Inter-Annual and Seasonal Variations of Water Quality and Trophic Status of a Reservoir with Fluctuating Monsoon Precipitation.

Ye-eun Moon,Hyun-su Kim

doi:10.3390/ijerph18168499

Abstract

Long-term evaluation from 2000 to 2020 of a temperate reservoir indicated that water quality and trophic status were not critically controlled by the inter-annual dynamics of monsoon precipitation. The fluctuation of annual concentrations of TP, TSS, and EC did not always correlate with the variation of precipitation. BOD and COD demonstrated monotonically increasing trends with Sen’s slope of 0.02 and 0.01, respectively, while Chl-a manifested a decreasing trend (slope = −0.23). The increases of different magnitudes in the levels of TP, TSS, and Chl-a in the monsoon and the early post-monsoon periods were observed in the drought, flood, and normal years. The drought years showed distinct seasonal variations in many parameters, while those in the flood and the normal years were very similar. Pearson correlation and empirical regression analyses resulted in weaker correlation between water quality and hydrological parameters than other reservoirs, which, along with low impact of precipitation, was attributed to the low drainage ratio (28.8) of the study area. BOD/COD ratios were higher than 0.5 in the reservoir, indicating the presence of a significant fraction of biodegradable organic matter. The ratio increased in the longitudinal flow direction (>50% in the drought years), implying the possibility of autochthonous sources of organic matter. TSID evaluation resulted in variation of limiting factors not related to the fluctuation of annual precipitation. The loadings of the significant principal components were very similar among the different precipitation groups, supporting the other findings that annual precipitation governed by monsoon intensity would not solely control the water quality dynamics of the study area.

Highlights

Global water use has increased almost six times over the last 100 years, and is expected to grow around the world in the near future [1]
The loadings of the significant principal components were very similar among the different precipitation groups, supporting the other findings that annual precipitation governed by monsoon intensity would not solely control the water quality dynamics of the study area
The purpose of this study is to evaluate the interaction between water quality variables and hydrological characteristics, including the inter-annual variation of monsoon precipitation, by analyzing long-term monitoring data of the Okjeong Reservoir, a large multi-purpose reservoir located in Korea, where two local governments are in conflict over the development of the reservoir’s water surface

Summary

Introduction

Global water use has increased almost six times over the last 100 years, and is expected to grow around the world in the near future [1]. Annual precipitation has increased in the last century, the rate of increase was not high enough to keep up with the increasing demand, causing water scarcity in many parts of the world [2]. The imbalance between demand and supply has become a serious problem, especially in East Asia, including South Korea, where more than a half of annual rainfall is concentrated over a couple of months in the summer [3]. Many artificial dams have been built by blocking rivers to create reservoirs for the storage and stable supply of water throughout the year, and there are approximately 19,000 reservoirs in Korea [4]. As many of the reservoirs are utilized as drinking water sources, water quality management is one of the primary goals of reservoir management [5,6]

Objectives

Results

Conclusion