The impact of light pollution on suburban stream ecosystems
This diploma thesis examined the response of aquatic insects to different light pollution situations in a suburban area near Zurich. The objective was to test dierent methods and sampling designs, and to carry out a pilot study. An extensive literature review on the ecological eects of light pollution is provided too.
The impact of dierent types of street and halogen lamps was examined along four streams in Dubendorf using emergence and combi-traps. Sticky traps were attached to windows of an EAWAG building near the Chriesbach to test the response of insects to building lights.
The experiments showed enhanced light attraction for Diptera, Trichoptera, Ephemeroptera and Lepidoptera, and to a smaller extent for Hemiptera and Apocrita. Concerning the relative abundance, Trichoptera were underrepresented in combi-traps at control sites and over-represented in combi-traps in front of the light source compared to the emergence traps. Ephemeroptera were found in small numbers in combi-traps, but also attached to the lamp and they were seen in the surroundings of the lamp. The catches of the combi-traps per night represented an emergence rate of 9 m2 water surface for Diptera, of 35 m2 for Trichoptera and of 22 m2 for Ephemeroptera per night. The number of insects caught diered between dark and illuminated sites when the combi-traps were placed directly in front of the light source. The emergence traps did not show a dierence in the number of insects caught
per night between illuminated and dark sites.
The sticky traps attachted to illuminated windows of the EAWAG building caught up to 14'500 insects per m2. This corresponded to an emergence rate of 110 m2 water surface. No insects were caught at dark windows. The number of insects caught diered for size categories and the distance from the ground although a general trend was missing.
Combi-traps worked best when placed in front of the light source. The catchability of Ephemeroptera and Odonata was small in emergence traps and in combi-traps. For the sticky traps, larger surface areas are suggested. Photos should be taken over the course of the night to quantify the insect phenology.
Further experiments are necessary to examine the reaction of aquatic insects on a low taxonomic level and to study the eect on populations at illuminated sites over several years. Moon illuminance, weather parameters, and instream conditions need to be considered too.