Long term follow-up of pCO2, pCH4 and emissions from Eastmain 1 boreal reservoir, and the Rupert diversion bays, Canada

Abstract

Eastmain 1 reservoir (James Bay area, Quebec, Canada) is a 600km2 boreal reservoir, created in November 2005 in the Eastmain River watershed. To increase the volume of water transiting in Eastmain 1 (EM 1), the Rupert River was diverted. Partial flooding of the Rupert diversion bays (RD) took place in 2009 and the flooding was completed in 2011. CO2 and CH4 partial pressures and emissions were monitored for 7 years on the reservoir and bays.According to field campaigns measurements at Eastmain-1 reservoir, average ice-free period pCO2 varied between 969μatm and 2230μatm, whereas the average pCO2 of the reference sampled lakes and Eastmain River stations was 592μatm (±101) before the impoundment. Contrary to pCO2, pCH4 partial pressures presented any pattern to outline after flooding of the Eastmain 1 reservoir and varied between 21 and 250μatm, with an overall average of 106μatm (SD±91). CO2 diffusive emissions at the air–water interface of the Eastmain-1 reservoir ranged between −113mg C-CO2m−2day−1 and 8237mg C-CO2m−2day−1. CH4 fluxes ranged from null to 102mg C-CH4m−2day−1. This article also shows that the impoundment of the Rupert River and the related transport of sediment and organic matter into Eastmain 1 Reservoir did not have a significant long term effect on pCO2.Remarkably, the different approaches/methods used to monitor these variables showed comparable results: a net decrease in CO2 emissions in the first three years followed by stabilization around seven years after the reservoir creation. Therefore, we advocate for long-term, around 10 years, GHG monitoring. The use of various methods, beforehand intercalibrated, offers a non-negligible flexibility, reducing the sampling costs, which should favor an increase in this kind of studies worldwide.