## 2 Results and Discussion
### Sources and Influencing Factors of T/O Compounds in Freshwater Bodies of the World
#### 2.5.1 Biotic Factors
However, positive correlations have been reported with _Phormidium_ in various water bodies (Huangpu River [58], Lake Yangcheng in China [47], raw water from drinking water treatment plants [78], and Lake Kasumigaura [9] and Lake Kasumigaura in Japan [17]), and a positive correlation has been observed with _Lyngbya_ in a specific study (California Aqueduct in the US [24]). In comparison, there has been relatively less extensive research on CYC and ION. Studies such as Taihu Lake [23; 64] and Dianchi Lake in China [46] have shown a positive correlation between Chl-\(a\) and both CYC and ION. Additionally, in Liangxi River [51] and 13 eutrophic lakes in China [48], there was a positive association between Chl-\(a\) and CYC. However, in certain locations, including DECL (this study) and nine sampling sites along the main canal of the Middle Route of South-to-North Water Diversioncanal of the Middle Route of South-to-North Water Diversion Project in China [71], ION was not correlated with Chl-_a_. Concerning cyanobacteria, a positive correlation with both CYC and ION was observed in Dianchi Lake in China [46], while in DECL (this study), there was no association. Specifically for _Microcysts_, studies such as seven landscape lakes in Beijing [45; 69], Taiwan Lake [23; 64], Western Chaohu Lake [42], Eastern Chaohu Lake [33] and Dianchi Lake in China [46], and Lake Winnebago in the US [40] have shown a positive correlation between CYC and _Microcysts_, and ION was positively correlated with CYC in Taihu Lake [23; 64] and Dianchi Lake in China [46]. However, in DECL (this study), both CYC and ION were unrelated to _Microcysts_. Furthermore, CYC and _Dolicospermum_ exhibited no significant correlation, whereas ION demonstrated a positive correlation with _Dolicospermum_ in this study. In Taihu Lake of China, both CYC and ION were unrelated to _Oscillatoria_[64]. It is worth noting that both GSM and MIB are often produced by bacteria. Therefore, some studies have explored their relationship with bacteria. For instance, in Phayao Lake in Thailand [87], Lake Kasumigaura in Japan [17], and Paldang Lake in Korea [82]), GSM exhibited a positive correlation with actinomycetes. It is noteworthy to mention that alternative findings have been reported by [PERSON] et al. (2020) in the context of Paldang Lake in Korea [15], where the sampling period ranged from June to September 2021, as reported by [PERSON] et al. (2016) [82]. In this study, there was no discernible association observed between GSM and actinomycetes. In Eagle Creek Reservoir in the US [29], GSM was positively correlated with _a-Proteobacteria_. MIB showed a positive correlation with actinomycetes in Eagle Creek Reservoir in the US [28] and fishponds in China [70], while in Eagle Creek Reservoir in the US, MIB displayed a positive correlation with _Fluobacterium_[29]. A positive correlation between the copy number of the synthesis gene and T/O compounds has been identified in various studies, including those conducted in Paldang Lake in Korea [84], Qingcaosha Reservoir [61], and Lushui Reservoir in China [59]. Consequently, [PERSON] et al. (2023) [62] proposed that the abundance of the MIB synthesis gene (mic) in both the DNA and RNA forms could serve as valuable parameters for early warning systems associated with MIB production. The comprehensive findings revealed significant positive correlations among Chl-_a_, phycocyanin, cyanobacteria (_Microcysts_, _Dolicospermum_, _Merismopedia_, _Oscillatoria_, _Phormidium_, _Planktontirix_, _Pseudanabena_, _Cylindrospermopsis_, _Coelosphaerium_, and _Lungbya_), diatoms, and certain T/O compounds (Table 4). These identified biotic factors were implicated in the potential generation of T/O compounds in natural water bodies affected by algal blooms. As in some eutrophic lakes, cyanobacteria and T/O compounds, such as MIB and GSM, exhibited a significant positive correlation with Chl-_a_. This underscored that the nutritional status, particularly Chl-_a_, served as an excellent indicator for T/O compounds [14; 97].