Water quality improves with increased spatially surface hydrological connectivity in plain river network areas

Area of Science:

• Environmental Science
• Hydrology
• Water Quality Management

Background:

• Urbanization and changing river networks complicate water quality management in river-lake systems.
• The impact of hydrological connectivity on water quality in urbanized plain river networks is not well understood.

Purpose of the Study:

• To quantify hydrological connectivity in the northern Taihu Lake Basin.
• To investigate the threshold effects of hydrological connectivity on water quality parameters.
• To evaluate the relationship between hydrological connectivity and water quality using various modeling techniques.

Main Methods:

• A connectivity topological model based on graph theory and landscape ecology was used to quantify hydrological connectivity.
• XG-Boost models were employed to identify potential thresholds for hydrological connectivity's impact on water quality.
• Linear mixed-effect (LME) models, incorporating land use as a random effect, assessed the response relationship between connectivity and water quality.

Main Results:

• Hydrological connectivity in the study area has decreased over the past 20 years.
• A threshold value (Pij = 0.02) was identified, above which hydrological connectivity significantly impacts water quality.
• Enhanced connectivity correlated with lower concentrations of total nitrogen (TN), total phosphorus (TP), ammonia nitrogen (NH3-N), and chemical oxygen demand (CODMn), and higher dissolved oxygen (DO).

Conclusions:

• Hydrological connectivity is a critical factor influencing water quality in urban river-lake systems.
• Optimizing river network topology, sluice operations, and removing dikes can restore connectivity and improve water quality.
• This study provides a framework for water quality improvement strategies in complex urban river networks through connectivity management.