Eutrophication often results in the loss of submerged vegetation in shallow lakes and turns the lake to be a turbid state. Recovery of submerged macrophytes is the key in the restoration of shallow eutrophic lakes to create a clear water state. However, internal loading control was considered as the critical process for the recovery of submerged macrophytes in shallow lakes after the external nutrient reduction. Phoslock® (Lanthanum modified bentonite) is a useful passivation material in controlling the internal loadings (release of phosphorus from the sediments), which was applied to restore the eutrophic lakes. However, the effects of Phoslock® on the growth and life strategies of submerged macrophytes are less focused so far. In the present study, we studied the responses in the growth and morphological characteristics of Myriophyllum spicatum to the addition of Phoslock® to the sediments. Our results showed that the addition of Phoslock® significantly decreased the contents of bioavailable forms of phosphorus in the sediments, such as redox-sensitive phosphorus bound to Fe and Mn compounds (BD–P), phosphorus bound to aluminum (Al–P) and organic phosphorus (Org–P). However, the concentration of the non-bioavailable forms of phosphorus in the sediments, such as calcium bound phosphorus (Ca–P), increased significantly in the Phoslock® treatments compared with the controls. At the end of the experiments, the total biomass, aboveground biomass and relative growth rate (RGR) of M. spicatum decreased significantly in the Phoslock® mesocosms compared with the controls. In contrast, the wet root biomass, root–shoot biomass ratio, root numbers and root length of M. spicatum were significantly higher in the Phoslock® treatments than that in the controls. Our results indicated that the growth of M. spicatum was suppressed by the addition of Phoslock®, and thus the biomass was decreased; however, the increase of root biomass might be beneficial to the inhibition of phosphorus release and resuspension of sediments and to the restoration of the lake ecosystem.
The geodesic active contour (GAC) model has been widely used due to the high precision of edge detection and the continuity of boundaries. However, compared to the gradient vector flow (GVF) field, it usually has poor performance in the object boundaries with concave shape. In this paper, the improvements that integrate the good performance of the GAC model and the GVF field are described in detail and the GAC_GVF&B model combining the GAC model with the GVF field and a balloon force is proposed. The experimental results demonstrate that the proposed method is insensitive to the positions of initial curves and can segment complex-shape or multiobjects images correctly with higher convergence.
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