Title:

The influence of lake productivity on methane production and ebullition from temperate and arctic lake sediments

Methane (CH4) is a potent greenhouse gas that has a large impact on climate via atmospheric warming. Freshwater lake ecosystems are a major source of CH4 emissions, which can be enhanced by eutrophication and climate warming. Few studies have investigated the impacts of lake productivity on sediment potential CH4 production and ebullition (bubbling) rates along a trophic gradient in various climates. To understand potential drivers of these relationships, we analyzed water quality samples, collected sediment cores, and measured ebullition rates at 9 temperate lakes along a trophic gradient in NH and 3 arctic lakes in northern Sweden. We identified groupings of chemical variables that significantly correlated together, which aided our understanding of the lake environments and their influence on limnological CH4 cycling. Drivers of sediment potential CH4 production and ebullition rates were suggested for correlations with water chemistry for all lakes or by ecoregion, rather than by individual trophic classes. Increased turbidity and decreased water temperature were identified as potential drivers of sediment potential CH4 production for all lakes. Increased sediment carbon for all lakes and increased sediment potential CH4 production rates for NH lakes were determined as potential drivers of ebullition. Sweden showed no significant correlations with water and sediment chemistry, highlighting the need for further investigation of sediment dynamics and increased sample size. Lake productivity, using chlorophyll α (chlα) as a proxy, was inversely correlated with sediment CH4 production and ebullition in NH, which was best explained by a seasonal decline in chlα in early summer following spring turnover and the limited sampling period in the growing season. Overall, assessment of these relationships along a trophic gradient was not ideal considering the classifications were outdated and had extremely limited sample size (n = 3 per class). Rather, assessment of whole lake chemistry provided a better understanding of lake CH4 cycling.

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