## 2 Results and Discussion
### Sources and Influencing Factors of T/O Compounds in Freshwater Bodies of the World
#### 2.5.3 Nutrients  
The relationships between T/O compounds and various nitrogen forms have been investigated across multiple studies. Although positive correlations have been identified in specific instances, such as the association between GSM and total nitrogen in seven important reservoirs in eastern China [21] and the correlations of MIB, CYC, and ION with total nitrogen in East Taihu Lake, China [44], as well as ION with total nitrogen in Liangxi River, China [51], the majority of studies conducted by [PERSON] et al. (2014) [49], [PERSON] et al. (2023) [50], [PERSON] et al. (2019) [44] and [PERSON] et al. (2019) [22], as well as the present investigation did not observe significant correlations. Furthermore, variations have been noted in the relationships with nitrate and ammonia nitrogen among different compounds across various studies. Specifically, for nitrate, GSM exhibited a positive correlation with it in DECL (this study), Songhua Lake [22], and Liangxi River in China [51], while no correlation was observed in Taihu Lake in China [22; 44] or Eagle Creek Reservoir in the US [49]. MIB exhibited a positive correlation with nitrate in nine sampling sites along the main canal of the Middle Route of the South-to-North Water Diversion Project in China [71]. Conversely, no significant correlation was discerned in DECL (this study), Songhua Lake [22], Chaohu Lake [22], Taihu Lake in China [22], and Eagle Creek Reservoir in the US [49]. Similarly, CYC demonstrated a positive correlation with nitrate in the specified sampling sites [71], while no significant correlation was evident in the present study. In the case of ION, it displayed a positive correlation with nitrate in Songhua Lake [22] and nine sampling sites along the main canal of the Middle Route of the South-to-North Water Diversion Project in China [71]. Conversely, a negative correlation was observed in East Taihu Lake [44], and no significant correlation was found in DECL (this study), Chaohu Lake [22], or Taihu Lake in China [22]. Examining ammonia nitrogen, GSM demonstrated a positive correlation with it in Songhua Lake [22], while no significant correlation was observed in DECL (this study), Chaohu Lake [22] and Taihu Lake in China [22; 44], or Eagle Creek Reservoir in the US [49]. MIB showed a positive correlation with ammonia nitrogen in DECL in China (this study) and Eagle Creek Reservoir in the US [49], a negative correlation in seven landscape lakes in Beijing [45; 69], and no significant correlation in Songhua Lake, Chaohu Lake, Taihu Lake [22], and Feng-Shen Reservoir in China [57]. In this study, CYC was unrelated to ammonia nitrogen. Furthermore, ION exhibited a positive correlation with ammonia nitrogen in Songhua Lake [22] and Liangxi River in China [51], while no significant correlation was noted in DECL (this study), Chaohu Lake, or Taihu Lake in China [22]. [PERSON] et al. (2014) also investigated total Kjeldahl nitrogen, finding a positive correlation with GSM in Eagle Creek Reservoir in the US and no correlation with MIB [49]. In the investigation of odorants and total phosphorus, there was a lack of research on a positive correlation between GSM and total phosphorus. Conversely, in Chaohu Lake, GSM exhibited a negative correlation with total phosphorus [22]. In subsequent studies, namely, in DECL (this study), Taihu Lake in China [22; 44], and Eagle Creek Reservoir in the US [49], no correlation was observed between GSM and total phosphorus. However, MIB showed a positive correlation with total phosphorus in Taihu Lake in China [23; 50] and Eagle Creek Reservoir in the US [49] and a negative correlation in Lake Yangcheng, China [47]. In DECL (this study), Songhua Lake [22], Chaohu Lake [22], and Taihu Lake in China [22], MIB was unrelated to total phosphorus. CYC exhibited a positive correlation with total phosphorus in Western Chaohu Lake [42], Taihu Lake [23], and 13 eutrophic lakes in China [48] and was unrelated in DECL in China (this study).