Temporal Patterns of Methane Emissions From Two Streams With Different Riparian Connectivity

Streams are regionally important sources of CH4 to the atmosphere, but the temporal variability in and control on CH4 concentrations and emissions are not well understood. Especially, lack of long-term data hampers our ability to predict CH4 emissions from streams. Here, we present a 7-year data set of biweekly CH4 concentration and underlying potential drivers from two adjacent small German streams with contrasting riparian area characteristics. Over the 7-year study period, mean CH4 concentration and emissions were 0.20 and 0.07 mu mol L-1 and 2.01 and 0.84 mmol m(-2) d(-1) for the two streams, respectively. Our findings suggest that the combination of seasonality and topography ultimately shaped the considerable temporal variations of CH4. CH4 oxidation and production in the streams were probably of minor importance. Instead, fluctuations in CH4 concentrations likely reflected a temporal pattern of CH4 input from soils of the riparian zone with larger CH4 variations in the stream with more riparian lands. Structural equation modeling revealed dissolved organic carbon and nitrate as important predictors of CH4 concentration. However, we did not identify predictors of the considerable short-term variability, nor the explicit pathways of CH4 delivery to streams. The discrepancy of the CH4 flux between streams was likely triggered by different connectivities to riparian soils with higher CH4 emissions in the hydrologically more connected stream. Interannual comparison showed that changing hydrologic conditions, rather than warming, may impact future CH4 emissions from temperate streams. We predict that higher CH4 emissions occur in wetter years in streams with close connectivity to riparian soils.

Automated summary

The study suggests that seasonality and topography play a significant role in the temporal variations of CH4 concentrations in streams. Fluctuations in CH4 concentrations may reflect a temporal pattern of CH4 input from riparian soils, with larger variations in streams with more riparian lands.