Response of Eutrophication Development to Variations in Nutrients and Hydrological Regime: A Case Study in the Changjiang River (Yangtze) Basin

Xianqiang Tang,Ding Han,Rui Li,Miklas Scholz

doi:10.3390/w12061634

Abstract

Data and literature related to water quality as well as nutrient loads were used to evaluate the Changjiang River (also Yangtze or Yangzi) Basin with respect to its hydrological regime, sediment transport, and eutrophication status. Waterbodies exhibited different eutrophic degrees following the ranking order of river < reservoir < lake. Most of the eutrophic lakes and reservoirs distributed in the upstream Sichuan Basin and Jianghan Plain are located in the middle main stream reaches. During the past decade, the water surface area proportion of moderately eutrophic lakes to total evaluated lakes continually increased from 31.3% in 2009 to 42.7% in 2018, and the trophic level of reservoirs rapidly developed from mesotrophic to slightly eutrophic. Construction and operation of numerous gates and dams changed the natural transportation rhythm of runoff, suspended solids (SS), and nutrients, and reduced flow velocity, resulting in decreased discharge runoff, slow water exchange, and decreased connectivity between rivers and lakes as well as accumulated nutrient and SS, which are the main driving forces of eutrophication. To mitigate eutrophication, jointly controlling and monitoring nutrient concentrations and flux at key sections, strengthening water quality management for irrigation backwater and aquaculture wastewater, and balancing transportation among runoff, SS, and nutrients is recommended.

Highlights

Eutrophication is the process by which a body of water becomes enriched in dissolved nutrients, which stimulate the growth of aquatic plant life usually resulting in the depletion of dissolved oxygen
This study examines authoritative monitoring and assessment data and published literature regarding runoff, sediment, nutrients, wastewater discharge, fertilizer application, aquaculture, algal density, and water quality from the previous decade to
Data for water quality and trophic level for rivers, lakes, and reservoirs as well as wastewater discharge volumes were collected from the Water Resources Bulletin of the Changjiang River Basin and Southwest Rivers (2006–2018), which was annually issued by the Changjiang River Water Resources

Summary

Introduction

Eutrophication is the process by which a body of water becomes enriched in dissolved nutrients (such as phosphorus), which stimulate the growth of aquatic plant life usually resulting in the depletion of dissolved oxygen. Water 2020, 12, 1634 can accelerate the deterioration of water quality and lead to detrimental impacts on the aquatic ecosystem This phenomenon is often referred to as algal blooming [1]. Eutrophication occurs around the world, and the following four factors can stimulate the eutrophication process: (1) Sufficient supply of nutrients (nitrogen and phosphorus) and organic matter [2], (2) suitable meteorological conditions in terms of temperature and light [3], (3) hydrodynamic processes such as slow water flow and long hydraulic retention time [4], and (4) loss of control of algal growth through the aquatic food web, algae biomass exceeded the prey capacity for algophagous zooplankton and fish [5]. Retention and regulation of runoff and sediment by dams or gates cause slow water flow, declining runoff, and the accumulation of nutrients, which subsequently trigger the development of water eutrophication

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Results

Conclusion