| The Oncomelania hupensis snail is the only intermediate host of Schistosoma japonicum,which determines the prevalence and distribution of schistosomiasis.Effective surveillance and control of snail is very important for achieving the goal of schistosomiasis elimination in Jiangsu Province.Based on the database of the spatial-temporal distribution and environmental factors of the water-network snails along the Beijing-Hangzhou Grand Canal and the Danyang-Jintan-Liyang Canal in Jiangsu Province,using spatio-temporal analysis,this conclude analysis of spatio-temporal distribution,the identification of snails'diffusion factors,the field verification of snails'diffusion and the evaluation of measures to prevent snails'diffusion and provide technical support for snail control.Firstly,the global and local spatial autocorrelation analysis,buffer zone analysis,standard deviational ellipse and other methods were carried out to analyze the spatio-temporal distribution characteristics of the water-network snail of theBeijing-Hangzhou Grand Canal and the Danyang-Jintan-Liyang Canal.From 2012to 2017,the number of snail habitats was increasing(P<0.05).Snail habitats are mainly distributed within 1 000 m buffer zone of the Danyang-Jintan-Liyang Canal.The distribution of snail points is mainly along the old Jiuqu river which is located at the interchange of the Beijing-Hangzhou Grand Canal and the Danyang-Jintan-Liyang Canal in danyang district.In 2014,2016 and 2017,the global Moran's I spatial autocorrelation index of snails showed statistically significant(P<0.05),and the values were all greater than 0,showing a global spatial cluster trend,while the distribution in other years were random.From 2001 to 2012(except for 2009),the local autocorrelation Getis-Ord Gi~*index was statistically significant(P<0.05),and the hotspot area was mainly the intersection area of the Beijing-Hangzhou Grand Canal and the Danyang-Jintan-Liyang Canal.On the whole,the azimuth angle and rotation of the standard deviation ellipse of the snail distribution increased,and the snail distribution gradually changed to the northeast-southwest direction.The spatial distribution of O.hupensis snails along the Beijing-Hangzhou Grand Canal and the Danyang-Jintan-Liyang Canal is complicated,and it may spread from the upstream to the downstream.The prevention and control efforts of snails should be strengthened.Secondly,to use remote sensing technology to extract the environmental indicators of the research area,and Ordinary least squares(OLS),Geographically weighted regression(GWR),Geographically and temporally weight regression,(GTWR)models were used to quantitatively analyze the factors affecting the distribution of snails in the region.With the increase of Normalized Difference Vegetation Index(NDVI)and elevation value,the number of snail habitats in the area increased and then decreased.The number of snail habitats with NDVI values between-0.01-0.05 is the largest(composition ratio accounts for 51.52%),and the snail habitats with the elevation value within the range of 3-12m has the most distribution(92.38%).The AIC values of OLS,GWR and GTWR model are 1124.972,862.7152and 1013.254,respectively,which contribute to the interpretation of the density changes of living snails is 0.23,0.563 and 0.273.GWR Model is the optimal model in this study.The GWR model results show that the parameters evaluation of the average water level in the flood season is 0.01,namely,the snail density will increase by 1%with 1%increasing in the average water level in the flood season,the snail density will increase by 1%;The parameters evaluation of the average distance from the screw point to the main channel is-0.01,that is,the average snail density will decrease by 22%with 1%increasing in the average distance from the screw point to the main channel.The main factors affecting snail density in the study area are different in time and space.The main factors are the average water level in flood season and the distance between snail point and main channel.Thirdly,the snail difusion was surveyed by salvage method,snail luring method with rice straw curtains and GPS simulated floating debris.From June to September2018,38 monitoring points were set up in the water way in the study area.4827 other aquatic snails were caught by straw curtain,1 dead O.hupensis snails were found at the monitoring point of Lianhu Central River(upstream tributary of Beijing Hangzhou canal)in Danyang City,and 937 other aquatic snails were found by fishing floating objects,but no snails were found.10 GPS simulated floating debris were put into 5 monitoring points of the main channel,and all of them finally drifted into the tributaries on both sides and stayed on the bank;it was found that the floater could drift upstream.No live snails were found by straw curtain and fishing floating objects at the monitoring points,which is closely related to the implementation of measures to prevent the spread of snails in the main channel and the timely cleaning of floating objects by the"system of river-leader".The floating debris all entered the tributary,which proves that the snails can diffuse downstream with the floater.The tributary of the river should be the key area of the snail diffusion monitoring.Finally,retrospective investigation and on-site investigations were used to evaluate the effectiveness of the measures to prevent snails'diffusion.The diffusion path of the snail is from the Yangtze and rivers connecting with Yangtze river to the downstream channel,and from the channel to the irrigation system.Evaluation point were set at the source of snail diffusion,the channel diversion and branch canals to evaluate the snail densities before and after snail control measures implementation such as sand-burying,leading water from middle level of water body,full-net snail screen and plastic film covering.The snail density decreased by 100%after the sand-burying extermination was reconstructed,and no snails were found in the 6consecutive years;the density of snails decreased by 100%after the implementation of leading water from middle level of water body,but snails were found after 2 years;the density of snails decreased by 84.0%in the first year after the implementation of full-net snail screen,but snails reappeared 5 years later;decreased by 79.6%in the first year after plastic film covering.Chemical molluscicides alone can effectively reduce the snail density,but the snail is easy to reproduce.Sand-burying,leading water from middle level of water body,full-net snail screen and plastic film covering can effectively kill and blocking the snail in a short time.However,regular project maintenance should be adopted to maintain the effect for a longer time.In conclusion,the methods such as spatial-temporal analysis,mathematical statistics and site validation were applied to discuss and confirm the spatial-temporal distribution and diffusion law of the snail along the Beijing-Hangzhou Grand Canal and the Danyang-Jintan-Liyang Canal from 2012 to 2017,and found that there is a risk of diffusion from upstream to downstream in this area.It is clear that river tributary is the key area for snail control.Sand-burying,leading water from middle level of water body,full-net snail screen and plastic film covering can effectively prevent the diffusion of snails in a short time,but the project maintenance and continuous implementation should be strengthened to ensure the long-term effect of snails control. |
PDF Full Text Request