Abstract
Treatment cost and quality of domestic water are highly correlated with raw water quality in reservoirs. This study aims to identify the key factors that influence the trophic state levels and correlations among Carlson trophic state index (CTSI) levels, water quality parameters and weather factors in four major reservoirs in Taiwan from 2000 to 2017. Weather (e.g., air temperature, relative humidity, total precipitation, sunlight percentage and cloud cover) and water quality parameters (e.g., pH, chemical oxygen demand, suspended solids (SS), ammonia, total hardness, nitrate, nitrite and water temperature) were included in the principal component analysis and absolute principal component score models to evaluate the main governing factors of the trophic state levels (e.g., CTSI). SS were washed out by precipitation, thereby influencing the reservoir transparency tremendously and contributing over 50% to the CTSI level in eutrophicated reservoirs (e.g., the Shihmen and Chengchinghu Reservoirs). CTSI levels in the mesotrophic reservoir (e.g., Liyutan Reservoir) had strong correlation with chlorophyll-a and total phosphorus. Results show that rainfall/weather factors were the key driving factors that affected the CTSI levels in Taiwan eutrophicated reservoirs, indicating the need to consider basin management and the impacts of extreme precipitation in reservoir management and future policymaking.
Highlights
The quality of water bodies has deteriorated
The trophic state index (TSI)(SD) level was the major contributor to the Carlson trophic state index (CTSI) level in the reservoirs of Shihmen, Wushantou and Chengchinghu; whereas the TSI(Chl-a) level was the key factor in the Liyutan Reservoir
The highest CTSI occurred in spring for Shihmen, summer for the Liyutan and winter for Wushantou and Chengchinghu Reservoirs
Summary
The quality of water bodies has deteriorated. This phenomenon has been observed for several decades because humans prioritize their short-term economic goals over the long-term environmental sustainability of reservoir. Reservoir eutrophication has been investigated globally because it causes serious damage to reservoir ecosystem resilience. Increased nutrient loading generated from industrial wastewater, municipal sewage and irrigation water causes the eutrophication of freshwater lakes, thereby increasing the growth of algae and high plants [2,3]. Correlation of chlorophyll-a (Chl-a) abundance with eutrophication has frequently been investigated using the integration approach of multivariate statistical analysis [4,5]. According to several studies, increased temperature, total precipitation and nutrient runoff are the main factors that enhances the eutrophication process in nature [5,6,7,8].
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