The effects of artificial light at night on stream and riparian ecosystems
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Measuring light levels in the Spree River in Berlin Mitte |
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Project Motivation
Artificial light at night is wide-spread across the globe and while astronomers have been calling attention to it for many years, ecologists have only just begun to ask what effects these lights might have on ecosystems. I'm particularly interested in looking into how artificial lighting might affect stream and riparian systems, as these systems are often central to human settlements and are therefore likely to be exposed to all forms of urbanization, including light pollution.
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Research flumes at the German Environmental Protection Agency which I used in my drift experiment |
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Artificial light and drifting stream invertebrates
Previous studies have noted that stream invertebrates, such as larval mayflies and gammarids, are less likely to drift in a stream's current on nights when there was a full moon present. Later researchers found the same effect when these animals were exposed to low light levels in the laboratory. However, these studies were all short-term, simply looking at drift behavior over the course of one night. I was interested in seeing if drift rates would remain suppressed with chronic exposure to light at night, similar to what these organisms might experience in an urban environment. I was able to conduct this study at the German Environmental Protection Agency and take advantage of their wonderful facilities for stream experiments.
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Flight intercept traps and lights along the Spree River outside Berlin |
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Adult aquatic insect dispersal
When I first talked to Klement about the artificial light topic, we were both really excited about researching how artificial light might disrupt the dispersal of adult aquatic insects. Because there are so many aquatic insects, and they are so small, it is almost impossible to find a way to track them, but we feel we came up with a good way around this problem. In order to test our hypotheses about lights blocking aquatic insect dispersal, we installed real street lights around the edge of an island located in the Spree River, approximately 35 km from Berlin. We installed insect traps at various heights and locations on the edge, as well as in the center of the island to determine how many insects were caught at the lights and how many made it through the light "gauntlet" and reached the center of the field.
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Experimental stream reach in MKRF |
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Stream ecosystem functioning
My final field project of my doctoral work was to find a way to tie it all together and see if changes in drift and flight behavior might lead to altered ecosystem processes. For this experiment, I was fortunate enough to work under the tutelage of John Richardson in the University of British Columbia's Malcolm Knapp Research Forest (MKRF). Four streams were used, each with a dark control and lit experimental reach of approximately 40 m long. We did a mark-recapture study of the resident cutthroat trout, measured aquatic insect emergence, terrestrial inputs, leaf litter decomposition, standing stocks of algae, and invertebrate drift.
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Measuring stream velocity in front of a drift net at MKRF |
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Photo credit: Photo of measuring light at night by Patrick Baudisch; photos from UBC field research by Nora Schlenker
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