Study On The Health Assessment Methods Of Medium And Small River Ecosystem

As the source of material and energy for large rivers such as the Yangtze River,Medium and Small rivers health status,the lifeline of rural drinking water safety,has become a global concern.In the context of the great protection of the Yangtze River,the construction of a health assessment system for medium and small rivers is of great significance for improving the health assessment system of rivers in China and is the theoretical basis for promoting the healthy development of the Yangtze River aquatic ecosystem.In this paper,the health of Qiaobian River(QBR),a tributary of Yangtze River,China was evaluated by investigating the distribution of macroinvertebrates,chemical and physical parameters during Jan.2019(low flow season)and Aug.2019(high flow season).Based on habitat suitability of dominant macroinvertebrates,the key habitat factors were screened by canonical correspondence analysis(CCA)and Pearson correlation analysis.This paper initial proposed a new river health assessment method,macroinvertebrates habitat suitability curves(M-HSC),to evaluated medium and small rivers health status.On the other hand,comprehensive indicator method—Pressure-State-Response model(PSR)was also applied in the estimated work.To selected apt assessment method between the comprehensive indicator method and the biological monitoring method to the assessment of the health of medium and small river ecosystems and to provide a theoretical basis for future ecological restoration of them,the M-HSC evaluation results were compared with the PSR evaluation results.Here are the results of our research:Temporal and spatial characteristics of habitat factors in the QBR:Chemical and physical factors in QBR indicated the habitat conditions in high flow season are relatively good,the average values of ?(TN)and ?(TP)were 0.470 mg/L and 0.078 mg/L,respectively,and both did not exceed the GB 3838-2002 Class II standard limit.The habitat condition of QBR in low season was worse than that in high season,and all water quality indicators had increased compared with the high season.Among the species of macroinvertebrates in the QBR,Arthropoda were the most abundant,accounting for 68.4% of the total species,followed by Mollusca,accounting for 26.3% of the total species,and Annelida were the least,accounting for 5.3% of the total species.The community structure of macroinvertebrates in the upper,middle,and lower regions of the QBH changed swiftly,but the changes were slowly in each season(dry season,high season).The results of biodiversity survey showed that the biodiversity of macroinvertebrates in QBR was at the general level.Assessment of QBR health based on macroinvertebrates habitat suitability curves:The results showed CODMn?TN?Tur?Dep were the variables with the greatest negative impact and DO had the greatest positive influence.Most suitable conditions for Corbicula fluminea containing chemical oxygen demand(CODMn)of 1.48 mg L-1,total nitrogen(TN)of 0.27 mg L-1,dissolved oxygen(DO)of 11.17 mg L-1,p H of 8.42,turbidity of 1.76 NTU,and water depth(Dep)of 0.35 m.The health status of QBR is spatially heterogeneous with the apparently better upstream than the downstream.The health evaluation results showed that there were two samples in the natural state of the QBR in the low season,S8 and S7,which are basically distributed upstream and near the source.There was a sample in the healthy state,S6,which is located in Tucheng Country Tour;S5 was in a sub-health state;S4 and S3 were in an unhealthy state;a total of two diseased sites were S2 and S1,located near the estuary.There were 3 samples in the natural state during the high season,which are S8,S7,and S6;S5,S4,and S3 were in a sub-health state,and S3,S2,and S1 were in an unhealthy state.The health status of QBR showed obvious spatial heterogeneity.The upstream health status was better.The further downstream,the worse the health status.Both low season and high season showed the same trend.The temporal heterogeneity of the health status of the QBR was also noticeable,the health status in high season is significantly better than in low season.Assessment of QBR health based on PSR method:Based on the PSR model,a health assessment index system containing the pressure layer,the state layer,and the response layer was devised.It covers the change rate of precipitation,population density,water resource development and utilization,river connectivity,water temperature variation,and eutrophic Degree of environmental protection,ecological base flow compliance rate,urban domestic sewage treatment rate and related laws and regulations.The evaluation index weight is expressed as pressure layer> state layer> response layer.The results of the health evaluation showed that there were two samples of the QBR above the healthy state in low season,S8 and S7,respectively,which are basically distributed near the upstream and the source;one sample was in a sub-healthy state,S6,and is located in the rural tourism of Tucheng;The remaining samples were in an unhealthy state,accounting for 62.5% of the total samples.There were 3 samples that were above the healthy state during high season,S8,S7,and S6,respectively;S5,S4,and S3 were in sub-healthy state,and the estuary samples S2 and S1 were unhealthy.Consistency analysis of different river health assessment methods,the biological monitoring method and the comprehensive indicator method:The applicability of the comprehensive indicator method in the dry season is better than the biological monitoring method,and the biological monitoring method in the high season is better than the comprehensive indicator method.What's more,the comprehensive indicator method in population gathering areas and urban areas was better than that of the biological monitoring method,and as of the sparsely populated areas and mountain areas,the biological monitoring method is better than the comprehensive indicator method.