# Characteristics and Release Risk of Phosphorus from Sediments in a Karst Canyon Reservoir, China
## 4 Discussion  
### Potential Relationships between Sediment Phosphorus Forms  
The correlation analysis (Figure 6) revealed highly significant correlations (\(p<0.01\)) between sediment Ca-Pi in the Wanfeng Reservoir and Ca-Po, H\({}_{2}\)O-Pi, H\({}_{2}\)O-Po, NaHCO\({}_{3}\)-Pi, NaHCO\({}_{3}\)-Po, Fe/Al-Pi, Res-P, and TP. It was also significantly correlated (\(p<0.05\)) with Fe/Al-Po. These results highlight the importance of Ca-P as a crucial component of phosphorus in reservoir sediments.  
Figure 5: Distribution of sediment organic phosphorus (OP) fractions across the sampling sites (WF1-3).  
Figure 6: Heatmap for correlation analysis of cumulative phosphorus fugacity patterns.  
The correlation coefficients of sediment H\({}_{2}\)O-Pi with Ca-Pi, NaHCO\({}_{3}\)-Pi, Fe/Al-Pi, Resp, and TP were 0.965, 0.985, 0.859, 0.956, and 0.954, respectively. However, the correlation coefficients with each form of OP were 0.692, 0.509, 0.399, and 0.503, respectively. These results indicate that other forms of phosphorus also influence the sediment-water interface H\({}_{2}\)O-Pi. It also suggests that controlling eutrophication in the water may not be sufficient in the presence of attenuated exogenous contamination, as endogenous release can become a new source of contamination.  
Fe/Al-Pi exhibited highly significant positive correlations (\(p<0.01\)) with Res-P and TP, with correlation coefficients of 0.838 and 0.901, respectively. Fe/Al-P is considered a relatively active form of phosphorus in water and is primarily influenced by factors such as pH and redox potential. Sources of Fe/Al-P typically include domestic sewage and industrial wastewater, an essential indicator of the eutrophication status of the water [46]. It is an essential indicator of the eutrophication status of the water. Under alkaline conditions, the sorption capacity of oxidizable metals such as Fe/Mn for phosphate is reduced, leading to enhanced phosphate release [47].  
Sediment Ca-Pi in the Wanfeng Reservoir was highly significantly correlated (\(p<0.01\)) with H\({}_{2}\)O-P, NaHCO\({}_{3}\)-P, Fe/Al-P, Res-P, and TP. These findings emphasize the importance of Ca-P as a crucial component of phosphorus in reservoir sediments. Ca-Pi mainly consists of detritus phosphorus and apatite, which are generally not rapidly released by sediments. Only when the water's pH drops will a portion of Ca-Pi be released into the water [48]. Due to the unique geographical characteristics of karst canyon reservoirs, which have weakly alkaline water, the release of Ca-P is highly unlikely, resulting in its minimal contribution to water eutrophication.  
The correlation coefficients between reservoir sediment H\({}_{2}\)O-Pi and Ca-Pi, NaHCO\({}_{3}\)-Pi, Fe/Al-Pi, Res-P, and TP were 0.965, 0.985, 0.859, 0.956, and 0.954, respectively. However, the correlation coefficients with each form of OP were 0.692, 0.509, 0.399, and 0.503, respectively. These results indicate that other forms of phosphorus also influence the sediment-water interface H\({}_{2}\)O-Pi. It suggests that controlling eutrophication in water may not be sufficient, and endogenous phosphorus release can become a new source of contamination.  
NaHCO\({}_{3}\)-Pi exhibited highly significant positive correlations (\(p<0.01\)) with Fe/Al-Pi, Res-P and TP, with correlation coefficients of 0.855, 0.963 and 0.950, respectively. This highlights the significant potential of NaHCO\({}_{3}\)-P as a phosphorus in the reservoir.  
Furthermore, Fe/Al-Pi had highly significant positive correlations (\(p<0.01\)) with Res-P and TP, with correlation coefficients of 0.838 and 0.901, respectively. Res-P, as the most stable form of phosphate in the sediment, is not easily involved in the phosphorus cycle in water.  
These findings highlight the significance of NaHCO\({}_{3}\)-P as a potential phosphorus source in karst canyon reservoirs and the role of Fe/Al-Pi in phosphorus dynamics. NaHCO\({}_{3}\)-P and Fe/Al-Pi play a crucial role in the overall phosphorus load and cycling within the karst canyon reservoirs ecosystem.