Mapping underwater sound noise and assessing its sources by using a self-organizing maps method

Natural and shipping underwater sound distribution in the Northern Adriatic Sea basin and possible application on target areas

The underwater sound distribution generated by natural sources, shipping and trawling activities has been computed by the Quonops© modelling webservice for the Northern Adriatic Sea (NAS) during 2020, a year characterized by the COVID-19 lockdown restrictions. Modelling has been calibrated by using a year-long time series of field measurements covering the domain of interest. Sound levels (50th percentile) ranged between 75 and 90 dB re 1μPa for all the considered frequencies (63 Hz, 125 Hz, 250 Hz third octave bands). Noisier NAS areas match with the shipping lanes and the distribution of trawling activity. Pressure sound indices based on masking effect were computed for two Ecologically/Biologically Significant Marine Areas (EBSA) located in the NAS. Results indicated a significant contribution of vessel and fishery-generated noise to the local soundscape and provide a basis for addressing NAS underwater noise pollution, with special reference to the Marine Spatial Planning approach.

Automated identification and assessment of environmental noise sources

Noise pollution is one of the major health risks in urban life. The approach to measurement and identification of noise sources needs to be improved and enhanced to reduce high costs. Long measurement times and the need for expensive equipment and trained personnel must be automated. Simplifying the identification of main noise sources and excluding residual and background noise allows more effective measures. By spatially filtering the acoustic scene and combining unsupervised learning with psychoacoustic features, this paper presents a prototype system capable of automated calculation of the contribution of individual noise sources to the total noise level. Pilot measurements were performed at three different locations in the city of Ljubljana, Slovenia. Equivalent sound pressure levels obtained with the device were compared to the results obtained by manually marking individual parts of each of the three measurements. The proposed approach correctly identified the main noise sources in the vicinity of the measurement points.

Characterization of the underwater noise produced by recreational and small fishing boats (<14 m) in the shallow-water of the Cres-Lošinj Natura 2000 SCI

Recreational boats are a dominant source of underwater noise in coastal areas, but reliable boat noise assessment is generally lacking. Here the Underwater Radiated Noise (URN) of seven recreational and small fishing boats moving at two different speeds was measured in the shallow waters of the Cres-Lošinj Natura 2000 SCI (Croatia). Measurements were undertaken considering the internationally recognized standards and published guidelines for shallow waters. URN was provided in 1/3 octave band spectra and in narrow band spectra, to highlight the tonal components. Engine power and type rather than the boat length and design result to be more predictive of URN. Highest speeds induce highest noise levels only in a very limited frequency range and different boats with similar speed but different engines show a shift in the spectra. Relevance of the achieved results for the tested area is further discussed.

Anthropogenic noise influences on marine soundscape variability across coastal areas

Acoustic data was collected across 15 sites distributed through the coastal area of Rio de Janeiro, Brazil, encompassing regions of different natural characteristics. Noise levels and the acoustic complexity index were calculated. Quantity and composition of anthropogenic sound sources varied across recording sites, with at least one type of sound source being registered in each location. A cluster analysis using third-octave levels from eight frequency bands divided recording sites into two groups, one considered as impacted by anthropogenic noise and the other as less-impacted. The noisiest recording locations were those with higher numbers of anthropogenic sound sources, specifically large ships. It was evidenced that anthropogenic noise affects not only noise levels, but also low-frequency acoustic complexity, which decreased in the presence of vessel traffic. The constant noise input of human activities tended to mask natural variability in the soundscape at lower frequencies.

Mapping sea surface observations to spectra of underwater ambient noise through self-organizing map method

This letter presents a model for mapping sea surface observations to the spectra of underwater ambient noise through the self-organizing map method (SOM). The data used to train and test the proposed model include observations of wind speed, atmospheric pressure, and significant wave height from public databases, as well as observations of ambient noise from two deep-water experiments. SOM extracts nonlinear relations from the data and is more suitable for the study of nonlinear dynamics in the ocean than conventional methods. Results indicate the proposed model is reliable with coefficients of determination above 0.9 and root-mean-square errors below 1 dB.

Tackling challenges for Mediterranean sustainable coastal tourism: An ecosystem service perspective

Coastal tourism is a growing industry sector in the Mediterranean Basin. This and the other human activities occurring along the coastline share space and resources, leading to conflicts for divergent uses. Moreover, the overexploitation of natural resources degrades and depletes coastal habitats, with negative feedback effects for all human activities. Hence, both tourism and the other human activities have to consider their dependence on coastal ecosystem services, and act at technical and policy level to reach a compromise that preserves natural resources in the long term. Here we provide a conceptual framework illustrating the complex relationships and trade-offs among threats from coastal tourism and from other human activities and coastal ecosystem services, with a focus on cultural ones. We discuss the negative feedbacks on tourism development and provide examples of geospatial analysis on cumulative threats generated by other human activities and affecting tourism itself. The proposed conceptual framework and the threat analysis aim at highlighting the negative feedback effects of human driven threats on the development of Mediterranean coastal tourism, through an ecosystem service perspective. Both tools provide valuable insight for supporting decision makers and planners in achieving integrated coastal management, with a focus on sustainable tourism.

Underwater noise assessment in the Gulf of Trieste (Northern Adriatic Sea, Italy) using an MSFD approach

In the marine environment, underwater noise is one of the most widespread input of man-made energy. Recently, the European Commission has stressed the necessity of establishing threshold levels as a target for the descriptor 11.2.1 "Continuous low frequency sounds" in the Marine Strategy Framework Directive (MSFD). In 2012, a monthly underwater noise monitoring programme was conducted in the Gulf of Trieste (Northern Adriatic Sea, Italy); the collected acoustic samples (frequency range: 10-20,000 Hz) were analysed in the 1/3 octave bands. The stations have been further clustered following the 63 and 125 Hz bands noise levels. Average SPL levels resulted similar to those previously computed for proximate areas, indicating that the Adriatic Sea sub-region experiences high noise pressure in the marine waters. In its turn this claims for a scientific and technical international cooperation, as requested by the EU programme. No seasonal variation in local noise levels has been found.

Underwater noise pollution in a coastal tropical environment

Underwater noise pollution has become a major concern in marine habitats. Guanabara Bay, southeastern Brazil, is an impacted area of economic importance with constant vessel traffic. One hundred acoustic recording sessions took place over ten locations. Sound sources operating within 1 km radius of each location were quantified during recordings. The highest mean sound pressure level near the surface was 111.56±9.0 dB re 1 μPa at the frequency band of 187 Hz. Above 15 kHz, the highest mean sound pressure level was 76.21±8.3 dB re 1 μPa at the frequency 15.89 kHz. Noise levels correlated with number of operating vessels and vessel traffic composition influenced noise profiles. Shipping locations had the highest noise levels, while small vessels locations had the lowest noise levels. Guanabara Bay showed noise pollution similar to that of other impacted coastal regions, which is related to shipping and vessel traffic.

Dolphin changes in whistle structure with watercraft activity depends on their behavioral state

Dolphins rely on whistles to identify each other and to receive and convey information about their environment. Although capable of adjusting these signals with changing environments, there is little information on how dolphins acoustically respond to different watercraft activities and if this response depends on dolphin behavioral state. Bottlenose dolphin whistles were recorded in the presence of research and dolphin-watching boats. Dolphins emitted lower frequency and longer whistles when interacting with dolphin-watching boats, particularly during foraging activities. This study suggests that dolphin-watching boat traffic significantly hinders dolphin communication during important behavioral states.