Variations of the nitrate isotopic composition in the St. Lawrence River caused by seasonal changes in atmospheric nitrogen inputs.

Thibodeau, Benoit, Hélie, Jean-François and Lehmann, Moritz F. (2013) Variations of the nitrate isotopic composition in the St. Lawrence River caused by seasonal changes in atmospheric nitrogen inputs. Biogeochemistry, 115 (1-3). pp. 287-298. DOI 10.1007/s10533-013-9834-4.

[img] Text
Thibodeau et.al.pdf - Published Version
Restricted to Registered users only

Download (651Kb)

Supplementary data:

Abstract

We present 42 dual-isotope nitrate analyses of fresh water samples collected in the St. Lawrence River between June 2006 and July 2008. Measured δ15N–NO3 − and δ18O–NO3 − values correlate negatively, while δ18O–NO3 − displays no negative correlation with nitrate concentration. This suggests that nitrate uptake and/or elimination by denitrification is not the main driver of observed variations in nitrate concentration and isotopic signature in the St. Lawrence River. In addition, δ18O–NO3 − is negatively correlated with the seasonally variable δ18O of ambient water, indicating that the variation in the isotopic signature of nitrate is barely modulated by in-stream nitrate regeneration (nitrification). It rather is constrained by along-river changes in the external sources of nitrate. Given the distinct nitrogen (N) and oxygen (O) isotopic signature of atmospheric nitrate, we argue that observed seasonal variations of δ15N–NO3 − and δ18O–NO3 − in the St. Lawrence River are due to variable contributions of snowmelt-derived water. Based on a N and O isotope mass balance, we show that total nitrate loading in the St. Lawrence River is dominated by a N input from the Great Lakes (47 ± 28 %) and from nitrate regeneration of both internal and external N (48 ± 22 %). While temporal nitrate N and O isotope dynamics in the St. Lawrence River are mainly influenced by the atmospheric N input fluctuations, with an increase in atmospheric loading during spring, atmospheric N plays overall a rather insignificant role with regards to the N budget (5 ± 4 %).

Document Type: Article
Keywords: St. Lawrence ; Hydrology ; Time series ; Nitrogen ; Isotope ; Eutrophication
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1007/s10533-013-9834-4
ISSN: 0168-2563
Projects: Transdrift, Laptev Sea System
Date Deposited: 15 Jan 2014 08:25
Last Modified: 04 Jun 2014 11:18
URI: http://oceanrep.geomar.de/id/eprint/23103

Actions (login required)

View Item View Item

Document Downloads

More statistics for this item...