Abstracts Category : Other

Ecosystem metabolism in salt marsh tidal creeks and ponds : applying triple oxygen isotopes and other gas tracers to novel environments

by Evan M Howard

Salt marshes are physically, chemically, and biologically dynamic environments found globally attemperate latitudes. Tidal creeks and marshtop ponds may expand at the expense of productive grass-coveredmarsh platform. It is therefore important to understand the present magnitude and drivers ofproduction and respiration in these submerged environments in order to evaluate the future role of saltmarshes as a carbon sink. This thesis describes new methods to apply the triple oxygen isotope tracer ofphotosynthetic production in a salt marsh. Additionally, noble gases are applied to constrain air-waterexchange processes which affect metabolism tracers. These stable, natural abundance tracers complementtraditional techniques for measuring metabolism. In particular, they highlight the potential importance ofdaytime oxygen sinks besides aerobic respiration, such as rising bubbles. In tidal creeks, increasingnutrients may increase both production and respiration, without any apparent change in the netmetabolism. In ponds, daytime production and respiration are also tightly coupled, but there is highbackground respiration regardless of changes in daytime production. Both tidal creeks and ponds havehigher respiration rates and lower production rates than the marsh platform, suggesting that expansion ofthese submerged environments could limit the ability of salt marshes to sequester carbon.