Predicting Methane Formation Rates of Freshwater Sediments in Different Biogeographic Regions

Freshwater lakes and reservoirs cover a small fraction of the Earth, however their emission of the greenhouse gas methane (CH4) from the sediment to the atmosphere is disproportionately high. Currently, there is still a limited understanding of the links between sediment characteristics and CH4 formation. Earlier studies have indicated that sediment age and nitrogen content are related to sediment CH4 formation rates, but it is uncertain such relationships are valid across gradients of sediment characteristics. We therefore measured potential CH4 formation rates in multiple layers of sediment sampled from nine lakes situated in the temperate, boreal and alpine biogeographic regions of Sweden, thus differing in productivity, catchment and climate properties. Potential CH4 formation varied over 3 orders of magnitude, and was broadly related to the quantity and reactivity of organic matter, and generally decreased with sediment depth. Sediment age and total nitrogen content were found to be the key controlling factors of potential CH4 formation rates, together explaining 62% of its variability. Moreover, the model developed from the Swedish lake sediment data was able to successfully predict the potential CH4 formation rates in reservoirs situated in different biogeographic regions of Brazil (R2 = 0.62). Therefore, potential CH4 formation rates in sediments of highly contrasting lakes and reservoirs, from Amazonia to alpine tundra, could be accurately predicted using one common model (RMSE = 1.6 in ln-units). Our model provides a valuable tool to improve estimates of CH4 emission from lakes and reservoirs, and illustrates the fundamental regulation of microbial CH4 formation by organic matter characteristics. Lakes and reservoirs are important emitters of methane, a strong greenhouse gas, to the atmosphere. Methane is produced in absence of oxygen by specific microbes that degrade the organic matter in the sediment. Currently, it is still uncertain which specific sediment properties control the production of methane, and if such properties are the same across lakes and reservoirs located in different ecosystem. To test this, we collected sediment cores from several lakes across different ecosystems in Sweden, and we measured potential methane formation rates. Methane formation rates varied greatly among lakes and was related to the quality and quantity of organic matter in the sediment. From this experiment, we calculated an empirical model that can predict methane formation rates as a function of sediment age and nitrogen content. Moreover, we found that our model could well predict potential methane formation rates in tropical reservoirs. In conclusion, sediment age and nitrogen content are universal controlling factors of methane formation rates across lakes and reservoirs in different ecosystems, from tropics to arctic tundra. Our findings provide a valuable tool to improve estimates of methane emission from lakes and reservoirs and illustrates how sediment characteristics play a crucial role in regulating methane formation rates. Methane (CH4) formation rates in lake sediment varied greatly among nine Swedish lakes located in different biogeographic regionsCH4 formation rates are related to reactivity and quantity of organic matter in the sediment, primarily to sediment age and total nitrogenCH4 formation rates measured in contrasting sediment, spanning from Amazonia to Arctic tundra could be predicted by a common empirical model