Ecosystem carbon exchange and nitrogen removal rates in two 33-year-old constructed salt marshes are similar to those in a nearby natural marsh 2018-11-30 to 2020-03-08 (NCEI Accession 0227949)

We conducted a year-long study with the main objective of comparing seasonal plant productivity, ecosystem respiration (ER), denitrification, and dissimilatory nitrate reduction to ammonium (DNRA) between two 33-year-old constructed marshes (CON-1, CON-2) and a nearby natural reference marsh (NAT). Marsh productivity was measured instantaneously as Net Ecosystem Exchange (NEE) using an acrylic chamber with an in-line carbon dioxide analyzer (LiCOR-820). Likewise, ER was measured in each marsh under dark conditions using the same chamber set-up. Gross ecosystem productivity (GEP) was calculated by taking the difference between NEE and ER. Negative values for NEE and GEP represent carbon dioxide flux into the marsh (i.e., CO2 sink), whereas positive ER values represent flux out of the marsh (i.e., CO2 source). Sediment samples were collected from each marsh to measure rates of dissimilatory nitrate reduction to ammonium (DNRA) and denitrification using a membrane inlet mass spectrometer. Plant biomass and soil organic matter were collected as an indicator for carbon stocks in each marsh. Nutrient stocks for phosphate, ammonium, nitrate + nitrite, and hydrogen sulfides from each marsh were measured from porewater samples taken from 10 cm depth in each marsh.