Ecological Investigation On Aquatic Ecological Restoration In Jialu River And Research On Ecosystem Functioning

With the economic growth and urbanization development,increasing industrial and domestic wastewaters were discharges into the Huaihe River basin,result in seriously river pollution.As a secondary tributary of the Huaihe River,the Jialu River has been regarded as a typical polluted urban receiving river.The Jialu River system is serious polluted,affecting people’s normal life and farmland irrigation in the river basin.Under this conditions,the nation launch a series of ecological restoration projects.Our lab undertook one of the project,the Research and Demonstration Project of Key Techniques of Aquatic Ecological Restoration of Ditch Rivers under Normal Flow Conditions(2012ZX07204-004-003).Based on various ecological surveys and ecological function research on the Jialu River,an ecological technology for the Jialu River was proposed.These include the restoration threshold based hydrobiological biodiversity restoration technology,the environmental flow identification based construction technology of aquatic biological function groups,and the food chain restoration technology of ditch river ecosystem.Combining with technologies such as shallow banks and deep trenches,ecological islands,ecological spur dike,ecological riverbank,as well as tool species equivalence technology,a 30 km long project against the ecological restoration of Jialu River was carried out.The current paper is the result of the basic ecological survey and related mechanism research before and after the implementation of this project.The mian results are as follows:1.The post-project water status including water quality improvements and the steadiness of such improvements in Jialu River were investigated.After the restoration project,the average concentrations of dissolved oxygen(DO),ammonia nitrogen(NH4+-N),total nitrogen(TN),total phosphorus(TP),and chemical oxygen demand(COD)were 4.47 1.48,11.85,0.66 and 18.89 mg·L-1 respectively.Part of the water indices(DO,COD and NH4+-N)in part of the river segment had been under III level of the Chinese surface water standard.These values keep steady post the project,indicating the sustained and stable water purification capacity of the project.Comparing to the pre-project,the water quality was improved significantly.Overall,the average reduction of the concentrations of TN,TP,COD,NH4+-N were 38.69%,40.52%,39.06%and 45.07%,respectively.2.The richness and distribution of the native species of Jialu River were investigated,and the restore degree of the wetland ecosystem was assessed by comparing the changes between pre-and post-project along the river segment.Besides the species from zooplankton and phytoplankton that distributed evenly regardless of monitoring sites and date,species richness belonging to other groups display dramatically different.Totally we found 155 species,belonging to 94 family.Shore plant account for the largest part of the family(26.53%),followed by zooplankton,zoobenthos,and then phytoplankton.Most of the species occur only in one or two sites,with 78 species in one(account for 51.32%)and 31 in two sites(20.39%).Only 9.87%species(occurred in at least five sites)is widely distributed.Poaceae with 12 species was the largest family,and had higher species richness in most of the monitoring sites,followed by Asteraceae(7 species),Fragilariaceae(6 species),Naviculaceae(5 species),Amaranthaceae(4 species),Cyperaceae and Cyprinidae(4 species).Compared with July 2013,on July 2015 we found more species with the average species increment was 65.61%.Totally 31 novel dominant species was found on July 2015.Among them shore plants had 12 species.3.The ecological functional characteristics of plant-animal-decomposition community of Jialu River were studied.The detrital food chain of shrimp-plant detrital-microbial decomposers was studied by investigating the direct(grazing)and indirect(feces)effects of shrimp Neocaridina denticulate on the decomposition of Typha angustifolia litters.During the 140-day decomposition period,the net overall effects of shrimp enhanced decomposition by 63.5%,which was 32.8%of mass loss.Shrimp grazing contributed 81.7%of the enhanced decomposition,whereas feces contributed 18.5%.During the decomposition process,the early stage displayed the net effect of feces,whereas in the final days it was mainly attributed to intensive grazing,which maintained litter breakdown at high speed.The presence of shrimp greatly improved the hydrolytic extracellular enzyme activities,especially peroxidase and phenol oxidase.Meanwhile,the presence of shrimp greatly enriched the water nutrients,total phosphorus in particular.However,selective absorption of NH4+-N by microorganisms caused its shortage for decomposers,suggesting their great demands for NH4+.Redundancy analysis showed that water physical and chemical properties could explain 73.5%of the variation of enzymatic activities.Besides directly grazing of shrimp,the main factors affecting decomposition were enzymatic activities in the absence of shrimp,while in the presence of shrimp,the factors changed to water physical and chemical properties(mainly pH,total nitrogen and phosphorus,and NO3--N).Our results demonstrated that in detrital food chain some aquatic animals,like shrimp,not only breakdown leaf litters by grazing,but also stimulate the microbial activities by their byproducts such as feces.4.The effects of algae-shrimp on decomposition system in the Jialu River aquatic ecosystem were studied through microcosm experiments.Net-separation method was employed to manipulate the leaf litters of T.angustifolia to expose them to fecal pellet and/or shrimp grazing or not.Then the green algae Chlorella vulgaris was supplied,the effects of primary producer on the detrital food chain was studied through the shrimp feeding/fecal pellet-organic residue decomposition system.Algae supplement largely shorten the microbial conditioning time for shrimp grazing,with grazing occur after 42 days(maybe earlier),while this occur after 84 days without C.vulgaris addition.The overall effects with C.vulgaris on enhancing litter decomposition was 25.0%of AFDM loss,which increase 62.2%comparing to the effect that no C.vulgaris addition.Fecal pellet(rich in ash content)improved the grazing effect of shrimp on litters,promoting the decomposition.Without shrimp grazing,algae supplement provide a limited promoting effect on litter decomposition.Both algae supplement and fecal pellet promoted the shrimp grazing on the leaf litters,while shrimp grazing in trun enhance the stimulating effect of algae supplement and fecal pellet on litter decomposition.They form a synergistic relationship in promoting litter breakdown.Shrimp grazing not reduce the microbial activities(i.e.,activities of extracellular enzymes)but rather enhance it,especially in the presence of both algae enrichment and fecal pellet,in which condition microbial biomass was the highest.The regulation on microbial decomposers by shrimp grazing,algae supplement and fecal pellet lead to the carbon reduction and nitrogen enrichment in the decomposing T.angustifolia leaf litters,significantly increasing the litter quality.The research showed that primary producers can significantly stimulate the detrital food chain,improve the decomposition efficiency,and promote material cycling.5.The distribution of arbuscular mycorrhizal fungi(AMF)on the shore plants of the Jialu River was investigated,and the regulation and functions in ecosystems of the plant-AMF symbiotic system in Jialu River were studied.Through microcosm experiments,the effects of nutrient requirements of producers on the decomposition system through the AMF symbiotic system were studied and the regulatory mechanism was elucidated.Results showed that AMF colonization had no significant effect on litter decomposition under normal soil nutrient conditions.However,litter decomposition was accelerated significantly under lower nutrient conditions.Soil microbial biomass in decomposition system was significantly increased.Especially,in moderate lower nutrient treatment(condition of half normal soil nutrient),litters exhibited the highest decomposition rate,AMF hypha revealed the greatest density,and enzymes(especially nitrate reductase)showed the highest activities as well.Meanwhile,the immobilization of nitrogen(N)in the decomposing litter remarkably decreased.The results suggested that the ecological function AMF played in decomposition ecosystem were largely affected by soil nutrient levels.At normal soil nutrient level,AMF exhibited limited effects in promoting decomposition.When soil nutrient level decreased,the promoting effect AMF on litter decomposition began to appear,especially on N mobilization.However,under extremely low nutrient conditions,AMF showed less influence on decomposition,may even compete with decomposer microorganisms for nutrients.In summary,after undergone ecological restoration,water quality of the Jialu River has been greatly and steadily improved;the constructed ecological project has a sustainable water purification capacity.The Jialu River’s native species richness has been significantly improved,and the species number has increased by an average of 65.61%,including a large number of new found species.In detrital food chain,aquatic animals not only directly(feeding)but also indirectly(byproducts)exert ecosystem functions on decomposition system and regulate the ecological processes.The primary producers have a strong regulatory effect on the sauteed food chain and interact with the predators to regulate the functions of the ecosystem.The shore producers of river can through nutrient demand using the belowground AMF symbiosis system to regulate the decomposition system to perform ecological functions.