Lakes are considered the second largest natural source of atmospheric methane (CH4). However, current estimates are still uncertain and do not account for diel variability of CH4 emissions. In this study, we performed high-resolution measurements of CH4 flux from several lakes, using an automated and sensor-based flux measurement approach (in total 4,580 measurements), and demonstrated a clear and consistent diel lake CH4 flux pattern during stratification and mixing periods. The maximum of CH4 flux were always noted between 10:00 and 16:00, whereas lower CH4 fluxes typically occurred during the nighttime (00:00–04:00). Regardless of the lake, CH4 emissions were on an average 2.4 higher during the day compared to the nighttime. Fluxes were higher during daytime on nearly 80% of the days. Accordingly, estimates and extrapolations based on daytime measurements only most likely result in overestimated fluxes, and consideration of diel variability is critical to properly assess the total lake CH4 flux, representing a key component of the global CH4 budget. Hence, based on a combination of our data and additional literature information considering diel variability across latitudes, we discuss ways to derive a diel variability correction factor for previous measurements made during daytime only.

Abstract. A major bottleneck regarding the efforts to better quantify greenhouse gas fluxes, map sources and sinks, and understand flux regulation is the shortage of low-cost and accurate-enough measurement methods. The studies of methane (CH4) – a long-lived greenhouse gas increasing rapidly but irregularly in the atmosphere for unclear reasons, and with poorly understood source–sink attribution – suffer from such method limitations. This study presents new calibration and data processing approaches for use of a low-cost CH4 sensor in flux chambers. Results show that the change in relative CH4 levels can be determined at rather high accuracy in the 2–700 ppm mole fraction range, with modest efforts of collecting reference samples in situ and without continuous access to expensive reference instruments. This opens possibilities for more affordable and time-effective measurements of CH4 in flux chambers. To facilitate such measurements, we also provide a description for building and using an Arduino logger for CH4, carbon dioxide (CO2), relative humidity, and temperature.

This is of the same order of magnitude as the CO 2 emissions from land use change, or the carbon transport from continents to the ocean (Ciais et al., 2013), making CO 2 emissions from lakes important in the global carbon cycle. Lakes are concentrated in boreal regions, which contain roughly 30% of global lakes (Downing et al., 2006;Verpoorter et al., 2014), and together with the arctic region contribute 17% of global lake CO 2 emissions (Aufdenkampe et al., 2011). Potential climate change effects in boreal lakes, including increased runoff (Larsen et al., 2011;Weyhenmeyer et al., 2015) and increased carbon mineralization rates (Bergström Abstract Lakes are generally supersaturated in carbon dioxide (CO 2 ) and emitters of CO 2 to the atmosphere. However, estimates of CO 2 flux ( CO 2 E F ) from lakes are seldom based on direct flux measurements and usually do not account for nighttime emissions, yielding risk of biased assessments.Here, we present direct CO 2 E F measurements from automated floating chambers collected every 2-3 hr and spanning 115 24 hr periods in three boreal lakes during summer stratification and before and after autumn mixing in the most eutrophic lake of these. We observed 40%-67% higher mean CO 2 E F in daytime during periods of surface water CO 2 supersaturation in all lakes. Day-night differences in wind speed were correlated with the day-night CO 2 E F differences in the two larger lakes, but in the smallest and most wind-sheltered lake peaks of CO 2 E F coincided with low-winds at night. During stratification in the eutrophic lake, CO 2 was near equilibrium and diel variability of CO 2 E F insignificant, but after autumn mixing CO 2 E F was high with distinct diel variability making this lake a net CO 2 source on an annual basis.We found that extrapolating daytime measurements to 24 hr periods overestimated CO 2 E F by up to 30%, whereas extrapolating measurements from the stratified period to annual rates in the eutrophic lake underestimated CO 2 E F by 86%. This shows the importance of accounting for diel and seasonal variability in lake CO 2 emission estimates.Plain Language Summary Considerable carbon cycling occurs within lakes, and carbon inputs from the catchment can be processed internally, stored in sediment and biomass or transported downstream. Additionally, carbon is exchanged with the atmosphere, resulting in lake uptake or atmospheric emission of carbon dioxide. Carbon dioxide exchanges from lakes have globally significant implications, but may be highly variable in time in ways that are not yet accounted for in emission estimates. Here, we estimated carbon dioxide exchange during multiple days and nights in three lakes with different nutrient levels during summer and autumn. For the most nutrient rich lake we also covered the period of water column mixing in autumn, which constitutes a critical time for carbon exchange. When carbon dioxide emission exceeded uptake, we found 40%-67% higher average exchange rates during daytime than nighttime. In contrast, the most nutrient...

Abstract. A major bottleneck regarding the efforts to better quantify greenhouse gas fluxes, map sources and sinks, and understand flux regulation, is the shortage of low-cost and accurate-enough measurement methods. The studies of methane (CH4) – a long-lived greenhouse gas increasing rapidly but irregularly in the atmosphere for unclear reasons, and with poorly understood source-sink attribution – suffer from such method limitations. This study present new calibration and data processing approaches for use of a low-cost CH4 sensor in flux chambers. Results show that the change in relative CH4 levels can be determined at rather high accuracy in the 2–700 ppm range, with modest efforts of collecting reference samples in situ, and without continuous access to expensive reference instruments. These results open for more affordable and time-effective measurements of CH4 in flux chambers. To facilitate such measurements, we also provide a description for building and using an Arduino logger for CH4, carbon dioxide (CO2), humidity, and temperature.

We have designed a system for targeted gene expression that allows the selective activation of any cloned gene in a wide variety of tissue-and cell-specific patterns. The gene encoding the yeast transcriptional activator GAL4 is inserted randomly into the Drosophila genome to drive GAL4 expression from one of a diverse array of genomic enhancers. It is then possible to introduce a gene containing GAL4 binding sites within its promoter, to activate it in those cells where GAL4 is expressed, and to observe the effect of this directed misexpression on development. We have used GAL4-directed transcription to expand the domain of embryonic expression of the homeobox protein even-skipped. We show that even-skipped represses wingless and transforms cells that would normally secrete naked cuticle into denticle secreting cells. The GAL4 system can thus be used to study regulatory interactions during embryonic development. In adults, targeted expression can be used to generate dominant phenotypes for use in genetic screens. We have directed expression of an activated form of the Dras2 protein, resulting in dominant eye and wing defects that can be used in screens to identify other members of the Dras2 signal transduction pathway.