Spatial and Seasonal Variations in Dissolved Methane Across a Large Lake
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2023-08Author
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<jats:title>Abstract</jats:title><jats:p>Lakes process large volumes of organic carbon (OC), are important sources of methane (CH<jats:sub>4</jats:sub>), and contribute to climatic warming. However, there is a lack of data from large lakes >500 km<jats:sup>2</jats:sup>, which creates uncertainty in global budgets. In this data article, we present dissolved CH<jats:sub>4</jats:sub>, OC bioreactivity measurements, water chemistry, and algal biovolumes at 11 stations across Lake Mälaren, the third largest (1,074 km<jats:sup>2</jats:sup>) Swedish lake. Total phosphorus concentrations show that during the study period the lake was classed as mesotrophic/eutrophic. Overall mean CH<jats:sub>4</jats:sub> concentration from all stations, sampled five times to cover seasonal variation, was 2.51 μg l<jats:sup>−1</jats:sup> (0.98–5.39 μg l<jats:sup>−1</jats:sup>). There was no significant seasonal variation although ranges were greatest during summer. Concentrations of CH<jats:sub>4</jats:sub> were greatest in shallow waters close to anthropogenic nutrient sources, whilst deeper, central basins had lower concentrations. Methane correlated positively with measures of lake productivity (chlorophyll <jats:italic>a</jats:italic>, total phosphorus), and negatively to water depth and oxygen concentration, with oxygen emerging as the sole significant driver in a linear mixed effects model. We collated data from other lakes >500 km<jats:sup>2</jats:sup> (<jats:italic>n</jats:italic> = 21) and found a significant negative relationship between surface area and average CH<jats:sub>4</jats:sub> concentration. Large lakes remain an understudied contributor to the global CH<jats:sub>4</jats:sub> cycle and future research efforts should aim to quantify the spatial and temporal variation in their diffusive and ebullitive emissions, and associated drivers.</jats:p>
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