The ambient soundscape of inland waters in Seattle, Washington: bridge traffic as a source of urban underwater noise pollution?

Abstract

[author abstract] Increasing human population is adding anthropogenic sources of noise to natural ambient sound levels and threatening marine ecosystem function and viability. Overwater bridges, features of the Seattle urban environment, are a potential conductor of traffic noise to the underwater environment potentially complicating the underwater soundscape. This study utilized both custom and commercially built piezo-element hydrophones to sample sound underwater. The accuracy of hydrophones was analyzed comparatively in a test pool, finding that each hydrophone responded within 10 decibels of one another. The hydrophones were also used to sample ten stations along a transect of the urban waterfront between the University of Washington and Shilshole Marina, including a station directly beneath the Interstate-5 (I-5) Bridge. All stations showed uniform idealized sound signatures regardless of their distance from the I-5 Bridge, suggesting that bridge noise is not a unique signature in the Seattle urban waterfront.