1 Introduction
Water, as the source of life, is a fundamental component of all living
organisms and sustains all vital activities in the human body (Sajeev et
al., 2020; Westall and Brack, 2018). Nevertheless, the overuse and
pollution of water resources by human activities (continuous population
growth, rapid progress in agriculture and industry, and high rates of
urbanization) have rendered water resources one of the most threatened
resources in the world (Varol, 2019). As the important tool for humans
to utilize water resources, reservoirs play an extremely prominent role
in the agricultural irrigation of rural acres, the living supply of
urban residents, the storage project during the drought season, and the
flood control project during the rainstorm season (Mamun et al., 2020).
However, increased environmental degradation has substantially reduced
the role of reservoirs. And under the combined influence of natural and
anthropogenic factors (Liu et al., 2022; Paerl and Otten, 2013), causing
severe environmental problems of water eutrophication worldwide (Le Moal
et al., 2019). When eutrophication occurs in reservoirs, surplus
nutrients stimulate the excessive growth of algae, phytoplankton, and
other aquatic plants in the water, decreasing DO and increasing Chl-a
levels (Li et al., 2021). Currently, the eutrophication of reservoirs
has resulted in multiple impacts on ecosystems and social stability
(Chen et al., 2020; Mäler, 2000), such as water hypoxia, water bloom,
aquatic animal mortality, simplification of food webs, and reduction of
biodiversity. According to the studies, eutrophication has occurred in
up to 54% of reservoirs in Asia, and its incidence continues to
increase (Fink et al., 2018). In conclusion, reservoir eutrophication
has been recognized as the most frequent and severe environmental hazard
in aquatic ecosystems (Wu et al., 2018).
Proactive gathering of reliable information on changes in water quality
for eutrophication management in reservoirs, which has been demonstrated
in many countries and regions (Astel et al., 2006; Behmel et al., 2016;
Romero et al., 2016). At present, various multivariate statistical
analysis techniques are applied in the academic community for multiple
and complex data on water quality, such as Cluster Analysis (CA)
(Hajigholizadeh and Melesse, 2017), Discriminant Analysis (DA) (Li et
al., 2018), Factor Analysis (FA) (Mamun et al., 2021), Principal
Component Analysis (PCA) (Zeinalzadeh and Rezaei, 2017), Correlation
Analysis (Liu et al., 2010), and Analysis of Variance (ANOVA) (Chen and
Lu, 2014), not only do they provide an effective tool for interpreting
monitoring data sets, but they also provide significant assistance in
identifying the major factors affecting water quality. In addition, the
academic community has likewise developed multiple methods for
evaluating water quality, examples include the fuzzy mathematical method
(Peche and Rodríguez, 2012), gray clustering method (Wong and Hu, 2014),
neural network method (Zhou et al., 2020), matter element analysis
method (Chen et al., 2012), Water Quality Index (WQI) (Wang et al.,
2019), and Trophic level Index (TLI) (Li et al., 2021), they provide an
excellent foundation for comprehensively characterizing the degree of
eutrophication in reservoirs and for scientifically improving reservoir
water quality.
Chuzhou City is located in the eastern part of China’s Anhui Province,
with a land area of 13,300 km2, and belongs to the
Yangtze and Huaihe River Basin, which is a typical area of the Jianghuai
Watershed. The average annual precipitation is 1,035.5mm, and the total
water resource is 33.5×108m3, but
the per capita water resource is only 908m3, which is
far lower than the national average value of 2,304m3,
and is also lower than the water scarcity warning line of
1,000m3, which is a water scarcity area. Therefore,
sufficient and healthy water resource is particularly essential for the
city. The three reservoirs in Chuzhou City (Shahe Reservoir, Huanglishu
Reservoir, and Chengxi Reservoir) have been tasked with alleviating
water scarcity since their construction. However, as the central
lifeblood of the city, the reservoirs have been suffering from
eutrophication of water bodies in recent years, which directly or
indirectly affects the normal life of the people in the area and the
sustainable economic development of the city (Dokulil et al., 2000).
Consequently, the evaluation of eutrophication in reservoirs has great
significance in providing the scientific basis and control strategies
for local water quality management and ecological protection.
Given the limitations of multivariate statistical analysis techniques
for water quality assessment when used alone (Chen and Lu, 2014; Güler
et al., 2002), in this study, multiple statistical analysis techniques
were jointly applied to minimize their limitations and preserve their
respective strengths (Chen et al., 2016; Zhou et al., 2007). At the same
time, selected a higher scientific basis of the TLI method to analyze
and evaluate the trophic state of three reservoirs in Chuzhou City (Liu
et al., 2021). Aims: (1) To research the drivers of water quality
parameter changes over time in three reservoirs between 2019 and 2021;
(2) To evaluate the trophic levels and causes of occurrence in
reservoirs using the TLI method; (3) To analyze the differences in
nutrient levels in the water bodies of the three reservoirs.