Diverse drivers of long-term pCO2 increases across thirteen boreal lakes and streams

Anna C Nydahl,Marcus B Wallin,Gesa A Weyhenmeyer

doi:10.1080/20442041.2020.1740549

Anna C Nydahl, Marcus B Wallin + Show 1 more

Open Access

https://doi.org/10.1080/20442041.2020.1740549

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Abstract

ABSTRACT Understanding the mechanisms driving carbon dioxide (CO2) concentrations in inland waters is important to foresee CO2 responses to environmental change, yet knowledge gaps persist regarding which processes are the key drivers. Here we investigated possible drivers across 13 Swedish lakes and streams where the partial pressure of CO2 (pCO2) has increased over a 21-year period. Overall, we could not identify a single dominating mechanism responsible for the observed pCO2 increase. In the 8 lakes, we found that pCO2 increased, driven either by a possible dissolved organic carbon (DOC) stimulation of microbial mineralization or by water color primary production suppression. In streams, the dominating mechanism for a pCO2 increase was either a change in the carbonate system distribution or a possible nutrient-driven decrease in primary production. This is the first study to demonstrate and explain consistent positive pCO2 temporal trends in freshwater ecosystems, and our results should be taken into account when predicting future emission of CO2 from inland waters.

Highlights

Inland waters are active components of the global carbon cycle by processing, transporting, and storing vast amounts of carbon (Cole et al 1988, 2007, Lapierre and del Giorgio 2012)
4 key processes regulate pressure of CO2 (pCO2) in inland waters: (1) CO2 production through microbial and photochemical mineralization of dissolved organic carbon (DOC; e.g., Tranvik 1992, Hope et al 1996); (2) CO2 consumption via primary production (e.g., Balmer and Downing 2011); (3) distribution changes within the carbonate system as a result of pH changes (e.g., Lazzarino et al 2009); and (4) CO2 input from the surrounding catchment driven by catchment hydrology (e.g., Jones and Mulholland 1998, Striegl and Michmerhuizen 1998, Palmer et al 2001)
Using partial least squares (PLS) to predict the synchronous increase in surface water pCO2 in the studied lakes and streams, we found that total phosphorous (TP), C:N, and DOC were important variables for explaining the variability in surface water pCO2 when lakes and streams were combined in the same model

Summary

Introduction

Inland waters are active components of the global carbon cycle by processing, transporting, and storing vast amounts of carbon (Cole et al 1988, 2007, Lapierre and del Giorgio 2012). The terrestrial input of carbon (C) to inland waters has been estimated at 1.9–5.1 Pg y−1 (Cole et al 2007, Battin et al 2009, Tranvik et al 2009, Drake et al 2018). 4 key processes regulate pCO2 in inland waters: (1) CO2 production through microbial and photochemical mineralization of dissolved organic carbon (DOC; e.g., Tranvik 1992, Hope et al 1996); (2) CO2 consumption via primary production (e.g., Balmer and Downing 2011); (3) distribution changes within the carbonate system as a result of pH changes (e.g., Lazzarino et al 2009); and (4) CO2 input from the surrounding catchment driven by catchment hydrology (e.g., Jones and Mulholland 1998, Striegl and Michmerhuizen 1998, Palmer et al 2001)

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