ZOU Yan1,2, ZHOU Zhongfa1,2, KONG Jie1,2, LI Yongliu1,2, WANG Cui1,2,
WEN Chaocheng1,2, XIE Jiangting1,2

（1. College of Geography And Environmental Sciences/Karst Research Institute, Guizhou Normal University, Guiyang 550001, China;
2. The State Key Laboratory Incubation Base for Karst Mountain Ecology Environment of Guizhou Province, Guiyang, 550001, China）

Abstract： To investigate the distribution characteristics and influence mechanisms of carbon and nitrogen nutrients in water bodies of dammed reservoirs in karst areas, Pingzhai Reservoir was studied, with water bodies of reservoirs and inlet rivers been sampled and monitored in January, May, July and September of 2020. The surface and profile characteristics of hydrochemistry factors and total organic carbon (TOC) and total nitrogen (TN) in the water bodies were analyzed by using mathematical statistics and correlation analysis. The results show that: (1) The water chemistry indexes varied greatly among rivers, with the highest concentration of TOC and TN been observed in autumn, and lower values were found in wet seasons than that in dry seasons; the spatial distribution pattern were: upstream of rivers < catchment area < reservoir area. (2) TOC and TN concentrations in the vertical profile were influenced by the thermal stratification period of the reservoir in summer and autumn, and both had large fluctuations in summer and autumn. (3) There were different controlling factors for TOC and TN concentrations and changes in water bodies. The dilution effect causes the TOC concentration to be lower in the wet season than in the dry season period, and the accumulation of land-based materials in autumn resulted in its significantly increase in September, while the special geological background of karst reservoirs and the biological carbon sequestration formed by the slower hydrodynamic conditions in the reservoir area were the reasons for the increase in concentration after the river sinks into the reservoir area; the changes in TN concentration were mainly influenced by external input. Therefore, the protection of Pingzhai Reservoir must involve the controlling of the external input of human activities and strengthen the management of industrial and agricultural production and domestic activities around the watershed.

Key words：total organic carbon;total nitrogen; profile features; influence mechanism; karst reservoir

EARTH AND ENVIRONMENT Vol.51, No.3, Tot No.353, 2023, Page 255