Plain River Network Region Research Articles

Temporal and Spatial Characterization of Sediment Bacterial Communities from Lake Wetlands in a Plain River Network Region

Sediment bacterial communities are a vital component of microbial communities in aquatic and terrestrial ecosystems and they play a critical role in lake wetlands. We aimed to investigate the effect of season, depth and regional environmental factors on the composition and diversity of bacterial communities in a plain river network area from Taihu Basin. The millions of Illumina reads (16S rRNA gene amplicons) at the surface 25 cm inside samples of the study area were examined using a technically consistent approach. Results from the diversity index, relative abundance, principal component analysis (PCA), redundancy analysis (RDA) and linear discriminant analysis effect size (LEfSe) analysis indicated that the diversity of the bacterial community in summer was generally higher than in other seasons. Proteobacteria were the most abundant phylum in the sediment samples in different seasons (43.15–57.41%) and different layers (39.66–77.97%); the autumn sediments were enriched with Firmicutes (5.67%) and Chloroflexi (12.5%); in all four seasons the sediments were enriched with Betaproteobacteria (14.98–23.45%), Gammaproteobacteria (11.98–14.36%) and Deltaproteobacteria (8.68–14.45%). In the bottom sediments (10–25 cm), Chloroflexi were abundant (average value 10.42%), while Bacteroidetes was the dominant phylum in the surface sediments; redundancy analysis found that total phosphorus (TP) (p = 0.036) was the main environmental factor influencing the sediment bacterial community in different layers. This study provides a reference for further understanding the effects of seasonal changes on sediment microorganisms in lake wetlands.

Hydrochemical characteristics of groundwater in a plain river network region: Establishing linkages between source and water quality variables

The chemical characteristics of groundwater can indicate water quality condition and provide useful information for pollution source identification. This study aimed to understand the effects of dissolved organic matter (DOM) on ionic composition of groundwater and identify the main ions and sources of pollution. The Lake Taihu is a typical eutrophic lake in China. In this study, the hydrochemical composition of groundwater in the surrounding aquifer of Lake Taihu Basin was analyzed. The results showed that the values of water quality index (WQI) range from 13.29 to 56.26 (good water quality). The dominant hydrochemical type of groundwater was Ca–Mg–HCO3 type, and the rock dominance was the major mechanism controlling the groundwater chemistry. With an increasing concentration in dissolved organic carbon (DOC), the Na+, Mg2+, and HCO3– concentrations all showed a sharp increase followed by a slow increase, while the NO3– concentration showed an opposite trend, indicating the DOM can affect the ions composition. In addition, K+ was positively correlated with NO3–, As, and Cd. Hence, DOM input may directly or indirectly change the hydrochemistry of groundwater. Besides, the NO3– concentration in groundwater was much higher than that in Lake Taihu, indicating that the NO3– in groundwater mainly came from surface soil leaching. The anthropogenic sources are probably the main sources of different ions, including K+, NO3–, As, and Cd. This study can help to better understand the effects of lake eutrophication on groundwater and its pathways.

Online Storage Technology of the Separate Sewage System: Demonstration Study in a Typical Plain River Network City

Due to the high underground water level, frequent rainfall, and large amounts of infiltration and inflow (I/I) into the sewage system, a city in the plain river network region had to face a series of problems caused by the high water-level operation of the drainage system. Suzhou, a city in the Yangtze River Delta region of China, can be a representative of cities in plain river networks, where this research was carried out. The amount of I/I into the sewage system was evaluated, and the storm water management model (SWMM) was used to further calculate the sewer water storage capacity under dry and wet weather with multi-year average rainfall. Based on the offline model calculation and artificial experiences, the rule-based online regulation and storage real-time control strategy (RTC) is verified, and the online regulation and storage intelligent scheduling demonstration is carried out in the central-city district of Suzhou. The results showed that the infiltration in dry weather accounted for about 20–25% of the total collected wastewater; in wet weather (36 mm precipitation), the extraneous water induced by I/I peaked at 73.64%. The collaborative control of regional multi-stage pumping stations through RTC of the sewage system can effectively avoid the high water-level operation caused by peak sewage flows on dry days. In combination with rainfall forecasting, the coordinated control of plants and pumping stations to pre-empty the sewer pipelines prior to rainfall can, to some extent (up to 35 mm of rainfall in this study), cope with the increase in I/I induced by rainfall.

Exploring the Cumulative Selectivity of Polycyclic Aromatic Hydrocarbons in Phytoplankton, Water, and Sediment in Typical Urban Water Bodies

To understand the interactions among eutrophication, algal bloom, and POPs (persistent organic pollutants) in freshwater ecosystems, the cumulative selectivity of PAHs (polycyclic aromatic hydrocarbons) in phytoplankton, water, and sediment with different eutrophication level waters were identified in a typical plain river network region located in Nanjing City. Results showed that a total of 33 algal species belonging to 27 genera and 4 phyla were identified in 15 sites of urban water bodies, and most of them belonged to the type Cyanobacteria–Bacillariophyta. The eutrophication level of these rivers and lakes led to the sample site specificity of algal composition and abundance. The planktonic algae mainly accumulated the 2-ring and 3-ring PAHs, and the sediment mainly enriched the high-ring PAHs. However, the enrichment capacity of planktonic algae on PAHs was much higher than that of sediment. Cyanophyta and some species of Bacillariophyta and Chlorophyta in mesotrophic (βm) and meso-eutrophic water bodies (ßαm) preferentially accumulated lower-ring PAHs (naphthalene, acenaphthylene, and phenanthrene). Some other specific algae species, such as Euglenophyta, some species of Bacillariophyta, and most Chlorophyta in mesotrophic and moderate eutrophic water bodies, had strong capacities to enrich high-ring PAHs subsuming benzo[a]anthracene, chrysene, and anthracene. The eutrophication level of water bodies affected the cumulative selectivity of PAHs by shaping the site specificity of phytoplankton composition, which may be related to water quality, sediment characteristics, phytoplankton composition, and the algal cell walls.

Incorporating receiving waters responses into the framework of spatial optimization of LID-BMPs in plain river network region

Deep insights into the receiving waters responses to optimal spatial allocation of LID-BMPs are considered extremely important. This study addressed the urgent need to incorporate receiving waters responses into the spatial allocation optimization of LID-BMPs and demonstrated the efficiency of the approach to guide watershed management. The integration of an overland-river coupling model and the NSGA-III algorithm resulted in the proposal of a general simulation-optimization framework for the optimal layout of LID-BMPs. The coupled model was swapped out for the surrogates to increase computational efficiency. When 40.71%, 36.06%, and 61.80% reductions in runoff volume, flood volume, and TP concentration are achieved, the newly proposed framework can save 34.44% and 16.31% cost compared to the approach that does not consider receiving waters responses and refined spatial allocation, respectively. Results indicate that the incorporation of receiving waters responses and refined spatial allocation are essential for the optimal design of LID-BMPs. This new framework offers the potential for more cost-effective high-cost solutions. The results of spatial optimization are significantly influenced by imperviousness.

Spatial patterns of associations among ecosystem services across different spatial scales in metropolitan areas: A case study of Shanghai, China

Understanding the spatial patterns of ecosystem service (ESs) supply and their multiscale associations are prerequisites for optimizing blue-green space planning and sustainable management in metropolitan areas. This study selected Shanghai as a typical metropolitan area in the plain river network region, and five key ESs were mapped. Based on ESs supply efficiency, an ESs cumulative curve method was proposed to identify ESs hot spots. The bivariate local Moran’s I was used to compare the trade-offs and synergies among ESs and their spatial distributions across the four grid scales and two administrative division scales. The results showed a strong spatial heterogeneity of ESs supply and a scale dependency of the associations among them. The high-value areas of the ESs supply were mainly distributed in the west, north, and south. The hot spots of each ecosystem service accumulated more than 55% of each service, but only occupied areas less than 30% of the whole area. The synergies of four of ten pairs of ESs remained consistent across all scales. At the grid scales, they were all synergistic. The synergies of nine pairs of ESs decreased as the scale increased, and the other pair showed the opposite trend. At the administrative division scales, almost all pairs exhibited the strongest synergies at the district scale, and six pairs were trade-offs at the subdistrict scale. The scale effects indicated that the district scale was appropriate for decision-making in metropolitan areas, but the subdistrict-scale results should not be directly used as a reference. Finally, hierarchical planning and conservation policies and differentiated management policies at different administrative division scales were proposed. This study contributes to creating win–win options and improving human well-being. The analytical framework can be applied to across regions and to assess the ESs supply under various planning scenarios.

Dissolved oxygen variation in the North China Plain river network region over 2011–2020 and the influencing factors

The 2011–2020 data of dissolved oxygen (DO) and nutrients—total phosphorus (TP), solution reactive phosphorus (SRP), total nitrogen (TN), ammoniacal nitrogen (NH3–N), and chemical oxygen demand (CODCr)—in the North China Plain river network region were analyzed. Moreover, the DO variation trend and the influencing factors were investigated. The results showed that between 2011 and 2020, the DO concentration steadily increased from <3 mg L−1 to >5 mg L−1. Negative relationships were observed between the DO and CODCr (R = −0.34, p < 0.01), TN (R = −0.41, p < 0.01), NH3–N(R = −0.40, p < 0.01), TP (R = −0.28, p < 0.01), and SRP (R = −0.19, p < 0.01), indicating that a reduction in the nutrient input promoted the increase in the DO concentration in the past decade. The DO concentration in the rainy season was lower than that in the dry season, which suggests that nonpoint-source pollution caused by heavy storm runoff was the main factor affecting the water quality. The average DO concentration in the suburban rivers (4.88 mg L−1) was higher than that in urban rivers (3.41 mg L−1). Furthermore, comprehensive analysis indicated that the loss of riparian buffer, river solidification, pollutant input, and sluice dam operations are the main factors affecting DO concentration decrease and water quality deterioration. Finally, measures for water improvement and DO recovery in the river network region, namely pollutant input control, reduction in the impact of water conservancy projects, and river ecological restoration, were examined. Overall, this study shows that water quality has improved over the past decade. The study results provide a reference for the continuous improvement of water quality and the continuous recovery of DO in river network regions.

Atmospheric and human‐induced impacts on temporal variability of water level extremes in the Taihu Basin, China

AbstractUnderstanding the variation of water level extremes with their potential drivers can provide insights for flood risk management. In this study, temporal variability of water level extremes is investigated across the plain river network region of the Taihu Basin. The driving force analysis on water level extremes is mainly conducted for atmospheric (rainfall, climatic index, and tide) and anthropogenic forcing. The quantile perturbation method is employed to examine variability of extreme values and the Spearman correlation analysis to identify potential drivers of extreme water level variability. Considering water level extremes in all seasons, the 1990s have statistically significant positive anomalies, while the late 1960s to the 1970s and the 2000s have significant negative anomalies. The oscillation pattern of anomaly in summer has a higher variability than that in the other three seasons. Significant correlations are detected between the anomalies of water level extremes and rainfall (tide level) during summer and winter. Water level extremes in summer and winter have a strong connection to the Pacific Decadal Oscillation and North Atlantic Oscillation/Arctic Oscillation, respectively. Conversely, no consistent significant correlations between water level extremes and climatic indices are found in spring and autumn, which is mainly related to hydraulic structure construction and operation.

Non-stationarity analysis of extreme water level in response to climate change and urbanization in the Taihu Basin, China

Regional climate change as well as urbanization are likely to introduce characteristics of non-stationarity in the extreme water levels (EWL), which in turn will affect the possibility of flooding in the plain river network region. For this study, China’s Taihu Basin as a typical case for analyzing the impacts that climate change and urbanization will have on changes in the EWL. Additionally, changes in the response that EWL will have toward future climate change and urbanization are also studied. A generalized additive model for location, scale and shape (GAMLSS) model with time (t), precipitation (pre) and population (pop) as major predictors was constructed to empirically investigate. Results indicate that the time dependent variables of the GAMLSS clearly describe the temporal variation of the EWL. The GAMLSS with physically-based covariates can capture additional details regarding the changing properties of EWL. According to changes exhibited in the EWL Akaike information criterion values, it is found that the impacts of climate change covariates are larger than that of the urbanization covariates. Additionally, for the study’s sample period of 2015–2099, an increasing trend is found for EWL under the RCP2.6 and RCP4.5 scenarios. It is concluded that flooding risk is likely to increase in China’s Taihu Basin with changing environment conditions, and that some necessary measures should be taken by local water resource management authorities to address the potential risks posed to the region.

Characteristic Analysis and Loss Accounting for Water Pollution in Plain River Network Region - A Case Study of the Yangtze Delta

Because there are many water systems, severe human activities, increasingly serious water pollution problems and great economic loss in the plain river network region, the establishment of scientific and reasonable economic loss function is necessary to guide the protection and management of water resources. Taking the Yangtze Delta as an example, the characteristics of water pollution in the same period are that the flood season is stronger than the non-flood season. The analysis based on the physical mechanism shows that the process of economic loss of water pollution not only accords with S-type curve but also gives a reason for the S-type curve from the aspect of mechanism. The water pollution loss rate function which is constructed on the basis of hyperbolic tangent function divides the development stage into such three stages as non-enrichment, enrichment and saturation of pollutants, gives turning points of each stage as well as the solution and significance of parameters and enriches the physical process of models. The results of living samples show that the comprehensive water grades can be obtained easily and quickly through the river length failure rate. Their good correlation has certain promotion significance. The total water pollution economic loss is bigger. The average economic loss in the flood period from May to July is bigger than that in the flood period from August to September and non-flood period. The living samples prove that there exists pollutant diffusion phenomenon in the flood period.

Effects of anthropogenic activities on long-term changes of nitrogen budget in a plain river network region: A case study in the Taihu Basin

Over recent decades, Taihu Lake, the third largest freshwater lake in China, has borne the brunt of intensive human activities. Non-point source pollutants and discharges of domestic wastewater are now the main cause of eutrophication. To control non-point source pollution, it is useful to have a good understanding of the spatial and temporal distribution of N (nitrogen). In this study, we applied Export Coefficient Model (ECM) and the Net Anthropogenic Nitrogen Inputs (NANI) method to estimate the N loads in the Taihu Basin at county scale since 1980. We found that N inputs and exports had increased from 6432 and 3170 kg N km−2 yr−1 in 1980 to 9722 and 4582 kg N km−2 yr−1 in 2010, respectively. The 151% increase of N inputs, but 144% increase of riverine N outputs suggested the more N was retained within the Taihu Basin. Both the population density and the urban areas were strongly correlated with N inputs and exports. Approximately 38% of the N inputs were exported in 2010, but only 19% were exported in 1980. This ratio illustrated that human activities, especially urbanization and population growth, have upset N budget in the Taihu Basin. This study supported by empirical models provides a case to demonstrate the N cascade in the Taihu Basin and can also be used to support decision making and to facilitate the development of measures to control N in the future.

Characteristics of shallow groundwater and its influences in plain river network region of Taihu Basin

鉴于浅层地下水在维持区域生态功能方面的重要作用，基于2005-2015年太湖平原水网地区苏州市的14个浅层地下水监测井水位及2005-2014年降水、河道水位和蒸发等日尺度数据，开展浅层地下水埋深动态特征及影响因素研究.结果显示：苏州市浅层地下水总体呈由北往南、自西向东的流场方向，主要受地形因素的影响；年际及丰水期埋深有所减小，枯水期反之，各区域变化过程不一致；枯水期浅层地下水动态特征受不同量级降水总量和次数的显著影响，且与地表水过程关系密切，汛期反之.此外均受到引排水和下垫面变化等因素的影响；浅层地下水埋深对降水具有滞后性，多滞后1~2 d；通过对地形地貌条件、土地利用类型、河湖密度以及浅层地下水埋深状况等因素的综合分析，浅层地下水动态特征可表达为耕地区、水网密布区、高度城镇化区及低山林区4种特征类型.;In view of the important role in the maintenance of regional ecologic function, the spatio-temporal characteristics of shallow groundwater burial depth (SGBD) and its influential factors were studied based on the daily SGBD data (from 2005 to 2015) and regional precipitation, water level and evaporation data (from 2005 to 2014) in Taihu Basin. The results indicated that:The shallow groundwater in Suzhou showed a flow direction from north to south, and from west to east, which is mainly affected by regional topographic conditions. The regional SGBD showed a slightly reduction in annual and flood season scale, while increase in non-flood seasons. The change processes varied among regions. The variation of SGBD is significantly related to the amount and frequency of different precipitation ranks in non-flood seasons, and affected by surface water. Moreover, the diversion and drainage, and underlying surface change were also the influential variables. While these features were opposite in flood seasons. The variation of SGBD often lags 1 to 2 days to precipitation. The characterization of shallow groundwater could be divided to four types, such as the agricultural, watery, urbanized and low mountainous regions, through the overlay of the influential variables, such as geomorphologic conditions, land use types, densities of rivers and lakes, and shallow groundwater burial depth.

Prediction of the future flood severity in plain river network region based on numerical model: A case study

Suzhou is one of China's most developed regions, located in the eastern part of the Yangtze Delta. Due to its location and river features, it may at a high risk of flood under the climate change background in the future. In order to investigate the flood response to the extreme scenario in this region, 1-D hydrodynamic model with real-time operations of sluices and pumps is established. The rain-runoff processes of the urban and rural areas are simulated by two lumped hydrologic models, respectively. Indicators for a quantitative assessment of the flood severity in this region are proposed. The results indicate that the existing flood control system could prevent the Suzhou Downtown from inundation in the future. The difficulty of draining the Taihu Lake floods should be given attention to avoid the flood hazard. The modelling approach based on the in-bank model and the evaluation parameters could be effective for the flood severity estimation in the plain river network catchment. The insights from this study of the possible future extreme flood events may assist the policy making and the flood control planning.

Optimal Operation Research of Flood Retarding in Plain River Network Region

The operation of flood retarding areas does not attract much attention, although they are important components of flood control systems. Poor operation of such areas restricts not only the socio-economic development of the flood retarding area, but also limits scientific flood control options. As the second-largest flood retarding area in China, with more than 2000 km2 and 300 polders, the Hongze Lake vicinity was taken as a case study of graded flood retarding. A one and two-dimensional coupled hydrodynamic model was established to simulate flood routing in the Hongze Lake area. Fifteen different schemes involving different flood magnitudes and flood retarding operations were simulated. The results show that (1) having a flood retarding area is essential; and (2) the “graded flood retarding” scheme is superior to “no grading flood retarding” scheme; and (3) a “two-grade flood retarding” scheme is recommended.

Watershed delineation using hydrographic features and a DEM in plain river network region

Watershed delineation is a required step when conducting any spatially distributed hydrological modelling. Automated approaches are often proposed to delineate a watershed based on a river network extracted from the digital elevation model (DEM) using the deterministic eight-neighbour (D8) method. However, a realistic river network cannot be derived from conventional DEM processing methods for a large flat area with a complex network of rivers, lakes, reservoirs, and polders, referred to as a plain river network region (PRNR). In this study, a new approach, which uses both hydrographic features and DEM, has been developed to address the problems of watershed delineation in PRNR. It extracts the river nodes and determines the flow directions of the river network based on a vector-based hydrographic feature data model. The river network, lakes, reservoirs, and polders are then used to modify the flow directions of grid cells determined by D8 approach. The watershed is eventually delineated into four types of catchments including lakes, reservoirs, polders, and overland catchments based on the flow direction matrix and the location of river nodes. Multiple flow directions of grid cells are represented using a multi-direction encoding method, and multiple outflows of catchments are also reflected in the topology of catchments. The proposed approach is applied to the western Taihu watershed in China. Comparisons between the results obtained from the D8 approach, the ‘stream burning’ approach, and those from the proposed approach clearly demonstrate an improvement of the new approach over the conventional approaches. This approach will benefit the development of distributed hydrological models in PRNR for the consideration of different types and multiple inlets and outlets of catchments. Copyright © 2015 John Wiley & Sons, Ltd.

Status of heavy metals in soils following long-term river sediment application in plain river network region, southern China

Purpose Using river sediments as a soil amendment has hundreds to a thousand years of history in the river plain network region of southern China. This study aimed to investigate the pollution conditions of heavy metals in cultivated soils consistently amended with river sediments for a long term.

Spatial–temporal evolution of the distribution pattern of river systems in the plain river network region of the Taihu Basin, China

Understanding the spatial–temporal distribution characteristic and evolution tendency of river systems is important in integrated river basin management. In this paper, six indicators were adopted to describe the physical characteristic of river systems. The spatial–temporal evolution of the distribution pattern of river systems in the plain river network region of the Taihu Basin (PRNRTB) during the 1960s–2000s was analyzed using exploratory spatial data analysis (ESDA) and the gravity centre model. The impacts of urbanization were then investigated. Results indicated that the global distribution patterns of box dimension and river density were all statistically significant spatially clustered, and river sinuosity was partially spatially clustered, while water surface ratio, main river area length ratio and river development coefficient were not spatially clustered. Moreover, the water surface ratio was the most stable parameter, box dimension was also relatively stable parameter, but the others were unstable. Meanwhile, the mutual transformations of hot and cold spots of river systems especially water surface ratio, river development coefficient, and river sinuosity were frequent. The hot spot regions were mainly located in the northeast region. In addition, most gravity centres migrated gradually from southeast to northwest with low distance, except those of river development coefficient and river density. These aforementioned differences were caused by the rapid urbanization. Based on the integrated river basin management suggestions for PRNRTB, the river density, box dimension and river sinuosity should be maintained and restored across the whole watershed, and the river conservation and restoration should focus on countermeasures against the reduction of river development coefficient, and main attention should be paid on the river systems conserving and restoring in Haiyan and Haining in southeast PRNRTB.

Assessment of the sources and transformations of nitrogen in a plain river network region using a stable isotope approach

The great spatial and temporal variability in hydrological conditions and nitrogen (N) processing introduces large uncertainties to the identification of N sources and quantifying N cycles in plain river network regions. By combining isotopic data with chemical and hydrologic measurements, we determined the relative importance of N sources and biogeochemical N processes in the Taige River in the East Plain Region of China. The river was polluted more seriously by anthropogenic inputs in winter than in summer. Manure and urban sewage effluent were the main nitrate (NO3−) sources, with the nitrification of N-containing organic materials serving as another important source of NO3−. In the downstream, with minor variations in hydrological conditions, nitrification played a more important role than assimilation for the decreasing ammonium (NH4+-N) concentrations. The N isotopic enrichment factors (ε) during NH4+ utilization ranged from −13.88‰ in March to −29.00‰ in July. The ratio of the increase in δ18O and δ15N of river NO3− in the downstream was 1.04 in January and 0.92 in March. This ratio indicated that NO3− assimilation by phytoplankton was responsible for the increasing δ15N and δ18O values of NO3− in winter. The relationships between δ15N of particulate organic nitrogen and isotopic compositions of dissolved inorganic nitrogen indicated that the phytoplankton in the Taige River probably utilized NH4+ preferentially and mainly in summer, while in winter, NO3− assimilation by phytoplankton was dominant.

Temporal and spatial variation of water level in urbanizing plain river network region.

As one of the most developed regions in China, the plain of East China is undergoing gradually increased flooding under the obvious urbanization process. This paper mainly analyses the trend of water level time series in the region during the past decades, and assesses the temporal and spatial variation of water level and indicators of hydrological alteration. The results show that there is a trend of increasing water level. Bigger slope and higher significant level can be observed in monthly minimum than in monthly maximum water level, in peri-urban than in urban areas. Meanwhile, it is observed that the mean monthly minimum and maximum water level increased in both urban and peri-urban regions, while decreased coefficients of variation (Cv) in urban and increased Cv in peri-urban regions were calculated. Most indicators of hydrologic alteration in urban stations are concentrated to the range of variability approach target, while most indicators are discrete in peri-urban stations. And the degree of hydrologic alteration is higher in peri-urban than in urban regions.

Estimation of impervious surface percentage of river network regions using an ensemble leaning of CART analysis

The rapid expansion of impervious surface has become a major factor affecting ecosystem health of the high density river network. This paper provides an approach to estimate impervious surface percent( ISP) through the ensemble leaning of CART analysis based on variable precision rough sets( VPRS). Landsat TM and ALOS imagery were utilized to construct the ISP predictive model; then,in order to get the best attribute variables of CART decision tree,the authors adopted VPRS to extract optimum feature subset from multi- source feature sets. The results illustrate the validity of this ensemble leaning,and prove that this method can obtain estimated accuracy better than the traditional single CART method. However,in the initial estimation results,ISP's high value area is underestimated relatively seriously. The authors have discovered that the temperature vegetation dryness index( TVDI) and ISP have an intensive relationship with each other: the increase of ISP will cause the increase of local TVDI significantly. Therefore,the post- processing rule extracted from the relationship is used to improve the results. According to the verification results,the method combined with VPRS reduction and post- processing rule in CART algorithm has fairly higher analysis precision than the traditional single CART learning algorithm. The root mean square error between estimated ISP value and reference ISP is 10. 0%,with the correlation coefficient being 0. 89,so it can be used to estimate the ISP in plain river network region.