Key Takeaways & Executive Findings
- •• • Middle Route SPM is dominated by coarse particles (>63 μm, 61.43%–94.68%) with TP <0.01 mg·L−1, indicating low nutrient levels and algal-driven aggregation; this necessitates targeted algal bloom control to prevent deposition and potential nutrient release. • • East Route SPM is dominated by fine particles (<20 μm, 51.26%–88.61%) with TP ranging from 0.03 to 1.11 mg·L−1, reflecting high external nutrient loading; fine particles enhance nutrient adsorption, requiring sedimentation and wetland strategies to mitigate pollution. • • Carbon and nitrogen isotope analysis shows that Middle Route SPM is predominantly autochthonous (algae contribution >46.75%), whereas East Route SPM is a mix of terrestrial C3 plants and algae, indicating different source management priorities. • • Chlorophyll a correlates significantly with coarse particles (r=0.60) in the Middle Route, confirming that algal aggregation is a key mechanism for particle formation; this correlation can be used as a monitoring indicator for algal proliferation and water quality management.
Abstract
This study investigates the spatiotemporal differentiation of suspended particulate matter (SPM) characteristics, sources, and their impacts on water quality between the Middle Route (closed artificial channel) and East Route (open natural water system) of the South-to-North Water Diversion Project. Thirty sampling sites (13 on the Middle Route, 17 on the East Route) were established, and samples were collected during dry and wet seasons. Water quality parameters and SPM characteristics were analyzed, including particle size distribution, total suspended solids (TSS), chlorophyll a, and stable carbon and nitrogen isotopes. Results show that the Middle Route maintains good and stable water quality, with SPM dominated by coarse particles (>63 μm, 61.43%–94.68%), total phosphorus (TP) <0.01 mg·L−1, and a significant positive correlation between chlorophyll a and coarse particles (r=0.60), indicating algal aggregation dominates particle formation. In contrast, the East Route exhibits high and fluctuating nitrogen and phosphorus concentrations, with SPM dominated by fine particles (<20 μm, 51.26%–88.61%), TP ranging from 0.03 to 1.11 mg·L−1, and a positive correlation with fine particles, suggesting significant external inputs. Carbon and nitrogen isotope analysis reveals that Middle Route SPM primarily originates from autochthonous algae (contribution >46.75%), while East Route SPM is influenced by both terrestrial C3 plants and algae. The distinct engineering and management approaches of the two routes lead to significant differences in SPM characteristics and sources, thereby affecting water quality dynamics. The Middle Route requires an 'algal reduction and hydrodynamic optimization' strategy to control algal-derived coarse particle deposition, whereas the East Route benefits from 'retention-sedimentation and wetland purification' to reduce external fine particles and pollutant inputs. This research provides theoretical support and practical guidance for differentiated SPM management in long-distance water diversion systems.
1. Introduction
The South-to-North Water Diversion Project is a monumental infrastructure endeavor addressing water scarcity in northern China. However, the two main routes—the Middle Route, a closed concrete-lined canal, and the East Route, an open system utilizing natural waterways and lakes—present fundamentally different hydrodynamic and ecological contexts. Existing water quality management strategies often overlook these differences, applying uniform approaches that may be ineffective or even counterproductive. The behavior of suspended particulate matter (SPM), which plays a critical role in nutrient cycling and pollutant transport, is particularly sensitive to these engineering differences. Yet, a comprehensive understanding of how SPM characteristics and sources differ between the two routes and how they influence water quality has been lacking, hindering the development of tailored management protocols.
This study addresses this gap by conducting a systematic comparative analysis of SPM along both routes, integrating particle size distribution, elemental composition, and stable isotope fingerprinting. By identifying the dominant sources and transport mechanisms of SPM, we provide evidence-based recommendations for route-specific water quality management. The findings reveal that the Middle Route's SPM is largely autochthonous, driven by algal growth, while the East Route's SPM is a complex mixture of external and internal sources. These insights enable the formulation of targeted strategies—algal control and hydrodynamic optimization for the Middle Route, and sedimentation and wetland purification for the East Route—to enhance water quality and ensure the safety of this vital water supply.
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ZHANG Junzhi, CHEN Borong, DONG Chenyu, CHANG Zhibing, ZHONG Mingyuan, ZHU Wenhao, YU Jianwei, ZHANG Honggang (2026). Differentiated Characteristics of Suspended Particulate Matter and Their Effects on Water Quality in the Middle and East Routes of the South-to-North Water Diversion Project. Chinese Journal of Environmental Engineering. https://doi.org/10.12030/j.cjee.202507085
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Frequently Asked Questions
What are the dominant particle size fractions in the Middle and East Routes, and how do they relate to nutrient concentrations?
In the Middle Route, SPM is predominantly coarse (>63 μm, 61.43%–94.68%), with total phosphorus (TP) below 0.01 mg·L−1, indicating low nutrient levels. In contrast, the East Route has a high proportion of fine particles (<20 μm, 51.26%–88.61%) and TP ranging from 0.03 to 1.11 mg·L−1, showing a positive correlation with fine particles, which enhances nutrient adsorption.
How does the source of SPM differ between the two routes, and what are the implications for management?
Stable isotope analysis (δ13C and δ15N) indicates that the Middle Route SPM is primarily autochthonous, with algae contributing over 46.75%, while the East Route SPM is influenced by both terrestrial C3 plants and algae. This suggests that the Middle Route requires strategies to control algal growth, whereas the East Route needs to address external inputs through sedimentation and wetland purification.
What is the correlation between chlorophyll a and coarse particles in the Middle Route, and why is it significant?
Chlorophyll a shows a significant positive correlation (r=0.60) with coarse particles in the Middle Route. This indicates that algal aggregation is a key mechanism for particle formation, which can be used as a monitoring indicator for algal proliferation and potential risks of nutrient release from deposited particles.
What are the recommended management strategies for each route, and what are the expected outcomes?
For the Middle Route, an 'algal reduction and hydrodynamic optimization' strategy is recommended to inhibit the deposition of algal-derived coarse particles. For the East Route, a 'retention-sedimentation and wetland purification' strategy is suggested to reduce external fine particles and pollutant inputs. These approaches are expected to improve water quality by addressing the specific sources and behaviors of SPM in each system.
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