Loss of darkness by skyglow in a large protected area

The world's protected areas are intended to buffer biodiversity from anthropogenic pressures. One such pressure is artificial nighttime lighting (originating from streetlights, houses, business premises and other such infrastructure), which has profound biological impacts that extend from gene expression to ecosystem function. While a high proportion of protected areas are already experiencing artificial nighttime lighting, and this proportion and the extent of individual protected areas affected are increasing, the influence is thought to be limited in larger-sized protected areas. Although satellite remote sensing provides a measure of artificial light at night, it only partially captures skyglow as experienced at the ground surface, highlighting the potential value of complementary ground-based measurements for characterising this ecologically relevant light pollution. Here we use a photographic ground-based imaging system to determine the extent of skyglow during astronomical darkness, across Kruger National Park (Kruger Park), South Africa, one of the preeminent protected areas in the world, and one of the largest terrestrial parks globally. If applying a conservative threshold value of what constitutes light pollution (21.2 magSQC /arcsec 2 ), 87% (48/55) of various images collected inside the park show some signs of anthropogenic skyglow in at least a portion of the image, and 7% (4/55) of images show light pollution at the zenith. Regions closer to the border of the park show more skyglow, especially at the horizon. In consequence, various areas in the park are already affected by skyglow, and skyglow can be detected nearly 50 km 2 within the borders of the park. Our analysis suggests the potential for biological impacts from skyglow even in large protected areas.