental factors which are predicted to vary with projected global change. MarshFlux, therefore, aims to address fundamental gaps in understanding of how the global cooling potential of coastal marshes will be affected by responses of biogeochemical reaction rates and GHG fluxes to global change. This research is critical for effective management of coastal wetlands to maintain their Blue Carbon value under future global change. This is particularly crucial as more countries look to natural climate solutions to offset their greenhouse gas emissions and there are increasing calls for blue carbon to be included in national greenhouse gas inventories.

The primary objective of MarshFlux is to determine the response of biogeochemical reaction rates and greenhouse gas (GHG) fluxes in salt marshes to a variety of environmental factors, which are expected to vary due to future global climate and land-use change. There are three research objectives to achieve this overall aim; 1) to determine the effect, both individually and combined, of changes in nutrient concentrations, salinity and temperature on GHG fluxes in soils from salt marshes along a climatic-gradient, 2) to determine the relative importance and strengths of the various pathways of N2O and CH4 production and consumption in marsh soils, under varying nutrient concentrations, salinity and temperature and 3) to develop indices of the magnitude and direction of GHG fluxes under projected future climate and land-use scenarios to allow more accurate prediction of future GHG emissions from salt marshes. These will be determined by measuring GHG fluxes from the entire marsh system, incorporating soil, water and vegetation, representative of in-situ conditions, under varying environmental stressors (nutrient concentrations, salinity, temperature) and vegetation-types.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The project investigated the effect of global environmental change on salt marsh greenhouse gas fluxes and rates of nitrogen biogeochemistry to understand the climate cooling potential and nutrient filtering potential of salt marshes now and in the future. An in-situ study in a Quebec salt marsh, showed surprisingly high CH4 emissions, higher than most published values, from one elevation zone. Salt marshes are typically expected to have low CH4 emissions, this zone was expected to have one of the lowest at this site due to high salinity. This has large implications for climate feedbacks with sea level rise, where shifting elevation zones may reduce the salt marsh climate cooling effect. This suggests that salinity alone is not always a good indicator of CH4 fluxes, as we typically assume salt marshes have low CH4 emissions because of their high salinity this could mean that the climate cooling effect of salt marshes is lower than previously thought. Incubation experiments were conducted with soils from two vegetation types (Sporobolus alterniflorus. Sporobolus pumilus) in two climatic regions (Quebec, Louisiana) at ambient and elevated treatments. The elevated treatments had increased temperature and nutrient loading to represent future global change. N2O fluxes were small and negative for all marsh sites but became large and positive under elevated treatments. A one day increase in temperature and nutrient loading was found to produce N2O emissions which offset 15-60% of the annual N2O sink. CH4 fluxes showed more complicated responses between marsh sites and were higher from the Louisiana sites, where salinity was much lower. Denitrification-derived N2O fluxes under current conditions were all negligible but these emissions increased under elevated treatments with Quebec soils switching from more complete denitrification (N2 emission) under current conditions to more incomplete denitrification (N2O emission) under future conditions. This has large implications for the future global cooling potential of salt marshes, especially as N2O is a potent greenhouse gas, with increased N2O emissions offsetting some of the climate cooling feedback from C sequestration in salt marsh soils. The project also included a novel in-situ incubation of intact cores under ambient environmental conditions conducted in a restored, UK salt marsh. We found high N2 versus N2O production resulting from denitrification, with denitrification-derived N2 fluxes much higher than denitrification-derived N2O fluxes. Despite this, the denitrification-derived N2O fluxes accounted for 80% of the total N2O emissions. Denitrification was responsible for the majority of N2O emissions from this salt marsh despite N2O being a minor product of denitrification. This indicates that the nitrogen pollution attenuation benefit provided by salt marshes may come at a cost of offsetting some of the value of the carbon sequestration potential. These results indicate the large effect future global change is likely to have on salt marsh biogeochemistry. This has large implications for the value of the carbon sequestered in salt marsh soils as the amount stored is offset by soil greenhouse gas emissions of N2O and CH4, and these results show that multiple drivers including sea level rise, increasing temperatures and increasing reactive nitrogen loading all cause increased emissions. One day of increased N2O emissions from elevated temperature and nitrogen loading offset 15-60% of the annual N2O salt marsh sink, showing that even short periods of extreme conditions are all that is needed to have large consequences. As salt marsh restoration becomes increasingly relevant and discussed by policy makers we need to fully understand the C sequestration potential of these systems before making decisions on their locations, value. The project shows the additional ecosystem service of nutrient filtration potential that salt marshes can have and considers the fate of this nitrogen, this important ecosystem service should also be considered by policy makers. The project results have been disseminated to a wide range of audiences within Europe and globally, these audiences have included the scientific community as well as stakeholders and industry partners. Results are also effectively disseminated through publications and availability of data in the Zenodo data centre.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Findings from the project have been published with further publications to follow. Results have been presented at multiple international conferences, local science/stakeholder meetings, departmental seminars and public outreach events. The work undertaken here is expected to further our understanding of how critical salt marsh ecosystem services will be affected by global change, which is crucial if we are to successfully restore and protect salt marshes to provide sevices such as flood management, habitat, carbon sequestration and nutrient filtration.

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