Research papers
Distribution, transfer process and influence factors of phosphorus at sediment-water interface in the Huaihe River

https://doi.org/10.1016/j.jhydrol.2022.128079Get rights and content

Highlights

  • Phosphorus concentration decreased in water and increased in sediment in 3 years.

  • Sediment absorbed phosphorus and acted as “pollution sink” over sampling time.

  • Water and sediment from upstream were significant pollution sources to downstream.

  • Land use within 8 km buffer scale had important effects on phosphorus pollution in the river.

  • Farmland was the most important source (more than 30%) to phosphorus pollution.

Abstract

A better understanding of phosphorus-transfer process and influence factors at Sediment-Water Interface (SWI) is essential to develop effective and efficient river managements strategies. In this study, overlying water, pore water and riverbed sediment samples were collected in the Huaihe River (HR), a highly polluted river in Eastern China, in May 2013, July 2013 and June 2016, respectively. Models were developed to analyze influence factors on phosphorus by Bayesian Networks (BNs), which could describe complex interdependencies between dependent/independent variables conveniently compared to traditional statistical models. The transfer process and effects of land use on phosphorus at the SWI were evaluated. Results indicated that phosphorus concentration decreased in overlying water and pore water similarly but increased in riverbed sediment from 2013 to 2016. The concentrations in overlying/pore water reached a maximum at the middle of the research area, while those in riverbed sediment increased from upstream to downstream. Phosphorus was transferred from overlying water to riverbed sediment through pore water mainly in a dissolved phase, indicating that riverbed sediment could absorb contaminants and act as “pollution sink” in the HR. Upstream water and sediment were important sources of downstream phosphorus with the influence coefficients ranging from 0.294 to 0.491. Land use within 1 km river buffer had most significant influence on total phosphorus in overlying water and 2 km river buffer to riverbed sediment while land use had the most noteworthy effects on particulate/dissolved phosphorus in 2 km and 8 km river buffer respectively. Farmland, urban and rural residential land were important sources of phosphorus at the SWI, and farmland contributed most (>30%) in the HR. The study not only provides insights into phosphorus-transfer process and influence factors at the SWI in the HR, but the proposed model also could be applicable in other polluted rivers.

Introduction

Phosphorus is an essential nutrient for all living organisms in river ecosystems (David and Schindler, 2012, Wang et al., 2020b). However, excess phosphorus in water bodies arising from anthropogenic activities, such as fertilization, rapid urbanization, and discharge of industrial wastewater and domestic sewage, can lead to eutrophication and subsequent degradation of water quality (Doan et al., 2018, McCrackin et al., 2018, Todeschini, 2016, Zhang et al., 2017).

Sediment plays a crucial role in phosphorus transportation in aquatic ecosystem and acts as pollutant sink and/or source. Fertilizer-derived phosphorus accumulated in soil and then infiltrated into groundwater as a dissolved phase or transported into rivers by sediment-bound particulate phase (Shen et al., 2020). Sediment, especially fine sediment particles, could act as contaminants’ sink by absorbing phosphorus in rivers and then depositing in riverbed (Gao et al., 2020, Wang et al., 2018, Wang et al., 2020b). However, sediment resuspension may lead to the release of sediment-bound phosphorus in response to physicochemical or biogeochemical changes, and in this case sediment acts as a phosphorus source (Fatimah et al., 2016, Kraal et al., 2013, Shaughnessy et al., 2019). Previous research have pointed out that riverbed sediment has significant impact on phosphorus levels in rivers. Ding et al. (2018) found that internal phosphorus source (phosphorus released from sediment particles) made more than half contribution for total phosphorus increase in water column in the Lake Taihu in China. Compared to the terrestrial source, remobilized phosphorus releasing from sediment was a more important source of phosphorus in the Chesapeake Bay (Boynton, 1996, Joshi et al., 2015). Numerous studies reported the phenomenon that contaminants releasing from sediment particles could frustrate improvement of water quality after controlling external pollution sources (Alvarez et al., 2012, Liu et al., 2016, Macintosh et al., 2018, Yin et al., 2016). The Sediment-Water Interface (SWI) where mass transportation and energy exchange occurring plays a critical role in pollutant transfer in rivers (Newcomer et al., 2018). Many previous studies highlighted the importance of focusing on the dynamic distribution of phosphorus at the SWI, however, in-depth understanding of phosphorus-transfer process is still limited in previous studies which needs to pay more attention to (Doan et al., 2018, Liao et al., 2020, Wijesiri et al., 2019).

The physicochemical properties, such as water temperature and pH, can significantly affect the adsorption capacity of sediment and consequently the transfer process of phosphorus at the SWI, especially during sediment resuspension process (Li et al., 2018, Zhang et al., 2018). Anthropogenic activities alongside waterbody, producing considerable amount of pollutants, is another key factor influencing phosphorus levels in rivers, which could be evaluated by different types of land use (Gao et al., 2020, Jennett and Zheng, 2018, Wen et al., 2020). Tudesque et al. (2014) found that the strength of the relationship between land use and water chemistry increased from local to basin scales in France. However, Mainali and Chang (2018) found that land use in local-scale had a greater explanatory power for water quality than that in sub-watershed scale in South Korea. These studies indicated that the most relative spatial scales between land use and water pollution tended to be different. The buffer zone between river and the surrounding territory has important effects on river environment (Ouyang et al., 2013). Thus, different spatial scales alongside river buffers should be considered comprehensively to determine the most relative scales, which was crucial in implementing effective and efficient water management strategies.

The transfer process of phosphorus at the SWI and potential influencing factors could be evaluated by two methods. One is to use coupled models consisting of hydrodynamics, sediment and phosphorus transportation modules to describe sediment dynamics and phosphorus adsorption/desorption process (Barrow, 2015, Huang et al., 2015). Another way is to use high-resolution dialysis and diffusive gradients in thin films (DGT) to determine phosphorus-transfer flux (Ding et al., 2018, Ren et al., 2020, Yu et al., 2019). However, these two methods are either computation-consuming or process-complex. In the study, a “data driven” model is proposed in which information can be extracted from data in a simple and direct way, to determine direction of phosphorus transfer and evaluate influence factors on phosphorus distribution at the SWI (Detenbeck et al., 2016, Li et al., 2014). Complex factors influence phosphorus concentration at the SWI, accordingly, phosphorus concentration in water and riverbed sediment are determined by natural conditions and human activities in river basins. Besides, these factors also affect phosphorus-transfer process at the SWI, which in returns changes phosphorus distribution in water and sediment. Because of the complicated interdependencies, the contribution rates of all influence factors on phosphorus at the SWI are hard to describe and evaluate by traditional statistical models. The Bayesian Network (BN), decomposing a global distribution into a set of local conditional distributions, is a feasible choice for determining the transfer process of phosphorus at the SWI and its influencing factors. Therefore, the BN model was applied in our studies and the following analysis was based on it.

In this study, physicochemical conditions and land use type were assumed to be potential factors affecting the distribution and transfer process of phosphorus at the SWI. As pore water is an important contributor to biogeochemical cycles between overlying water and riverbed sediment, two possible directions that phosphorus transferred at the SWI were assumed, accordingly, overlying water to riverbed sediment (Direction I) or from riverbed sediment to overlying water (Direction II) through pore water (Cook et al., 2018, Wilson et al., 2016). The potential transfer direction in the HR was determined by the model which had the best performance. The main objectives of this study were to investigate (1) the spatial and temporal distributions of phosphorus at the SWI; (2) possible transfer direction of phosphorus at the SWI based on the BN model; and (3) the effects of physicochemical conditions and land use type on different forms of phosphorus at the SWI. Based on the research, transfer patterns and influence factors on phosphorus at the SWI could be clarified. Moreover, the sampling methods and modeling approaches in the paper are not only applicable in the HR, but also in other polluted rivers worldwide.

Section snippets

Study area

The Huaihe River (HR; 30°∼36°N, 111°∼121°E) is one of the most polluted rivers in Eastern China (Fig. 1(a)). The river originates from Henan province and discharges into the Hongze Lake in Jiangsu province with a catchment area of about 270,000 km2 and an altitude drop of 200 m (Jin et al., 2020, Xu et al., 2019). The Shaying River (SR) and Guo River (GR) are two main tributaries flowing into the HR (Fig. 1(b)). The HR is the transition zone of climate in China with wet and hot weather in

Temporal distribution of phosphorus at the SWI

Water samples were collected in May 2013, July 2013 and June 2016, respectively. The maximum, minimum, average and standard deviation of physicochemical parameters and three phosphorus phases at the SWI were determined, and the differences among the sampling experiments were evaluated by T-test (Xu et al., 2018). The details of phosphorus concentration were shown in Table 2.

Because of climate characteristics in the HRB, the water temperature was different in May, June and July, which ranged

Conclusions

To better understand distribution patterns and influence factors of phosphorus-transfer process at the SWI in the HR, water and sediment samples were collected in 2013 May 2013 July and 2016 June, respectively. Physicochemical conditions in water and land use both affected phosphorus at the SWI. Moreover, phosphorus-transfer process also made changes to its concentration values in water and sediment. In order to quantify the complex relationship between influence factors and phosphorus

CRediT authorship contribution statement

Jing Xu: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Software, Validation, Visualization, Writing – original draft. Yuming Mo: Investigation, Writing – review & editing. Hongwu Tang: Funding acquisition, Project administration, Resources. Kun Wang: Methodology, Software. Qingfeng Ji: Methodology, Software. Pei Zhang: Methodology, Software. You-Gan Wang: Investigation, Methodology, Supervision, Validation. Guangqiu Jin: Funding acquisition,

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This research was supported by the Belt and Road Special Foundation of the State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering (2021491811) and the Natural Science Foundation of China (51239003). Data used in the analysis presented in the paper can be obtained by sending a request to the corresponding author ([email protected]).

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