Title

Quantifying nitrogen process rates in a constructed wetland using natural abundance stable isotope signatures and stable isotope amendment experiments

Document Type

Article

Publication details

Erler, DV & Eyre, BD 2010, 'Quantifying nitrogen process rates in a constructed wetland using natural abundance stable isotope signatures and stable isotope amendment experiments ', Journal of Environmental Quality, vol. 39, no. 6, pp. 2191-2199.

Published version available from:

http://dx.doi.org/10.2134/jeq2010.0067

Peer Reviewed

Peer-Reviewed

Abstract

This study describes the spatial variability in nitrogen (N) transformation within a constructed wetland (CW) treating domestic effluent. Nitrogen cycling within the CW was driven by settlement and mineralization of particulate organic nitrogen and uptake of NO3 The concentration of NO3 was found to decrease, as the δ15N-NO3 signature increased, as water flowed through the CW, allowing denitrification rates to be estimated on the basis of the degree of fractionation of δ15N-NO3 Estimates of denitrification hinged on the determination of a net isotope effect (η), which was influenced by processes that enrich or deplete 15NO3 (e.g., nitrification), as well as the rate constants associated with the different processes involved in denitrification (i.e., diffusion and enzyme activity). The influence of nitrification on η was quantified; however, it remained unclear how η varied due to variability in denitrification rate constants. A series of stable isotope amendment experiments was used to further constrain the value of η and calculate rates of denitrification, and nitrification, within the wetland. The maximum calculated rate of denitrification was 956 ± 187 μmol N m−2 h−1, and the maximum rate of nitrification was 182 ± 28.9 μmol N m−2 h−1 Uptake of NO3 was quantitatively more important than denitrification throughout the wetland. Rates of N cycling varied spatially within the wetland, with denitrification dominating in the downstream deoxygenated region of the wetland. Studies that use fractionation of N to derive rate estimates must exercise caution when interpreting the net isotope effect. We suggest a sampling procedure for future natural abundance studies that may help improve the accuracy of N cycling rate estimates.