Design and implementation of an illumination system to mimic skyglow at ecosystem level in a large-scale lake enclosure facility

Light pollution is an environmental stressor of global extent that is growing exponentially in area and intensity. Artificial skyglow, a form of light pollution with large range, is hypothesized to have environmental impact at ecosystem level. However, testing the impact of skyglow at large scales and in a controlled fashion under in situ conditions has remained elusive so far. Here we present the first experimental setup to mimic skyglow at ecosystem level outdoors in an aquatic environment. Spatially diffuse and homogeneous surface illumination that is adjustable between 0.01 and 10 lx, resembling rural to urban skyglow levels, was achieved with white light-emitting diodes at a large-scale lake enclosure facility. The illumination system was enabled by optical modeling with Monte-Carlo raytracing and validated by measurements. Our method can be adapted to other outdoor and indoor skyglow experiments, urgently needed to understand the impact of skyglow on ecosystems

Wildfire-derived pyrogenic carbon modulates riverine organic matter and biofilm enzyme activities in an in-situ flume experiment

Wildfires produce large amounts of pyrogenic carbon (PyC), including charcoal, known for its chemical recalcitrance and sorption affinity for organic molecules. Wildfire-derived PyC can be transported to fluvial networks. Here it may alter dissolved organic matter (DOM) concentration and composition as well as microbial biofilm functioning. Employing in-stream flumes with a control vs treatment design (PyC pulse addition), we present evidence that field-aged PyC inputs to rivers can increase dissolved organic carbon (DOC) concentration, and alter DOM composition. Decreased DOM aromaticity indicated by lower SUVA245 (-0.31 units), and higher pH (0.25 units) were associated with changes in enzymatic activities in benthic biofilms, including a lower recalcitrance index (β-glucosidase/phenol oxidase), suggesting preferential usage of recalcitrant over easily available DOM by biofilms. Particulate PyC deposition onto biofilms may further modulate the impacts of PyC due to direct contact with the biofilm matrix