Forest streams are important sources for nitrous oxide emissions

• Streams and river networks are increasingly recognized as significant sources for the greenhouse gas nitrous oxide (N2O). N2O is a transformation product of nitrogenous compounds in soil, sediment and water. Agricultural areas are considered a particular hotspot for emissions because of the large input of nitrogen (N) fertilizers applied on arable land. However, there is little information on N2O emissions from forest streams although they constitute a major part of the total stream network globally. Here, we compiled N2O concentration data from low-order streams (~1,000 observations from 172 stream sites) covering a large geographical gradient in Sweden from the temperate to the boreal zone and representing catchments with various degrees of agriculture and forest coverage. Our results showed that agricultural and forest streams had comparable N2O concentrations of 1.6±2.1 and 1.3±1.8µgN/L, respectively (mean±SD) despite higher total N (TN) concentrations in agricultural streams (1,520±1,640 vs. 780±600µgN/L). Although clear patterns linking N2O concentrations and environmental variables were difficult to discern, the percent saturation of N2O in the streams was positively correlated with stream concentration of TN and negatively correlated with pH. We speculate that the apparent contradiction between lower TN concentration but similar N2O concentrations in forest streams than in agricultural streams is due to the low pH (<6) in forest soils and streams which affects denitrification and yields higher N2O emissions. An estimate of the N2O emission from low-order streams at the national scale revealed that ~1.8×109g N2O-N are emitted annually in Sweden, with forest streams contributing about 80% of the total stream emission. Hence, our results provide evidence that forest streams can act as substantial N2O sources in the landscape with 800×109gCO2-eq emitted annually in Sweden, equivalent to 25% of the total N2O emissions from the Swedish agricultural sector. © 2019 The Authors. Global Change Biology published by John Wiley & Sons Ltd

Ämnesord

NATURVETENSKAP  -- Biologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences (hsv//eng)

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Environmental Sciences (hsv//eng)

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Oceanografi, hydrologi och vattenresurser (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Oceanography, Hydrology and Water Resources (hsv//eng)

Nyckelord

agriculture

forest

greenhouse gas

nitrogen

nitrous oxide

river

stream

agriculture; forest; greenhouse gas; nitrogen; nitrous oxide; river; stream

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)