Study On Aquatic Food Web Structure Of Typical Wetland In Sanjiang Plain

The typical wetland in Sanjiang plain is one of the most distributed areas of freshwater marsh in Northeast China.The function and structure of these wetlands have been affected by human activities such as grazing,reclamation and pollutant discharge.In order to characterize wetland food web structure after human disturbance,the stable isotopic values of primary production and main consumers were determined in this study.Among the natural,restored and impacted wetlands,we analyzed the relationship between the ontogenetic variation of fish and stable isotopes and calculated the trophic position and structure of the dominant fishes and the aquatic invertebrates.We also analyzed the basic food sources of the main fish species and the aquatic invertebrates and revealed the energy flow pathways of different carbon sources in food web,and then built up the simplified models of the wetland food web.Significant difference were observed among four kinds of basal resources for?¹³C values and?¹⁵N values.POM had the most depleted?¹³C values?-31.11‰?in natural wetland,macrophytes had the more enriched?¹³C values?-27.39‰?in impacted wetland.The?¹³C values of four kinds of food sources in the restored wetland varied from-27.20‰to^-30.80‰,which had intermediate?¹³C values between those of basal resources of the natural wetland and the impacted wetland.The?¹⁵N values of basal resources in natural and restored wetlands were 1.77‰⁴.31‰and 0.81‰¹0.53‰respectively.Food sources of disturbed isotope signatures varied from 1.19‰¹0.37‰for?¹⁵N,the average of?¹⁵N values was 4.37‰.The stable isotopes of fishes had no significant correlation with their body length and weight except Culter mongolicus and Pseudorasbora parva.The stable nitrogen isotopes showed a total of four trophic levels in the typical wetland food webs of Sanjiang Plain.However,there were differences in the trophic level of natural wetland,restored wetland and impacted wetland.In the natural wetland,thirty-two aquatic invertebrates represented the primary consumers,their trophic levels ranged from 0.02 to 2.60,the trophic levels of sixteen fish species varied between 3.14and 4.25.In the restored wetland food webs,the average trophic level of seven fish species was 3.75,with a range from 3.42 to 4.10.Eleven aquatic invertebrates were represented the primary consumers with the average trophic level 2.0.In the impacted wetland,nineteen aquatic invertebrates represented the primary consumers and their trophic levels ranged from 0.71 to 4.87.The average trophic levels of fish species showed obviously variations that varied between 3.09 and 4.87.The mean trophic levels of fish species from the natural wetland were significantly increased with the comparison of the restored and impacted wetland?p<0.05?,while there was no significant difference in the trophic levels of fish in restored marsh and impacted marsh.Based on calculating stable isotopic quantitative metrics of different biologic taxes in Sanjiang plain,we found that natural wetland food web had the longest food chain length and the largest?¹³C range,indicating that a wider range of food sources for its consumers,a higher diversity basal food sources and a larger type of trophic pathways in its food web.Results from SIAR model indicated that algal resource and wetland plant were dominanted in the diet of aquatic invertebrates,while POM was the most important carbon sources for fish species in the typical freshwater wetland of Sanjiang Plain.POM made the highest contribution to piscivores in natural while it made the lowest contribution in the impacted wetland.We also found that the significant contribution to the diet of most aquatic invertebrates were algae,macrophyte and SOM.Algae and macrophyte were the important food sources for the primary consumers of natural wetlands,the basic carbon source of Diptera and Odonata in restored wetland mainly originated from SOM and macrophyte,the food sources of aquatic invertebrates in the impacted wetland were relatively complex,and SOM and algae contributed the most to the food of Diptera,snail and zooplankton.A food web model of the freshwater wetland of Sanjiang plain was preliminary constructed based on the stable isotope technique.All consumers could divide into four trophic groups including detritivoreous/alage feeders,omnivores,carnivores and piscivores.Four main energy and two main carbon flow pathways in natural wetland food web were been found.The first was the grazing food chain based on algae and macrophytes,the second was the detrital food chain based on POM and SOM as primary carbon sources.We found three main energy and two main carbon flow pathways in restored and impacted wetland food webs,and the detrital and grazing food chain were the same as in the natural wetland.Suggesting that the natural wetland was more stable to resist the disturbance that restored and influenced wetland.