Spatial variability of CH4 and CO2 emissions

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Institute for Landscape Ecology, WWU Münster. Introduction. Recent studies have shown ... controlling greenhouse gas emissions. CH4 and CO2 fluxes were ...

Leandra Praetzel

Poster No. EGU2017-14870

Marcel Schmiedeskamp, Tanja Broder, Ulrike Metzelder, Caroline Hüttemann, Laura Jansen, Ronya Wallis, Klaus-Holger Knorr, and Christian Blodau Ecohydrology & Biogeochemistry Group Institute for Landscape Ecology, WWU Münster

Spatial and temporal variability of greenhouse gas emissions from a small and shallow temperate lake Methods Recent studies have shown that small and often shallow inland waters (< 100 ha) capture crucially larger areas than previously assumed. Due to their frequency and high metabolic activity they are assumed to be significant sources of carbon dioxide (CO2) and methane (CH4) to the atmosphere and exhibit feedback mechanisms with climate change.

© Marcel Schmiedeskamp

So far, little is known about the spatial and temporal variability of carbon dioxide (CO2) and methane (CH4) emissions and in-lake dynamics of CH4 production and oxidation in small, epilimnetic lakes in the temperate zone. Of particular interest is the potential occurrence of “hot spots” and “hot moments” that could contribute significantly to total emissions as well as biological, chemical and physical controls on emissions, production and oxidation processes.

CH4 flux (µmol m-2 h-1)

CO2 flux (µmol m-2 h-1)

Spatial variability of CH4 and CO2 emissions

site

CH4 emissions were – against our expectations – highest in the center of the lake and also showed a higher variability there. Ebullition accounted between 43 and 85 % of total fluxes at sites T1, T3 and T4, whereas the other sites were dominated by diffusive flux. CO2 emissions were highly variable between and within the sites especially at sites T3 and T4. Both slight uptake as well as high emissions rates were observed.

Fig. 2: CH4 and CO2 emissions from Lake Windsborn measured with a floating chamber in summer 2015

Lake Windsborn is a 1.4 ha large and max. 1.5 m deep crater lake located in the Eifel uplands in South-west Germany. As it has a small catchment area (8 ha), lies isolated from the groundwater and has no surficial inflows, it serves well as a model systems for the identification of factors and processes controlling greenhouse gas emissions. CH4 and CO2 fluxes were measured with small Fig. 1: Location of floating chambers, meteorological data and CO2 the study area and water concentrations were monitored from a © Google Earth sites floating platform in the center of the lake. To cover the spatial variability of emissions, eight sites had been selected covering both central and littoral parts of the lake (see Fig. 1). Chamber flux measurements were carried out with a high temporal resolution infra-red Greenhouse Gas Analyzer in summer 2015, CO2 surface water concentrations were measured from 2015 to 2017.

© Marcel Schmiedeskamp

© Andreas Malkus

Temporal variability of CO2 surface water concentrations

CO2 concentration (ppm)

Introduction

Conclusions & Outlook The greenhouse gas emissions from lake Windsborn seem to differ both spatially between littoral and central parts of the lake and temporally on an annual and diurnal scale. To better understand the driving factors and processes of CH4 and CO2 emissions and their variability we will: I. Study emissions at a higher spatial and temporal resolution II. Examine CH4 oxidation and production patterns in the sediments and water column at different sites of the lake III. Survey biological, chemical and physical parameters of the lakes and its catchment, and IV. Compare this model system to other lakes

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hour

Fig. 3: CO2 surface water concentrations measured at the center of Lake Windsborn. Annual cycle of data from 2015 – 2017 (left) and diurnal cycle of data from 2015. Bold lines are the median, boxes show the 25 and 75 percentile, whiskers indicate minima and maxima within 1.5 times the interquartile range. Single points show outlier.

Regarding the temporal scale, the lake is mostly oversaturated with CO2 compared to atmospheric concentrations, which indicates a positive efflux of CO2 from the lake to the atmosphere. It only acts as a CO2 sink in spring and early summer. CO2 concentrations generally showed a positive correlation with surface water temperature and pH and a negative correlation with photosynthetic active radiation (PAR) and wind speed.

Project Quantification and controls of carbon fluxes of the Windsborn lake (Eifel) http://www.uni-muenster.de/Ecohydrology/en/kohlenstofffluesse_seen.html

Contact information: [email protected]