DIVERGENT CONTROLS ON STREAM GREENHOUSE GAS CONCENTRATIONS ACROSS A LAND USE GRADIENT

Inland waters can be significant sources of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) to the atmosphere. However, considerable uncertainty remains in regional and global estimates of greenhouse gas (GHG) emissions from freshwater ecosystems, particularly streams. Controls on GHG production in fluvial ecosystems, such as water chemistry and sediment characteristics, are also poorly understood. The main objective of this study was to quantify spatial and temporal variability in GHG concentrations in 20 streams across a landscape with considerable variation in land use and land cover. Stream water was consistently supersaturated in CO2, CH4, and N2O, suggesting that small streams are potentially large sources of GHGs to the atmosphere in this landscape. Results show that concentrations of dissolved CO2, CH4 and N2O differed in their spatial and temporal patterns and in their relationship to stream chemistry. Both bivariate and multivariate analyses revealed a unique combination of predictor variables for each gas, suggesting variation in the landscape attributes and in-stream processes that control GHG concentrations. We also provide evidence suggesting that stream sediments play an important role in fluvial CH4 dynamics. Developing an understanding of the factors controlling GHG dynamics in streams can help assess and predict how fluvial ecosystems will respond to changes in climate and land use and can be used to incorporate emissions from streams into regional and global GHG emission inventories