Ecosystem Health of the Beiyun River Basin (Beijing, China) as Evaluated by the Analytic Hierarchy Process Method

57 Ecosystem services provided by river ecosystems rely on healthy ecosystem structure and ecological 58 processes. The Beijing-Tianjin-Hebei urban is a typical water-deficient area. As an important part of the 59 urban-rural integration construction, evaluating the health status of the Beiyun River Basin and 60 discovering the weak links in the water environment is the basis for improving the health of the basin. In 61 this study, Analytic Hierarchy Process was used to establish an evaluation index system for the Beiyun 62 River Basin from 5 aspects including water quality, biology, habitat, hydrology, and social functions, and 63 to assign weights to the index layer. The evaluation results showed that the health evaluation results of 64 the Beiyun River Basin in 2019 are “sub-healthy”, and the overall health status is gradually worsening 65 from northwest to southeast. In the middle reaches of the region, the evaluation result is "healthy", 66 followed by the upstream, and the downstream is the worst. The results showed that areas with less 67 human interference are in better health. The factors that affect the overall health evaluation status in the 68 basin are the level of nutrition, biodiversity, and vegetation coverage. For the comprehensive 69 management of the Beiyun River, the improvement of water quality and habitat ecological restoration is 70 the key to the health of the upstream ecosystem health status. The improvement of the health status of 71 the downstream should focus on equal emphasis on water quality and quantity, restoration of biodiversity, 72 and improvement of the quality of the riparian ecological environment.


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River ecosystems provide a variety of ecological services for human society. These ecosystem 77 services rely on a healthy and functionally intact ecosystem. In recent years, the acceleration of China's 78 industrialization and urbanization has increased the disturbance to the natural ecosystem (Rubinato et al. 79 2020). The discharge of pollutants from industrial production and agricultural activities seriously exceeds 80 the purification capacity of the aquatic environment (Peng and Deng 2020). As a result, the ecosystem 81 of the river basin was destroyed, the water quality of the water body deteriorated, and the biodiversity 82 decreased (Pereda et al. 2021). Urban river pollution negatively affects the stable performance of aquatic 83 ecosystem functions and sustainable social development (Kakar and Khan 2021). Therefore, Sustainable 84 management assessment of river health is necessary.

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River health includes the natural health of the river, the ability to provide a good ecological 86 environment, and social service functions (Wu et al. 2020b). Since the concept of river health was put    2021) . However, analyze the overall health status of the Beiyun River basin from the aspects of water 106 environment, water ecology, and water resources is still lacking. Therefore, this paper uses the AHP to 107 evaluate the Beiyun River basin with 13 indicators from 5 aspects: water quality, habitat, hydrology, 108 biology, and social functions. The primary purpose of this study is to analyze the overall health of the 7 monsoon, with an average annual rainfall of about 650 mm, 75% of which is concentrated between July 121 and August (Wu et al. 2020a     Where, aij represents the importance of the i-th element and the j-th element relative to a factor in 147 the previous layer. Matrix A is the judgment matrix (or paired comparison matrix).

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When the matrix A=(aij)n×n satisfies aij＞0 and aij= 1 (i, j=1, 2, …,n), it is called a positive and 149 negative matrix. Compare the values of matrix elements aij in pairs using numbers 1-9 (See Table 1  (2) 162 Where, λ max represents the maximum eigenvalue of matrix A.

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CI=0 means completely consistent, the larger the CI, the more inconsistent； 164 Query the random consistency index RI according to

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The total ranking of levels is to calculate the relative importance of all factors of a level to the 172 highest level. As shown in Table 3.

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The total ranking random consistency ratio of the B layer is: Where, CI(j), (j = 1, 2, ..., m) is the consistency index of level single ordering, which is the B level

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When CR<0.10, it is considered that the total ranking result of the level has a satisfactory 183 consistency and the analysis result is accepted.

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The above AHP calculation is conducted in SPSS 22 software.

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(1) Riparian environmental quality was scored according to Table 4.

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NDVI 215 Where NDVI is the normalized difference vegetation index, NIR is the near-infrared band, and R is 217 the infrared band. The NIR and R bands of Sentinel-2 were band 8 and Band 4, respectively.

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VFC 219 Where NDVI soil is the NDVI value of completely bare soil or non-vegetated area, and NDVIveg is 221 the NDVI value of pure vegetation pixels.

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(3) As shown in the The amount of water is large, and the river water is submerged on both sides of the river bank, or there is a very small amount of river exposed.
The water volume is large, and the river floods about 75% of the river course.
The amount of water is average, and the river floods 25-75% of the river course.
The amount of water is very small and the river is dry.     Where C0 is the total water resource utilization, and C1 is the total water resource utilization.

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The monthly water quality monitoring status in 2019 is shown in Fig. 2. The water quality in the 282 middle reaches was the best in terms of conventional water quality parameters and trophic levels and

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The evaluation results are shown in Fig. 3 (a). In general, the upstream evaluation is higher than the 326 midstream, and the downstream is the last, especially in the lower reaches of the Beiyun River,

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Fenggangjian River, and Xinfeng River. In the densely populated middle reaches of Haidian District,

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Dongcheng District, and Xicheng District, the environmental quality of the regional riparian zone is also 329 excellent. The overall evaluation average is 63, indicating that the environmental quality level of the 330 riparian zone in the Beiyun River Basin is "healthy". Among the three indicators, the riparian habitat 331 type had the lowest score, and the slope erosion index and the water-water landscape comfort had 332 relatively high scores.      Table 7, the 407 results showed that the phytoplankton diversity index ranged from 0.85 to 4.07, with an average of 2.73, 408 and the evaluation result was "healthy". As we can be seen in the fig. 5 (a), the community structure of 409 the catchment is rich. In the Wenyu River's upper reaches, the middle reaches of the Beiyun River, and 410 the Xinfeng River, the diversity index was low, and the water quality was poor. The community structure 411 was most abundant in Middle reaches of the Beiyun River Basin. The water body was also cleaner, and 412 the habitat quality was excellent. The benthic diversity index ranged between 0 and 2.06, with an average 413 of 0.83. According to the benthic diversity, it is evaluated as "sick". Compared with the phytoplankton 414 diversity, the benthos diversity index is relatively small, and the evaluated habitat quality type is average.

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The results showed that the concentrations of N and P and the ratio of N to P had significant effects

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According to this index, the community structure of phytoplankton in the Beiyun River Basin was rich.

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Considering that the samples were collected in January and February, less benthos was collected this

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evaluation result is shown in Fig 6. The average water quality compliance rate is 74%, and the evaluation 432 grade is "healthy". Compared with the water quality management targets set during the Thirteenth Five-

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Year Plan period, the situation is more optimistic. Some rivers such as Xipaigan, Guanyintang Minggou,   is in a "sub-healthy" state. In the middle reaches of the area, with a developed economy and the best 457 health in the entire basin, the evaluation result is "healthy". In upstream areas where land use is mainly 458 woodland and cultivated land, and the health evaluation result is "sub-healthy". In the Xinfeng River

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(downstream), which is dominated by townships and cultivated land, and the health evaluation result is 460 "unhealthy". The results show that the health status of the areas less disturbed by human activity is better.

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Therefore, in the future, we can coordinate the relationship between economy and nature through human

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On the whole, the health assessment result of the Beiyun River Basin is "sub-healthy", and the 468 overall health status shows that the northwest mountainous area is better than the southeast plain.

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Specifically, the evaluation result is "healthy" in the middle reaches of the region, and the upstream 470 evaluation result is "sub-healthy", and the Xinfeng River region located downstream is "unhealthy". In The maps of Beiyun River Basin Note: The designations employed and the presentation of the material on this map do not imply the expression of any opinion whatsoever on the part of Research Square concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors.    whatsoever on the part of Research Square concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors.  Water quality standards of each reach in the Beiyun River Basin Comprehensive health assessment of the Beiyun River Basin Note: The designations employed and the presentation of the material on this map do not imply the expression of any opinion whatsoever on the part of Research Square concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors.