Stream denitrification and total nitrate uptake rates measured using a field ¹⁵N tracer addition approach

Abstract

We measured denitrification and total nitrate uptake rates in a small stream (East Fork of Walker Branch in eastern Tennessee) using a new field 15 N tracer addition and modeling approach that quantifies these rates for entire stream reaches. The field experiment consisted of an 8-h addition of 99 atom% K 15 NO 3 and a conservative solute tracer. Two 15 N tracer addition experiments were performed on consecutive days, the first under ambient NO concentra- (Ͼ99%) and comprised about 16% (Ϯ10%) of total NO uptake rate under ambient NO concentrations and about1% (Ϯ1%) of total NO 3 uptake rate with NO addition. Denitrification rate expressed on a mass flux basis was AcknowledgmentsWe thank Jeff Houser, Ramie Wilkerson, and Erica Lewis for their help in the field and laboratory; Suzanne Thomas for analysis of 15 N samples at the Marine Biological Lab; and Melody Bernot and Jennifer Tank for kindly providing the gas sampling vials. We also appreciate advice on sampling and sample analysis from Jennifer Tank and Melody Bernot. We thank David Harris, Stable Isotope Laboratory, University of California, Davis, for performing most of the 15 N analysis. We benefited greatly from discussions with Jim McClelland on transformations of the isotope data and with Wil Wollheim on model development. We also thank two anonymous reviewers for their constructive comments on an earlier version of the manuscript.

Land use influences stream nitrate uptake in the Lake Taupo catchment

“…denitrification and DNRA) such as oxygen conditions (water column DO concentrations) and organic carbon (benthic organic matter content) (Tiedje 1988), although U did increase in response to lower DO concentrations. This suggests that much of the demand for NO 3 ( in the Taupo streams during summer was probably assimilatory and is consistent with other studies showing that assimilatory processes tend to dominate instream NO 3 ( uptake (Mulholland et al 2004(Mulholland et al , 2008Arango et al 2008).…”

The saturation of N cycling in Central Plains streams: 15N experiments across a broad gradient of nitrate concentrations

“…The rate of denitrification occurring within the stream was determined by using longitudinal flux of tracer 15 N 2 with the model presented by Mulholland et al (2004). Flux of total 15 N 2 was calculated by multiplying the mole fraction of 15 N in the N 2 gas at each station during the 15 NO 3 -experiment by the measured mass of dissolved N 2 in the water, multiplied by the stream discharge.…”

Effectiveness of a Natural Headwater Wetland for Reducing Agricultural Nitrogen Loads

“…For example, Whitmire and Hamilton [45] using push-pull techniques found that nitrate added to groundwater and re-injected into wetland sediments disappeared rapidly relative to conservative tracers without any lag time, and was depleted to below detection limits (10-15 µg N L −1 ) within 5 to 20 h. In a 15 N denitrification study in a similar natural riparian wetland intercepting shallow groundwater, Burns and Nguyen [46] measured >90% removal of injected 15 NO 3 -N along a 100 cm flow path through the organic wetland soil, with essentially all of the 15 NO 3 -N-removed within 30 cm. Extensive 15 N tracer study performed on small headwater agricultural streams in the USA by Peterson [21] showed that NH 4 -N and NO x -N entering the streams was removed within tens to hundreds of meters and in one of the streams the denitrification rate was 0.045 µg N m −2 s −1 [47]. Denitrification consisted almost entirely of N 2 production (99%), with very little N 2 O production occurring.…”

“…To describe the temperature response of denitrification, we used Arrhenius equation, which is most commonly used in this case and where the temperature has a stronger effect on the denitrification at lower temperatures [4,47]. Several authors have reported that denitrification has a "breakpoint" temperature, below which denitrification rates decrease more rapidly [9,48,49].…”