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CO 2 supersaturation along the aquatic conduit in Swedish watersheds as constrained by terrestrial respiration, aquatic respiration and weathering
Author(s) -
HUMBORG CHRISTOPH,
MÖRTH CARLMAGNUS,
SUNDBOM MARCUS,
BORG HANS,
BLENCKNER THORSTEN,
GIESLER REINER,
ITTEKKOT VENUGOPALAN
Publication year - 2010
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1111/j.1365-2486.2009.02092.x
Subject(s) - respiration , streams , environmental chemistry , aquatic ecosystem , environmental science , weathering , supersaturation , anoxic waters , carbon cycle , total organic carbon , groundwater , dissolved organic carbon , hydrology (agriculture) , biogeochemical cycle , ecology , chemistry , ecosystem , geology , biology , botany , geomorphology , computer network , geotechnical engineering , organic chemistry , computer science
We tested the hypothesis that CO 2 supersaturation along the aquatic conduit over Sweden can be explained by processes other than aquatic respiration. A first generalized‐additive model (GAM) analysis evaluating the relationships between single water chemistry variables and p CO 2 in lakes and streams revealed that water chemistry variables typical for groundwater input, e.g., dissolved silicate (DSi) and Mg 2+ had explanatory power similar to total organic carbon (TOC). Further GAM analyses on various lake size classes and stream orders corroborated the slightly higher explanatory power for DSi in lakes and Mg 2+ for streams compared with TOC. Both DSi and TOC explained 22–46% of the p CO 2 variability in various lake classes (0.01–>100 km 2 ) and Mg 2+ and TOC explained 11–41% of the p CO 2 variability in the various stream orders. This suggests that aquatic p CO 2 has a strong groundwater signature. Terrestrial respiration is a significant source of the observed supersaturation and we may assume that both terrestrial respiration and aquatic respiration contributed equally to p CO 2 efflux. p CO 2 and TOC concentrations decreased with lake size suggesting that the longer water residence time allow greater equilibration of CO 2 with the atmosphere and in‐lake mineralization of TOC. For streams, we observed a decreasing trend in p CO 2 with stream orders between 3 and 6. We calculated the total CO 2 efflux from all Swedish lakes and streams to be 2.58 Tg C yr −1 . Our analyses also demonstrated that 0.70 Tg C yr −1 are exported to the ocean by Swedish watersheds as HCO 3 − and CO 3 2− of which about 0.56 Tg C yr −1 is also a residual from terrestrial respiration and constitute a long‐term sink for atmospheric CO 2 . Taking all dissolved inorganic carbon (DIC) fluxes along the aquatic conduit into account will lower the estimated net ecosystem C exchange (NEE) by 2.02 Tg C yr −1 , which corresponds to 10% of the NEE in Sweden.