Spatial and temporal characteristics, influencing factors and prediction models of water quality and algae in early stage of Middle Route of South-North Water Diversion Project

Abstract It is of great significance to find a scientific way to assess the water quality of the middle route of the South-North Water Diversion Project. In this paper, the spatio-temporal changes of the 26 water quality indicators in eight key monitoring stations along the middle route since the project was put into use were analyzed, and the modified Nemerow index method was employed to assess the water quality of the route in its early stage of operation. The results show that the water quality remained good in the period of study. Important water quality indicators were identified, including temperature, permanganate index, dissolved oxygen, total phosphorus, total nitrogen, mercury content, and density of planktonic algae. It is advised that potential ecological risks related to algae and shellfish reproduction in the open canal deserve special attention.

Water scarcity in densely populated areas is a global concern. In China, ensuring water supply and quality in the middle of the South-to-North Water Diversion Project has become a major challenge due to the complexity and diversity of landscape features and the trunk canal construction in the crossing area of this route. Precise assessments of the pressures on water protection along the route are urgently needed. This article provides a rigorous methodological framework to assess water quality protection, identifying the intensity of human disturbance along the route within 2-km radius buffer areas on both sides of the trunk canal, based on land-use changes from 2005 to 2015. The results show that more than 10,000 ha of pervious surfaces were transformed into impervious surfaces, leading to undesirable outcomes. The results of this study can be used for decisive support in China’s environmental management, such as with main functional zoning policy and ecological red lines policy.

Abstract As the first span and aqueduct of the Middle Route of the South-to-North Water Diversion Project, Diaohe Aqueduct has brought good engineering and social benefits since its completion. In order to understand the present water quality of the Diaohe River section of the route, four samplings were conducted at Diaohe Aqueduct in the winter of 2018. The main results of this study are as follows: 62 species (or variants) of phytoplankton belonging to 32 genera, 22 families and six phyla were identified during the study period, among which Bacillariophyta are the most dominant species. The identified phytoplankton fall into eight indicator grades: os; ps, αm; ps, αm, βm; αm; αm, βm; αm, βm, os; βm; and βm, os. A total of 17 functional groups are detected, among which TB is the absolute dominant functional group. Based on the composition characteristics of phytoplankton, the water quality trophic state of Diaohe Aqueduct is mesotrophic. However, other physical indexes show that the water quality of the Middle Route of the South-to-North Water Diversion Project is good. The conclusions drawn using phytoplankton alone as the evaluation index may not be comprehensive. In future research, how to build a comprehensive index system combining other water quality indexes for the Middle Route of the South-to-North Water Diversion Project needs yet to be improved and tested.