Human sounds and associated tonality disrupting perceived soundscapes in protected natural areas

In protected natural areas (PNAs), at popular scenic spots, visitors often contribute to noise pollution through their behaviour. The decibel-focused monitoring doesn't capture the quality of an acoustic environment, human behaviour and perception. A mixed-methods framework, based on the ISO 12913 series, was tested in four European PNAs to address this gap. During five soundwalks (7-12 km long) organised by the Silenzi in Quota initiative, 443 questionnaires were gathered across 28 evaluation points, alongside corresponding binaural measurements. Acoustic environments as silent as L_Aeq = 31 dB and as loud as L_Aeq = 76 dB were observed, eliciting perceptions from very calm to chaotic. Psychophysical measures (loudness, sharpness, roughness, fluctuation strength and tonality) were calculated. The impact of the perceived sound source dominance, visual landscape quality and psychophysical and environmental acoustic features on the perceived soundscape pleasantness and eventfulness was analysed via Linear Mixed-Effects Models (LMMs). Perceived sound source type data- and psychophysical data-based models demonstrated higher predictive power than those based on sound pressure level metrics. Amongst the sounds of nature, water sounds demonstrated the strongest association with higher pleasantness and eventfulness. Unlike in urban context, presence of human sounds, associated with increased tonality, was the major factor driving the perception of chaotic soundscapes, revealing the detrimental effect of human behaviour on the experience of PNAs.