Development of a new water ecological health assessment method for small river in Shanghai, China

Seventeen indices were selected to structure a new water ecological health assessment system, consisting of water quality, ecological system, and ecological landscape, for evaluation of small rivers in Shanghai, China. There are 200 samples taken from 56 rivers distributed in ten districts from 2014 to 2015 in Shanghai, which were selected to constitute the study case, and the mean value of each indicator was used in the evaluation. According to various features, including natural geographical condition, social development level, etc., these rivers were classified as one of three types: central urbanization watercourse (CW), new town watercourse (NW), and village watercourse (VW). The results showed that the investigated rivers were at a medium health level, ranging from 1.79 to 3.59, with the average being 2.95. The ecological health of streams in rural areas is better than that of CW rivers and NW rivers. This study is expected to provide accurate statistics and appraisal for the improvement of river health. This is an Open Access article distributed under the terms of the Creative Commons Attribution Licence (CC BY 4.0), which permits copying, adaptation and redistribution, provided the original work is properly cited (http://creativecommons.org/licenses/by/4.0/). doi: 10.2166/wcc.2020.231 ://iwaponline.com/jwcc/article-pdf/12/4/1123/896268/jwc0121123.pdf Houtao Xu Linkui Cao (corresponding author) School of Agriculture and Biology, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China E-mail: clk@sjtu.edu.cn Liqing Wang Centre for Research on Environmental Ecology and Fish Nutrient of the Ministry of Agriculture, Key Laboratory of Exploration and Utilization of Aquatic Genetic Resources of the Ministry of Education, National Demonstration Center for Experimental Fisheries Science Education, Shanghai Ocean University, Shanghai 201306, China Xiaoyan Zheng Shanghai Aquatic Environmental Engineering Co., Ltd, Shanghai 201306, China


INTRODUCTION
The ecosystem degradation of small rivers has become a shortcoming for the water environment, which seriously affects the overall urban environment. Rivers gradually deteriorate in many functions, such as drinking water and fisheries, and are vital to economic prosperity (Costanza et al. ; Xu et al. ). Simultaneously, how to utilize practical objectives for supporting healthy river ecosystems is also becoming an object of concern for society. The issue of river health research has become one of the heated debates in the field of river ecosystems.
There are two methods for river health assessment currently used: one of which is biological monitoring with indicator species as representative biota; the other is comprehensive indicator methods (Zhao & Yang ; Zhang et al. ). Conventional biological monitoring methods include the IBI (index of biological integrity) (Karr ) and RIVPACS (River Invertebrate Prediction and Classification System) (Wright et al. ). Comprehensive indicator methods emphasize the ecological integrity (Fairweather ; Karr ). Such practices include rapid bioassessment protocols (RBPs) (Barbour et  In the process of city formation and development, rivers, as the critical carriers of resources in the natural environment, contribute an essential factor influencing the style and beauty of the urban environment and restricting urban development. Urban rivers have numerous functions, not only functions within natural systems but also social and economic services. Therefore, an urban river system is a complex system which is composed of a natural ecology subsystem and a landscape environment subsystem.
River ecosystem health is a relative concept, which is both objective and subjective, including people's individual expectations for the improvement of river ecological conditions. In this paper, the evaluation index system for river health was structured based on chemical, biological, and

Study area and data
Shanghai city is surrounded by the Yangtze River delta plain area and contains numerous lakes and rivers. The town includes 697 km 2 of water area, which accounts for 11% of the total area ( Figure 1). Around 2000, the Shanghai government implemented a channel improvement project in the form of a 'three-year act on environmental protection.' The project focuses on water quality as well as the aquatic ecosystem (Zhao et al. ).
Water quality data, biological data, and social data were collected from 56 rivers belonging to ten districts, with 200 samples taken from 2014 to 2015. These rivers are capable of representing all types of small streams in Shanghai.
Based on differing characteristics, these 56 rivers were classified as one of three kinds: eight central urbanization watercourses (CW), 20 new town watercourses (NW), and 28 village watercourses (VW). One-way analysis of variance (ANOVA) was used to test the differences among the three types of rivers, and differences were considered statistically significant at p < 0.05.

Evaluation indicator system
In this study, 17 indices were selected to structure an evaluation indicator system, which consists of chemical, biological, and social elements.

Chemical elements
where D G is diversity of fish genera and D F is diversity of fish families.
, S j is the number of species in j, S is the number of species in the list, and p is the number of the genus in the list.
S ki is the number of species in genus K in the directory, S k is the number of species in the family k in the directory, n is the number of genera in family k, and m is the number of fish in the directory.

Social elements
This indicator is a qualitative indicator that fully evaluates the ecological landscape condition and harmony with the surroundings. The ecological landscape condition was determined using surveys of nearby residents in the form of a questionnaire, while professionals scored harmony with the surroundings of each river. In consideration of its practical and operability conditions, ten professors and ten graduate students, who are studying river ecology, were 1. Determine the judgment matrix. First, the hierarchical structure model regarding the Shanghai river ecological evaluation system as the total object layer is built (A); second, river water quality (B 1 ), ecosystem (B 2 ), ecological landscape (B 3 ) are established as the first sub-object, and each specific index as the third one (C 1 , C 2 …… C 17 ) (Table 1).
Then, more than 20 experts in ecology, environmental science, and hydrology fields were invited to mark the 1-9 scale method proposed by Professor T. L. Satty (Table 2) to construct the judgment matrix.
2. The analytic hierarchy process determines the weight.
The weights of every aspect and total hierarchical order of each indicator are rated by the priority order and coherence verification.
Assuming a normal vector A at the same order, so that XA ¼ λmaxA, A in this characteristic equation is the weight of each evaluation factor after being normalized.
Due to the complexity of material things and the one-sided understanding of things, the constructed judgment matrix may not be a consistency matrix. Therefore, after obtaining λmax, consistency, and randomness tests need to be performed. The formula is as follows: In the formula CI is the consistency index; λ max is the maximum characteristic root; n is the matrix order; RI is the average random consistency index; CR is the random consistency ratio. A comparison matrix is expected to be consistent if the CR value is observed to be less than 0.10 (Table 3)

Evaluation standards
The indicators are given a numerical value or rating based on a five-point scale that provides a comparison with healthy conditions, as shown in Table 8

Indicator system
The evaluation result was calculated as follows: Index value of the secondary index The value of comprehensive evaluation index where A is the value of the comprehensive evaluation index, B is the evaluation value of secondary indicators, C is the evaluation value of three-level indicators, W i is the weight of the three-level indicators, and W j weight of the secondary The reciprocal of the above scale The scale of element i to j is a ij , contrarily is a ji where TLI is trophic level index; the unit for Chla is μg/L, and the unit for SD (transparency) is m.
A series of 0-100 consecutive numbers is adopted to grade the eutrophication level (Table 9).
Using the subjective evaluation method to evaluate the ecological landscape effect (Table 12), the rationality of plant collocation and visual esthetics were evaluated and divided into five grades with a point value of 1 to 5.

Quality of river water
The output of the evaluation model for water quality of 56 small rivers is shown in Figure 2. Those rivers are in central urbanization, new town, and village areas, respectively. The results show that the water quality scores are between 2.08 and 3.60 in CW, between 1.73 and 4.16 in NW, and between 2.29 and 3.88 in VW. Our results implied that the water quality of CW could be classified as medium; NW and VW can be classified as sub-healthy. Generally, the water quality in the CW was significantly worse than in NW and VW (p < 0.05), while there was no difference between NW and VW (p ¼ 0.15).

Ecological status
From the samples collected in Shanghai small rivers from 2014 to 2015, the ecological status evaluation results indicated that all the river reaches were at the sub-unhealthy and medium levels. The average scores for CW, NW, and VW were 1.75, 2.30, and 2.45, respectively; the ecological status of CW rivers was dramatically worse than for NW and VW rivers (p < 0.05), and the VW rivers had better ecological status scores (Figure 3).

Ecological landscape effect
According to the results of the questionnaire survey and evaluation, public satisfaction with river ecological landscapes is poor in the central urban area, and 62.5% of the rivers were classified as sub-unhealthy or unhealthy. The proportion of the ecological landscape in NW that was classified as sub-unhealthy or unhealthy was as high as

CONCLUSIONS
Our study structured a new water ecological health assessment, including physical and chemical, biological, and landscape elements for assessing river health, and selected 17 indices to describe these elements. Through a     However, due to the complexity of the aquatic ecosystem, more scientific and systematic research needs to be further optimized and deepened due to the influence of sample quantity and data accumulation.