Greenhouse gas emissions from lakes along a permafrost gradient in western Canada; climate feedback dominated by methane
Abstract
Small lakes with organic-rich sediments are important global sources of methane and carbon dioxide, yet emission sensitivity at high latitudes to climate change is poorly known and likely influenced by warming temperatures and permafrost thaw. In this study we monitored 20 lakes along a 1700 km transect from continuous permafrost to south of the permafrost boundary within the Mackenzie River Basin, a major global peatland region. Methane and carbon dioxide emissions from lakes had opposing trends across the permafrost gradient from north to south, with methane emissions increasing fourfold while carbon dioxide fluxes shifted from net sources to net sinks. Parallel increases from north to south in base cation, nutrient, and dissolved organic carbon concentrations suggest increased lake hydrological connectivity with both deep groundwater and shallow peatland porewater. However, methane and carbon dioxide emissions were decoupled, despite both having latitudinal trends, potentially due to different environmental drivers. Methane emissions were positively correlated with increasing water temperature and lake depth. Conversely, carbon dioxide emissions were negatively correlated with increasing nutrient and chlorophyll a concentrations, predominantly found in the sporadic and permafrost free permafrost zones. Permafrost conditions thus likely play a key role in regulating lake productivity and carbon dioxide exchange. Our results suggest that both direct impacts of temperature change and indirectly effects of permafrost thaw will interact strongly with climate warming to determine future net greenhouse gas balance. Using spatial trends and simple atmospheric perturbation models to project future lake greenhouse gas emissions suggests a positive net radiative forcing this century dominated by increasing methane emissions that is only partially offset by reduced carbon dioxide emissions.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMB018.0006K
- Keywords:
-
- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 0458 Limnology;
- BIOGEOSCIENCES;
- 0495 Water/energy interactions;
- BIOGEOSCIENCES