| As one of the main lake areas of Baiyangdian in Hebei Province,it plays an important role in maintaining the stability of the whole ecosystem of Baiyangdian.Nowadays,the lake is suffering from eutrophication and shortage of biological resources.In order to solve this problem,a series of ecological restoration measures were carried out to build the enclosure in Shihoudian lake.In order to comprehensively evaluate the effect of ecological restoration,carbon and nitrogen stable isotope method and Ecopath model were used to comprehensively and deeply evaluate the changes of ecosystem nutrient structure and energy flow in the experimental area.The results are as follows:1.The physical and chemical indexes of the experimental area and the control area inside and outside the enclosure were analyzed,The total phosphorus(P<0.05)and total nitrogen(P<0.05)in the experimental area were significantly lower than those in the control area in August;ammonia nitrogen was significantly lower than that in the control area in June(P<0.05);nitrate nitrogen and nitrite nitrogen were significantly lower than that in the control area in September(P<0.05);permanganate index was significantly lower than that in the control area in October(P<0.05);chlorophyll was significantly lower than that in the control area in July,August and September(P<0.05).The comprehensive nutritional state index of the experimental area was significantly lower than that of the control area in April(P<0.05),and significantly lower than that of the control area in July and August(P<0.05).It can be seen that the nutritional state index of the experimental area in summer was lower than that of the control area,and the water quality was better than that of the control area.Summer was the season with the highest activity of floating bed plants,which absorbed more nutrients such as nitrogen and phosphorus in the water.The results showed that the ecological restoration of the experimental area played a positive role in water quality improvement.2.147 species of phytoplankton from 7 phyla were detected in the control area of Wudian lake,including 62 species of Chlorophyta,25 species of diatom,33 species of Cyanophyta,15 species of nudophyta,8 species of dinoflagellate,3 species of cryptophylum and 1 species of Chrysophyta;118 species of phytoplankton from 7 phyla were detected in the experimental area,including 57 species of Chlorophyta,24 species of diatom,23 species of Cyanophyta,7 species of nudophyta,3 species of dinoflagellate,3 species of cryptophylum and 1 species of Chrysophyta.The proportion of Cyanophyta in the experimental area and the control area is the second,and the proportion of Cyanophyta in the control area is higher than that in the experimental area.The results of variance analysis showed that there was no significant difference in the density of algae between the experimental area and the control area(P>0.05);there was no significant difference in the biodiversity index between the two areas(P>0.05).The results showed that there was a significant positive correlation between the species of phytoplankton and permanganate index(P<0.05),between the density of phytoplankton and the physical and chemical indexes of total nitrogen and chlorophyll(P<0.05),and between the density of phytoplankton and total nitrogen(P<0.05)This shows that the ecological restoration measures in the experimental area control the population density of algae by reducing the concentration of physical and chemical indicators.3.The results of fish resources investigation showed that 19 species of fish were collected from 3 orders,8 families and 19 families,including 17 species of fish from 7 families in the experimental area and 14 species of fish from 6 families in the control area,which was significantly less than that in the experimental area.There are 8 dominant species in the experimental area,including Culter erythropterus,crucian carp,carp,ear of wheat,carp like,silver carp,catfish and grass carp;there are 6 dominant species in the control area,including Culter erythropterus,crucian carp,carp,ear of wheat,carp like and silver carp.The dominant species in the two regions basically coincide,but there are more catfish and grass carp in the experimental area;the silver carp has the highest dominance in the two regions,the second and third experimental areas are Culter erythropterus and crucian carp,and the control areas are wheat ear fish and similar fish.From the perspective of fish body shape,the problem of fish miniaturization in the control area is more serious than that in the experimental area.The breeding and releasing of the experimental area and the construction of artificial fish nests have played a certain role in the recovery of fish resources.The fish biodiversity index of the three quarters in the area was in the general rich range;the richness of the experimental area was significantly higher than that of the control area,and the biodiversity index was also higher than that of the control area,although the difference was not significant(P>0.05),it also showed that the fish resources in the experimental area were more abundant than that in the control area.4.The results of stable carbon and nitrogen isotope analysis showed that the range of carbon isotope ratio in the experimental area was larger than that in the control area,which indicated that the food sources in the experimental area were more extensive;there was no significant difference between δ13C values of different food fishes in the control area(P>0.05);there was significant difference between δ13C values of different food fishes in the experimental area.There was no significant difference in δ 15N value between different feeding fishes in the control area(P>0.05).and there was significant difference in δ 15N value between different feeding fishes in the experimental area(P<0.05).The results showed that there was no significant difference in δ13C and δ15N between the two regions(P>0.05).The stable isotope coordinates of fish show that:the fish in the control area at the top of the polygon include carnivorous erythropterus culter,ophiocephalus Argus,omnivorous hellfish and loach;the fish in the test area at the top include carnivorous erythropterus culter,Siniperca chuatsi,catfish,omnivorous hellfish,loach,Chinese hellfish,herbivorous grass carp and bream.This shows that the nutritional structure of the experimental area is more complex than that of the control area,and there are more species of fish at the top of the experimental area than that of the control area,which shows that some measures such as proliferation and drainage in the experimental area have played a positive role in improving the nutritional structure of the ecosystem;however,no filter feeding fish in the control area and the experimental area are at the top,and only one filter feeding fish is found in the fish resource investigation,which is beneficial to the development of the ecosystem In the ecosystem,the energy flow of organic debris,zooplankton and plants into the food web is unfavorable.The average trophic level of fish in the control area and the experimental area was 3.09 and 2.80 respectively,the difference was not significant(P>0.05),but the trophic level of the same fish in the control area was slightly higher than that in the experimental area.This may be caused by the eutrophication of water quality in the control area and the entry of nutrients into the food chain,which results in the nutritional level of the whole food web in the control area slightly higher than that in the test area.The ratio of organic detritus and algae nitrogen in the control area was significantly higher than that in the experimental area,which was also confirmed by the difference of trophic level of benthos.5.Compared with the control area,the feeding chain of the ecosystem in the experimental area of yingyingdian lake has some changes,with the top predators increasing catfish and mandarin fish;the addition of phytophagous fish is conducive to the energy flow of aquatic plants into the ecosystem,increasing the complexity and energy utilization efficiency of the ecosystem,which is consistent with the results of stable isotope analysis.The energy conversion efficiency(Ⅱ-Ⅴ:0.0521,0.0205,0.0144,0.006)in the test area was higher than that in the control area(Ⅱ-Ⅴ:0.0406,0.0138,0.00854,0.00717);the total energy conversion efficiency(2.5%)in the test area was significantly higher than that in the control area(1.7%).This shows that the energy transfer efficiency in the ecosystem of the experimental area is improved by means of proliferation and release,which is beneficial to the development of the ecosystem.The increase of the total primary productivity/total respiratory value in the experimental area indicates that the development degree of the ecosystem in the experimental area is higher than that in the control area;the change of the connection coefficient and the omnivorous index in the experimental area indicates that the structure of the food web in the experimental area tends to be complicated,which reflects that the ecological measures such as proliferation and drainage promote the development of the ecosystem in the experimental area.Finn’s cycle index and Finn’s average path length(0.61 and 2.08)in the experimental area are lower than those in the control area(1.73 and 2.20),which is caused by the increase of phytophagous fish.The addition of phytophagous fish has a downward effect on the ecosystem of the experimental area.Top predators do not get nutrition from them,while producers and plankton are inhibited by phytophagous fish.It can be concluded that the further improvement of ecosystem supply and the improvement of ecosystem stability in the experimental area can be carried out from two aspects:appropriate fishing of phytophagous fish and increase of large-scale carnivorous fish. |
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