Sunlight surveillance: a simplified approach for the monitoring of harmful ultraviolet radiation in freshwater ecosystems

Ultraviolet radiation (UVR) has a range of strong effects on freshwater ecosystems, and changing UVR is implicated in global amphibian declines. The link between UVR and amphibian declines is not well understood, largely due to limited understanding of actual UVR exposure regimes in freshwater ecosystems. Logistical challenges in measuring aquatic UVR regimes in situ have impeded progress, including the design of cost-effective radiometric monitoring tools and the measurement of UVR at ecologically relevant scales. We designed novel underwater UVR loggers and deployed them in southeast Queensland creeks to log near-continuous underwater ultraviolet index (UVI) for 11 days across four sampling events within the peak amphibian breeding season. We compared these data with solar modelling, dosimetric and handheld radiometric techniques. The dataset (2616 h from 39 UV sensors) revealed a highly heterogenous daily UVR microenvironment that showed capacity for harmful UVI exposures at both sites. Traditional cumulative or periodic UVR monitoring approaches often missed these acute high UVR exposures. Fine scale UVR data logging was proven to be a cost-effective approach for monitoring the UVR microenvironment in freshwater systems. While no single method can be considered universally optimal, our results highlight the advantages of continuous in situ UV monitoring, particularly for capturing short-duration ultraviolet fluctuations relevant to aquatic organisms.