Greenhouse gas emissions (CO<sub>2</sub>, CH<sub>4</sub> and N<sub>2</sub>O) from perialpine and alpine hydropower reservoirs

Abstract

Abstract. In eleven reservoirs located at different altitudes in Switzerland depth profiles of greenhouse gas (CO2, CH4, and N2O) concentrations were measured several times during spring and summer. Trace gas emissions were calculated using surface concentrations, wind speeds and transfer velocities. Additionally we assessed methane loss at the turbine and the methane input by inflowing water. All reservoirs were net emitters of CO2 with an average of 1030±780 mg m−2 d−1 and of methane with an average of 0.20±0.15 mg m−2 d−1. One reservoir (Lake Wohlen) emitted methane at a much higher rate (160±110 mg m−2 d−1), most of which (>98%) was due to ebullition. Only lowland reservoirs were sources for N2O (72±22 μg m−2 d−1), while the subalpine and alpine reservoirs seem to be in equilibrium with atmospheric concentrations. Methane loss at the turbine was as large as the diffusive flux from the surface for two subalpine reservoirs and around five times smaller for a lowland reservoir. The available data suggests greenhouse gas emissions from reservoirs in the Alps are minor contributors to the global greenhouse gas emissions.

Oxidation and emission of methane in a monomictic lake (Rotsee, Switzerland)

“…Our studies over the last 5 years showed that almost all of the investigated lakes and reservoirs in Switzerland are a source for methane (Diem et al 2008). Similarly for Lake Rotsee, we show that, although most of the methane is oxidized during its way through the water column, the lake surface is still oversaturated in methane compared to the atmosphere and serves as a source of methane.…”

“…They were at minimum 40 times higher (February, 80 nM) and up to 600 times higher in November (1,200 nM), demonstrating that the surface water of Lake Rotsee was always oversaturated and, therefore, a source of methane to the atmosphere. This holds true for all lakes and reservoirs in Switzerland that we have investigated over the last 5 years (Diem et al 2008). Methane emission values calculated from the boundary layer model using the formula by Cole and Caraco (1998) were two times higher than values derived using the formula from Crusius and Wanninkhof (2003) in November (Table 2).…”