Ecological Health Diagnosis Of Northern Coastal Urban Rivers With Rainfall Sources ——Case Of Jiahe River

Rivers are support systems for life on Earth.It is an important channel for material transfer and energy flow,which contains rich resources and has an important impact on the development of humanities and economy.With the acceleration of urbanization,urban river ecosystems have been damaged to varying degrees.Rain-sourced rivers in northern coastal cities have the characteristics of insufficient water source,complex hydrodynamics and poor self-purification ability.Its health diagnosis lacks theoretical basis.This paper takes the Jia River in Yantai City,Shandong Province as the research area,selects fish and benthic animals as the index species,the ecological health diagnosis model of rain-sourced rivers in northern coastal cities was established,and the structural characteristics of benthic fauna and the biological evaluation of water quality were analyzed.The main research contents are as follows:（1）Identification of water environment factor indicators and analysis of water environment status of each habitatBased on the large-scale habitat survey method,the velocity（V）,water depth（Dep）,substrate（Sub）,dissolved oxygen（DO）,ammonia nitrogen（NH₃-N）,slope protection vegetation（Vegetation）and Bank Protection（Bank Protection）and other index factors to provide data support for diagnosing river health.According to the characteristics of rain-sourced rivers in northern coastal cities,the rivers are divided into 5 habitat reaches:tidal reach,urban reach,semi-natural reach,natural reach and source reach.The results of the habitat survey showed that there was little seasonal difference in water depth and flow velocity.The water depth of the natural reach and source reach are significantly lower than that of other reaches,while the flow velocity is opposite.In terms of water quality,spring and summer are slightly better than winter and autumn,and the water quality of different habitats varies greatly.The water quality of different habitat reaches is quite different.The water quality of the tidal reach and urban reach only reach Class IV water or even below,and the water quality of semi-natural reach,natural reach and source reach can basically reach Class III.Except for the seasonal changes in vegetation,the riverbed topographic factors can not change significantly,and the semi-natural reach and natural reach have higher diversity and heterogeneity than the tidal reach,urban reach and source reach.（2）Construction of Jiahe Ecological Health Diagnosis Model Based on Index Fish and Analysis of River Ecological HealthThe tolerant fish Pelteobagrus fulvidraco（adult stage,spawning stage）and Anguilla japonica（adult stage）were selected as research objects.Based on fuzzy mathematics,using CURrent S software and combined with the selected indicator fish,the hydrological factors,water quality factors and river bed landform factors are integrated,and fuzzy sets and fuzzy rules were formulated according to the fish’s demand for index factors.Based on this,a river ecological health diagnosis model based on fish habitat suitability was constructed and ecological health analysis was carried out.The results showed that the habitat status of the target fish is not optimistic.The average habitat suitability index（AHSI）of Pelteobagrus fulvidraco during spawning and adult stages are 0.54 and 0.58,respectively.The velocity and substrate were the key factors limiting their survival.The habitat condition of the sensitive fish Anguilla japonica in adult stage is even worse,the AHSI was only 0.42 and there are large and extremely unsuitable patches.The limiting factors were water depth and water quality factors.The ecological health status of tidal reach,urban reach and source reach were slightly worse than that of semi-natural reach and natural reach.（3）Jia River ecological health diagnosis based on the characteristics of benthic faunaA total of 22,829 benthic animals were collected in the study area,belonging to 4 phyla,11 classes,27 orders,78 families,137 genera and 162 species.Among them,arthropods are the main ones,accounting for 80.57%,followed by annelida,granulifusus kiranus and platyhelminthes.The species composition of benthic animals varies greatly in space,and the community structure generally presents the characteristics of relatively single structure and strong pollution resistance.Arthropods accounted for the largest proportion of density,but their biomass was low;on the contrary,mollusks accounted for the largest proportion of biomass,but their habitat density was low.The habitat density and existing benthic fauna of the urban river reach were significantly lower than those of other river reaches.Based on the biological evaluation of water quality of benthic animals,the results show that all river reaches are polluted to different degrees.The benthic richness,diversity index and water quality of the natural and source reaches were significantly better than those of other habitats.The BI in summer is concentrated from 1.37 to 4.21,and the water quality is very clean,while the BI of the other three seasons is from 4.5 to 8.5.Only 1/3 of the points are in the clean range,and the others are in light and moderate pollution.The benthic richness,diversity index and water quality of the source and natural reaches were significantly better than those of other habitats.Through field research,screening of index species and index factors,division of habitat river segments,establishment of ecological health diagnosis model of rain-sourced rivers in northern coastal cities,analysis of benthic community structure characteristics and biological evaluation of water quality.The results show that all the habitats of Jiahe River are polluted to different degrees and the water environment is not optimistic.