Study On Heavy Metal Pollution And Food Network Structure Of Gaobazhou Reservoir In Qingjiang

With the rapid development of the social economy in China,the living standard of the society has been improved.As a result,the demand for fresh water products is increasing.Aquaculture has become the main source of aquatic products in China because of the reduction in natural fishing production.On the other hand,a large-scale aquaculture production has brought a series of problems,such as food safety and environmental pollution.As an important base for aquaculture,it is necessary to have a comprehensive understanding of the heavy metal pollution in Qingjiang Gaobazhou reservoir and to provide a theoretical basis for us to conduct aquaculture scientifically and safely.The food web is the most powerful way to understand the trophic relationships in ecosystem.The trophic structure in reservoir is of great significance for understanding the food web structure,resource utilization and nutrition interaction.This study analyzed the content and distribution of heavy metals in different fishes as well as the sediments of Gaobazhou reservoir.And the influence of cage culture on water environment was discussed.Stable isotope technique was applied for analyzing the value of?¹³C and?¹⁵N.By calculating each trophic level of consumers,the food web in the reservoir was constructed to explore the source of the basic carbon for different consumers.Here are the results of the study:?1?Siniperca chuatsi had the highest concentration of Hg?65.18?g/kg?and Rhodeinae sp.had the lowest concentration?15.65?g/kg?.The highest concentration of Pb was found in Rhinogobio cylindricus gunther with 208.68?g/kg,and the lowest value was 4.24?g/kg in Lucioperca lucioperca.Rhodeinae sp.had the highest concentration of Cu with 2813?g/kg,and the lowest concentration of Cu was 160.16?g/kg in L.lucioperca.Rhodeinae sp.had the highest concentration of Cd?36.05?g/kg?and Spinibarbus sinensis had the lowest concentration?1.36?g/kg?.The highest of46.39 mg/kg Zn was found in Rhodeinae sp.and the lowest of Zn was S.sinensis with4.43 mg/kg.According to our national limitation standard of pollutant in food?GB2762-2017?and UNFAO's limitation standard for heavy metal in fish,we found that the heavy metal contents of all fish we researched met the standards,except for the zinc concentration in Rhodeinae sp.?40 mg/kg?.From calculating the metal pollution index,17 kinds of fish in this research were polluted mildly or slightly except for Hypophthalmichthys molitrix which was non-polluted.It showed that the pollution degree of heavy metals in the fish was lower in Gaobazhou reservoir.?2?The contents of 7 kinds of heavy metals in the reservoir sediment were analyzed.The rank of average concentration from the highest to lowest was Mn,Zn,Cu,Pb,As,Cd and Hg.Referring to the standard of national soil environmental quality,the concentrations of heavy metals in reservoir sediment all met the standard.By calculating Geoaccumulation Index in the sediments from 10 sampling sites,the sediment was mildly polluted by Mn.It was not polluted by other 6 heavy metals.And the concentration of Mn was significantly correlated with Pb,which means that they may have the same source.?3?In the aquatic food web of Gaobazhou reservoir,the primary producers mainly were POM,sessile algae,Polygonum hydropiper and Alternanthera philoxeroides.The?¹³C values of each primary producer were much different.The consumers were two kinds of benthic macroinvertebrates and fishes.The values of?¹⁵N,and?¹³C among consumers were not significantly different.The results showed that the food web of Gaobazhou reservoir had three trophic levels.The highest nutritional grade was L.lucioperca with the mount of 3.77 which ranked the top of the food web.?4?Based on the Bayesian hybrid model,we analyzed the basic carbon source of different fish with different feeding habits in the reservoir.The result showed that the main carbon source of carnivorous fish was sessile algae.The main carbon source of omnivorous fish was P.hydropiper.There were no obvious differences in the contribution of four basic carbon sources for filter-feeding fish,phytophagous fish and herbivory fish.