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Tidal wetland fluxes of particulate organic matter and carbon (POM, POC) are important terms in global budgets but remain poorly constrained. Given the link between sediment fluxes and wetland stability, POM and POC fluxes should also be related to stability. We measured POM and POC fluxes in eight microtidal salt marsh channels, with net POM fluxes ranging between -12133 (export) and10228 (import)gOMm(-2)year(-1) and net POC fluxes ranging between -5214 and4312gCm(-2)year(-1). A regression employing two measures of stability, the unvegetated-vegetated marsh ratio (UVVR) and elevation, explained >95% of the variation in net fluxes. The regression indicates that marshes with lower elevation and UVVR import POM and POC while higher elevation marshes with high UVVR export POM and POC. We applied these relationships to marsh units within Barnegat Bay, New Jersey, USA, finding a net POM import of 2,3551,570Mg OM/year (15 +/- 10g OMm(-2)year(-1)) and a net POC import of 1,263 +/- 632Mg C/year (8 +/- 4g Cm(-2)year(-1)). The magnitude of this import was similar to an estimate of POM and POC export due to edge erosion (-2,535Mg OM/year and-1,291Mg C/year), suggesting that this system may be neutral from a POM and POC perspective. In terms of a net budget, a disintegrating wetland should release organic material, while a stable wetland should trap material. This study quantifies that concept and demonstrates a linkage between POM/POC flux and geomorphic stability.

Plain Language Summary The worldwide budgets of organic material, especially carbon, are important to understand future climate change, environmental health, and habitat change. Tidal wetlands and salt marshes are large banks of organic material and carbon that can store material over centuries or lose it quickly if they are eroded by waves or submerged by sea level rise. We measured the deposits and withdrawals from this organic material bank, at eight salt marshes across the United States. We found a wide range of deposits and withdrawals and determined that the budget is related to how stable the marsh is. Marshes with a lot of plants and more height were more likely to have deposits of organic materials, while marshes with less plants and less height had withdrawals. These results will help complete the accounting of organic material and carbon in worldwide budgets.