The effects of elevated CO2and eutrophication on surface elevation gain in a European salt marsh.
Salt marshes can play a vital role in mitigating the effects of global environmental change by dissipating incident storm wave energy and, through accretion, tracking increasing water depths consequent upon sea level rise. Atmospheric CO2concentrations and nutrient availability are two key variables that can affect the biological processes that contribute to marsh surface elevation gain. We measured the effects of CO2concentrations and nutrient availability on surface elevation change in intact mixed-species blocks of UK salt marsh using six open-top chambers receiving CO2-enriched (800 ppm) or ambient (400 ppm) air. We found more rapid surface elevation gain in elevated CO2conditions: an average increase of 3.4 mm over the growing season relative to ambient CO2. Boosted regression analysis to determine the relative influence of different parameters on elevation change identified that a 10% reduction in microbial activity in elevated CO2-grown blocks had a positive influence on elevation. The biomass of Puccinellia maritima also had a positive influence on elevation, while other salt marsh species (e.g. Suaeda maritima) had no influence or a negative impact on elevation. Reduced rates of water use by the vegetation in the high CO2treatment could be contributing to elevation gain, either directly through reduced soil shrinkage or indirectly by decreasing microbial respiration rates due to lower redox levels in the soil. Eutrophication did not influence elevation change in either CO2treatment despite doubling aboveground biomass. The role of belowground processes (transpiration, root growth and decomposition) in the vertical adjustment of European salt marshes, which are primarily minerogenic in composition, could increase as atmospheric CO2concentrations rise and should be considered in future wetland models for the region. Elevated CO2conditions could enhance resilience in vulnerable systems such as those with low mineral sediment supply or where migration upwards within the tidal frame is constrained.
Cambridge Coastal Research Unit, Department of Geography, University of Cambridge, Downing Site, Cambridge, CB2 3EN, United Kingdom.|School of Earth, Atmosphere and Environment, Monash University, Clayton, VIC, 3800, Australia.
Ruth
R
Reef
Cambridge Coastal Research Unit, Department of Geography, University of Cambridge, Downing Site, Cambridge, CB2 3EN, United Kingdom.
Tom
T
Spencer
Cambridge Coastal Research Unit, Department of Geography, University of Cambridge, Downing Site, Cambridge, CB2 3EN, United Kingdom.
Iris
I
Mӧller
School of Biological Science, The University of Queensland, St Lucia, QLD, 4072, Australia.
Catherine E
CE
Lovelock
Cambridge Coastal Research Unit, Department of Geography, University of Cambridge, Downing Site, Cambridge, CB2 3EN, United Kingdom.
Elizabeth K
EK
Christie
Cambridge Coastal Research Unit, Department of Geography, University of Cambridge, Downing Site, Cambridge, CB2 3EN, United Kingdom.
Anna L
AL
McIvor
Cambridge Coastal Research Unit, Department of Geography, University of Cambridge, Downing Site, Cambridge, CB2 3EN, United Kingdom.
Ben R
BR
Evans
Cambridge Coastal Research Unit, Department of Geography, University of Cambridge, Downing Site, Cambridge, CB2 3EN, United Kingdom.
James A
JA
Tempest
D018533:Biomass; D002245:Carbon Dioxide; D005068:Eutrophication; D006109:Poaceae; D012987:Soil; D053833:Wetlands
D012987:Soil; D002245:Carbon Dioxide

Puccinellia maritima
; United Kingdom; boosted regression analysis; carbon dioxide; climate change; salt marsh; sea level rise; wetland