Study On The Simulation Of Biomanipulation In Yundang Lagoon Using Ecological Models

Eutrophication has become a major environmental issue for the aquatic and coastal ecosystems around the world in the last 40 years,measures have been taken to reduce eutrophication in various parts of the world,but in some developing countries the problem of eutrophication is still very serious.The ecological restoration is the measures to help the damaged,degraded or destroyed ecosystem to restore their structure,functions and services on the premise of obeying the laws of nature and social needs.A series of physical,chemical and biological measures have been developed to promote eutrophication and biomanipulation which have the advantages of long-term repair effect and relatively low repair cost compared to other methods.In this study,we analyzed the food web structure,energy flow and other basic ecosystem characteristics of the Yundang Lagoon ecosystem by using the Ecopath model.The diagnosis and analysis of the Yundang Lagoon ecosystem were conducted from the ratio of the trophic level spectrum theory and the important ratio of ecosystems to the relationship between trophic levels.The model of Yundang Lagoon Biomanipulation was used to simulate the biomanipulation measures of 'cutting peaks and filling valleys'.The results of this study are as follows:(1)The Ecopath model of Yundang Lagoon was constructed based on the data from the 2008 and 2017 surveys,The Ecopath model in 2008 is comprised of 17 functional groups,and the model of 2017 added the functional group-Bryozoan.The results show that the seabirds in the top of the food web and their trophic levels are 3.59 and 3.7 in 2008 and 2017,respectively.The total system throughput is 19903 t/km2/year and 17892.16 t/km2/year respectively in two years,of which about 54%of primary energy come from primary producers and 46%from detritus.The average energy transfer efficiency of this ecosystem is 2.57%to 2.71%,which is lower than most of the lagoon ecosystem.Through the Ecopath network analysis,it is concluded that the highest niche overlap in Yundang Lagoon is Tilapia and Mugil,and the Keystone functional group of which includes piscivorous fish and seabirds.The values of TPP/TR and TPP/TB which describe the maturity of the ecosystem are 9.335 and 43 respectively in 2008,indicating that this ecosystem is a low mature situation according to the ecological indicators of the Yundang Lagoon ecosystem,although the situation in 2017 is better than 2008.(2)The trophic level spectrum of Yundang Lagoon shows that the biomass of this ecosystem is in the 4 orders of magnitude.The biomass of each functional group decreased with the increase of trophic level,with a slope value of approximately 16%to 18%and there are some fluctuations in the changes.The important ratios of P/B,Q/B and R/B in Yundang Lagoon show a downward trend with the increase of trophic level.Most of the important ratios of medium-trophic function groups are below the trend line in this model,the values of which are underestimated.The production of the top predator-piscivorous fish differs by 4 orders of magnitude compared to the production of primary producers,indicating that the energy transfer efficiency between the ecosystems is low,indicating that there is a certa in imbalance in the ecosystem.(3)The results of scenario simulation for the Biomanipulation Model in Yundang Lagoon show that based on the situation in 2008 and 2017,the implementation of stocking piscivorous fish,removing the crabs in the two years and removing the Mugil in the model of 2017 can achieve of the purpose of reducing the biomass of phytoplankton.And then,the effect of comprehensive biomanipulation is better than the single species biomanipulation.In addition,the crap manipulation is the best for the biomanipulation of single species.Moreover,the effects of comprehensive biomanipulation are higher 3.5%and 7%than that of crab biomanipulation in 2008 and 2017,respectively.Therefore,through the important ecological indicators of Yundang Lagoon,we can assume that comprehensive biomanipulation can effectively reduce the phytoplankton biomass,improve the maturity of the ecosystem and the complexity of the food web.Overall,the comprehensive biomanipulation plays a better ecological restoration.