Study On The Accumulation And Transfer Mechanism Of Mercury In Urban Forest Food Webs Of Birds

Mercury（Hg）is one of the most toxic and ubiquitous heavy metals in the environment.Methylmercury（Me Hg）,one of its organic forms with strong neurotoxic,bioavailable,and readily biomagnified in biota via food webs,posing a potential threat to humans and animals.The accumulation of Hg in the aquatic food web and its extraordinary biomagnification have long been well documented.However,compared with the abundant knowledge of Hg accumulation in aquatic food webs.The accumulation and transfer of Hg in terrestrial food web is a little scarce.Recent studies in Hg mining areas and background areas have shown that the bioaccumulation and biomagnification of Hg also exist in terrestrial ecosystems.However,studies on Hg in the food web of urban forests affected by human activities have not been reported,the accumulation and transfer mechanism of Hg in the food web of urban forests remains unclear.This study takes urban forest ecosystem as the research object,and selected three urban parks of Changpoling National Forest Park（CFP）,Aha Lake National Wetland Park（AHH）,and Luchongguan Forest Park（LCG）as the study area.To understand the accumulation and transfer of Hg in urban forest food webs of birds,we investigated the total Hg（THg）and Me Hg concentrations,and stable carbon and nitrogen isotope(δ¹³C andδ¹⁵N)composition of soil,plant,invertebrate and nestling feather samples in urban forest ecosystem.The following conclusions can be obtained:（1）The concentrations of THg in soil and plant followed the order:LCG>AHH>CPL.The distribution trend of THg,Me Hg,and the percent of Hg present as Me Hg（Me Hg%）in invertebrates was as follows:spiders>carnivorous or omnivorous insects>herbivorous insects.Although there was no significant difference in the THg of nestling feather,but there was significant difference in the Me Hg and Me Hg%among the three parks,which follows the order:LCG>AHH>CPL.（2）The values ofδ¹⁵N in the three parks were follows the order:spider>nestlings>carnivorous or omnivorous insects>herbivorous insects>plants.Based on the isotopic composition of carbon and nitrogen in the biota from three parks,the clear bird food chain of"plant-insect-nestlings"in urban forest was established.（3）The concentrations of THg and Me Hg in the three parks showed an increasing trend with the increase of trophic level in CPL,AHH,and LCG,and indicating that there was obvious biomagnification effect of Hg.The biomagnification factors for Me Hg(BMF_{Me Hg})were higher than biomagnification factors for THg(BMF_THg)under the same predation relationship,indicating that the biomagnification effect of Me Hg in the food web of urban pine forest was more significant.The Trophic magnification slope（TMS）for THg in the three parks was basically the same（0.16-0.18）,and the TMS for Me Hg was follows the order:LCG（0.57）>AHH（0.48）>CPL（0.37）,which further indicated that there was a significant biomagnification effect of Hg in the urban forest ecosystem.