Analysis of Organic Matter Decomposition in the Salt Marshes of the Venice Lagoon (Italy) Using Standard Litter Bags

Abstract

Tidal salt marshes are widespread along the World's coasts, and are ecologically and economically important as they provide several valuable ecosystem services. In particular, their significant primary production, coupled with sustained vertical accretion rates, enables marshes to sequester and store large amounts of organic carbon and makes them one of the most carbon-rich ecosystems on Earth. Organic carbon accumulation results from the balance between inputs, i.e. organic matter produced by local plants or imported, and outputs through decomposition and erosion. Additionally, organic matter deposition actively contributes to marsh vertical accretion, thus critically affecting the resilience of marsh ecosystems to rising relative sea levels. A better understanding of organic-matter dynamics in salt marshes is key to address salt-marsh conservation issues and to elucidate marsh importance within the global carbon cycle. Toward this goal, we empirically derived rates of organic matter decomposition by burying 712 commercially available tea bags at different marshes in the microtidal Venice Lagoon (Italy), and by analyzing them following the Tea Bag Index protocol. We find values of the decomposition rate (k) and stabilization factor (S) equal to 0.012±0.003 day -1 and 0.15±0.063, respectively. Water temperature critically affects organic matter decomposition, enhancing decomposition rates by 8% per °C on average. We argue that, at least in the short term, the amount of undecomposed organic matter that actively contributes to carbon sequestration and marsh vertical accretion strongly depends on the initial organic matter quality, which is a function of marsh and vegetation characteristics.

Blue Carbon assessment in the salt marshes of the Venice Lagoon: dimensions, variability and influence of storm-surge regulation.

“…For each core, soil samples were taken at 12 depths (0, 5,10,15,20,25,30,35,40,45,50, 75 cm from the surface, see 57) and subsamples were prepared for different analyses, including soil density, organic matter and carbon content.…”

“…Plant tissues, litter and organic matter (OM) are buried into the soil by mineral sediment settling on the marsh, thus also contributing to offset sea-level rise (12)(13)(14)(15). Moreover, by inhibiting microbial aerobic activity and by slowing down decomposition (20), tidal conditions further foster soil organic carbon (SOC) preservation, thus locking away carbon from the atmosphere over centennial to millennial time scales (5).…”

“…However, climate change and anthropogenic disturbances dramatically alter salt-marsh biomorphodynamic equilibrium, jeopardizing their survival (4,6,21,22), affecting carbon sequestration (23), and even shifting marshes from net sinks to sources of carbon (4,18). Global warming, increased carbon dioxide concentration, and sea-level rise have the potential to alter biomass production, organic soil decomposition and surface accretion (19,21,24,25). Human activities directly and indirectly interfere with marsh dynamics through land use changes and alterations of nutrient inputs, sediment dynamics and subsidence rates (21,26).…”

Analysis of Organic Matter Decomposition in the Salt Marshes of the Venice Lagoon (Italy) Using Standard Litter Bags

“…All data needed to evaluate the conclusions in the paper are available at https://researchdata.cab.unipd.it/ id/eprint/871 (Puppin et al, 2022). Meteorological and tide level data for the Venice Lagoon are also freely available at www.comune.venezia.it/content/dati-dalle-stazioni-rilevamento and www.venezia.isprambiente.it/ rete-meteo-mareografica.…”