How dark is a river? Artificial light at night in aquatic systems and the need for comprehensive night‐time light measurements

Abstract

Freshwater ecosystems are hotspots of biodiversity. They are of major importance for humans because they provide vital ecosystem services. However, as humans tend to settle near freshwaters and coastal areas, these ecosystems are also over‐proportionally affected by anthropogenic stressors. Artificial light at night can occur as a form of environmental pollution, light pollution. Light pollution affects large areas on a worldwide scale, is growing exponentially in radiance and extent and can have diverse negative effects on flora, fauna and on human health. While the majority of ecological studies on artificial light at night covered terrestrial systems, the studies on aquatic light pollution have unraveled impact on aquatic organisms, ecosystem functions as well as land‐water‐interactions. Although monitoring of light pollution is routinely performed from space and supported by ground‐based measurements, the extent and the amount of artificial light at night affecting water bodies is still largely unknown. This information, however, is essential for the design of future laboratory and field experiments, to guide light planners and to give recommendations for light pollution regulations. We analyze this knowledge gap by reviewing night‐time light measurement techniques and discuss their current obstacles in the context of water bodies. We also provide an overview of light pollution studies in the aquatic context. Finally, we give recommendations on how comprehensive night‐time light measurements in aquatic systems, specifically in freshwater systems, should be designed in the future. This article is categorized under: Water and Life > Stresses and Pressures on Ecosystems Water and Life > Conservation, Management, and Awareness Water and Life > Methods

Effects of Artificial Lighting at Night on Predator Density and Salmonid Predation

“…With continuing human development along rivers, estuaries, and coastlines, it will be increasingly important to consider the impacts of ALAN on aquatic organisms and ecosystems (Davies et al 2014;Jechow and Hölker 2019;Zapata et al 2019). Elsewhere, ALAN has attracted young salmonids and their predators, resulting in elevated predation rates (Tabor et al 2004(Tabor et al , 2017.…”

“…Predation risk is exacerbated in clear waters (Gregory and Levings 1998) and out-migrating salmonids employ nocturnal migrations as one strategy to minimize this risk (Chapman et al 2013;Clark et al 2016;Furey et al 2016). However, in many ecosystems, salmonid out-migration traverses anthropogenically altered habitat and urban centers (Michel et al 2013(Michel et al , 2015Schroeder et al 2015), likely leading to increased ALAN exposure (Jechow and Hölker 2019;Zapata et al 2019). Given that ALAN aggregates and slows out-migrating salmon, attracts predators (including fishes, birds, and mammals), and increases piscivore consumption of salmonids (Yurk and Trites 2000;Tabor et al 2004;Celedonia et al 2011;Tabor et al 2017), increased migratory ALAN exposure likely increases juvenile salmonid predation risk and mortality.…”

Light Pollution, Circadian Photoreception, and Melatonin in Vertebrates

“…Another panchromatic sensor used in the context of ALAN (but not in melatonin studies) is a 871 sky quality meter (SQM) that measures the zenith night sky radiance in a spectral band that is close Figure A1. Schematic drawing of different radiometric parameters: (a) geometry of sky and zenith radiance and surface irradiance measurements; (b) vector and scalar irradiance; (c) different spectral bands: single (panchromatic), multiple (multi-spectral), and full spectrum (hyperspectral) (after Reference [173]).…”

Assessing long‐term effects of artificial light at night on insects: what is missing and how to get there

“…Currently, the best instrument for monitoring ALAN from space is the day night band (DNB) of the visible infrared imaging radiometer suite (VIIRS) on board of the Suomi NPP satellite. However, there are certain issues with this approach including the spatial resolution of only 750 m, the lack of sensitivity in the blue spectrum (Kyba et al ., 2017) but also the unknown ratio of light emitted towards the satellite and light emitted into a certain habitat, particularly for aquatic ones (Jechow & Hölker, 2019b). This is particularly problematic when changing spectral composition from e.g.…”