Effect of rising atmospheric CO2 on sediment and water 15N interactions in experimental riparian wetland

Abstract

The experiment was conducted to ascertain net production and consumption rates of 15NH4+ and 15NO3− for water and sediment in a wetland. This was done using 15N isotope pool dilution methodology under ambient and elevated atmospheric CO2 concentrations in experimental riparian wetlands to obtain the gross N transformation rates. The 15N budget for sediment was also estimated. The results suggested that the differences in high proportion of 15N concentration in the overlying water body under elevated CO2 could be attributed to the low production and high consumption rates of 15NH4+ in sediment. The elevated CO2 effect on production and consumption of NH4+ decreased by 144 % (P = 0.014) and increased by 153 % (P = 0.009), respectively. Thereby, 15NH4+ production rates are negatively related with 15NO3− consumption rates and this accounted for the decreases in net 15NO3− consumption under CO2 enrichment in the wetland sediment by 11 % (P = 0.528). Therefore, 15NO3− production and consumption rates may strongly depend on NH4+ production. Inorganic 15N and total 15N exported from sediment to overlying water body by the effect of CO2 were 41 % (P = 0.071) and 18 % (P = 0.000), respectively. Therefore, low net 15NH4+ production and high 15NH4+ consumption rates under elevated CO2 may partly explain the significant reduction of N from the sediment.