| Spatial and quantitative assessment of watershed pollination service function is of great significance for improving the value of pollination service,strengthening agricultural production management and biodiversity conservation in the region.Based on the basic geographic data of land use,soil properties,temperature and topography from 1980 to 2015,the dynamic change and spatial distribution of pollination service function in Nansihu Lake basin were simulated and evaluated with InVEST model.And explore the relationship between natural geographical factors such as humidity,precipitation,topography,and the dynamic changes of socio-economic factors such as population,land use intensity,gross national product(GDP)and the spatial pattern of pollination service functions,and identify the regions with high relative pollination potential,which could provide scientific basis for further improving the value of pollination service in river basins.The results show that(1)the land use change in the Nansihu Lake basin from 1980 to 2015is mainly characterized by urban expansion and reduction of cultivated land(paddy and dry land).Among them,the construction land and water area increased by 40.24%(1546.44 km~2)and11.46%(172.33 km~2),respectively.The area of dry land,paddy field,forest land,grassland and unused land decreased by 4.11%(801.77 km~2),9.61%(189.31 km~2),23.54%(200.98 km~2),22.67%(347.62 km~2),72.85%(174.86 km~2),respectively.Land use change in the basin,especially the expansion of construction land,dryland,woodland,and grassland area,have led to widespread destruction of wild pollination insect nests,reduced available habitat area,caused sever habitat fragmentation,and threatened the biodiversity of pollinators.(2)The county with high Index of Abundance(IOA)of pollinator in 2015 was concentrated in Shanting District,Shizhong District and Feixian County in the low hilly area of the east;the county with IOA at the upper middle level was mainly distributed in the eastern part of the basin;The county with IOA was at the lower middle level mainly distributed in the western,the southern and the northern areas of Nansihu Lake basin;the county with IOA at a low level were Weishan County and Jiuli District.From 1980 to 2015,the average pollination abundance index of the Nansihu Lake basin decreased from 0.1492 to 0.1387.The number of IOAs with high levels of IOA(0.25-1.0)in the 35a basin decreased from 4 to 3,while at the lower-middle level(0.08-0.16)increased by one.The IOA value of the grassland in the Nansihu Lake basin is the highest,0.497;the second is the forest land,which is 0.457.The county level distribution of IOA is closely related to the type of land use.The low mountain and hilly areas in the east are subject to increased intensity of human activities such as agricultural production,and priority protection is needed.(3)Relative Pollination Potential(RPP)of Nansihu Lake basin presents the spatial distribution pattern of high level RPP in the eastern hilly areas,middle level RPP in the western plain regions,low level RPP in construction land and waterbodies.Relative pollination potential tends to decrease from east to west with the decrease of elevation.RPP of different land use types follows this order:grassland,forested land,dry land and unused land in a certain range at the edge of grassland and forested land in hilly areas>scattered rural settlements,suburbs and riverbanks>dry land in plain>construction land and paddy land>waterbodies.Pollination deficit area is mainly distributed in lake areas,reservoir pond and construction area.The highest RPP value of grassland was 0.3577,followed by woodland,which was 0.3260.Relative pollination potential of 20 sub-basins in Nansihu Lake basin(excluding Nansihu Lake areas)was found to be in the middle-lower level(0.07-0.15),including all sub-basins in the west plain,the Guanfu river basin and Hanzhuang river basin in the eastern of the basin,while RPP of the other seven sub-basins in the eastern of the basin was in the upper-middle level(0.15-0.30).In the county with a relatively high pollination potential,only the Shanting District,and the number of counties in the middle and lower levels remained at 29.The relative pollination potential of Qufu City has dropped from the upper-middle level to the lower-middle level,resulting in a decrease in the middle-upper level of relative pollination potential to 11.The relative pollination potential of Dongping County dropped from the lower-middle level to the lower level,resulting in the number in low-level counties increasing to two.In view of the obvious decline in the number of wild bees,according to the spatial distribution characteristics of relative pollination potential,the area with large pollination potential can be selected,and the wild insect pollination nature reserve can be appropriately added to increase the suitable habitat to expand the population of wild bees,thereby achieving the purpose of improving the function of the watershed pollination service.(4)Land use changes are the main factors of affecting pollination service function.IOA and RPP were positively correlated with the area of grassland,forested land and dry land,while IOA and RPP were negatively correlated with construction land.There was no significant relationship between IOA and RPP with paddy land,water body and unused land.In this study,IOA and RPP were significant positively correlated with Digital Elevation Model(DEM)and slope,significantly negatively correlated with the humidity and intensity of land use.There was no significant correlation with temperature,precipation,average wind velocity,sunshine duration,NDVI,population,GDP.The results can provide scientific support for macro-decision-making such as agricultural production planing and socio-economic development,avoiding risks for policy makers and stakeholders. |
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