# Evaluation of Algal Control Measures in Eutrophic Reservoir Based on Aquatic Ecosystem Models
## 3 Results and Discussions  
### Reservoir Water Level Scheme Analysis  
In the reservoir's water level design scheme, the figure displays the results for both the reservoir center (Figure 6) and the overall reservoir (Figure 7). The results (Figure 6) of the reservoir area simulation indicate the following conclusion: (1) As the water level rises, there is a significant decrease in blue-green algae carbon (BC) content in the reservoir center. For instance, in scheme one, the blue-green algae carbon amount is approximately 48% higher at a water level of 75 m compared to scheme three at a water level of 85 m. This result aligns with the actual algal outbreak in the reservoir between July and April 2020 at a water level of 75 m, and the same period in 2021 and 2022 at a water level of around 85 m.  
(2) There are minimal variations in the total nitrogen and total phosphorus content in the reservoir center across different water level schemes, with slight fluctuations observed. Over time, it can be observed that the concentration of nutrients in the water transitions from being higher at low water levels to being relatively consistent at high water levels. This is because the model-simulated total nitrogen and total phosphorus encompass all nitrogen and phosphorus substances in the water, including algal nitrogen and phosphorus, detrital nitrogen and phosphorus, inorganic nitrogen, and inorganic phosphates. With no changes at the inflow and outflow boundaries, the main factors influencing changes in the total nitrogen and phosphorus content are nitrogen and phosphorus deposits and their release from the bottom sediment. On one hand, the decrease in water levels leads to an increase in water temperature and light intensity, particularly impacting shallow areas and the overall flow velocity in the reservoir. This results in excessive water exchange and an overall rise in nutrient concentration, fostering increased algal growth and reproduction. On the other hand, following algal death, detritus settles at the reservoir's bottom, carrying nitrogen and phosphorus into the sediment. As nitrogen and phosphorus concentrations in the water decrease due to algal absorption, the concentration gradient between the interstitial water in the sediment and the overlying water intensifies, leading to an increase in nutrient release  
Figure 6: (**a**) Comparison of carbon content of blue-green algae (BC) in different water level scenarios; (**b**) comparison of total nitrogen (TN) concentration in different water level scenarios; (**c**) comparison of total phosphorus (TP) concentration in different water level scenarios. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Scenario**} & **Survival Quantity** & **Fish Fry** & **Feed Intake (Daily** & **Feed Intake (Daily** & **Hydraulic Conditions** \\  & **(Ten Thousand)** & **(g/piece)** & **Weight Percentage, 1/d)** & **Weight Percentage, 1/d)** & Idealized setting for sediment reduction to quantify the benefits of dredging, Actual projects should consider safe dredging with negative effects on sediment disturbance and consider zoning, staging, and negative impact. All settings are based on the 2020 modeling parameters. \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Ecological farming. from the sediment. This relationship is a dynamic equilibrium tied to water temperature. Ultimately, the overall change in total nitrogen and total phosphorus tends towards a stable state, with slightly different variations as the seasons shift. The results (Figure 7) of the reservoir area simulation indicate the following conclusion: (1) Blue-green algae and chlorophyll are primarily distributed in various bays and areas with different water depths, with a higher biomass of blue-green algae observed in the dock area compared to other regions. The overall distribution of blue-green algae and chlorophyll demonstrates a spatial decreasing trend from the inflow to the dam.