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Published on: November 18, 2015
Functional hydrological connectivity reshapes nutrient source-response relationships in plain river networks
Zhixiang Sun1, Qingqing Zuo2, Jiayu Jiang2
1State Key Laboratory of Regional Environment and Sustainability, School of Environment, Beijing Normal University, Beijing, 100875, China; Research and Development Center for Watershed Environmental Eco-Engineering, Beijing Normal University, Zhuhai, 519085, China.
Abstract:
Management of diffuse nutrient pollution in sluice-regulated plain river networks is hindered by a critical disconnect: source hotspots often fail to align with zones of water-quality impairment. Here, we developed a Hydrological Connectivity Index under Sluice regulation (HCIS) by integrating hydraulic activation, regulation-mediated release, and network-scale propagation. We then combined HCIS with source-pressure estimation and water-quality observations in a typical plain catchment in China to examine how functional connectivity mediates source-response relationships. The results showed mismatched source-response types accounted for 57.1% (TN) and 64.3% (TP) of sections, exceeding high-source/high-concentration matches. Source pressure alone explained limited variation in TN reduction rates, whereas hierarchical regression showed that HCIS increased model R² from 0.21 to 0.39 (β = 0.43, p = 0.006). In contrast, TP, NH₄⁺-N and chemical oxygen demand (COD) showed weaker or non-monotonic responses to HCIS. Four diagnostic types were identified for managing nutrient risk based on the coupling of source pressure, functional activation, and retention-release processes. These findings show that HCIS can identify when structural pathways become functionally activated and help distinguish activated export corridors from retention-dominated or hidden internal-risk zones.
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