# Evaluation of Algal Control Measures in Eutrophic Reservoir Based on Aquatic Ecosystem Models
## 3 Results and Discussions
### Analysis of the Impact of the Sediment Pollution Reduction Plan  
In the reservoir's sediment pollution reduction scheme, the figure displays the results for both the reservoir center (Figure 8) and the overall reservoir (Figure 9).  
The results (Figure 8) of the reservoir area simulation indicate the following conclusion:  
Figure 9: Comparison of carbon content of blue-green algae (**a**,**e**,**i**), chlorophyll concentration (**b**,**f**,**i**), total nitrogen concentration (**c**,**g**,**k**), and total phosphorus concentration (**d**,**h**,**l**) in original sediment cleaning (**a**–**d**), 20% sediment cleaning (**e**–**h**), and 50% sediment cleaning (**i**–**l**) scenarios.  
(1) The reduction in bottom sediment has a minimal impact on the growth of blue-green algae, slightly decreasing the algal biomass.  
(2) The reduction in bottom sediment significantly affects the concentration of nutrients in the reservoir center, notably decreasing the concentration of total phosphorus and total nitrogen. A 25% reduction leads to a 6% decrease in total nitrogen and an 8% decrease in total phosphorus. A reduction of 50% results in a 12% decrease in total nitrogen and a 14% decrease in total phosphorus.  
The results (Figure 9) of the reservoir area simulation indicate the following conclusion:  
(1) Overall, dredging and cleaning the bottom sediment has a greater impact on algal growth in the dock and shallow water areas of the bays compared to the deepwater areas of the reservoir. This is because, on the one hand, although there is a reduction in nutrients in the deepwater areas, the diffusion of released nutrients from the bottom to the surface is weaker, resulting in a smaller effect compared to the shallow water areas. On the other hand, the two-dimensional model considers the time cost and averages the algal concentration vertically at the grid scale [57]. However, the actual distribution of algae is not uniform, with the majority existing in the surface layer within the photic zone. Assessing algal growth by removing the influence of water depth, possibly using g/m\({}^{2}\), might be more appropriate.  
(2) Overall, the reduction in internal sources in the reservoir significantly decreases the concentration of total nitrogen and total phosphorus, but they still remain above the threshold levels of 0.6 mg/L for total nitrogen and 0.03 mg/L for total phosphorus. In terms of the inhibitory effect on algal growth, although algal biomass has decreased, the effect is not as significant as the decrease in nutrient concentration. The total nitrogen and total phosphorus from the river inflows at Huokou and Rixi still represent the largest input of nutrients into Shanzai Reservoir. Merely carrying out internal dredging is not enough to achieve the environmental threshold of 0.6 mg/L for total nitrogen and 0.03 mg/L for total phosphorus. To some extent, reducing nutrient levels does not play a decisive role in algal growth, given the strong influence of light and water temperature.  
From the results of the model simulation from July to September, it is evident that under an appropriate water temperature and sufficient light intensity, the role of nutrients in algal growth is much less significant than the influence of light and water temperature. Therefore, in the prevention and control of algae, paying continuous attention to temperature and light conditions is particularly crucial [58].