Integrated assessment of water quality characteristics and ecological compensation in the Xiangjiang River, south-central China

Highlights

• Decreasing trends of water quality in the river system were more universal.

• Significant spatial and temporal variability were observed in Xiangjiang River basin.

• Economically developed areas were mainly payers of pollution losses.

• Compensation standard model highlighted the most payment in Changsha City.

Abstract

Xiangjiang river, as a transboundary river in Hunan Province, south-central China, is facing serious water pollution and conflict. Integral investigation of water quality status and resulting pollution loss compensation are of importance for effective water management. The 13 water quality parameters at 40 sampling sites during 2008–2016 were selected to analyze their trends and spatio-temporal variations using Mann-Kendall test, one-way ANOVA and spatial autocorrelation. A compensation standard model based on pollution loss and contribution rate was designed and then employed to calculate the compensation amount for adjacent administrative districts. Results showed that significant downward trends were detected for COD_Mn, BOD₅, Cu, Zn, Cr, and As. pH and TP showed upward or downward trends with approximately half of the stations displaying no trends. A significant spatial variation was found for all water quality indicators except for Hg, which were also correlated positively (Moran’s I > 0). All water quality indicators showed relatively higher concentration during the dry season with the exception of COD_Mn and Zn. The calculated results based on compensation standard model indicated that Changsha City payed the most compensation amount (9.807 million CNY) to Xiangtan City. This study provides important information regarding objective solution of regional compensation standard, which is conducive to governments’ financial transfer decision.

Introduction

River often serves as important sources for agriculture, industry, drinking water and habitat conservation (Shi et al., 2017, Zhang et al., 2019). Ecosystem services provided by watersheds to humans and ecosystems have captured a wealth of attention (Brauman et al., 2007). Ling et al., 2019, Wu et al., 2018 reported that the accurate quantification of the value of water ecosystem services not only can benefit the effective implementation of pollution control measures, but also provide scientific reference to formulate reasonable compensation mechanism in similar river basins. Surface water quality is regarded as a significant factor quantifying the monetary value of water ecosystem services, and has become a serious concern for public and decision makers (He et al., 2015).

Variations in water quality within a local aquatic ecosystem are subjected to precipitation inputs (Jeznach et al., 2017, Liu et al., 2018, Longyang, 2019), land use (Shi et al., 2017, Wan et al., 2014), and industrial activities (Van Wezel et al., 2018). Numerous studies on surface water quality at catchment scale have been undertaken. These studies have been conducted to evaluate spatio-temporal patterns adopting multivariate analysis (Haji Gholizadeh et al., 2016), unravel the relationship between environment variables (Diamantini et al., 2018, Epele et al., 2018), detect gradual and abrupt changes in water quality records (Lloyd et al., 2014), identify major drivers affecting watershed environmental quality (Bostanmaneshrad et al., 2018), quantify the contribution of different pollution sources to the total datasets (Huang et al., 2010), assess human health and ecological risk (Chen and Wu, 2018, Zeng et al., 2015), delineate effective water pollution control measures (Chen et al., 2012, Dehghani Darmian et al., 2018), and evaluate ecological compensation within a regional watershed (Wang et al., 2018). However, existing research conducted in the Xiangjiang River has mainly focused on heavy metals and rare elements in the sediments (Sun et al., 2011, Xu et al., 2017). There have been comparatively few studies that have comprehensively investigated the watershed water quality (Fang et al., 2019, Han et al., 2014, Zhang et al., 2010). Therefore, understanding water pollution episodes through exploring trends and distribution patterns is basic but critical for river management and ecological conservation.

Ecological compensation is a market-based mechanism, mainly relying on economic means, that aims to coordinate and regulate the interests of stakeholders and achieve ecological protection and economic development (Sun et al., 2017). The key of eco-compensation mechanism is the accounting of compensation standard. At present, eco-compensation standard at watershed scale is determined based on services value provided by river ecosystem (Ling et al., 2019) or on cost inputs for water protection (Kosoy et al., 2007). However, due to the complex whole ecosystem and the vague boundary of various ingredients, the calculated value may appear double counting. Moreover, the diversity of ecosystem services limits their extensive application in compensation assessments (Pang et al., 2013). Furthermore, most river compensation cases did not consider location socioeconomic level, and the compensation standard is separated from natural and social contexts and seldom adopted in practice

Based on aforementioned problems, some studies have determined payment criteria according to the loss from ecosystem damage behaviors in the field of hydropower generation and agricultural water (Pang et al., 2013, Yin et al., 2018). However, little research has been conducted on compensation standard quantification for water damage practices. In addition, few studies have considered the effects of water damage measures (e.g., contribution to downstream water quality). Therefore, we designed an objective and novel method of compensation standard based on pollution loss and contribution rate, taking the Xiangjiang River as a case study.

The main purpose of this research was to investigate water quality status and resulting pollution loss compensation in Xiangjiang River basin. Correspondingly, based on the method of pollution loss and contribution rate, an objective solution of compensation standard was advanced for adjacent administrative regions in the Xiangjiang River. This research that concentrated on the lower limits of compensation standard explored the research gap in the field. We expect this study would provide a methodological proposal for decision makers to quantify ecological compensation.