Wetland soils and hyporheic zones at the base of streams develop redox gradients, producing regions of aerobic and anaerobic microbial activity that make them active sites for denitrification. Laboratory studies on pure cultures have highlighted that the bioavailability of Cu may limit denitrification, especially the step involving conversion of N2O to N2. However, the factors controlling this copper limitation in natural aquatic systems, such as wetlands and stream sediments, are not well understood. In this study, we collected soils and sediments from three different natural aquatic systems, a stream sediment in Tennessee, riparian wetlands in South Carolina and marsh wetlands in Illinois, to evaluate if the natural Cu concentrations at the sites limit denitrification. The background concentrations of Cu were either less than or close to the optimal concentration required for denitrification in pure cultures. Consequently, we quantified the uptake behavior of Cu on the selected sediments to obtain an estimate of the environmental inputs that may bring its bioavailable concentrations to optimal levels required for denitrification. To better understand the role of Cu limitation on denitrification, microcosm experiments were conducted under anoxic conditions using artificial stream water containing an initial nitrate concentration of 1 mM. Experiments were conducted with no copper addition and with Cu additions that yielded dissolved concentration in either the range of 10-60 nM or 100-600 nM. Samples obtained from riparian wetland and stream sediment showed N2O accumulation in microcosms without Cu addition, however the concentration of N2O in the headspace decreased significantly in the microcosms amended with Cu. The addition of Cu did not affect the denitrification process in marsh wetland samples as no N2O accumulation was observed in any of the studied microcosms. A kinetic model was used to estimate the rates of nitrate, nitrite and N2O reduction in microcosms with and without Cu addition for all the studied sites. The study suggests that Cu limitation can inhibit denitrification in natural systems; and hence addition of Cu in trace amounts can help decrease the N2O emissions from the wetland soils and hyporheic zone sediments.

Role of copper availability on denitrification in natural aquatic systems

ACS Spring Meeting 2021

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