The Characteristics Of Underwater Noise Of The Bridge Across The River In Nanjing,Jiangsu And Analysis Of Its Influence On The Yangtze Finless Porpoise

The Yangtze finless porpoise(Neophocaena asiaeorientalis)is the flagship species of the Yangtze River ecosystem,with a well-developed sonar system and auditory system.In recent years,its protection status has gradually increased,and the decline of natural populations has been eased,but the protection situation is still severe.With the implementation of the Yangtze River’s comprehensive ban on fishing,the impact of overfishing has basically been eliminated.Underwater noise generated by human wading projects such as shipping vessels,crossing river channels,and wharf construction has gradually become an important factor affecting the Yangtze finless porpoise,and the extent of the impact,etc.It is not clear yet,and targeted research is needed to analyze the actual impact of related wading projects on the Yangtze finless porpoise.There are many bridges crossing the river in the Nanjing Yangtze River finless porpoise provincial nature reserve,which overlaps with the habitat of the Yangtze finless porpoise.This experiment investigates the characteristics of underwater noise generated by two representative bridges across the river(road bridge,railway bridge)in the reserve,and simultaneously investigates the distribution of the Yangtze finless porpoise population in the reserve,in order to grasp the noise characteristics of different types of bridges across the river,To explore whether different types of bridges and their superimposed effects will affect the Yangtze finless porpoise and the possible degree of impact,so as to provide a scientific basis for in-situ protection of the Yangtze finless porpoise in the Nanjing section of the Yangtze River.The main results and conclusions are as follows:From September 22 to October 2,2020,the Nanjing Dashengguan Yangtze River Bridge(railway bridge),the Nanjing Ring High-speed River Crossing Bridge(road bridge)and the underwater lines along the south and north lines of the Yangtze River were collected.Noise information.When a train passes a railway bridge,the underwater noise energy caused by the train is mainly concentrated in the low frequency band(< 1 k Hz),and as the water depth increases,the energy contained in the low frequency band(< 1 k Hz)increases significantly.The underwater noise at different distances from the bridge along the river has no obvious change trend.The 1/3 octave sound pressure level intensity of each point shows a downward trend as the frequency increases.In most of the high frequency range,the 1/3octave sound pressure level of underwater noise at the bottom of the bridge at different locations is higher than the hearing threshold of the Yangtze finless porpoise.When a vehicle passes on a highway bridge,the underwater noise of the vehicle cannot be accurately identified,and the possibility of being masked by the current noise is higher.However,the1/3-octave sound pressure level of underwater noise at different locations on the bridge bottom is higher than the hearing threshold of the Yangtze finless porpoise,which can be perceived by it.A total of 4 quarters of annual surveys of the reserve will be carried out in the summer(July),autumn(November),winter(January),and spring 2021(March)in 2020.The estimated numbers of Yangtze finless porpoises are 56 and 41 respectively.Heads,36 heads and 31 heads.The investigation found that the Yangtze River finless porpoise is mainly active in the lower reaches of the highway bridge and in the waters of the north bank(the north branch of the island),and lives in clusters(≥ 2).The protection is divided into 4 regions.There are significant differences in the distribution of the Yangtze finless porpoise among the regions(one-way ANOVA,F= 9.357,P < 0.05),and the distribution of the Yangtze finless porpoise in the third region(i.e.from the highway bridge to the water area near the Nanjing Yangtze River Tunnel)It is significantly higher than other areas,and the density of the Yangtze finless porpoise in the water between the two bridges is extremely low.According to the distribution characteristics of the Yangtze finless porpoise,it is speculated that the bridges across the river have blocked the Yangtze finless porpoise,which may affect the normal migration of the Yangtze finless porpoise for a long time.Underwater noise may adversely affect the vocalization and hearing of the Yangtze finless porpoise.It is recommended to reduce the use of wading bridge piers in future bridge construction planning.In addition,in the waters where the Yangtze finless porpoise is active,strengthen ship management,avoid concentrated passage of ships,and take measures to slow down and reduce noise.