LEDs, rivers and insect attraction: distance thresholds for attracting adult aquatic insects from their river habitat to artificial lights.

Abstract

The availability of cheap LED lamp technology may result in a shift in the spatial extent and quality of night time outdoor lighting. The impact of LED lamps on sensitive habitats such as streams and riparian areas is largely unknown, despite lighting often being installed close to lakes and rivers. Increasing light pollution therefore poses an additional risk for taxa such as Ephemeroptera and Trichoptera which are already threatened by water pollution and habitat degradation. Terrestrial adults of many aquatic insect species are known to be attracted by artificial lighting, yet little information is available to support applied conservation practice. To address this gap, we undertook a controlled field experiment by placing LED lamps and modified flight intercept traps at different distances from a light-naïve river. We had the following questions a. Is there a lighting effect on the abundance of Ephemeroptera and Trichoptera? b. What is the magnitude of the lighting effect? c. Is proximity of the lamp to the river important? d. Is there a river proximity threshold for impacts? We could show that the light treatment has a significant positive effect and distance a significant negative effect on abundance of both taxa. We could show that abundance around LED lamps reduces in a non-linear manner, with distinct river-proximity thresholds. Our results could be used to directly inform lighting management along freshwater bodies to reduce ecological impacts.