Intertidal marshes store significant amounts of coastal ‘blue carbon’ through carbon sequestration. Conventionally, gas flux measurements in intertidal salt marshes are taken on undisturbed sediment patches which show no sign of animal activity. However, salt marshes are known to harbor high densities of burrowing crabs, an intrinsic factor which is not generally taken into account using conventional flux sampling methods. Burrowing crabs have been shown to alter soil biogeochemistry. The effects related to the bioturbation activities of these crustaceans increases the complexity in understanding carbon processes as well as measuring gas fluxes in these coastal ecosystems. Each burrow is connected to the surface and increases the sediment-air interface. This creates an additional and reactive interface area which mediates gas exchange and may influence gas flux and hence its measurements. Here, we discuss the importance of Minuca pugnax burrows as an untended factor within carbon stock calculations. We hypothesized an increase in carbon dioxide release with an augmentation in M. pugnax burrow density. Using a full factorial design, a high and low organic matter salt marsh area was distinguished and within each area a bare sediment and Spartina alterniflora zone was identified at the outlet of the Herring River in Wellfleet, Massachusetts, US. The CO2 flux was measured over M. pugnax burrows at three different burrow densities within the natural salt marshes. Measurements were conducted over the course of 4 consecutive weeks (n=12).
Results/Conclusions
The CO2 flux increased exponentially with an increase in burrow density, within all areas and zones. The CO2 flux increased by 66% per m2 when burrow density tripled, within bare and high organic matter wetland sediment. This increase was found smaller within areas with S. alterniflora. Our results so far show an underestimation of CO2 flux measurements when dismissing crab burrows from CO2 gas flux assessments. Therefore, we propose a new conceptual approach to assess carbon fluxes within intertidal marshes by not overlooking important bioturbators. These ecosystems play a crucial role in mitigating global climate change because of their potential to store high amounts of carbon. Hence, we believe it is imperative to take crab burrows into account in order to accurately assess carbon fluxes and overall budgets within wetlands, and thus avoid overlooking the flux linked to this faunal component.