## 2 Results and Discussion
### Sources and Influencing Factors of T/O Compounds in Freshwater Bodies of the World
#### 2.5.1 Biotic Factors  
To address odor issues in water bodies, it is crucial to study their sources and primary influencing factors. Typically, studies explored the relationship between biological factors and the concentration of odor substances to identify their producers. Biotic factors were generally assessed by examining the biomass or density of total cyanobacteria, specific genera and/or species, and various indices, including Chl-\(a\), phycocyanin, and genes associated with T/O compounds synthesis. The concentrations of GSM in various water bodies exhibit diverse correlations with Chl-\(a\) and other factors. Several studies have found positive correlations between GSM concentrations and Chl-\(a\). For instance, [PERSON] et al. (2013) observed this positive correlation in Taihu Lake, China [23], while [PERSON] et al. (2021b) reported a similar trend in seven important reservoirs in eastern China [21]. Additionally, [PERSON] et al. (2002) noted a positive correlation in Cheney Reservoir in the United States. However, contrasting results have been observed in other water bodies [14]. In the current study, no significant correlation was found between GSM concentrations and Chl-\(a\) in DECL. Similarly, [PERSON] et al. (2019) reported no significant correlation in Chaohu Lake and Songhua Lake in China, as well as in Taihu Lake, also in China [22]. [PERSON] et al. (2007) found no correlation in Dianchi Lake in China [46], [PERSON] et al. (2011) found no correlation in Wahnbach Reservoir in Germany [16], and [PERSON] et al. (2014) found no correlation in Eagle Creek Reservoir in the United States [49]. Similar variability was observed for the correlation between cyanobacteria and GSM concentrations. Positive correlations were found in some water bodies (e.g., Phayao Lake in Thailand [87], Bukhan River and Namhan River in South Korea [18], and Paldang Lake in Korea [15]), while in others (DECL (this study), Dianchi Lake in China [46], and Eagle Creek Reservoir in the US [49]), there was no apparent relationship between cyanobacteria and GSM. Notably, specific types of cyanobacteria, such as _Microystis_, _Dolichospermum_, and _Pseudomanabena_, have been extensively researched in relation to GSM. Positive correlations between GSM and _Microystis_ were observed in various water bodies, including Taihu Lake in China [23], California Aqueduct in the US [24], Bukhan River and Namhan River in South Korea [18], and Lake Wirnebago in the US [40]. Moreover, in specific lakes, such as Western Chaohu Lake [42] and Dianchi Lake in China [46], Paldang Lake in Korea [82], Bukhan River and Namhan River in South Korea [18], raw water from drinking water treatment plants in Japan [78], and Diamond Valley Lake in the US [25], GSM showed positive correlations with _Dolichospermum_, while in others (Taihu Lake in China [65], nine sampling sites along the main canal of the Middle Route of South-to-North Water Diversion Project in China [71], San Vicente Reservoir [93] and Lake Skinner in the US [93], and Lake Y in Japan [80]), it exhibited a positive correlation with _Pseudomanabena_. However, it is crucial to note that some studies report scenarios in which no correlation was observed. Furthermore, positive correlations between GSM and other factors, such as _Merismopedia_ (Namhan River in South Korea [18]), _Phormidium_ (Lake Kasumigaura in Japan [9]), _Plankton trix_ (Eagle Creek Reservoir in the US [28]), _Cylindospermopsis rachiorskii_ (Eagle Creek Reservoir in the US [49]), and _Coelosphaerium_ (Lake Shinji in Japan [77]), have been reported in certain studies. For MIB, its relationship with various factors mirrors that of GSM, displaying positive or non-correlative associations with Chl-\(a\), cyanobacteria, _Microystis_, _Pseudoanabena_, _Oscillatoria_, _Plankton trix_, and diatoms.